Patent Publication Number: US-2021180015-A1

Title: Membrane-Receiver Complex Therapeutics

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. Ser. No. 62/161,196 filed May 13, 2015, the contents of which are incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     The field of the invention is pharmaceutical compositions for the treatment of diseases and disorders. 
     SEQUENCE LISTING 
     The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on May 12, 2016, is named R2081-7011WO_SL.txt and is 67,028 bytes in size. 
     BACKGROUND 
     The circulatory system permits blood and lymph circulation to transport, e.g., nutrients, oxygen, carbon dioxide, cellular waste products, hormones, cytokines, blood cells, and pathogens to and from cells in the body. Blood is a fluid comprising, e.g., plasma, red blood cells, white blood cells, and platelets that is circulated by the heart through the vertebrate vascular system. The circulatory system becomes a reservoir for many toxins and pathogenic molecules upon their introduction to or production by the body. The circulatory system also serves as a reservoir for cellular secretions or detritus from within the body. The perpetual or aberrant circulation and proliferation of such molecules and entities can drive disease and/or exacerbate existing conditions. 
     There is an ongoing need to provide therapeutic compositions through the circulatory system that alleviate or prevent such diseases and conditions. There is a further a need for methods and compositions that increase the half-life, safety profile, and/or efficacy of such therapeutic compositions. Aspects of the invention address one or more of the shortcomings of current methods and compositions. 
     SUMMARY 
     In some aspects, the disclosure provides isolated erythroid cell population comprising enucleated erythroid cells each comprising copies of an exogenous polypeptide, e.g., a cytosolic exogenous polypeptide. In some aspects, the disclosure provides isolated erythroid cell population comprising at least 80% enucleated erythroid cells each comprising at least 1,000 copies of a cytosolic exogenous polypeptide. 
     In some embodiments, the population comprises at least 85%, 90%, 95%, 97%, 98% or at least 99% enucleated erythroid cells. In some embodiments, each erythroid cell comprises at least 5,000, 10,000, 25,000, 50,000, 100,000, 250,000, 500,000, or 1,000,000, 2,500,000, 5,000,000, 10,000,000, 25,000,000, or 50,000,000 copies of the cytosolic exogenous polypeptide. 
     In some embodiments, the cytosolic exogenous polypeptide is fused to a membrane-anchored polypeptide, e.g., they form part of a fusion protein produced by translation of a chimeric nucleic acid. In some embodiments, the membrane-anchored polypeptide is a transmembrane polypeptide. In some embodiments, fusion of the cytosolic exogenous polypeptide to the membrane-anchored polypeptide generates a chimeric fusion polypeptide. In some embodiments, the membrane-anchored polypeptide is an exogenous polypeptide or an endogenous polypeptide. 
     In some embodiments, the erythroid cell is an erythrocyte or a platelet. 
     In some embodiments, the cytosolic exogenous polypeptide has enzymatic activity. In some embodiments, the enzymatic activity is specific to a toxin or a metabolite. 
     In some embodiments, the cytosolic exogenous polypeptide is capable of binding, sequestering and/or degrading an anti-drug antibody. 
     In some embodiments, the population has an osmotic fragility of less than 50% cell lysis at 0.3%, 0.35%, 0.4%, 0.45%, or 0.5% NaCl. In some embodiments, the population has hemoglobin levels of at least 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 pg. In some embodiments, the population has a phosphatidylserine content as measured by Annexin V staining of less than 30%, 25%, 20%, 15%, 10%, or 5%. 
     In some embodiments, the erythroid cells are immunologically omnicompatible. In some embodiments, the erythroid cells lack one or more antigen selected from Diego, RHAG, Kx, GLOB, I, Ch/Rg, Colton, Kidd, Rhesus (RhD, RhCE), Kell, Yt, Scianna, Dombrock, LW, H, Cromer, Knops, Indian, OK, JMH, GIL, ABO, Lewis, P, Raph, Xg, Lutheran, MNS, Gerbich, and Duffy, or any combination thereof. In some embodiments, the erythroid cells have a reduced glycosylation level, e.g., of less than 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.25%, or of less than 0.1% compared to a control erythroid cell. In some embodiments, the erythroid cells: i) do not comprise a MHC antigen, or ii) comprise no more than one type of MHC antigen, e.g., the cells arise from a population of homozygous or hemizygous progenitor cells. 
     In some aspects, the disclosure provides a method of producing an isolated erythroid cell population as described herein, the method comprising: 
     providing erythroid cells, 
     introducing an exogenous nucleic acid encoding the cytosolic exogenous polypeptide into the erythroid cells, 
     culturing the erythroid cells, 
     inducing enucleation of the erythroid cells, and 
     purifying the enucleated erythroid cells, e.g., to produce a population of at least 80% enucleated erythroid cells. In some embodiments, the resulting cells comprise the cytosolic exogenous polypeptide, and during enucleation the cytosolic exogenous polypeptide is retained by the enucleated erythroid cell whereas the exogenous nucleic acid is not retained by the enucleated erythroid cell. 
     In some embodiments, the method further comprises the step of expanding the erythroid cells after the cytosolic exogenous polypeptide is introduced. In some embodiments, the erythroid cells are expanded by at least 5,000-fold, 10,000-fold, 20,000-fold, 30,000-fold, 40,000-fold, or by at least 50,000-fold. In some embodiments, expansion is not carried out by co-culturing of the erythroid cells with an adherent stromal layer. 
     In some embodiments, the purifying step comprises one or more (e.g., 2, 3, 4, 5, or more) passage(s) of the erythroid cell population through a de-leukocyting filter. 
     In some embodiments, the method further comprises rendering the erythroid cells immunologically omnicompatible, e.g., as described herein. In some embodiments, the method further comprises rendering the erythroid cells immunologically omnicompatible comprises: i) reducing the number of antigenic glycans, ii) reducing the number of antigenic polypeptides, or iii) both reducing the number of antigenic glycans and reducing the number of antigenic polypeptides, on the surface of the cells, thereby reducing their immunogenicity. 
     In some embodiments, reducing the number of antigenic glycans comprises contacting the cells with an enzyme capable of glycan trimming for a time sufficient to detach the antigenic glycans and then removing the detached glycans from the cells. In some embodiments, reducing the number of antigenic polypeptides comprises contacting the cells with an enzyme capable of cleaving polypeptides for a time sufficient to detach the antigenic polypeptides and then removing the detached polypeptides from the cells. In some embodiments, the reducing the number of antigenic glycans comprises contacting the cells with an exogenous nucleic acid encoding an agent capable of repressing glycan biosynthesis or processing. In some embodiments, the reducing the number of antigenic polypeptides comprises contacting the cells with an exogenous nucleic acid encoding an agent capable of repressing polypeptide biosynthesis or processing. 
     In some embodiments, the agent is CRISPR/Cas9 or a short interfering RNA. In some embodiments, the agent acts on a gene encoding a fucosyltransferase (e.g. FUT1 or FUT2 genes) or a glycosyltransferase (e.g. an ABO gene). In some embodiments, the agent is transiently active in the erythroid cell and is not maintained after enucleation. 
     In some embodiments, the method further comprises the step of irradiating the erythroid cell population. 
     In some embodiments, the provided erythroid cells are erythroid precursors, erythrocytes, or platelets. 
     In some embodiments, culturing comprises contacting the erythroid cells with one or more culturing factors selected from the group consisting of stem cell factor, IL-3, IL-6, insulin, transferrin, erythropoietin, hydrocortisone, and estrogen. 
     In some embodiments, the erythroid cell population is cultured in a bioreactor. 
     In some aspects, the disclosure provides a method of preserving an isolated erythroid cell population described herein. The method can comprise one or more of, e.g., all of: 
     providing the erythroid cell population, 
     contacting the erythroid cell population with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere, and 
     storing the contacted erythroid cell population. 
     In some embodiments, contacting a cell or cell population with an inert or noble gas comprises contacting medium comprising the cell population with the inert or noble gas. 
     In some embodiments, the erythroid cell population is stored in an atmosphere comprising the inert or noble gas. 
     In some embodiments, the erythroid cell population is stored at a refrigerated temperature above the freezing point. 
     In some embodiments, oxygen residing in the erythroid cell population is purged. 
     In some embodiments, the inert or noble gas is selected from the group consisting of helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe). 
     In some embodiments, hemolysis of the erythroid cell population is less than 5%, 4%, 3%, 2% or less than 1% after storage of at least 10 days, 15 days, 20 days, 25 days, 30 days, 35 days, 40 days, or at least 45 days. 
     In some aspects, the disclosure provides a method of transporting an erythroid cell population described herein. The method can comprise providing an erythroid cell population described herein, wherein the erythroid cell population is in contact with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere, and wherein optionally the erythroid cell population is at a refrigerated temperature above the freezing point, and transporting the erythroid cell population to a recipient. 
     In some aspects, the disclosure provides a method of receiving an erythroid cell population described herein. The method can comprise receiving an erythroid cell population described herein, wherein the erythroid cell population is in contact with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere, and wherein optionally the erythroid cell population is at a refrigerated temperature above the freezing point, and optionally putting the erythroid cell population in contact with naturally occurring atmosphere or an atmosphere typical of a cell incubator, and optionally raising the temperature of the erythroid cell population, e.g., to room temperature or body temperature (e.g., 37 degrees). 
     In some aspects, the disclosure provides an isolated erythroid cell population comprising at least 80% enucleated erythroid cells each comprising a high-density target substrate interaction surface, wherein the high-density target substrate interaction surface comprises at least 10,000 copies of polypeptide receiver on the plasma membrane of the erythroid cell, wherein the polypeptide receiver comprises a first polypeptide domain that is surface exposed and has an enzymatic activity, and a second polypeptide domain that is associated with the membrane of the erythroid cell, wherein the first and second polypeptide domain are not of the same natural origin, wherein the domain that has enzymatic activity is not naturally found membrane-associated, and wherein the domain that has enzymatic activity is capable of interacting and modifying the target substrate. 
     In some embodiments, the population comprises at least 85%, 90%, 95%, 97%, 98% or at least 99% enucleated erythroid cells. In some embodiments, each erythroid cell comprises at least 25,000 copies, 50,000 copies, or at least 100,000 copies of the polypeptide receiver. 
     In some embodiments, the second polypeptide domain is a transmembrane polypeptide. 
     In some embodiments, the target substrate is a self-antibody, a complement cascade factor, a clotting cascade factor, an immune complex, a serum amyloid protein, a toxin, a metabolite, or an anti-drug antibody. 
     In some embodiments, the erythroid cell is an erythrocyte or a platelet. 
     In some embodiments, the population has an osmotic fragility of less than 50% cell lysis at 0.3%, 0.35%, 0.4%, 0.45%, or 0.5% NaCl. In some embodiments, the population has a phosphatidylserine content as measured by Annexin V staining of less than 30%, 25%, 20%, 15%, 10%, or 5%. 
     In some embodiments, the erythroid cells are immunologically omnicompatible. In some embodiments, the erythroid cells lack one or more of an A antigen, a B antigen, an RhD antigen, or any combination thereof. In some embodiments, the erythroid cells lack one or more antigen selected from Diego, RHAG, Kx, GLOB, I, Ch/Rg, Colton, Kidd, Rhesus (RhD, RhCE), Kell, Yt, Scianna, Dombrock, LW, H, Cromer, Knops, Indian, OK, JMH, GIL, ABO, Lewis, P, Raph, Xg, Lutheran, MNS, Gerbich, and Duffy, or any combination thereof. 
     In some embodiments, the erythroid cells have a reduced glycosylation level of less than 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.25%, or of less than 0.1% compared to a control erythroid cell. In some embodiments, the erythroid cells: i) do not comprise a MHC antigen, or ii) comprise no more than one type of MHC antigen, e.g., the cells arise from a population of homozygous or hemizygous progenitor cells. 
     In some embodiments, the method does not comprise chemical disruption of the cell membrane, e.g., the method does not comprise introducing a nucleic acid into the cell by performing chemical disruption of the cell membrane. 
     In some embodiments, the high-density target substrate interaction surface has one or more of the following properties: 
     i) has a Koff rate, with respect to the target substrate, that is substantially lower than (e.g., less than 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.25%, of 0.1% lower than) that of a surface with a lower number of binding sites or a single binding site, 
     ii) has a dissociation constant (Kd), with respect to the target substrate, that is substantially lower than (e.g., less than 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.25%, of 0.1% lower than) that provided by a surface with a lower number of binding sites or a single binding site, 
     iii) has an affinity, with respect to the target substrate, that is substantially higher than (e.g., at least 10%, 20%, 50%, 2-fold, 5-fold, 10-fold, 20-fold, 50-fold, 100-fold, 200-fold, 500-fold, or 1,000-fold higher than) that provided by a surface with a lower number of binding sites or a single binding site, 
     iv) has an avidity, with respect to the target substrate, that is substantially higher than (e.g., at least 10%, 20%, 50%, 2-fold, 5-fold, 10-fold, 20-fold, 50-fold, 100-fold, 200-fold, 500-fold, or 1,000-fold higher than) that provided by a surface with a lower number of binding sites or a single binding site, 
     v) results in a local concentration of the target substrate that is substantially higher than (e.g., at least 10%, 20%, 50%, 2-fold, 5-fold, 10-fold, 20-fold, 50-fold, 100-fold, 200-fold, 500-fold, or 1,000-fold higher than) that resulting from a surface with a lower number of binding sites or a single binding site. 
     In some embodiments, the surface with a lower number of binding sites has less than 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.25%, of 0.1% the number of binding sites on the high-density target substrate interaction surface. 
     In some embodiments, the high-density target substrate interaction surface has one or more of the following properties: i) a koff rate of less than 5×10-2 s−1, 2×10-2 s−1, 1×10-2 s−1, 5×10-3 s−1, 2×10-3 s−1, 1×10-3 s−1, 5×10-4 s−1, 2×10-4 s−1, 1×10-4 s−1, 5×10-5 s−1, 2×10-5 s−1, 1×10-5 s−1, 5×10-6 s−1, 2×10-6 s−1, 1×10-6 s−1, with respect to the target substrate, or ii) a Kd of less than 10 mM, 5 mM, 2 mM, 1 mM, 500 μM, 200 μM, 100 μM, 50 μM, 20 μM, 10 μM, 5 μM, 2 μM, 1 μM, 500 nM, 200 nM, 100 nM, 50 nM, 20 nM, 10 nM, 5 nM, 2 nM, 1 nM, 500 pM, 200 pM, 100 pM, 50 pM, 20 pM, 10 pM, 5 pM, 2 pM, or 1 pM with respect to the target substrate, iii) or both i) and ii). 
     In some aspects, the disclosure provides a method of producing an isolated erythroid cell population described herein. The method can comprise one or more of, e.g., all of: 
     providing erythroid cells, 
     introducing an exogenous nucleic acid encoding the cytosolic exogenous polypeptide into the erythroid cells, 
     culturing the erythroid cells, 
     inducing enucleation of the erythroid cells, and 
     purifying the enucleated erythroid cells, e.g., to produce a population of at least 80% enucleated erythroid cells. 
     The resulting population of cells, in some embodiments, comprises the cytosolic exogenous polypeptide, wherein during enucleation the cytosolic exogenous polypeptide is retained by the enucleated erythroid cell whereas the exogenous nucleic acid is not retained by the enucleated erythroid cell. 
     In some embodiments, the method further comprises the step of expanding the erythroid cells after the cytosolic exogenous polypeptide is introduced. In some embodiments, the erythroid cells are expanded by at least 5,000-fold, 10,000-fold, 20,000-fold, 30,000-fold, 40,000-fold, or by at least 50,000-fold. In some embodiments, expansion is not carried out by co-culturing of the erythroid cells with an adherent stromal layer. 
     In some embodiments, the purifying step comprises one or more (e.g., 2, 3, 4, 5, or more) passage(s) of the erythroid cell population through a de-leukocyting filter. 
     In some embodiments, method further comprises rendering the erythroid cells immunologically omnicompatible. In some embodiments, rendering the erythroid cells immunologically omnicompatible comprises: i) reducing the number of antigenic glycans, ii) reducing the number of antigenic polypeptides, or iii) both reducing the number of antigenic glycans and reducing the number of antigenic polypeptides, on the surface of the cells, thereby reducing their immunogenicity. 
     In some embodiments, reducing the number of antigenic glycans comprises contacting the cells with an enzyme capable of glycan trimming for a time sufficient to detach the antigenic glycans and then removing the detached glycans from the cells. In some embodiments, reducing the number of antigenic polypeptides comprises contacting the cells with an enzyme capable of cleaving polypeptides for a time sufficient to detach the antigenic polypeptides and then removing the detached polypeptides from the cells. In some embodiments, reducing the number of antigenic glycans comprises contacting the cells with an exogenous nucleic acid encoding an agent capable of repressing glycan biosynthesis or processing. In some embodiments, reducing the number of antigenic polypeptides comprises contacting the cells with an exogenous nucleic acid encoding an agent capable of repressing polypeptide biosynthesis or processing. 
     In some embodiments, the agent is CRISPR/Cas9 or a short interfering RNA. In some embodiments, the agent acts on a gene encoding a fucosyltransferase (e.g. FUT1 or FUT2 genes) or a glycosyltransferase (e.g. an ABO gene). In some embodiments, the agent is transiently active in the erythroid cell and is not maintained after enucleation. 
     In some embodiments, the method further comprises the step of irradiating the erythroid cell population. 
     In some embodiments, the provided erythroid cells are erythroid precursors, erythrocytes, or platelets. 
     In some embodiments, culturing comprises contacting the erythroid cells with one or more culturing factors selected from the group consisting of stem cell factor, IL-3, IL-6, insulin, transferrin, erythropoietin, hydrocortisone, and estrogen. 
     In some embodiments, the erythroid cell population is cultured in a bioreactor. 
     In some aspects, the disclosure provides a method of preserving the isolated erythroid cell population described herein. The method can comprise one or more of: 
     providing the erythroid cell population, 
     contacting the erythroid cell population with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere, and 
     storing the contacted erythroid cell population. 
     In some embodiments, the erythroid cell population is stored in an atmosphere comprising the inert or noble gas. In some embodiments, the erythroid cell population is stored at a refrigerated temperature above the freezing point. In some embodiments, the oxygen residing in the erythroid cell population is purged. In some embodiments, the inert or noble gas is selected from the group consisting of helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe). In some embodiments, the hemolysis of the erythroid cell population is less than 5%, 4%, 3%, 2% or less than 1% after storage of at least 10 days, 15 days, 20 days, 25 days, 30 days, 35 days, 40 days, or at least 45 days. 
     In some aspects, the disclosure provides a method of reducing the circulatory concentration of a target anti-drug antibody, the method comprising: administering to a human subject suffering from or at risk of developing an anti-drug antibody mediated disease, disorder or condition, a pharmaceutical composition comprising an erythroid cell as described herein, e.g., an erythroid cell population having a high density of surface-expressed polypeptides, wherein the pharmaceutical composition is administered in an amount effective to substantially reduce the circulatory concentration of the target anti-drug antibody. 
     In some aspects, the disclosure provides an enucleated, synthetic erythroid cell comprising on its surface at least about 1,000 copies of an exogenous docking polypeptide comprising a high-affinity acceptor site, wherein the docking polypeptide is less than about 50 kDa, and wherein the acceptor site has an affinity for a donor molecule of about 100 picomolar or less using suitable reaction conditions such as in 1× phosphate buffered saline (PBS) on ice. In some embodiments, suitable reaction conditions include comprise serum at 37 degrees. 
     In some embodiments, the docking polypeptide is expressed from an exogenous nucleic acid, and wherein during enucleation the docking polypeptide is retained by the erythroid cell whereas the exogenous nucleic acid is not retained. 
     In some embodiments, the erythroid cell comprises at least 5,000, 10,000, 25,000, 50,000, 100,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 25,000,000, or 50,000,000, copies of the docketing polypeptide. 
     In some embodiments, the docking polypeptide comprises a membrane-anchored polypeptide. In some embodiments, the membrane-anchored polypeptide is a transmembrane polypeptide. In some embodiments, the docketing polypeptide is a chimeric fusion polypeptide with a first part comprising the high-affinity acceptor site and a second part comprising the membrane-anchored polypeptide being from different origin. 
     In some embodiments, the erythroid cell is an erythrocyte or a platelet. 
     In some embodiments, the acceptor site has an affinity for a donor molecule selected from the group consisting of biotin, digoxin, and FITC. In some embodiments, the donor molecule is a small organic molecule. 
     In some embodiments, the docking polypeptide comprises an antibody molecule such as a scFv. 
     In some embodiments, the acceptor site has an affinity for the donor molecule of about 50 picomolar, 20 picomolar, 10 picomolar, 5 picomolar, 2 picomolar, 1 picomolar, 500 femtomolar, 250 femtomolar, 100 femtomolar, 50 femtomolar, 25 femtomolar, or about 10 femtomolar or less. 
     In some embodiments, the docking polypeptide is less than about 45 kDa, 40 kDa, 35 kDa, 30 kDa, or less than about 25 kDa. 
     In some embodiments, the cell further comprises a receiver polypeptide, wherein the receiver polypeptide binds to the high affinity acceptor site of the docking polypeptide. In some embodiments, the receiver polypeptide is conjugated to a donor molecule that binds to the acceptor site, thereby attaching the receiver polypeptide to the erythroid cell. In some embodiments, the receiver polypeptide is capable of interacting with a target molecule. 
     In some embodiments, the target molecule is a self-antibody, a complement cascade factor, a clotting cascade factor, an immune complex, a serum amyloid protein, a toxin, a metabolite, or an anti-drug antibody. 
     In some embodiments, the erythroid cells are immunologically omnicompatible. In some embodiments, the erythroid cells lack one or more antigen selected from Diego, RHAG, Kx, GLOB, I, Ch/Rg, Colton, Kidd, Rhesus (RhD, RhCE), Kell, Yt, Scianna, Dombrock, LW, H, Cromer, Knops, Indian, OK, JMH, GIL, ABO, Lewis, P, Raph, Xg, Lutheran, MNS, Gerbich, and Duffy, or any combination thereof. In some embodiments, the erythroid cells have a reduced glycosylation level of less than 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.25%, or of less than 0.1% compared to a control erythroid cell. In some embodiments, the erythroid cells: i) do not comprise a MHC antigen, or ii) comprise no more than one type of MHC antigen, wherein the cells arise from a population of homozygous or hemizygous progenitor cells. 
     In some aspects, the disclosure provides a pharmaceutical composition comprising an erythroid cell or erythroid cell population described herein and a pharmaceutically acceptable excipient. In some embodiments, pharmaceutical composition further comprises one anti-coagulant. In some embodiments, the pharmaceutical composition is provided in a storage container, e.g., a container that does not comprise DEHP plasticizer. In some embodiments, the erythroid cell population in the storage container is substantially purged of oxygen and/or is contacted with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere. 
     In some aspects, the disclosure provides a dosage form comprising a pharmaceutical composition described herein, wherein the dosage form is formulated as a liquid suspension. In some embodiments, the liquid suspension is formulated for intravenous administration to a subject. In some embodiments, the liquid suspension comprises at least 1e5 erythroid cells provided in a volume of between 10 nl and 500 ml. In some embodiments, the liquid suspension comprises at least 1e6, 1e7, 1e8, 1e9, or at least 1e10 erythroid cells. 
     In some aspects, the disclosure provides a method of producing a population of enucleated synthetic erythroid cells. The method can comprise one or more of, e.g., all of: 
     providing isolated erythroid cells, 
     introducing an exogenous nucleic acid encoding a docking polypeptide comprising a high-affinity acceptor site into the erythroid cells, 
     culturing the erythroid cells, and 
     inducing enucleation of the erythroid cells to obtain a population of enucleated erythroid cells comprising a docking polypeptide. 
     In some embodiments, the docking polypeptide is less than about 50 kDa, and/or the acceptor site has an affinity for a donor molecule of about 100 picomolar or less in suitable reaction conditions such as 1× phosphate buffered saline (PBS) on ice. In some embodiments, during enucleation at least 1,000 copies of the docking polypeptide are retained by the erythroid cell whereas the exogenous nucleic acid is not retained. 
     In some embodiments, the acceptor site has an affinity for the donor molecule of about 50 picomolar, 20 picomolar, 10 picomolar, 5 picomolar, 2 picomolar, 1 picomolar, 500 femtomolar, 250 femtomolar, 100 femtomolar, 50 femtomolar, 25 femtomolar, or about 10 femtomolar or less. 
     In some embodiments, the method further comprises the step of expanding the erythroid cells after the docking polypeptide is introduced. In some embodiments, the erythroid cells are expanded by at least 5,000-fold, 10,000-fold, 20,000-fold, 30,000-fold, 40,000-fold, or by at least 50,000-fold. In some embodiments, expansion is not carried out by co-culturing of the erythroid cells with an adherent stromal layer. 
     In some embodiments, the method further comprises contacting the erythroid cells with a receiver polypeptide comprising a donor molecule with affinity to the acceptor site of the docking polypeptide. 
     In some embodiments, the method further comprises purifying the enucleated erythroid cells to produce a population of at least 80% enucleated erythroid cells. In some embodiments, the purifying step comprises one or more (e.g., 2, 3, 4, 5, or more) passage(s) of the erythroid cell population through a de-leukocyting filter. 
     In some embodiments, the method further comprises rendering the erythroid cells immunologically omnicompatible. In some embodiments, rendering the erythroid cells immunologically omnicompatible comprises: i) reducing the number of antigenic glycans, ii) reducing the number of antigenic polypeptides, or iii) both reducing the number of antigenic glycans and reducing the number of antigenic polypeptides, on the surface of the cells, thereby reducing their immunogenicity. 
     In some embodiments, reducing the number of antigenic glycans comprises contacting the cells with an enzyme capable of glycan trimming for a time sufficient to detach the antigenic glycans and then removing the detached glycans from the cells. In some embodiments, reducing the number of antigenic polypeptides comprises contacting the cells with an enzyme capable of cleaving polypeptides for a time sufficient to detach the antigenic polypeptides and then removing the detached polypeptides from the cells. In some embodiments, the reducing the number of antigenic glycans comprises contacting the cells with an exogenous nucleic acid encoding an agent capable of repressing glycan biosynthesis or processing. In some embodiments, the reducing the number of antigenic polypeptides comprises contacting the cells with an exogenous nucleic acid encoding an agent capable of repressing polypeptide biosynthesis or processing. 
     In some embodiments, the agent is CRISPR/Cas9 or a short interfering RNA. In some embodiments, the agent acts on a gene encoding a fucosyltransferase (e.g. FUT1 or FUT2 genes) or a glycosyltransferase (e.g. an ABO gene). In some embodiments, the agent is transiently active in the erythroid cell and is not maintained after enucleation. 
     In some embodiments, the method further comprises the step of irradiating the erythroid cell population. 
     In some embodiments, the provided isolated erythroid cells are erythroid precursors, erythrocytes, or platelets. 
     In some embodiments, culturing comprises contacting the erythroid cells with one or more culturing factors selected from the group consisting of stem cell factor, IL-3, IL-6, insulin, transferrin, erythropoietin, hydrocortisone, and estrogen. In some embodiments, the erythroid cells are cultured in a bioreactor. 
     In some embodiments, the method further comprises contacting the erythroid cells with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere and storing the contacted erythroid cell population. In some embodiments, the erythroid cells are stored in an atmosphere comprising the inert or noble gas. In some embodiments, the erythroid cells are stored at a refrigerated temperature above the freezing point. In some embodiments, the method further comprises purging the oxygen residing in the erythroid cells. In some embodiments, the inert or noble gas is selected from the group consisting of helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe). In some embodiments, hemolysis of the erythroid cells is less than 5%, 4%, 3%, 2% or less than 1% after storage of at least 10 days, 15 days, 20 days, 25 days, 30 days, 35 days, 40 days, or at least 45 days. 
     In some embodiments, contacting the receiver polypeptide comprising the donor molecule results in binding of the receiver polypeptide to the acceptor site, thereby attaching the receiver polypeptide to the erythroid cell. 
     In some embodiments, the receiver polypeptide is capable of interacting with a target molecule. 
     In some embodiments, the target molecule is a self-antibody, a complement cascade factor, a clotting cascade factor, an immune complex, a serum amyloid protein, a toxin, a metabolite, or an anti-drug antibody. 
     In some aspects, the disclosure provides an enucleated erythroid cell, e.g., an isolated enucleated erythroid cell, comprising an exogenous polypeptide (e.g., a polypeptide described herein), wherein phosphatidylserine exposure, e.g., the level of phosphatidylserine exposure, on the surface of the isolated enucleated erythroid cell is the same as, or no more than 10%, 20%, 30%, 40%, 50%, 2-fold, 3-fold, 5-fold, or 10-fold greater than, the level of phosphatidylserine exposure on the surface of a control cell, e.g., e.g., wild type unmodified enucleated erythroid cell from the same species or an otherwise similar cultured erythroid cell that does not express the receiver polypeptide. 
     In some aspects, the disclosure provides a population of enucleated erythroid cells comprising an exogenous polypeptide (e.g., a polypeptide described herein), and wherein phosphatidylserine exposure, e.g., the level of phosphatidylserine exposure, on the surface of the population of enucleated erythroid cells is the same as, or no more than 10%, 20%, 30%, 40%, 50%, 2-fold, 3-fold, 5-fold, or 10-fold greater than, the level of phosphatidylserine exposure on the surface of a control population of cells, e.g., of wild type unmodified enucleated erythroid cell from the same species or an otherwise similar population of cultured erythroid cells that does not express the receiver polypeptide. 
     In some aspects, the disclosure provides an isolated enucleated erythroid cell comprising an exogenous polypeptide, wherein the level of phosphatidylserine exposure on the surface of the isolated enucleated erythroid cell is less than the level of phosphatidylserine exposure on the surface of a control cell, e.g., a primary RBC that has been loaded by hypotonic dialysis. 
     In some aspects, the disclosure provides a population of isolated enucleated erythroid cells comprising an exogenous polypeptide, wherein the level of phosphatidylserine exposure on the surface of the population of enucleated erythroid cells is less than the level of phosphatidylserine exposure on the surface of a control population, e.g., a primary RBC that has been loaded by hypotonic dialysis. 
     In embodiments, the exogenous polypeptide: is intracellular; does not comprise a reporter, e.g., a fluorescent protein, e.g., GFP; comprises an enzyme, an antibody molecule, a human polypeptide, a polypeptide having at least 85%, 905, 95%, 96%, 97%, 98%, or 99% identity to a human polypeptide, an extracellular domain greater than 10, 15, 20, 25, 30, 35, 40, 45, or 50 amino acids; does not comprise a sortase acceptor sequence or sortase donor sequence, e.g., extracellularly and/or within 1, 2, 3, 4, 5, 10, 20, or 50 amino acids of a transmembrane region; was not formed by sortase mediated conjugation; or comprises an RNA that encodes the entire exogenous polypeptide, e.g., wherein the RNA encodes an extracellular domain greater than 10, 15, 20, 25, 30, 35, 40, 45, or 50 amino acids, or does not encode a sortase acceptor sequence or sortase donor sequence; or any combination thereof. 
     In embodiments, phosphatidylserine exposure is measured by annexin-V binding, e.g., in a flow cytometry assay. In embodiments, the enucleated cell has less than about 1×10 4 , 2×10 4 , 3×10 4 , 5×10 4 , or 1×10 5  FL4-H of bound annexin-V, e.g., by the assay of Example 91. In embodiments, the enucleated cell has at least about 1×10 2 , 2×10 2 , 5×10 2 , 1×10 3 , or 2×10 3  FL4-H of bound annexin-V. In embodiments, the enucleated cell has about 1×10 2 -2×10 2 , 2×10 2 -5×10 2 , 2×10 2 -1×10 3 , 2×10 2 -2×10 3 , 2×10 2 -5×10 3 , 2×10 2 -1×10 4 , 2×10 2 -2×10 4 , or 2×10 2 -5×10 4  FL4-H of bound annexin-V. 
     In embodiments, at least 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% of the enucleated cells in the population have the same level of phosphatidylserine exposure as a control cell, e.g., e.g., wild type unmodified enucleated erythroid cell from the same species or an otherwise similar cultured erythroid cell that does not express the receiver polypeptide. In embodiments, up to about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% of the enucleated cells in the population have the same level of phosphatidylserine exposure as a control cell, e.g., e.g., wild type unmodified enucleated erythroid cell from the same species or an otherwise similar cultured erythroid cell that does not express the receiver polypeptide. In embodiments, about 50%-95%, 55%-95%, 60%-95%, 65%-95%, 70%-95%, 75%-95%, 80%-95%, 85%-95%, 90%-95%, 91%-95%, 92%-95%, 93%-95%, or 94%-95% of the enucleated cells in the population have the same level of phosphatidylserine exposure as a control cell, e.g., e.g., wild type unmodified enucleated erythroid cell from the same species or an otherwise similar cultured erythroid cell that does not express the receiver polypeptide. 
     In embodiments, at least about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% of the enucleated cells in the population have less than a predetermined threshold of bound annexin-V, e.g., 3×10 4  FL4-H of bound annexin-V, e.g., by the assay of Example 91. In embodiments, up to about 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% of the enucleated cells in the population have less than a predetermined threshold of bound annexin-V, e.g., 3×10 4  FL4-H of bound annexin-V, e.g., by the assay of Example 91. In embodiments, about 50%-95%, 55%-95%, 60%-95%, 65%-95%, 70%-95%, 75%-95%, 80%-95%, 85%-95%, 90%-95%, 91%-95%, 92%-95%, 93%-95%, or 94%-95% of the enucleated cells in the population have less than a predetermined threshold of bound annexin-V, e.g., 3×10 4  FL4-H of bound annexin-V, e.g., by the assay of Example 91. 
     In embodiments, the population has a unimodal distribution of the amount of phosphatidylserine exposure per cell, such that, when the amount of phosphatidylserine exposure per cell is graphed with phosphatidylserine level on the x-axis and number of cells on the y-axis, the distribution forms a single peak. 
     In embodiments, the population has a mean of less than about 300,000, 250,000, 200,000, 154,111, 150,000, 107,190, 100,000, 80,000, 76,503, or 60,000 FL4-H of bound annexin-V, e.g., by the assay of Example 91. In embodiments, the mean is at least 10,000, 20,000, 30,000, 40,000, 50,000, or 60,000 FL4-H of bound annexin-V. In embodiments, the population has a mean of between 60,000-100,000, 60,000-150,000, 60,000-200,000, 60,000-250,000, or 60,000-300,000 FL4-H of bound annexin-V. 
     In embodiments, the population has a median of less than about 100,000, 90,000, 80,000, 70,000, 63,018, 62,212, 60,826, 60,000, 50,000, 40,000, or 30,000 FL4-H of bound annexin-V, e.g., by the assay of Example 91. In embodiments, the median is at least 10,000, 20,000, or 30,000 FL4-H of bound annexin-V. In embodiments, the population has a median of between 30,000-60,000, 30,000-70,000, 30,000-80,000, 30,000-90,000, or 30,000-100,000 FL4-H of bound annexin-V. 
     In some aspects, the disclosure provides an enucleated erythroid cell, e.g., an isolated enucleated erythroid cell, comprising an exogenous polypeptide (e.g., a polypeptide described herein) wherein the enucleated cell does not lyse in a solution consisting of 0.3%, 0.35%, 0.4%, 0.45%, or 0.5% NaCl in water. In embodiments, the cell does not lyse in a solution consisting of 0.35-0.5%, 0.4-0.5%, 0.45-0.5%, 0.35-0.5%, 0.35-0.55%, 0.4-0.55%, 0.45-0.55%, or 0.5-0.55% NaCl in water. 
     In some aspects, the disclosure provides a population of enucleated erythroid cells, wherein a plurality of the enucleated cells comprise an exogenous polypeptide (e.g., a polypeptide described herein) and wherein the population has an osmotic fragility of less than 50% cell lysis in a solution consisting of 0.3%, 0.35%, 0.4%, 0.45%, or 0.5% NaCl in water. In embodiments, the osmotic fragility is greater than 50% cell lysis in a solution consisting of 0.1% or 0.2% NaCl in water. In embodiments, the osmotic fragility is 50% lysis in a solution consisting of 0.2-0.5%, 0.3-0.5%, 0.35-0.5%, 0.45-0.5%, 0.2-0.55%, 0.3-0.55%, 0.35-0.55%, or 0.45-0.55% NaCl in water. 
     In some aspects, the disclosure provides an enucleated erythroid cell, e.g., an isolated enucleated erythroid cell, comprising an exogenous polypeptide (e.g., a polypeptide described herein), wherein the osmotic fragility of the enucleated cell is close to, e.g., the same as or within 20%, 15%, 10%, 5%, 4%, 3%, 2%, or 1% of, the osmotic fragility of a naturally occurring red blood cell. 
     In some aspects, the disclosure provides a population of enucleated erythroid cells, wherein a plurality of the enucleated cells comprise an exogenous polypeptide (e.g., a polypeptide described herein), and wherein the population has an osmotic fragility that is close to the osmotic fragility of a population of naturally occurring red blood cells. 
     In embodiments, osmotic fragility is measured by the assay of Example 90. 
     In some aspects, the disclosure provides an enucleated erythroid cell, e.g., an isolated enucleated erythroid cell, comprising an exogenous polypeptide (e.g., a polypeptide described herein), wherein the enucleated cell has a volume of about 62-412 fL, e.g., 412 fL, wherein cell volume is measured by the Coulter counter assay of Example 89. 
     In some aspects, the disclosure provides a population of enucleated erythroid cells, wherein a plurality of the enucleated cells comprise an exogenous polypeptide (e.g., a polypeptide described herein), wherein the population has a volume range of 62-412 fL, wherein optionally 9% of the cells have a volume of &lt;100 fL, approximately 15% of the cells have a volume of &lt;113 fL, approximately 32% of the cells have a volume of &lt;135 fL, approximately 46% of the cells have a volume of &lt;156 fL, and/or approximately 71% of the cells have a volume of &lt;202 fL, and wherein cell volume is measured by the Coulter counter assay of Example 89. 
     In some aspects, the disclosure provides an enucleated erythroid cell, e.g., an isolated enucleated erythroid cell, comprising an exogenous polypeptide (e.g., a polypeptide described herein), wherein the enucleated cell has a volume of about 150 fL, e.g., about 140-160, 130-170, or 120-180 fL, or at least about 100, 110, 120, 130, 140, 150, 160, 170, 180, or 190 fL. In embodiments, the enucleated cell has a volume of up to about 160, 170, 180, or 190 fL. 
     In some aspects, the disclosure provides a population of enucleated erythroid cells, wherein a plurality of the enucleated cells comprise an exogenous polypeptide (e.g., a polypeptide described herein), and wherein the population has a mean cell volume of about 150 fL, about 140-160, 130-170, 120-180, 110-190, or 100-200 fL, or at least about 140, 150, 160, 170, or 180 fL. In embodiments, at least 50, 60%, 70%, 80%, or 90% of the cells in the population have a cell volume within about 140-160, 130-170, 120-180, 110-190, or 100-200 fL. 
     In some aspects, the disclosure provides an enucleated erythroid cell, e.g., an isolated enucleated erythroid cell, comprising an exogenous polypeptide (e.g., a polypeptide described herein), wherein the enucleated cell has a diameter of about 6, 6.5, or 7 urn, or at least about 6, 6.5, 7, or 7.5 urn, and optionally up to about 8 um. In some aspects the disclosure provides a population of enucleated erythroid cells, wherein a plurality of the enucleated cells comprise an exogenous polypeptide (e.g., a polypeptide described herein), and wherein the cells have a mean diameter of about 6, 6.5, or 7 urn, or at least about 6, 6.5, 7, or 7.5 urn, and optionally up to about 8 um. In embodiments, diameter is measured by Coulter counter, e.g., in the assay of Example 89. 
     In some aspects, the disclosure provides a population of enucleated erythroid cells, wherein a plurality of the enucleated cells comprise an exogenous polypeptide (e.g., a polypeptide described herein), and wherein at least about 50%, 60%, 70%, 80%, 90%, 95%, or 99% of the cells in the population have a volume of between about 140-160, 130-170, 120-180, 110-190, or 100-200 fL. In embodiments, at least about 50%, 60%, 70%, 80%, 90%, 95%, or 99% of the cells in the population have a volume of between about 100-200 fL. In embodiments, at least about 50%, 60%, 70%, 80%, 90%, 95%, or 99% of the cells in the population have a volume of between about 120-180 fL. In embodiments, at least about 50% of the cells in the population have a volume of between about 120-180 fL or between about 100-200 fL. 
     In some aspects, the disclosure provides an enucleated erythroid cell, e.g., an isolated enucleated erythroid cell, comprising an exogenous polypeptide (e.g., a polypeptide described herein), wherein the enucleated cell comprises fetal hemoglobin, e.g., at least about 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 pg of fetal hemoglobin. In some aspects and embodiments, the enucleated cell comprises at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or 19 pg of fetal hemoglobin. In some embodiments, the cell comprises up to about 26, 28, or 30 pg of fetal hemoglobin. In embodiments, the cell comprises about 1-30, 5-30, 10-30, 15-30, or 20-30 pg of fetal hemoglobin. 
     In some aspects, the disclosure provides a population of enucleated erythroid cells, wherein a plurality of the enucleated cells comprise an exogenous polypeptide (e.g., a polypeptide described herein), and wherein a plurality of the enucleated cells comprise fetal hemoglobin, e.g., the cell population has an average of about 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 pg of fetal hemoglobin per cell. In some aspects and embodiments, the population comprises at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, or 19 pg of fetal hemoglobin per cell. In some embodiments, the population comprises up to about 26, 28, or 30 pg of fetal hemoglobin per cell. In embodiments, the population comprises about 1-30, 5-30, 10-30, 15-30, or 20-30 pg of fetal hemoglobin per cell. 
     In embodiments, fetal hemoglobin levels are measured using Drabkin&#39;s reagent, e.g., the assay of Example 33. 
     In embodiments, the population described herein comprises one or more nucleated erythroid cells. 
     In embodiments, the population described herein comprises at least 80%, 85%, 90%, 95%, 97%, 98% or 99% enucleated erythroid cells. In embodiments, the population comprises at least 30%, 35%, 40%, 50%, 60%, or 70% enucleated erythroid cells. In embodiments, the population comprises up to about 90%, 95%, 96%, 97%, 98%, or 99% enucleated erythroid cells. 
     In embodiments, the exogenous polypeptide is encoded by an exogenous nucleic acid that is not retained by the enucleated cell, and/or the exogenous polypeptide is not loaded into the enucleated cell. In embodiments, the exogenous polypeptide comprises a transmembrane segment, e.g., a red blood cell transmembrane protein or transmembrane portion thereof, e.g., a type I, type II, or type III red blood cell transmembrane protein. In embodiments, the exogenous polypeptide is localized intracellularly, e.g., is not associated with the membrane of the enucleated cell. In embodiments, the exogenous polypeptide is a fusion protein. In embodiments, the exogenous polypeptide comprises a flexible linker, an epitope tag, an enzyme, a protease, a nuclease, a receiver, an antibody-like molecule, a ligand of an antibody, a growth factor, a cytokine, a chemokine, a growth factor receptor, a cytokine receptor, a chemokine receptor, an enzymatic recognition sequence, a transpeptidase recognition sequence, a protease recognition sequence, a cleavable domain, an intein, a DNA binding protein, and RNA binding protein, a complement regulatory molecule, a complement cascade molecule, a clotting cascade molecule, a chelator, a complement regulatory domain, an SCR domain, a CCP domain, an immunoglobulin or immunogloblulin-like domain, an armadillo repeat, a leucine zipper, a dealth effector domain, a cadherein repeat, an EF hand, a phosphotyrosine binding domain, a pleckstrin homology domain, an SCR homology 2 domain, a zinc finger domain, a cyclic peptide, or a cell-penetrating peptide. 
     In certain aspects, the present disclosure provides an enucleated erythroid cell comprising exogenous RNA. In embodiments, the cell further comprises a polypeptide encoded by the exogenous RNA. In embodiments, the RNA was transcribed from an exogenous DNA that is not retained by the enucleated cell. In embodiments, the polypeptide is a receiver, e.g., a receiver described herein. 
     In certain aspects, the present disclosure provides a method of producing a plurality of enucleated erythroid cells comprising an exogenous protein, comprising contacting an erythroid cell or erythroid cell precursor with RNA (e.g., isolated RNA or in vitro transcribed RNA) encoding the protein, under conditions that allow at least 50%, 60%, 70%, 80%, or 85% of the cells in the plurality to produce the protein, thereby producing an enucleated erythroid cell comprising an exogenous protein. In embodiments, the cell undergoes enucleation after being contacted with the RNA. In embodiments, the method comprises performing transfection or electroporation. In embodiments, the cell population has at least 50%, 60%, 70%, 80%, 85%, 90%, or 95% cell viability. 
     In some aspects, the disclosure provides an enucleated erythrocyte cell comprising about 5×10 5 , 1×10 6 , 2×10 6 , 5×10 6 , 5.6×10 6 , or 1×10 7  copies of an exogenous protein, e.g., a protein comprising PAH. In some aspects, the disclosure provides an enucleated erythrocyte cell comprising about 5×10 5 , 7.4×10 5 , 1×10 6 , 2×10 6 , 5×10 6 , or 1×10 7  copies of an exogenous protein, e.g., a protein comprising PAL. In some aspects, the disclosure provides an enucleated erythrocyte cell comprising about 5×10 5 , 6.2×10 5 , 1×10 6 , 2×10 6 , 5×10 6 , or 1×10 7  copies of an exogenous protein, e.g., a protein comprising MGL. In embodiments, the erythroid cell comprises at least about 5×10 5 , 6.2×10 5 , 7.4×10 5 , 1×10 6 , 2×10 6 , 5×10 6 , 5.6×10 6 , or 1×10 7  copies of the exogenous protein, e.g., PAH, PAL, or MGL. In some aspects, the disclosure provides a population of enucleated erythrocyte cells having an average of about 1×10 5 , 2×10 5 , 4×10 5 , 5×10 5 , 1×10 6 , 2×10 6 , 5×10 6 , 5.6×10 6 , or 1×10 7  copies per cell of an exogenous protein, e.g., a protein comprising PAH or PAL. In embodiments, the population has an average of at least about 1×10 5 , 2×10 5 , 4×10 5 , 5×10 5 , 1×10 6 , 2×10 6 , 5×10 6 , 5.6×10 6 , or 1×10 7  copies per cell of the exogenous protein. In some embodiments, the standard deviation of copies of exogenous polypeptide per cell in the population is less than about 1×10 6 , 5×10 5 , 2.7×10 5 , 2×10 5 , 1×10 5 , 5×10 4 , or 2×10 4 . 
     In some aspects, the disclosure provides an enucleated erythrocyte cell comprising an exogenous polypeptide comprising ADAMTS13, CFI (Complement Factor I), PAH, or PAL, or a derivative or functional fragment thereof. 
     In embodiments, the polypeptide comprising ADAMTS13 further comprises a transmembrane domain, e.g., GPA or the transmembrane region thereof and optionally the intracellular region of GPA. In embodiments, the enucleated erythrocyte cell comprising ADAMTS13 cleaves a vWF subdomain A2, e.g., in the assay of Example 86. In embodiments, the enucleated erythrocyte cell comprising ADAMTS13 is more active than a similar amount of purified ADAMTS13, e.g., in the assay of Example 86. 
     In embodiments, the polypeptide comprising CFI further comprises a transmembrane domain, e.g., GPA or the transmembrane region thereof and optionally the intracellular region of GPA. In embodiments, the enucleated erythroid cell comprising CFI cleaves recombinant complement factor C3b, e.g., in the assay of Example 87. 
     In embodiments, the polypeptide comprising PAH or PAL is a cytoplasmic free PAH or PAL, or further comprises a transmembrane domain, e.g., GPA or the transmembrane region thereof and optionally the intracellular region of GPA. In embodiments, the enucleated erythrocyte cell comprising PAH or PAL produces tyrosine from phenylalanine in the presence of BH4 co-factor, e.g., in the assay of Example 88. 
     The disclosure contemplates all combinations of any one or more of the foregoing aspects and/or embodiments, as well as combinations with any one or more of the embodiments set forth in the detailed description and examples. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The figures are meant to be illustrative of one or more features, aspects, or embodiments of the invention and are not intended to be limiting. 
         FIG. 1A - FIG. 1F  are a collection of flow cytometry plots of red blood cells contacted with fluorescently labeled IgG encapsulated within liposomes. Cells are shown that are incubated with no liposomes ( FIG. 1A ,  FIG. 1D ), a low dose of liposomes ( FIG. 1B , FIG.  1 E), and a high dose of liposomes ( FIG. 1C ,  FIG. 1F ). On the  FIG. 1D - FIG. 1F  histograms, the percentage of cells that are fluorescent is shown. 
         FIG. 2  is a plot of cell surface expression levels assessed by quantitative flow cytometry. The plot shows of various cell surface receptors—glycophorin A (solid triangles), cKIT (dashed squares), transferrin receptor (dotted diamonds)—and an exogenous surface transgene (open circles) during the course of erythroid cell differentiation. 
         FIG. 3A - FIG. 3AP  is a collection of flow cytometry plots and Western blots that demonstrate the expression of a vast array of exemplary receivers on the surface, in the cytoplasm, as fusions, and as intact proteins, in three cell types, enucleated erythroid cells, nucleated erythroid precursor cells, and erythroleukemic cells. 
         FIG. 3A - FIG. 3N  shows the exogenous expression of surface and cytoplasmic proteins on enucleated cultured erythroid cells. 
         FIG. 3A —Expression of glycophorin A with an HA epitope tag at the cytoplasmic C terminus assessed by expression of co-translated GFP. 
         FIG. 3B —Expression of glycophorin A with an HA epitope tag at the N terminus between the leader sequence and the body of the gene assessed by anti-HA staining. 
         FIG. 3C —Expression of complement receptor 1-derived fragment of ˜70 kDa with an HA epitope tag at the N terminus assessed by anti-HA staining. 
         FIG. 3D —Expression of antibody scFv as N terminal fusion to glycophorin A assessed by anti-HA staining. 
         FIG. 3E —Expression of antibody scFv fused to C terminus of Kell-derived fragment of 71 amino acids assessed by anti-HA staining. 
         FIG. 3F —Expression of antibody scFv fused to C terminus of Kell-derived fragment of 79 amino acids assessed by anti-HA staining. 
         FIG. 3G —Expression of CD55 with HA epitope tag at the extracellular N terminus after the leader sequence assessed by anti-HA staining. 
         FIG. 3H —Expression of CD59 with HA epitope tag at the extracellular N terminus after the leader sequences assessed by anti-HA staining. 
         FIG. 3I —Expression of antibody scFv fused to N-terminus of CD55-derived fragment of 37 amino acids, assessed by anti-HA Western blot. 
         FIG. 3J —Cytoplasmic expression of adenosine deaminase fused to HA tag assessed by anti-HA Western blot. Expected size approximately 40 kDa. 
         FIG. 3K —Cytoplasmic expression of phenylalanine hydroxylase fused to HA tag assessed by anti-HA Western blot. Expected size approximately 33 kDa. 
         FIG. 3L —Cytoplasmic expression of phenylalanine hydroxylase fused to adenosine deaminase and an HA tag assessed by anti-HA Western blot. 
         FIG. 3M —Cytoplasmic expression of adenosine deaminase fused to the intracellular C terminus of glycophorin A assessed by anti-HA Western blot. Expected size approximately 55 kDa. 
         FIG. 3N —Cytoplasmic expression of phenylalanine hydroxylase fused to the intracellular C terminus of glycophorin A assessed by anti-HA Western blot. Expected size approximately 50 kDa. 
         FIG. 3O -FIG. AJ shows the exogenous expression of surface and cytoplasmic proteins on nucleated cultured erythroid precursor cells. 
         FIG. 3O —Expression of glycophorin A with an HA epitope tag at the cytoplasmic C terminus assessed by expression of co-translated GFP. 
         FIG. 3P —Expression of glycophorin A with an HA epitope tag at the N terminus between the leader sequence and the body of the gene assessed by anti-HA staining. 
         FIG. 3Q —Overexpression of complement receptor 1 assessed by anti-CR1 staining. 
         FIG. 3R —Expression of complement receptor 1-derived fragment of ˜70 kDa with an HA epitope tag at the N terminus assessed by anti-HA staining. 
         FIG. 3S —Expression of complement receptor 1-derived fragment of ˜210 kDa with an HA epitope tag at the N terminus assessed by anti-HA staining. 
         FIG. 3T —Expression of complement receptor 1-derived fragment of ˜230 kDa fused to the N terminus of glycophorin A with an HA epitope tag at the N terminus assessed by anti-HA staining. 
         FIG. 3U —Expression of antibody scFv as N terminal fusion to glycophorin A assessed by anti-HA staining. 
         FIG. 3V —Expression of antibody scFv fused to the extracellular C terminus of Kell, assessed by anti-HA staining. Expected size approximately 108 kDa. 
         FIG. 3W —Expression of HA tag fused to the extracellular C terminus of Kell, assessed by anti-HA staining. 
         FIG. 3X —Expression of Kell-derived fragment of 71 amino acids with HA tag at the C (extracellular) terminus assessed by anti-HA staining. 
         FIG. 3Y —Expression of Kell-derived fragment of 79 amino acids with HA tag at the C terminus assessed by anti-HA staining. 
         FIG. 3Z —Expression of antibody scFv fused to C terminus of Kell-derived fragment of 71 amino acids assessed by anti-HA staining. 
         FIG. 3AA —Expression of antibody scFv fused to C terminus of Kell-derived fragment of 79 amino acids assessed by anti-HA staining. 
         FIG. 3AB —Expression of CD55 with HA epitope tag at the extracellular N terminus after the leader sequence assessed by anti-HA staining. 
         FIG. 3AC —Expression of CD59 with HA epitope tag at the extracellular N terminus after the leader sequences assessed by anti-HA staining. 
         FIG. 3AD —Expression of antibody scFv fused to N-terminus of CD55-derived fragment of 37 amino acids, assessed by anti-HA staining. 
         FIG. 3AE —Expression of antibody scFv fused to N-terminus of CD59 assessed by anti-HA staining. 
         FIG. 3AF —Cytoplasmic expression of adenosine deaminase fused to HA tag assessed by anti-HA Western blot. Expected size approximately 40 kDa. 
         FIG. 3AG —Cytoplasmic expression of phenylalanine hydroxylase fused to HA tag assessed by anti-HA Western blot. Expected size approximately 33 kDa. 
         FIG. 3AH —Cytoplasmic expression of phenylalanine hydroxylase fused to adenosine deaminase and an HA tag assessed by flow cytometry for fluorescence from co-translated GFP. 
         FIG. 3AI —Cytoplasmic expression of adenosine deaminase fused to the intracellular C terminus of glycophorin A assessed by anti-HA Western blot. Expected size approximately 55 kDa. 
         FIG. 3AJ —Cytoplasmic expression of phenylalanine hydroxylase fused to the intracellular C terminus of glycophorin A assessed by anti-HA Western blot. Expected size approximately 50 kDa. 
         FIG. 3AK - FIG. 3AP  shows the exogenous expression of surface and cytoplasmic proteins on K562 erythroleukemia cells. 
         FIG. 3AK —Overexpression of complement receptor 1 assessed by anti-CR1 staining. 
         FIG. 3AL —Expression of antibody scFv as N terminal fusion to glycophorin A assessed by anti-HA staining. 
         FIG. 3AM —Expression of antibody scFv fused to N-terminus of CD55-derived fragment of 37 amino acids, assessed by anti-HA staining. 
         FIG. 3AN —Expression of antibody scFv fused to N-terminus of CD59 assessed by anti-HA staining. 
         FIG. 3AO —Cytoplasmic expression of adenosine deaminase fused to HA tag assessed by anti-HA Western blot. Expected size approximately 40 kDa. 
         FIG. 3AP —Cytoplasmic expression of phenylalanine hydroxylase fused to HA tag assessed by anti-HA Western blot. Expected size approximately 33 kDa. 
         FIG. 4A - FIG. 4C  is a collection of flow cytometry histograms that measure fluorescence in primary platelets that have been transfected with mRNA encoding a fluorescent protein (GFP). ( FIG. 4A ) Untransfected platelets. ( FIG. 4B ) Platelets transfected with 3 ug GFP mRNA. ( FIG. 4C ) Platelets transfected with 6.8 ug GFP mRNA. 
         FIG. 5A - FIG. 5D  show protein expression and enzymatic activity of transgenic erythroid cells in culture. ( FIG. 5A ) is a Western blot of exogenously expressed adenosine deaminase detected with an anti-HA antibody over the course of differentiation, from nucleated precursor cells (“Diff I D5”) through to enucleated erythroid cells (“Diff III D8”). ( FIG. 5B ) is a bar chart of inosine produced from adenosine by intact adenosine deaminase-expressing 293T cells. ( FIG. 5C ) is a Western blot of the exogenously expressed phenylalanine hydroxylase detected with an anti-HA antibody at various time points over the course of differentiation, from nucleated precursor cells (“Diff I D5”) through to enucleated erythroid cells (“Diff III D8”). ( FIG. 5D ) is a bar chart of tyrosine produced from phenylalanine by lysates of cultured phenylalanine hydroxylase-expressing enucleated erythroid cells. 
         FIG. 6A - FIG. 6B  show immune complex capture and transfer to macrophages by cultured erythroid cells that overexpress complement receptor 1 (CR1). ( FIG. 6A ) is a flow cytometry plot that shows the capture of fluorescent immune complexes (white histogram) and complement-deficient immune complexes (shaded histogram) by cultured erythroid cells that overexpress CR1. ( FIG. 6B ) is a bar chart of flow cytometry data assessing the uptake of fluorescent immune complexes (hashed bars), complement deficient immune complexes (gray bars), or no immune complexes (black bars) by macrophages (left set) or macrophages incubated with cultured erythroid cells that overexpress CR1 (right set). 
         FIG. 7A - FIG. 7D  show the activity of an antibody scFv that binds hepatitis B surface antigen (scFv) on the surface of a cultured erythroid cell. ( FIG. 7A ) is a flow cytometry histogram showing binding of 450 nM antigen (white histogram) or no antigen (gray histogram). ( FIG. 7B ) is a titration of binding signal assessed by flow cytometry for a range of antigen concentrations. ( FIG. 7C - FIG. 7D ) are flow cytometry plots of blood cells from mice that had been injected with fluorescent antigen and cultured erythroid cells that ( FIG. 7C ) do not or ( FIG. 7D ) do express scFv. The y-axis measures antigen fluorescence. The x-axis measures fluorescence of the cultured cells. 
         FIG. 8A - FIG. 8D  shows the specific clearance of circulating antibodies mediated by membrane-receiver complexes in vivo. ( FIG. 8A ) is a set of flow cytometry plots that show no binding (left) and binding (right) of circulating Dylight650-labeled mouse anti-HA antibody to CFSE-labeled cultured human erythroid cells isolated from a recipient mouse that either do not (left) or do (right) express HA epitope tag on their surface. The x-axis measures CFSE fluorescence. The y-axis measures anti-HA antibody Dylight650 fluorescence. ( FIG. 8B ) is data from an HA epitope tag substrate ELISA comparing anti-HA antibody levels over time in plasma collected from mice injected with anti-HA antibody (open circles, solid line), anti-HA antibody followed by cultured human erythroid cells that do not express HA epitope tag (dashed line), or anti-HA antibody followed by cultured human erythroid cells that do express HA epitope tag (dotted line). ( FIG. 8C ) is a set of flow cytometry plots that show no binding (left) and binding (right) of Dylight650-labeled mouse anti-biotin antibody to CFSE-labeled primary human erythrocytes that either are not (left) or are (right) conjugated with biotin on their surface. The x-axis measures CFSE fluorescence. The y-axis measures anti-biotin antibody Dylight650 fluorescence. ( FIG. 8D ) is data from a biotin substrate ELISA comparing anti-biotin antibody levels over time in plasma collected from mice injected with anti-biotin antibody (open circles, solid line), anti-biotin antibody followed by cultured human erythroid cells that are not conjugated to biotin (dashed line), or anti-biotin antibody followed by cultured human erythroid cells that are conjugated to biotin (dotted line). 
         FIG. 9A - FIG. 9B  shows the clearance rate of cultured human eyrthroid cells in a mouse. ( FIG. 9A ) is a representative flow cytometry dot-plot of drawn blood, stained for human glycophorin A (y-axis) and CFSE (x-axis), in which human cultured cells are double-positive. ( FIG. 9B ) is a plot of the clearance rate over time as a percentage of double-positive cells remaining after NSG mice were injected with human red blood cells (solid circles), cultured enucleated erythroid cells (dashed diamonds), cultured enucleated erythroid cells that express an intracellular exogenous protein (dotted squares) and cultured enucleated erythroid cells that express a surface exogenous protein (open triangles). 
         FIG. 10A - FIG. 10D  is an assessment of adverse events following injection of cultured human erythroid cells into a mouse. ( FIG. 10A - FIG. 10B ) show levels of ( FIG. 10A ) fibrinopeptide A and ( FIG. 10B ) fibrinopeptide B assessed by ELISA in plasma collected from mice 20 minutes (black), 6 hours (gray), and 48 hours (white) after injection with (1) human red blood cells, (2) cultured human erythroid cells, (3) cultured human erythroid cells expressing an exogenous cytoplasmic protein, (4) cultured human erythroid cells expressing an exogenous surface transgene, or (5) recombinant protein. ( FIG. 10C - FIG. 10D ) show microscope images of histologically stained sections of spleen for mice injected with ( FIG. 10C ) cultured human erythroid cells and ( FIG. 10D ) recombinant protein. 
         FIG. 11A - FIG. 11B  tracks the expression of exogenous protein on cultured erythroid cells in circulation. ( FIG. 11A ) is flow cytometry data of blood drawn from a mouse that was injected with cultured human erythroid cells expressing an exogenous surface protein, showing the percent of cultured human erythroid cells that are HA-positive over time. ( FIG. 11B ) is a Western blot of blood drawn from two mice, wherein one mouse was injected with cultured human erythroid cells expressing an exogenous cytoplasmic protein, and wherein the other mouse was injected with the purified recombinantly-produced exogenous protein in the absence of any cells, showing the level of HA-containing protein in the blood over time. 
         FIG. 12A - FIG. 12C  is an assessment of expansion and differentiation of cultured human erythroid cells. ( FIG. 12A ) is a plot of expansion rates for distinct cultures of in vitro differentiated erythroid cells that contain transgenes (dashed line and dotted line) and cells that do not contain a transgene (solid line). ( FIG. 12B ) is a flow cytometry plot of cell surface markers GPA and CKIT for distinct cultures of cultured human erythroid cells that do not (left) or do (right) contain a transgene. ( FIG. 12C ) is a flow cytometry plot of cultured human erythroid cells that do not (left) or do (right) contain a transgene, wherein the cells are stained with DNA stain DRAQ5 (y-axis) and anti-glycophorin A (x-axis), which identifies distinct populations of (1) enucleated cells, (2) nucleated cells, and (3) nuclei. 
         FIG. 13A  is a schematic of a synthetic membrane-receiver complex comprising a receiver polypeptide. The left panel depicts the flux of a target substrate across the membrane of the synthetic membrane-receiver complex. The target substrate is altered by an internally localized enzymatic receiver polypeptide and the resulting product of the enzymatic reaction either remains in the synthetic membrane-receiver complex or exits through the membrane. The right panel depicts a synthetic membrane-receiver complex that contains at least two receivers (e.g., receiver polypeptides), one being localized on the surface and one being internally localized. In this example, the surface-localized receiver aids a substrate to enter the synthetic membrane-receiver complex, e.g., by carrying out a transporter function. The second receiver, localized internally, alters the substrate enzymatically. The resulting product of the enzymatic reaction either remains in the synthetic membrane-receiver complex or exits through the membrane, optionally aided by the first surface-localized receiver. 
         FIG. 13B  is a schematic of another synthetic membrane-receiver complex comprising a receiver polypeptide.  FIG. 13B  depicts a receiver polypeptide localized on the surface of the synthetic membrane-receiver complex. As shown, a target substrate can be acted upon directly by the receiver. In the exemplified configuration, the target substrate does not need to cross the membrane to be enzymatically converted to a product. Optionally, the surface-localized enzymatic receiver polypeptide can be made cleavable, e.g., if the complex enters a specific microenvironment. In that instance, the receiver polypeptide will be cleaved and become active in the extracellular space. 
         FIG. 13C  is a schematic of yet another synthetic membrane-receiver complex comprising a receiver.  FIG. 13C  depicts the lysis of a synthetic membrane-receiver complex containing internally-localized receiver (e.g., a polypeptide) and optional payload (e.g., a therapeutic agent) which may result from a variety of stimuli. Upon lysis, the internally-localized receiver and optional payload is released into the microenvironment where it may act on a target substrate. 
         FIG. 14A  is a schematic of three ways in which a receiver may be localized in a synthetic membrane-receiver complex.  FIG. 14B  is a schematic of three ways in which a receiver localized in or on a synthetic membrane-receiver complex may act on a target in circulation.  FIG. 14C  is a schematic of an auto-catalytic fusion of an endogenous polypeptide anchor to a receiver utilizing a SpyTag-SpyCatcher mechanism. 
         FIG. 15A - FIG. 15B  shows expression of a chimeric construct of ADAMTS13 fused to GPA on K562 erythroleukemia cells.  FIG. 15A  is a histogram showing transduced cells (black histogram) are compared to untransduced cells (gray histogram) by flow cytometry staining with an anti-HA antibody.  FIG. 15B  is a photo of a Western blot showing protein extracts of the same cells and presence of the ADAMTS13-GPA fusion protein is detected using an anti-HA developing antibody. 
         FIG. 16  is a photo of a Western blot showing enzymatic activity of various ADAMTS13-containing constructs. Activity is measured by cleavage of the A2 domain of von Willebrand Factor (vWF-A2, recombinant) which is detected by Western blot with an anti-vWF-A2 antibody. The lanes on the gel are: (1) recombinant vWF-A2, (2) vWF-A2 plus recombinant ADAMTS13 (75 ng), (3) vWF-A2 plus untransduced K562 cells, and (4) vWF-A2 plus K562 cells expressing ADAMTS13-GPA (13 ng total ADAMTS13). Uncleaved vWF-A2 appears as the higher band around 18.8 kDa; cleaved vWF-A2 appears as the lower band around 12.4 kDa. 
         FIG. 17A - FIG. 17C  shows expression and activity of a chimeric construct of Complement Factor I (CFI) fused to GPA (CFI-GPA).  FIG. 17A  are flow cytomotry plots showing the expression of CH-GPA on K562 cells measured by flow cytometry with an anti-HA antibody.  FIG. 17B  are flow cytomotry plots showing the expression of CFI-GPA on cultured erythroid cells measured by flow cytometry with an anti-CFI antibody.  FIG. 17C  is a photo of a Western blot showing activity of the CFI-GPA-expressing K562 cells. Activity is detected as the cleavage of recombinant C3b into its cleavage products, which appear at around 45 kDa and are detected with an anti-C3 antibody. 
         FIG. 18A - FIG. 18D  are Western blots showing expression and activity various phenylalanine hydroxylase (PAH) constructs in cultured erythroid cells of total protein-matched cell lysates with an anti-HA antibody.  FIG. 18A  is a Western blot showing PAH expression detected at various stages of erythroid cell differentiation.  FIG. 18B  is a Western blot showing expression of a chimeric fusion of PAH at the C-terminus of GPA (GPA-PAH) at various stages of erythroid cell differentiation.  FIG. 18C  is a Western blot showing quantification of PAH from terminally differentiated cells compared to recombinant PAH at various known concentrations.  FIG. 18D  shows the activity of PAH in cultured erythroid cells, measured as the production of tyrosine from phenylalanine in the presence of BH4 co-factor and measured by colorimetric readout (Biovision Inc. Milpitas Calif.). 
         FIG. 19  is a chart showing the expression of a range of constructs expressed on the surface of cultured erythroid cells. The size of the construct is shown at right. The expression level is measured by flow cytometry with an anti-HA antibody. The cells are transduced at day 6 of culture and tested for expression at various times until terminal differentiation at day 20. 
         FIG. 20  is a schematic of a universal acceptor erythroid cell. A progenitor cell is contacted with an exogenous nucleic acid encoding a docking polypeptide comprising a high-affinity acceptor site. The cell is differentiated to an erythroid cell and the docking polypeptide is expressed on the cell surface. A receiver polypeptide that contains a small donor molecule that binds to the high-affinity acceptor site of the docking polypeptide (R*) is introduced and the docking polypeptide captures the small molecule. The resulting erythroid cell comprises the receiver polypeptide on the surface. 
         FIG. 21  is a plot showing expression of various constructs of differing sizes on K562 erythroleukemia cells following lentiviral transduction. Each data point represents a unique construct. Expression is measured by flow cytometry with an anti-HA antibody, as every construct contains the appropriate epitope tag. The constructs are arrayed by provirus length, which is the length of nucleic acid in the viral genome (including the transgene itself) that will be integrated into the target cell genome. 
         FIG. 22  is a plot showing a characterization of lentivirus particles that contain transgenes of various lengths such that the provirus ranges from approximately 3.5 kb to approximately 8.5 kb. The y-axis shows RNA copies per ug of p24. The number of RNA copies per mL of viral supernatant is measured by qPCR. The amount of p24 (ug) per mL of viral supernatant is measured by ELISA against p24. The ratio of the two measured values gives the number of RNA copies per mass p24. 
         FIG. 23  are flow cytometry histograms showing the expression of GFP in K562 cells and erythroid cells cultured from primary progenitors as measured by flow cytometry 24 hrs following electroporation of cells with GFP mRNA using conditions optimized for K562 cells. 
         FIG. 24A ,  FIG. 24B , and  FIG. 24C  are flow cytometry histograms showing the expression of GFP in erythroid cells cultured from primary progenitors as measured by flow cytometry 24 hrs following electroporation of cells with GFP mRNA. 12 different conditions are shown (numbers 1-12). In the first column, GFP fluorescence is detected. In the second column, cell viability is measured with Life Technologies LIVE/DEAD stain, wherein the dead cells are stained by the dye, such that the percentage of live cells is 100%−% Fluorescent Cells. 
         FIG. 25  are flow cytometry histograms showing expression of GFP in erythroid cells cultured from primary progenitors at various stages of differentiation as measured by flow cytometry 24 hrs following electroporation of cells with GFP mRNA. Untransfected cells are compared to GFP mRNA transfected cells. The columns refer to the number of days of erythroid differentiation prior to transfection. The percent viability is measured with Life Technologies LIVE/DEAD stain and is reported as the % of viable cells, that is, cells that stain negative for the dye. 
         FIG. 26  are flow cytometry histograms showing the expression of GFP in erythroid cells cultured from primary progenitors as measured by flow cytometry 24 hrs following electroporation of cells with GFP mRNA. Cells were transfected at day 9 of culture then returned to differentiation media and re-analyzed at day 13. At day 13, cells were re-electroporated with GFP mRNA and analyzed for expression 24 hrs later. 
         FIG. 27A - FIG. 27B  are plots showing cell volume as measured by Coulter Counter (Moxi Z, Orflo Technologies). In  FIG. 27A , populations of primary human red blood cells (RBC, open circles), erythroid cells cultured from primary progenitors (cRBC, black circles), and Liquichek (Bio-Rad) reticulocyte standard (Retic, gray circles) are measured and their volume distributions overlaid. In  FIG. 27B , the cumulative cell population by volume is plotted for RBC (open circles) and cRBC (black circles). 
         FIGS. 28A and 28B  show the volume distribution of different types of erythrocytes.  FIG. 28A  shows the distribution of volumes for untreated, treated, loaded, and human RBC cells.  FIG. 28  shows the distribution of volumes for cultured erythroid cells that are untransfected or transfected. 
         FIG. 29  is a plot showing the osmotic fragility of primary human red blood cells (RBC, open squares), primary human red blood cells loaded with recombinant protein by hypotonic dialysis (HD-RBC, black circles), erythroid cells cultured from primary progenitors (cultured RBCs, gray), and erythroid cells cultured from primary progenitors that express a therapeutic enzyme (cultured RBCs+ enzyme, open gray). Cells are exposed to solutions of varying osmotic strengths (% NaCl) and osmotic fragility is measured as % lysis as read by absorbance at 450 nm. 
         FIG. 30  shows phosphatidylserine (PS) exposure on erythroid cells cultured from primary progenitors as measured by flow cytometry staining with Annexin V-APC. In  FIG. 30  top, the full cell population is shown as analyzed by forward and side scatter and various gates are drawn. In  FIG. 30  left, cells are stained with DNA stain (DRAQ5, Life Technologies) and anti-GPA antibody, and it is demonstrated that nuclei (DNA+ GPA-low) are excluded in FSC/SSC gate 1. In  FIG. 30  right, gate 1 cells are analyzed for Annexin V staining, either cultured erythroid cells or cultured erythroid cells that express a therapeutic cytoplasmic enzyme. 
         FIG. 31A-13B  shows phosphatidylserine (PS) exposure on primary RBCs and primary RBCs that have been loaded with a protein by hypotonic dialysis (HD-RBCs) as measured by flow cytometry staining with Annexin V-APC. In  FIG. 31A , cells are analyzed by forward- and side-scatter and various gates are drawn. In  FIG. 31B , Annexin V staining histograms of the cell populations for various FSC/SSC gates are shown. 
         FIGS. 32A-32E  show flow cytometry plots of cell populations, and the phosphatidylserine exposure of different sub-populations. 
         FIGS. 33A-33D  show flow cytometry plots of cell populations, and the phosphatidylserine exposure of a filtered sub-population enriched for enucleated cells. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Therapeutic technologies attempting to employ circulating agents have been developed in the past to address some of the challenges in delivering treatments such as pharmaceutical drugs to patients. None possess one or many of the features and benefits of the synthetic membrane-receiver complexes provided herein. Aspects of the invention provide compositions capable of multiple, distinct utilities, which utilize biochemical and biophysical mechanisms not previously addressed. Aspects of the invention relate to compositions and methods for performing, e.g., functions related to circulating clearance and functions related to metabolic enzyme delivery, and methods for treating or preventing a variety of diseases, disorders and conditions. Accordingly, the compositions and methods disclosed herein address the long sought after need for therapeutic compositions that are distributed through the circulatory system that have increased half-life, safety profile, and/or efficacy that avoid shortcomings associated with previous approaches such as undesirable immunological reactions, short half-life due to rapid clearance from the circulation, and off-target effects, among others. 
     Functions related to circulating clearance include activities characterized by, e.g., the specific binding, degradation, and/or sequestration of a target (e.g., a pathogenic substance or toxic molecule) in the circulatory system of a subject by a synthetic membrane-receiver complex comprising a receiver capable of interacting with a target as described herein. Synthetic membrane-receiver complexes are introduced or capable of being introduced into the circulation of a subject. In some embodiments, the bound or sequestered targets are guided to the liver, spleen, or any other site in which they may be removed from the circulatory system. 
     Functions related to metabolic enzyme delivery include activities characterized by, e.g., removal of a target (e.g., a pathogenic substance or toxic molecule), in circulation of a subject by a synthetic membrane-receiver complex as described herein that comprises, e.g., one or more metabolic enzyme receiver polypeptides within the complex or on the surface of the complex, such that the receiver polypeptide interacts with and modifies the target. Modification of the target includes, e.g., alteration of the bioavailability of the target, cleaving, degrading, and/or otherwise inactivating the target by the receiver. In some embodiments, the enzymatic polypeptide is protected from the immune system. In some embodiments, the half-life of the enzyme is extended and/or an immunogenic reaction is reduced when administered in the subject. 
     It is to be understood that this invention is not limited to particular methods, reagents, compounds, compositions or biological systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to be limiting. 
     All of the features disclosed in this specification may be combined in any combination. Each feature disclosed in this specification may be replaced by an alternative feature serving the same, equivalent, or similar purpose. Thus, unless expressly stated otherwise, each feature disclosed is only an example of a generic series of equivalent or similar features. 
     Many modifications and other embodiments of the inventions set forth herein will easily come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 
     As used in this specification and the appended claims, the singular forms “a”, “an” and “the” include plural references unless the content clearly dictates otherwise. 
     The use of the alternative (e.g., “or”) should be understood to mean either one, both, or any combination thereof of the alternatives. 
     The term “about” as used herein when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass variations of ±20% or ±10%, more preferably ±5%, even more preferably ±1%, and still more preferably ±0.1% from the specified value, as such variations are appropriate to perform the disclosed methods. 
     As used herein, any concentration range, percentage range, ratio range, or integer range is to be understood to include the value of any integer within the recited range and, when appropriate, fractions thereof (such as one tenth and one hundredth of an integer), unless otherwise indicated. 
     “Comprise,” “comprising,” and “comprises” and “comprised of” as used herein are synonymous with “include”, “including”, “includes” or “contain”, “containing”, “contains” and are inclusive or open-ended terms that specifies the presence of what follows e.g. component and do not exclude or preclude the presence of additional, non-recited components, features, element, members, steps, known in the art or disclosed therein. 
     As used herein, the terms “such as”, “for example” and the like are intended to refer to exemplary embodiments and not to limit the scope of the present disclosure. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although any methods and materials similar or equivalent to those described herein can be used in the practice for testing of the present invention, preferred materials and methods are described herein. 
     All publications and patent applications cited in this specification are herein incorporated by reference in their entirety for all purposes as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference for all purposes. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the inventors described herein are not entitled to antedate such disclosure by virtue of prior invention or for any other reason. 
     Definitions 
     “Administration,” “administering” and variants thereof means introducing a composition, such as a synthetic membrane-receiver complex, or agent into a subject and includes concurrent and sequential introduction of a composition or agent. The introduction of a composition or agent into a subject is by any suitable route, including orally, pulmonarily, intranasally, parenterally (intravenously, intramuscularly, intraperitoneally, or subcutaneously), rectally, intralymphatically, or topically. Administration includes self-administration and the administration by another. A suitable route of administration allows the composition or the agent to perform its intended function. For example, if a suitable route is intravenous, the composition is administered by introducing the composition or agent into a vein of the subject. Administration can be carried out by any suitable route, 
     “Anchor” or “anchor domain” or “A domain” is used to refer to the portion of a receiver polypeptide, including a fusion or chimeric receiver polypeptide that is in contact with the lipid layer of a synthetic membrane-receiver polypeptide complex. The receiver polypeptide may interact with the lipid layer via a phospholipid tail insertion, covalent binding to a lipid layer constituent, an ionic bond, hydrogen bond, or via a single or multi-pass transmembrane polypeptide domain that cross one or more of the lipid layers. 
     As used herein, the term “antibody” encompasses an immunoglobulin whether natural or partly or wholly synthetically produced, and fragments thereof. The term also covers any protein having a binding domain which is homologous to an immunoglobulin binding domain. These proteins can be derived from natural sources, or partly or wholly synthetically produced. “Antibody” further includes a polypeptide comprising a framework region from an immunoglobulin gene or fragments thereof that specifically binds and recognizes an antigen. Use of the term antibody is meant to include whole antibodies, polyclonal, monoclonal and recombinant antibodies, fragments thereof, and further includes single-chain antibodies, humanized antibodies; murine antibodies; chimeric, mouse-human, mouse-primate, primate-human monoclonal antibodies, anti-idiotype antibodies, antibody fragments, such as, e.g., scFv, (scFv)2, Fab, Fab′, and F(ab′)2, F(ab1)2, Fv, dAb, and Fd fragments, diabodies, and antibody-related polypeptides. Antibody includes bispecific antibodies and multispecific antibodies so long as they exhibit the desired biological activity or function. 
     The term “antigen binding fragment” used herein refers to fragments of an intact immunoglobulin, and any part of a polypeptide including antigen binding regions having the ability to specifically bind to the antigen. For example, the antigen binding fragment may be a F(ab′)2 fragment, a Fab′ fragment, a Fab fragment, a Fv fragment, or a scFv fragment, but is not limited thereto. A Fab fragment has one antigen binding site and contains the variable regions of a light chain and a heavy chain, the constant region of the light chain, and the first constant region CHI of the heavy chain. A Fab′ fragment differs from a Fab fragment in that the Fab′ fragment additionally includes the hinge region of the heavy chain, including at least one cysteine residue at the C-terminal of the heavy chain CHI region. The F(ab′)2 fragment is produced whereby cysteine residues of the Fab′ fragment are joined by a disulfide bond at the hinge region. A Fv fragment is the minimal antibody fragment having only heavy chain variable regions and light chain variable regions, and a recombinant technique for producing the Fv fragment is well known in the art. Two-chain Fv fragments may have a structure in which heavy chain variable regions are linked to light chain variable regions by a non-covalent bond. Single-chain Fv (scFv) fragments generally may have a dimer structure as in the two-chain Fv fragments in which heavy chain variable regions are covalently bound to light chain variable regions via a peptide linker or heavy and light chain variable regions are directly linked to each other at the C-terminal thereof. The antigen binding fragment may be obtained using a protease (for example, a whole antibody is digested with papain to obtain Fab fragments, and is digested with pepsin to obtain F(ab′)2 fragments), and may be prepared by a genetic recombinant technique. A dAb fragment consists of a VH domain. Single-chain antibody molecules may comprise a polymer with a number of individual molecules, for example, dimmer, trimer or other polymers. 
     The term “anti-drug antibody” refers to an antibody with affinity for a therapeutic such as a therapeutic protein, e.g., a therapeutic antibody. In some embodiments, the anti-drug antibody is produced by the subject&#39;s immune system after administration of the therapeutic to the subject. For example, a subject may develop an immune reaction against a therapeutic antibody such as infliximab, adalimumab, etanercept, or certolizumab which results in the production of anti-drug antibodies in the subject. The therapeutic protein or antibody may comprise sequence derived from a non-human species such as a rodent, e.g., mouse. In some embodiments, the therapeutic comprises a mouse antibody or portion thereof, e.g., a chimeric antibody. In some embodiments, the therapeutic comprises infliximab, adalimumab, etanercept, or certolizumab. 
     “Applicator” refers to any device used to connect to a subject. This includes, e.g., needles, cannulae, catheters, and tubing. 
     “Associated with” when used to describe the relationships among multiple compounds or molecules encompasses such as, e.g., any interaction between a receiver and a target or between a synthetic membrane-receiver complex and a target. This includes enzymatic interaction, ionic binding, covalent binding, non-covalent binding, hydrogen bonding, London forces, van der Waals forces, hydrophobic interaction, lipophilic interactions, magnetic interactions, electrostatic interactions, and the like. 
     “Associated with” when used to describe the relationships among a target, entity, compound, agent, or molecule and a disease, disorder, condition, symptom or phenotype is any link that may reasonably be made between them, including a causal link, or a statistical significant link, an empirically established link, a suggested link, whether or not causative of the disease, disorder, condition, symptom or phenotype. 
     “Autoimmune disorders” generally are conditions in which a subject&#39;s immune system attacks the body&#39;s own cells, causing tissue destruction. Autoimmune disorders may be diagnosed using blood tests, cerebrospinal fluid analysis, electromyogram (measures muscle function), and magnetic resonance imaging of the brain, but antibody testing in the blood, for self-antibodies (or auto-antibodies) is particularly useful. Usually, IgG class antibodies are associated with autoimmune diseases. 
     “Binding” describes an interaction among compounds or molecules, e.g., between a receiver and a target or between a synthetic membrane-receiver complex and a target, that comes about by covalent binding or non-covalent binding, including ionic binding, electrostatic interactions, hydrogen bonding, London forces, van der Waals forces, hydrophobic interaction, lipophilic interactions, and similar. 
     The “biological activity of a polypeptide” refers to any molecular activity or phenotype (such as, e.g., binding, signal transduction, catalytic, etc.) that is caused by the polypeptide, such as a receiver polypeptide. 
     As used herein, the term “biological sample” refers to any type of material of biological origin isolated from a subject, including, for example, DNA, RNA, lipids, carbohydrates, and protein. The term “biological sample” includes tissues, cells and biological fluids isolated from a subject. Biological samples include, e.g., but are not limited to, whole blood, plasma, serum, semen, saliva, tears, urine, fecal material, sweat, buccal, skin, cerebrospinal fluid, bone marrow, bile, hair, muscle biopsy, organ tissue or other material of biological origin known by those of ordinary skill in the art. Biological samples can be obtained from, e.g., biopsies of internal organs or from cancers. Biological samples can be obtained from subjects for diagnosis or research or can be obtained from healthy subjects, as controls or for basic research. 
     The “clearance rate” as used herein is calculated by measuring the amount or concentration of, e.g., target, receiver, target-receiver, or synthetic membrane-receiver complexes remaining in the circulatory system of a subject over time. For example, 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or 99% of target detected in a first sample may still be detected in a second sample that is taken 1 hour, 5 hours, 10 hours, 24 hours, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 2 weeks, 3 weeks, 4 weeks, 2 months, 3 months, 4 months, 5 months, 6 months, 7 months, 8 months, 9 months, 10 months, 11 months, 12 months, 2 years, 3 years, 4 years, or 5 years later. The clearance rate may alternatively be expressed as: number of entities (e.g., target/receiver) per unit of time (e.g., per day). An increase in clearance rate is a rate greater than that exhibited in an untreated or healthy suitable control subject. A decrease in clearance rate is a rate less than that exhibited in an untreated or healthy suitable control subject. The increase or decrease may be 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 150%, 200%, 500%, 1000% or may be 1.1-fold, 1.2-fold, 1.3 fold, 1.4-fold, 1.5-fold, 2-fold, 3-fold, 4-fold, 5-fold, 10-fold, 20-fold, 50-fold, 100-fold, 500-fold, or 1000-fold. An increase in clearance rate of a target includes, e.g., a slow down in the accumulation of a target, a reaching of a new equilibrium of generation and degradation, and a reversal of an accumulation, e.g., a decrease in the number or concentration of the target in circulation. 
     “Cleaving” as used herein is a process that disrupts a bonding interaction present in a target, such as a polypeptide or nucleic e.g., to produce two or more entities that after cleaving can be separated from one another. The separation can involve, e.g., disrupt an ionic bond, a covalent bond, a polar covalent bond, a non-polar covalent bond, or a metallic bond. As cleaving applies to polypeptide targets, cleavage can involve breaking one or more peptide bonds. As cleaving applies to small molecule targets, cleavage can involve breaking one or more carbon or sulfide bonds. As cleaving applies to nucleotide sequences, cleavage can involve breaking one or more phosphodiester bonds. As cleaving applies to microbes such as bacteria, fungi, or viruses, cleavage can involve lysis of a membrane or capsid structure. Cleaving can be carried out by an enzyme, e.g., a catalytically active receiver polypeptide. Receivers can comprise, e.g., exonuclease, endonuclease, or protease activity. 
     The “circulatory system of a subject,” as used herein, encompasses the space occupied by whole blood and optionally the lymphatic system in a human, inclusive of plasma and all circulating cells and molecules, and distributed throughout arteries, veins, capillaries, and lymphatic vessels of all tissues. The “circulatory concentration” is the concentration of a target, e.g., a cell, polypeptide (such as an antibody, pathogenic antigen, etc.), therapeutic agent, small molecule, metabolite or other entity, a receiver or a synthetic membrane-receiver complex in the space defined as the circulatory system. In certain embodiments, the concentration may be defined as the number of free (unbound) entities in a given volume. In other embodiments, the concentration may be defined as the total number of entities in a given volume. 
     The term “complementarity determining region (CDR)” used herein refers to an amino acid sequence found in the variable region of a heavy chain or a light chain of an immunoglobulin. The CDRs determine the specificity of an antibody and may provide a contact residue for binding to a specific epitope of an antigen. The heavy chain and the light chain may respectively include three CDRs (CDRH1, CDRH2, and CDRH3, and CDRL1, CDRL2, and CDRL3). Four framework regions, which have more highly conserved amino acid sequences than the CDRs, separate the CDR regions in the VH or VL. 
     A “complex” as used herein comprises an association of two or more entities. A complex may comprise one or more polypeptides, nucleic acid, lipids, carbohydrates, inorganic compounds, organic compounds, and the like. A complex can be functional (multiunit polypeptides) or non-functional (e.g., aggregates or precipitates) and may have beneficial or detrimental properties (e.g., immune complexes). Complexes may be naturally occurring or may be man-made or synthetic. Synthetic complexes include higher order entities, e.g., subcellular structures and cells if they comprise a synthetic compound or molecule. For example, a synthetic membrane-receiver complex includes a cell comprising a receiver. 
     As to amino acid sequences, one of skill will recognize that individual substitutions, deletions or additions to a nucleic acid, peptide, polypeptide, or protein sequence which alters, adds or deletes a single amino acid or a small percentage of amino acids in the encoded sequence is a “conservatively modified variant” where the alteration results in the substitution of an amino acid with a chemically similar amino acid. As used herein the term “conservative amino acid substitution” is illustrated by a substitution among amino acids within each of the following groups: (1) glycine, alanine, valine, leucine, and isoleucine, (2) phenylalanine, tyrosine, and tryptophan, (3) serine and threonine, (4) aspartate and glutamate, (5) glutamine and asparagine, and (6) lysine, arginine and histidine. 
     “Decrease,” in the context of a symptom of a treated disease, disorder or condition, refers to a reduction in measurable or conveyable parameters associated with the disease or condition that manifest as symptoms. Examples of measurable parameters are a reduction in the subject&#39;s body temperature, a reduction in the concentration of targets in a sample taken from the subject, reduction in the intensity of inflammation or size of an inflamed area, reduction in the number of infiltrating cells, reduction in the number of episodes associated with the disease, disorder or condition, increase/decrease in organ size, weight gain/loss, etc. Examples of conveyable parameters are, e.g., the subject&#39;s own assessment of well being and quality of life. For example, for self-antibody mediated diseases, the decrease may be quantified as one, or a combination of, the following parameters: reduced inflammation, reduced flare-ups, reduced fatigue, reduced blood clotting, reduced swelling, increased energy, or increased hair growth, etc. The parameters that may be quantified are those appropriate for assessing the specific disease, disorder or condition that is being treated. Delay, in the context of symptoms of a treated disease, disorder or condition, refers to the significant extension of a manageable health condition that would otherwise become exacerbated, using a treatment. 
     “Degrading” is defined as the process in which a target is either directly, or indirectly, reduced, inactivated, decomposed, deconstructed, lysed, dissolved, broken, lessened, impaired, weakened, deteriorated, diminished, or partitioned. 
     “Different polypeptide origin” refers to the organism or species from which a genetic sequence encoding the polypeptide, the polypeptide, or portion thereof, is sourced. In certain embodiments, a fusion comprising polypeptides of different polypeptide origin may include a receiver polypeptide that is encoded by the genetic sequence for human adenosine deaminase and the genetic sequence for phenylalanine hydroxylase from  Chromobacterium violaceum.    
     A “domain” is a part of a polypeptide, such as a receiver polypeptide that is generally having a 3-dimensional structure and may exhibit a distinct activity, function, such as, e.g., a catalytic, an enzymatic, a structural role, or a binding function. 
     Duration refers to the period of time that a portion of the synthetic membrane-receiver polypeptide complex exists in a specific tissue or an organism as a whole. This applies to 0.1% 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100% of the initial dose or concentration of the synthetic membrane-receiver polypeptide complex. In some embodiments, the synthetic membrane-receiver complex is formulated for long-term duration. In some embodiments, the synthetic membrane-receiver complex is formulated for short-term duration. 
     By an “enriched population of cells” it is meant a population of cells that is substantially comprised of a particular cell of interest. In an enriched population, 50% or more of the cells in the population are the cells of interest, e.g., 50%, 60%, 70%, usually 80%, 85%, 90%, more usually 92%, 95%, 96%, 97%, 98%, or 99%, sometimes as much as 100% of the cells in the population. The separation of cells of interest from a complex mixture or heterogeneous culture of cells may be performed by any convenient means known in the art, for example, by affinity separation techniques such as magnetic separation using magnetic beads coated with an affinity reagent, affinity chromatography, or “panning” with an affinity reagent attached to a solid matrix, e.g., plate, or other convenient technique. Other techniques providing accurate separation include fluorescence activated cell sorters, which can have varying degrees of sophistication, such as multiple color channels, low angle and obtuse light scattering detecting channels, impedance channels, etc. The cells may be selected against dead cells by employing dyes associated with dead cells. Any technique may be employed which is not unduly detrimental to the viability of the desired cells. 
     “Enucleation” is the rendering of a cell to a non-replicative state, either through inactivation or removal of the nucleus. 
     An “epitope” includes any segment on an antigen to which an antibody or other ligand or binding molecule binds. An epitope may consist of chemically active surface groupings of molecules such as amino acids or sugar side chains and usually have specific three dimensional structural characteristics, as well as specific charge characteristics. In some embodiments, receivers comprise specific epitopes. In some embodiments, targets comprise specific epitopes. 
     “Erythroid cells” as used herein, include nucleated red blood cells, red blood cell precursors, and enucleated red blood cells and those listed in Table 2. For example, the erythroid cells are a cord blood stem cell, a CD34+ cell, a hematopoietic stem cell (HSC), a spleen colony forming (CFU-S) cell, a common myeloid progenitor (CMP) cell, a blastocyte colony-forming cell, a burst forming unit-erythroid (BFU-E), a megakaryocyte-erythroid progenitor (MEP) cell, an erythroid colony-forming unit (CFU-E), a reticulocyte, an erythrocyte, an induced pluripotent stem cell (iPSC), a mesenchymal stem cell (MSC), a polychromatic normoblast, an orthochromatic normoblast, or a combination thereof. In some embodiments, the erythroid cells are immortal or immortalized cells. For example, immortalized erythroblast cells can be generated by retroviral transduction of CD34+ hematopoietic progenitor cells to express Oct4, Sox2, Klf4, cMyc, and suppress TP53 (e.g., as described in Huang et al., Mol Ther 2013, epub ahead of print September 3). In addition, the cells may be intended for autologous use or provide a source for allogeneic transfusion. Erythroid cells can be contacted with a receiver to generate a synthetic membrane-receiver complex. Erythroid cells comprising a receiver are one example of a synthetic membrane-receiver complex. In some embodiments, erythroid cells are cultured. In some embodiments, erythroid progenitor cells are contacted with a receiver to generate a synthetic membrane-receiver complex. 
     As used herein, the term “excipient” refers to an inert substance added to a pharmaceutical composition to further facilitate administration of a compound. Examples of excipients include, but are not limited to, calcium carbonate, calcium phosphate, various sugars and types of starch, cellulose derivatives, gelatin, vegetable oils, anti-coagulants, and polyethylene glycols. 
     The receiver, including a receiver polypeptide is “exogenous” or “heterologous”, thus it may either not naturally exist, such as a fusion or chimera comprising domains of different polypeptide or species origin, it may not naturally occur in a naturally occurring cell, such as an unmodified erythrocyte or platelet, it may not function in the same way as a naturally occurring polypeptide would, or it may not naturally occur in the quantity that the receiver polypeptide occurs, e.g., in embodiments in which the synthetic membrane-receiver polypeptide complex is a cell-derived polypeptide receiver that is overexpressed as compared to the expression of a naturally occurring polypeptide in an unmodified cell. In some embodiments, the polypeptide receiver is expressed from an exogenous nucleic acid. In some embodiments, the receiver is isolated from a source and loaded into or conjugated to a synthetic membrane-receiver complex. 
     The term “exogenous” when used in the context of nucleic acid includes a transgene and recombinant nucleic acids. 
     As used herein, the term “expression” refers to the process to produce a polypeptide, such as a receiver polypeptide including transcription and translation. Expression may be, e.g., increased by a number of approaches, including: increasing the number of genes encoding the polypeptide, increasing the transcription of the gene (such as by placing the gene under the control of a constitutive promoter), increasing the translation of the gene, knocking out of a competitive gene, or a combination of these and/or other approaches. 
     A synthetic membrane-receiver complex that is “formulated for long-term duration” is, in some embodiments, one that is part of a population of synthetic membrane-receiver complexes wherein a substantial fraction of the population resides in the circulatory system for more than 10 days, e.g., 15, 21, 25, 35, 45, 50, 60, 90, 100, 110, or 120 days. In some embodiments, the population may have an increased half-life, e.g., 1.5×, 2×, 5×, 10×, 20×, 50×, 100× more time in circulation, when formulated for long-term duration compared to the duration exhibited by a population of unformulated complexes. In some embodiments, an entity such as a receiver may have an increased half-life, e.g., 1.5×, 2×, 5×, 10×, 20×, 50×, 100× more time in circulation, when formulated for long-term duration compared to the duration that entity would exhibit in an unmodified state. 
     A synthetic membrane-receiver complex that is “formulated for short-term duration” is, in some embodiments, one that is part of a population of synthetic membrane-receiver complexes wherein a substantial fraction of the population resides in the circulatory system for less than 10 days, e.g., 9, 8, 7, 6, 5, 4, 3, 2 days, 1 day, 12 hours, or 6 hours. In some embodiments, the population may have a decreased half-life, e.g., 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 99% less time in circulation, when formulated for short-term duration compared to the duration exhibited by a population of unformulated complexes. In some embodiments, an entity such as a receiver may have a reduced half-life, e.g., 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 99% less time in circulation, when formulated for short-term duration compared to the duration that entity would exhibit in an unmodified state. 
     “Formulated for residency in the circulatory system”, as used herein, describes one or more modifications to an entity, such as a synthetic membrane-receiver complex formulated for administration to the circulatory system of a subject that substantially decrease recognition, modification, degradation, and/or destruction of the entity by components of the circulatory system (e.g., circulating immune cells, antibodies, enzymatic activities) thereby increasing the half-life of the entity when compared to an unmodified entity. 
     A “functional” receiver or synthetic membrane-receiver complex refers to a synthetic membrane-receiver complex or a receiver that exhibits a desired or specified activity or characteristic, including enzymatic, catalytic or metabolic activity, structural integrity, immunogenic complementarity, target binding, and correct localization or is capable of promoting a desired or specified effect or phenotype. 
     “Fusion or chimera” is defined as a polypeptide sequence, or corresponding encoding nucleotide sequence, that is derived from the combination of two or more sequences that are not found together in nature. This may be a combination of separate sequences derived from separate genes within the same genome, or from heterologous genes derived from distinctly different species&#39; genomes. 
     “Genetic material” refers to nucleic acid molecules having nucleotide sequences of adenosine, thymine, uracil, cytosine, and guanine capable of encoding a gene. 
     The term “heavy chain” used herein is understood to include a full-length heavy chain including a variable region (VH) having amino acid sequences that determine specificity for antigens and a constant region having three constant domains (CH1, CH2, and CH3), and fragments thereof. In addition, the term “light chain” used herein is understood to include a full-length light chain including a variable region (VL) having amino acid sequences that determine specificity for antigens and a constant region (CL), and fragments thereof. 
     The term “homolog” indicates polypeptides, including receiver polypeptide that have the same or conserved residues at a corresponding position in their primary, secondary or tertiary structure. Functional homologs include receivers and other polypeptides that exhibit similar function and/or specificity (e.g., for a particular target). 
     A naturally occurring intact antibody, or immunoglobulin, includes four polypeptides: two full-length light chains and two full-length heavy chains, in which each light chain is linked to a heavy chain by disulfide bonds. Each heavy chain has a constant region and a variable region. Similarly, each light chain has a constant region and a variable region. There are five heavy chain classes (isotypes): gamma (γ), mu (μ), alpha (α), delta (δ), or epsilon (ε), and additionally several subclasses gamma 1 (γ1), gamma 2(γ2), gamma 3(γ3), gamma 4(γ4), alpha 1(α1), and alpha 2(α2). The light chain constant region can be either kappa (κ) or lambda (λ) type. The variable regions differ in sequence among antibodies and are used in the binding and specificity of a given antibody to its particular antigen. 
     As used herein, the term “increase,” “enhance,” “stimulate,” and/or “induce” (and like terms) generally refers to the act of improving or increasing, either directly or indirectly, a concentration, level, function, activity, or behavior relative to the natural, expected, or average, or relative to a control condition. 
     As used herein, the term “inhibit,” “suppress,” “decrease,” “interfere,” and/or “reduce” (and like terms) generally refers to the act of reducing, either directly or indirectly, a concentration, level, function, activity, or behavior relative to the natural, expected, or average, or relative to a control condition. 
     A “library” as used herein includes a collection of nucleic acid molecules (e.g., DNA, RNA) having diverse nucleic acid sequences, a genetically diverse collection of clones, a collection of diverse polypeptides, a diverse collection of cells, etc. 
     As used herein, “a mammalian subject” includes all mammals, including without limitation, humans, domestic animals (e.g., dogs, cats and the like), farm animals (e.g., cows, sheep, pigs, horses and the like) and laboratory animals (e.g., monkey, rats, mice, rabbits, guinea pigs and the like). The terms “individual,” “subject,” “host,” and “patient,” are used interchangeably herein and refer to any mammalian subject for whom diagnosis, treatment, or therapy is desired, particularly humans. The methods described herein are applicable to both human therapy and veterinary applications. In some embodiments, the subject is a mammal, and in other embodiments the subject is a human. 
     “Medical device” refers to any device, apparatus or machine used to deliver a dose of a synthetic membrane-receiver complex and/or a therapeutic agent. This includes containers, bottles, vials, syringes, bags, cartridges, cassettes, magazines, cylinders, or canisters. 
     “Medical kit” refers to a packaged unit that includes a medical device, applicator, appropriate dosage of synthetic membrane-receiver complex optionally including a therapeutic agent, and relevant labeling and instructions. 
     As used herein, the term “modulate,” “modulating”, “modify,” and/or “modulator” generally refers to the ability to alter, by increase or decrease, e.g., directly or indirectly promoting/stimulating/upregulating or interfering with/inhibiting/downregulating a specific concentration, level, expression, function or behavior, such as, e.g., to act as an antagonist or agonist. In some instances a modulator may increase and/or decrease a certain concentration, level, activity or function relative to a control, or relative to the average level of activity that would generally be expected or relative to a control level of activity. 
     “Membrane” as used herein is a boundary layer that separates an interior space from an exterior space comprising one or more biological compounds, typically lipids, and optionally polypeptides. Membranes can be lipid bilayers. In certain embodiments, membranes comprise one or more of phosphatidylcholine, sphingomyelin, lysophosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, or phosphatidic acid. In some embodiments, membranes comprise one or more polypeptides such as ankyrin and coenzyme Q10. Included in the definition of membrane are cell membranes comprising, e.g., a phospholipid bilayer and cell membrane associated polypeptides. The synthetic membrane-receiver complex comprises a membrane as defined herein. 
     The phrase “nucleic acid molecule” refers to a single or double-stranded polymer of deoxyribonucleotide or ribonucleotide bases. It includes chromosomal DNA and self-replicating plasmids, vectors, mRNA, tRNA, siRNA, etc. which may be recombinant and from which exogenous polypeptides may be expressed when the nucleic acid is introduced into a cell. 
     Orthologs are defined as genes in different species that evolved from a common ancestral gene by speciation. 
     The term “pharmaceutically-acceptable” and grammatical variations thereof, refers to compositions, carriers, diluents and reagents capable of administration to or upon a subject without the production of undesirable physiological effects to a degree that would prohibit administration of the composition. For example, “pharmaceutically-acceptable excipient” includes an excipient that is useful in preparing a pharmaceutical composition that is generally safe, non-toxic, and desirable, and includes excipients that are acceptable for veterinary use as well as for human pharmaceutical use. Such excipients can be solid, liquid, semisolid, or, in the case of an aerosol composition, gaseous. 
     As used herein, the term “pharmaceutically acceptable carrier” includes any of the standard pharmaceutical carriers, such as a phosphate buffered saline solution, water, emulsions such as an oil/water or water/oil, and various types of wetting agents. The term also encompasses any of the agents approved by a regulatory agency of the US Federal government or listed in the US Pharmacopeia for use in animals, including humans, as well as any carrier or diluent that does not cause significant irritation to a subject and does not abrogate the biological activity and properties of the administered compound. 
     Some agents may be administered as “pharmaceutically acceptable salt”, e.g., prepared from inorganic and organic acids. Salts derived from inorganic acids include hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid, and the like. Salts derived from organic acids include acetic acid, propionic acid, glycolic acid, pyruvic acid, oxalic acid, malic acid, malonic acid, succinic acid, maleic acid, fumaric acid, tartaric acid, citric acid, benzoic acid, cinnamic acid, mandelic acid, methanesulfonic acid, ethanesulfonic acid, p-toluene-sulfonic acid, salicylic acid, and the like. Salts can also be prepared from inorganic and organic bases. Salts derived from inorganic bases, include by way of example only, sodium, potassium, lithium, ammonium, calcium and magnesium salts. Salts derived from organic bases include, but are not limited to, salts of primary, secondary and tertiary amines. Any ordinary skilled person in the art will know how to select a proper pharmaceutically acceptable carrier, a pharmaceutically acceptable salt thereof for implementing this invention without undue experimentation. 
     As used herein, the term “pharmaceutical composition” refers to one or more of the compounds described herein, such as, e.g., a synthetic membrane-receiver polypeptide complex mixed or intermingled with, or suspended in one or more other chemical components, such as physiologically acceptable carriers and excipients. One purpose of a pharmaceutical composition is to facilitate administration of a compound to a subject. 
     Certain embodiments provide various polypeptide molecules having sequences associated with a desired function or activity, such as receiver polypeptides. A polypeptide is a term that refers to a chain of amino acid residues, regardless of post-translational modification (e.g., phosphorylation or glycosylation) and/or complexation with additional polypeptides, synthesis into multisubunit complexes, with nucleic acids and/or carbohydrates, or other molecules. Proteoglycans therefore also are referred to herein as polypeptides. In certain embodiments, the synthetic membrane-receiver complex comprises a polypeptide receiver and is referred to a “synthetic membrane-receiver polypeptide complex.” In certain embodiments, the synthetic membrane-receiver complex comprises one or more non-receiver polypeptides that are optionally membrane-associated and that exhibit catalytic and/or metabolic activity independent of the receiver. For example, the non-receiver polypeptides may have catalytic activity for an organic compound including a metabolite. In certain embodiments, the synthetic membrane-receiver complex comprises a sufficient number of non-receiver polypeptides (and optionally non-protein co-factors) to support a metabolic pathway. 
     The term “pharmaceutically active agent” or “pharmaceutical agent” is defined as any compound, e.g., a small molecule drug, or a biologic (e.g., a polypeptide drug or a nucleic acid drug) that when administered to a subject has a measurable or conveyable effect on the subject, e.g., it alleviates or decreases a symptom of a disease, disorder or condition. In some embodiments, the pharmaceutical agent may be administered prior to, in combination with, or following the delivery of a synthetic membrane-receiver polypeptide complex. In some embodiments, the pharmaceutically active agent exerts a synergistic treatment effect with the synthetic membrane-receiver polypeptide complex. In some embodiments, the pharmaceutically active agents exerts an additive treatment effect with the synthetic membrane-receiver polypeptide complex. 
     A “promoter” is defined as an array of nucleic acid control sequences that direct transcription of an operably linked nucleic acid. Promoters include necessary nucleic acid sequences near the start site of transcription. A promoter also optionally includes distal enhancer or repressor elements. A “constitutive” promoter is a promoter that is active under most environmental and developmental conditions. An “inducible” promoter is a promoter that is active under environmental or developmental regulation. The term “operably linked” refers to a functional linkage between a nucleic acid expression control sequence (such as a promoter, or array of transcription factor binding sites) and a second nucleic acid sequence, wherein the expression control sequence directs transcription of the nucleic acid corresponding to the second sequence. 
     A “receiver,” as used herein, is an entity capable of interacting with a target, e.g., to associate with or bind to a target. A receiver can comprise or can consist essentially of a polypeptide. In some embodiments, the receiver comprises a polypeptide, a carbohydrate, a nucleic acid, a lipid, a small molecule, or a combination thereof. In embodiments in which a receiver is a naturally occurring compound or molecule, the receiver is “synthetic” in the sense that it is an exogenous or heterologous compound or molecule with regard to its presence in the synthetic membrane-receiver complex. In other embodiments the receiver is “synthetic” in the sense that it is a man-made compound or molecule, such as a fusion or chimera, a non-naturally occurring polypeptide, carbohydrate, nucleic acid, lipid, or combination thereof, or a man-made small molecule or other therapeutic agent. For example, the receiver may comprise a fusion or chimera comprising one or more of an S domain, an A domain and a U domain. The S domain is a surface domain exposed to the environment around the synthetic membrane-receiver complex, such as the circulatory system of a subject. The A domain is an anchor domain that attaches the S domain to the synthetic membrane of the synthetic membrane-receiver polypeptide complex. The U domain faces the unexposed side of or is located within the synthetic membrane-receiver complex, i.e. the side that is not exposed to the external environment of the circulatory system of a subject. Irrespective of any domains, a receiver may be located on the surface of the synthetic membrane-receiver polypeptide complex or may be located within the complex. The receiver may be associated with the membrane of the synthetic membrane-receiver complex, e.g., the receiver is anchored in, conjugated to or otherwise bound to the membrane. In some embodiments, the receiver may be conjugated to the membrane of the synthetic membrane-receiver complex by chemical or enzymatic conjugation. In other embodiments, the receiver is not conjugated to the membrane. In some embodiments, the receiver is not associated with the membrane of the synthetic membrane-receiver complex and is located within the membrane-encapsulated volume of the complex. In some embodiments, a receiver located within the synthetic membrane-receiver complex does not substantially diffuse out of the complex and/or may not permeate the membrane. In other embodiments, the receiver may substantially diffuse out of the complex and/or may permeate the membrane. In some embodiments, the receiver is loaded, e.g., introduced into or put onto the synthetic membrane-receiver complex. A receiver that is loaded is not biologically synthesized by the synthetic membrane-receiver complex. A receiver suitable for loading may be e.g., produced in a cell-based expression system, isolated from a biological sample, or chemically or enzymatically synthesized, and then loaded into or onto the synthetic membrane-receiver complex. In some embodiments, the receiver may be further modified by the synthetic membrane-receiver complex after loading. In other embodiments, the receiver is not modified after loading. In some embodiments, the receiver polypeptide is not loaded onto or into the complex. In some embodiments, the receiver is made, e.g., biologically synthesized by the synthetic membrane-receiver complex. Typically a receiver polypeptide is expressed by the synthetic membrane-receiver complex from an exogenous nucleic acid molecule (e.g., a DNA or mRNA) that was introduced into the complex. The receiver may bind to and/or sequester a target. Alternatively or in addition the receiver may exhibit a catalytic activity toward the target, e.g., the receiver may convert or modify the target, or may degrade the target. A product may then optionally be released from the receiver. 
     “Residency” of a synthetic membrane-receiver complex refers to the period of time it spends in a physiological location. The specific location of the synthetic membrane-receiver complex may change during its lifetime and “residency” applies to the period of time spent in various environments, including vascular circulation, peripheral tissues, capillaries, digestive system, pulmonary system, nasal tissues, epidermal surface, and interstitial tissue. In specific embodiments, the synthetic membrane-receiver complex resides in the circulatory system of a subject. 
     “Replicating nucleic acid” refers to deoxyribonucleic acid (DNA) that is capable of being copied by enzymes dedicated to the increasing the number of copies of the DNA. Usually, DNA replication leads to the production of two identical replicas from one original DNA molecule. DNA replication comprises the incorporation of nucleotides into a growing DNA strand by DNA polymerase matched to the template strand one at a time via the creation of phosphodiester bonds. 
     The term “same” is used herein to denote substantial similarity in a given measurement. For example, in comparing a measurement taken on two cells, the two cells can have the same value of the measurement if the value is within the error of detection for the assay being used, or if repeated measurements are taken, there is no statistically significant difference between the values received for each cell. As another example, in comparing two populations of cells, the two populations can have the same value of the measurement if the value is within the error of detection for the assay being used, or if there is no statistically significant difference between the values received for each population. In embodiments, the two cells or two populations of cells the same value of the measurement if the values are within 10%, 8%, 6%, 5%, 4%, 3%, 2%, or 1% of each other. 
     “Sequestering” is defined as cloistering, occluding, separating, segregating, hiding, insulating, or isolating of a target and preventing it from freely interacting with its environment. 
     “Specifically binding” or “specifically interacting”, as used herein, describes any interaction between two entities (e.g., a target with a receiver, such as an antibody with an antigen, a receptor with a ligand, an enzyme with a substrate, biotin with avidin, etc.) that is saturable, often reversible and so competitive, as these terms are understood by those of ordinary skill in the chemical and biochemical arts. e.g., Specific binding involving biological molecules such as, e.g., proteins, peptides and nucleic acid occurs when one member of the binding pair has a site with a shape and distribution of charged, polar, or hydrophobic moieties such that the interaction of the cognate ligand with that site is characterized by favorable energetics (i.e., a negative free energy of binding). The specificity of the interaction may be measured or expressed as a binding constant (Kd). The Kd may range from a mM range to a pM range, including μM ranges and nM ranges. Typical Kd values are below about 10 −6  M, below about 10 −7  M, below about 10 −8  M, and in some embodiments below about 10 −9  M. 
     As used herein, the term “substantially” or “substantial” refers, e.g., to the presence, level, or concentration of an entity in a particular space, the effect of one entity on another entity, or the effect of a treatment. For example, an activity, level or concentration of an entity is substantially increased if the increase is 2-fold, 3-fold, 4-fold, 5-fold, 10-fold, 50-fold, 100-fold, or 1000-fold relative to a baseline. An activity, level or concentration of an entity is also substantially increased if the increase is 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 200%, or 500% relative to a baseline. An entity may be substantially present in a particular space if it can be detected by methods known in the art. An entity may not be substantially present in a particular space if it is present at levels below the limit of detection for assays and methods known in the art. In some embodiments, an entity may not be substantially present in a particular space if it is barely detectable but only in non-functional quantities or minute quantities that do not cause or change a phenotype. In other embodiments, an entity may not be substantially present in a particular population if it is present and can be detected only in a small number of constituents making up the population, e.g., less than 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3% 2% or less than 1%, 0.5%, 0.1% of constituents of the population. For example, an exogenous nucleic acid may not be retained upon enucleation, the cell is rendered non-replicative, and the enucleated cell is incapable of continued expression of the receiver polypeptide encoded by the exogenous nucleic acid. The loss of the ability of the cell to continue to significantly translate the exogenous polypeptide “effectively terminates” protein expression. In certain embodiments, the synthetic membrane-receiver complex is substantially incapable of self-replication, e.g., the replication of nucleic acids. For example, the synthetic membrane-receiver polypeptide complex does not substantially incorporate a nucleoside if contacted with labeled nucleoside, such as thymidine, in an incorporation assay. In some embodiments, the synthetic membrane-receiver polypeptide complex does not contain a substantial amount of self-replicating nucleic acids. The term “substantial identity” of polynucleotide or nucleic acid sequences means that a polynucleotide comprises a sequence that has at least 25% sequence identity. Alternatively, percent identity can be any integer from 25% to 100%. More preferred embodiments include at least: 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 99% compared to a reference sequence using the programs described herein; preferably BLAST using standard parameters. 
     “Synthetic” refers to a compound or molecule that is either man-made and non-naturally occurring, or if it is naturally occurring is placed in a context or location that it would not naturally exist, or if it naturally exists in the context or location is in a state of purity, or is present in an amount, concentration or number that it would not naturally be present in the context or location. Synthetic entities can be isolated or purified compounds that are optionally chemically or enzymatically modified from their natural state, exogenous nucleic acids, exogenous (heterologous) receivers, and the like. The presence of a synthetic compound or molecule, as defined herein, in any entity renders the entire entity “synthetic”. For example, a cell comprising a receiver is a synthetic cell. 
     A “target,” as used herein, is an entity capable of interacting with a receiver, e.g., to associate with or bind to a receiver. A “target” includes, but is not limited to a polypeptide (e.g., an antibody or antibody-related polypeptide, a complement constituent, an amyloid protein, a pathogen, a toxin, a prion), a molecule (e.g., a metabolite, a steroid, a hormone, a carbohydrate; an oligosaccharide; a chemical; a polysaccharide, a DNA; an RNA; a lipid, an amino acid, an element, a toxin or pathogen), a complex (e.g., an immune complex), or a cell (e.g., a cancer cell, a macrophage, a bacterium, a fungus, a virus, or a parasite). A target is intended to be detected, diagnosed, impaired, destroyed or altered (e.g., functionally complemented) by the methods provided herein. The specific target may occur free or is associated with other entities in the circulatory system of a subject. 
     A “target self-antibody,” as used herein, is a self-antibody associated with an autoimmune disease. Such self-antibodies may be detected and analyzed using antibody binding tests involving contacting the subject&#39;s antibodies to samples of the subject&#39;s own tissue, usually thyroid, stomach, liver, and kidney tissue. Antibodies binding to the “self” tissue (comprising self-antigens) indicate an autoimmune disorder. 
     “Transgene” or “exogenous nucleic acid” refers to a foreign or native nucleotide sequence that is introduced into a synthetic membrane-receiver complex. Transgene and exogenous nucleic acid are used interchangeably herein and encompass recombinant nucleic acids. 
     As used herein, “treat,” “treating,” and/or “treatment” are an approach for obtaining beneficial or desired clinical results, pharmacologic and/or physiologic effect, e.g., alleviation of the symptoms, preventing or eliminating said symptoms, and refer to both therapeutic treatment and prophylactic or preventative treatment of the specific disease, disorder or condition. Beneficial or desired clinical results, pharmacologic and/or physiologic effect include, but are not limited to, preventing the disease, disorder or condition from occurring in a subject that may be predisposed to the disease, disorder or condition but does not yet experience or exhibit symptoms of the disease (prophylactic treatment), alleviation of symptoms of the disease, disorder or condition, diminishment of extent of the disease, disorder or condition, stabilization (i.e., not worsening) of the disease, disorder or condition, preventing spread of the disease, disorder or condition, delaying or slowing of the disease, disorder or condition progression, amelioration or palliation of the disease, disorder or condition, and combinations thereof, as well as prolonging survival as compared to expected survival if not receiving treatment. 
     A “therapeutic agent” or “therapeutic molecule” includes a compound or molecule that, when present in an effective amount, produces a desired therapeutic effect, pharmacologic and/or physiologic effect on a subject in need thereof. 
     The term “therapeutically effective amount” or “effective amount” is an amount of an agent being administered to a subject sufficient to effect beneficial or desired clinical results, pharmacologic and/or physiologic effects. An effective amount can be administered in one or more administrations. An effective amount is typically sufficient to palliate, ameliorate, stabilize, reverse, slow or delay the progression of the disease state. The effective amount thus refers to a quantity of an agent or frequency of administration of a specific quantity of an agent sufficient to reasonably achieve a desired therapeutic and/or prophylactic effect. For example, it may include an amount that results in the prevention of, treatment of, or a decrease in, the symptoms associated with a disease or condition that is being treated, e.g., the diseases or medical conditions associated with a target polypeptide. The amount of a therapeutic composition administered to the subject will depend on the type and severity of the disease and on the characteristics of the individual, such as general health, pathologic conditions, diets, age, sex, body weight and tolerance to drugs. It will also depend on the degree, severity and type of disease. Further, the effective amount will depend on the methods of formulation and administration used, e.g., administration time, administration route, excretion speed, and reaction sensitivity. The skilled artisan will be able to determine appropriate dosages depending on these and other factors. The compositions can also be administered in combination with one or more additional therapeutic compounds. A desirable dosage of the pharmaceutical composition may be in the range of about 0.001 to 100 mg/kg for an adult. In one example, an intravenous administration is initiated at a dose which is minimally effective, and the dose is increased over a pre-selected time course until a positive effect is observed. Subsequently, incremental increases in dosage are made limiting to levels that produce a corresponding increase in effect while taking into account any adverse affects that may appear. Non-limited examples of suitable dosages can range, for example, from 1×10 10  to 1×10 14 , from 1×10 11  to 1×10 13 , or from 5×10 11  to 5×10 12  synthetic membrane-receiver polypeptide complexes of the present invention. Specific examples include about 5×1e, 6×10 10 , 7×10 10 , 8×10 10 , 9×10 10 , 1×10 11 , 2×10 11 , 3×10 11 , 4×10 11 , 5×10 11 , 6×10 11 , 7×10 11 , 8×10 11 , 9×10 11 , 1×10 12 , or more synthetic membrane-receiver polypeptide complexes of the present invention. Each dose of synthetic membrane-receiver polypeptide complexes can be administered at intervals such as once daily, once weekly, twice weekly, once monthly, or twice monthly. 
     “Unbound” refers to the state of a target with which the receiver is capable of interacting. An unbound target is not associated with another entity or a receiver. An unbound receiver is not associated with another entity or a target. A target is considered “bound” once it is associated with the receiver or another entity. Unbound targets include soluble forms of the target in circulation. Bound targets include targets that are embedded, associated with, linked to, or otherwise interacting with entities in circulation or peripheral tissue. Entities with which a target may interact include circulating cells, peripheral endothelial tissue, immune complexes, glycolipids, microbes, immunoglobulins, serum albumin, clotting factors, lipoproteins, and electrolytes. 
     A “variant” is a polypeptide which differs from the original protein by one or more amino acid substitutions, deletions, insertions, or other modifications. These modifications do not significantly change the biological activity of the original protein. In many cases, a variant retains at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or 100% of the biological activity of original protein. The biological activity of a variant can also be higher than that of the original protein. A variant can be naturally-occurring, such as by allelic variation or polymorphism, or be deliberately engineered. 
     The amino acid sequence of a variant is substantially identical to that of the original protein. In many embodiments, a variant shares at least 50%, 60%, 70%, 80%, 85%, 90%, 95%, 99%, or more global sequence identity or similarity with the original protein. Sequence identity or similarity can be determined using various methods known in the art, such as Basic Local Alignment Tool (BLAST), dot matrix analysis, or the dynamic programming method. In one example, the sequence identity or similarity is determined by using the Genetics Computer Group (GCG) programs GAP (Needleman-Wunsch algorithm). The amino acid sequences of a variant and the original protein can be substantially identical in one or more regions, but divergent in other regions. 
     As used herein, the term “vector” is a nucleic acid molecule, preferably self-replicating, which transfers and/or replicates an inserted nucleic acid molecule, such as a transgene or exogenous nucleic acid into and/or between host cells. It includes a plasmid or viral chromosome into whose genome a fragment of recombinant DNA is inserted and used to introduce recombinant DNA, or a transgene, into a synthetic membrane-receiver polypeptide complex. 
     The “volume of distribution” (VD) is a pharmacological, theoretical volume that the total amount of administered drug would have to occupy (if it were uniformly distributed), to provide the same concentration as it is in blood plasma. A VD greater than the blood plasma indicates that an agent is distributed in tissue in the rest of the body. The VD is influenced by solubility, charge, size, etc. Generally, non-polar agents with high lipid solubility, agents with low rates of ionization or low plasma binding capabilities have higher volumes of distribution than agents that are more polar, more highly ionized or exhibit high plasma binding. The volume of distribution is given by the following equation: V D =total amount of drug in the body/drug blood plasma concentration. The units for Volume of Distribution are typically reported in (ml or liter)/kg body weight. A volume of distribution “equal to plasma volume” is relative to the volume of the circulatory system exclusive of circulating cells. 
     Synthetic Membrane-Receiver Complexes 
     Provided herein are synthetic membrane-receiver complexes, populations, pharmaceutical compositions, and dosage forms thereof, as well as medical devices and kits comprising a formulation of the synthetic membrane-receiver complexes. 
     The synthetic membrane-receiver complexes described herein comprise a receiver (e.g., a polypeptide) that is capable of interacting with a target and further comprise a membrane comprising a polypeptide that is not the receiver. The synthetic membrane-receiver complex has catalytic activity independent of the receiver. Optionally, the synthetic membrane-receiver complexes comprise a payload, for example a therapeutic agent. 
     In some embodiments, synthetic membrane-receiver complex are generated using cells as a source material. In certain embodiments, generating a synthetic membrane-receiver complex comprises the step of contacting an erythroid cell and platelets with a receiver. In certain embodiments, generating a synthetic membrane-receiver complex comprises the step of contacting a cell derived from a hematopoietic stell cell with a receiver. 
     In certain embodiments, synthetic membrane-receiver complexes are administered, e.g., intravenously to the circulatory system of a mammalian subject, such as a human. In some embodiments, the membrane-receiver complexes provide a natural barrier between a receiver and optionally a payload (e.g., therapeutic agent) and the immune system. In some embodiments, the synthetic membrane-receiver complexes are capable of residing in the circulatory system of a subject for an extended period of time allowing delivery of a therapeutic effect for a longer period of time than what can be achieved by delivery through other methods currently used. 
     Synthetic membrane-receiver complexes may interact with a target in the circulatory system of the subject. In some embodiments, the concentration of an unbound target or total target in the circulatory system of the subject is reduced subsequent to its interaction with the receiver exhibited in or on the synthetic membrane-receiver complex. In certain embodiments, the presence or elevated concentration of a target in circulation is associated with a disease, disorder or condition and reducing the concentration of the target leads to a reduction in disease burden, may alleviate a symptom of the disease or has some other treatment effect. In some embodiments, a reduction in the concentration of the target prevents the onset of a disease, disorder or condition. 
     Biodistribution is a substantial hurdle in drug delivery and efficacy. After a drug enters the systemic circulation, it is distributed to the body&#39;s tissues. Distribution is generally uneven because of differences in blood perfusion, tissue binding (e.g., because of lipid content), regional pH, and permeability of cell membranes. The entry rate of a drug into a tissue depends on the rate of blood flow to the tissue, tissue mass, and partition characteristics between blood and tissue. Distribution equilibrium (when entry and exit rates are the same) between blood and tissue is reached more rapidly in richly vascularized areas, unless diffusion across cell membranes is the rate-limiting step. After equilibrium, drug concentrations in tissues and in extracellular fluids are reflected by the plasma concentration. Metabolism and excretion occur simultaneously with distribution, making the process dynamic and complex. 
     The synthetic membrane-receiver complexes when formulated in a pharmaceutical compositions suitable for administration into the circulatory system of a subject can have a volume of distribution equal to the plasma volume of the subject. Advantages of the volume of distribution characteristic of the synthetic membrane-receiver complexes include that the biodistribution of the receiver when administered as a synthetic membrane-receiver complex into the circulatory system of a subject may be accurately predicted and/or that potential adverse extravascular effects of the receiver (e.g., an inflammatory response, an immune response, toxicity, etc.) are substantially reduced. 
     Distribution of a therapeutic composition out of the bloodstream and into surrounding tissue increases the apparent volume of distribution to be greater than the plasma volume of the subject. Therapeutic compositions that exit the bloodstream and interact with surrounding tissue, e.g., adipose tissue or muscle, may interact with those tissues in unpredictable ways and trigger adverse events. A therapeutic composition, such as a composition comprising a synthetic membrane-receiver complex described herein, whose volume of distribution does not substantially exceed the plasma volume of the subject typically has a safety profile that is superior to a therapeutic composition with a large volume of distribution. Further, the amount of a therapeutic composition that must be loaded to be effective (the effective amount) is in part dependent on the bioavailability of the therapeutic composition. Bioavailability is related to the composition&#39;s profile and rate of distribution into extra-vascular tissues, and thus its volume of distribution. By maintaining a precise and predictable volume of distribution, typically a therapeutic composition, such as a composition comprising a synthetic membrane-receiver complex described herein, will have a more precise and predictable dose-effect relationship than a therapeutic composition with a less precise and predictable volume of distribution. 
     For example, the drug distribution rate for interstitial fluids of most tissues is determined primarily by perfusion. For poorly perfused tissues (e.g., muscle, fat), distribution is very slow, especially if the tissue has a high affinity for the drug. Endothelial cells lining the vessel wall are connected by adherens, tight and gap junctions. These junctional complexes are related to those found at epithelial junctions but with notable changes in terms of specific molecules and organization. Endothelial junctional proteins play important roles in tissue integrity but also in vascular permeability, leukocyte extravasation and angiogenesis. Small molecules, protein therapeutics, and viruses measure 1-30 nm and are capable of diffusing far beyond the vasculature based on lipophilicity, ability to bind plasma proteins, and charge. A drug that is confined to the vasculature has a lesser volume of tissue to occupy and thus may remain at an effective, therapeutic concentration. In addition, the drug is unable to interact with peripheral tissues and potential off-target toxicity effects are limited. Larger circulatory agents (e.g., between 1 micron and 20 microns) do not pass through endothelial tight junctions which are less than 100 nm in width and endothelial cells are incapable of facilitating the transcytosis of agents of that size. In some embodiments, the synthetic membrane-receiver complexes described herein measure between 1 micron and 20 microns. The vascular properties of these agents limit their diffusive capabilities to the bloodstream and concentrate the therapeutic effect of any receiver or payload. 
     The synthetic membrane-receiver complexes described herein, in some embodiments, exhibit advantageous clearance properties. In some embodiments, synthetic membrane-receiver complexes may be degraded using a natural degradation process, through the reticulo-endothelial system. Such degradation typically does not cause any or little side effects. In some embodiments, receivers displayed on the synthetic membrane-receiver complexes can be selectively trapped by organs of the reticulo-endothelial system. 
     The synthetic membrane-receiver complexes described herein are, in some embodiments, incapable of self-replication. In some embodiments, the synthetic membrane-receiver complexes do not contain self-replicating nucleic acids. Thus, such complexes do not carry a risk of uncontrolled cellular division, undesired protein expression and/or the potential of triggering cytokine release syndrome. 
     Membrane Compositions of the Synthetic Membrane-Receiver Complexes 
     1. Lipids 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a membrane that has a mass of approximately 1×10{circumflex over ( )}-12 g and a density of approximately 1.15 g/cm{circumflex over ( )}3. The mass of the membrane component can be assessed by separating it from the remainder of the complex using hypotonic solutions of mildly alkaline buffer, see e.g., protocols in Dodge et al 1963, Arch Biochem Biophys 100:119. 
     The synthetic membrane-receiver complex comprises a membrane. In some embodiments, the membrane comprises phosphatidylcholine, sphingomyelin, lysophosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, or phosphatidic acid. In some embodiments, the membrane is a cell membrane. 
     In one embodiment the synthetic membrane-receiver polypeptide complex comprises lipid molecules of the class of choline phospholipids, acidic phospholipids, and phosphatidylethanolamine. 
     In one embodiment the synthetic membrane-receiver polypeptide complex comprises phosphatidylcholine, sphingomyelin, lysophosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, or phosphatidic acid. 
     In one embodiment the synthetic membrane-receiver polypeptide complex comprises choline phospholipids in an approximate amount of 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, or 65% relative to the total lipid content of the complex. 
     In one embodiment the synthetic membrane-receiver polypeptide complex comprises acidic phospholipids in an approximate amount of 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20% relative to the total lipid content of the complex. 
     In one embodiment the synthetic membrane-receiver polypeptide complex comprises phosphatidylcholine in an amount greater than 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%. 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or greater than 50% relative to the total lipid content of the complex. 
     In one embodiment the synthetic membrane-receiver polypeptide complex comprises sphingomyelin in an amount greater than 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%. 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or greater than 50% relative to the total lipid content of the complex. 
     In one embodiment the synthetic membrane-receiver polypeptide complex comprises lysophosphatidylcholine in an amount greater than 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or greater than 10% relative to the total lipid content of the complex. 
     In one embodiment the synthetic membrane-receiver polypeptide complex comprises phosphatidylethanolamine in an amount greater than 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%. 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or greater than 50% relative to the total lipid content of the complex. 
     In one embodiment the synthetic membrane-receiver polypeptide complex comprises phosphatidylserine in an amount greater than 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%. 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or greater than 50% relative to the total lipid content of the complex. 
     In one embodiment the synthetic membrane-receiver polypeptide complex comprises phosphatidylinositol in an amount greater than 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or greater than 10% relative to the total lipid content of the complex. 
     In one embodiment the synthetic membrane-receiver polypeptide complex comprises phosphatidic acid in an amount greater than 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or greater than 10% relative to the total lipid content of the complex. 
     In one embodiment the synthetic membrane-receiver polypeptide complex comprises molecules from at least one, two, or three, of the following classes of molecules, including, but not limited to, choline phospholipids, acidic phospholipids, and phosphatidylethanolamine. 
     In one embodiment the molar ratio of choline phospholipids to acidic phospholipids in the synthetic membrane-receiver polypeptide complex is less than 1:1000, approximately 1:1000, approximately 1:500, approximately 1:250, approximately 1:100, approximately 1:50, approximately 1:25, approximately 1:10, approximately 1:9, approximately 1:8, approximately 1:7, approximately 1:6, approximately 1:5, approximately 1:4, approximately 1:3, approximately 1:2, approximately 1:1, approximately 2:1, approximately 3:1, approximately 4:1, approximately 5:1, approximately 6:1, approximately 7:1, approximately 8:1, approximately 9:1, approximately 10:1, approximately 25:1, approximately 50:1, approximately 100:1, approximately 250:1, approximately 500:1, approximately 1000:1, or greater than approximately 1000:1. 
     In one embodiment the molar ratio of choline phospholipids to phosphatidyl ethanolamine in the synthetic membrane-receiver polypeptide complex is less than 1:1000, approximately 1:1000, approximately 1:500, approximately 1:250, approximately 1:100, approximately 1:50, approximately 1:25, approximately 1:10, approximately 1:9, approximately 1:8, approximately 1:7, approximately 1:6, approximately 1:5, approximately 1:4, approximately 1:3, approximately 1:2, approximately 1:1, approximately 2:1, approximately 3:1, approximately 4:1, approximately 5:1, approximately 6:1, approximately 7:1, approximately 8:1, approximately 9:1, approximately 10:1, approximately 25:1, approximately 50:1, approximately 100:1, approximately 250:1, approximately 500:1, approximately 1000:1, or greater than approximately 1000:1. 
     In one embodiment the molar ratio of phosphatidylethanolamine to acidic phospholipids in the synthetic membrane-receiver polypeptide complex is less than 1:1000, approximately 1:1000, approximately 1:500, approximately 1:250, approximately 1:100, approximately 1:50, approximately 1:25, approximately 1:10, approximately 1:9, approximately 1:8, approximately 1:7, approximately 1:6, approximately 1:5, approximately 1:4, approximately 1:3, approximately 1:2, approximately 1:1, approximately 2:1, approximately 3:1, approximately 4:1, approximately 5:1, approximately 6:1, approximately 7:1, approximately 8:1, approximately 9:1, approximately 10:1, approximately 25:1, approximately 50:1, approximately 100:1, approximately 250:1, approximately 500:1, approximately 1000:1, or greater than approximately 1000:1. 
     In one embodiment the synthetic membrane-receiver polypeptide complex comprises molecules from at least one, two, three, four, five, six, or seven of the following classes of molecules, including, but not limited to, phosphatidylcholine, sphingomyelin, lysophosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, or phosphatidic acid. 
     The lipid composition of the synthetic membrane-receiver polypeptide complex can be experimentally measured using methods known in the art including, e.g., gas-liquid chromatography or thin layer chromatography, see for example Dodge &amp; Phillips, J Lipid Res 1967 8:667. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a lipid bilayer composed of an inner leaflet and an outer leaflet. The composition of the inner and outer leaflet can be determined by transbilayer distribution assays known in the art, see e.g., Kuypers et al. Biohim Biophys Acta 1985 819:170. In one embodiment, the composition of the outer leaflet is between approximately 70-90% choline phospholipids, between approximately 0-15% acidic phospholipids, and between approximately 5-30% phosphatidylethanolamine. In one embodiment, the composition of the inner leaflet is between approximately 15-40% choline phospholipids, between approximately 10-50% acidic phospholipids, and between approximately 30-60% phosphatidylethanolamine. 
     2. Cholesterol 
     In one embodiment the synthetic membrane-receiver polypeptide complex comprises cholesterol. In one embodiment the cholesterol content is between approximately 3.0-5.5 nmol cholesterol per 10{circumflex over ( )}7 complexes. In one embodiment, the cholesterol content is between approximately 1.8-3.5 nmol cholesterol per 10{circumflex over ( )}7 complexes. In one embodiment the molar ratio of cholesterol to phospholipids in the complex is between approximately 0.5-1.5. In a preferred embodiment the molar ratio of cholesterol to phospholipids is between approximately 0.8-1.2. In a preferred embodiment the molar ratio of cholesterol to phospholipids is between approximately 0.84-0.9. In a preferred embodiment the molar ratio of cholesterol to phospholipids is between approximately 0.5-0.75. In a preferred embodiment the molar ratio of cholesterol to phospholipids is between approximately 0.55-0.6. 
     3. Lipids, Proteins, and Carbohydrates 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises polypeptides other than the receiver polypeptide. In one embodiment, approximately 52% of the membrane mass is protein, approximately 40% is lipid, and approximately 8% is carbohydrate. In one embodiment, approximately 7% of the carbohydrate content is comprised of glycosphingolipids and approximately 93% of the carbohydrate content is comprised of O-linked and N-linked oligosaccharides on membrane-associated polypeptides. 
     In one embodiment the mass ratio of lipid to protein in the synthetic membrane-receiver polypeptide complex is less than 1:1000, approximately 1:1000, approximately 1:500, approximately 1:250, approximately 1:100, approximately 1:50, approximately 1:25, approximately 1:10, approximately 1:9, approximately 1:8, approximately 1:7, approximately 1:6, approximately 1:5, approximately 1:4, approximately 1:3, approximately 1:2, approximately 1:1, approximately 2:1, approximately 3:1, approximately 4:1, approximately 5:1, approximately 6:1, approximately 7:1, approximately 8:1, approximately 9:1, approximately 10:1, approximately 25:1, approximately 50:1, approximately 100:1, approximately 250:1, approximately 500:1, approximately 1000:1, or greater than approximately 1000:1. 
     In one embodiment the mass ratio of lipid to carbohydrate in the synthetic membrane-receiver polypeptide complex is less than 1:1000, approximately 1:1000, approximately 1:500, approximately 1:250, approximately 1:100, approximately 1:50, approximately 1:25, approximately 1:10, approximately 1:9, approximately 1:8, approximately 1:7, approximately 1:6, approximately 1:5, approximately 1:4, approximately 1:3, approximately 1:2, approximately 1:1, approximately 2:1, approximately 3:1, approximately 4:1, approximately 5:1, approximately 6:1, approximately 7:1, approximately 8:1, approximately 9:1, approximately 10:1, approximately 25:1, approximately 50:1, approximately 100:1, approximately 250:1, approximately 500:1, approximately 1000:1, or greater than approximately 1000:1. 
     In one embodiment the mass ratio of carbohydrate to protein in the synthetic membrane-receiver polypeptide complex is less than 1:1000, approximately 1:1000, approximately 1:500, approximately 1:250, approximately 1:100, approximately 1:50, approximately 1:25, approximately 1:10, approximately 1:9, approximately 1:8, approximately 1:7, approximately 1:6, approximately 1:5, approximately 1:4, approximately 1:3, approximately 1:2, approximately 1:1, approximately 2:1, approximately 3:1, approximately 4:1, approximately 5:1, approximately 6:1, approximately 7:1, approximately 8:1, approximately 9:1, approximately 10:1, approximately 25:1, approximately 50:1, approximately 100:1, approximately 250:1, approximately 500:1, approximately 1000:1, or greater than approximately 1000:1. 
     In one embodiment the area occupancy of protein in the synthetic membrane-receiver polypeptide complex is approximately 23% and the area occupancy of lipid in the synthetic membrane-receiver polypeptide complex is approximately 77%. 
     In one embodiment the synthetic membrane-receiver polypeptide complex comprises a polypeptide selected from the following list, including but not limited to, spectrin, myosin-like polypeptide, band 3, SLC4A1, actin, actin-like polypeptide, glyceraldehyde 3-P dehydrogenase (G3PD). 
     In one embodiment the synthetic membrane-receiver polypeptide complex comprises at least one, two, three, four, five, six, or seven of the polypeptides selected from the following list, including but not limited to, spectrin, myosin-like polypeptide, band 3, SLC4A1, actin, actin-like polypeptide, glyceraldehyde 3-P dehydrogenase (G3PD). 
     4. Additional Polypeptides 
     In some embodiments, the synthetic membrane-receiver complex comprises at least one polypeptide that is not the receiver. In some embodiments, the synthetic membrane-receiver complex comprises at least two, at least three, at least four, at least five, at least six, at least seven, at least eight, at least nine or at least ten polypeptides that are not the receiver. In certain instances, the polypeptide is capable of an enzymatic or catalytic function independent of the receiver. The non-receiver polypeptide may be associated with the membrane of the synthetic membrane-receiver complex. 
     In some embodiments, the non-receiver polypeptide may, e.g., stabilize the synthetic membrane-receiver complex, target the synthetic membrane-receiver complex to particular cells and tissues, engage the reticulo-endothelial system, protect the synthetic membrane-receiver complex from macrophages and other phagocytic cells, and/or evade other components of the innate immune system. Suitable polypeptides include, e.g., complement regulatory polypeptides, inhibitors of cell-mediated degradation (e.g., CD47, CD55, and CD59), and anti-inflammatory polypeptides. Alternatively or in addition, non-receiver polypeptides may shorten or control the half-life of the complex, including targeting to macrophages or other phagocytic cells. Suitable non-receiver polypeptides may promote apoptosis or otherwise trigger opsonization. In some embodiments, non-receiver polypeptides include polypeptide carriers, pumps, and channels; Glut1, Band3, aquaporin 1, RhAH, NA/K ATPase, Ca ATPase, Na—H exchanger, KCa3.1, KCl cotransporter, and coenzyme Q10. 
     As many drugs are systemically delivered to the blood circulatory system, the answer to the problem of effective drug delivery often focuses on maintaining the drug in the blood for extended periods of time. Thus, the development of long-circulating (long half-life) therapeutics that remain biologically available in the blood for extended time periods is an unmet need. The synthetic membrane-receiver complexes described herein can be modified to increase or decrease their half-life in circulation. In some embodiments, the half-life of the receiver and optionally the payload in circulation may be modified by altering the half-life of the synthetic membrane-receiver complex. In some instances, the half-life is increased and the increase may be, for instance from about 1.5-fold to 20-fold increase in serum half-life. 
     In some embodiments, receivers may reside in circulation and may remain functional and active for substantially the duration of the synthetic membrane-receiver complex in circulation. In some embodiments, receivers may reside in circulation and may remain functional and active for more than 21 days in circulation. In some instances, synthetic membrane-receiver complexes and receivers may reside in circulation for 30 days, 45 days, 60 days, 100 days, 120 days, or longer. In other embodiments, the synthetic membrane-receiver complexes and receivers may reside in circulation for several hours to several days, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 days. Residency in the circulatory system, in certain embodiments, is determined by the presence or absence of certain polypeptides on the synthetic membrane-receiver complex. For example, the synthetic membrane-receiver complex may comprise a CD47, CD55, or CD59 polypeptide or a functional fragment thereof. 
     CD47 is a membrane protein that interacts with the myeloid inhibitory immunoreceptor SIRPa (also termed CD172a or SHPS-1) that is present, e.g., on macrophages. Engagement of SIRPa by CD47 provides a down-regulatory signal that inhibits host cell phagocytosis. For example, high levels of CD47 allow cancer cells to avoid phagocytosis despite the presence pro-phagocytic signals, such as high levels of calreticulin. CD47 also has further roles in cell adhesion, e.g., by acting as an adhesion receptor for THBS1 on platelets and in the modulation of integrins. CD47 interaction with SIRPa further prevents maturation of immature dendritic cells, inhibits cytokine production by mature dendritic cells. CD47 interaction with SIRPγ mediates cell-cell adhesion, enhances superantigen-dependent T-cell-mediated proliferation and co-stimulates T-cell activation. 
     CD47 is a 50 kDa membrane receptor that has extracellular N-terminal IgV domain, five transmembrane domains, and a short C-terminal intracellular tail. There are four alternatively spliced isoforms of CD47 that differ only in the length of their cytoplasmic tail. In some embodiments, the synthetic membrane-receiver complex may comprise a CD47 or a functional fragment thereof comprising one or more of: the extracellular N-terminal IgV domain, one, two, three, four, or five transmembrane domains, and/or the short C-terminal intracellular tail. The cytoplasmic tail can be found as four different splice isoforms ranging from 4 to 36 amino acids. The 16 amino acid form 2 is expressed in all cells of hematopoietic origin and in endothelial and epithelial cells. The 36 amino acid form 4 is expressed primarily in neurons, intestine, and testis. The 4 amino acid form 1 is found in epithelial and endothelial cells. The expression pattern of the 23 amino acid form 3 resembles that of form 4. In some embodiments, the synthetic membrane-receiver complex comprises CD47 or a functional fragment thereof that is of one of form 1, from 2, form 3, or from 4. In some embodiments, the synthetic membrane-receiver complex does not comprise form 2. In some embodiments, the synthetic membrane-receiver complex comprises CD47 polypeptide or a functional polypeptide fragment thereof in an amount or copy number sufficient to reside in circulation for 15 days, 21 days, 30 days, 45 days, 60 days, 100 days, 120 days, or longer. In some embodiments, the synthetic membrane-receiver complex comprises a modified CD47, such as a conformational change. For example, a conformational change in CD47 is introduced so that the modified CD47 is capable of interacting with TSP-1. In one embodiment, the modified CD47 comprising the conformational change creates a different binding site for SIRPα. In some embodiments, the synthetic membrane-receiver complex comprises a modified CD47 polypeptide or a functional polypeptide fragment thereof comprising a conformational change in an amount or copy number sufficient to reside in circulation for less than 10, 9, 8, 7, 6, 5, 4, 3, 2, or less than 1 day. In certain embodiments, the synthetic membrane-receiver complex comprises a fusion of a CD47 isoform to the extracellular domain of a native erythroid polypeptide. For example, the N terminus of glycophorin A may be fused to the CD47 polypeptide or functional fragment thereof, which may lead to a reduction of the SIRPα-mediated signal to macrophages to phagocytose the synthetic membrane-receiver complex. 
     In some embodiments, generating synthetic membrane-receiver complexes includes the step of contacting a receiver (e.g., a polypeptide) with a cell, such as an erythroid cell or a platelet. CD47 is expressed in erythrocytes and platelets to mediate phagocytosis. In some embodiments, the natural levels of CD47 are altered in erythrocytes or platelets, e.g., by over-expression or inhibition of CD47 expression using any suitable method, such as the introduction of exogenous nucleic acids (e.g., expression vectors, CD47 mRNA, CD47 siRNA, and the like). In some embodiments, the natural levels of CD47 are altered such that the synthetic membrane-receiver complex resides in circulation for 15 days, 21 days, 30 days, 45 days, 60 days, 100 days, 120 days, or longer. In some embodiments, the natural levels of CD47 are altered such that the synthetic membrane-receiver complex resides in circulation for less than 10, 9, 8, 7, 6, 5, 4, 3, 2, or less than 1 day. 
     For example, synthetic membrane-receiver complexes that are administered to a subject may comprise elevated CD47 levels when compared to native levels of a suitable control. Elevated CD47 levels may be achieved, e.g., by exogenous expression by the synthetic membrane-receiver complex of CD47 from an exogenous nucleic acid, by loading of CD47 mRNA into the complex, or by conjugating CD47 polypeptide to the surface of the complex. Elevated CD47 levels are useful to increase the half-life of the population of synthetic membrane-receiver complexes in the circulatory system of the subject. The synthetic membrane-receiver complexes comprise a receiver and optionally a payload, such as a therapeutic agent. In some embodiments, increasing the half-life of the synthetic membrane-receiver complex increases the half-life of the receiver and/or the optional payload in circulation, thereby potentially increasing the therapeutic window in which the receiver and/or payload is active. In one instance, a population of 10 11  synthetic membrane-receiver polypeptide complexes comprises an adenosine deaminase receiver and an exogenous CD47 polypeptide on its surface. When administered to a subject with an enzyme deficiency, such as ADA-SCID, the half-life of the synthetic membrane-receiver polypeptide complex is extended beyond that of a complex not comprising exogenous CD47 polypeptide and the subject requires less frequent dosing. Half-life extension is a particular advantage when compared to current enzyme therapies not involving synthetic membrane-receiver polypeptide complexes. 
     In some embodiments, CD47 is altered by heparin and/or chondroitin sulfate glycosaminoglycan (GAG) chains. In some embodiments, the synthetic membrane-receiver complex expresses CD47 as a proteoglycan. In some embodiments, the synthetic membrane-receiver complex comprises a CD47 proteoglycan that is conjugated to the complex. In one embodiment, the CD47 proteoglycan comprises heparin and/or chondroitin sulfate glycosaminoglycan (GAG) chains. In one embodiment, that CD47 proteoglycan has a size of greater than 150 kDa, 200 kDa, or greater than 250 kDa. In one embodiment, CD47 comprises one or more GAG chains at Ser64. 
     In some embodiments, the residency of a synthetic membrane-receiver complex, e.g., generated using erythroid cells or platelets can be further modulated by changing the amount or number of oxidized lipids on the membrane of the synthetic membrane-receiver complex. In one embodiment, the synthetic membrane-receiver complex comprises oxidized lipids in an amount effective to reside in circulation for less than 10, 9, 8, 7, 6, 5, 4, 3, 2, or less than 1 day. In one embodiment, the synthetic membrane-receiver complex comprises oxidized lipids in an amount effective to reside in circulation for 15 days, 21 days, 30 days, 45 days, 60 days, 100 days, 120 days, or longer. In some embodiments, the amount of oxidized lipids in the membrane are altered such that mobility of CD47 is increased or decreased, thereby aiding or hindering, respectively the ability of CD47 to cluster on the membrane. (See, Olsson, Department of Integrative Medical Biology, Section for Histology and Cell Biology, Umea University, Umea, Sweden, 2008). 
     CD55, also known as complement decay-accelerating factor or DAF, is a 70 kDa membrane protein. CD55 recognizes C4b and C3b fragments of the complement system that are created during C4 (classical complement pathway and lectin pathway) and C3 (alternate complement pathway) activation. It is thought that interaction of CD55 with cell-associated C4b and C3b proteins interferes with their ability to catalyze the conversion of C2 and factor B to active C2a and Bb and thereby prevents the formation of C4b2a and C3bBb, the amplification convertases of the complement cascade. CD55 is thought to block the formation of membrane attack complexes. CD55 may prevent lysis by the complement cascade. In some embodiments, the synthetic membrane-receiver complex comprises CD55 polypeptide or a functional polypeptide fragment thereof in an amount or copy number sufficient to reside in circulation for 15 days, 21 days, 30 days, 45 days, 60 days, 100 days, 120 days, or longer. In some embodiments, the synthetic membrane-receiver complex comprises an exogenous CD55 polypeptide and an exogenous CD47 polypeptide or functional polypeptide fragments thereof in an amount, copy number and/or ratio sufficient to reside in circulation for 15 days, 21 days, 30 days, 45 days, 60 days, 100 days, 120 days, or longer. 
     CD59 glycoprotein also known as MAC-inhibitory protein (MAC-IP), membrane inhibitor of reactive lysis (MIRL), protectin, or HRF is a protein that attaches to host cells via a glycophosphatidylinositol (GPI) anchor. When complement activation leads to deposition of C5b678 on host cells, CD59 can prevent C9 from polymerizing and forming the complement membrane attack complex. CD59 may prevent lysis by the complement cascade. In some embodiments, the synthetic membrane-receiver complex comprises CD59 polypeptide or a functional polypeptide fragment thereof in an amount or copy number sufficient to reside in circulation for 15 days, 21 days, 30 days, 45 days, 60 days, 100 days, 120 days, or longer. In some embodiments, the synthetic membrane-receiver complex comprises an exogenous CD59 polypeptide and an exogenous CD47 polypeptide or functional polypeptide fragments thereof in an amount, copy number and/or ratio sufficient to reside in circulation for 15 days, 21 days, 30 days, 45 days, 60 days, 100 days, 120 days, or longer. 
     In some embodiments, the synthetic membrane-receiver complex comprises one or more of an exogenous CD55 polypeptide, an exogenous CD59 polypeptide and/or an exogenous CD47 polypeptide or functional polypeptide fragments thereof in an amount, copy number and/or ratio sufficient to reside in circulation for 15 days, 21 days, 30 days, 45 days, 60 days, 100 days, 120 days, or longer. 
     Effective amounts of CD47, CD55, and CD59 include 10 2 , 10 3 , 10 4 , 10 5 , 10 6 , 10 7 , 10 9  polypeptides per synthetic membrane-receiver complex. Alternatively, an effective amount is the amount capable of extending the synthetic membrane-receiver polypeptide complex&#39;s half-life by 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 200%, 400%, 800%, 1,000%, or 10,000% relative to the half-life that the synthetic membrane-receiver polypeptide complex would exhibit without the polypeptides. 
     Receivers 
     Provided herein are receivers that are exhibited by synthetic membrane-receiver complexes. In some embodiments, a receiver is capable of interacting with a target, e.g., to associate with or bind to a target. A receiver can comprise or may consist essentially of a polypeptide. In some embodiments, the receiver comprises a polypeptide, a carbohydrate, a nucleic acid, a lipid, a small molecule, or a combination thereof. In some embodiments receivers do not interact with a target but act as payloads to be delivered by the synthetic membrane-receiver complex to a cell, tissue or other site in the body of a subject. 
     In some embodiments, receivers comprise polypeptides. Receiver polypeptides may range in size from 6 amino acids to 3000 amino acids and may exceed 6, 10, 15, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100, 150, 200, 300, 400 or may exceed 500 amino acids. Receiver polypeptides may range in size from about 20 amino acids to about 500 amino acids, from about 30 amino acids to about 500 amino acids or from about 40 amino acids to about 500 amino acids. 
     In some embodiments, the receiver polypeptide comprises a chimeric or fusion protein which may comprise two or more distinct protein domains. These chimeric receivers are heterologous or exogenous in the sense that the various domains are derived from different sources, and as such, are not found together in nature and can be encoded e.g., by exogenous nucleic acids. Receiver polypeptides can be produced by a number of methods, many of which are well known in the art and also described herein. For example, receiver polypeptides can be obtained by extraction (e.g., from isolated cells), by expression of an exogenous nucleic acid encoding the receiver polypeptide, or by chemical synthesis. Receiver polypeptides can be produced by, for example, recombinant technology, and expression vectors encoding the polypeptide introduced into host cells (e.g., by transformation or transfection) for expression of the encoded receiver polypeptide. 
     There are a variety of conservative changes that can generally be made to an amino acid sequence without altering activity. These changes are termed conservative substitutions or mutations; that is, an amino acid belonging to a grouping of amino acids having a particular size, charge or other characteristic can be substituted for another amino acid. Substitutions for an amino acid sequence may be selected from other members of the class to which the amino acid belongs. For example, the nonpolar (hydrophobic) amino acids include alanine, leucine, isoleucine, valine, proline, phenylalanine, tryptophan, methionine, and tyrosine. The polar neutral amino acids include glycine, serine, threonine, cysteine, tyrosine, asparagine and glutamine. The positively charged (basic) amino acids include arginine, lysine and histidine. The negatively charged (acidic) amino acids include aspartic acid and glutamic acid. Such alterations are not expected to substantially affect apparent molecular weight as determined by polyacrylamide gel electrophoresis or isoelectric point. Conservative substitutions also include substituting optical isomers of the sequences for other optical isomers, specifically D amino acids for L amino acids for one or more residues of a sequence. Moreover, all of the amino acids in a sequence may undergo a D to L isomer substitution. Exemplary conservative substitutions include, but are not limited to, Lys for Arg and vice versa to maintain a positive charge; Glu for Asp and vice versa to maintain a negative charge; Ser for Thr so that a free ˜OH is maintained; and Gln for Asn to maintain a free NH 2 . Moreover, point mutations, deletions, and insertions of the polypeptide sequences or corresponding nucleic acid sequences may in some cases be made without a loss of function of the polypeptide or nucleic acid fragment. Substitutions may include, e.g., 1, 2, 3, or more residues. Any teaching of a specific amino acid sequence or an exogenous nucleic acid encoding the polypeptide or teaching of the name of the name thereof includes any conservative substitution point mutations, deletions, and insertions of those polypeptide sequences or corresponding nucleic acid sequences and any sequence deposited for the protein or gene in a database that can be made without a loss of function of the polypeptide or nucleic acid fragment. 
     In some embodiments, the receiver polypeptide is associated with the membrane of the synthetic membrane-receiver polypeptide complex. In other embodiments, the receiver polypeptide is not associated with the membrane of the synthetic membrane-receiver polypeptide complex. 
     In one embodiment the mass ratio of lipid to receiver in the synthetic membrane-receiver polypeptide complex is less than 1:1000, approximately 1:1000, approximately 1:500, approximately 1:250, approximately 1:100, approximately 1:50, approximately 1:25, approximately 1:10, approximately 1:9, approximately 1:8, approximately 1:7, approximately 1:6, approximately 1:5, approximately 1:4, approximately 1:3, approximately 1:2, approximately 1:1, approximately 2:1, approximately 3:1, approximately 4:1, approximately 5:1, approximately 6:1, approximately 7:1, approximately 8:1, approximately 9:1, approximately 10:1, approximately 25:1, approximately 50:1, approximately 100:1, approximately 250:1, approximately 500:1, approximately 1000:1, approximately 10,000:1, approximately 100,000:1, approximately 1,000,000:1, approximately 10,000,000:1, approximately 100,000,000:1, approximately 1,000,000,000:1 or greater than approximately 1,000,000,000:1. 
     In one embodiment the mass ratio of non-receiver polypeptide to receiver in the synthetic membrane-receiver polypeptide complex is less than 1:1000, approximately 1:1000, approximately 1:500, approximately 1:250, approximately 1:100, approximately 1:50, approximately 1:25, approximately 1:10, approximately 1:9, approximately 1:8, approximately 1:7, approximately 1:6, approximately 1:5, approximately 1:4, approximately 1:3, approximately 1:2, approximately 1:1, approximately 2:1, approximately 3:1, approximately 4:1, approximately 5:1, approximately 6:1, approximately 7:1, approximately 8:1, approximately 9:1, approximately 10:1, approximately 25:1, approximately 50:1, approximately 100:1, approximately 250:1, approximately 500:1, approximately 1000:1, approximately 10,000:1, approximately 100,000:1, approximately 1,000,000:1, approximately 10,000,000:1, approximately 100,000,000:1, approximately 1,000,000,000:1 or greater than approximately 1,000,000,000:1. 
     In certain embodiments, the polypeptide receiver is located on the surface and is exposed to the environment around the synthetic membrane-receiver polypeptide complex. In some embodiments, the polypeptide receiver is located inside and faces the unexposed side of the synthetic membrane-receiver polypeptide complex. 
     In certain embodiments, the polypeptide receiver comprises at least one of the following domains, an S domain (surface), an A domain (anchor), and/or a U domain (unexposed), wherein the S domain is a surface domain exposed to the environment around the synthetic membrane-receiver polypeptide complex, wherein the A domain is an anchor, and wherein the U domain is located within and/or faces the unexposed side of the synthetic membrane-receiver polypeptide complex. 
     Optionally the receiver polypeptide comprises i) one or more additional S domains, termed S′ domains, or ii) one or more additional U domains, termed U′ domains. 
     In some embodiments, the S domain and the A domain form part of the same polypeptide chain. 
     In some embodiments, the A domain and the U domain form part of the same polypeptide chain. 
     In some embodiments, any one or more of the S, A, U domain is added to the synthetic membrane-receiver polypeptide complex externally. 
     In some embodiments, any one or more of the S, A, U domain is produced within the synthetic membrane-receiver polypeptide complex. 
     In some embodiments, any one or more of the S, A, U domain is a polypeptide. 
     In some embodiments, any one or more of the S, A, U domain is not a polypeptide. 
     Schematics of exemplary conformations of receivers within or on synthetic membrane-receiver complexes are shown in  FIGS. 14A, 14B, and 14C . 
     1. The A Domain 
     In certain embodiments, the A domain is a membrane polypeptide. The A domain can be, e.g., an integral membrane polypeptide or a membrane associated polypeptide. 
     The A domain may be selected from one of the following classes, including but not limited to, for example, alpha-helical bitopic, alpha-helical polytopic, beta-barrel transmembrane, all alpha monotopic/peripheral, all beta monotopic/peripheral, alpha/beta monotopic/peripheral, alpha+beta monotopic/peripheral, alpha helical peptides, beta-hairpin peptides, beta-helical peptides, type 1 transmembrane protein (N-terminus extracellular), type 2 transmembrane protein (N-terminus intracellular), type 3 transmembrane protein, type 4A transmembrane protein, type 4B transmembrane protein, lipid-anchored protein, glycosylphosphatidylinositol (GPI) anchored protein, prenyl chain anchored protein, or peptides of nonregular structure. 
     In certain embodiments, the A domain is endogenous, e.g., endogenous to an erythroid cell, a platelet, or a hematopoietic cell. In some embodiments, the A domain is endogenous to a mammalian cell. 
     In certain embodiments, the A domain is exogenous, e.g., exogenous to an erythroid cell, a platelet, or a hematopoietic cell. In some embodiments, the A domain is exogenous to a mammalian cell. 
     The A domain may be selected from the following molecules or fragments thereof, including but not limited to, CD1, CD2, CD3, CD4, CD5, CD6, CD7, CD8, CD9, CD10, CD11a, CD11b, CD11c, CD12w, CD13, CD14, CD15, CD16, CDw17, CD18, CD19, CD20, CD21, CD22, CD23, CD24, CD25, CD26, CD27, CD28, CD29, CD30, CD31, CD32, CD33, CD34, CD35, CD36, CD37, CD38, CD39, CD40, CD41, CD42, CD43, CD44, CD45, CD46, CD47, CD48, CD49a, CD49b, CD49c, CD49d, CD49e, CD49f, CD53, CD54, CD55, CD56, CD57, CD58, CD59, CD61, CD62E, CD62L, CD62P, CD63, CD68, CD69, CD71, CD72, CD73, CD74, CD80, CD81, CD82, CD83, CD86, CD87, CD88, CD89, CD90, CD91, CD95, CD96, CD100, CD103, CD105, CD106, CD107, CD107a, CD107b, CD109, CD117, CD120, CD122, CD123, CD127, CD132, CD133, CD134, CD135, CD138, CD141, CD142, CD143, CD144, CD147, CD151, CD152, CD154, CD155, CD156, CD158, CD163, CD165, CD166, CD168, CD184, CDw186, CD195, CD197, CDw199, CD209, CD202a, CD220, CD221, CD235a, CD271, CD279, CD303, CD304, CD309, CD326, Ras-Related protein 1A, semaporin 7A precursor, Calcium and integrin-binding protein 1, 55 kDa erythrocyte membrane protein, Flotillin-1, Flotillin-2, Erythroid membrane-associated protein, eukaryotic translation initiation factor 2C 2, cytochrome b5 reductase, cell division control protein 42 homolog, KIAA1363 protein, band3, annexin VII, aquaporin, Ecto-ADP-ribosyltransferase 4, Kell, LFA-3, soulute carrier family 2 member 1, LGALS3 protein, Urea transporter, Rh blood CE group antigen polypeptide, Rh-associated glycoprotein, Dematin, ABO blood groups, Aquaporin 3, Aubergers, Band 3, Basigin, C41, CD44, Cis AB, Colton antigen, Complement Component 4, CR1, DAF, Diego, Duffy, Hh/Bombay antigen, ii antigen, Indian blood group, Kell, Kidd, Lewis antigen, Lutheran antigen, MNS antigen system, Cost group, Er group, Dematin, Stomatin, Tropomyosin, Glucose transporter, Adducin, Rabphilin, C1 tetrahydrofolate synthase, Vel group, Lan antigen, At antigen, Jr antigen, AnWj antigen, Sd antigen, Batty, Bilkes, Box, Christiansen, HJK, HOFM, JFV, JONEs, Jensen, Katagiri, Livesay, Milne, Oldeide, Peters, Rasmussen, Reid, REIT, SARA, Rhesus blood D group, Aldolase, Tropomodulin, Arginase, Creatine kinase, B-Cam protein, Rap 1A, Bennett-Goodspeed, P antigen system, Rh blood groupXg antigen system, XK protein, Yt/Cartwright antigen system, CD58, Rh, Scianna, Radin, DARC (Duffy), CR1 Knops-McCoy, DAF Cromer, Gerbich (GYPC), CD47, Glycophorin A, Band 3 (AE3), GYPB Ss, C4A, C4B Chido, Rodgers C4 component of complement, HLA Bg HLA class I, RHAG Rh-associated Ammonium transport, Glycoprotein, Colton (Co) Water channel protein, ACHE Cartwright (Yt) Acetylcholinesterase, Glutathione transferase, Glycophorin C, Aquaporin, Erythroblast associated membrane protein, CD44, Synaptobrevin 2, Ribonuclease, Duodenal cytochrome B, ABO glycosyl transferases, CD59, CD44 Indian (In), AnWj Adhesion receptor, MER2, DOK Dombrock ADP-ribosyltransferase, SEMA7A JMH Putative adhesion receptor, UMOD Sda Tamm-Horsfall protein (uromodulin), Diego (Di), Wright (Wr) Anion channel protein (band 3, AE1), Kidd (Jk) Urea transporter, FUT3 Lewis (Le) alpha(1,3) fucosyltransferase, OK Oka Neurothelin, putative adhesion molecule, LW Adhesion receptor, FUT2 Secretor (Se) alpha(1,2) fucosyltransferase, FUT1 Hh alpha(1,2) fucosyltransferase, LU Lutheran (Lu) Adhesion receptor, P1 Glycosyltransferase, XK Kx Putative neurotransmitter transporter, XG Xg formerly called PBDX, MIC2, Hemoglobin, Ankyrin, Spectrin, KEL Kell (forms K, k, Kp, Js) Metalloproteinase, Torkildsen antigen, coenzyme Q10, Rab 35, Ral A binding protein, Zona pellucida binding protein, Lyn B protein, KIaa1741 protein, DC38, Calcium transporting ATPase, GPIX, GPIba, GPIbb, GPV, GPIb-IX-V, GPVI, GPIa/IIa, GPIIb/IIIa, GPV/IIa. 
     2. The S Domain 
     In some embodiments, the S domain is a protein or a polypeptide. In other embodiments, the S domain is a nucleic acid. In some embodiments, the S domain is a chemical. In certain embodiment the S domain is a small molecule. 
     In some embodiments, the S domain is a polypeptide selected from or derived from one or more of the following classes, including but not limited to, a flexible linker, an epitope tag, an enzyme, a protease, a nuclease, a receiver, an antibody-like molecule, a ligand of an antibody, a growth factor, a cytokine, a chemokine, a growth factor receptor, a cytokine receptor, a chemokine receptor, an enzymatic recognition sequence, a transpeptidase recognition sequence, a protease recognition sequence, a cleavable domain, an intein, a DNA binding protein, and RNA binding protein, a complement regulatory molecule, a complement cascade molecule, a clotting cascade molecule, a chelator, a complement regulatory domain, an SCR domain, a CCP domain, an immunoglobulin or immunogloblulin-like domain, an armadillo repeat, a leucine zipper, a dealth effector domain, a cadherein repeat, an EF hand, a phosphotyrosine binding domain, a pleckstrin homology domain, an SCR homology 2 domain, a zinc finger domain, a cyclic peptide, a cell-penetrating peptide. 
     In some embodiments, the S domain is a non-polypeptide molecule, for example a nucleic acid, a carbohydrate, or a small molecule. In some embodiments, the S domain is a nucleic acid selected from one or more of the following classes, including but not limited to, a DNA aptamer, an RNA aptamer, an siRNA, a shRNA, a single-strand RNA probe, a single strand DNA probe, an mRNA, a chemically modified oligonucleotide. In some embodiments, the S domain is a small molecule selected from one or more of the following classes, including but not limited to, a chelator, DOTA, a radionuclide, an isotope, an imaging agent, a fluorescent molecule, a chemiluminescent molecule, a gas. 
     3. The U Domain 
     In some embodiments, the U domain is a protein or a polypeptide. In other embodiments, the U domain is a nucleic acid. In some embodiments, the U domain is a chemical. In certain embodiment the U domain is a small molecule. 
     In some embodiments, the U domain is a polypeptide selected from or derived from one or more of the following classes, including but not limited to, a flexible linker, an epitope tag, an enzyme, a protease, a nuclease, a receiver, an antibody-like molecule, a ligand of an antibody, a growth factor, a cytokine, a chemokine, a growth factor receptor, a cytokine receptor, a chemokine receptor, an enzymatic recognition sequence, a transpeptidase recognition sequence, a protease recognition sequence, a cleavable domain, an intein, a DNA binding protein, and RNA binding protein, a complement regulatory molecule, a complement cascade molecule, a clotting cascade molecule, a chelator, a complement regulatory domain, an SCR domain, a CCP domain, an immunoglobulin or immunogloblulin-like domain, an armadillo repeat, a leucine zipper, a dealth effector domain, a cadherein repeat, an EF hand, a phosphotyrosine binding domain, a pleckstrin homology domain, an SCR homology 2 domain, a zinc finger domain, a cyclic peptide, a cell-penetrating peptide, a kinase domain, aphosphatase domain, a cytoskeletal protein, a protein that interacts with the cytoskeletal protein, a G-protein coupled receptor, a tyrosine kinase, an ITIM domain, an ITAM domain. 
     In some embodiments, the U domain is a non-polypeptide molecule, for example a nucleic acid, a carbohydrate, or a small molecule. In some embodiments, the U domain is a nucleic acid selected from one or more of the following classes, including but not limited to, a DNA aptamer, an RNA aptamer, an siRNA, a shRNA, a single-strand RNA probe, a single strand DNA probe, an mRNA, a chemically modified oligonucleotide. In some embodiments, the U domain is a small molecule selected from one or more of the following classes, including but not limited to, a chelator, DOTA, a radionuclide, an isotope, an imaging agent, a fluorescent molecule, a chemiluminescent molecule, a gas. 
     Examples of Receiver Polypeptides 
     Examples of receiver polypeptides include: the polypeptide receiver comprises glycophorin A with HA epitope tag at the N terminus; the polypeptide receiver comprises the leader sequence of glycophorin A, HA epitope tag, and the body sequence of glycophorin A; the polypeptide receiver comprises complement receptor 1 (CR1); the polypeptide receiver comprises the leader sequence of CR1, HA epitope tag, the body sequence of CR1; the polypeptide receiver comprises the leader sequence of CR1, HA epitope tag, six SCR domains of LHR-A and LHR-B of CR1, the membrane proximal two SCR domains of CR1, the transmembrane region of CR1, and the intracellular region of CR1; the polypeptide receiver comprises the leader sequence of CR1, HA epitope tag, nine SCR domains of LHR-A and LHR-B and LHR-C of CR1, the membrane proximal two SCR domains of CR1, the transmembrane region of CR1, and the intracellular region of CR1; the polypeptide receiver comprises the leader sequence of CR1, LHR-A of CR1, LHR-B of CR1, LHR-C of CR1, the membrane proximal two SCR domains of CR1, the transmembrane region of CR1, and the intracellular region of CR1; the polypeptide receiver comprises leader sequence of CR1, LHR-A of CR1, LHR-B of CR1, LHR-C of CR1, the membrane proximal two SCR domains of CR1, the transmembrane region and intracellular region of glycophorin A; the polypeptide receiver comprises the leader sequence of glycophorin A, an antibody scFv against hepatitis B surface antigen (scFv), a (Gly3Ser)2 (SEQ ID NO: 23) flexible linker, HA epitope tag, and the body of glycophorin A; the polypeptide receiver comprises Kell, a (Gly3Ser)2 (SEQ ID NO: 23) flexible linker, HA epitope tag, and scFv; the polypeptide receiver comprises Kell and HA epitope tag; the polypeptide receiver comprises a 71-amino acid N-terminal fragment of Kell and an HA epitope tag; the polypeptide receiver comprises a 71-amino acid N-terminal fragment of Kell, a (Gly3Ser)2 (SEQ ID NO: 23) flexible linker, and an HA epitope tag; the polypeptide receiver comprises a 79-amino acid N-terminal fragment of Kell and an HA epitope tag; the polypeptide receiver comprises a 79-amino acid N-terminal fragment of Kell, a (Gly3Ser)2 (SEQ ID NO: 23) flexible linker, and an HA epitope tag; the polypeptide receiver comprises a 71-amino acid N-terminal fragment of Kell, a (Gly3Ser)2 (SEQ ID NO: 23) flexible linker, scFv, and an HA epitope tag; the polypeptide receiver comprises a 79-amino acid N-terminal fragment of Kell, a (Gly3Ser)2 (SEQ ID NO: 23) flexible linker, scFv, and an HA epitope tag; the polypeptide receiver comprises the leader sequence of CD55, scFv, an HA epitope tag, and the terminal 37 amino acids of CD55; the polypeptide receiver comprises the leader sequence of CD55, an HA epitope tag, and the body of CD55. In one embodiment, the polypeptide receiver comprises the leader sequence of CD59, scFv, an HA epitope tag, and the body of CD59; the polypeptide receiver comprises the leader sequence of CD59, and HA epitope tag, and the body of CD59; the polypeptide receiver comprises adenosine deaminase and an HA epitope tag; the polypeptide receiver comprises phenylalanine hydroxylase and an HA epitope tag; the polypeptide receiver comprises adenosine deaminase, a (Gly3Ser)2 (SEQ ID NO: 23) flexible linker, phenylalanine hydroxylase, and an HA epitope tag; the polypeptide receiver comprises glycophorin A, adenosine deaminase at the cytoplasmic C terminus, and an HA epitope tag; the polypeptide receiver comprises glycophorin A, phenylalanine hydroxylase at the cytoplasmic C terminus, and an HA epitope tag. 
     In certain embodiments, the receiver is capable or interacting with a macrophage. The receiver polypeptide may comprise one or more of: the complement receptor (Rieu et al., J. Cell Biol. 127:2081-2091 (1994)), the scavenger receptor (Brasseur et al., Photochem. Photobiol. 69:345-352 (1999)), the transferrin receptor (Dreier et al., Bioconjug. Chem. 9:482-489 (1998); Hamblin et al., J. Photochem. Photobiol. 26:4556 (1994)); the Fc receptor (Rojanasakul et al., Pharm. Res. 11:1731-1733 (1994)); and the mannose receptor (Frankel et al., Carbohydr. Res. 300:251-258 (1997); Chakrabarty et al., J. Protozool. 37:358-364 (1990)). 
     Other receivers capable or interacting with a macrophages include: low density lipoproteins (Mankertz et al., Biochem. Biophys. Res. Commun. 240:112-115 (1997); von Baeyer et al., Int. J. Clin. Pharmacol. Ther. Toxicol. 31:382-386 (1993)), very low density lipoproteins (Tabas et al., J. Cell Biol. 115:1547-1560 (1991)), mannose residues and other carbohydrate moieties (Pittet et al., Nucl. Med. Biol. 22:355-365 (1995)), poly-cationic molecules, such as poly-L-lysine (Hamblin et al., J. Photochem. Photobiol. 26:45-56 (1994)), liposomes (Bakker-Woudenberg et al., J. Drug Target. 2:363-371 (1994); Betageri et al., J. Pharm. Pharmacol. 45:48-53 (1993)) and 2-macroglobulin (Chu et al., J. Immunol. 152:1538-1545 (1994)). 
     In some embodiments, the synthetic membrane-receiver complex does not comprise a receiver comprising an extracellular domain of an HIV coreceptor. In some embodiments, the synthetic membrane-receiver complex does not comprise a receiver capable of binding to a virus. In some embodiments, the synthetic membrane-receiver complex does not comprise a receiver comprising CD4. In some embodiments, the synthetic membrane-receiver complex does not comprise a receiver comprising an HIV coreceptor. In some embodiments, the synthetic membrane-receiver complex does not comprise a receiver comprising CXCR4, CCR5, CCR1, CCR2, CCR3, CCR4, CCR8, CXCR1, CXCR2, CXCR3, CXCR6, GPR15, APJ, CMKLR1, or CX3CR1 or a combination thereof. 
     In some embodiments, the synthetic membrane-receiver complex does not contain an exogenous nucleic acid encoding an adenosine deaminase receiver. In some embodiments, the synthetic membrane-receiver complex does not comprise a receiver comprising adenosine deaminase (ADA). 
     In some embodiments, the synthetic membrane-receiver complex does not comprise an exogenous nucleic acid encoding an oncogene. In some embodiments, the synthetic membrane-receiver complex does not comprise a receiver comprising oncogene. 
     In some embodiments, the synthetic membrane-receiver complex does not contain an exogenous nucleic acid encoding cdx1, cdx2, or cdx4. In some embodiments, the synthetic membrane-receiver complex does not comprise a receiver comprising cdxl, cdx2, or cdx4, or a combination thereof. 
     In some embodiments, the synthetic membrane-receiver complex does not comprise a receiver comprising a chimeric polypeptide comprising a ligand binding domain. In some embodiments, the synthetic membrane-receiver complex does not comprise a receiver comprising an S domain that is capable of binding a ligand. In some embodiments, the synthetic membrane-receiver complex does not comprise a receiver comprising CD3ζ, CD3η, an IL-2 receptor, an IL-3 receptor, an IL-4 receptor, an IL-7 receptor, an IL-11 receptor, an IL-13 receptor, a GM-CSF receptor, a LIF receptor, a CNTF receptor, an oncostatin M receptor, a TGF-β receptor, an EGF receptor, ATR2/neu, a HER2/neu, a HER3/c-erbB-3, Xmrk, an insulin receptor, an IGF-1 receptor, IRR, PDGF receptor, a CSF-1 receptor, c-kit, STK-1/flk-2, an FGF receptor, flg, bek, an NGF receptor, Ror1 and Ror2. 
     In some embodiments, the synthetic membrane-receiver complex does not comprise a receiver comprising E6 or E7 genes of human papillomavirus. 
     In some embodiments, the synthetic membrane-receiver complex does not comprise a receiver comprising a tumor antigen. 
     In some embodiments, the synthetic membrane-receiver complex does not comprise a receiver comprising glucocerebrosidase. 
     In some embodiments, the synthetic membrane-receiver complex does not comprise a receiver comprising asparaginase. 
     In some embodiments, the synthetic membrane-receiver complex does not comprise a receiver comprising arginine deiminase. 
     Provided herein are compositions containing functional erythroid cells comprising a receiver having functional activities that are either i) not present in native erythroid cells of the same lineage, or ii) present in native erythroid cells of the same lineage in reduced levels or reduced activity levels as compared to the erythroid cells comprising the receiver. Such functional activities include complement inhibition, immune complex clearance, artificial antigen presentation, modulation of the coagulation cascade, oxygen transfer, drug delivery, cytotoxin adsorption, avoidance of phagocytosis, and extension of circulation time. 
     In some embodiments, functional erythroid cells have higher levels of a complement receptor polypeptide, such as CR1, than native erythroid cells of the same lineage by virtue of comprising a CR-1 receiver. In an alternative embodiment, the functional erythroid cells comprising a receiver have higher levels of a complement receptor agonist polypeptide or complement associated polypeptide than native erythroid cells of the same lineage, including but not limited to, the polypeptides listed in table 7 and table 10. The complement receptor receiver polypeptide comprises a human Complement Receptor-1 (CR1) polypeptide, variant, or functional fragment thereof. The CR1 receiver polypeptide may be derived from one or more than one of the native alleles of CR1, e.g., the A allele (also termed the F allele or CR1*1 allele), the B allele (also termed the S allele or CR1*2 allele), the C allele (also termed the F′ allele or CR1*3 allele), or the D allele (also termed the CR1*4 allele). The sequences and database accession numbers for these native forms are provided in table 4. In some embodiments, the CR1 receiver polypeptide contains a domain of a CR1 polypeptide. For example, the CR1 polypeptide may comprise one or more short consensus repeat (SCR) domains, also termed complement control protein (CCP) modules or Sushi domains, e.g., Genbank accession number AAV65577.1. In one embodiment, the CR1 receiver polypeptide comprises one or more Short Consensus Repeats (SCRs), e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44 or greater than 44 SCRs. In another embodiment, the CR1 receiver polypeptide comprises one or more long homologous repeat (LHR) units of CR1, e.g., LHR-A, LHR-B, LHR-C, or LHR-D, e.g., 1, 2, 3, 4, 5, 6 or greater than 6 LHR domains. In another embodiment, the CR1 receiver polypeptide may comprise one or more than one extracellular domains of CR1 fused to another cell membrane protein, e.g., glycophorin A, glycophorin B, glycophorin C, glycophorin D, kell, band 3, aquaporin 1, glut 1, kidd antigen protein, rhesus antigen, including, but not limited to the cell surface moieties listed in table 1 and table 7. 
     In some embodiments, a functional erythroid cell contains an exogenous nucleic acid encoding a complement receptor receiver polypeptide, or alternatively or in combination, a complement receptor agonist receiver polypeptide or complement associated receiver polypeptide including but not limited to, the polypeptides, and agonists to the polypeptides, listed in table 10. In some embodiments, the functional erythroid cells further contain an exogenous decay-accelerating factor (CD59, GenBank: CAG46523.1) polypeptide, or an exogenous membrane cofactor (CD46, GenBank: BAA12224.1) polypeptide, or a variant or functional fragment thereof, or a combination thereof. 
     CR1 activities include binding to C3b-containing immune complexes and shuttling of these immune complexes from circulation to liver and spleen macrophages of the reticuloendothelial system. Upon encounter with cells of the reticuloendothelial system, the immune complex is endocytosed by the phyagocytic cell but the red blood cell is spared to continue its circulation. The removal of the immune complex sometimes results in proteolytic cleavage of CR1 from the surface of the red blood cell. To measure binding activity, one can perform an in vitro binding assay between erythroid cells and immune complexes. To measure sparing of the erythroid cell, one can perform an in vitro phagocytosis assay with phagocytic cells and immune complex-loaded erythroid cells. To measure in vivo clearance of circulating immune complexes to the liver, one can perform a clearance and biodistribution assay using radiolabeled immune complexes. 
     Provided are compositions containing functional erythroid cells containing a receiver comprising a native polypeptide at a level greater than that of a hematopoietic cell of the same lineage not comprising the receiver polypeptide. For example, populations of functional erythroid cells contain receivers, such as complement receptor 1 levels at least about 1.1, e.g., 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, or more than 10000 times greater than corresponding hematopoietic cells of the same lineage that lack the CR1 receiver polypeptide. CR1 levels on reticulocytes and erythrocytes are typically between 50-2000 molecules per cell (Lach-Trifilieff, J Immunol 1999, 162:7549). Provided are compositions that contain populations of functional erythroid cells with CR1 levels of at least about 2500, 5000, 6000, 7000, 8000, 9000, 10000, 15000, 20000, 25000, 30000, 40000, 50000, 100000, 200000, 300000, 400000, 500000, 600000, 700000, 800000, 900000, 1000000, or more than 1000000 molecules per cell. CR1 levels in wild-type and synthetic membrane-receiver polypeptide complexes can be measured and quantified by, for example, flow cytometry with antibodies specific for CR1. 
     In some embodiments, the receiver interacts with a circulating pathogen, such as a virus or a bacterium. In some embodiments, the functional erythroid cell expresses an exogenous gene encoding an antibody, scFv, or nanobody specific for the circulating pathogen. The antibody, scFv, or nanobody may be expressed as a fusion protein. In other embodiments, the antibody, scFv, or nanobody receiver or another receiver with affinity to circulating pathogens is loaded into or onto the erythroid cell. The antibody, scFv, or nanobody receiver or the other receiver with affinity to circulating pathogens may be localized intracellularly or extracellularly. In some embodiments, the receiver is specific for a viral or bacterial antigen, such as a surface, envelope or capsid antigen. 
     In some embodiments, the receiver interacts with a toxin, preferably a foreign toxin, such as derived from a pathogen or otherwise from the environment. In some embodiments, the functional erythroid cell expresses a exogenous gene encoding a receiver comprising an amino acid sequence derived from lipopolysaccharide-binding protein (LBP), bactericidal/permeability-increasing protein (BPI), amyloid P component, or a cationic protein. Toxin-binding receivers may be expressed as a fusion protein. In other embodiments, toxin-binding receivers may be loaded into or onto the erythroid cell. Toxin-binding receivers may be localized intracellularly or extracellularly. In some embodiments, the toxin binding receiver is specific for a bacterial toxin such as botulinum or anthrax. 
     Further, synthetic membrane-receiver complexes may express a receiver capable of enhancing its ability to sequester a target. Potential sequestration enhancement receivers include the polypeptide transporters including, but not limited to, those in table 1. 
     In one embodiment, the receiver comprises a polypeptide that comprises an amino acid sequence derived from Duffy Antigen Receptor for Chemokines (DARC). In one embodiment, the functional erythroid cell expresses a exogenous gene encoding an amino acid sequence derived from Duffy Antigen Receptor for Chemokines (DARC). The DARC receiver may be expressed as a full-length protein or a fragment thereof. DARC may be expressed as a fusion protein. In other embodiments, DARC protein is loaded into or onto the erythroid cell. In some embodiments, the loaded DARC is additionally functionalized or otherwise modified. The DARC receiver molecule may be localized intracellularly or extracellularly. 
     DARC was identified as a potent multi-ligand chemokine receptor. DARC belongs to the family of rhodopsin-like seven-helix transmembrane proteins. Besides erythrocytes DARC is expressed in post capillary venular endothelial cells, which are the primary site of leukocyte transmigration in most tissues. DARC provides a highly specific binding site for both CC and CXC chemokines. DARC is thought to possess a higher affinity for ELR motif CXC chemokines. CXC chemokines are neutrophil chemoattractants and may potentially be pro-angiogenic. 
     Interaction between DARC and CXCL8 has demonstrated a dissociation constant (Kd) of 5 nmol/L and receptor binding sites estimated at 1000-9000 per erythrocyte (Hadley, Blood, 1997) Unlike other seven-transmembrane chemokine receptors, DARC lacks the highly conserved G protein coupling motif located in the second cytoplasmic loop (Meny, Immunohematology, 2010). DARC is not G-protein coupled and has no known alternative signaling mechanism. The biological role of DARC is not fully understood. DARC is thought to be a) multi-specific; b) unable to initiate intracellular signals, and c) chemokines bound to erythrocyte surface are believed to be inaccessible to their normal target inflammatory cells (Neote, J Biol Chem, 1993). Erythrocytes may play a role in the regulation of inflammatory processes through the presence of DARC 
     Inflammatory signaling molecules, such as cytokines, can trigger local and systemic tissue damage when present in high concentrations. Bursts of cytokines are implicated in the pathogenesis of bacterial sepsis, rheumatoid arthritis, and several other inflammatory diseases. Functional erythroid cells that exogenously express natural cytokine receptors or synthetic antibody-like receptor mimics can sequester the inflammatory cytokines. An exemplary chemokine receptor is DARC. Provided herein are functional erythroid cells comprising a receiver that is a cytokine receptor or chemokine receptor, including, but not limited to DARC. For example, functional erythroid cells expressing DARC receiver (thereby increasing the amount present on native erythrocytes) may be used to modulate chemokine levels in circulation and/or within the body&#39;s peripheral tissues. The functional erythroid cells comprising a DARC receiver can either be marked for destruction or can slowly release the inflammatory mediators back into circulation, but at a low and diffuse concentration. The functional erythroid cell comprising a receiver that comprises a chemokine or cytokine receptor may act as a reservoir for signal transduction peptides. 
     In one embodiment, the receiver comprises a polypeptide that comprises an amino acid sequence derived from an antibody. In one embodiment, the functional erythroid cell expresses a exogenous gene encoding an amino acid sequence derived from an antibody. The antibody receiver may be expressed as a full-length protein or a fragment thereof. The antibody may be expressed as a fusion protein. In other embodiments, the antibody protein is loaded into or onto the erythroid cell. In some embodiments, the loaded antibody is additionally functionalized or otherwise modified. The antibody receiver may be localized intracellularly or extracellularly. In one embodiment, the receiver comprises an antibody amino acid sequence that is specific for a desired target. In some embodiments, the antibody is a scFv. In other embodiments, the antibody is a nanobody. 
     In certain embodiments, the functional erythroid cells comprise a receiver that comprises an antibody or fragment thereof that is specific for a target and is located on the cell surface. For example, a variable fragment (Fv) of an antibody specific for botulinum toxin binding is expressed on the surface of the erythroid cell. Botulinum toxin binding antibodies are known in the art (Amersdorfer, Inf and Immunity, 1997), as is the expression of the Fv portion of an antibody (Hoedemaeker, Journ of Bio Chemistry, 1997). Upon binding, the toxin is retained by the erythroid cell through the Fv region, sequestered and shuttled via the circulatory system to the liver for clearance from the body. 
     In one embodiment, the receiver comprises a polypeptide that comprises an amino acid sequence derived from a scFv antibody. In one embodiment, the functional erythroid cell expresses a exogenous gene encoding an amino acid sequence derived from a scFv antibody. The scFv antibody receiver may be expressed as a full-length protein or a fragment thereof. The scFv antibody may be expressed as a fusion protein. In other embodiments, the scFv protein is loaded into or onto the erythroid cell. Suitable scFv receiver polypeptides that may be expressed by functional erythroid cells include, but are not limited to, those listed in table 7. 
     scFv antibodies have been constructed mainly from hybridoma, spleen cells from immunized mice, and B lymphocytes from human. The variable region of an antibody is formed by the noncovalent heterodimer of the variable domains of the V(H) and V(L) domains, which can then be used in the construction of a recombinant scFv antibody. 
     The production of scFvs is known in the art and require mRNA to first be isolated from hybridoma (or also from the spleen, lymph cells, and bone morrow) followed by reverse transcription into cDNA to serve as a template for antibody gene amplification (PCR). With this method, large libraries with a diverse set of antibody-derived scFvs (a set comparable to that of the original antibodies from which the scFvs are modeled) can be created. 
     The scFv receiver may be made specific to any target molecule including, but not limited to, those in table 5. 
     In one example, a scFv receiver specific for anthrax toxin may be expressed on a functional erythroid cell. Upon administration to a subject in need thereof an effective dose of a population of erythroid cell comprising a receiver molecule specific for anthrax toxin can be used to capture and sequester the anthrax toxin. The erythroid cell migrates to the liver where clearance occurs. 
     In certain embodiments, erythrocytes comprise a receiver comprising a camelid-derived nanobody expressed on the surface of the cell. Nanobodies are usually 12-15 kDa. They are considerably smaller than antibodies and scFv. Nanobodies may thus be easier to transfect, and the nanobody receiver will be more easily expressed, translated and or transported to the cell surface in an erythroid cell. In certain embodiments, nanobody receivers are employed to minimize immunogenic effects caused by a specific receiver. Nanobodies because of their small size will offer reduced immunogenic potential. In certain embodiments, receiver nanobodies are employed because they limit changes in the mechanical and morphological behavior of the plasma membrane of the functional erythroid cell. This may allow the functional erythroid cell to exhibit normal circulatory red blood cell behavior. In certain embodiments, receiver nanobodies are employed because they have an increased ability to recognize hidden or uncommon epitopes compared to standard antibodies. For example, they can bind to small enzymatic cavities of a target and modulate the molecular behavior of the target. 
     In certain embodiments, functional erythroid cells comprise receiver nanobodies with specificity to target epitopes of molecules in the human complement system. Such functional erythroid cells may be administered to a subject in need thereof to selectively deplete one or more over-active factors of the complement system. For example, C5 may be targeted by erythroid cells comprising receiver nanobodies with specificity to target epitopes of C5 and cleared from the system by the erythroid cells upon administration of the cells into a subject. This approach is suitable to provide a therapeutic effect, e.g., for a complement disorder, such as paroxysmal nocturnal hemoglobinuria. In certain embodiments, functional erythroid cells comprise receiver nanobodies with specificity to target epitopes of molecules including, but not limited to, those listed in table 5. 
     In some embodiments, the receiver comprises a polypeptide that comprises an amino acid sequence derived from one of proteases, nucleases, amylase, lyase (sucrase) or hydrolase (DNase, lipase). In one embodiment, the functional erythroid cell expresses a exogenous gene encoding an amino acid sequence derived from one of proteases, nucleases, amylase, lyase (sucrase) or hydrolase (DNase, lipase). Receiver proteases, nucleases, amylases, lyases and hydrolases may be expressed as a full-length protein or a fragment thereof. Receiver proteases, nucleases, amylases, lyases and hydrolases may be expressed as a fusion protein. In other embodiments, receiver proteases, nucleases, amylases, lyases or hydrolases are loaded into or onto the erythroid cell. In some embodiments, the loaded receiver proteases, nucleases, amylases, lyases or hydrolases are additionally functionalized or otherwise modified. The receiver protease, nuclease, amylase, lyase or hydrolase receiver molecule may be localized intracellularly or extracellularly. 
     In certain embodiments, functional erythroid cells comprise a receiver comprising a protease, a nuclease, an amylase, a lyase or a hydrolase. The functional erythroid cell comprising a protease, a nuclease, an amylase, a lyase or a hydrolase receiver is capable of degrading a target on the erythroid cell independent of circulatory clearance, e.g., by macrophages in the liver. In certain embodiments, functional erythroid cells comprising a receiver comprising a protease, a nuclease, an amylase, a lyase or a hydrolase may be administered to a subject in need thereof to treat a cancer by selectively degrading metabolites that are essential for cancer cell growth. For example, asparaginase is used to decrease local asparagine levels to treat acute lymphoblastic leukemia and acute myeloid leukemia. Suitable receivers may, e.g., comprise one or both of the two major classes of enzymes capable of degrading target molecules, lyases and hydrolases. In certain embodiments, functional erythroid cells are provided comprising a receiver comprising a molecule including but not limited to those listed in table 7. 
     In certain embodiments, erythrocytes comprise a receiver comprising a lyase. In one embodiment, the lyase is valine decarboxylase. Valine decarboxylase receiver may be expressed within the intracellular space of the erythroid cell. Functional erythroid cells comprising a valine decarboxylase receiver may be administered to a subject in need thereof to modulate valine levels within the blood. Erythroid cells comprising a valine decarboxylase receiver are suitable to treat valinemia, an inherited disorder that increases levels of the amino acid valine in the blood. Affected individuals typically develop vomiting, failure to thrive, intellectual disability, and fatigue. Valinemia is caused by a deficiency of the valine transaminase enzyme and has an autosomal recessive pattern of inheritance. 
     In certain embodiments, erythrocytes comprise a receiver comprising a hydrolase. In one embodiment, the hydrolase is deoxyribonuclease I (DNase I). DNase I receiver may be expressed on the surface of the erythroid cell. Functional erythroid cells comprising a DNase I receiver may be administered to a subject in need thereof to preferentially cleave circulating DNA at phosphodiester linkages adjacent to a pyrimidine nucleotide, yielding 5′-phosphate-terminated polynucleotides with a free hydroxyl group on position 3′. On average tetra-nucleotides are produced. Erythroid cells comprising a DNase I receiver are suitable to treat conditions exacerbated by high levels of immunogenic DNA in circulation, such as systemic lupus erythematosus (SLE). 
     In certain embodiments the receiver is capable of responding to an external stimulus, e.g., upon binding to a ligand or contacting the stimulus, wherein responding entails, for example, moving, re-folding, changing conformation, forming a dimer, forming a homodimer, forming a heterodimer, forming a multimer, transducing a signal, emitting energy in a detectable form (e.g., fluorescence), functionally interacting with another receiver, or functionally interacting with a non-receiver polypeptide. 
     In some embodiments, the synthetic membrane-receiver complex does not comprise a fusion molecule capable of promoting fusion of the synthetic membrane-receiver complex to a target cell that is i) different from and/or ii) acts independent of the receiver, wherein the receiver is capable of interacting with a target. In some embodiments, the synthetic membrane-receiver complex does not comprise a receiver comprising Syncytin-1. 
     In some embodiments, the synthetic membrane-receiver complex does not comprise a photosensitive synthetic compound, such as, e.g. a compound that can be activated by photons or quenchable compounds. In some embodiments, the synthetic membrane-receiver complex does not comprise an activatable molecular detection agent capable of producing a detectable response. In some embodiments, the synthetic membrane-receiver complex does not comprise a diagnostic compound. In some embodiments, the synthetic membrane-receiver complex does not comprise a virus or bacterium. 
     Provided herein are synthetic membrane receiver complexes comprising a receiver polypeptide (e.g. polypeptides identified in Tables 14 and 15) that comprise U domains and optionally A domains, or that comprise S domains and optionally A domains. In some embodiments, the receiver polypeptide comprises U domains and optionally A domains and no more than about 1%, 3%, 5%, 7%, 10%, 15%, 20%, or no more than about 25% of the amino acids contribute to an S domain. In some embodiments, the receiver polypeptide comprises S domains and optionally A domains and no more than about 1%, 3%, 5%, 7%, 10%, 15%, 20%, or no more than about 25% of the amino acids contribute to a U domain. In some embodiments, populations of enucleated erythroid cells are provided comprising cytosolic exogenous polypeptide receivers. In some embodiments, populations of enucleated erythroid cells are provided comprising polypeptide receivers on the surface of the cells. In some embodiments, the receivers comprise enzymatic activity. In some embodiments, the polypeptide receivers are present in the erythroid cells at a high copy number, e.g. at least about 1,000 copies, 5,000 copies, 10,000 copies, 50,000 copies, 100,000 copies, 500,000 copies, 1,000,000 copies, or at least about 5,000,000 copies. In some embodiments, the high copy number, e.g. for receiver polypeptides that reside on the surface, provides a high-density or high-avidity surface for interactions with one or more target molecules, such as substrates. For example, an erythroid cell comprising a high-density surface comprising a receiver polypeptide may specifically interact with a particular target in the circulatory system of a subject after having been administered to the subject. The receiver polypeptide may catalyze a reaction that modifies (e.g. cleaves or degrades) the substrate. In some embodiments, the high density surface of receivers provided by the erythroid cell is necessary to catalyze the reaction efficiently in circulation. In some embodiments, a high avidity surface is necessary for efficient interaction of the target to the receiver to facilitate a catalytic reaction. For example, some enzymatic interactions or protein-protein interactions are relatively weak, e.g. they have a high dissociation constant (k d ) and the substrate is likely to escape. Some interactions are in the milimolar (mM) range, some are in the micromolar (μM) range, others in the picomolar range. In some embodiments, the high-density or high-avidity surface provided on the surface of the eryhtroid cells is particularly suitable for weakly interacting targets, e.g. those in the millimolar, micromolar or high picomolar range. In other embodiments, the high-density or high-avidity surface provided on the surface of the eryhtroid cells is particularly suitable for interactions with highly diluted targets (e.g. targets with a low presence in the circulatory system of the subject). In that case, in the rare event of a contact, it is advantageous to increase to probability of binding of the target to the receivers on the surface of the erythroid cell by providing a high-density or high-avidity surface. 
     In some embodiments, erythroid cells are provided expressing polypeptide receivers having an enzymatic activity that are not naturally associated with a plasma membrane. In some embodiments, erythroid cells are provided expressing polypeptide receivers having an enzymatic activity that are not naturally found in the cytosol of circulating cells. In some embodiments, the polypeptide receiver comprises a first polypeptide domain that is surface exposed and has an enzymatic activity, and a second polypeptide domain that is associated with the membrane of the erythroid cell. In some embodiments, the polypeptide receiver comprises a first polypeptide domain that is exposed to the cytosol and has an enzymatic activity, and a second polypeptide domain that is associated with the membrane of the erythroid cell. 
     Provided herein are synthetic membrane receiver complexes comprising a receiver polypeptide that comprises ADAMTS13 (Gene ID 11093, UniProt Q76LX8) or a functional fragment thereof. The protein ADAMTS13 is endogenous to humans and is secreted into the bloodstream. ADAMTS13 is also known as von Willebrand Factor (vWF)-cleaving protease. ADAMTS13 is a protease whose function is to cleave ultra-large aggregates of vWF (UL-vWF) into smaller vWF proteins. In the disease Thrombotic Thrombocytopenic Purpura (TTP), patients are deficient in ADAMTS13 which results in accumulation of UL-vWF and free-floating vWF-platelet microthrombi that cause diffuse clots throughout the body. Symptoms of TTP include purplish bruises on the skin or mucous membranes (such as in the mouth), pinpoint-sized red or purple dots on the skin, paleness or jaundice (a yellowish color of the skin or whites of the eyes), fatigue (feeling very tired and weak), fever, a fast heart rate or shortness of breath, and occasionally neurological symptoms. TTP can be caused by inhibitory antibodies (acquired TTP) or by a genetic deficiency in ADAMTS13 (hereditary TTP; Upshaw-Schulman Syndrome). 
     Current treatment options for TTP include plasma exchange or, in an emergency, fresh frozen plasma infusion. Recombinant ADAMTS13 is in preclinical development as a therapeutic (Plaumauer et al., J Thrombosis Haemostasis 2011, 9:936-944). 
     Provided herein are synthetic membrane receiver complexes comprising a receiver polypeptide that comprises ADAMTS13 that is expressed on the surface of the complex. In some embodiments, the synthetic membrane receiver complexes comprise a high-density surface of receivers comprising ADAMTS13, such as surfaces comprising at least about 1,000 copies, 5,000 copies, 10,000 copies, 50,000 copies, 100,000 copies, 500,000 copies, 1,000,000 copies, or at least about 5,000,000 copies of ADAMTS13 polypeptide receivers. In some embodiments, the receiver comprising ADAMTS13 comprises an S domain (comprising ADAMTS13 or a functional fragment thereof) and an A domain, which can be selected as desired, and may include any suitable anchor, such as, e.g. a membrane protein or domain thereof. In some embodiments, erythroid cells are generated that express an ADAMTS13 polypeptide receiver from an exogenous nucleic acid sequence that encodes ADAMTS13 fused to a nucleic acid sequence encoding an erythroid membrane protein or membrane-interacting fragment thereof, e.g. glycophorin A, glycophorin B, Kell, Band3, CD55, CD59, CD46, or CR1. 
     By attaching ADAMTS13, an enzyme not naturally associated with a plasma membrane, to the surface of a synthetic membrane receiver complex, e.g. an erythroid cell the circulating half-life of the enzyme may be prolonged, retention in the vasculature may be improved, and/or the activity of the enzyme is increased through avidity effects. 
     In some embodiments, erythroid cells comprising the ADAMTS13 polypeptide receiver or pharmaceutical compositions thereof are administered to a subject in need thereof, e.g. a subject having or suspected of having or developing TTP in an effective amount to decrease the number or concentration of UL-vWF in circulation in the subject. By attaching ADAMTS13, an enzyme not naturally associated with a plasma membrane, to the surface of the erythroid cell the circulating half-life of the enzyme may be prolonged, retention in the vasculature may be improved, and/or the activity of the enzyme is increased through avidity effects. 
     In one embodiment, a subject having or suspected of having or developing acquired or inherited TTP is administered a composition of ADAMTS-expressing erythroid cells in an amount effective to treat, prevent, or reduce the symptoms of TTP. In some embodiments, the effect of the treatment can be assessed by detecting an improved clinical presentation and/or by measuring a reduction in microthrombi formation using assays known in the art. 
     Provided herein are synthetic membrane receiver complexes comprising a receiver polypeptide that comprises Complement Factor I (CFI) (Gene ID 3426, Uniprot P05156) or a functional fragment thereof. CFI is a secreted enzyme that plays an important role in the regulation of the complement cascade. In its native function, CFI cleaves cell-bound or fluid phase complement components C3b and C4b. The absence of CFI can cause a range of medical conditions, including susceptibility to infection caused by over-activation and depletion of complement component C3, and hemolytic uremic syndrome or similar disease of overactive and improperly regulated complement activity. 
     Provided herein are synthetic membrane receiver complexes comprising a receiver polypeptide that comprises CFI that is expressed on the surface of the complex. In some embodiments, the synthetic membrane receiver complexes comprise a high-density surface of receivers comprising CFI, such as surfaces comprising at least about 1,000 copies, 5,000 copies, 10,000 copies, 50,000 copies, 100,000 copies, 500,000 copies, 1,000,000 copies, or at least about 5,000,000 copies of CFI polypeptide receivers. In some embodiments, the receiver comprising CR comprises an S domain (comprising CFI or a functional fragment thereof) and an A domain, which can be selected as desired, and may include any suitable anchor, such as, e.g. a membrane protein or domain thereof. In some embodiments, erythroid cells are generated that express an CFI polypeptide receiver from an exogenous nucleic acid sequence that encodes CFI fused to a nucleic acid sequence encoding an erythroid membrane protein or membrane-interacting fragment thereof, e.g. glycophorin A, glycophorin B, Kell, Band3, CD55, CD59, CD46, or CR1. 
     By attaching CFI, an enzyme not naturally associated with a plasma membrane, to the surface of a synthetic membrane receiver complex, e.g. an erythroid cell the circulating half-life of the enzyme may be prolonged, retention in the vasculature may be improved, and/or the activity of the enzyme is increased through avidity effects. 
     In one embodiment, a subject having or suspected of having or developing a complement over-activation disorder, e.g. such as hemolytic uremic syndrome is administered a composition of CH-expressing erythroid cells in an amount effective to treat, prevent, or reduce the symptoms of the disorder. 
     In another embodiment, a subject having or suspected of having or developing a C3-depletion-associated infection is administered a composition of CFI-expressing erythroid cells in an amount effective to treat, prevent, or reduce the symptoms of the infection. 
     In some embodiments, the effect of the treatment can be assessed by detecting an improved clinical presentation and/or by measuring a reduction in complement-mediated hemolysis using assays known in the art. 
     Provided herein are synthetic membrane receiver complexes comprising a receiver polypeptide that comprises a component of the coagulation cascade. For example, the receiver polypeptide may comprise Factor V (F5, Gene ID 2153, Uniprot P12259), Factor VII (F7, Gene ID 2155, Uniprot P08709), Factor VIII (F8, Gene ID 2157, Uniprot P00451), Factor IX (F9, Gene ID 2158, Uniprot P00740), Factor X (F10, Gene ID 2159, Uniprot P00742), Factor II (F2, thrombin, or prothrombin, Gene ID 2147, Uniprot P00734), Factor III (F3, tissue factor, Gene ID 2152, Uniprot P13726), Factor XI (F11, Gene ID 2160, Uniprot P03951), Factor XII (F12, Gene ID 2161, Uniprot P00748), Factor XIII-a (F13a, Gene ID 2162, Uniprot P00488), Factor XIII-b (F13b, Gene ID 2165, Uniprot P05160), those additional factors listed in Tables 14 and 15, or any functional fragment or combination of functional fragments thereof. Component of the coagulation cascade are typically secreted into the bloodstream and play an important role in stimulating and regulating the coagulation cascade. The precise interactions between the components have been well characterized and are known in the medical literature, see e.g. Schmaier, Alvin H.; Lazarus, Hillard M. (2011). Concise guide to hematology. Wiley-Blackwell. 
     Deficiencies in these factors can lead to diseases and disorders of aberrant coagulation, for example hemophilia A, hemophilia B, factor X deficiency, generalized bleeding disorders, overactive clotting disorders, and those conditions listed in Table 15. For these conditions, replacement of the deficient or defective factor is standard of care. The factors are provided either as recombinant proteins, as a purified preparation from a human donor, or as unpurified plasma from a human donor (see e.g. Oldenburg, Blood 2015, 125(13):2038-2044). 
     Provided herein are synthetic membrane receiver complexes comprising a receiver polypeptide that comprises a coagulation cascade factor that is expressed on the surface of the complex. In some embodiments, the synthetic membrane receiver complexes comprise a high-density surface of receivers comprising the coagulation cascade factor, such as surfaces comprising at least about 1,000 copies, 5,000 copies, 10,000 copies, 50,000 copies, 100,000 copies, 500,000 copies, 1,000,000 copies, or at least about 5,000,000 copies of the coagulation cascade factor polypeptide receivers. In some embodiments, the receiver comprising the coagulation cascade factor comprises an S domain (comprising the coagulation cascade factor or a functional fragment thereof) and an A domain, which can be selected as desired, and may include any suitable anchor, such as, e.g. a membrane protein or domain thereof. In some embodiments, erythroid cells are generated that express a coagulation cascade factor polypeptide receiver from an exogenous nucleic acid sequence that encodes the coagulation cascade factor fused to a nucleic acid sequence encoding an erythroid membrane protein or membrane-interacting fragment thereof, e.g., glycophorin A, glycophorin B, Kell, Band3, CD55, CD59, CD46, or CR1. 
     By attaching the coagulation cascade factor, an enzyme not naturally associated with a plasma membrane, to the to the surface of a synthetic membrane receiver complex, e.g. an erythroid cell the circulating half-life of the enzyme may be prolonged, retention in the vasculature may be improved, and/or the activity of the enzyme is increased through avidity effects. 
     In one embodiment, a subject having or suspected of having or developing a coagulation disorder, e.g. hemophilia A or B is administered a composition of coagulation factor-expressing erythroid cells in an amount effective to treat, prevent, or reduce the symptoms of the disorder. In some embodiments, the effect of the treatment can be assessed by detecting an improved clinical presentation and/or by measuring an increase in the rate of clotting and/or detecting a reduction in the number of uncontrolled bleeding events using assays known in the art. 
     Provided herein are synthetic membrane receiver complexes comprising a receiver polypeptide that comprises an enzyme capable of degrading phenylalanine. For example, the receiver polypeptide may comprise phenylalanine hydroxylase (PAH, Gene ID 5053, Uniprot P00439), phenylalanine hydroxylase from  Chromobacterium violaceum  (cPAH, Gene ID 2827919, Uniprot P30967), phenylalanine ammonia lyase from  Anabaena variabilis  (PAL, Gene ID 3758891, Uniprot Q3M5Z3), or homologues thereof derived from other taxonomic groups including eukaryotes, animals, chordates, apicomplexans, cellular slime molds, red algae, green plants, choanoflagellates, kinetoplastids, Longamoebia, Capsaspora, bacteria, proteobacteria, g-proteobacteria, actinobacteria, green sulfur bacteria, cyanobacteria, GNS bacteria, archaea, euryarchaeotes, crenarchaeotes, or other. 
     Deficiency in the metabolism of phenylalanine leads to the disease phenylketonuria, a hereditary condition in which the buildup of phenlylalanine causes neurotoxicity. Subjects suffering from phenylketonuria require strict adherence to a low-phenylalanine diet. Recombinant phenylalanine degrading enzymes are in clinical development but suffer from short half-life and immunogenicity. 
     Provided herein are synthetic membrane receiver complexes comprising a receiver polypeptide that comprises a phenylalanine-degrading enzyme that is expressed on the surface of the complex. In some embodiments, the synthetic membrane receiver complexes comprise a high-density surface of receivers comprising the phenylalanine-degrading enzyme, such as surfaces comprising at least about 1,000 copies, 5,000 copies, 10,000 copies, 50,000 copies, 100,000 copies, 500,000 copies, 1,000,000 copies, or at least about 5,000,000 copies of the phenylalanine-degrading enzyme polypeptide receivers. In some embodiments, the receiver comprising the phenylalanine-degrading enzyme comprises an S domain (comprising the phenylalanine-degrading enzyme or a functional fragment thereof) and an A domain, which can be selected as desired, and may include any suitable anchor, such as, e.g. a membrane protein or domain thereof. In some embodiments, erythroid cells are generated that express a phenylalanine-degrading enzyme polypeptide receiver from an exogenous nucleic acid sequence that encodes the phenylalanine-degrading enzyme fused to a nucleic acid sequence encoding an erythroid membrane protein or membrane-interacting fragment thereof, e.g. glycophorin A, glycophorin B, Kell, Band3, CD55, CD59, CD46, or CR1. 
     Provided herein are synthetic membrane receiver complexes comprising a receiver polypeptide that comprises a phenylalanine-degrading enzyme that is expressed in the unexposed interior of the complex. In some embodiments, the receiver comprising the phenylalanine-degrading enzyme comprises a U domain (comprising the phenylalanine-degrading enzyme or a functional fragment thereof) and an A domain, which can be selected as desired, and may include any suitable anchor, such as, e.g. a membrane protein or domain thereof. In some embodiments, erythroid cells are generated that express a phenylalanine-degrading enzyme polypeptide receiver from an exogenous nucleic acid sequence that encodes the phenylalanine-degrading enzyme fused to a nucleic acid sequence encoding an erythroid membrane protein or membrane-interacting fragment thereof, e.g., glycophorin A, glycophorin B, Kell, Band3, CD55, CD59, CD46, or CR1. 
     By attaching the phenylalanine-degrading enzyme, an enzyme not naturally associated with a plasma membrane, to the surface of a synthetic membrane receiver complex, e.g. an erythroid cell, or by expressing the enzyme in the interior of the complex (e.g. the cytosol of an erythroid cell) the circulating half-life of the enzyme may be prolonged, retention in the vasculature may be improved, and/or the activity of the enzyme is increased through avidity effects. 
     In one embodiment, a subject having or suspected of having or developing phenylketonuria is administered a composition of phenylalanine degrading enzyme-expressing erythroid cells in an amount effective to treat, prevent, or reduce the symptoms of the disorder. In some embodiments, the effect of the treatment can be assessed by detecting an improved clinical presentation and/or by measuring a reduction in the concentration of phenylalanine in circulation following consumption of dietary phenylalanine and a reduction in the number and/or frequency of neurological episodes. Suitable assays are known in the art. 
     Provided herein are synthetic membrane receiver complexes comprising a receiver polypeptide that comprises an enzyme capable of degrading methionine. For example, the receiver polypeptide may comprise Methionine Gamma Lyase from  Pseudomonas putida  (MGL, Gene ID 1041604, Uniprot P13254) or  Arabiodopsis thaliana  (MGL, Gene ID AT1G64660, Uniprot Q9SGU9), L-amino acid oxidase, methionine dipeptidase, S-adenosylmethionine synthetase, or engineered cystathione-gamma-lyase (see e.g. Stone et al., ACS Chem Biol 2012 7(11):1822-29), or functional fragment thereof or homologue thereof found in other taxonomic groups. 
     Several cancers are known to dependent on exogenous methionine, and it has been known for nearly a half century that human tumors, including those derived from the nervous system such as glioblastomas, medulloblastoma, and neuroblastomas are much more sensitive than normal tissues to methionine starvation. The administration of a methionine-degrading enzyme is of therapeutic value in treating these diseases and conditions, as a means of selectively-killing cancer tissue and leaving normal tissue unaffected. 
     Provided herein are synthetic membrane receiver complexes comprising a receiver polypeptide that comprises a methionine degrading enzyme that is expressed on the surface of the complex. In some embodiments, the synthetic membrane receiver complexes comprise a high-density surface of receivers comprising the methionine-degrading enzyme, such as surfaces comprising at least about 1,000 copies, 5,000 copies, 10,000 copies, 50,000 copies, 100,000 copies, 500,000 copies, 1,000,000 copies or at least about 5,000,000 copies of the methionine-degrading enzyme polypeptide receivers. In some embodiments, the receiver comprising the methionine-degrading enzyme comprises an S domain (comprising the methionine-degrading enzyme or a functional fragment thereof) and an A domain, which can be selected as desired, and may include any suitable anchor, such as, e.g. a membrane protein or domain thereof. In some embodiments, erythroid cells are generated that express a methionine-degrading enzyme polypeptide receiver from an exogenous nucleic acid sequence that encodes the methionine-degrading enzyme fused to a nucleic acid sequence encoding an erythroid membrane protein or membrane-interacting fragment thereof, e.g., glycophorin A, glycophorin B, Kell, Band3, CD55, CD59, CD46, or CR1. 
     Provided herein are synthetic membrane receiver complexes comprising a receiver polypeptide that comprises a methionine-degrading enzyme that is expressed in the unexposed interior of the complex. In some embodiments, the receiver comprising the methionine-degrading enzyme comprises a U domain (comprising the methionine-degrading enzyme or a functional fragment thereof) and an A domain, which can be selected as desired, and may include any suitable anchor, such as, e.g. a membrane protein or domain thereof. In some embodiments, erythroid cells are generated that express a methionine-degrading enzyme polypeptide receiver from an exogenous nucleic acid sequence that encodes the methionine-degrading enzyme fused to a nucleic acid sequence encoding an erythroid membrane protein or membrane-interacting fragment thereof, e.g., glycophorin A, glycophorin B, Kell, Band3, CD55, CD59, CD46, or CR1. 
     By attaching the methionine-degrading enzyme, an enzyme not naturally associated with a plasma membrane, to the surface of a synthetic membrane receiver complex, e.g. an erythroid cell, or by expressing the enzyme in the interior of the complex (e.g. the cytosol of an erythroid cell) the circulating half-life of the enzyme may be prolonged, retention in the vasculature may be improved, and/or the activity of the enzyme is increased through avidity effects. 
     In one embodiment, a subject having or suspected of having or developing glioblastoma is administered a composition of methionine-degrading enzyme-expressing erythroid cells in an amount effective to treat, prevent, or reduce the symptoms of the cancer. In some embodiments, the effect of the treatment can be assessed by detecting a reduction in the size of the tumor, an increase of the progression-free time during which the tumor is static, and/or a reduction of circulating levels of methionine in the blood. 
     Provided herein are synthetic membrane receiver complexes comprising a receiver polypeptide that comprises porphobilinogen deaminase (PBGD, Gene ID 3145, Uniprot P08397) or another enzyme of the heme synthesis pathway, e.g. Amino levulinic acid dehydrogenase, Uroporphyrinogen III synthase, Uroporphyrinogen III decarboxylase, coporoporphyrinogen III oxidase, protoporphyrin III oxidase, ferrochelatase, or functional fragment thereof, or homologues thereof derived from other taxonomic groups. 
     Deficiencies in heme synthesis, for example Acute Intermittent Porphyria and Cutania Tarda, lead to a buildup of heme precursor metabolites, most commonly prophobilinogen. Symptoms of these conditions include pain, peripheral neuropathy, urinary symptoms, constipation, muscle weakness, tachycardia, neuropsychiatric symptoms, seizure, and occasionally rash. 
     Supplementation with heme is the standard of care, though the short half-life of the molecule makes the treatment inconvenient and side effects can be very severe. Treatment with replacement of the deficient enzyme has been tested in preclinical models, both with recombinant porphobilinogen deaminase and with gene therapies (see, e.g. Harding, Human Gene Therapy 2013, 24(12):968-969). 
     Provided herein are synthetic membrane receiver complexes comprising a receiver polypeptide that comprises porphobilinogen deaminase or another heme synthesis enzyme that is expressed on the surface of the complex. In some embodiments, the synthetic membrane receiver complexes comprise a high-density surface of receivers comprising the porphobilinogen deaminase or another heme synthesis enzyme. In some embodiments, the receiver comprising the porphobilinogen deaminase or another heme synthesis enzyme comprises an S domain (comprising porphobilinogen deaminase or another heme synthesis enzyme) and an A domain, which can be selected as desired, and may include any suitable anchor, such as, e.g. a membrane protein or domain thereof, e.g., glycophorin A, glycophorin B, Kell, Band3, CD55, CD59, CD46, or CR1. 
     Provided herein are synthetic membrane receiver complexes comprising a receiver polypeptide that comprises porphobilinogen deaminase or another heme synthesis enzyme that is expressed in the unexposed interior of the complex. In some embodiments, the receiver comprising porphobilinogen deaminase or another heme synthesis enzyme comprises a U domain (comprising porphobilinogen deaminase or another heme synthesis enzyme) and an A domain, which can be selected as desired, and may include any suitable anchor, such as, e.g. a membrane protein or domain thereof, e.g., glycophorin A, glycophorin B, Kell, Band3, CD55, CD59, CD46, or CR1. 
     By attaching porphobilinogen deaminase or another heme synthesis enzyme, an enzyme not naturally associated with a plasma membrane, to the surface of a synthetic membrane receiver complex, e.g. an erythroid cell, or by expressing the enzyme in the interior of the complex (e.g. the cytosol of an erythroid cell) the circulating half-life of the enzyme may be prolonged, retention in the vasculature may be improved, and/or the activity of the enzyme is increased through avidity effects. 
     In one embodiment, a subject having or suspected of having or developing acute intermittent porphyria is administered a composition of porphobilinogen deaminase-expressing erythroid cells in an amount effective to treat, prevent, or reduce the symptoms of the disease. In some embodiments, the effect of the treatment can be assessed by detecting a reduction in the level of pain, the amount of muscle weakness, a resolution of constipation and urinary symptoms, and/or a reduction in the concentration of porphobilinogen or other precursors in circulation. 
     Receiver Contacting 
     In certain embodiments, the polypeptide receiver is expressed within the synthetic membrane-receiver polypeptide complex. The polypeptide receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex or may reside within the synthetic membrane-receiver polypeptide complex. 
     In certain embodiments, the polypeptide receiver is conjugated to the synthetic membrane-receiver polypeptide complex. The polypeptide receiver usually is conjugated to the surface of the synthetic membrane-receiver polypeptide complex. Conjugation may be achieved chemically or enzymatically, by methods known in the art and described herein. Non-polypeptide receivers may also be conjugated to a synthetic membrane-receiver complex. In some embodiments, the receiver is not conjugated to the synthetic membrane-receiver complex. 
     In certain embodiments, the polypeptide receiver is loaded into the synthetic membrane-receiver polypeptide complex. Non-polypeptide receivers may also be loaded within a synthetic membrane-receiver complex. In some embodiments, the receiver is not loaded into or onto the synthetic membrane-receiver complex. 
     In some embodiments, the synthetic membrane-receiver complex comprises a receiver that is optionally expressed from an exogenous nucleic acid, conjugated to the complex, loaded into or onto the complex, and any combination thereof. Optionally, the synthetic membrane-receiver complex comprises a therapeutic agent or other payload. 
     In some embodiments, the synthetic membrane-receiver complex is generated by contacting a suitable isolated cell, e.g., an erythroid cell, a reticulocyte, an erythroid cell precursor, a platelet, or a platelet precursor, with an exogenous nucleic acid encoding a receiver polypeptide. In some embodiments, the receiver polypeptide is encoded by a DNA, which is contacted with a nucleated erythroid precursor cell or a nucleated platelet precursor cell. In some embodiments, the receiver polypeptide is encoded by an RNA, which is contacted with a platelet, a nucleate erythroid cell, a nucleated platelet precursor cell, or a reticulocyte. In some embodiments, the receiver is a polypeptide, which is contacted with a primary platelet, a nucleated erythroid cell, a nucleated platelet precursor cell, a reticulocyte, or an erythrocyte. 
     A receiver polypeptide may be expressed from a transgene introduced into an erythroid cell by electroporation, chemical or polymeric transfection, viral transduction, mechanical membrane disruption, or other method; a receiver polypeptide that is expressed from mRNA that is introduced into a cell by electroporation, chemical or polymeric transfection, viral transduction, mechanical membrane disruption, or other method; a receiver polypeptide that is over-expressed from the native locus by the introduction of an external factor, e.g., a transcriptional activator, transcriptional repressor, or secretory pathway enhancer; and/or a receiver polypeptide that is synthesized, extracted, or produced from a production cell or other external system and incorporated into the erythroid cell. 
     In certain embodiments, the polypeptide receiver is expressed within the synthetic membrane-receiver polypeptide complex. The polypeptide receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex or may reside within the synthetic membrane-receiver polypeptide complex. 
     In certain embodiments, the synthetic membrane-receiver polypeptide complex is a cell, e.g., an erythroid cell or a platelet expressing a receiver polypeptide. Receiver polypeptides can be introduced by transfection of single or multiple copies of genes, transduction with a virus, or electroporation in the presence of DNA or RNA. Methods for expression of exogenous proteins in mammalian cells are well known in the art. For example, expression of exogenous factor IX in hematopoietic cells is induced by viral transduction of CD34+ progenitor cells, see Chang et al., Nat Biotechnol 2006, 24:1017. 
     Nucleic acids such as DNA expression vectors or mRNA for producing the receiver polypeptide may be introduced into progenitor cells (e.g., an erythroid cell progenitor or a platelet progenitor and the like) that are suitable to produce the synthetic membrane-receiver polypeptide complexes described herein. The progenitor cells can be isolated from an original source or obtained from expanded progenitor cell population via routine recombinant technology as provided herein. In some instances, the expression vectors can be designed such that they can incorporate into the genome of cells by homologous or non-homologous recombination by methods known in the art. 
     In some instances, e.g., for a synthetic membrane-receiver polypeptide complex that is an erythroid cell comprising a receiver polypeptide, a nucleic acid encoding a non-receiver polypeptide that can selectively target and cut the genome, for example a CRISPR/Cas9, transcriptional activator-like effector nuclease (TALEN), or zinc finger nuclease, is used to direct the insertion of the exogenous nucleic acid of the expression vector encoding the receiver polypeptide to a particular genomic location, for example the CR1 locus (1q32.2), the hemoglobin locus (11p15.4), or another erythroid-associated protein including, but not limited to, those listed in table 1 and table 3. 
     In some instances, the exogenous nucleic acid is an RNA molecule, or a DNA molecule that encodes for an RNA molecule, that silences or represses the expression of a target gene. For example, the molecule can be a small interfering RNA (siRNA), an antisense RNA molecule, or a short hairpin RNA (shRNA) molecule. 
     Methods for transferring expression vectors into progenitor cells that are suitable to produce the synthetic membrane-receiver polypeptide complexes described herein include, but are not limited to, viral mediated gene transfer, liposome mediated transfer, transformation, gene guns, transfection and transduction, e.g., viral mediated gene transfer such as the use of vectors based on DNA viruses such as adenovirus, adenoassociated virus and herpes virus, as well as retroviral based vectors. Examples of modes of gene transfer include e.g., naked DNA, CaPO 4  precipitation, DEAE dextran, electroporation, protoplast fusion, lipofection, and cell microinjection. 
     A progenitor cell subject to transfer of an exogenous nucleic acid that encodes a polypeptide receiver can be cultured under suitable conditions allowing for differentiation into mature enucleated red blood cells, e.g., the in vitro culturing process described herein. The resulting enucleated red blood cells display proteins associated with mature erythrocytes, e.g., hemoglobin, glycophorin A, and receiver polypeptides which can be validated and quantified by standard methods (e.g., Western blotting or FACS analysis). Isolated mature enucleated red blood cells comprising a receiver and platelets comprising a receiver are two examples of synthetic membrane-receiver polypeptide complexes of the invention. 
     In some embodiments, the synthetic membrane-receiver complex is generated by contacting a reticulocyte with an exogenous nucleic acid encoding a receiver polypeptide. In some embodiments, the receiver polypeptide is encoded by an RNA which is contacted with a reticulocyte. In some embodiments, the receiver is a polypeptide which is contacted with a reticulocyte. 
     Isolated reticulocytes may be transfected with mRNA encoding a receiver polypeptide to generate a synthetic membrane-receiver comple. Messenger RNA may be derived from in vitro transcription of a cDNA plasmid construct containing the coding sequence corresponding to the receiver polypeptide. For example, the cDNA sequence corresponding to the receiver polypeptide may be inserted into a cloning vector containing a promoter sequence compatible with specific RNA polymerases. For example, the cloning vector ZAP Express® pBK-CMV (Stratagene, La Jolla, Calif., USA) contains T3 and T7 promoter sequence compatible with T3 and T7 RNA polymerase, respectively. For in vitro transcription of sense mRNA, the plasmid is linearized at a restriction site downstream of the stop codon(s) corresponding to the end of the coding sequence of the receiver polypeptide. The mRNA is transcribed from the linear DNA template using a commercially available kit such as, for example, the RNAMaxx® High Yield Transcription Kit (from Stratagene, La Jolla, Calif., USA). In some instances, it may be desirable to generate 5′-m7GpppG-capped mRNA. As such, transcription of a linearized cDNA template may be carried out using, for example, the mMESSAGE mMACHINE High Yield Capped RNA Transcription Kit from Ambion (Austin, Tex., USA). Transcription may be carried out in a reaction volume of 20-100 μl at 37° C. for 30 min to 4 h. The transcribed mRNA is purified from the reaction mix by a brief treatment with DNase I to eliminate the linearized DNA template followed by precipitation in 70% ethanol in the presence of lithium chloride, sodium acetate or ammonium acetate. The integrity of the transcribed mRNA may be assessed using electrophoresis with an agarose-formaldehyde gel or commercially available Novex pre-cast TBE gels (e.g., Novex, Invitrogen, Carlsbad, Calif., USA). 
     Messenger RNA encoding the receiver polypeptide may be introduced into reticulocytes using a variety of approaches including, for example, lipofection and electroporation (van Tandeloo et al., Blood 98:49-56 (2001)). For lipofection, for example, 5 μg of in vitro transcribed mRNA in Opti-MEM (Invitrogen, Carlsbad, Calif., USA) is incubated for 5-15 min at a 1:4 ratio with the cationic lipid DMRIE-C (Invitrogen). Alternatively, a variety of other cationic lipids or cationic polymers may be used to transfect cells with mRNA including, for example, DOTAP, various forms of polyethylenimine, and polyL-lysine (Sigma-Aldrich, Saint Louis, Mo., USA), and Superfect (Qiagen, Inc., Valencia, Calif., USA; See, e.g., Bettinger et al., Nucleic Acids Res. 29:3882-3891 (2001)). The resulting mRNA/lipid complexes are incubated with cells (1-2×10 6  cells/me for 2 h at 37° C., washed and returned to culture. For electroporation, for example, about 5 to 20×10 6  cells in 500 μl of Opti-MEM (Invitrogen, Carlsbad, Calif., USA) are mixed with about 20 μg of in vitro transcribed mRNA and electroporated in a 0.4-cm cuvette using, for example, and Easyject Plus device (EquiBio, Kent, United Kingdom). In some instances, it may be necessary to test various voltages, capacitances and electroporation volumes to determine the useful conditions for transfection of a particular mRNA into a reticulocyte. In general, the electroporation parameters required to efficiently transfect cells with mRNA appear to be less detrimental to cells than those required for electroporation of DNA (van Tandeloo et al., Blood 98:49-56 (2001)). 
     Alternatively, mRNA may be transfected into a reticulocyte using a peptide-mediated RNA delivery strategy (See, e.g., Bettinger et al., Nucleic Acids Res. 29:3882-3891 (2001)). For example, the cationic lipid polyethylenimine 2 kDA (Sigma-Aldrich, Saint Louis, Mo., USA) may be combined with the melittin peptide (Alta Biosciences, Birmingham, UK) to increase the efficiency of mRNA transfection, particularly in post-mitotic primary cells. The mellitin peptide may be conjugated to the PEI using a disulfide cross-linker such as, for example, the hetero-bifunctional cross-linker succinimidyl 3-(2-pyridyldithio) propionate. In vitro transcribed mRNA is preincubated for 5 to 15 min with the mellitin-PEI to form an RNA/peptide/lipid complex. This complex is then added to cells in serum-free culture medium for 2 to 4 h at 37° C. in a 5% CO 2  humidified environment and then removed and the transfected cells allowed to continue growing in culture. 
     In some embodiments, the synthetic membrane-receiver complex is generated by contacting a suitable isolated erythroid cell precursor or a platelet precursor with an exogenous nucleic acid encoding a receiver polypeptide. In some embodiments, the receiver polypeptide is encoded by a DNA, which is contacted with a nucleated erythroid precursor cell or a nucleated platelet precursor cell. In some embodiments, the receiver polypeptide is encoded by an RNA, which is contacted with a platelet, a nucleate erythroid cell, or a nucleated platelet precursor cell. 
     Receivers may be genetically introduced into erythroid cell precursors, platelet precursor, or nucleated erythroid cells prior to terminal differentiation using a variety of DNA techniques, including transient or stable transfections and gene therapy approaches. The receiver polypeptides may be expressed on the surface and/or in the cytoplasm of mature red blood cell or platelet. 
     Viral gene transfer may be used to transfect the cells with DNA encoding a receiver polypeptide. A number of viruses may be used as gene transfer vehicles including Moloney murine leukemia virus (MMLV), adenovirus, adeno-associated virus (AAV), herpes simplex virus (HSV), lentiviruses such as human immunodeficiency virus 1 (HIV 1), and spumaviruses such as foamy viruses, for example (See, e.g., Osten et al., HEP 178:177-202 (2007)). Retroviruses, for example, efficiently transduce mammalian cells including human cells and integrate into chromosomes, conferring stable gene transfer. 
     A receiver polypeptide may be transfected into an erythroid cell precursor, a platelet precursor, or a nucleated erythroid cell, expressed and subsequently retained and exhibited in a mature red blood cell or platelet. A suitable vector is the Moloney murine leukemia virus (MMLV) vector backbone (Malik et al., Blood 91:2664-2671 (1998)). Vectors based on MMLV, an oncogenic retrovirus, are currently used in gene therapy clinical trials (Hossle et al., News Physiol. Sci. 17:87-92 (2002)). For example, a DNA construct containing the cDNA encoding a receiver polypeptide can be generated in the MMLV vector backbone using standard molecular biology techniques. The construct is transfected into a packaging cell line such as, for example, PA317 cells and the viral supernatant is used to transfect producer cells such as, for example, PG13 cells. The PG13 viral supernatant is incubated with an erythroid cell precursor, a platelet precursor, or a nucleated erythroid cell that has been isolated and cultured or has been freshly isolated as described herein. The expression of the receiver polypeptide may be monitored using FACS analysis (fluorescence-activated cell sorting), for example, with a fluorescently labeled antibody directed against the receiver polypeptide, if it is located on the surface of the synthetic membrane-receiver polypeptide complex. Similar methods may be used to express a receiver polypeptide that is located in the inside of the synthetic membrane-receiver polypeptide complex. 
     Optionally, a fluorescent tracking molecule such as, for example, green fluorescent protein (GFP) may be transfected using a viral-based approach (Tao et al., Stem Cells 25:670-678 (2007)). Ecotopic retroviral vectors containing DNA encoding the enhanced green fluorescent protein (EGFP) or a red fluorescent protein (e.g., DsRed-Express) are packaged using a packaging cell such as, for example, the Phoenix-Eco cell line (distributed by Orbigen, San Diego, Calif.). Packaging cell lines stably express viral proteins needed for proper viral packaging including, for example, gag, pol, and env. Supernatants from the Phoenix-Eco cells into which viral particles have been shed are used to transduce e.g., erythroid cell precursors, platelet precursors, or a nucleated erythroid cells. In some instances, transduction may be performed on a specially coated surface such as, for example, fragments of recombinant fibronectin to improve the efficiency of retroviral mediated gene transfer (e.g., RetroNectin, Takara Bio USA, Madison, Wis.). Cells are incubated in RetroNectin-coated plates with retroviral Phoenix-Eco supernatants plus suitable co-factors. Transduction may be repeated the next day. In this instance, the percentage of cells expressing EGFP or DsRed-Express may be assessed by FACS. Other reporter genes that may be used to assess transduction efficiency include, for example, beta-galactosidase, chloramphenicol acetyltransferase, and luciferase as well as low-affinity nerve growth factor receptor (LNGFR), and the human cell surface CD24 antigen (Bierhuizen et al., Leukemia 13:605-613 (1999)). 
     Nonviral vectors may be used to introduce genetic material into suitable erythroid cells, platelets or precursors thereof to generate synthetic membrane-receiver polypeptide complexes. Nonviral-mediated gene transfer differs from viral-mediated gene transfer in that the plasmid vectors contain no proteins, are less toxic and easier to scale up, and have no host cell preferences. The “naked DNA” of plasmid vectors is by itself inefficient in delivering genetic material encoding a receiver polypeptide to a cell and therefore is combined with a gene delivery method that enables entry into cells. A number of delivery methods may be used to transfer nonviral vectors into suitable erythroid cells, platelets or precursors thereof including chemical and physical methods. 
     A nonviral vector encoding a receiver polypeptide may be introduced into suitable erythroid cells, platelets or precursors thereof using synthetic macromolecules such as cationic lipids and polymers (Papapetrou et al., Gene Therapy 12:S118-S130 (2005)). Cationic liposomes, for example form complexes with DNA through charge interactions. The positively charged DNA/lipid complexes bind to the negative cell surface and are taken up by the cell by endocytosis. This approach may be used, for example, to transfect hematopoietic cells (See, e.g., Keller et al., Gene Therapy 6:931-938 (1999)). For erythroid cells, platelets or precursors thereof the plasmid DNA (approximately 0.5 μg in 25-100 μL, of a serum free medium, such as, for example, OptiMEM (Invitrogen, Carlsbad, Calif.)) is mixed with a cationic liposome (approximately 4 μg in 25 μL of serum free medium) such as the commercially available transfection reagent Lipofectamine™ (Invitrogen, Carlsbad, Calif.) and allowed to incubate for at least 20 min to form complexes. The DNA/liposome complex is added to suitable erythroid cells, platelets or precursors thereof and allowed to incubate for 5-24 h, after which time transgene expression or the receiver polypeptide may be assayed. Alternatively, other commercially available liposome transfection agents may be used (e.g., In vivo GeneSHUTTLE™, Qbiogene, Carlsbad, Calif.). 
     Optionally, a cationic polymer such as, for example, polyethylenimine (PEI) may be used to efficiently transfect erythroid cell progenitor cells, for example hematopoietic and umbilical cord blood-derived CD34+ cells (See, e.g., Shin et al., Biochim Biophys. Acta 1725:377-384 (2005)). Human CD34+ cells are isolated from human umbilical cord blood and cultured in Iscove&#39;s modified Dulbecco&#39;s medium supplemented with 200 ng/ml stem cell factor and 20% heat-inactivated fetal bovine serum. Plasmid DNA encoding the receiver polypeptide is incubated with branched or linear PEIs varying in size from 0.8 K to 750 K (Sigma Aldrich, Saint Louis, Mo., USA; Fermetas, Hanover, Md., USA). PEI is prepared as a stock solution at 4.2 mg/ml distilled water and slightly acidified to pH 5.0 using HCl. The DNA may be combined with the PEI for 30 min at room temperature at various nitrogen/phosphate ratios based on the calculation that 1 μg of DNA contains 3 nmol phosphate and 1 μl of PEI stock solution contains 10 nmol amine nitrogen. The isolated CD34+ cells are seeded with the DNA/cationic complex, centrifuged at 280×g for 5 min and incubated in culture medium for 4 or more h until gene expression of the receiver polypeptide is assessed. 
     A plasmid vector may be introduced into suitable erythroid cells, platelets or precursors thereof using a physical method such as particle-mediated transfection, “gene gun”, biolistics, or particle bombardment technology (Papapetrou, et al., (2005) Gene Therapy 12:S118-S130). In this instance, DNA encoding the receiver polypeptide is absorbed onto gold particles and administered to cells by a particle gun. This approach may be used, for example, to transfect erythroid progenitor cells, e.g., hematopoietic stem cells derived from umbilical cord blood (See, e.g., Verma et al., Gene Therapy 5:692-699 (1998)). As such, umbilical cord blood is isolated and diluted three fold in phosphate buffered saline. CD34+ cells are purified using an anti-CD34 monoclonal antibody in combination with magnetic microbeads coated with a secondary antibody and a magnetic isolation system (e.g., Miltenyi MiniMac System, Auburn, Calif., USA). The CD34+ enriched cells may be cultured as described herein. For transfection, plasmid DNA encoding the receiver polypeptide is precipitated onto a particle, for example gold beads, by treatment with calcium chloride and spermidine. Following washing of the DNA-coated beads with ethanol, the beads may be delivered into the cultured cells using, for example, a Biolistic PDS-1000/He System (Bio-Rad, Hercules, Calif., USA). A reporter gene such as, for example, beta-galactosidase, chloramphenicol acetyltransferase, luciferase, or green fluorescent protein may be used to assess efficiency of transfection. 
     Optionally, electroporation methods may be used to introduce a plasmid vector into suitable erythroid cells, platelets or precursors thereof. Electroporation creates transient pores in the cell membrane, allowing for the introduction of various molecules into the cells including, for example, DNA and RNA as well as antibodies and drugs. As such, CD34+ cells are isolated and cultured as described herein Immediately prior to electroporation, the cells are isolated by centrifugation for 10 min at 250×g at room temperature and resuspended at 0.2-10×10{circumflex over ( )}6 viable cells/ml in an electroporation buffer such as, for example, X-VIVO 10 supplemented with 1.0% human serum albumin (HSA). The plasmid DNA (1-50 μg) is added to an appropriate electroporation cuvette along with 500 μl of cell suspension. Electroporation may be done using, for example, an ECM 600 electroporator (Genetronics, San Diego, Calif., USA) with voltages ranging from 200 V to 280 V and pulse lengths ranging from 25 to 70 milliseconds. A number of alternative electroporation instruments are commercially available and may be used for this purpose (e.g., Gene Pulser Xcell™, BioRad, Hercules, Calif.; Cellject Duo, Thermo Science, Milford, Mass.). Alternatively, efficient electroporation of isolated CD34+ cells may be performed using the following parameters: 4 mm cuvette, 1600 μF, 550 V/cm, and 10 μg of DNA per 500 μl of cells at 1×105 cells/ml (Oldak et al., Acta Biochimica Polonica 49:625-632 (2002)). 
     Nucleofection, a form of electroporation, may also be used to transfect suitable erythroid cells, platelets or precursors thereof. In this instance, transfection is performed using electrical parameters in cell-type specific solutions that enable DNA (or other reagents) to be directly transported to the nucleus thus reducing the risk of possible degradation in the cytoplasm. For example, a Human CD34 Cell Nucleofector™ Kit (from amaxa inc.) may be used to transfect suitable erythroid cells, platelets or precursors thereof. In this instance, 1-5×10 6  cells in Human CD34 Cell Nucleofector™ Solution are mixed with 1-5 μg of DNA and transfected in the Nucleofector™ instrument using preprogrammed settings as determined by the manufacturer. 
     Erythroid cells, platelets or precursors thereof may be non-virally transfected with a conventional expression vector which is unable to self-replicate in mammalian cells unless it is integrated in the genome. Alternatively, erythroid cells, platelets or precursors thereof may be transfected with an episomal vector which may persist in the host nucleus as autonomously replicating genetic units without integration into chromosomes (Papapetrou et al., Gene Therapy 12:S118-5130 (2005)). These vectors exploit genetic elements derived from viruses that are normally extrachromosomally replicating in cells upon latent infection such as, for example, EBV, human polyomavirus BK, bovine papilloma virus-1 (BPV-1), herpes simplex virus-1 (HSV) and Simian virus 40 (SV40). Mammalian artificial chromosomes may also be used for nonviral gene transfer (Vanderbyl et al., Exp. Hematol. 33:1470-1476 (2005)). 
     Exogenous nucleic acids encoding a polypeptide receiver may be assembled into expression vectors by standard molecular biology methods known in the art, e.g., restriction digestion, overlap-extension PCR, and Gibson assembly. 
     Exogenous nucleic acids may comprise a gene encoding a polypeptide receiver that is not normally expressed on the cell surface, e.g., of an erythroid cell, fused to a gene that encodes an endogenous or native membrane protein, such that the receiver polypeptide is expressed on the cell surface. For example, a exogenous gene encoding a receiver polypeptide can be cloned at the N terminus following the leader sequence of a type 1 membrane protein, at the C terminus of a type 2 membrane protein, or upstream of the GPI attachment site of a GPI-linked membrane protein. 
     Standard cloning methods can be used to introduce flexible amino acid linkers between two fused genes. For example, the flexible linker is a poly-glycine poly-serine linker such as [Gly4Ser]3_(SEQ ID NO: 24) commonly used in generating single-chain antibody fragments from full-length antibodies (Antibody Engineering: Methods &amp; Protocols, Lo 2004), or ala-gly-ser-thr polypeptides such as those used to generate single-chain Arc repressors (Robinson &amp; Sauer, PNAS 1998). In some embodiments, the flexible linker provides the receiver polypeptide with more flexibility and steric freedom than the equivalent construct without the flexible linker. This added flexibility is useful in applications that require binding to a target, e.g., an antibody or protein, or an enzymatic reaction of the receiver for which the active site must be accessible to the substrate (e.g., the target). 
     An epitope tag may be placed between two fused genes, such as, e.g., a nucleic acid sequence encoding an HA epitope tag—amino acids YPYDVPDYA (Seq. ID No. 4), a CMyc tag—amino acids EQKLISEEDL (Seq. ID No. 5), or a Flag tag—amino acids DYKDDDDK (Seq. ID No. 6). The epitope tag may be used for the facile detection and quantification of expression using antibodies against the epitope tag by flow cytometry, western blot, or immunoprecipitation. 
     In some embodiments, the synthetic membrane-receiver polypeptide comprises a receiver polypeptide and at least one other heterologous polypeptide. The second polypeptide can be a fluorescent protein. The fluorescent protein can be used as a reporter to assess transduction efficiency. In some embodiments, the fluorescent protein is used as a reporter to assess expression levels of the receiver polypeptide if both are made from the same transcript. 
     In some embodiments, the at least one other polypeptide is heterologous and provides a function, such as, e.g., multiple antigens, multiple capture targets, enzyme cascade. In one embodiment, the recombinant nucleic acid comprises a gene encoding a receiver and a second gene, wherein the second gene is separated from the gene encoding the receiver by a viral-derived T2A sequence (gagggcagaggaagtcttctaacatgcggtgacgtggaggsgsstcccggccct (Seq. ID No. 7)) that is post-translationally cleaved into two mature proteins. 
     In some embodiments, the receiver polypeptide is complement receptor 1 (CR-1). The gene sequence for complement receptor 1 is amplified using PCR. In some embodiments, the exogenous nucleic acid encoding a receiver polypeptide comprises a gene sequence for a scFv against hepatitis B antigen that is fused to the 3′ end of the sequence for Kell and amplified using PCR. In some embodiments, the exogenous nucleic acid encoding a receiver polypeptide comprises a gene sequence for a scFv against hepatitis B antigen that is fused to a poly-glycine/serine linker, followed by the 3′ end of the sequence for Kell, and amplified using PCR. In some embodiments, the exogenous nucleic acid encoding a receiver polypeptide comprises the 3′ end of a gene sequence for a scFv against hepatitis B antigen that is fused to an epitope tag sequence, of which may be one, or a combination of, an; HA-tag, Green fluorescent protein tag, Myc-tag, chitin binding protein, maltose binding protein, glutathione-S-transferase, poly(His)tag, thioredoxin, poly(NANP), FLAG-tag, V5-tag, AviTag, Calmodulin-tag, polyglutamate-tag, E-tag, S-tag, SBP-tag, Softag-1, Softag-3, Strep-tag, TC-tag, VSV-tag, Xpress-tag, Isopeptag, SpyTag, biotin carboxyl carrier protein, Nus-tag, Fc-tag, or Ty-tag. The entire construct is fused to the 3′ end of the sequence for Kell and then amplified using PCR. The exogenous gene constructs encoding the various receiver polypeptides are, for example, subsequently loaded into a lentiviral vector and used to transduce a CD34+ cell population. 
     In one embodiment, the gene comprising an adenosine deaminase receiver is placed in the pSP64 vector. The vector is linearized and RNA polymerase generates mRNA coding for the receiver polypeptide. In one embodiment, a population of neutrophils is electroporated using an Ingenio electroporation kit such that 10, 100, 1,000, 10,000 TU/ml of mRNA coding for surface expression of GluN1 receiver to generate a synthetic membrane-receiver polypeptide complex. In one embodiment, a population of platelet cells is incubated with Trans-IT mRNA and 10, 100, or 1000 TU/ml (transducing units/ml) of mRNA coding for thymidine phosphorylase protein receiver to generate a synthetic membrane-receiver polypeptide complex. In one embodiment, a population of erythroid cells is incubated with lentiviral vectors comprising exogenous nucleic acid encoding a receiver polypeptide, specific plasmids of which may include; pLKO.1 puro, PLKO.1—TRC cloning vector, pSico, FUGW, pLVTHM, pLJM1, pLionII, pMD2.G, pCMV-VSV-G, pCI-VSVG, pCMV-dR8.2 dvpr, psPAX2, pRSV-Rev, and pMDLg/pRRE to generate a synthetic membrane-receiver polypeptide complex. The vectors may be administered at 10, 100, 1,000, 10,000 pfu and incubated for 12 hrs. 
     In one embodiment, a population of erythroid cells is incubated with Lipofectamine 2000 and 10, 100, or 1000 TU/ml (transducing units/ml) of DNA coding for oxalase receiver. 
     In certain embodiments, the polypeptide receiver is conjugated to the synthetic membrane-receiver polypeptide complex. The polypeptide receiver usually is conjugated to the surface of the synthetic membrane-receiver polypeptide complex. Conjugation may be achieved chemically or enzymatically. Non-polypeptide receivers may also be conjugated to a synthetic membrane-receiver complex. 
     In some embodiments, the synthetic membrane-receiver complex comprises a receiver that is chemically conjugated. Chemical conjugation of a receiver may be accomplished by covalent bonding of the receiver to another molecule, with or without use of a linker. The formation of such conjugates is within the skill of artisans and various techniques are known for accomplishing the conjugation, with the choice of the particular technique being guided by the materials to be conjugated. The addition of amino acids to the polypeptide (C- or N-terminal) which contain ionizable side chains, e.g., aspartic acid, glutamic acid, lysine, arginine, cysteine, histidine, or tyrosine, and are not contained in the active portion of the polypeptide sequence, serve in their unprotonated state as a potent nucleophile to engage in various bioconjugation reactions with reactive groups attached to polymers, e.g., homo- or hetero-bi-functional PEG (e.g., Lutolf and Hubbell, Biomacromolecules 2003; 4:713-22, Hermanson, Bioconjugate Techniques, London. Academic Press Ltd; 1996). Receiver conjugation is not not restricted to polypeptides, e.g., a peptide ligand, an antibody, an antibody fragment, or aptamer but is applicable also for non-polypeptide receivers, e.g., lipids, carbohydrates, nucleic acids, and small molecules. 
     In an embodiment, the receiver may be bound to the surface of a synthetic membrane-receiver complex through a biotin-streptavidin bridge. For example, a biotinylated antibody receiver may be linked to a non-specifically biotinylated surface of the synthetic membrane-receiver complex through a streptavidin bridge. Antibodies can be conjugated to biotin by a number of chemical means (See, e.g., Hirsch et al., Methods Mol. Biol. 295: 135-154 (2004)). Any surface membrane proteins of a synthetic membrane-receiver complex may be biotinylated using an amine reactive biotinylation reagent such as, for example, EZ-Link Sulfo-NHS—SS-Biotin (sulfosuccinimidyl 2-(biotinamido)-ethyl-1,3-dithiopropionate; Pierce-Thermo Scientific, Rockford, Ill., USA; See, e.g., Jaiswal et al., Nature Biotech. 21:47-51 (2003)). For example, isolated erythroid cells may be incubated for 30 min at 4° C. in 1 mg/ml solution of sulfo-NHS-SS in phosphate-buffered saline. Excess biotin reagent is removed by washing the cells with Tris-buffered saline. The biotinylated cells are then reacted with the biotinylated antibody receiver in the presence of streptavidin to form the synthetic membrane-receiver complex. 
     In another embodiment, the receiver may be attached to the surface of, e.g., an erythroid cell or platelet with a bispecific antibody to generate the synthetic membrane-receiver complex. For example, the bispecific antibody can have specificity for the erythroid cell or platelet and the receiver. 
     In another embodiment, the receiver is attached to, e.g., an erythroid cell or platelet via a covalent attachment to generate a synthetic membrane-receiver complex. For example, the receiver may be derivatized and bound to the erythroid cell or platelet using a coupling compound containing an electrophilic group that will react with nucleophiles on the erythroid cell or platelet to form the interbonded relationship. Representative of these electrophilic groups are α,β unsaturated carbonyls, alkyl halides and thiol reagents such as substituted maleimides. In addition, the coupling compound can be coupled to a receiver polypeptide via one or more of the functional groups in the polypeptide such as amino, carboxyl and tryosine groups. For this purpose, coupling compounds should contain free carboxyl groups, free amino groups, aromatic amino groups, and other groups capable of reaction with enzyme functional groups. Highly charged receivers can also be prepared for immobilization on, e.g., erythroid cells or platelets through electrostatic bonding to generate synthetic membrane-receiver complexes. Examples of these derivatives would include polylysyl and polyglutamyl enzymes. 
     The choice of the reactive group embodied in the derivative depends on the reactive conditions employed to couple the electrophile with the nucleophilic groups on the erythroid cell or platelet for immobilization. A controlling factor is the desire not to inactivate the coupling agent prior to coupling of the receiver immobilized by the attachment to the erythroid cell or platelet. Such coupling immobilization reactions can proceed in a number of ways. Typically, a coupling agent can be used to form a bridge between the receiver and the erythroid cell or platelet. In this case, the coupling agent should possess a functional group such as a carboxyl group which can be caused to react with the receiver. One way of preparing the receiver for conjugation includes the utilization of carboxyl groups in the coupling agent to form mixed anhydrides which react with the receiver, in which use is made of an activator which is capable of forming the mixed anhydride. Representative of such activators are isobutylchloroformate or other chloroformates which give a mixed anhydride with coupling agents such as 5,5′-(dithiobis(2-nitrobenzoic acid) (DTNB), p-chloromercuribenzoate (CMB), or m-maleimidobenzoic acid (MBA). The mixed anhydride of the coupling agent reacts with the receiver to yield the reactive derivative which in turn can react with nucleophilic groups on the erythroid cell or platelet to immobilize the receiver. 
     Functional groups on a receiver polypeptide, such as carboxyl groups can be activated with carbodiimides and the like activators. Subsequently, functional groups on the bridging reagent, such as amino groups, will react with the activated group on the receiver polypeptide to form the reactive derivative. In addition, the coupling agent should possess a second reactive group which will react with appropriate nucleophilic groups on the erythroid cell or platelet to form the bridge. Typical of such reactive groups are alkylating agents such as iodoacetic acid, α, β unsaturated carbonyl compounds, such as acrylic acid and the like, thiol reagents, such as mercurials, substituted maleimides and the like. 
     Alternatively, functional groups on the receiver can be activated so as to react directly with nucleophiles on, e.g., erythroid cells or platelets to obviate the need for a bridge-forming compound. For this purpose, use is made of an activator such as Woodward&#39;s Reagent K or the like reagent which brings about the formation of carboxyl groups in the receiver into enol esters, as distinguished from mixed anhydrides. The enol ester derivatives of receivers subsequently react with nucleophilic groups on, e.g., an erythroid cell or platelet to effect immobilization of the receiver, thereby creating a synthetic membrane-receiver complex. 
     In some embodiments, the synthetic membrane-receiver complex is generated by contacting an erythroid cell with a receiver and optionally a payload, wherein contacting does not include conjugating the receiver to the erythroid cell using an attachment site comprising Band 3 (CD233), aquaporin-1, Glut-1, Kidd antigen, RhAg/Rli50 (CD241), Rh (CD240), Rh30CE (CD240CE), Rh30D (CD240D), Kx, glycophorin B (CD235b), glycophorin C (CD235c), glycophorin D (CD235d), Kell (CD238), Duffy/DARCi (CD234), CR1 (CD35), DAF (CD55), Globoside, CD44, ICAM-4 (CD242), Lu/B-CAM (CD239), XG1/XG2 (CD99), EMMPRIN/neurothelin (CD147), JMH, Glycosyltransferase, Cartwright, Dombrock, C4A/CAB, Scianna, MER2, stomatin, BA-1 (CD24), GPIV (CD36), CD108, CD139, or H antigen (CD173). 
     In some embodiments, the synthetic membrane-receiver complex comprises a receiver that is enzymatically conjugated. 
     In specific embodiments, the receiver can be conjugated to the surface of, e.g., an erythroid cell or platelet by various chemical and enzymatic means, including but not limited to those listed in table 9 to generate a synthetic membrane-receiver complex. These methods include chemical conjugation with bifunctional cross-linking agents such as, e.g., an NHS ester-maleimide heterobifunctional crosslinker to connect a primary amine group with a reduced thiol group. These methods also include enzymatic strategies such as, e.g., transpeptidase reaction mediated by a sortase enzyme to connect one polypeptide containing the acceptor sequence LPXTG (SEQ ID NO: 25) or LPXTA (SEQ ID NO: 26) with a polypeptide containing the N-terminal donor sequence GGG, see e.g., Swee et al., PNAS 2013. The methods also include combination methods, such as e.g., sortase-mediated conjugation of Click Chemistry handles (an azide and an alkyne) on the antigen and the cell, respectively, followed by a cyclo-addition reaction to chemically bond the antigen to the cell, see e.g., Neves et al., Bioconjugate Chemistry, 2013. 
     If desired, a catalytic bond-forming polypeptide domain can be expressed on or in e.g., an erythroid cell or platelet, either intracellularly or extracellularly. Many catalytic bond-forming polypeptides exist, including transpeptidases, sortases, and isopeptidases, including those derived from Spy0128, a protein isolated from  Streptococcus pyogenes.    
     It has been demonstrated that splitting the autocatalytic isopeptide bond-forming subunit (CnaB2 domain) of Spy0128 results in two distinct polypeptides that retain catalytic activity with specificity for each other. The polypeptides in this system are termed SpyTag and SpyCatcher. Upon mixing, SpyTag and SpyCatcher undergo isopeptide bond formation between Asp117 on SpyTag and Lys31 on SpyCatcher (Zakeri and Howarth, JACS 2010, 132:4526). The reaction is compatible with the cellular environment and highly specific for protein/peptide conjugation (Zakeri, B.; Fierer, J. O.; Celik, E.; Chittock, E. C.; Schwarz-Linek, U.; Moy, V. T.; Howarth, M. Proc. Natl. Acad. Sci. U.S.A. 2012, 109, E690-E697). SpyTag and SpyCatcher has been shown to direct post-translational topological modification in elastin-like protein. For example, placement of SpyTag at the N-terminus and SpyCatcher at the C-terminus directs formation of circular elastin-like proteins (Zhang et al, Journal of the American Chemical Society, 2013). 
     The components SpyTag and SpyCatcher can be interchanged such that a system in which molecule A is fused to SpyTag and molecule B is fused to SpyCatcher is functionally equivalent to a system in which molecule A is fused to SpyCatcher and molecule B is fused to SpyTag. For the purposes of this document, when SpyTag and SpyCatcher are used, it is to be understood that the complementary molecule could be substituted in its place. 
     A catalytic bond-forming polypeptide, such as a SpyTag/SpyCatcher system, can be used to attach the receiver to the surface of, e.g., an erythroid cell, to generate a synthetic membrane-receiver complex. The SpyTag polypeptide sequence can be expressed on the extracellular surface of the erythroid cell. The SpyTag polypeptide can be, for example, fused to the N terminus of a type-1 or type-3 transmembrane protein, e.g., glycophorin A, fused to the C terminus of a type-2 transmembrane protein, e.g., Kell, inserted in-frame at the extracellular terminus or in an extracellular loop of a multi-pass transmembrane protein, e.g., Band 3, fused to a GPI-acceptor polypeptide, e.g., CD55 or CD59, fused to a lipid-chain-anchored polypeptide, or fused to a peripheral membrane protein. The nucleic acid sequence encoding the SpyTag fusion can be expressed within a synthetic membrane-receiver complex. A receiver polypeptide can be fused to SpyCatcher. The nucleic acid sequence encoding the SpyCatcher fusion can be expressed and secreted from the same erythroid cell that expresses the SpyTag fusion. Alternatively, the nucleic acid sequence encoding the SpyCatcher fusion can be produced exogenously, for example in a bacterial, fungal, insect, mammalian, or cell-free production system. Upon reaction of the SpyTag and SpyCatcher polypeptides, a covalent bond will be formed that attaches the receiver to the surface of the erythroid cell to form a synthetic membrane-receiver complex. An erythroid cell comprising the receiver polypeptide fusion is an example of a synthetic membrane-receiver polypeptide complex that comprises a conjugated receiver. 
     In one embodiment, the SpyTag polypeptide may be expressed as a fusion to the N terminus of glycophorin A under the control of the Gata1 promoter in an erythroid cell. A receiver polypeptide, for example complement receptor 1 and the receivers listed in table 7, fused to the SpyCatcher polypeptide sequence can be expressed under the control of the Gata1 promoter in the same erythroid cell. Upon expression of both fusion polypeptides, an isopeptide bond will be formed between the SpyTag and SpyCatcher polypeptides, forming a covalent bond between the erythroid cell surface and the receiver polypeptide. An erythroid cell comprising the receiver polypeptide fusion is an example of a synthetic membrane-receiver polypeptide complex that comprises a conjugated receiver. 
     In another embodiment, the SpyTag polypeptide may be expressed as a fusion to the N terminus of glycophorin A under the control of the Gata1 promoter in an erythroid cell. A receiver polypeptide, for example complement receptor 1, fused to the SpyCatcher polypeptide sequence can be expressed in a suitable mammalian cell expression system, for example HEK293 cells. Upon expression of the SpyTag fusion polypeptide on the erythroid cell, the SpyCatcher fusion polypeptide can be brought in contact with the cell. Under suitable reaction conditions, an isopeptide bond will be formed between the SpyTag and SpyCatcher polypeptides, forming a covalent bond between the erythroid cell surface and the receiver polypeptide. An erythroid cell comprising the receiver polypeptide fusion is an example of a synthetic membrane-receiver polypeptide complex that comprises a conjugated receiver. 
     A catalytic bond-forming polypeptide, such as a SpyTag/SpyCatcher system, can be used to anchor a receiver molecule to the intracellular space of an erythroid cell. The SpyTag polypeptide sequence can be expressed in the intracellular space of the erythroid cell by a number of methods, including direct expression of the transgene, fusion to an endogenous intracellular protein such as, e.g., hemoglobin, fusion to the intracellular domain of endogenous cell surface proteins such as, e.g., Band 3, glycophorin A, Kell, or fusion to a structural component of the erythroid cytoskeleton. The SpyTag sequence is not limited to a polypeptide terminus and may be integrated within the interior sequence of an endogenous polypeptide such that polypeptide translation and localization is not perturbed. A receiver polypeptide can be fused to SpyCatcher. The nucleic acid sequence encoding the SpyCatcher fusion can be expressed within the same erythroid cell that expresses the SpyTag fusion. Upon reaction of the SpyTag and SpyCatcher polypeptides, a covalent bond will be formed that acts to anchor the receiver polypeptide in the intracellular space of the erythroid cell. An erythroid cell comprising the receiver polypeptide fusion is an example of a synthetic membrane-receiver polypeptide complex that comprises a conjugated receiver. 
     In one embodiment, an erythroid cell may express SpyTag fused to hemoglobin beta intracellularly. The erythroid cell may be genetically modified with a gene sequence that includes a hemoglobin promoter, beta globin gene and a SpyTag sequence such that upon translation, intracellular beta globin is fused to SpyTag at is C terminus. In addition, the erythroid cell expresses a Gata1 promoter-led gene that codes for SpyCatcher driving phenylalanine hydroxylase (PAH) expression such that upon translation, intracellular PAH is fused to SpyCatcher at its N terminus. Upon expression of both fusion proteins the SpyTag bound beta globin is linked through an isopeptide bond to the SpyCatcher bound PAH in the intracellular space, allowing PAH to be anchored to beta globin and retained during maturation. An erythroid cell comprising the receiver polypeptide fusion is an example of a synthetic membrane-receiver polypeptide complex that comprises a conjugated receiver. 
     In another embodiment, the SpyTag polypeptide can be expressed as a fusion to the receiver polypeptide within an erythroid cell. The SpyCatcher polypeptide can be expressed as a fusion to the C terminus (intracellular) of glycophorin A within the same erythroid cell. Upon expression of both fusion polypeptides, an isopeptide bond will be formed between the SpyTag and SpyCatcher polypeptides, forming a covalent bond between the membrane-anchored endogenous erythroid polypeptide and the receiver molecule. An erythroid cell comprising the receiver polypeptide fusion is an example of a synthetic membrane-receiver polypeptide complex that comprises a conjugated receiver. 
     Other molecular fusions may be formed between polypeptides and include direct or indirect conjugation. The polypeptides may be directly conjugated to each other or indirectly through a linker. The linker may be a peptide, a polymer, an aptamer, or a nucleic acid. The polymer may be, e.g., natural, synthetic, linear, or branched. Receiver polypeptides can comprise a heterologous fusion protein that comprises a first polypeptide and a second polypeptide with the fusion protein comprising the polypeptides directly joined to each other or with intervening linker sequences and/or further sequences at one or both ends. The conjugation to the linker may be through covalent bonds or ionic bonds. 
     In certain embodiments, the polypeptide receiver is loaded into the synthetic membrane-receiver polypeptide complex. Non-polypeptide receivers may also be loaded within a synthetic membrane-receiver complex. In some embodiments, synthetic membrane-receiver complexes are generated by loading, e.g., erythroid cells or platelets with one or more receivers, such that the one or more receivers are internalized within the erythroid cells or platelets. Optionally, the erythroid cells or platelets may additionally be loaded with a payload, such as, e.g., a therapeutic agent. 
     A number of methods may be used to load, e.g., erythroid cells or platelets with a receiver and optionally a payload (e.g., a therapeutic agent). Suitable methods include, for example, hypotonic lysis, hypotonic dialysis, osmosis, osmotic pulsing, osmotic shock, ionophoresis, electroporation, sonication, microinjection, calcium precipitation, membrane intercalation, lipid mediated transfection, detergent treatment, viral infection, diffusion, receptor mediated endocytosis, use of protein transduction domains, particle firing, membrane fusion, freeze-thawing, mechanical disruption, and filtration. Any one such method or a combination thereof may be used to generate the synthetic membrane-receiver complexes described herein. 
     For hypotonic lysis, e.g., erythroid cell are exposed to low ionic strength buffer causing them to burst. The receiver or the payload (e.g., a therapeutic agent) distributes within the cells. Erythroid cell, specifically red blood cells may be hypotonically lysed by adding 30-50 fold volume excess of 5 mM phosphate buffer (pH 8) to a pellet of isolated red blood cells. The resulting lysed cell membranes are isolated by centrifugation. The pellet of lysed red blood cell membranes is resuspended and incubated in the presence of the receiver and/or therapeutic agent in a low ionic strength buffer, e.g., for 30 min. Alternatively, the lysed red blood cell membranes may be incubated with the receiver or the payload (e.g., a therapeutic agent) for as little as one minute or as long as several days, depending upon the best conditions determined to efficiently load the erythroid cells. 
     Alternatively, erythroid cells, specifically red blood cells may be loaded with a receiver and optionally a payload (e.g., a therapeutic agent) using controlled dialysis against a hypotonic solution to swell the cells and create pores in the cell membrane (See, e.g., U.S. Pat. Nos. 4,327,710; 5,753,221; and 6,495,351). For example, a pellet of isolated red blood cells is resuspended in 10 mM HEPES, 140 mM NaCl, 5 mM glucose pH 7.4 and dialyzed against a low ionic strength buffer containing 10 mM NaH 2 PO 4 , 10 mM NaHCO 3 , 20 mM glucose, and 4 mM MgCl 2 , pH 7.4. After 30-60 min, the red blood cells are further dialyzed against 16 mM NaH 2 PO 4 , pH 7.4 solution containing the receiver or the payload (e.g., a therapeutic agent) for an additional 30-60 min. All of these procedures may be advantageously performed at a temperature of 4° C. In some instances, it may be beneficial to load a large quantity of erythroid cells, specifically red blood cells with a therapeutic agent by a dialysis approach and a specific apparatus designed for this purpose may be used (See, e.g., U.S. Pat. Nos. 4,327,710, 6,139,836 and 6,495,351 B2). 
     The loaded erythroid cells, specifically red blood cells can be resealed by gentle heating in the presence of a physiological solution such as, for example, 0.9% saline, phosphate buffered saline, Ringer&#39;s solution, cell culture medium, blood plasma or lymphatic fluid. For example, well-sealed membranes may be generated by treating the disrupted erythroid cells, specifically red blood cells for 1-2 mM in 150 mM salt solution of, for example, 100 mM phosphate (pH 8.0) and 150 mM sodium chloride at a temperature of 60° C. Alternatively, the cells may be incubated at a temperature of 25-50° C. for 30 min to 4 h (See, e.g., U.S. Patent Application 2007/0243137 A1). Alternatively, the disrupted red blood cells may be resealed by incubation in 5 mM adenine, 100 mM inosine, 2 mM ATP, 100 mM glucose, 100 mM Na-pyruvate, 4 mM MgCl2, 194 mM NaCl, 1.6 M KCl, and 35 mM NaH 2 PO 4 , pH 7.4 at a temperature of 37° C. for 20-30 min (See, e.g., U.S. Pat. No. 5,753,221). 
     For electroporation, e.g., erythroid cells or platelets are exposed to an electrical field which causes transient holes in the cell membrane, allowing the receiver and optional payload (e.g., therapeutic agent) to diffuse into the cell (See, e.g., U.S. Pat. No. 4,935,223). Erythroid cells, specifically red blood cells, for example, are suspended in a physiological and electrically conductive media such as platelet-free plasma to which the receiver and optional payload (e.g., therapeutic agent) is added. The mixture in a volume ranging from 0.2 to 1.0 ml is placed in an electroporation cuvette and cooled on ice for 10 min. The cuvette is placed in an electroporation apparatus such as, for example, an ECM 830 (from BTX Instrument Division, Harvard Apparatus, Holliston, Mass.). The cells are electroporated with a single pulse of approximately 2.4 milliseconds in length and a field strength of approximately 2.0 kV/cm. Alternatively, electroporation of erythroid cells, specifically red blood cells may be carried out using double pulses of 2.2 kV delivered at 0.25 μF using a Bio-Rad Gene Pulsar apparatus (Bio-Rad, Hercules, Calif., USA) to achieve a loading capacity of over 60% (Flynn et al., Cancer Lett. 82:225-229 (1994)). The cuvette is returned to the ice bath for 10-60 min and then placed in a 37° C. water bath to induce resealing of the cell membrane. Any suitable electroporation method may be used to generate the synthetic membrane-receiver complexes described herein. 
     For sonication, erythroid cells are, for example, exposed to high intensity sound waves, causing transient disruption of the cell membrane allowing the receiver and optional payload (e.g., therapeutic agent) to diffuse into the cell. Any suitable sonication method may be used to generate the synthetic membrane-receiver complexes described herein. 
     For detergent treatment, erythroid cells, for example, are treated with a mild detergent which transiently compromises the cell membrane by creating holes through which the receiver and optional payload (e.g., therapeutic agent) may diffuse. After cells are loaded, the detergent is washed from the cells. For example, the detergent may be saponin. Any suitable detergent treatment method may be used to generate the synthetic membrane-receiver complexes described herein. 
     For receptor mediated endocytosis, erythroid cells, for example, may have a surface receptor which upon binding of the receiver or payload (e.g., therapeutic agent) induces internalization of the receptor and the associated receiver or payload (e.g., therapeutic agent). Any suitable endocytosis method may be used to generate the synthetic membrane-receiver complexes described herein. 
     In some embodiments, the receiver and optional payload (e.g., therapeutic agent) may be loaded, e.g., into an erythroid cell or platelet by fusing or conjugating the receiver or payload to proteins and/or polypeptides capable of crossing or translocating the plasma membrane (See, e.g., U.S. Patent Application 2002/0151004 A1). Examples of protein domains and sequences that are capable of translocating a cell membrane include, for example, sequences from the HIV-1-transactivating protein (TAT), the  Drosophila antennapedia  homeodomain protein, the herpes simplex-1 virus VP22 protein, and transportin, a fusion between the neuropeptide galanin and the wasp venom peptide mastoparan. For example, a payload may be fused or conjugated to all or part of the TAT peptide. A receiver fusion protein containing all or part of the TAT peptide and/or a fusion protein containing all or part of the TAT peptide and the payload (e.g., a therapeutic agent, such as an antibody, enzyme, or peptide) may be generated using standard recombinant DNA methods. Alternatively, all or part of the TAT peptide (including receivers comprising all or part of the TAT peptide) may be chemically coupled to a functional group associated with the payload (e.g., therapeutic agent) such as, for example, a hydroxyl, carboxyl or amino group. In some instances, the link between the TAT peptide and the payload may be pH sensitive such that once the conjugate or fusion has entered the intracellular environment, the therapeutic agent is separated from the TAT peptide. 
     In some embodiments, the synthetic membrane-receiver complex is generated by contacting an erythroid cell with a receiver and optionally a payload without lysing and resealing the cells to incorporate the receiver and/or payload. In some embodiments, the synthetic membrane-receiver complex is generated by contacting an erythroid cell with a receiver and optionally a payload, wherein contacting does not comprise hypotonic dialysis. 
     In some embodiments, the synthetic membrane-receiver complex is generated by contacting an erythroid cell with a receiver and optionally a payload, wherein contacting does not include loading the receiver and/or payload into or onto the erythroid cell. In some embodiments, the receiver is generated in an entity that is not the erythroid cell to be contacted and/or the receiver is isolated from a sample that does not comprise the erythroid cell to be contacted. For example, for a polypeptide receiver suitable entities include a cell line, an in vitro expression system, a bacterial expression system, etc. 
     For mechanical firing, erythroid cells, for example, may be bombarded with the receiver and optional payload (e.g., therapeutic agent) attached to a heavy or charged particle such as, for example, gold microcarriers and are mechanically or electrically accelerated such that they traverse the cell membrane. Microparticle bombardment may be achieved using, for example, the Helios Gene Gun (from, e.g., Bio-Rad, Hercules, Calif., USA). Any suitable microparticle bombardment method may be used to generate the synthetic membrane-receiver complexes described herein. 
     In some embodiments, erythroid cells or platelets may be loaded with a receiver and optional payload (e.g., therapeutic agent) by fusion with a synthetic vesicle such as, for example, a liposome. In this instance, the vesicles themselves are loaded with the receiver and optional payload using one or more of the methods described herein or known in the art. Alternatively, the receiver and optional payload (e.g., therapeutic agent) may be loaded into the vesicles during vesicle formation. The loaded vesicles are then fused with the erythroid cells or platelets under conditions that enhance cell fusion. Fusion of a liposome, for example, with a cell may be facilitated using various inducing agents such as, for example, proteins, peptides, polyethylene glycol (PEG), and viral envelope proteins or by changes in medium conditions such as pH (See, e.g., U.S. Pat. No. 5,677,176). Any suitable liposomal fusion method may be used to generate the synthetic membrane-receiver complexes described herein. 
     For filtration, erythroid cells or platelets and the receiver and optional payload (e.g., therapeutic agent) may be forced through a filter of pore size smaller than the cell causing transient disruption of the cell membrane and allowing the receiver and optional therapeutic agent to enter the cell. Any suitable filtration method may be used to generate the synthetic membrane-receiver complexes described herein. 
     For freeze thawing, erythroid cells are subjected to several freeze thaw cycles, resulting in cell membrane disruption (See, e.g., U.S. Patent Application 2007/0243137 A1). In this instance, a pellet of packed red blood cells (0.1-1.0 ml) is mixed with an equal volume (0.1-1.0 ml) of an isotonic solution (e.g., phosphate buffered saline) containing the receiver and optional payload (e.g., therapeutic agent). The red blood cells are frozen by immersing the tube containing the cells and receiver and optional payload into liquid nitrogen. Alternatively, the cells may be frozen by placing the tube in a freezer at −20° C. or −80° C. The cells are then thawed in, e.g., a 23° C. water bath and the cycle repeated if necessary to increase loading. Any suitable freeze-thaw method may be used to generate the synthetic membrane-receiver complexes described herein. 
     The receiver and optional payload (e.g., therapeutic agent) may be loaded into a cell, e.g., an erythroid cell or platelet in a solubilized form, e.g., solubilized in an appropriate buffer prior to loading into erythroid cells or platelets. 
     Alternatively, the receiver and optional payload (e.g., therapeutic agent) may be loaded into a cell, e.g., an erythroid cell or platelet in a particulate form as a solid microparticulate (See, e.g., U.S. Patent Applications 2005/0276861 A1 and U.S. 2006/0270030 A1). In this instance, the receiver or payload may be poorly water-soluble with a solubility of less than 1-10 mg/ml. Microparticles of poorly water-soluble receivers or payloads can be made of less than 10 μm using a variety of techniques such as, for example, energy addition techniques such as milling (e.g., pearl milling, ball milling, hammer milling, fluid energy milling, jet milling), wet grinding, cavitation or shearing with a microfluidizer, and sonication; precipitation techniques such as, for example, microprecipitation, emulsion precipitation, solvent-anti solvent precipitation, phase inversion precipitation, pH shift precipitation, infusion precipitation, temperature shift precipitation, solvent evaporation precipitation, reaction precipitation, compressed fluid precipitation, protein microsphere precipitation; and other techniques such as spraying into cryogenic fluids (See, e.g., U.S. Patent Application 2005/0276861 A1). Water soluble receivers or payloads may also be used to form solid microparticles in the presence of various polymers such as, for example, polylactate-polyglycolate copolymer (PLGA), polycyanoacrylate, albumin, and/or starch (See, e.g., U.S. Patent Application 2005/0276861 A1). Alternatively, a water soluble receivers or payloads may be encapsulated in a vesicle to form a microparticle. The microparticles composed of the receiver and optional payload (e.g., therapeutic agent) may be incorporated into a cell, such as an erythroid cell or platelet using the methods described herein. 
     In specific embodiments, synthetic membrane-receiver complexes are generated from erythrocytes. For example, erythrocytes may be loaded with a receiver polypeptide or mRNA encoding a receiver polypetide by controlled cell injury. The cell injury can be caused by, for example, pressure induced by mechanical strain or shear forces, subjecting the cell to deformation, constriction, rapid stretching, rapid compression, or pulse of high shear rate. The controlled cell injury leads to uptake of material, e.g., a receiver and optionally a payload into the cytoplasm of the cell from the surrounding cell medium. Any suitable controlled injury method may be used to generate the synthetic membrane-receiver complexes described herein. 
     Using controlled cell injury based on controlled cell deformation (e.g., mechanical deformation of the cell as it passes through the constriction) leads to uptake of material, e.g., a receiver and optionally a payload by diffusion rather than endocytosis. The material, e.g., a receiver and optionally a payload is present in the cytoplasm rather than in endosomes following cellular uptake upon the controlled injury thereby making the material readily available to the cell. Controlled cell injury, e.g., by controlled deformation, preserves cell viability (e.g., greater than 50%, 70%, or greater than 90%). In certain embodiments, controlled cell injury, e.g., by controlled deformation, preserves the state of cellular differentiation and activity. If desired, a combination treatment is used, e.g., controlled injury by deformation followed by or preceded by, e.g., electroporation or another cell membrane permeability increasing method. Optionally, surfactants may be used. 
     Mechanical deformation methods are particularly suitable for cells that do not tolerate other membrane permeability increasing methods well, e.g., show decreased viability or a different state of differentiation after performing such methods. Mechanical deformation methods are also suitable for material, e.g., a receiver and optionally a payload that does not tolerate other membrane permeability increasing methods well. Alternatively or in addition, the receiver or payload may not be sufficiently introduced into the cell using alternative methods, e.g., because of e.g., charge, hydrophobicity, or size of the payload. 
     One exemplar method of controlled injury by deformation and devices suitable for such methods is described, e.g., in PCT Publication No. WO2013059343 INTRACELLULAR DELIVERY, incorporated herein by reference. 
     In a specific embodiment, a population of reticulocytes is provided that has been subjected to controlled cell injury by controlled deformation to introduce a receiver, thereby generating a synthetic membrane-receiver complex. The cells can, e.g., be compressed and deformed by passage through a micro-channel having a diameter less than that of an individual reticulocyte, thereby causing perturbations in the cell membrane such that the membrane becomes porous. Cells are moved, e.g., pushed, through the channels or conduits by application of pressure. The compression and deformation occurs in a delivery medium comprising, e.g., receiver polypeptide or oligonucleotide (e.g., DNA, RNA, such as mRNA) and optionally a payload. For example, the delivery medium may comprise a receiver including but not limited to those listed in table 7 or coding mRNA thereof. Upon deformation the reticulocyte takes up and retains the exogenous material. Following controlled injury to the cell by constriction, stretching, and/or a pulse of high shear rate, the cells are optionally incubated in a delivery medium that contains the material, e.g., a receiver and optionally a payload. The cells may be maintained in the delivery medium for a few minutes to recover, e.g., to close the injury caused by passing through the constriction. This may occur at room temperature. 
     Controlled cell injury as used herein includes: i) virus-mediated transfection (e.g., Herpes simplex virus, Adeno virus, Adeno-associated virus, Vaccinia virus, or Sindbis virus), ii) chemically-mediated transfection, e.g., cationic polymer, calcium phosphate, cationic lipid, polymers, and nanoparticles, such as cyclodextrin, liposomes, cationic liposomes, DEAE-dextran, polyethyleneimine, dendrimer, polybrene, calcium phosphate, lipofectin, DOTAP, lipofectamine, CTAB/DOPE, DOTMA; and iii) physically-mediated transfection, including direct injection, biolistic particle delivery, electroporation, laser-irradiation, sonoporation, magnetic nanoparticles, and controlled deformation (e.g., cell squeezing), as exemplified by micro-needle, nano-needle, femtosyringe, atomic-force microscopy (AFM) tip, gene gun (e.g., gold nanoparticles), Amaxa Nucleofector, phototransfection (multi-photon laser), impalefection, and magnetofection, and other suitable methods known in the art. Any suitable method may be used to obtain a synthetic membrane-receiver complex described herein comprising one or more DNA, RNA (e.g., mRNA encoding a receiver polypeptide), or receiver polypeptides and optionally a payload (e.g., a therapeutic agent). 
     Polypeptide receivers can be detected on the synthetic membrane-receiver complex. The presence of the receiver polypeptide can be validated and quantified using standard molecular biology methods, e.g., Western blotting or FACS analysis. Receiver polypeptides present in the intracellular environment may be quantified upon cell lysis or using fluorescent detection. 
     For example, a population of erythroid cells is loaded with adenosine deaminase (ADA) using the Pro-Ject protein transfection reagent kit to generate a synthetic membrane-ADA receiver complex. The population of synthetic membrane-ADA receiver complexes is then characterized for active enzyme loading using LCMS to quantify adenosine and inosine. 
     Alternatively, the population of erythroid cells is incubated in a solution of 10 mM, 100 mM, 500 mM chlorpromazine and 0.01, 0.1, 1.0, 10, 100 mg/ml of adenosine deaminase (ADA). The population of synthetic membrane-ADA receiver complexes are then washed and fluorescent imaging is used to quantify ADA loading. 
     In one embodiment, a population of erythrocytes is incubated in a hypotonic salt solution containing a concentration of 0.01, 0.1, 1.0, 10 mg/ml of asparaginase to generate a synthetic membrane-asparaginase receiver complex. The cell population is incubated for 1 hr and then resealed by incubation in a hypertonic solution for 10 min. The population of synthetic membrane-asparaginase receiver complexes is then incubated in an asparagine solution for 1 hr and the asparagine and aspartate concentrations are quantified using LCMS. 
     To generate a synthetic membrane-thymidine phosphorylase receiver complex, a population of erythrocytes is incubated in a PBS solution containing a concentration of 0.01, 0.1, 1.0, 10 mg/ml of thymidine phosphorylase that has been fused via both the C and N termini to one or more cell penetrating peptides, including; Penetratin, Antenapedia, TAT, SynB1, SynB3, PTD-4, PTD-5, FHV Coat-(35-49), BMV Gag-(7-25), HTLV-II Rex-(4-16), D-TAT, R9-Tat, Transportan, MAP, SBP, FBP, MPG ac, MPG(NLS), Pep-1, Pep-2, polyarginines, polylysines, (RAca)6R, (RAbu)6R, (RG)6R, (RM)6R, R10, (RA)6R, R7. Following incubation, synthetic membrane-thymidine phosphorylase receiver complexes are placed in a solution of thymidine for 1 hr and samples are quantified for thymine and thymidine content using LCMS. 
     Cells may be loaded using a microfluidic device that transiently porates the cells, allowing a payload to enter when the cells are pressured through the system. In one embodiment, a population of erythrocytes is pressured through a system of microfluidic channels in a buffer solution containing 0.01, 0.1, 1.0, 10 mg/ml of phenylalanine ammonia hydroxylase. The cell suspension is then characterized for enzymatic activity using LCMS to quantify phenylalanine and trans-cinnamic acid. 
     In one embodiment, a synthetic cell membrane-receiver complexes are incubated in a hypotonic solution containing 1 mM of adenosine deaminase for 1 hr. The synthetic membrane-receiver complexes are then transferred to an isotonic solution and allowed to equilibrate and seal in the soluble protein. 
     In some embodiments, universal acceptor erythroid cells comprising a docking polypeptide may be used to attach a payload (e.g. a polypeptide) or a receiver (e.g. a polypeptide receiver) to the cell. 
     Provided herein are erythroid cells comprising a docking polypeptide on its surface that comprises a high-affinity acceptor site for specific small donor molecules. In some embodiments, the docking polypeptide is less than about 75 kDa, 70 kDa, 65 kDa, 60 kDa, 55 kDa, 50 kDa, 45 kDa, 40 kDa, 35 kDa, 30 kDa, 25 kDa, or less than about 20 kDa. In some embodiments, the docking polypeptide is at least about 5 kDa, 10 kDa, 15 kDa or at least about 20 kDa. In some embodiments, the docking polypeptide is encoded by an exogenous nucleic acid that can be transfected by any method known in the art or described herein. In some embodiments, the transfected erythroid cells are induced to undergo enucleation in culture. In such embodiments, the docking polypeptide is retained by the erythroid cell whereas the exogenous nucleic acid is not retained. If desired, the erythroid cell may comprise a high density of docking polypeptides on its surface, such as, e.g., at least about 5,000 copies, 10,000 copies, 25,000 copies, 50,000 copies, 100,000 copies, 500,000 copies, 1,000,000 copies, or at least about 5,000,000 copies of the docking polypeptide. In some embodiments, substantially homogenous populations of erythroid cells comprising a docking polypeptide are generated, such as populations in which at least about 60%, 70%, 80%, 90%, 95%, 97%, 98%, 99%, or at least about 99.8% of erythroid cells are enucleated. 
     If desired, these populations of cells can be further purified as described herein and then contacted with a polypeptide that comprises a donor molecule that binds to the acceptor site of the docking polypeptide with high affinity, thereby attaching the polypeptide to the erythroid cell. Any desired polypeptide can be attached. In some embodiments, the polypeptide is a receiver polypeptide. The binding of the acceptor site and the donor molecule may be very strong, such that the dissociation constant (K d ) for the binding between the acceptor site and the donor molecule of about 100 nanomolar (nM), 10 nM, 1 nM, 100 picomolar (pM), 10 pM, 1 pM, 500 femtomolar (fM), 250 fM, 100 fM, 50 fM, 25 fM, or about 10 fM or less. The dissociation constant (the equilibrium dissociation constant between the acceptor site and the donot molecule) can be measured using any technique known in the art (see, e.g. Orosz, et al. J. Immunol. Meth. 270, 2002, 155-162; Pollard T D, Mol. Biol. Cell, 2010, vol. 21 no. 23 4061-4067). The dissociation constant can be, e.g., measured in phosphate buffered saline at a low temperature (e.g. on ice), such as 4° C. In some embodiments, the dissociation constant is measured in a system that mimics in vivo conditions, such as, for example in serum at 37° C. The stringency of the condition can be adjusted as desired, e.g. by increasing the temperature, lowering or increasing the salt concentration, and increasing the serum concentration (e.g. 1%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% up to 100% serum). 
     Any receiver molecule comprising a suitable donor molecule may be attached to the erythroid cell through the interaction of the donor molecule and the acceptor site, thereby allowing for the generation of any desired therapeutic erythroid cell, carrying a receiver polypeptide with a specific function. In some embodiments, the receiver polypeptide is capable of interacting with a target molecule, e.g. in the circulatory system of a subject upon administration of an effective amount of the erythroid cells comprising the receiver (bound to the docking polypeptide) to a subject in need thereof. In some embodiments, the target molecule is a circulating self-antibody, a circulating complement cascade factor, a circulating clotting cascade factor, a circulating immune complex, a circulating serum amyloid protein, a circulating toxin, a circulating metabolite, or an anti-drug antibody. 
     Exogenous nucleic acids encoding the docking polypeptide (e.g. DNA or mRNA) can be introduced into the cells at early stages of differentiation, e.g. into erythroid progenitor or erythroid precursor cells that still contain a nucleus, by any suitable method known in the art and described herein. The transfected cells may be cultured and the docking polypeptide expressed. In some embodiments, the docking polypeptide can be targeted to the cell surface, e.g. by comprising a secretory signal, and/or the docking polypeptide may comprise a transmembrane or membrane-associating domain such that the docking protein is retained on the cell surface. The docking polypeptide is then retained on the cell surface during terminal differentiation of the erythroid cell, which includes enucleation. The membrane-associating domain can be exogenous or endogenous to the erythroid cell. In some embodiments, the docking polypeptide is a chimeric fusion, for example a fusion of an exogenous domain comprising the high-affinity acceptor site to an endogenous erythroid membrane protein, e.g. GPA. 
     It has been shown herein that the number of polypeptides expressed per erythroid cell is inversely correlated to the size of the polypeptide. Smaller polypeptides are more highly expressed ( FIG. 19 ). In some embodiments, the docking polypeptide is less than about 75 kDa, 70 kDa, 65 kDa, 60 kDa, 55 kDa, 50 kDa, 45 kDa, 40 kDa, 35 kDa, 30 kDa, 25 kDa, or less than about 20 kDa to provide for high levels of expression, e.g. at least about 5,000 copies, 10,000 copies, 25,000 copies, 50,000 copies, 100,000 copies, 500,000 copies, 1,000,000 copies, or at least about 5,000,000 copies of the docketing polypeptide. 
     In some embodiments, in which it is not possible to express large polypeptide receivers (e.g. polypeptide receivers of at least about 80 kDa, 90 kDa, 100 kDa, 150 kDa, 200 kDa, 250 kDa, 300 kDa, 400 kDa, or at least about 500 kDa), such as complex single- or multi-domain proteins, it is advantageous to generate erythroid cells comprising a small docking polypeptide on the surface comprising a high affinity site and then attaching a separately produced receiver polypeptide comprising a donor molecule that binds to the high affinity site to the erythroid cell. For the production of receiver polypeptides any suitable protein expression system may be used, many of which are routinely used in the art. Donor molecules can routinely be attached to the polypeptide receivers using well known chemical and/or enzymatic methods, e.g. employing linkers or by directly attaching the donor molecule to a suitable amino acid side chain of the receiver polypeptide. The conjugation of the donor molecule to the receiver polypeptide may occur either in a site-specific or site-non-specific manner and/or with one-to-one stoichiometry or greater than one-to-one stoichiometry. For chemical conjugation, the small donor molecule may be modified with, e.g. an NHS ester to bind free amines or a maleimide group to bind free sulfhydryls on the polypeptide receiver. The receiver polypeptide can be produced recombinantly with a tag such that the conjugation reaction takes place site-specifically, e.g. a BirA biotin acceptor tag for in situ biotinylation, or a sortag to enable sortase-mediated conjugation of the small donor molecule to the receiver polypeptide. 
     In some embodiments, the docking polypeptide comprising the high-affinity acceptor site is generated recombinantly, e.g. by using a recombinant protein expression system and isolated. The isolated recombinant docking polypeptide is then contacted with the surface of a primary erythroid cell. Conditions are selected that are suitable for the insertion of the docking polypeptide into the plasma membrane of the cell. Subsequently, the erythroid cell comprising the inserted docking polypeptide is contacted with a recombinantly produced polypeptide comprising the donor molecule (such as a polypeptide receiver) under conditions suitable for binding of the donor molecule to the acceptor site to generate erythroid cells comprising the polypeptide on the surface. This method does not employ transfections of exogenous nucleic acids encoding the docking polypeptide and does not rely on the expression of the docking polypeptide by the cell. In some embodiments, the erythroid cells comprising the docking polypeptide that comprises the high affinity acceptor site are contacted with the receiver polypeptide comprising the donor molecule under conditions sufficient for binding to occur. For example, the reaction temperature, buffer conditions (e.g. salt concentrations and pH) and incubations time may be suitably adjusted. The resulting erythroid cell comprises a polypeptide receiver with the desired functionality that is tightly attached to the surface of the cell. See,  FIG. 20 . 
     The high affinity acceptor site and the donor molecule may bind with very high affinity, such as picomolar or femtomolar affinity. For example, the biotin-avidin interaction is known to be about 50 fM. In some embodiments, the high affinity acceptor site (on the docking polypeptide) comprises an scFv. In some embodiments, the donor molecule (linked to the receiver polypeptide) is a small molecule such as biotin, digoxin or FITC. Such interactions create high-affinity binding, see e.g. Boder et al., Proc Natl Acad Sci USA. 2000 Sep. 26; 97(20):10701-5). High-affinity binding interactions in the picomolar or femtomolar range are functionally equivalent to a covalent bond. For example, a 10 fM interaction is estimated to dissociate with a half-life of about 22 years, a 100 fM dissociates with a half-life of about 2 years, and a 1 pM dissociates with a half-life of about 1.5 months. The half-life typically expected for erythroid cells in circulation is from between days and weeks (e.g. about 10 days, 20 days, 40 days, 60 days, 80 days, 100 days, or 120 days). Typical polypeptide binders to a native erythroid cell protein, e.g. a polypeptide binder of GPA dissociate with a half-life of minutes to hours (see e.g. Kontos et al., Proc Natl Acad Sci USA. 2013 Jan. 2; 110(1):E60-8). A further advantage of the high-affinity binding is that the contacting of the receiver polypeptide and the erythroid cell results in high efficiency binding, without the need for a large excess of receiver polypeptide or enzymes to catalyze the conjugation (as e.g. a sortase, see e.g. PCT Publication No. WO 2014/183071). 
     In some embodiments, the surface of the erythroid cells is not biotinylated. In some embodiments, a biotinylated receiver polypeptide is used to attach the receiver to the erythroid cell, however, the cell is not biotinylated but comprises a docking polypeptide that comprises a high affinity acceptor site for the biotin donor molecule on the receiver polypeptide. In embodiments using biotinylated polypeptide receivers, the receivers are not attached to the surface of the erythroid cell through a streptavidin or avidin sandwich (See, e.g. Muzykantov et al., Transl Stroke Res 2012 3(1):114-121, and U.S. Pat. No. 8,211,656). The use of avidin or streptavidin to attach the receiver polypeptide is thought to elicit an immune response by a human subject&#39;s immune system in response to the highly immunogenic avidin or streptavidin. The immune response in turn is thought to lead to a rapid clearing of the avidin or streptavidin coated erythroid cell from the circulatory system of the subject, thereby potentially significantly decreasing the half-life of the erythroid cell in circulation and thereby its therapeutic utility. Further, biotinylation of the surface of the cell by direct chemical conjugation is thought to damage the cell&#39;s surface which can be detrimental to its efficient circulation in vivo (see e.g. Wang, Langer, et al., Advanced Drug Delivery Reviews 2014 in press). 
     Further provided herein are methods for generating erythroid cells comprising a docking polypeptide on their surface. The methods, in some embodiments, include the steps of: providing isolated erythroid cells, introducing an exogenous nucleic acid encoding a docking polypeptide comprising a high-affinity acceptor site into the erythroid cells, culturing the erythroid cells, and inducing enucleation of the erythroid cells to obtain a population of enucleated erythroid cells comprising a docking polypeptide. 
     Provided herein are culture-based methods for the modification, expansion and differentiation of erythroid cells that express or comprise an exogenous receiver polypeptide such that, when administered to the patient, the receiver enhanced erythroid cell is therapeutically or diagnostically active. A culture-based platform is significantly broader than a primary cell-based platform in which primary erythroid cells are modified with a recombinantly-expressed biotherapeutic, as the marginal effort required to test a new receiver polypeptide is limited only by gene synthesis and protein expression. Additionally, the erythroid cells produced from a culture process are, in some embodiments, i) homogeneous, ii) at the same stage of maturation, and/or iii) can be controlled to express a consistent amount of receiver polypeptide within populations of cells. 
     In some embodiments, erythroid cells, for example red blood cells, reticulocytes, or erythrocytes, are provided that comprise a receiver polypeptide that acts as a therapeutic agent. Methods for the delivery of an exogenous nucleic acid encoding the receiver polypeptide into an erythroid cell, for example an erythroid progenitor or erythroid precursor cell, are provided. These methods are particularly useful because they leverage the endogenous nuclear and cytoplasmic protein-manufacturing machinery of the erythroid cell to produce the receiver at potentially high levels, e.g. more than 1,000 copies, more than 5,000 copies, more than 10,000 copies, more than 25,000 copies, more than 50,000 copies, more than 75,000 copies, more than 100,000 copies, more than 500,000 copies, more than 1,000,000 copies, more than 2,000,000 copies, or more than 5,000,000 copies within the erythroid cell or on the surface of the erythroid cell. In some embodiments, the receiver is subjected to post-translational modifications by the endogenous protein machinery. It is desirable to use methods of delivery of exogenous nucleic acids that do not greatly damage the cytoskeleton or cell membrane components of the target erythroid cell. 
     Hypotonic dialysis, a common method for the introduction of exogenous nucleic acids and polypeptides to a cell, e.g., an erythrocyte ghost, suffers from major drawbacks, such as, e.g. that the process damages erythrocyte membranes, changes their osmotic fragility and phosphatidylserine externalization, and causes cytoskeletal rearrangements. (Favretto, M. E. Control. Release Off. J. Control. Release Soc. 170, 343-351 (2013); Gutierrez Millán, C. M. Mol. Dis. 33, 132-140 (2004)). These changes negatively affect the biophysical properties of the cells. For example, hypotonically-treated erythrocytes are cleared more rapidly than expected from circulation (2-3 weeks) and suffer significantly reduced shelf-life that prevents their long-term storage (only 72 hours). (Erytech Pharma. 2013 Annual Financial Report and Management Report. (2014)). Erythrocyte ghosts are subject to rapid clearance by the reticulo-endothelial system (see, e.g., Loegering et al. 1987 Infect Immun 55(9):2074). Hypotonic dialysis can induce a high degree of hemolysis, irreversible modifications in the morphology of the cells and phosphotidyl serine exposure, which has been recognized as an important parameter associated with premature red blood cells removal and induction of transfusion-related pathologies (Favretto 2013 J Contr Rel). 
     Other methods that include, e.g., chemical surface modification of cells, damage erythrocytes and also result in their rapid clearance from circulation. (Wang, Q. et al. Adv. Drug Deliv. Rev. (2014)). 
     Provided herein are methods for introducing exogenous nucleic acids to erythroid cells that include culturing of the cells. Such methods provide advantages over hypotonically treated erythrocytes. For example, cultured erythroid cells can express multiple classes of polypeptides, including surface polypeptides and intracellularly (cytosolic) located polypeptides. In some embodiments, the polypeptide receivers are over-expressed native membrane proteins. In some embodiments, the polypeptide receivers comprise chimeric fusions to membrane proteins. In such cases, the membrane portion of the chimeric fusion may be of a membrane protein that is endogenous to the cell or it may be exogenous to the cell. 
     In certain embodiments, receiver polypeptides that are expressed by the eryhtroid cell in culture from the exogenous nucleic acid incorporated in the cell exhibit proper post-translational modifications. In some embodiments, the cells are derived from a human and the receivers display post-translational modifications typically detected in humans. For exogenous polypeptides that are incorporated post-translational into a cell, e.g. by hypotonic dialysis, the post-translational modification displayed by the exogenous polypeptide depend on production host (such as, e.g. a bacterium, yeast, fly cell, frog, bird etc.). In case of non-human or non-mammalian expression hosts the post-translational modification may prove, e.g., to be immunogenic or toxic, which can have important consequences on efficacy and raise safety concerns for in vivo treatments of human subjects. (Moremen, K. W. Nat. Rev. Mol. Cell Biol. 13, 448-462 (2012)). 
     One method commonly used to introduce exogenous nucleic acid content into an erythroid cell is to use a virus, e.g. a retrovirus or a lentivirus. This method does not rely on hypotonic dialysis. Viral gene delivery has a number of advantages, including high efficiency transduction, easy production, commercially available reagents, and high evolved infectivity. A challenge to virus-mediated transduction of erythroid cells is that the efficiency of transduction is inversely correlated with the size of the genetic payload or exogenous nucleic acid, i.e. with the size of the provirus, which is the genetic material of a virus that is incorporated into, and able to replicate with, the genome of the host cell. This phenomenon has been explored, e.g. by Kumar et al., Human Gene Therapy, 2001, 12:1893-1905 and by Yacoub et al., Journal of Gene Medicine, 2007, 9: 579-584. What is observed is that the transduction efficiency, as measured by the number of cells in culture that successfully express the transgene, is reduced by one log when the provirus reaches a length of about 7 kb. Commercially-available lentivirus vectors have backbones that often comprise non-insert regions such as, e.g., the promoter, 5′ and 3′ untranslated regions, poly-A tail, selection marker, GFP or other fluorescent protein for identifying efficiency of transduction, and multiple cloning site. These functionalities contribute to reducing the amount of sequence available for the insert. For example, the lenti vector pCDH available from System Biosciences Inc. has a backbone non-insert size of approximately 3000 nucleotides. Inserts of more than 3-4 kb will significantly reduce the number of productive lentiviruses. 
     Provided herein are methods for the delivery of large exogenous nucleic acids, such as nucleic acids of about 1 kb, 1.5 kb, 2 kb, 2.5 kb, 3 kb, 3.5 kb, 4 kb, 4.5 kb, 5 kb, 5.5 kb, 6 kb or more that when packaged inside a viral vector do not achieve high transduction efficiencies within erythroid cells in culture. High transduction efficiencies included at least 10% transfected cells, at least 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or at least 95% transfected cells. 
     Receiver polypeptides that may be encoded by large exogenous nucleic acids and which may not effectively be transfected using viral delivery (such as, e.g., lentiviral delivery) include, but are not limited to factors of the coagulation cascade, e.g., Factor V, Factor VIII, or ADAMTS13; enzymes of the complement cascade, e.g., Factor H and Complement Receptor 1; or cell-modifying enzymes, e.g., Cas9 and TALENs. Provided herein are non-viral delivery methods specifically suited for delivery of large exogenous nucleic acids (that encode a polypeptide receiver) to cells, such as erythroid cells. It should be understood that the methods may also be used for delivery of short exogenous nucleic acids (that encode a polypeptide receiver), e.g. nucleic acids of less than 1 kb, 0.75 kb, 0.5 kb, or less than 0.25 kb to cells. 
     In some embodiments, the methods provided herein for the delivery of large exogenous nucleic acids (specifically RNAs, such as mRNA) into erythroid cells (such as, e.g., precursor or progenitor cells) include contacting the erythroid cell with the exogenous nucleic acid and introducing the nucleic acid by electroporation under conditions effective for delivery of the nucleic acid to the cell, such as those described herein. Suitable electroporators include, but are not limited to, the Bio-Rad GENE PULSER and GENE PULSER II; the Life Technologies NEON; BTX GEMINI system; and MAXCYTE electroporator. These methods do not require viral delivery or the use of viral vectors. Suitable nucleic acids include RNAs, such as mRNAs. Suitable nucleic acids also include DNAs, including transposable elements, stable episomes, plasmid DNA, or linear DNA. 
     Conditions for the electroporation of cell lines, e.g. K562 erythroleukemia cells, have been described in the literature, e.g. by Van Tendeloo et al., Blood 2001 98(1):49-56. Effective conditions for cultured erythroid cells that were differentiated from primary cell progenitors have not been described. It has been shown herein (see Examples) that the conditions differ and that electroporation conditions and parameters must be adapted to promote successful uptake of large exogenous nucleic acids by erythroid cells. More than 50 different conditions for electroporation were tested. Transfection efficiencies generally ranged from 0.1% transfected cells to more than 85% transfected cells. Further, as the cells continue to differentiate in culture, different electroporation conditions were found to be required to achieve high transgene uptake and expression (e.g. at least 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or at least 97%) while maintaining high viability (e.g. at least 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or at least 97%). More than 50 conditions were tested on cells over the course of an approximately 20 day differentiation culture to identify conditions that were conducive to good transfection and good viability. 
     Suitable electroporation conditions for the methods described herein include for a Life Technologies Neon Transfection System: a pulse voltage ranging from about 500 to about 2000 V, from about 800 to about 1800 V, or from about 850 to about 1700 V; a pulse width ranging from about 5 to about 50 msec, or from about 10 to about 40 msec; and a pulse number ranging from 1 to 2 pulses, 1 to 3 pulses, 1 to 4 pulses, or 1 to 5 pulses. 
     Particularly suitable conditions for electroporation of erythroid cells in culture under differentiation conditions include, e.g. for 4 days: a) pulse voltage 1300-1400, pulse width: 10-20 msec, number of pulses: 1-3; b) pulse voltage 1400, pulse width: 10 msec, number of pulses: 3; c) pulse voltage 1400, pulse width: 20 msec, number of pulses: 1; and d) pulse voltage 1300, pulse width: 10 msec, number of pulses: 3. 
     Particularly suitable conditions for electroporation of erythroid cells in culture under differentiation conditions include, e.g. for 8-9 days: a) pulse voltage: 1400-1600, pulse width: 20, number of pulses: 1; b) pulse voltage: 1100-1300, pulse width: 30, number of pulses: 1; c) pulse voltage: 1000-1200, pulse width: 40, number of pulses: 1; d) pulse voltage: 1100-1400, pulse width: 20, number of pulses: 2; e) pulse voltage: 950-1150, pulse width: 30, number of pulses: 2; f) pulse voltage: 1300-1600, pulse width: 10, number of pulses: 3. These conditions generally lead to transfections efficiencies of at least about 60% or more (e.g. at least about 65%, 70%, 75%, 80%, 85%, 90%, 95% or at least about 97%, or more), and cell viability of at least about 70% or more (e.g. at least about 75%, 80%, 85%, 90%, 95% or at least about 97%, or more). 
     Particularly suitable conditions for electroporation of erythroid cells in culture under differentiation conditions include, e.g. for 12-13 days: a) pulse voltage: 1500-1700, pulse width: 20, number of pulses: 1; and b) pulse voltage: 1500-1600, pulse width: 10, number of pulses: 3. These conditions generally lead to transfections efficiencies of at least about 50% or more (e.g. at least about 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or at least about 97%, or more), and cell viability of at least about 70% or more (e.g. at least about 75%, 80%, 85%, 90%, 95% or at least about 97%, or more). 
     The conditions disclosed herein with reference to the Life Technologies Neon system can easily be adjusted by one of ordinary skill in the art to fit a different electroporator and/or different electroporation set-ups with only routine experimentation and the specific electroporator described herein is not limiting for the methods disclosed. 
     In some embodiments, using the electroporation conditions described herein cultured erythroid cells are electroporated for a first time, then cultured for a desired period of time (optionally under differentiation conditions) and then re-electroporated a second time. In some embodiments, cultured erythroid cells are electroporated for a first time, then cultured for a desired period of time (optionally under differentiation conditions) and then re-electroporated a second, third, fourth, fifth, or sixth time. Optionally, the culturing period in between the first and second, the second and third, etc. electroporation can be varied. For example, the period in between electroporations may be adjusted as desired, e.g. the period may be 30 minutes, 1 hour, 6 hours, 12, hours, 18 hours, 24 hours, 30 hours, 36 hours, 48 hours, 3 days, 4 days, 5 days, 6 days, 7 days, 8 days, 9 days, 10 days, 11 days 12 days, 13 days 14 days, or, e.g. 21 days. For example, cells may be electroporated on day 1 and 2, 1 and 3, 1 and 4, 1 and 5, 1 and 6, 1 and 7, 1 and 8, 1 and 9, 1 and 10, 1 and 11, 1 and 12, 1 and 13, 1 and 14, 1 and 15, or 1 and 16. In another example, cells may be electroporated on day 2 and 3, 2 and 4, 2 and 5, 2 and 6, 2 and 7, 2 and 8, 2 and 9, 2 and 10, 2 and 11, 2 and 12, 2 and 13, 2 and 14, 2 and 15, or 2 and 16. In yet another example, cells may be electroporated on day 3 and 4,3 and 5,3 and 6,3 and 7,3 and 8, 3 and 9, 3 and 10, 3 and 11, 3 and 12, 3 and 13, 3 and 14, 3 and 15, or 3 and 16. In yet another example, cells may be electroporated on day 4 and 5, 4 and 6, 4 and 7, 4 and 8, 4 and 9, 4 and 10, 4 and 11, 4 and 12, 4 and 13, 4 and 14, 4 and 15, or 4 and 16. In yet another example, cells may be electroporated on day 5 and 6, 5 and 7, 5 and 8, 5 and 9, 5 and 10, 5 and 11, 5 and 12, 5 and 13, 5 and 14, 5 and 15, or 5 and 16. In yet another example, cells may be electroporated on day 6 and 7, 6 and 8, 6 and 9, 6 and 10, 6 and 11, 6 and 12, 6 and 13, 6 and 14, 6 and 15, or 6 and 16. In yet another example, cells may be electroporated on day 7 and 8, 7 and 9, 7 and 10, 7 and 11, 7 and 12, 7 and 13, 7 and 14, 7 and 15, or 7 and 16. In yet another example, cells may be electroporated on day 8 and 9, 8 and 10, 8 and 11, 8 and 12, 8 and 13, 8 and 14, 8 and 15, or 8 and 16. In yet another example, cells may be electroporated on day 9 10, 9 and 11, 9 and 12, 9 and 13, 9 and 14, 9 and 15, or 9 and 16. In yet another example, cells may be electroporated on day 10 and 11, 10 and 12, 10 and 13, 10 and 14, 10 and 15, or 10 and 16. In yet another example, cells may be electroporated on day 11 and 12, 11 and 13, 11 and 14, 11 and 15, or 11 and 16. In yet another example, cells may be electroporated on day 12 and 13, 12 and 14, 12 and 15, or 12 and 16. In yet another example, cells may be electroporated on day 13 and 14, 13 and 15, or 13 and 16. In yet another example, cells may be electroporated on day 14 and 15, or 14 and 16. Optionally, the erythroid cells may be electroporated more than twice, e.g., three times, four times, five times, or six times and the interval may be selected as desired at any points of the differentiation process of the cells. 
     In some embodiments, using the electroporation conditions described herein, cultured erythroid cells are electroporated on day 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16 of differentiation. 
     In some embodiments, using the electroporation conditions described herein, cultured erythroid cells are electroporated when the cells (e.g., at least 50%, 60%, 70%, 80%, 90%, or 95% of the cells in a population) are at one of the following stages in erythrocyte differentiation, which are listed in temporal order of differentiation: 
     Progenitor Cells: 
     Hematopoietic stem/progenitor cell (HSC, HSPC) 
     Common myeloid progenitor cell (CMP) 
     Megakaryocyte erythrocyte progenitor cell (MEP) 
     Burst-forming unit—erythrocyte (BFU-E) 
     Colony-forming unit—erythrocyte (CFU-E) 
     Precursor Cells: 
     Pro-erythroblast 
     Early basophilic erythroblast (“early baso”) 
     Late basophilic erythroblast (“late baso”) 
     Polychromatic erythroblast (“poly”) 
     Orthochromatic erythroblast (“ortho”) 
     Reticulotye 
     Erythrocyte 
     More specifically, in some embodiments, the cells are electroporated when at least 50%, 60%, 70%, 80%, or 90% of the cells are CFU-E cells. In some embodiments, the cells are electroporated when at least 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the cells are precursors, e.g., one or more of pro-erythroblast, early basophilic erythroblast, or late basophilic erythroblast. 
     In some embodiments, using the electroporation conditions described herein, cultured erythroid cells are electroporated when the cells (e.g., at least 50%, 60%, 70%, 80%, 90%, or 95% of the cells in a population) display one or more of the following marker combinations, which are listed in temporal order of differentiation: 
     GPA-negative, IL3R-positive 
     GPA-negative, IL3R-negative, e.g., also CD34-positive, CD36-negative 
     GPA-negative, IL3R-negative, e.g., also CD34-positive, CD36-positive 
     GPA-negative, IL3R-negative, e.g., also CD34-negative, CD36-positive 
     GPA-positive, e.g., also Band 3-negative, Alpha 4 integrin-positive 
     GPA-positive, e.g., also Band 3-positive, Alpha 4 integrin-positive 
     GPA-positive, e.g., also Band 3-positive, Alpha 4 integrin-negative 
     More specifically, in some embodiments, the cells are electroporated when at least 50%, 60%, 70%, 80%, or 90% of the cells are GPA-negative, CD34-positive, and CD36-positive. In some embodiments, the cells are electroporated when at least 40%, 50%, 60%, 70%, 80%, or 90% of the cells are CPA-negative. In some embodiments, the cells are electroporated when at least 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the cells are GPA-positive. 
     Another suitable marker is C-Kit, which is a stem cell factor receptor and is typically high in progenitor cells. 
     In some embodiments, the cells are electroporated when the cells (e.g., at least 50%, 60%, 70%, 80%, 90%, or 95% of the cells in a population) are positive for one or more of C-kit, GPA, IL3R, CD34, CD36, CD71, Band 3, hemoglobin, and Alpha 4 integrin, or a combination thereof. In some embodiments, the cells are electroporated when the cells (e.g., at least 50%, 60%, 70%, 80%, 90%, or 95% of the cells in a population) are negative for one or more of C-kit, GPA, IL3R, CD34, CD36, Band 3, and Alpha 4 integrin, or a combination thereof. 
     In some embodiments, the cells are electroporated when the cells (e.g., at least 50%, 60%, 70%, 80%, 90%, or 95% of the cells in a population) are positive for one or more of GPA, IL3R, CD34, CD36, Band 3, hemoglobin, and Alpha 4 integrin, or a combination thereof. In some embodiments, the cells are electroporated when the cells (e.g., at least 50%, 60%, 70%, 80%, 90%, or 95% of the cells in a population) are negative for one or more of GPA, IL3R, CD34, CD36, CD71, Band 3, and Alpha 4 integrin, or a combination thereof. 
     In some embodiments, the cells are electroporated when the cells (e.g., at least 50%, 60%, 70%, 80%, 90%, or 95% of the cells in a population) are positive for one or more of C-kit, GPA, and CD34 or a combination thereof. In some embodiments, the cells are electroporated when the cells (e.g., at least 50%, 60%, 70%, 80%, 90%, or 95% of the cells in a population) are negative for one or more of C-kit, GPA, and CD34, or a combination thereof. 
     In some embodiments, the cells are electroporated when the cells (e.g., at least 50%, 60%, 70%, 80%, 90%, or 95% of the cells in a population) are positive for one or both of C-kit and GPA. In some embodiments, the cells are electroporated when the cells (e.g., at least 50%, 60%, 70%, 80%, 90%, or 95% of the cells in a population) are negative for one or both of C-kit and GPA. 
     In some embodiments, the erythroid cells are transfected using the electroporation methods described herein with an mRNA encoding a desired receiver polypeptide or another polypeptide. Unlike viral DNA vectors such as a lentivirus, the mRNAs do not integrate into the genome of the host cell. In some embodiments, the transfected mRNA is only transiently expressed, e.g. for 1-6 hours, 6-12 hours, 12-18 hours, 18-24 hours, 24-30 hours, 30-36 hours, up to 48 hours, up to 72 hours, up to 96 hours, up to 5 days, up to 6 days, up to 7 days, up to 8 days, up to 9 days, up to 10 day, up to 11 days, up to 12 days, up to 13 days, or up to 14 days. If desired, an erythroid cell may be transiently transfected once, twice, three times, four times or more times, e.g. to boost the levels of the expressed polypeptide at different time periods and/or intervals or, e.g., for the entire period required for an erythroid cell to arrive at the desired stage of differentiation in culture. 
     The transient nature of the expression of the desired polypeptide (such as a receiver polypeptide) further provides a significant advantage when the transiently transfected erythroid cell population has reached the desired state of differentiation and the cells are purified and formulated into a pharmaceutical product as described herein. In some embodiments, at the state of desired differentiation, the erythroid cells do not retain a significant amount of transfected, exogenous mRNA because the mRNA does not integrate into the host genome (e.g. the amount of exogenous mRNA is below the level of detection or at a level that otherwise is considered safe or harmless). Such populations of cells may optionally be purified and then may safely be formulated into a pharmaceutical composition or dosage form described herein. In some embodiments, the lack of exogenous genetic material in such erythroid cell populations is an improvement (e.g. in terms of safety profile) over erythroid populations that have been transfected with viral vectors of which the genetic material integrates into the host cell genome. 
     In some embodiments, it may be desirable to introduce a factor, e.g. a transcription factor or a signaling molecule or an effector molecule, that can induce the erythroid cell to proliferate rather than differentiate, e.g. to promote higher rates of expansion of progenitor cells in culture. Many such factors have been described in the art, see e.g. Hattangadi et al., Blood 2011, 118. Such factors, when introduced genetically or permanently, induce progenitor cells to proliferate greater than 1×10 10 -fold but make it nearly impossible to terminally differentiate the cells into mature erythrocytes. (Huang et al., Molecular Therapy 2014, 22(2):451-463; Hirose et al., Stem Cell Reports 2013 1:499-508). Low levels of enucleation rates on the order of only 0.1-10% of cells are consistently achieved by such methods. Low terminal maturation rate make these methods largely unsuitable in a commercial setting. Provided herein are transient transfection methods comprising contacting erythroid cells with exogenous mRNA and electroporating the cells under the conditions described herein, wherein i) the polypeptide expressed by the transfected erythroid cells from the exogenous mRNA is a factor (such as, e.g., a proto-oncogene including RAS, WNT, MYC, ERK, and TRK) that promotes self-renewal and expansion of the erythroid cells; ii) the expression of the self-renewal factor is transient, e.g. up to 6 hours, 12 hours, 24 hours, 48 hours, 72 hours, 4 days, 5 days, 6 days, 7 days, 8 days, 10 days, 12 days or 14 days, during which the protein levels of the factor fall below the level required for its activity in the cell; and iii) upon which the population of erythroid progenitor cells terminally differentiates, optionally in a synchronous fashion, e.g. at least 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or at least 97% of cells terminally differentiate. Terminally differentiation may be assessed, e.g., by FACS, to determine, e.g., the loss of the nucleus, such that the cells are enucleated erythroid cells (e.g. erythrocytes and platelets). 
     In some embodiments, it may be desirable to introduce exogenous mRNA encoding a targeted nuclease to perform genome editing on the erythroid progenitor cell such that a genetic modification is carried forward to the terminally differentiated cells. For example, the targeted nuclease may be a zinc finger nuclease, a TALEN, a CRISPR system including a Cas9 nuclease and guide RNA, or a meganuclease. The electroporation methods using exogenous mRNA constructs described herein are particularly suitable for targeted nucleases, as many will not be effectively delivered by viral transduction (see, e.g. Cong et al., Science 2013, 339:819). 
     In some embodiments, the erythroid cells are contacted with an mRNA encoding an exogenous targeted nuclease and electroporated to express the targeted nuclease polypeptide within the erythroid cell. Upon expression, the exogenous targeted nuclease introduced one or more genetic modification(s). 
     The genetic modification may be a modification to make the cells less immunogenic, such as by knocking out a known immunogenic antigen. Suitable immunogenic antigens on erythroid cells include, e.g., Kell or histo-blood group ABO system transferase. In some embodiments, an erythroid cell from a heterologous donor may thereby be made into an acceptable match for transfusion. 
     Alternatively or in addition, the genetic modification may be intended to make the cells more therapeutically potent, e.g. by targeting integration of a separately-provided transgene to a strongly expressed locus, e.g. the hemoglobin locus, by introducing a genomic break at that locus. One significant challenge with targeted nucleases is the risk of off-target cutting, or introducing genomic breaks at non-target regions of the genome. The process of binding to a non-target site is governed by kinetics and thermodynamics. While not intending to be bound by any particular theory, it is believed that the longer a nuclease is present in the cell and at higher concentrations, the higher the likelihood of binding to a non-target site and cutting (see e.g. Zuris et al., Nature Biotechnology 2015, 33(1):73; and Fu et al., Nature Biotechnology 2013, 31:822). In some embodiments, the electroporation methods provided herein, providing a targeted nuclease to an erythroid cell on a transient basis (e.g. via an exogenous mRNA) significantly reduce off-target nuclease activity when compared to non-transient transfection methods, e.g. using viral delivery methods that lead to integration of the exogenous nucleic acid into the host genome. 
     High levels of mRNA translation that naturally occur very late in erythroid differentiation, at the erythroblast and reticulocyte stage during which the cells are actively translating hemoglobin mRNA and contain abundant ribosomes and other translational machinery. Provided herein are methods of contacting erythroid cells at a late stage in erythroid differentiation (e.g. at the erythroblast or reticulocyte stage) with a nucleic acid encoding a desired factor (including a receiver polypeptide) and electroporating the cells under conditions described herein, thereby achieving high levels of expression of the exogenous nucleic acid on a per cell basis. Such methods allow extensive culturing and expansion (if desired) and provide the ability to make a modification to the cells late in the culture process. This may reduce chances for variation in efficiency and toxicity that may significantly alter the culture process and the quality of the resulting erythroid cell population. Undesired variability may add time consuming and costly quality control checkpoints. 
     The electroporation methods described herein are applicable to and can easily be adapted for any RNA, such as, e.g. mRNA, sno-RNA, miRNA, siRNA, shRNA, lncRNA, piRNA and spliRNA. These RNA molecules can, e.g., be used to regulate the expression of endogenous genes or control self-renewal and differentiation. The encoded protein can be expressed on the surface of the cell, in the cytoplasm of the cell, in the nucleus of the cell, in an organelle of the cell, or be secreted from the cell. 
     The RNA can be comprised of unmodified or modified nucleobases. Naturally occurring RNAs are synthesized from four basic ribonucleotides: ATP, CTP, UTP and GTP, but may contain post-transcriptionally modified nucleotides. Further, approximately one hundred different nucleoside modifications have been identified in RNA (Rozenski, J, Crain, P, and McCloskey, J. (1999). The RNA Modification Database: 1999 update. Nucl Acids Res 27: 196-197). In some embodiments, the RNA (e.g. mRNA) comprises at least one nucleoside selected from the group consisting of pyiidin-4-one ribonucleoside, 5-aza-uridine, 2-thio-5-aza-midine, 2-thiouridine, 4-thio-pseudouridine, 2-thio-pseudouridine, 5-hydroxyuridine, 3-methyluridine, 5-carboxymethyl-uridine, 1-carboxymethyl-pseudouridine, 5-propynyl-uridine, 1-propynyl-pseudouridine, 5-taurinomethyluridine, 1-taurinomethyl-pseudouridine, 5-taurinomethyl-2-thio-uridine, 1-taulinomethyl-4-thio-uridine, 5-methyl-uridine, 1-methyl-pseudouridine, 4-thio-1-methyl-pseudouridine, 2-thio-1-methyl-pseudouridine, 1-methyl-1-deaza-pseudouridine, 2-thio-1-methyl-1-deaza-pseudomidine, dihydrouridine, dihydropseudouridine, 2-thio-dihydromidine, 2-thio-dihydropseudouridine, 2-methoxyuridine, 2-methoxy-4-thio-uridine, 4-methoxy-pseudouridine, and 4-methoxy-2-thio-pseudouridine. In some embodiments, the mRNA comprises at least one nucleoside selected from the group consisting of 5-aza-cytidine, pseudoisocytidine, 3-methyl-cytidine, N4-acetylcytidine, 5-formylcytidine, N4-methylcytidine, 5-hydroxymethylcytidine, 1-methyl-pseudoisocytidine, pyrrolo-cytidine, pyrrolo-pseudoisocytidine, 2-thio-cytidine, 2-thio-5-methyl-cytidine, 4-thio-pseudoisocytidine, 4-thio-1-methyl-pseudoisocytidine, 4-thio-1-methyl-1-deaza-pseudoisocytidine, 1-methyl-1-deaza-pseudoisocytidine, zebularine, 5-aza-zebularine, 5-methyl-zebularine, 5-aza-2-thio-zebularine, 2-thio-zebularine, 2-methoxy-cytidine, 2-methoxy-5-methyl-cytidine, 4-methoxy-pseudoisocytidine, and 4-methoxy-1-methyl-pseudoisocytidine. In some embodiments, the mRNA comprises at least one nucleoside selected from the group consisting of 2-aminopurine, 2,6-diaminopurine, 7-deaza-adenine, 7-deaza-8-aza-adenine, 7-deaza-2-aminopurine, 7-deaza-8-aza-2-aminopurine, 7-deaza-2,6-diarminopurine, 7-deaza-8-aza-2,6-diarninopurine, 1-methyladenosine, N6-methyladenosine, N6-isopentenyladenosine, N6-(cis-hydroxyisopentenyl)adenosine, 2-meth ylthio-N6-(cis-hydroxyisopentenyl) adenosine, N6-glycinylcarbamoyladenosine, N6-threonylcarbamoyladenosine, 2-methylthio-N6-threonyl carbamoyladenosine, N6,N6-dimethyladenosine, 7-methyladenine, 2-methylthio-adenine, and 2-methoxy-adenine. In some embodiments, the RNA (e.g. mRNA) comprises at least one nucleoside selected from the group consisting of inosine, 1-methyl-inosine, wyosine, wybutosine, 7-deaza-guanosine, 7-deaza-8-aza-guanosine, 6-thio-guanosine, 6-thio-7-deaza-guanosine, 6-thio-7-deaza-8-aza-guanosine, 7-methyl-guanosine, 6-thio-7-methyl-guanosine, 7-methylinosine, 6-methoxy-guanosine, 1-methylguanosine, N2-methylguanosine, N2,N2-dimethylguanosine, 8-oxo-guanosine, 7-methyl-8-oxo-guanosine, 1-methyl-6-thio-guanosine, N2-methyl-6-thio-guanosine, and N2,N2-dimethyl-6-thio-guanosine. 
     In some embodiments, modified nucleosides include pyridin-4-one ribonucleoside, 5-aza-uridine, 2-thio-5-aza-uridine, 2-thiomidine, 4-thio-pseudomidine, 2-thio-pseudowidine, 5-hydroxyuridine, 3-methylmidine, 5-carboxymethyl-uridine, 1-carboxymethyl-pseudoutidine, 5-propynyl-uridine, 1-propynyl-pseudomidine, 5-taurinomethyluridine, 1-taurinomethyl-pseudouridine, 5-taw.inomethyl-2-thio-utidine, 1-taurinomethyl-4-thio-uridine, 5-methyl-uridine, 1-methyl-pseudouridine, 4-thio-1-methyl-pseudouridine, 2-thio-1-methyl-pseudoutidine, 1-methyl-1-deaza-pseudomidine, 2-thio-1-methyl-1-deaza-pseudouridine, dihydrouridine, dihydropseudouridine, 2-thio-dihydromidine, 2-thio-dihydropseudoulidine, 2-methoxyuridine, 2-methoxy-4-thio-uridine, 4-methoxy-pseudomidine, and 4-methoxy-2-thio-pseudouridine. 
     In some embodiments, modified nucleosides include 5-aza-cytidine, pseudoisocytidine, 3-methyl-cytidine, N4-acetylcytidine, 5-formylcytidine, N4-methylcytidine, 5-hydroxymethylcytidine, 1-methyl-pseudoisocytidine, pyrrolo-cytidine, pyrrolo-pseudoisocytidine, 2-thio-cytidine, 2-thio-5-methyl-cytidine, 4-thio-pseudoisocytidine, 4-thio-1-methyl-pseudoisocytidine, 4-thio-1-methyl-1-deaza-pseudoisocytidine, 1-methyl-1-deaza-pseudoisocytidine, zebularine, 5-aza-zebulruine, 5-methyl-zebularine, 5-aza-2-thio-zebulru.ine, 2-thio-zebulaiine, 2-methoxy-cytidine, 2-methoxy-5-methyl-cytidine, 4-methoxy-pseudoisocytidine, and 4-methoxy-1-methyl-pseudoisocytidine. 
     In other embodiments, modified nucleosides include 2-aminopurine, 2,6-diaminopurine, 7-deaza-adenine, 7-deaza-8-aza-adenine, 7-deaza-2-aminopurine, 7-deaza-8-aza-2-aminopurine, 7-deaza-2,6-diaminopurine, 7-deaza-8-aza-2,6-diaminopurine, 1-methyladenosine, N6-methyladenosine, N6-isopentenyladenosine, N6-(cis-hydroxyisopentenyl)adenosine, 2-methylthio-N6-(cis-hydroxyisopentenyl) adenosine, N6-glycinylcarbamoyladenosine, N6-threonylcarbamoyladenosine, 2-methylthio-N6-threonyl carbamoyladenosine, N6,N6-dimethyladenosine, 7-methyladenine, 2-methylthio-adenine, and 2-methoxy-adenine. 
     In specific embodiments, a modified nucleoside is 5′-O-(1-Thiophosphate)-Adenosine, 5′-O-Thiophosphate)-Cytidine, 5′-O-(1-thiophosphate)-Guanosine, 5′-O-(1-Thiophophate)-Uridine or 5′-O-(1-Thiophosphate)-Pseudouridine. 
     In other embodiments, modified nucleosides include inosine, 1-methyl-inosine, wyosine, wybutosine, 7-deaza-guanosine, 7-deaza-8-aza-guanosine, 6-thio-guanosine, 6-thio-7-deaza-guanosine, 6-thio-7-deaza-8-aza-guanosine, 7-methyl-guanosine, 6-thio-7-methyl-guanosine, 7-methylinosine, 6-methoxy-guanosine, 1-methylguanosine, N2-methylguanosine, N2,N2-dimethylguanosine, 8-oxo-guanosine, 7-methyl-8-oxo-guanosine, J-methyl-6-thio-guanosine, N2-methyl-6-thio-guanosine, and N2,N2-dimethyl-6-thio-guanosine. 
     In some embodiments, the RNA comprises one or more pseudouridine nucleotides, 5-methyl cytosine nucleotides, or both pseudouridine nucleotides, 5-methyl cytosine nucleotides. In embodiments, the RNA does not comprise canonical uridine nucleotides, canonical cytosine nucleotides, or either of canonical uridine nucleotides and canonical cytosine nucleotides. 
     The electroporation methods described herein are also easily adaptable for the delivery of nucleic acids that are not mRNAs and in which the transient nature of mRNA delivery is undesired or disadvantageous. For example, if it is desired to express an exogenous factor early in erythroid differentiation (or early in culture) and have the factor present in all cells as they divide in culture, but it is not desired to transfect the factor via viral delivery, the methods can be adapted to provide the factor in a non-transient (or stable) manner, e.g. by using non-viral DNA sequences that persist during cell divisions. Non-viral DNA sequences that persist during cell divisions, include for example those based on integration, e.g. bacterial or other transposons (see e.g. Skipper et al., J Biomed Sci 2013, 20(1):92), stable episomal amplifiers, e.g. viral amplifiers from EBNA-1 or SV40 or a stable episome from HPV (see e.g. LaPorta and Taichman, Proc Nat Acad Sci USA 1982 79(11):3393-3397) or site-specific homologous recombination using a targeted nuclease. In another example, non-viral DNA sequences that persist during cell divisions include those based on replicating episomal DNA, e.g. from AAV (see e.g. Ehrhardt et al., J Virol 2003, 77(13):7689-7695) or modified plasmid DNA (Argyros et al., Gene Therapy 2008, 15(24):1593-1605). These methods are suitable for exogenous nucleic acids of any desired lengths, e.g. from 10 bp to 10,000 bp. 
     Payloads for Synthetic Membrane-Receiver Complexes 
     Synthetic membrane-receiver complexes may optionally be loaded with payloads such as peptides, proteins, DNA, RNA, siRNA, and other macromolecules and small therapeutic molecules. In some embodiments, the payload is transferred to a cell, e.g., an erythroid cell or platelet by applying controlled injury to the cell for a predetermined amount of time in order to cause perturbations in the cell membrane such that the payload can be delivered to the inside of the cell (e.g., cytoplasm). 
     The payload may be a therapeutic agent selected from a variety of known small molecule pharmaceuticals. Alternatively, the payload may be may be a therapeutic agent selected from a variety of macromolecules, such as, e.g., an inactivating peptide nuclei acid (PNA), an RNA or DNA oligonucleotide aptamer, an interfering RNA (iRNA), a peptide, or a protein. 
     In some embodiments, the synthetic membrane-receiver complex is generated from a reticulocyte. For example, reticulocytes may be loaded with an mRNA encoding for a therapeutic exogenous polypeptide by controlled cell injury. The mRNA may be naked or modified, as desired. mRNA modification that improve mRNA stability and/or decrease immunogenicity include, e.g., ARCA: anti-reverse cap analog (m 2   7,3′-O GP 3 G), GP 3 G (Unmethylated Cap Analog), m 7 GP 3 G (Monomethylated Cap Analog), m 3   2.2.7 GP 3 G (Trimethylated Cap Analog), m5CTP (5′-methyl-cytidine triphosphate), m6ATP (N6-methyl-adenosine-5′-triphosphate), s2UTP (2-thio-uridine triphosphate), and Ψ (pseudouridine triphosphate). 
     Synthetic membrane-receiver complexes may comprise two or more payloads, including mixtures, fusions, combinations and conjugates, of atoms, molecules, etc. as disclosed herein, for example including but not limited to, a nucleic acid combined with a polypeptide; two or more polypeptides conjugated to each other; a protein conjugated to a biologically active molecule (which may be a small molecule such as a prodrug); and the like. 
     In some embodiments, the pharmaceutical composition comprises one or more therapeutic agents and the synthetic membrane-receiver complex described herein. In some embodiments, the synthetic membrane-receiver complexes are co-administered with of one or more separate therapeutic agents, wherein co-administration includes administration of the separate therapeutic agent before, after or concurrent with administration of the synthetic membrane-receiver complex. 
     Suitable payloads include, without limitation, pharmacologically active drugs and genetically active molecules, including antineoplastic agents, anti-inflammatory agents, hormones or hormone antagonists, ion channel modifiers, and neuroactive agents. Examples of suitable payloads of therapeutic agents include those described in, “The Pharmacological Basis of Therapeutics,” Goodman and Gilman, McGraw-Hill, New York, N.Y., (1996), Ninth edition, under the sections: Drugs Acting at Synaptic and Neuroeffector Junctional Sites; Drugs Acting on the Central Nervous System; Autacoids: Drug Therapy of Inflammation; Water, Salts and Ions; Drugs Affecting Renal Function and Electrolyte Metabolism; Cardiovascular Drugs; Drugs Affecting Gastrointestinal Function; Drugs Affecting Uterine Motility; Chemotherapy of Parasitic Infections; Chemotherapy of Microbial Diseases; Chemotherapy of Neoplastic Diseases; Drugs Used for Immunosuppression; Drugs Acting on Blood-Forming organs; Hormones and Hormone Antagonists; Vitamins, Dermatology; and Toxicology, all incorporated herein by reference. Suitable payloads further include toxins, and biological and chemical warfare agents, for example see Somani, S. M. (ed.), Chemical Warfare Agents, Academic Press, New York (1992)). 
     In some embodiments, the synthetic membrane-receiver complex does not comprise a payload comprising a synthetic triphosphorylated nucleoside analog. In some embodiments, the synthetic membrane-receiver complex does not comprise a payload comprising 2′,3′-dideoxycytidine-5′-triphosphate (ddCTP) and/or 3′-azido-3′-deoxythymidine-5′-triphosphate (AZT-TP). 
     In some embodiments, the synthetic membrane-receiver complex does not comprise a payload comprising a bisphosphonate. 
     In some embodiments, the payload is a therapeutic agent, such as a small molecule drug or a large molecule biologic. Large molecule biologics include, but are not limited to, a protein, polypeptide, or peptide, including, but not limited to, a structural protein, an enzyme, a cytokine (such as an interferon and/or an interleukin), a polyclonal or monoclonal antibody, or an effective part thereof, such as an Fv fragment, which antibody or part thereof, may be natural, synthetic or humanized, a peptide hormone, a receptor, or a signaling molecule. 
     Large molecule biologics are immunoglobulins, antibodies, Fv fragments, etc., that are capable of binding to antigens in an intracellular environment. These types of molecules are known as “intrabodies” or “intracellular antibodies.” An “intracellular antibody” or an “intrabody” includes an antibody that is capable of binding to its target or cognate antigen within the environment of a cell, or in an environment that mimics an environment within the cell. Selection methods for directly identifying such “intrabodies” include the use of an in vivo two-hybrid system for selecting antibodies with the ability to bind to antigens inside mammalian cells. Such methods are described in PCT/GB00/00876, incorporated herein by reference. Techniques for producing intracellular antibodies, such as anti-β-galactosidase scFvs, have also been described in Martineau et al., J Mol Biol 280:117-127 (1998) and Visintin et al., Proc. Natl. Acad. Sci. USA 96:11723-1728 (1999). 
     Large molecule biologics include but is not limited to, at least one of a protein, a polypeptide, a peptide, a nucleic acid, a virus, a virus-like particle, an amino acid, an amino acid analogue, a modified amino acid, a modified amino acid analogue, a steroid, a proteoglycan, a lipid and a carbohydrate or a combination thereof (e.g., chromosomal material comprising both protein and DNA components or a pair or set of effectors, wherein one or more convert another to active form, for example catalytically). 
     A Large molecule biologic may include a nucleic acid, including, but not limited to, an oligonucleotide or modified oligonucleotide, an antisense oligonucleotide or modified antisense oligonucleotide, an aptamer, a cDNA, genomic DNA, an artificial or natural chromosome (e.g., a yeast artificial chromosome) or a part thereof, RNA, including an siRNA, a shRNA, mRNA, tRNA, rRNA or a ribozyme, or a peptide nucleic acid (PNA); a virus or virus-like particles; a nucleotide or ribonucleotide or synthetic analogue thereof, which may be modified or unmodified. 
     The large molecule biologic can also be an amino acid or analogue thereof, which may be modified or unmodified or a non-peptide (e.g., steroid) hormone; a proteoglycan; a lipid; or a carbohydrate. If the large molecule biologic is a polypeptide, it can be loaded directly into, e.g., an erythroid cell or a platelet according to the methods described herein. Alternatively, an exogenous nucleic acid encoding a polypeptide, which sequence is operatively linked to transcriptional and translational regulatory elements active in a cell at a target site, may be loaded. 
     Small molecules, including inorganic and organic chemicals, may also be used as payloads of the synthetic membrane-receiver complexes described herein. 
     In some embodiments, the small molecule is a pharmaceutically active agent. Useful classes of pharmaceutically active agents include, but are not limited to, antibiotics, anti-inflammatory drugs, angiogenic or vasoactive agents, growth factors and chemotherapeutic (anti-neoplastic) agents (e.g., tumour suppressers). 
     If a prodrug is loaded into the synthetic membrane-receiver complex in an inactive form it is often useful that the synthetic membrane-receiver complex further comprises a receiver such as an activating polypeptide which converts the inactive prodrug to active drug form. In an embodiment, activating receiver polypeptides include, but are not limited to, viral thymidine kinase (encoded by Genbank Accession No. J02224), carboxypeptidase A (encoded by Genbank Accession No. M27717), α-galactosidase (encoded by Genbank Accession No. M13571), β-glucuronidase (encoded by Genbank Accession No. M15182), alkaline phosphatase (encoded by Genbank Accession No. J03252 J03512), or cytochrome P-450 (encoded by Genbank Accession No. D00003 N00003), plasmin, carboxypeptidase G2, cytosine deaminase, glucose oxidase, xanthine oxidase, β-glucosidase, azoreductase, t-gutamyl transferase, β-lactamase, and penicillin amidase. 
     Either the receiver polypeptide or the exogenous gene encoding it may be loaded into, e.g., an erythroid cell or platelet, to generate a synthetic membrane-receiver complex. Both the prodrug and the activating receiver polypeptide may be encoded by genes on the same exogenous nucleic acid. Furthermore, either the prodrug or the activating receiver polypeptide of the prodrug may be transgenically expressed in a synthetic membrane-receiver complex. 
     The synthetic membrane-receiver complexes may also be labeled with one or more positive markers that can be used to monitor over time the number or concentration of synthetic membrane-receiver complexes in the blood circulation of an individual. The overall number of synthetic membrane-receiver complexes will decay over time following initial transfusion. In some embodiments, the signal from one or more positive markers are correlated with that of an activated molecular marker, generating a proportionality of signal that is independent of the number of synthetic membrane-receiver complexes remaining in the circulation. Suitable fluorescent compounds include those that are approved by the Food &amp; Drug Administration for human use including but not limited to fluorescein, indocyanin green, and rhodamine B. For example, synthetic membrane-receiver complexes may be non-specifically labeled with fluorescein isothiocyanate (FITC; Bratosin et al., Cytometry 46:351-356 (2001)). For example, a solution of FITC-labeled lectins in phosphate buffered saline (PBS) with 0.2 mM phenylmethysulfonyl fluoride (PMSF) is added to an equal volume of isolated erythroid cells or platelets in the same buffer. The cells are incubated with the FITC-labeled lectins for 1 h at 4° C. in the dark. The lectins bind to sialic acids and beta-galactosyl residues on the surface of the erythroid cells. 
     Other dyes may be useful for tracking synthetic membrane-receiver complexes in human and non-human circulation. A number of reagents may be used to non-specifically label a synthetic membrane-receiver complex. For example, erythroid cells or platelets may be labeled with PKH26 Red (See, e.g., Bratosin, et al., (1997) Cytometry 30:269-274). Erythroid cells or platelets (1-3×10 7  cells) are suspended in 1 ml of diluent and rapidly added to 1 ml or 2 μM PKH26 dissolved in the same diluent. The mixture is mixed by gentle pipetting and incubated at 25° C. for 2-5 min with constant stirring. The labeling may be stopped by adding an equal volume of human serum or compatible protein solution (e.g., 1% bovine serum albumin). After an additional minute, an equal volume of cell culture medium is added and the cells are isolated by centrifugation at 2000×g for 5 min Cells are washed three times by repeated suspension in cell culture medium and centrifugation. PHK26-labeled synthetic membrane-receiver complexes may be monitored with a maximum excitation wavelength of 551 nm and a maximum emission wavelength of 567 nm. 
     Synthetic membrane-receiver complexes may be tracked in vivo using VivoTag 680 (VT680; VisEn Medical, Woburn, Mass., USA), a near-infrared fluorochrome with a peak excitation wavelength of 670±5 nm and a peak emission wavelength of 688±5 nm. VT680 also contains an amine reactive NHS ester which enables it to cross-link with proteins and peptides. The surface of cells, e.g., erythroid cells or platelets may be labeled with VT680 (See, e.g., Swirski, et al., (2007) PloS ONE 10:e1075). For example, 4×10 6  cells/ml are incubated with VT680 diluted in complete culture medium at a final concentration of 0.3 to 300 μg/ml for 30 min at 37° C. The cells are washed twice with complete culture medium after labeling. Cells may be non-specifically labeled based on proteins expressed on the surface of the synthetic membrane-receiver complex. Alternatively, a specific protein, such as a receiver may be labeled with VT680. In some embodiments, a protein or peptide may be directly labeled with VT680 ex vivo and subsequently either attached to the surface of the cell or incorporated into the interior of the cell using methods described herein. In vivo monitoring may, for example, be performed using the dorsal skin fold. Laser scanning microscopy may be performed using, for example, an Olympus IV 100 in which VT680 is excited with a red laser diode of 637 nm and detected with a 660/LP filter. Alternatively, multiphoton microscopy may be performed using, for example, a BioRad Radiance 2100 MP centered around an Olympus BX51 equipped with a 20×/0.95 NA objective lens and a pulsed Ti:Sapphire laser tuned to 820 nm. The latter wavelength is chosen because VT680 has a peak in its two-photon cross-section at 820 nm. 
     Alternatively or in addition, a synthetic membrane-receiver complex may be labeled with other red and/or near-infrared dyes including, for example, cyanine dyes such as Cy5, Cy5.5, and Cy7 (Amersham Biosciences, Piscataway, N.J., USA) and/or a variety of Alexa Fluor dyes including Alexa Fluor 633, Alexa Fluor 635, Alexa Fluor 647, Alexa Fluor 660, Alexa Fluor 680, Alexa Fluor 700 and Alexa Fluor 750 (Molecular Probes-Invitrogen, Carlsbad, Calif., USA). Additional suitable fluorophores include IRD41 and IRD700 (LI-COR, Lincoln, Nebr., USA), NIR-1 and 1C5-OSu (Dejindo, Kumamotot, Japan), LaJolla Blue (Diatron, Miami, Fla., USA), FAR-Blue, FAR-Green One, and FAR-Green Two (Innosense, Giacosa, Italy), ADS 790-NS and ADS 821-NS (American Dye Source, Montreal, Calif.). Quantum dots (Qdots) of various emission/excitation properties may also be used for labeling synthetic membrane-receiver complexes (See, e.g., Jaiswal et al., Nature Biotech. 21:47-51 (2003)). Many of these fluorophores are available from commercial sources either attached to primary or secondary antibodies or as amine-reactive succinimidyl or monosuccinimidyl esters, for example, ready for conjugation to a protein or proteins either on the surface or inside the synthetic membrane-receiver complex. 
     Magnetic nanoparticles may be used to track synthetic membrane-receiver complexes in vivo using high resolution MRI (Montet-Abou et al., Molecular Imaging 4:165-171 (2005)). Magnetic particles may be internalized by several mechanisms. Magnetic particles may be taken up by a cell, e.g., an erythroid cell or a platelet through fluid-phase pinocytosis or phagocytosis. Alternatively, the magnetic particles may be modified to contain a surface agent such as, for example, a membrane translocating HIV TAT peptide which promotes internalization. In some instances, a magnetic nanoparticle such as, for example, Feridex IV®, an FDA approved magnetic resonance contrast reagent, may be internalized into, e.g., erythroid cells or platelets in conjunction with a transfection agent such as, for example, protamine sulfate (PRO), polylysine (PLL), and lipofectamine (LFA). 
     In some embodiments, the synthetic membrane-receiver polypeptide complexes are generated comprising contacting an erythroid cell with a receiver, such as a polypeptide. In some embodiments, the receiver polypeptide is encoded by an exogenous nucleic acid and is expressed by the erythroid cell. In some embodiments, a naturally occurring erythroid cell does not comprise the receiver. For example, a naturally occurring erythroid cell does not express an endogenous polypeptide that is structurally and functionally the same as the receiver polypeptide. In some embodiments, the erythroid cell comprises a receiver that is over-expressed. For example, the receiver is present in substantially higher copy numbers than it would be if it were endogenously expressed by a naturally occurring erythroid cell. In some embodiments, the synthetic membrane-receiver polypeptide complexes are generated by differentiating and maturing the erythroid cells in vitro or in vivo after contacting the cells with a receiver. It is known in the art that erythrocytes undergo a complex process of maturation as they differentiate from precursor cells. The maturation process includes a substantial cytoskeleton and membrane rearrangement and degradation or expulsion of non-essential polypeptides, see e.g., Liu J et al. (2010) Blood 115(10):2021-2027; and Lodish H F et al. (1975) Developmental Biology 47(1):59). For naturally occurring erythrocytes this maturation process happens in vivo, first in the bone marrow and then in circulation as reticulocytes mature into erythrocytes. For cultured erythrocytes this maturation process happens both ex vivo, in culture, and in vivo in circulation as cultured reticulocytes mature into eyrthrocytes (see e.g., Neildez-Nguyen et al. 2002 Nature Biotechnol 20:467). In some embodiments, the synthetic membrane-receiver polypeptide complexes generated from erythroid cells retain their receivers during the maturation process, in vitro or in vivo and the receivers are not lost. In some embodiments, the synthetic membrane-receiver polypeptide complexes generated from erythroid cells retain their receivers after maturation. In some embodiments, fully matured synthetic membrane-receiver polypeptide complexes generated from erythroid cells retain their receiver. The receiver may be retained in vitro, e.g., in culture and/or may be retained in vivo, e.g., after administration to the circulatory system of the subject. In some embodiments, the receiver may be retained by the synthetic membrane-receiver polypeptide complexes for the life of the complex in circulation. These findings are surprising in view of the art which suggested that receivers would be excluded from the erythroid cells during the maturation process. It was further unexpected that receivers would be retained and functionally active when the synthetic membrane-receiver polypeptide complexes generated from erythroid cells are administered to the circulatory system of a subject. In some embodiments culturing of eythroid cells comprising a receiver provides a method of producing a substantially more homogeneous and/or substantially more scalable population of therapeutic synthetic membrane-receiver complexes than is achievable by methods relying upon isolation and modification of non-cultured erythrocytes. Despite a great need for human erythroid cell-based treatment and preventive methods and recognition for its value in the art, no systems derived from modified cultured cells have previously been generated or shown to retain receiver activity in circulation, and the art suggested that such systems would not be achievable. When cultured human erythrocytes have been experimentally administered to a human subject previously they were unmodified (Giarratana et al., Blood 2011, 118:5071). 
     Targets 
     Provided herein are synthetic membrane-receiver polypeptide complexes comprising a receiver polypeptide capable of interacting with a target. Further provided herein are synthetic membrane-receiver complexes comprising a non-polypeptide receiver capable of interacting with a target. The synthetic membrane-receiver complexes may be administered to a subject in need thereof to modulate the amount or concentration of a target residing in the circulatory system of the subject. A suitable receiver may be chosen to interact with a specific target. Suitable targets include entities that are associated with a specific disease, disorder, or condition. However, targets may also be chosen independent of a specific disease, disorder, or condition. 
     In some embodiments, the target is an antibody or antibody-like molecule, for example an autoimmune or a self-antibody, or a foreign antibody, or a therapeutic antibody, including but not limited to, e.g., an antibody against beta-2 glycoprotein 1, an antibody against I/i antigen, an antibody against the NC1 domain of collagen a3(IV), an antibody against platelet glycoprotein, an antibody against phospholipase A2 receptor, an antibody against erythrocyte glycophorin A, B, or C, or an antibody against erythrocyte Rh antigen. 
     In some embodiments, the target is a molecule of the complement cascade, for example C1, C1r, C1s, C1q, C2, C2a, C2b, C3, C3a, C3b, C4, C4b, C4a, C3bBb, C3bBb3b, C4b2b, C4b2b3b, C5, C5a, C5b, C6, C7, C8, C9, poly-C9, membrane attack complex. Factor B, Factor D, Properdin, C3, C3a, C3b, iC3b, C3c, C3dg, C3dk, C3e, Bb, Factor I, C1 q, C1 r, C1s, C4, C4a, C4b, C2, C4 bp, Mannose-Binding Lectin (MBL), MBL-Associated Serine Protease 1 (MASP1), MBL-Associated Serine Protease 2 (MASP2), C5, C5a, C6, C7, C8, C9, CR1, CR2, CR3, CR4, C3aR, C3eR, Decay-accelerating factor (DAF), Membrane cofactor protein (MCP), CD59, C3 Beta chain Receptor, C1 inhibitor, C4 binding protein, Factor I, Factor H. 
     In some embodiments, the target is an immune complex, for example an IgG immune complex, an IgA immune complex, an IgM immune complex. 
     In some embodiments, the target is an amyloid placque, for example a placque comprised of beta amyloid, IAPP (Amylin), alpha-synuclein, PrPSc, huntingtin, calcitonin, atrial natriuretic factor, apolipoprotein AI, serum amyloid A, medin, prolactin, transthyretin, lysozyme, beta 2 microglobulin, gelsolin, keratoepithelin, cystatin, immunoglobulin light chain AL, S-IBM. 
     In some embodiments, the target is a bacterium, for example  Enterococcus, Streptococcus , or Mycobacteria,  Rickettsia, Mycoplasma, Neisseria meningitides, Neisseria gonorrheoeae, Legionella, Vibrio cholerae , Streptococci,  Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, Corynobacteria diphtheriae, Clostridium  spp., enterotoxigenic  Escherichia coli , and  Bacillus anthracis . Other pathogens for which bacteremia has been reported at some level include the following:  Rickettsia, Bartonella henselae, Bartonella quintana, Coxiella burnetii, chlamydia, Mycobacterium leprae, Salmonella; shigella; Yersinia enterocolitica; Yersinia pseudotuberculosis; Legionella pneumophila; Mycobacterium tuberculosis; Listeria monocytogenes; Mycoplasma  spp.;  Pseudomonas fluorescens; Vibrio cholerae; Haemophilus influenzae; Bacillus anthracis; Treponema pallidum; Leptospira; Borrelia; Corynebacterium diphtheriae; Francisella; Brucella melitensis; Campylobacter jejuni; Enterobacter; Proteus mirabilis; Proteus ; and  Klebsiella pneumoniae.    
     In some embodiments, the target is a virus, including but limited to, those whose infection involves injection of genetic materials into host cells upon binding to cell surface receptors, viruses whose infection is mediated by cell surface receptors. Non-limiting examples of these viruses can be selected from Paramyxoviridae (e.g., pneumovirus, morbillivirus, metapneumovirus, respirovirus or rubulavirus), Adenoviridae (e.g., adenovirus), Arenaviridae (e.g., arenavirus such as lymphocytic choriomeningitis virus), Arteriviridae (e.g., porcine respiratory and reproductive syndrome virus or equine arteritis virus), Bunyaviridae (e.g., phlehovirus or hantavirus), Caliciviridae (e.g., Norwalk virus), Coronaviridae (e.g., coronavirus or torovirus), Filoviridae (e.g., Ebola-like viruses), Flaviviridae (e.g., hepacivirus or flavivirus), Herpesviridae (e.g., simplexvirus, varicellovirus, cytomegalovirus, roseolovirus, or lymphocryptovirus), Orthomyxoviridae (e.g., influenza virus or thogotovirus), Parvoviridae (e.g., parvovirus), Picomaviridae (e.g., enterovirus or hepatovirus), Poxviridae (e.g., orthopoxvirus, avipoxvirus, or leporipoxvirus), Retroviridae (e.g., lentivirus or spumavirus), Reoviridae (e.g., rotavirus), Rhabdoviridae (e.g., lyssavirus, novirhabdovirus, or vesiculovirus), and Togaviridae (e.g., alphavirus or rubivirus). Specific examples of these viruses include human respiratory coronavirus, influenza viruses A-C, hepatitis viruses A to G, and herpes simplex viruses 1-9. 
     In some embodiments, the target is a parasite, including but not limited to, for example, intestinal or blood-borne parasites, protozoa, trypanosomes; haemoprotozoa and parasites capable of causing malaria; enteric and systemic cestodes including taeniid cestodes; enteric coccidians; enteric flagellate protozoa; filarial nematodes; gastrointestinal and systemic nematodes and hookworms. 
     In some embodiments, the target is a fungus, including but not limited to, for example,  Candida albicans, Candida glabrata, Aspergillus, T. glabrata, Candida tropicalis, C. krusei , and  C. parapsilosis.    
     In some embodiments, the target is a bacterial toxin, including but not limited to, for example, AB toxin, alpha toxin, anthrax toxin, bacteriocin, botunlinum toxin, cholesterol-dependent cytolysin,  Clostridium botulinum  C3 toxin,  Clostridium difficile  toxin A,  Clostridium difficile  toxin B,  Clostridium  enterotoxin,  Clostridium perfringens  alpha toxin,  Clostridium perfringens  beta toxin, Cord factor, Cry1Ac, Cryptophycin, Delta endotoxin, Diphtheria toxin, Enterotoxin type B, erythrogenic toxin, exfoliatin, haemolysin E, heat-labile enterotoxin, heat-stable enterotoxin, hemolysin, leukocidin, lipopolysaccharide, Listeriolysin O, microcin, Panton-Valentine leucocidin, pathogenicity island, phenol-soluble modulin, pneumolysin, pore-forming toxin,  Pseudomonas  exotoxin, RTX toxin, sakacin,  Staphylococcus aureus  alpha toxin,  Staphylococcus aureus  beta toxin,  Staphylococcus aureus  delta toxin, Streptolysin, Symplocamide A, tabtoxin, tetanolysin, tetanospasmin, thiol-activated cytolysin, tolaasin, toxic shock syndrome toxin, toxoflavin, trehalose dimycolate, verocytotoxin, and vibriocin. 
     In some embodiments, the target is a prion protein, including but not limited to, for example, PRP, PRPc, PRPsc, PRPres. 
     In some embodiments, the target is a cytokine or a chemokine or a growth factor, including but not limited to, for example, acylation stimulating protein, adipokine, albinterferon, CCL1, CCL11, CCL12, CCL13, CCL14, CCL15, CCL16, CCL17, CCL18, CCL19, CCL2, CCL20, CCL21, CCL22, CCL23, CCL24, CCL25, CCL26, CCL27, CCL28, CCL3, CCL5, CCL6, CCL7, CCL8, CCL9, colony-stimulating factor, CX3CL1, CX3CR1, CXCL1, CXCL10, CXCL11, CXCL13, CXCL14, CXCL15, CXCL16, CXCL17, CXCL2, CXCL3, CXCL5, CXCL6, CXCL7, CXCL9, erythropoietin, Gc-MAF, granulocyte colony-stimulating factor, granulocyte macrophage colony-stimulating factor, hepatocyte growth factor, IL 10 family, IL 17 family, ILIA, IL1B, interferon, interferon beta 1a, interferon beta 1b, interferon gamma, interferon type I, interferon type II, interferon type III, interleukin, interleukin 1 family, interleukin 1 receptor antagonist, interleukin 10, interleukin 12, interleukin 12 subunit beta, interleukin 13, interleukin 16, interleukin 2, interleukin 23, interleukin 23 subunit alpha, interleukin 34, interleukin 35, interleukin 6, interleukin 7, interleukin 8, interleukin-36, leukemia inhibitory factor, leukocyte-promoting factor, lymphokine, lymphotoxin, lymphotoxin alpha, lymphotoxin beta, macrophage colony-stimulating factor, macrophage inflammatory protein, macrophage-activating factor, monokine, myokine, myonectin, nicotinamide phosphoribosyltransferase, oncostatin M, oprelvekin, platelet factor 4, proinflammatory cytokine, promegapoietin, RANKL, stromal cell-derived factor 1, talimogene laherparepvec, tumor necrosis factor alpha, tumor necrosis factors, XCL1, XCL2, XCR1, angiopoietin, basic fibroblast growth factor, betacellulin, bone morphogenetic protein, brain-derived neurotrophic factor, CCN intercellular signaling protein, CTGF, darbepoetin alfa, endoglin, epidermal growth factor, epoetin alfa, epoetin beta, erythropoietin, FGF15, FGF15/19, fibroblast growth factor, fibroblast growth factor 23, filgrastim, GLIA maturation factor, granulocyte colony-stimulating factor, granulocyte macrophage colony-stimulating factor, growth differentiation factor-9, heberprot-P, hemopoietic growth factors, heparin-binding EGF-like growth factor, hepatocyte growth factor, insulin-like growth factor, insulin-like growth factor 1, insulin-like growth factor 2, keratinocyte growth factor, myostatin, nerve growth factor, neurotrophin-3, neurotrophin-4, oncomodulin, osteopromotive, palifermin, PDGFB, placental growth factor, platelet alpha-granule, platelet-derived growth factor, platelet-derived growth factor receptor, proliferative index, thrombopoietin, transforming growth factor, vascular endothelial growth factor. 
     In some embodiments, the target is a small molecule, for example a chemical, an amino acid, an atom, an element, an organic acid, &lt;2000 Da, &lt;1000 Da, &lt;500 Da, including but not limited to, for example, iron, copper, calcium, potassium, ethanol, methanol, glycine, alanine, valine, leucine, isoleucine, serine, cysteine, selenocysteine, threonine, methionine, proline, phenylalanine, tyrosine, tryptophan, histidine, lysine, arginine, aspartate, glutamate, asparagine, glutamine. 
     In some embodiments, the target is a lipid, lipid complex, proteolipid complex, or cholesterol, including but not limited to for example, LDL, VLDL, HDL, HDL2B, triglycerides, LP(a), cholesterol. 
     In some embodiments, the target is a mammalian cell, including but not limited to, for example, a human cell, a circulating cell, an immune cell, a neutrophil, an eosinophil, a basophil, a lymphocyte, a monocyte, a B cell, a T cell, a CD4+ T cell, a CD8+ T cell, a gamma-delta T cell, a regulatory T cell, a natural killer cell, a natural killer T cell, a macrophage, a Kupffer cell, a dendritic cell, a cancer cell, a cancer stem cell, a circulating tumor cell, a cancer cell from one of the following cancers including, but not limited to, ACUTE lymphoblastic leukaemia (ALL), ACUTE myeloid leukaemia (AML), anal cancer, bile duct cancer, bladder cancer, bone cancer, bowel cancer, brain tumours, breast cancer, cancer of unknown primary, cancer spread to bone, cancer spread to brain, cancer spread to liver, cancer spread to lung, carcinoid, cervical cancer, choriocarcinoma, chronic lymphocytic leukaemia (CLL), chronic myeloid leukaemia (CML), colon cancer, colorectal cancer, endometrial cancer, eye cancer, gallbladder cancer, gastric cancer, gestational trophoblastic tumours (GTT), hairy cell leukaemia, head and neck cancer, hodgkin lymphoma, kidney cancer, laryngeal cancer, leukaemia, liver cancer, lung cancer, lymphoma, melanoma skin cancer, mesothelioma, men&#39;s cancer, molar pregnancy, mouth and oropharyngeal cancer, myeloma, nasal and sinus cancers, nasopharyngeal cancer, non hodgkin lymphoma (NHL), oesophageal cancer, ovarian cancer, pancreatic cancer, penile cancer, prostate cancer, rare cancers, rectal cancer, salivary gland cancer, secondary cancers, skin cancer (non melanoma), soft tissue sarcoma, stomach cancer, testicular cancer, thyroid cancer, unknown primary cancer, uterine cancer, vaginal cancer, and vulval cancer. 
     In some embodiments, the target is not a cell. In some embodiments, the target is not an animal cell, such as, e.g. a human cell. In some embodiments, the target is not a human cancer cell. In some embodiments, the target is not a prokaryotic cell, such as a bacterium. In some embodiments, the target is not a eukarytic cell. In some embodiments, the target is not a virus, a bacterium, a parasite, a fungus, or a yeast cell. 
     In some embodiments, the target is an anti-drug antibody (ADA). Many biologics, such as, e.g. antibodies are hampered in their effectiveness because of their immunogenicity. The immune system can react against these biological agents by producing anti-drug antibodies (ADAs), which leads to the loss of efficacy of the drug and the occurrence of adverse events. ADA often results from structural characteristics of the biological agent. For example, chimeric monoclonal antibodies, including infliximab and rituximab (for which a high incidence of ADA can be observed in several diseases), are thought to have a higher immunogenicity when compared to human or fully human monoclonal antibodies, including adalimumab and golimumab. Many biologics comprise xenoantigens, for example mouse xenoantigens and/or neoantigens on junction sites, as in fusion proteins, or repetitive idiotypes that increase their immunogenic potential. As a result of an immune reaction neutralizing antibodies or clearing antibodies against the biological agent are produced. Symptoms include hypersensitivity reactions, which may be acute or delayed, and aplasia or thrombocytopenia. It has been observed that approximately 37% of non-responders to anti-infliximab have anti-drug antibodies, whereas responders usually fall within the group of those who do not develop ADA. (See, e.g. Matucci A et al., Clin. Dermatol., 2013, 2(2): 77-80). In some embodiments, the receiver has binding affinity to an anti-drug antibody and binds and/or sequesters the antibody. In some embodiments, synthetic membrane receiver complexes comprising a receiver capable of interacting with an anti-drug antibody are administered to a subject having developed or being suspected of developing anti-drug antibodies in an amount effective to reduce the concentration of anti-drug antibodies in the circulatory system of the subject. In some embodiments, the subject is selected from a group of non-responders to a biologic that was previously administered or is currently administered at the time of making the treatment decision. In some embodiments, ADAs are detected in the subject and a treatment decision is based on the detection of the ADAs. In some embodiments, the reduction of ADAs renders the biologic effective again if administered after or concurrent with the synthetic membrane receiver complex. 
     Sourcing 
     Synthetic membrane-receiver complexes can be generated by any method described herein. In some embodiments, the steps comprise contacting isolated optionally cultured cells derived from hematopoietic stem cells with a receiver. Hematopoietic stem cells give rise to all of the blood cell types found in mammalian blood including myeloid (monocytes and macrophages, neutorphils, basophils, eosinophils, erythrocytes, megakaryocytes/platelets, dendritic cells) and lymphoid lineages (T-cells, B-cells, NK-cells). Hematopoietic stem cells may be isolated from the bone marrow of adult bones including, for example, femur, hip, rib, or sternum bones. Cells may be obtained directly from the hip, for example, by removal of cells from the bone marrow using aspiration with a needle and syringe. Alternatively, hematopoietic stem cells may be isolated from normal peripheral blood following pre-treatment with cytokines such as, for example, granulocyte colony stimulating factor (G-CSF). G-CSF mobilizes the release of cells from the bone marrow compartment into the peripheral circulation. Other sources of hematopoietic stem cells include umbilical cord blood and placenta. 
     In some embodiments, the synthetic membrane-receiver complex is generated from megakaryocytes or platelets. In some embodiments, the synthetic membrane-receiver complex is generated from an erythroid cell, such as, e.g. an erythrocyte or a reticulocyte. In some embodiments, the synthetic membrane-receiver complex is not generated from a neutrophil, an eosinophil, or a basophil. In some embodiments, the synthetic membrane-receiver complex is not generated from a monocyte or a macrophage. 
     In some embodiments, the synthetic membrane-receiver complex is not generated from a CD34 + Thy-1 +  hematopoietic stem cell or cell populations enriched in CD34 + Lin −  or CD34 + Thy-1 + Lin −  cells. 
     In some embodiments, the synthetic membrane-receiver complex is not generated from or does not comprise an autologous CD34+ cell. 
     Isolated hematopoietic stem cells may be cultured, expanded and differentiated ex vivo to provide a variety of source material to generate synthetic membrane-receiver complexes. For example, hematopoietic stem cells isolated from bone marrow, cytokine-stimulated peripheral blood or umbilical cord blood may be expanded and differentiated ex vivo into mature erythrocytes (Giarratana et al., Nature Biotech. 23:69-74 (2005); U.S. Patent Application 2007/0218552). As such, CD34+ cells are isolated from bone marrow or peripheral or cord blood using, for example, magnetic microbead selection and Mini-MACS columns (Miltenyi Biotech). In one example, the cells are subsequently cultured in modified serum-free medium supplemented with 1% bovine serum albumin (BSA), 120 μg/ml iron-saturated human transferrin, 900 ng/nil ferrous sulfate, 90 ng/ml ferric nitrate and 10 μg/ml insulin and maintained at 37° C. in 5% carbon dioxide in air. Expansion and differentiation of the cell culture may occur in multiple steps. For example, in the initial growth step following isolation, the cells may be expanded in the medium described herein in the presence of multiple growth factors including, for example, hydrocortisone, stem cell factor, IL-3, and erythropoietin. In the second stage, the cells may optionally be co-cultured, for example, on an adherent stromal layer in the presence of erythropoietin. In a third stage, the cells may be cultured on an adherent stromal layer in culture medium in the absence of exogenous factors. The adherent stromal layer may be murine MS-5 stromal cells, for example. Alternatively, the adherent stromal layer may be mesenchymal stromal cells derived from adult hone marrow. The adherent stromal cells may be maintained in RPMI supplemented with 10% fetal calf serum, for example. In some embodiments, the erythroid precursor cells and cell populations derived therefrom are not co-cultured with non-erythroid cells, e.g., with an adherent stromal layer, i.e. they are cultured in the absence of non-erythroid cells. In some embodiments, erythroid cells comprising a receiver are cultured in the absence of non-erythroid cells and are differentiated so that greater than 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or greater than 98% of erythroid cells are enucleated and the population of enucleated cells is obtained without an enrichment step, such as gravitational separation, magnetic or fluorescent sorting, irradiation, poisoning of nucleated cells, and the like to select for enucleated cells. 
     In some instances, it may be desirable to expand and partially differentiate the CD34+ hematopoietic stem cells in vitro and to allow terminal differentiation into mature erythrocytes to occur in vivo (See, e.g., Neildez-Nguyen et al., Nature Biotech. 20:467-472 (2002)). Isolated CD34+ hematopoietic stem cells may be expanded in vitro in the absence of the adherent stromal cell layer in medium containing various factors including, for example, Flt3 ligand, stem cell factor, thrombopoietin, erythropoietin, and insulin growth factor. The resulting erythroid precursor cells may be characterized by the surface expression of CD36 and GPA, and may be transfused into a subject where terminal differentiation to mature erythrocytes is allowed to occur. 
     In some embodiments, the erythroid cell population comprises a plurality of enucleated functional erythroid cells that comprise a receiver polypeptide that is retained during enucleation. The resulting isolated enucleated functional erythroid cell comprising a receiver polypeptide exhibits substantially the same osmotic membrane fragility as a corresponding isolated, unmodified, uncultured erythroid cell. 
     In some embodiments, the erythroid cell population comprises a plurality of erythrocyte precursor cells in substantially the same stage of differentiation and/or cell cycle stage, wherein the precursor cells comprise an exogenous nucleic acid encoding a receiver. The majority of erythrocyte precursor cells that comprise an exogenous nucleic acid encoding a receiver are capable of differentiating into mature functional erythrocytes that retain the receiver without retaining the exogenous nucleic acid. 
     In some embodiments, the primary cells may be collected through venipuncture, capillary puncture, or arterial puncture. From the collected whole blood erythrocytes, platelets or other cells may then be isolated using one, or a combination of techniques including plasma depletion, density gradient, Hetastarch, PrepaCyte-CB, and centrifugation. 
     In some embodiments, generating a synthetic membrane-receiver complex comprises contacting isolated optionally cultured cells that are autologous and/or allogeneic to the subject with a receiver. For example, erythrocytes allogeneic to the subject include one or more of blood type specific erythrocytes or one or more universal donor erythrocytes. In some embodiments, synthetic membrane-receiver complexes may be generated through fusion of erythrocytes, e.g., between erythrocytes autologous to the subject and one or more allogeneic erythrocytes, liposomes, and/or artificial vesicles. 
     In certain embodiments, autologous transfusion of synthetic membrane-receiver complexes includes isolating erythrocytes, reticulocytes or hematopoietic stem cells from a subject, generating a suitable synthetic membrane-receiver complex by contacting the cell with a receiver by methods described herein and administering (e.g., by transfusion) the synthetic membrane-receiver complex into the same subject. 
     In certain embodiments, allogeneic transfusion of synthetic membrane-receiver complexes includes isolating erythrocytes, reticulocytes or hematopoietic stem cells from a donor, generating a suitable synthetic membrane-receiver complex by contacting the cell with a receiver by methods described herein and administering (e.g., by transfusion) the synthetic membrane-receiver complex into a subject that is different from the donor. Where allogeneic cells are used for transfusion, care needs to be taken to use a compatible ABO blood group to prevent an acute intravascular hemolytic transfusion reaction which is characterized by complement activation and lysis of incompatible erythrocytes. The ABO blood types are defined based on the presence or absence of the blood type antigens A and B, monosaccharide carbohydrate structures that are found at the termini of oligosaccharide chains associated with glycoproteins and glycolipids on the surface of the erythrocytes (reviewed in Liu et al., Nat. Biotech. 25:454-464 (2007)). Group O erythrocytes lack either of these antigenic monosaccharide structures. Subjects with group A erythrocytes have naturally occurring antibodies to group B erythrocytes whereas subjects with group B erythrocytes have antibodies to group A erythrocytes. Blood group AB subjects have neither antibody and blood group O individuals have both. Subjects with either anti-A and/or anti-B antibodies cannot receive a transfusion of blood containing the corresponding antigen. Because group 0 erythrocytes contain neither A nor B antigens, they can be safely transfused into recipients of any ABO blood group, e.g., group A, B, AB, or O recipients. Group O erythrocytes are considered universal and may be used in all blood transfusions. In contrast, group A erythrocytes may be given to group A and AB recipients, group B erythrocytes may be given to group B and AB recipients, and group AB erythrocytes may only be given to AB recipients. In embodiments in which synthetic membrane-receiver complexes are generated by connecting erythrocytes or their precursors with a receiver the sourced erythrocytes or their precursors are matched for compatibility with the recipient. 
     In some instances, it may be beneficial to convert a synthetic membrane-receiver complex comprising a non-group O erythrocyte to a universal blood type. Enzymatic removal of the immunodominant monosaccharides on the surface of group A and group B erythrocytes may be used to generate a population of group O-like synthetic membrane-receiver complexes (See, e.g., Liu et al., Nat. Biotech. 25:454-464 (2007)). Group B synthetic membrane-receiver complexes may be converted using an α-galactosidase derived from green coffee beans. Alternatively or in addition, α-N-acetylgalactosaminidase and α-galactosidase enzymatic activities derived from  E. meningosepticum  bacteria may be used to respectively remove the immunodominant A and B antigens (Liu et al., Nat. Biotech. 25:454-464 (2007)), if present on the synthetic membrane-receiver complexes. In one example, packed red blood cells isolated as described herein, are incubated in 200 mM glycine (pH 6.8) and 3 mM NaCl in the presence of either α-N-acetylgalactosaminidase and α-galactosidase (about 300 μg/ml packed red blood cells) for 60 mM at 26° C. After treatment, the red blood cells are washed by 3-4 rinses in saline with centrifugation and ABO-typed according to standard blood banking techniques. 
     In specific embodiments, the synthetic membrane-receiver complexes described herein may be generated in the following way. First, erythroid precursor cells are isolated. These cells may alternatively be autologous to the patient or from substantially universal donor blood. For example, the cells may be ABO type O, rhesus factor Rh r/r, Duffy −/−, and large Kell antigen K1 negative. In the course of differentiation from erythroid precursor cell to erythroid cell, an exogenous nucleic acid encoding the receiver is introduced. the exogenous nucleic acid encoding the receiver can be under the control of an erythroid-specific promoter, such as a GATA-1 promoter (see e.g., Repik et al., Clin Exp Immunol 2005, 140:230). the exogenous nucleic acid encoding the receiver can be introduced in any way known in the art, for example, as plasmid DNA, virus, or mRNA. Nucleic acid introduction can be achieved by a variety of standard methods, e.g., transfection, transduction, or electroporation. 
     In specific embodiments, the synthetic membrane-receiver complexes described herein may be generated by contacting platelets with a receiver. Each day an adult human produces 2×10 11  red blood cells, and about one-half as many white cells and platelets. In humans, nearly all blood cell production occurs in the red bone marrow that represents a hierarchical developmental system composed of hematopoietic stem cells, intermediate level progenitors and maturing cells committed to each lineage. 
     Although the morphology of all the major blood cell types is similar through their initial development stages, megakaryocytes, cells committed to platelet production, are marked by an obvious structural and functional departure beyond the blast cell level of differentiation growing to a size 10 times the diameter of most other bone marrow and blood cells, and containing up to 128 times the normal chromosomal complement, these cells give rise to blood platelets. After a series of normal cell divisions, the developing megakaryocyte precursor enters a unique cell cycle characterized by a brief (about 1 h) G1 phase, a typical (7 h) S phase, a very brief ( − 45 min) G2 phase, followed by the endomitotic phase (an aborted M phase). Once the cell develops a highly polyploid nucleus, it also develops demarcation membranes necessary for cytoplasmic fragmentation. This event is accompanied by expression of glycoprotein GPIIbIIIa (platelet fibrinogen receptor; Papayannopoulou et al., Exp. Hematol., 24: 660-9, 1996) and GPIb (von Willibrand factor receptor; Kaushansky et al., Nature, 369: 568-571, 1994), the granules that contain ADP, serotonin, -thromboglobulin, and other substances critical for mature platelet function. Finally, highly polyploid megakaryocytes undergo cytoplasmic partitioning, allowing the release of thousands of platelets (Choi et al., Blood, 85: 402-413, 1995; Cramer et al., Blood, 89: 2336-2346, 1997). 
     Like all blood cell precursors, megakaryocytes are derived from pluripotent marrow stem cells that retain the capacity to extensively self-renew, or to differentiate into all of the elements of the blood. Platelet production is in part regulated by signaling mechanisms induced by interaction between thrombopoietin (TPO) and its cellular receptor TPOR/MPUc-MPL. 
     Thrombopoietin (TPO) is a hematopoietic growth factor involved in stimulation of megakaryocytopoiesis and platelet production. TPO is expressed in liver and kidney, and, in response to platelet demand, its expression may be also upregulated in the bone marrow microenvironment (Kato et al., Stem Cells, 16: 322-328, 1998; McCarty et al., Blood, 86:3668-3675, 1995). As TPO expression is mostly constitutive, the TPO levels are believed to be regulated by sequestering by platelets (Fielder et al., Blood 87: 2154, 1996). 
     The gene encoding TPO has been cloned and characterized (Kuter et al., Proc. Natl. Acad. Sci. USA, 91:11104-11108, 1994; Bartley et al., Cell, 77:1117-1124, 1994; Kaushansky et al., Nature, 369:568-571, 1994; Wendling et al., Nature, 369:571-574, 1994, and de Sauvage et al., Nature, 369:533-538, 1994). Human TPO (hTPO) cDNA encodes a 353 amino acid-long polypeptide. The full-length hTPO secreted from mammalian cells after cleavage of the signal peptide consists of 332 amino acids. Although the predicted molecular mass of this protein is 38 kD, the molecular masses reported from measurements of material in serum or in culture fluid from recombinant cells vary from 18 to 85 kD (glycosylation, and post-translational proteolytic processing). 
     The cell surface receptor for TPO (TPOR/MPL/c-MPL) is a product of the protooncogene c-mpl, a homologue of v-mpl, an envelope protein of the myeloproliferative leukaemia virus (MPLV) shown to induce a pan-myeloid disorder (Wendling, Virol., 149:242-246, 1986). The human c-mpl gene codes for a protein of 635 aa having a predicted molecular weight of 71 kD (Vigon et al., Proc. Natl. Acad. Sci. USA, 89:5640-44, 1992; Mignotte et al., Genomics, 20: 5-12, 1994). 
     Mice rendered null for the expression of either TPO or its receptor (TPOR/MPL/c-MPL) manifest a severe thrombocytopenic phenotype (Gurney et al., Science, 265: 1445, 1994; Kaushansky et al., J. Clin. Invest., 96: 1683, 1995; de Sauvage et al., J. Exp. Med., 183: 651, 1996). 
     Multiple cytokines (e.g., stem cell factor [SCF], IL-1, IL-3, IL-6, IL-11, leukaemia inhibiting factor [LIF], G-CSF, GM-CSF, M-CSF, erythropoietin (EPO), kit ligand, and -interferon) have been shown to possess thrombocytopoietic activity. 
     The resulting platelets are small disc-shaped cell fragments which undergo a rapid transformation when they encounter sites of vascular damage. They become more spherical and extrude pseudopodia, their fibrinogen receptors are activated leading to aggregation, and they release their granule contents and eventually they form a plug which is responsible for primary hemostasis (Siess, W., Physiol. Rev. 69: 58-178, 1989). Activation of platelets is also implicated in the pathogenesis of unstable angina, myocardial infarction and stroke (Packham, M. A., Can J. Physiol Pharmacol. 72: 278-284). 
     Several physiological substances are involved in the activation of platelets such as collagen, which is exposed at the subendothelial surfaces, thrombin, generated by the coagulation cascade, and thromboxane A2 (TXA 2 ) and ADP, which are released from activated platelets. Collagen binds to several platelet membrane proteins including integrin a2131 leading to platelet activation through the release of TXA 2  and ADP (Shattil, S. J., et al., Curr. Opin. Cell Biol. 6: 695-704, 1994). In contrast, thrombin, TXA 2 , and ADP, activate G-protein coupled receptors directly and induce platelet aggregation and granule release (Hourani, S. M, and Cusack, N. J., Pharmacol. Rev. 43: 243-298, 1991). The major events involved in platelet activation are believed to be the result of the activation of β-isoforms of phospholipase C (PLC) leading to the generation of inositol 1,4,5 triphosphate and diacylglycerol. Platelets mainly contain two isoforms, PLC-β2 and PLC-β3. 
     Platelet receptors which mediate platelet adhesion and aggregation are located on the two major platelet surface glycoprotein complexes. These complexes are the glycoprotein Ib-IX complex which facilitates platelet adhesion by binding von Willebrand factor (vWF), and the glycoprotein IIb-IIIa complex which links platelets into aggregates by binding to fibrinogen. Patients with the Bernard-Soulier syndrome, a congenital bleeding disorder, show deficient platelet adhesion due to a deficiency in the glycoprotein Ib-IX complex which binds vWF, mild thrombocytopenia, and large lymphocoid platelets. 
     Glycoprotein V (GPV) is a major (≈12,000 molecules/platelet), heavily glycosylated platelet membrane protein (Mr 82,000). Exposure of platelets to thrombin liberates a 69 kDa soluble fragment termed GPVfl. GPV can interact non-covalently with the GPIb-IX complex a complex formed by the non-covalent association of GPIb (consisting of GPIba, a 145 kDa protein, disulfide linked to GPIbβ, a 24 kDa protein) with GPIX (a 22 kDa protein). The binding sites for von Willebrand factor and for thrombin on the GPIb-IX complex have been localized on GPIba. Since thrombin is now known to activate platelets by cleaving the thrombin receptor (Vu et. al., Cell 64:1057-1068 (1990)), a G-protein coupled receptor, it is unknown whether thrombin cleaves GPV incidentally as a consequence of thrombin binding to GPIba, or whether this cleavage has a physiological role. GPIBα, GPIBβ, and GPIX contain one or more homologous 24 amino acid leucine-rich domains. These domains are also found in a large family of leucine-rich glycoproteins (LRG). 
     GPV is a marker for the megakaryocytic cell lineage. A monoclonal antibody specific for GPV (SW16) does not bind to red cells, leukocytes endothelial cells, or cell lines such as HEL or MEG-01 which are known to express platelet megakaryocyte markers. 
     Mature GPV is composed of 543 amino acids which contain a single transmembrane domain, a short cytoplasmic domain (16 residues) and a large extracellular domain with 8 potential N-glycosylation sites. Analysis of the extracellular domain revealed the presence of 15 tandem Leu-rich repeats of 24 amino acids with homology to GPIba, and identified a cleavage site for thrombin near the C-terminus with homology to the Aa chain of fibrinogen. 
     Culturing 
     Sources for generating synthetic membrane-receiver complexes described herein include circulating cells such as erythroid cells. A suitable cell source may be isolated from a subject as described herein from patient-derived hematopoietic or erythroid progenitor cells, derived from immortalized erythroid cell lines, or derived from induced pluripotent stem cells, optionally cultured and differentiated. Methods for generating erythrocytes using cell culture techniques are well known in the art, e.g., Giarratana et al., Blood 2011, 118:5071, Huang et al., Mol Ther 2013, epub ahead of print September 3, or Kurita et al., PLOS One 2013, 8:e59890. Protocols vary according to growth factors, starting cell lines, culture period, and morphological traits by which the resulting cells are characterized. Culture systems have also been established for blood production that may substitute for donor transfusions (Fibach et al. 1989 Blood 73:100). Recently, CD34+ cells were differentiated to the reticulocyte stage, followed by successful transfusion into a human subject (Giarratana et al., Blood 2011, 118:5071). 
     Provided herein are culturing methods for erythroid cells and synthetic membrane-receiver complexes derived from erythroid cells. Erythroid cells can be cultured from hematopoietic progenitor cells, including, for example, CD34+ hematopoietic progenitor cells (Giarratana et al., Blood 2011, 118:5071), induced pluripotent stem cells (Kurita et al., PLOS One 2013, 8:e59890), and embryonic stem cells (Hirose et al. 2013 Stem Cell Reports 1:499). Cocktails of growth and differentiation factors that are suitable to expand and differentiate progenitor cells are known in the art. Examples of suitable expansion and differentiation factors include, but are not limited to, stem cell factor (SCF), an interleukin (IL) such as IL-1, IL-2, IL-3, IL-4, IL-5, IL-6, IL-7, IL-8, IL-9, IL-11, IL-12, CSF, G-CSF, thrombopoietin (TPO), GM-CSF, erythropoietin (EPO), Flt3, Flt2, PIXY 321, and leukemia inhibitory factor (LIF). 
     Erythroid cells can be cultured from hematopoietic progenitors, such as CD34+ cells, by contacting the progenitor cells with defined factors in a multi-step culture process. For example, erythroid cells can be cultured from hematopoietic progenitors in a three-step process. 
     The first step may comprise contacting the cells in culture with stem cell factor (SCF) at 1-1000 ng/mL, erythropoietin (EPO) at 1-100 U/mL, and interleukin-3 (IL-3) at 0.1-100 ng/mL. The first step optionally comprises contacting the cells in culture with a ligand that binds and activates a nuclear hormone receptor, such as e.g., the glucocorticoid receptor, the estrogen receptor, the progesterone receptor, the androgen receptor, or the pregnane×receptor. The ligands for these receptors include, for example, a corticosteroid, such as, e.g., dexamethasone at 10 nM-100 μM or hydrocortisone at 10 nM-100 μM; an estrogen, such as, e.g., beta-estradiol at 10 nM-100 μM; a progestogen, such as, e.g., progesterone at 10 nM-100 μM, hydroxyprogesterone at 10 nM-100 μM, 5a-dihydroprogesterone at 10 nM-100 μM, 11-deoxycorticosterone at 10 nM-100 μM, or a synthetic progestin, such as, e.g., chlormadinone acetate at 10 nM-100 μM; an androgen, such as, e.g., testosterone at 10 nM-100 μM, dihydrotestosterone at 10 nM-100 μM or androstenedione at 10 nM-100 μM; or a pregnane×receptor ligand, such as, e.g., rifampicin at 10 nM-100 μM, hyperforin at 10 nM-100 μM, St. John&#39;s Wort (hypericin) at 10 nM-100 μM, or vitamin E-like molecules, such as, e.g., tocopherol at 10 nM-100 μM. The first step may also optionally comprise contacting the cells in culture with an insulin-like molecule, such as, e.g., insulin at 1-50 μg/mL, insulin-like growth factor 1 (IGF-1) at 1-50 μg/mL, insulin-like growth factor 2 (IGF-2) at 1-50 μg/mL, or mechano-growth factor at 1-50 μg/mL. The first step further may optionally comprise contacting the cells in culture with transferrin at 0.1-5 mg/mL. 
     The first step may optionally comprise contacting the cells in culture with one or more interleukins (IL) or growth factors such as, e.g., IL-1, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-9, IL-11, IL-12, granulocyte colony-stimulating factor (G-CSF), macrophage colony-stimulating factor (M-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), thrombopoietin, fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), transforming growth factor beta (TGF-B), tumor necrosis factor alpha (TNF-A), megakaryocyte growth and development factor (MGDF), leukemia inhibitory factor (LIF), and Flt3 ligand. Each interleukin or growth factor may typically be supplied at a concentration of 0.1-100 ng/mL. The first step may also optionally comprise contacting the cells in culture with serum proteins or non-protein molecules such as, e.g., fetal bovine serum (1-20%), human plasma (1-20%), plasmanate (1-20%), human serum (1-20%), albumin (0.1-100 mg/mL), or heparin (0.1-10 U/mL). 
     The second step may comprise contacting the cells in culture with stem cell factor (SCF) at 1-1000 ng/mL and erythropoietin (EPO) at 1-100 U/mL. The second step may also optionally comprise contacting the cells in culture with an insulin-like molecule, such as e.g., insulin at 1-50 μg/mL, insulin-like growth factor 1 (IGF-1) at 1-50 μg/mL, insulin-like growth factor 2 (IGF-2) at 1-50 μg/mL, or mechano-growth factor at 1-50 μg/mL. The second step may further optionally comprise contacting the cells in culture with transferrin at 0.1-5 mg/mL. The second may also optionally comprise contacting the cells in culture with serum proteins or non-protein molecules such as, e.g., fetal bovine serum (1-20%), human plasma (1-20%), plasmanate (1-20%), human serum (1-20%), albumin (0.1-100 mg/mL), or heparin (0.1-10 U/mL). 
     The third step may comprise contacting the cells in culture with erythropoietin (EPO) at 1-100 U/mL. The third step may optionally comprise contacting the cells in culture with stem cell factor (SCF) at 1-1000 ng/mL. The third step may further optionally comprise contacting the cells in culture with an insulin-like molecule, such as e.g., insulin at 1-50 μg/mL, insulin-like growth factor 1 (IGF-1) at 1-50 μg/mL, insulin-like growth factor 2 (IGF-2) at 1-50 μg/mL, or mechano-growth factor at 1-50 μg/mL. The third step may also optionally comprise contacting the cells in culture with transferrin at 0.1-5 mg/mL. The third step may also optionally comprise contacting the cells in culture with serum proteins or non-protein molecules such as, e.g., fetal bovine serum (1-20%), human plasma (1-20%), plasmanate (1-20%), human serum (1-20%), albumin (0.1-100 mg/mL), or heparin (0.1-10 U/mL). 
     In some embodiments, methods of expansion and differentiation of the synthetic membrane-receiver complexes do not include culturing the synthetic membrane-receiver complexes in a medium comprising a myeloproliferative receptor (mpl) ligand. 
     The culture process may optionally comprise contacting cells by a method known in the art with a molecule, e.g., a DNA molecule, an RNA molecule, a mRNA, an siRNA, a microRNA, a lncRNA, a shRNA, a hormone, or a small molecule, that activates or knocks down one or more genes. Target genes can include, for example, genes that encode a transcription factor, a growth factor, or a growth factor receptor, including but not limited to, e.g., GATA1, GATA2, CMyc, hTERT, p53, EPO, SCF, insulin, EPO-R, SCF-R, transferrin-R, insulin-R. 
     In one embodiment, CD34+ cells are placed in a culture containing varying amounts of IMDM, FBS, glutamine, BSA, holotransferrin, insulin, dexamethasone, β-estradiol, IL-3, SCF, and erythropoietin, in three separate differentiation stages for a total of 22 days. 
     In one embodiment, CD34+ cells are placed in a culture containing varying amounts of IMDM, FBS, glutamine, BSA, holotransferrin, insulin, dexamethasone, β-estradiol, IL-3, SCF, and thrombopoietin, in three separate differentiation stages for a total of 14 days. 
     In one embodiment, CD34+ cells are placed in a culture containing varying amounts of IMDM, FBS, glutamine, BSA, holotransferrin, insulin, dexamethasone, β-estradiol, IL-3, SCF, and GCSF, in three separate differentiation stages for a total of 15 days. 
     Compositions 
     Provided herein are pharmaceutical compositions comprising synthetic membrane-receiver complexes that are suitable for administration to a subject. The pharmaceutical compositions generally comprise a population of synthetic membrane-receiver complexes and a pharmaceutically-acceptable carrier in a form suitable for administration to a subject. Pharmaceutically-acceptable carriers are determined in part by the particular composition being administered, as well as by the particular method used to administer the composition. Accordingly, there is a wide variety of suitable formulations of pharmaceutical compositions comprising a population of synthetic membrane-receiver complexes. (See, e.g., Remington&#39;s Pharmaceutical Sciences, Mack Publishing Co., Easton, Pa. 18th ed. (1990)). The pharmaceutical compositions are generally formulated as sterile, substantially isotonic and in full compliance with all Good Manufacturing Practice (GMP) regulations of the U.S. Food and Drug Administration. 
     Pharmaceutically-acceptable excipients include excipients that are generally safe, non-toxic, and desirable, including excipients that are acceptable for veterinary use as well as for human pharmaceutical use. Such excipients can be solid, liquid, semisolid, or, in the case of an aerosol composition, gaseous. 
     Examples of carriers or diluents include, but are not limited to, water, saline, Ringer&#39;s solutions, dextrose solution, and 5% human serum albumin. The use of such media and compounds for pharmaceutically active substances is well known in the art. Except insofar as any conventional media or compound is incompatible with the synthetic membrane-receiver complexes described herein, use thereof in the compositions is contemplated. Supplementary therapeutic agents may also be incorporated into the compositions. Typically, a pharmaceutical composition is formulated to be compatible with its intended route of administration. The synthetic membrane-receiver complexes can be administered by parenteral, topical, intravenous, oral, subcutaneous, intraarterial, intradermal, transdermal, rectal, intracranial, intraperitoneal, intranasal; intramuscular route or as inhalants. The synthetic membrane-receiver complexes can optionally be administered in combination with other therapeutic agents that are at least partly effective in treating the disease, disorder or condition for which the synthetic membrane-receiver complexes are intended. 
     Solutions or suspensions used for parenteral, intradermal, or subcutaneous application can include the following components: a sterile diluent such as water for injection, saline solution, fixed oils, polyethylene glycols, glycerine, propylene glycol or other synthetic solvents; antibacterial compounds such as benzyl alcohol or methyl parabens; antioxidants such as ascorbic acid or sodium bisulfite; chelating compounds such as ethylenediaminetetraacetic acid (EDTA); buffers such as acetates, citrates or phosphates, and compounds for the adjustment of tonicity such as sodium chloride or dextrose. The pH can be adjusted with acids or bases, such as hydrochloric acid or sodium hydroxide. The parenteral preparation can be enclosed in ampoules, disposable syringes or multiple dose vials made of glass or plastic. 
     Pharmaceutical compositions suitable for injectable use include sterile aqueous solutions (where water soluble) or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersion. For intravenous administration, suitable carriers include physiological saline, bacteriostatic water, Cremophor EL™ (BASF, Parsippany, N.J.) or phosphate buffered saline (PBS). In all cases, the composition must be sterile and should be fluid to the extent that easy syringeability exists. It must be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms such as bacteria and fungi. The carrier can be a solvent or dispersion medium containing, e.g., water, ethanol, polyol (e.g., glycerol, propylene glycol, and liquid polyethylene glycol, and the like), and suitable mixtures thereof. The proper fluidity can be maintained, e.g., by the use of a coating such as lecithin, by the maintenance of the required particle size in the case of dispersion and by the use of surfactants. Prevention of the action of microorganisms can be achieved by various antibacterial and antifungal compounds, e.g., parabens, chlorobutanol, phenol, ascorbic acid, thimerosal, and the like. In many cases, it will be preferable to include isotonic compounds, e.g., sugars, polyalcohols such as manitol, sorbitol, sodium chloride in the composition. Prolonged absorption of the injectable compositions can be brought about by including in the composition a compound which delays absorption, e.g., aluminum monostearate and gelatin. 
     Sterile injectable solutions can be prepared by incorporating the synthetic membrane-receiver complexes in an effective amount and in an appropriate solvent with one or a combination of ingredients enumerated herein, as desired. Generally, dispersions are prepared by incorporating the synthetic membrane-receiver complexes into a sterile vehicle that contains a basic dispersion medium and any desired other ingredients. In the case of sterile powders for the preparation of sterile injectable solutions, methods of preparation are vacuum drying and freeze-drying that yields a powder of the active ingredient plus any additional desired ingredient from a previously sterile-filtered solution thereof. The synthetic membrane-receiver complexes can be administered in the form of a depot injection or implant preparation which can be formulated in such a manner to permit a sustained or pulsatile release of the synthetic membrane-receiver complexes, their receiver(s) and/or their oprional payload(s). 
     Oral compositions generally include an inert diluent or an edible carrier. They can be enclosed in gelatin capsules or compressed into tablets. For the purpose of oral therapeutic administration, the synthetic membrane-receiver complexes can be incorporated with excipients and used in the form of tablets, troches, or capsules. Oral compositions can also be prepared using a fluid carrier for use as a mouthwash, wherein the compound in the fluid carrier is applied orally and swished and expectorated or swallowed. Pharmaceutically compatible binding compounds, and/or adjuvant materials can be included as part of the composition. The tablets, pills, capsules, troches and the like can contain any of the following ingredients, or compounds of a similar nature: a binder such as microcrystalline cellulose, gum tragacanth or gelatin; an excipient such as starch or lactose, a disintegrating compound such as alginic acid, Primogel, or corn starch; a lubricant such as magnesium stearate or Sterotes; a glidant such as colloidal silicon dioxide; a sweetening compound such as sucrose or saccharin; or a flavoring compound such as peppermint, methyl salicylate, or orange flavoring. 
     For administration by inhalation, the synthetic membrane-receiver complexes are delivered in the form of an aerosol spray from pressured container or dispenser which contains a suitable propellant, e.g., a gas such as carbon dioxide, or a nebulizer. 
     Systemic administration of compositions comprising synthetic membrane-receiver complexes can also be by transmucosal or transdermal means. For transmucosal or transdermal administration, penetrants appropriate to the barrier to be permeated are used in the formulation. Such penetrants are generally known in the art, and include, e.g., for transmucosal administration, detergents, bile salts, and fusidic acid derivatives. Transmucosal administration can be accomplished through the use of nasal sprays or suppositories. For transdermal administration, the modified red blood cells are formulated into ointments, salves, gels, or creams as generally known in the art. 
     The synthetic membrane-receiver complexes can also be prepared as pharmaceutical compositions in the form of suppositories (e.g., with conventional suppository bases such as cocoa butter and other glycerides) or retention enemas for rectal delivery. 
     In some embodiments, the synthetic membrane-receiver complexes are prepared with carriers that will decrease the rate with which synthetic membrane-receiver complexes are eliminated from the body of a subject. For example, controlled release formulation are suitable, including implants and microencapsulated delivery systems. Biodegradable, biocompatible polymers can be used, such as ethylene vinyl acetate, polyanhydrides, polyglycolic acid, collagen, polyorthoesters, and polylactic acid. Methods for preparation of such formulations will be apparent to those skilled in the art. The materials can also be obtained commercially from Alza Corporation and Nova Pharmaceuticals, Inc. 
     In one embodiment the pharmaceutical composition comprising synthetic membrane-receiver polypeptide complexes is administered intravenously into a subject that would benefit from the pharmaceutical composition. In other embodiments, the composition is administered to the lymphatic system, e.g., by intralymphatic injection or by intranodal injection (see e.g., Senti et al., 2008 PNAS 105(46):17908), or by intramuscular injection, by subcutaneous administration, by direct injection into the thymus, or into the liver. 
     In one embodiment, the pharmaceutical composition comprising synthetic membrane-receiver polypeptide complexes is administered as a liquid suspension. In one embodiment the pharmaceutical composition is administered as a coagulated formulation that is capable of forming a depot following administration, and in a preferred embodiment slowly release synthetic membrane-receiver polypeptide complexes into circulation, or in a preferred embodiment remain in depot form. 
     In one embodiment, the pharmaceutical composition comprising synthetic membrane-receiver complexes is stored using methods and buffer compositions that are capable of maintaining viability of the synthetic membrane-receiver complexes. For example, deoxygenation prior to storage to maintain an anaerobic state, manipulation of pH, supplementation of metabolic precursors, manipulation of osmotic balance, increasing of the volume of the suspending medium, and/or reduction of oxidative stress by adding protective molecules can be used to maintain the viability of the synthetic membrane-receiver complexes. Several studies employing a combination of these strategies have reported maintenance of viability of erythrocytes allowing an extension of storage beyond 6 weeks (see e.g., Yoshida and Shevkoplyas, Blood Transfus 2010 8:220). 
     Pharmaceutically acceptable carriers or excipients may be used to deliver the synthetic membrane-receiver polypeptides described herein. Excipient refers to an inert substance used as a diluent or vehicle. Pharmaceutically acceptable carriers are used, in general, with a compound so as to make the compound useful for a therapy or as a product. In general, for any substance, a pharmaceutically acceptable carrier is a material that is combined with the substance for delivery to a subject. Conventional pharmaceutical carriers, aqueous, powder or oily bases, thickeners and the like may be necessary or desirable. In some cases the carrier is essential for delivery, e.g., to solubilize an insoluble compound for liquid delivery; a buffer for control of the pH of the substance to preserve its activity; or a diluent to prevent loss of the substance in the storage vessel. In other cases, however, the carrier is for convenience, e.g., a liquid for more convenient administration. Pharmaceutically acceptable salts of the compounds described herein may be synthesized according to methods known to those skilled in the arts. 
     Typically, pharmaceutically acceptable compositions are highly purified to be free of contaminants, are biocompatible and not toxic, and are suited to administration to a subject. If water is a constituent of the carrier, the water is highly purified and processed to be free of contaminants, e.g., endotoxins. 
     The pharmaceutically acceptable carrier may be lactose, dextrose, sucrose, sorbitol, mannitol, starch, gum acacia, calcium phosphate, alginates, gelatin, calcium silicate, micro-crystalline cellulose, polyvinylpyrrolidone, cellulose, water, syrup, methyl cellulose, methylhydroxy benzoate, propylhydroxy benzoate, talc, magnesium stearate, and/or mineral oil, but is not limited thereto. The pharmaceutical composition may further include a lubricant, a wetting agent, a sweetener, a flavor enhancer, an emulsifying agent, a suspension agent, and/or a preservative. 
     Provided are pharmaceutical compositions containing synthetic membrane-receiver complexes having effective levels of receivers. Such compositions contain a plurality of synthetic membrane-receiver complexes, e.g., 1×10 3  complexes, or 1×10 4 , 1×10 5 , 1×10 6 , 1×10 7 , 1×10 8 , 1×10 9 , 1×10 10 , 1×10 11 , 1×10 12 , or greater than 1×10 12  complexes. In specific examples, synthetic membrane-receiver complexes generated from erythroid cells may be administered as packed red blood cells in a saline solution at a concentration of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or greater than 90% mass to volume ratio (% m/v). The time of administration to a patient may range from 10 minutes to four hours, or more. 
     In specific examples, synthetic membrane-receiver complexes generated from erythroid cells can be stored in an appropriate buffer, e.g., an FDA-approved anticoagulant preservative solution such as anticoagulant citrate-dextrose A (ACD-A), citrate-phosphate dextrose (CPD), Citratephosphate-dextrose-dextrose (CP2D), or citrate-phosphate-dextrose-adenine (CPDA-1). The compositions may be stored for up to 21 days. 
     Alternatively, synthetic membrane-receiver complexes generated from erythroid cells can be stored in an approved additive solution, e.g., AS-1 (Adsol), AS-3 (Nutricel), AS-5 (Optisol), or AS-7 (SOLX). 
     Alternatively, synthetic membrane-receiver complexes generated from erythroid cells can stored in a glycerol cryoprotective solution. The compositions may be frozen and stored for up to 10 years. Frozen cells may be thawed and deglycerolized by successive washing steps, for example with 0.9% sodium chloride before use. 
     Provided herein are compositions and pharmaceutical compositions comprising a plurality of cultured functional erythroid cells that comprise a receiver. The compositions and pharmaceutical compositions may comprise a solution of appropriate storage buffer such as, e.g., anticoagulant citrate-dextrose A. The compositions and pharmaceutical compositions comprising the plurality of cultured functional erythroid cells that comprise a receiver may additionally comprise an approved additive such as, e.g., Adsol. The compositions and pharmaceutical compositions comprising the plurality of cultured functional erythroid cells that comprise receiver may additionally comprise a glycerol cryoprotective solution for frozen storage. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex is able to form a multi-complex aggregate, e.g., a dimer, a trimer, a multimer, with another synthetic membrane-receiver polypeptide complex. 
     In one embodiment the synthetic membrane-receiver polypeptide complex is able to form a multi-complex aggregate, e.g., a dimer, a trimer, a multimer, with component of the circulatory system, e.g an erythrocyte, a reticulocyte, a platelet, a macrophage, a lymphocyte, a T cell, a B cell, a mast cell. 
     The dosing and frequency of the administration of the synthetic membrane-receiver complexes and pharmaceutical compositions thereof can be determined by the attending physician based on various factors such as the severity of disease, the patient&#39;s age, sex and diet, the severity of any inflammation, time of administration, and other clinical factors. In one example, an intravenous administration is initiated at a dose which is minimally effective, and the dose is increased over a pre-selected time course until a positive effect is observed. Subsequently, incremental increases in dosage are made limiting to levels that produce a corresponding increase in effect while taking into account any adverse affects that may appear. 
     Non-limited examples of suitable dosages can range, for example, from 1×10 10  to 1×10 14 , from 1×10 11  to 1×10 13 , or from 5×10 11  to 5×10 12  synthetic membrane-receiver complexes. Specific examples include about 5×10 10 , 6×10 10 , 7×10 10 , 8×10 10 , 9×10 10 , 1×10 11 , 2×10 11 , 3×10 11 , 4×10 11 , 5×10 11 , 6×10 11 , 7×10 11 , 8×10 11 , 9×10 11 , 1×10 12 , or more synthetic membrane-receiver complexes. Each dose of synthetic membrane-receiver complexes can be administered at intervals such as once daily, once weekly, twice weekly, once monthly, or twice monthly. 
     “Complex-based proportional dosage” is the number of synthetic membrane-receiver complexes administered as a dose relative to a naturally occurring quantity of circulating entities. The circulating entities may be cells, e.g., erythrocytes, reticulocytes, or lymphocytes, or targets, e.g., antigens, antibodies, viruses, toxins, cytokines, etc. The units are defined as synthetic membrane-receiver complex per circulating entity, ie SCMRC/CE. This dosage unit may include 10 −7 , 10 −6 , 10 −5 , 10 −4 , 10 −3 , 10 −2 , 10 −1 , 1, 10, 10 2 , 10 3 , 10 4 , 10 5 , 10 6 , 10 7 , 10 8 , 10 9 . 
     The pharmaceutical compositions described herein comprise a synthetic membrane-receiver complex and optionally a pharmaceutically active or therapeutic agent. The therapeutic agent can be a biological agent, a small molecule agent, or a nucleic acid agent. 
     Dosage forms are provided that comprise a pharmaceutical composition comprising a synthetic membrane-receiver complex described herein. In some embodiments, the dosage form is formulated as a liquid suspension for intravenous injection. 
     Medical devices are provided that comprise a container holding a pharmaceutical composition comprising a synthetic membrane-receiver complex described herein and an applicator for intravenous injection of the pharmaceutical composition to a subject. 
     Medical kits are provided that comprise a pharmaceutical composition comprising a synthetic membrane-receiver complex described herein and a medical device for intravenous injection of the pharmaceutical composition to a subject. 
     A pharmaceutically acceptable suspension of synthetic membrane-receiver complexes is preferably packaged in a volume of approximately 10 to approximately 250 ml. The packaging can be a syringe or an IV bag suitable for transfusions. Administration of the suspension is carried out, e.g., by intravenous or intra-arterial injection, optionally using a drip from an IV bag or the like. The administration is typically carried out intravenously in the arm or via a central catheter. For administrations exceeding 50 ml use of a drip is preferred. 
     Provided herein are pharmaceutical compositions and dosage forms comprising populations of erythroid cells, such as enucleated erythroid cells that comprise a receiver polypeptide. In some embodiments, the pharmaceutical preparations of erythroid cells contain little to no oxygen. In some embodiments, the oxygen saturation (SO 2 ) of the preparation is less than about 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, 1%, or less than about 0.5% oxygen. For long-term storage of the erythroid cell populations described herein it is desirable to reduce or eliminate oxidative damage to the erythroid cells during prolonged hypothermic storage. 
     In some embodiments, the erythroid cell populations are contacted with an inert or noble gas, such as, e.g. helium (He), neon (Ne), argon (Ar), krypton (Kr), or xenon (Xe) to improve their viability and/or longevity during storage. The methods include removal of oxygen from the erythroid population in a suitable container and contacting the cells with an inert or noble gas. The concentration of the noble gas is selected such that it is higher than the concentration it normally occurs in the atmosphere. The cell populations may be stored in an environment that maintains the concentration of the noble gas. In some embodiments, the cell populations are stored in refrigerated temperatures, such as e.g. below about 20° C., 15° C., 10° C., 5° C., or below about 4° C., however, the population is not kept at temperatures below the freezing point. The method may be carried out as described, e.g., in US Patent Publication No. 2014/0154666. 
     In one embodiment, the pharmaceutical preparation of erythroid cells is formulated under anaerobic conditions. In one embodiment, anaerobic erythroid cell preparations are made according to the following protocol. Erythroid cells are transferred to a 1L PVC transfer bag (Baxter Healthcare, Round Lake, IL) and oxygen is depleted (to an SO 2 &lt;3.6%) through six or more cycles of gas exchange with ultrapure argon. The erythroid cell preparation is subsequently transferred to a 600 ml transfer pack (Baxter) for storage in an anaerobic chamber (Difco BBL, Detroit, Mich.) that is prefilled with 10% hydrogen and 90% argon in the presence of a palladium catalyst to prevent reoxygenation and to further deplete oxygen during storage. The preparation is gently mixed and the chamber is recharged weekly for up to 9 weeks of storage. 
     If so desired, carbon dioxide (CO 2 ) may also be removed from the pharmaceutical compositions comprising erythroid cells. The lowering of carbon dioxide concentrations can improve metabolic parameters and in vivo recovery kinetics of the cells. In some embodiments, both oxygen and carbon dioxide are depleted and the erythroid cell population is stored in a container that is impermeable for oxygen and carbon dioxide. The depletion of oxygen and carbon dioxide may be performed as described in, e.g. US Patent Publication No. 2012/0225416. In some embodiments, the pharmaceutical composition comprising the erythroid cells that is suitable for storage comprises an acidified additive solution (e.g. of a pH ranging from 5.5 to 7.0). 
     If so desired, the erythroid cell populations may be treated with nitric oxide (NO) to enhance the storability of the erythroid population by converting most or all of the hemoglobin (Hb) to NO-bound Hb (e.g. alpha-nitrosyl-Hb). For example, at least about 70%, 80%, 90%, 95%, 97%, 99%, or at least about 99.9% of Hb may be NO-bound. Suitable methods include a deoxygenating step and contacting with a sufficient quantity of nitric oxide to covert the Hb to NO-bound Hb. The method may be carried out as described, e.g., in European Patent No. EP 0948337B1, Treatment of hemoglobin containing erythrocytes with nitric oxide. 
     In some embodiments, the storage conditions described herein provide significant reductions in hemolysis of the erythroid cell population. For example, the population may exhibit less than about 5%, 4%, 3%, 2%, 1%, 0.5%, or less than about 0.1% hemolysis when a suitably treated erythroid population is stored for at least 1 day, 2 days, 3 days, 4 days, 5 days, 6 days, 7 days, 2 weeks, 3 weeks, 4 weeks, 5 weeks, 6 weeks, 7 weeks, 8 weeks, 9 weeks, 10 weeks, 12 weeks, 14 weeks, 16 weeks, 18 weeks or for at least 20 weeks. 
     Any suitable container may be used to package the erythroid cell populations, optionally treated for long-term storage as described herein. Suitable containers include, e.g., tubes and bags. The shape, material and volume is non-limiting and can be selected by one of ordinary skill as desired. In some embodiments, the storage container comprises a DEHP plasticizer. In other embodiments, the storage container does not comprise a DEHP plasticizer. 
     Processes and Properties 
     In some embodiments, the membrane-receiver complex is generated using a precursor hematopoietic cell, e.g., a CD34+ cell, an erythrocyte, a platelet, a megakaryocyte, or a neutrophil as a source. In some embodiments, the precursor hematopoietic cell is isolated from a human donor by a GMP-compliant process. In some embodiments, the starting cells are sourced from an autologous donor. In some embodiments, the starting cells are sourced from an allogeneic donor. The donor may be typed for blood cell antigen polymorphisms and/or the donor is genotyped for blood cell antigens. The donor can be a universal blood donor. In some embodiments, the donor has the Bombay phenotype, .ie. does not express the H antigen. In some embodiments, the donor has ABO blood type O and is Rh-negative. 
     In some embodiments, the membrane-receiver complex is generated using CD34+ hematopoietic progenitor cells, mobilized peripheral CD34+ cells, or bone marrow-derived CD34+ cells as a source for the starting material. In some embodiments, the starting cells are derived from umbilical cord blood, are induced pluripotent stem cells or are embryonic stem cells. 
     The synthetic membrane-receiver complex may be cultured. Cultured complexes can be scaled up from bench-top scale to bioreactor scale. For example, the complexes are cultured until they reach saturation density, e.g., 1×10 5 , 1×10 6 , 1×10 7 , or greater than 1×10 7  complexes per ml. Optionally, upon reaching saturation density, the complexes can be transferred to a larger volume of fresh medium. The membrane-receiver complexes may be cultured in a bioreactor, such as, e.g., a Wave-type bioreactor, a stirred-tank bioreactor. Various configurations of bioreactors are known in the art and a suitable configuration may be chosen as desired. Configurations suitable for culturing and/or expanding populations of synthetic membrane-receiver complexes can easily be determined by one of skill in the art without undue experimentation. The bioreactor can be oxygenated. The bioreactor may optionally contain one or more impellers, a recycle stream, a media inlet stream, and control components to regulate the influx of media and nutrients or to regulate the outflux of media, nutrients, and waste products. 
     In some embodiments, the bioreactor may contain a population of human functional erythroid cells comprising a receiver that shed their intracellular DNA over the course of the culture process. For example, the bioreactor may contain a population of human erythroid cells, enucleated erythroid cells, and pyrenocytes after culture. In a specific embodiment, the human erythroid cells and enucleated erythroid cells comprise a receiver and the receiver is retained by the enucleated erythroid cell, whereas the exogenous nucleic acid encoding the receiver is not retained by the enucleated cell. In certain embodiments, the enucleated functional erythroid cell comprising the receiver exhibits substantially the same osmotic membrane fragility as a corresponding isolated unmodified, uncultured erythroid cell. 
     In one embodiment. The population of synthetic membrane-receiver complexes generated from erythroid cells or erythroid cell precursors in the bioreactor undergo a total expansion of greater than 5,000-fold, 10,000-fold, 15,000-fold, 20,000-fold, 25,000-fold, 30,000-fold, 35,000-fold or greater than 40,000-fold in 14 days. In some embodiments, the receiver is introduced into a cultured or freshly isolated erythroid cell precursor and after introduction of an exogenous nucleic acid encoding the receiver the population of synthetic membrane-receiver complexes generated from the erythroid cell precursors in the bioreactor expands in the bioreactor from the precursor cells by greater than 5,000-fold, 10,000-fold, 15,000-fold, 20,000-fold, 25,000-fold, 30,000-fold, 35,000-fold or greater than 40,000-fold in 14 days. 
     In some embodiments, the bioreactor is a Wave bioreactor or a impeller-driven agitator. The bioreactor may be aerated by means of a sparger. In one embodiment, the bioreactor is disposable. In one embodiment, the bioreactor is CIP (cleaned in place). The final complexes number of synthetic membrane-receiver complexes that may be obtained in a bioreactor setting as described herein can be greater than 10 9 , 10 10 , 10 11 , 10 12 , 10 13  or greater than 10 13  complexes. The density of synthetic membrane-receiver complexes may be monitored during culture by measuring cell density by hemacytometer counting or by optical density reading at 600 nm. Optionally, the culture process is monitored for pH levels, oxygenation, agitation rate, and/or recycle rate. 
     The identity of the membrane-receiver complexes can be assessed by in vitro assays. For example, the identity of the membrane-receiver complexes is assessed by counting the number of complexes in a population, e.g., by microscopy, by flow cytometry, or by hemacytometry. Alternatively or in addition, the identity of the membrane-receiver complexes is assessed by analysis of protein content of the complex, e.g., by flow cytometry, Western blot, immunoprecipitation, fluorescence spectroscopy, chemiluminescence, mass spectrometry, or absorbance spectroscopy. In one embodiment, the protein content assayed is a non-surface protein, e.g., an integral membrane protein, hemoglobin, adult hemoglobin, fetal hemoglobin, embryonic hemoglobin, a cytoskeletal protein. In one embodiment, the protein content assayed is a surface protein, e.g., a differentiation marker, a receptor, a co-receptor, a transporter, a glycoprotein. In one embodiment, the surface protein is selected from the list including, but not limited to, glycophorin A, CKIT, transferrin receptor, Band3, Kell, CD45, CD46, CD47, CD55, CD59, CR1. In some embodiments, the identity of the membrane-receiver complexes is assessed by analysis of the receiver content of the complex, e.g., by flow cytometry, Western blot, immunoprecipitation, fluorescence spectroscopy, chemiluminescence, mass spectrometry, or absorbance spectroscopy. For example, the identity of the membrane-receiver complexes can be assessed by the mRNA content of the complexes, e.g., by RT-PCR, flow cytometry, or northern blot. The identity of the membrane-receiver complexes can be assessed by nuclear material content, e.g., by flow cytometry, microscopy, or southern blot, using, e.g., a nuclear stain or a nucleic acid probe. Alternatively or in addition, the identity of the membrane-receiver complexes is assessed by lipid content of the complexes, e.g by flow cytometry, liquid chromatography, or by mass spectrometry. 
     In some embodiments, the identity of the membrane-receiver complexes is assessed by metabolic activity of the complexes, e.g by mass spectrometry, chemiluminescence, fluorescence spectroscopy, absorbance spectroscopy. Metabolic activity can be assessed by ATP consumption rate and/or the metabolic activity is assessed measuring 2,3-diphosphoglycerate (2,3-DPG) level in the synthetic membrane-receiver complex. The metabolic activity can be assessed as the rate of metabolism of one of the following, including but not limited to, Acetylsalicylic acid, N-Acetylcystein, 4-Aminophenol, Azathioprine, Bunolol, Captopril, Chlorpromazine, Dapsone, Daunorubicin, Dehydroepiandrosterone, Didanosin, Dopamine, Epinephrine, Esmolol, Estradiol, Estrone, Etoposide, Haloperidol, Heroin, Insulin, Isoproterenol, Isosorbide dinitrate, LY 217896, 6-mercaptopurine, Misonidazole, Nitroglycerin, Norepinephrine, Para-aminobenzoic acid. In some embodiments, the identity of the membrane-receiver complexes is assessed by partitioning of a substrate by the complexes, e.g by mass spectrometry, chemiluminescence, fluorescence spectroscopy, or absorbance spectroscopy. The substrate can be one of the following, including but not limited to, Acetazolamide, Arbutine, Bumetamide, Creatinine, Darstine, Desethyldorzolamide, Digoxigenin digitoxoside, Digoxin-16′-glucuronide, Epinephrine, Gentamycin, Hippuric acid, Metformin, Norepinephrine, p-Aminohippuric acid, Papaverine, Penicillin G, Phenol red, Serotonin, Sulfosalicylic acid, Tacrolimus, Tetracycline, Tucaresol, and Vancomycin. 
     In one embodiment, the population of synthetic membrane-receiver complexes is differentiated from a precursor cell or complex. In this embodiment, the differentiation state of the population of synthetic membrane-receiver complexes is assessed by an in vitro assay. The in vitro assays include those described herein for assessing the identity of the complexes, including but not limited to expansion rate, number, protein content or expression level, mRNA content or expression level, lipid content, partition of a substrate, catalytic activity, or metabolic activity. 
     In some embodiments, the membrane-receiver complexes are cultured and the differentiation state of the complexes is assessed at multiple time points over the course of the culture process. 
     Synthetic membrane-receiver complexes may be generated using reticulocytes as a source for starting material. The purity of isolated reticulocytes may be assessed using microscopy in that reticulocytes are characterized by a reticular (mesh-like) network of ribosomal RNA that becomes visible under a microscope with certain stains such as new methylene blue or brilliant cresyl blue. Surface expression of transferrin receptor (CD71) is also higher on reticulocytes and decreases and they mature to erythrocytes, allowing for enrichment and analysis of reticulocyte populations using anti-CD71 antibodies (See, e.g., Miltenyi CD71 microbeads product insert No. 130-046-201). Alternatively, analysis of creatine and hemoglobin A1C content and pyruvate kinase, aspartate aminotransferase, and porphobilinogen deaminase enzyme activity may be used to assess properties of the isolated reticulocytes relative to mature erythrocytes (See, e.g., Brun et al., Blood 76:2397-2403 (1990)). For example, the activity of porphobilinogen deaminase is nearly 9 fold higher whereas the hemoglobin A1C content is nearly 10 fold less in reticulocytes relative to mature erythrocytes. 
     In some embodiments, cells suitable for generating synthetic membrane-receiver complexes are differentiated ex vivo and/or in vivo from one or more stem cells. In one embodiment, the one or more stem cells are one or more hematopoietic stem cells. Various assays may be performed to confirm the ex vivo differentiation of cultured hematopoietic stem cells into reticulocytes and erythrocytes, including, for example, microscopy, hematology, flow cytometry, deformability measurements, enzyme activities, and hemoglobin analysis and functional properties (Giarratana et al., Nature Biotech. 23:69-74 (2005)). The phenotype of cultured hematopoietic stem cells may be assessed using microscopy of cells stained, for example, with Cresyl Brilliant blue. Reticulocytes, for example, exhibit a reticular network of ribosomal RNA under these staining conditions whereas erythrocytes are devoid of staining. Enucleated cells may also be monitored for standard hematological variables including mean corpuscular volume (MCV; femtoliters (fL)), mean corpuscular hemoglobin concentration (MCHC; %) and mean corpuscular hemoglobin (MCH; pg/cell) using, for example, an XE2100 automat (Sysmex, Roche Diagnostics). 
     In some embodiments, the synthetic membrane-receiver complexes are assessed for their basic physical properties, e.g., size, mass, volume, diameter, buoyancy, density, and membrane properties, e.g., viscosity, deformability fluctuation, and fluidity. 
     In one embodiment, the diameter of the synthetic membrane-receiver complexes is measured by microscopy or by automated instrumentation, e.g., a hematological analysis instrument. In one embodiment the diameter of the synthetic membrane-receiver complexes is between about 1-20 microns. In one embodiment, the diameter of the synthetic membrane-receiver complexes is at least in one dimension between about 1-20 microns. In one embodiment, the diameter of the synthetic membrane-receiver complexes is less than about 1 micron. In one embodiment, the diameter of the complexes in one dimension is larger than about 20 microns. In one embodiment, the diameter of the synthetic membrane-receiver complexes is between about 1 micron and about 20 microns, between about 2 microns and about 20 microns between about 3 microns and about 20 microns between about 4 microns and about 20 microns between about 5 microns and about 20 microns between about 6 microns and about 20 microns, between about 5 microns and about 15 microns or between about 10 microns and about 30 microns. 
     In one embodiment, the mean corpuscular volume of the synthetic membrane-receiver complexes is measured using a hematological analysis instrument. In one embodiment the volume of the mean corpuscular volume of the complexes is greater than 10 fL, 20 fL, 30 fL, 40 fL, 50 fL, 60 fL, 70 fL, 80 fL, 90 fL, 100 fL, 110 fL, 120 fL, 130 fL, 140 fL, 150 fL, or greater than 150 fL. In one embodiment the mean corpuscular volume of the complexes is less than 30 fL, 40 fL, 50 fL, 60 fL, 70 fL, 80 fL, 90 fL, 100 fL, 110 fL, 120 fL, 130 fL, 140 fL, 150 fL, 160 fL, 170 fL, 180 fL, 190 fL, 200 fL, or less than 200 fL. In one embodiment the mean corpuscular volume of the complexes is between 80-100 femtoliters (fL). 
     In one embodiment the average buoyant mass of the synthetic membrane-receiver complexes (pg/cell) is measured using a suspended microchannel resonatory or a double suspended microchannel resonatory (see e.g., Byun et al PNAS 2013 110(19):7580 and Bryan et al. Lab Chip 2014 14(3):569). 
     In one embodiment the dry density of the synthetic membrane-receiver complexes is measured by buoyant mass in an H2O-D20 exchange assay (see e.g., Feijo Delgado et al., PLOS One 2013 8(7):e67590). 
     In some embodiments, the synthetic membrane-receiver complexes have an average membrane deformability fluctuation of standard deviation greater than 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 or greater than 100 mrad as measured by spatial light interference microscopy (SLIM) (see e.g., Bhaduri et al., Sci Reports 2014, 4:6211). 
     In one embodiment, the average membrane viscosity of a population of synthetic membrane-receiver complexes is measured by detecting the average fluorescence upon incubation with viscosity-dependent quantum yield fluorophores (see e.g., Haidekker et al. Chem &amp; Biol 2001 8(2):123). 
     In one embodiment, the membrane fluidity of the synthetic membrane-receiver complexes is measured by fluorescence polarization, e.g., with BMG Labtech POLARstar Omega microplate reader. 
     For example, to measure deformability reticulocytes may be separated from nucleated cells on day 15 of culture, for example, by passage through a deleukocyting filter (e.g., Leucolab LCG2, Macopharma) and subsequently assayed using ektacytometry. The enucleated cells are suspended in 4% polyvinylpyrrolidone solution and then exposed to an increasing osmotic gradient from 60 to 450 mosM. Changes in the laser diffraction pattern (deformability index) of the cells are recorded as a function of osmolarity, to assess the dynamic deformability of the cell membrane. The maximum deformability index achieved at a physiologically relevant osmolarity is related to the mean surface area of erythrocytes. 
     In some embodiments, the synthetic membrane-receiver complexes are analyzed for hemoglobin contents. Assays of hemoglobin may be used to assess the phenotype of differentiated cells (Giarratana et al., Nature Biotech. 23:69-74 (2005)). For example, high performance liquid chromatography (HPLC) using a Bio-Rad Variant II Hb analyzer (Bio-Rad Laboratories) may be used to assess the percentage of various hemoglobin fractions. Oxygen equilibrium may be measured using a continuous method with a double-wavelength spectrophotometer (e.g., Hemox analyzer, TCS). The binding properties of hemoglobin may be assessed using flash photolysis. In this method, the rebinding of CO to intracellular hemoglobin tetramers are analyzed at 436 nm after photolysis with a 10 nanosecond pulse at 532 nm. 
     The synthetic membrane-receiver complexes described herein can be purified following manufacture if desired. Many suitable methods of purification are known in the art. For example, the synthetic membrane-receiver complexes are purified by centrifugation, magnetophoresis, irradiation, acoustophoresis, and chemical or physical enucleation. In one embodiment synthetic membrane-receiver complexes are purified by ex vivo maturation with, e.g., a stromal cell co-culture. 
     Provided herein are highly purified populations of erythroid cells comprising a receiver. Such populations may comprise, e.g., about 1×10 3 , 1×10 4 , 1×10 5 , 1×10 6 , 1×10 7 , 1×10 8 , 1×10 9 , 1×10 10 , 1×10 11 , 1×10 12 , 1×10 13 , 1×10 14 , or more erythroid cells. Such populations may comprise at least about 50%, 60%, 70%, 80%, 85%, 90%, 95%, 97%, 98%, 99%, or at least about 99.9% erythroid cells of a desired characteristic. In some embodiments, the erythroid cells comprised in the population are enucleated. In some embodiments, the highly purified populations are formulated into pharmaceutical compositions or dosage forms. In some embodiments, pharmaceutical compositions or dosage forms are provided comprising highly purified, enucleated erythroid populations of cells comprising a receiver polypeptide. In one embodiment, the pharmaceutical preparation contains &gt;95%, &gt;99%, &gt;99.5%, &gt;99.9% enucleated erythroid cells comprising a polypeptide receiver. In one embodiment, highly purified populations of enucleated erythroid cells are generated by passage of the cells through a suitable filter medium. In some embodiments, the suitable filter medium is a de-leukocyting filter. Leukocyte removing filter media are known in the art, e.g. U.S. Pat. Nos. 5,498,336; 5,830,755; 5,476,587; and 8,900,462, which are suitable for filtering red blood cells, and e.g. U.S. Pat. No. 7,140,497, which allows for the filtering of platelets to obtain a platelet filtrate free from leukocytes. In some embodiments, the suitable filter medium is an affinity medium that specifically enriches cells that express high levels of the receiver. For example, the receiver may contain a recognizable epitope—such as e.g. an epitope tag, an antibody Fc domain, a glutathione S transferase domain, a maltose-binding-protein domain, a biotin-binding domain, a FITC-binding domain, or another small molecule or polypeptide or oligosaccharide binding domain—that is then recognized by a suitable capture medium, e.g. an anti-epitope tag resin, Protein A or Protein G, glutathione resin, amylose resin, biotin-containing resin, FITC-containing resin, an affinity resin specific for the receiver polypeptide, or other suitable affinity medium. The various media generally exploit molecular affinities, electrostatic interactions, and/or size exclusion to accomplish the separation. 
     In one embodiment, synthetic membrane-receiver complexes are purified by chemical or enzymatic treatment of complexes, e.g by treatment with a deglycosylation enzyme and/or a protease to decrease the number of immunogenic glycosylation and the number of antigenic peptides, respectively. 
     Provided herein are populations of omnicompatible (OC) erythroid cells and methods of producing the omnicompatible cells. These erythroid cells are universal or compatible with a wide array of recipients. In some embodiments, OC erythroid cells are devoid of or possess a significantly reduced number of specific surface antigens. The lack or reduction of antigens on the OC erythroid cells may eliminate or significantly delay the development of alloimmunity and/or reduce the adverse and sometimes fatal reactions following blood transfusion or infusion. In some embodiments, OC erythroid cells are provided that lack all or a subset of specific carbohydrate structures on the glycoproteins. 
     Glycosylated proteins (glycoproteins) are polypeptides comprising covalently attached carbohydrate side chains. The oligosaccharide side chains of glycoproteins are linked enzymatically to the polypeptide during the normal course of its biosynthesis, are composed of several different monosaccharides; and usually branched. Attachment of side chains to the protein involves either an N-glycosidic or an O-glycosidic bond and four different linkages occur in proteins of mammalian origin. The most prevalent linkage, the N-linkage involving asparagine (Asn) and N-acetyl-D-glucosamine (GlcNAc), is present in most of the plasma glycoproteins as well as in many cell surface glycoproteins (Martinez et al. Lab Invest 57:240-257, 1987). The biosynthesis of O-linked glycoproteins is a one-step process with step-wise addition of sugars to a protein. For N-linked glycoproteins individual monosaccharides are first assembled into a high-mannose structure on a carrier lipid and the entire structure is then transferred in a single step to the peptide. The lipid, which is known as dolichol-phosphate (dolichol-P), is an unsaturated fatty acid containing 80 to 110 carbons and belonging to the polyprenol family. The glycosylated high-mannose structure, which is N-glycosidically linked in a single step to an asparagine moiety of the polypeptide, constitutes the precursor for oligosaccharide processing and the addition of peripheral sugars to the outer chain structure. The trimming of monosaccharides and the addition of peripheral sugars is an orderly process that is mediated by glycosidases and transferases present in the endoplasmic reticulum and Golgi apparatus. The final peripheral sugars which are generally added during oligosaccharide synthesis are sialic acid (SA) and/or fucose (Fuc). Linkage of SA can generally influence the physico-chemical and biologic properties of glycoproteins (Martinez et al. Lab Invest 57: 240-257, 1987). The structure of the sugar chain is determined by the high specificity of the glycosyltransferases recognizing proteins/glycoproteins as acceptor products and sugar-nucleotides as substrates. These enzymes also form specific types of glycosidic linkages (α or β) and transfer given monosaccharides specifically to a carbon of the growing protein-linked acceptor sugar. The completed glycoproteins are packaged into secretory vesicles in the Golgi apparatus and transferred to the blood after fusion of these vesicles with the cell membrane. (Molnar. Moll Cell Biochem; 6:3-14, 1975). 
     In some embodiments, OC cells comprise one or more disruptions engineered to occur in the glycosylation pathways to reduce the number of glycosylated proteins and/or alter the glycosylation patterns of the glycosylated proteins. In some embodiments, exogenous nucleic acids are introduced into the erythroid cells using the methods described herein that encode polypeptides capable of disrupting or altering one or more glycosylation pathways (e.g. disrupting or inhibiting the activity of one or more glycosyltransferase or fucosyltransferase enzymes required for the synthesis or modification of oligosaccharides on cell surface glycoproteins). In some embodiments, the exogenous nucleic acid is an interfering RNA (e.g. an siRNA) capable of inducing the elimination of endogenous mRNAs that encode an enzyme of a glycosylation pathway, thereby disrupting or altering the glycosylation pathway of the transfected erythroid cell. In one embodiment, the resulting OC erythroid cells are AB null. In another embodiment, the erythroid cells are of blood group type O. In another embodiment, the resulting cells are of blood group hh (or Bombay). 
     In other embodiments, the erythroid cells are treated with enzymes that can modify and/or cleave off monosaccharides or oligosaccharide side chains. Suitable enzymes include glycoside hydrolases, glycosidases, endoglycosidases, exoglycosidase and/or glycosyl hydrolases to remove sugar-based antigens from the surface of the erythroid cells. In one embodiment, the enzyme is  E. meningosepticum  alpha-N-acetyl-galactosaminidase. In one embodiment the enzyme is  B. fragilis  alpha-galactosidase A (FragA). In some embodiments, the hydrolase is  Streptococcus pneumoniae  SP3-BS71 (Sp3GH98) or a derivative thereof (see, e.g. Kwan D H, J Am Chem Soc. 2015 May 6; 137(17):5695-705). 
     For example, enzymatic conversion reactions are performed in 1 ml reaction mixtures containing 200 mM glycine, pH 6.8 and 3 mM NaCl with 30% packed erythroid cells and enzyme. Erythroid cells are prewashed 1:1 and 1:4 vol/vol in conversion buffer before addition of enzyme. The conversion reaction is incubated for 60 min with gentle mixing at 26° C., followed by four repeat washing cycles with 1:4 vol/vol of saline by centrifugation at 1,000 r.p.m. The washed enzyme-treated OC erythroid cells are then ABO-typed according to standard blood banking techniques using monoclonal antibody reagents. 
     The OC erythroid cells described herein may optionally lack one or more antigenic proteins on their surface. In some embodiments, the OC cells lack or have significant reductions in both glycosylation and antigenic proteins, thereby rendering the OC cell substantially non-immunogenic. In some embodiments, the glycosylation or antigenic protein levels are reduced compared to control erythroid cells, e.g., compared to a wild-type red blood cell, e.g., a red blood cell that is A, B, or AB. In some embodiments, OC erythroid cells are provided that are deficient in one or more surface proteins. Suitable surface proteins include, but are not limited to, proteins of the following blood group systems: Diego, RHAG, Kx, GLOB, I, Ch/Rg, Colton, Kidd, Rhesus (RhD, RhCE), Kell, Yt, Scianna, Dombrock, LW, H, Cromer, Knops, Indian, OK, JMH, GIL, ABO, Lewis, P, Raph, Xg, Lutheran, MNS, Gerbich, and/or Duffy. (see, e.g. Flegel W A, Blood Transfus., 2010, 8:2-4). 
     In one embodiment, the OC erythroid cell is generated by transfecting an erythroid cell precursor with an exogenous nucleic acid encoding CRISPR-Cas9 using one of the methods described herein. In some embodiments, OC cells are provided that lack more than one protein from a blood group system or lack proteins of more than one blood group system. Modifications may be introduced as desired to produce the OC cells. Optionally, the OC cells may further be purified (e.g. by passage through suitable filters, such as de-leukocyting filters) and formulated into pharmaceutical compositions and suitable dosage forms for delivery of the OC cell populations to subjects in need thereof. 
     In another embodiment, the OC erythroid cell is generated by contacting the cell with one or more proteases, such as, e.g. trypsin, or mixtures of proteases. In one embodiment, the resulting erythroid cells are MNS null. In another embodiment, the resulting erythroid cells are Duffy null. In another embodiment, the erythroid cells are Rh null. In another embodiment, the erythroid cells are MNS null and Duffy null. In another embodiment, the erythroid cells are type O, MNS null and Duffy null. In another embodiment, the erythroid cells are type O, Rh null, MNS null and Duffy null. In some embodiments, the OC erythroid cells are null for one or more of Diego, RHAG, Kx, GLOB, I, Ch/Rg, Colton, Kidd, Rhesus (RhD, RhCE), Kell, Yt, Scianna, Dombrock, LW, H, Cromer, Knops, Indian, OK, JMH, GIL, ABO, Lewis, P, Raph, Xg, Lutheran, MNS, Gerbich, Duffy, and any combination thereof. 
     Glycosylated polypeptides and the lack thereof may be identified by any suitable method, including those described in: Hirabayashi et al., (Proteomics 1:295-303 2001, “glyco-catch” method and “frontal affinity chromatography”), which describes isolation of a glycoprotein by lectin-affinity chromatography, digestion of the glycoprotein with proteases, a second isolation of the glycoprotein by lectin-affinity chromatography, purification of the isolated glycoprotein by HPLC and sequencing of the glycoprotein; Geng et al. (Journal of Chromatography B 752:293-306 2001) which describes a method for identification of glycoproteins based on affinity selection of glycopeptides from tryptic digests, which includes trypsin digestion, lectin selection, RPLC and analysis by mass spectrometry; Royle et al. (Analytical Biochemistry 304:70-90 2002), which describes a method for sequencing O-glycans released from glycoproteins, including deglycosylation of glycoproteins followed by analysis and identification of the released O-glycans using chromatographic and spectrometric methods; Kaji et al. (Nature Biotechnology, 2003, “IGOT” (isotope-coded glycosylation site-specific tagging) method), which describes a method for identification of N-linked glycoproteins including i) affinity capture of glycoproteins by a lectin from a biological sample; ii) tryptic cleavage of the glycoproteins and affinity capture of the glycopeptides by the same lectin; iii) peptide-N-glycosidase F (PNGase F) digestion of the glycopeptides in H2 18O and (iv) analysis of the 18O-tagged peptides by an integrated 2D LC-tandem MS technology; Wilson et al. (Journal of Proteome Research 1:521-529 2002), which describes a method for analysis of N and O-linked oligosaccharides released from glycoproteins, including enzymatic release of N-linked oligosaccharides using PNGase F followed by the chemical release of O-linked oligosaccharides using reductive β-elimination and analysis using LC-ESI-MS technology, wherein the glycoproteins are separated by 2D-PAGE and blotted onto a PVDF membrane before deglycosylation and digestion steps; and Rasamoelisolo M., US Publication No. 2004/0253659, which describes a first digestion step, a deglycosylation step and second digestion step that can provide a completely deglycosylated protein with an undamaged peptide backbone. Other analytical and quantitative methods employ, e.g., isoelectric focusing/immunoblotting with quantitation by laser densitometry (IEF/IB/LD), and microcolumn anion-exchange chromatography with quantitation by radio-immunoassay (MAEC-RIA). 
     In one embodiment the synthetic membrane-receiver polypeptide complexes are purified by disabling any residual replicative potential of the membrane-receiver polypeptide complexes. In one embodiment the synthetic membrane-receiver polypeptide complexes are subjected to radiation, e.g., X rays, gamma rays, beta particles, alpha particles, neutrons, protons, elemental nuclei, UV rays in order to damage residual replication-competent nucleic acids. 
     Ionizing radiation is energy transmitted via X rays, gamma rays, beta particles (high-speed electrons), alpha particles (the nucleus of the helium atom), neutrons, protons, and other heavy ions such as the nuclei of argon, nitrogen, carbon, and other elements. X rays and gamma rays are electromagnetic waves like light, but their energy is much higher than that of light (their wavelengths are much shorter). Ultraviolet (UV) light is a radiation of intermediate energy that can damage cells but UV light differs from the forms of electromagnetic radiation mentioned above in that it does not cause ionization (loss of an electron) in atoms or molecules, but rather excitation (change in energy level of an electron). The other forms of radiation—particles—are either negatively charged (electrons), positively charged (protons, alpha rays, and other heavy ions), or electrically neutral (neutrons). 
     Radiation-induced ionizations may act directly on the cellular component molecules or indirectly on water molecules, causing water-derived radicals. Radicals react with nearby molecules in a very short time, resulting in breakage of chemical bonds or oxidation (addition of oxygen atoms) of the affected molecules. The major effect in cells is DNA breaks. Since DNA consists of a pair of complementary double strands, breaks of either a single strand or both strands can occur. However, the latter is believed to be much more important biologically. Most single-strand breaks can be repaired normally thanks to the double-stranded nature of the DNA molecule (the two strands complement each other, so that an intact strand can serve as a template for repair of its damaged, opposite strand). In the case of double-strand breaks, however, repair is more difficult and erroneous rejoining of broken ends may occur. These so-called misrepairs result in induction of mutations, chromosome aberrations, or cell death. 
     Deletion of DNA segments is the predominant form of radiation damage in cells that survive irradiation. It may be caused by (1) misrepair of two separate double-strand breaks in a DNA molecule with joining of the two outer ends and loss of the fragment between the breaks or (2) the process of cleaning (enzyme digestion of nucleotides—the component molecules of DNA) of the broken ends before rejoining to repair one double-strand break. 
     Radiations differ not only by their constituents (electrons, protons, neutrons, etc.) but also by their energy. Radiations that cause dense ionization along their track (such as neutrons) are called high-linear-energy-transfer (high-LET) radiation, a physical parameter to describe average energy released per unit length of the track. (See the accompanying figure.) Low-LET radiations produce ionizations only sparsely along their track and, hence, almost homogeneously within a cell. Radiation dose is the amount of energy per unit of biological material (e.g., number of ionizations per cell). Thus, high-LET radiations are more destructive to biological material than low-LET radiations—such as X and gamma rays—because at the same dose, the low-LET radiations induce the same number of radicals more sparsely within a cell, whereas the high-LET radiations—such as neutrons and alpha particles—transfer most of their energy to a small region of the cell. The localized DNA damage caused by dense ionizations from high-LET radiations is more difficult to repair than the diffuse DNA damage caused by the sparse ionizations from low-LET radiations. 
     In one embodiment, a population of synthetic membrane-receiver polypeptide complexes are subjected to gamma irradiation using an irradiation dose of more than 1, 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100, or more than 100 kGy. 
     In one embodiment, a population of synthetic membrane-receiver polypeptide complexes are subjected to X-ray irradiation using an irradiation dose of more than 0.1, 0.5, 1, 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, or greater than 10000 mSv. 
     The purity of a population of synthetic membrane-receiver complexes can be assessed by measuring the homogeneity of the population. In one embodiment, the average distribution width of the synthetic membrane-receiver complexes is measured by a hematological analysis instrument. In one embodiment, the population of synthetic membrane-receiver complexes has a reticulocyte to non-reticulocyte ratio greater than 10, 100, 1000, 10 4 , 10 5 , 10 6 , or greater than 10 6 . The homogeneity of the population of synthetic membrane-receiver complexes may be assessed by measuring the stromal cell content of the population. In one embodiment, the population of synthetic membrane-receiver complexes has less than 1 ppb of stromal cells. Alternatively or in addition, the homogeneity of the population of synthetic membrane-receiver complexes is assessed by measuring the viral titer and/or a bacterial colony forming potential of the population. 
     In one embodiment the homogeneity of a population of synthetic membrane-receiver complexes is assessed by an in vitro assay. The in vitro assays include those described herein for assessing the identity of the complexes, including but not limited to expansion rate, number, protein content or expression level, mRNA content or expression level, lipid content, partition of a substrate, catalytic activity, or metabolic activity. 
     Mature erythrocytes for use in generating the synthetic membrane-receiver complexes may be isolated using various methods such as, for example, a cell washer, a continuous flow cell separator, density gradient separation, fluorescence-activated cell sorting (FACS), Miltenyi immunomagnetic depletion (MACS), or a combination of these methods (See, e.g., van der Berg et al., Clin. Chem. 33:1081-1082 (1987); Bar-Zvi et al., J. Biol. Chem. 262:17719-17723 (1987); Goodman et al., Exp. Biol. Med. 232:1470-1476 (2007)). 
     Erythrocytes may be isolated from whole blood by simple centrifugation (See, e.g., van der Berg et al., Clin. Chem. 33:1081-1082 (1987)). For example, EDTA-anticoagulated whole blood may be centrifuged at 800×g for 10 min at 4° C. The platelet-rich plasma and buffy coat are removed and the red blood cells are washed three times with isotonic saline solution (NaCl, 9 g/L). 
     Alternatively, erythrocytes may be isolated using density gradient centrifugation with various separation mediums such as, for example, Ficoll, Hypaque, Histopaque, Percoll, Sigmacell, or combinations thereof. For example, a volume of Histopaque-1077 is layered on top of an equal volume of Histopaque-1119. EDTA-anticoagulated whole blood diluted 1:1 in an equal volume of isotonic saline solution (NaCl, 9 g/L) is layered on top of the Histopaque and the sample is centrifuged at 700×g for 30 min at room temperature. Under these conditions, granulocytes migrate to the 1077/1119 interface, lymphocytes, other mononuclear cells and platelets remain at the plasma/1077 interface, and the red blood cells are pelleted. The red blood cells are washed twice with isotonic saline solution. 
     Alternatively, erythrocytes may be isolated by centrifugation using a Percoll step gradient (See, e.g., Bar-Zvi et al., J. Biol. Chem. 262:17719-17723 (1987)). For example, fresh blood is mixed with an anticoagulant solution containing 75 mM sodium citrate and 38 mA/1 citric acid and the cells washed briefly in Hepes-buffered saline. Leukocytes and platelets are removed by adsorption with a mixture of α-cellulose and Sigmacell (1:1). The erythrocytes are further isolated from reticulocytes and residual white blood cells by centrifugation through a 45/75% Percoll step gradient for 10 min at 2500 rpm in a Sorvall SS34 rotor. The erythrocytes are recovered in the pellet while reticulocytes band at the 45/75% interface and the remaining white blood cells band at the 0/45% interface. The Percoll is removed from the erythrocytes by several washes in Hepes-buffered saline. Other materials that may be used to generate density gradients for isolation of erythrocytes include OptiPrep™, a 60% solution of iodixanol in water (from Axis-Shield, Dundee, Scotland). 
     Erythrocytes may be separated from reticulocytes, for example, using flow cytometry (See, e.g., Goodman el al., Exp. Biol. Med. 232:1470-1476 (2007)). In this instance, whole blood is centrifuged (550×g, 20 min, 25° C.) to separate cells from plasma. The cell pellet is resuspended in phosphate buffered saline solution and further fractionated on Ficoll-Paque (1.077 density), for example, by centrifugation (400×g, 30 min, 25° C.) to separate the erythrocytes from the white blood cells. The resulting cell pellet is resuspended in RPMI supplemented with 10% fetal bovine serum and sorted on a FACS instrument such as, for example, a Becton Dickinson FACSCalibur (BD Biosciences, Franklin Lakes, N.J., USA) based on size and granularity. 
     Erythrocytes may be isolated by immunomagnetic depletion (See, e.g., Goodman, el al., (2007) Exp. Biol. Med. 232:1470-1476). In this instance, magnetic beads with cell-type specific antibodies are used to eliminate non-erythrocytes. For example, erythrocytes are isolated from the majority of other blood components using a density gradient as described herein followed by immunomagnetic depletion of any residual reticulocytes. The cells are pre-treated with human antibody serum for 20 min at 25° C. and then treated with antibodies against reticulocyte specific antigens such as, for example, CD71 and CD36. The antibodies may be directly attached to magnetic beads or conjugated to PE, for example, to which magnetic beads with anti-PE antibody will react. The antibody-magnetic bead complex is able to selectively extract residual reticulocytes, for example, from the erythrocyte population. 
     Erythrocytes may also be isolated using apheresis. The process of apheresis involves removal of whole blood from a patient or donor, separation of blood components using centrifugation or cell sorting, withdrawal of one or more of the separated portions, and transfusion of remaining components back into the patient or donor. A number of instruments are currently in use for this purpose such as for example the Amicus and Alyx instruments from Baxter (Deerfield, Ill., USA), the Trima Accel instrument from Gambro BCT (Lakewood, Colo., USA), and the MCS+9000 instrument from Haemonetics (Braintree, Mass., USA). Additional purification methods may be necessary to achieve the appropriate degree of cell purity. 
     In some embodiments, the synthetic membrane-receiver complexes are differentiated ex vivo and/or in vivo from one or more reticulocytes. Reticulocytes may be used to generate synthetic membrane-receiver complexes. Reticulocytes are immature red blood cells and compose approximately 1% of the red blood cells in the human body. Reticulocytes develop and mature in the bone marrow. Once released into circulation, reticulocytes rapidly undergo terminal differentiation to mature erythrocytes. Like mature erythrocytes, reticulocytes do not have a cell nucleus. Unlike mature erythrocytes, reticulocytes maintain the ability to perform protein synthesis. In some embodiments, exogenous nucleic acid (such as mRNA) encoding a receiver is introduced into reticulocytes to generate synthetic membrane-receiver complexes. 
     Reticulocytes of varying age may be isolated from peripheral blood based on the differences in cell density as the reticulocytes mature. Reticulocytes may be isolated from peripheral blood using differential centrifugation through various density gradients. For example, Percoll gradients may be used to isolate reticulocytes (See, e.g., Noble el al., Blood 74:475-481 (1989)). Sterile isotonic Percoll solutions of density 1.096 and 1.058 g/ml are made by diluting Percoll (Sigma-Aldrich, Saint Louis, Mo., USA) to a final concentration of 10 mM triethanolamine, 117 mM NaCl, 5 mM glucose, and 1.5 mg/ml bovine serum albumin (BSA). These solutions have an osmolarity between 295 and 310 mOsm. Five milliliters, for example, of the first Percoll solution (density 1.096) is added to a sterile 15 ml conical centrifuge tube. Two milliliters, for example, of the second Percoll solution (density 1.058) is layered over the higher density first Percoll solution. Two to four milliliters of whole blood are layered on top of the tube. The tube is centrifuged at 250×g for 30 min in a refrigerated centrifuge with swing-out tube holders. Reticulocytes and some white cells migrate to the interface between the two Percoll layers. The cells at the interface are transferred to a new tube and washed twice with phosphate buffered saline (PBS) with 5 mM glucose, 0.03 mM sodium azide and 1 mg/ml BSA. Residual white blood cells are removed by chromatography in PBS over a size exclusion column. 
     Alternatively, reticulocytes may be isolated by positive selection using an immunomagnetic separation approach (See, e.g., Brun et al., Blood 76:2397-2403 (1990)). This approach takes advantage of the large number of transferrin receptors that are expressed on the surface of reticulocytes relative to erythrocytes prior to maturation. Magnetic beads coated with an antibody to the transferrin receptor may be used to selectively isolate reticulocytes from a mixed blood cell population. Antibodies to the transferrin receptor of a variety of mammalian species, including human, are available from commercial sources (e.g., Affinity BioReagents, Golden, Colo., USA; Sigma-Aldrich, Saint Louis, Mo., USA). The transferrin antibody may be directly linked to the magnetic beads. Alternatively, the transferrin antibody may be indirectly linked to the magnetic beads via a secondary antibody. For example, mouse monoclonal antibody 10D2 (Affinity BioReagents, Golden, Colo., USA) against human transferrin may be mixed with immunomagnetic beads coated with a sheep anti-mouse immunoglobulin G (Dynal/Invitrogen, Carlsbad, Calif., USA). The immunomagnetic beads are then incubated with a leukocyte-depleted red blood cell fraction. The beads and red blood cells are incubated at 22° C. with gentle mixing for 60-90 min followed by isolation of the beads with attached reticulocytes using a magnetic field. The isolated reticulocytes may be removed from the magnetic beads using, for example, DETACHaBEAD® solution (from Invitrogen, Carlsbad, Calif., USA). Alternatively, reticulocytes may be isolated from in vitro growth and maturation of CD34+ hematopoietic stem cells using the methods described herein. 
     Terminally-differentiated, enucleated erythrocytes can be separated from other cells based on their DNA content. In a non-limiting example, cells are first labeled with a vital DNA dye, such as Hoechst 33342 (Invitrogen Corp.). Hoechst 33342 is a cell-permeant nuclear counterstain that emits blue fluorescence when bound to double-stranded DNA. Undifferentiated precursor cells, macrophages or other nucleated cells in the culture are stained by Hoechst 33342, while enucleated erythrocytes are Hoechst-negative. The Hoechst-positive cells can be separated from enucleated erythrocytes by using fluorescence activated cell sorters or other cell sorting techniques. The Hoechst dye can be removed from the isolated erythrocytes by dialysis or other suitable methods. 
     A population of synthetic membrane-receiver complexes can be purified by reducing the nuclear material content of the population of complexes. For example, the enucleation rate of the population of complexes is increased, and/or the number of enucleated synthetic membrane-receiver complexes is increased or enriched. 
     Populations of synthetic membrane-receiver complexes can be incubated with a small molecule, e.g., an actin inhibitor, e.g., cytochalasin A, B, C, D, E, F, H, J, and then centrifuged to remove nuclear material. Alternatively or in addition, a population of synthetic membrane-receiver complexes can be mechanically manipulated by passing through progressively smaller size-restrictive filters to remove nuclear material. The population of synthetic membrane-receiver complexes may also be incubated on a fibronectin-coated plastic surface to increase the removal of nuclear material. In one embodiment, the population of synthetic membrane-receiver complexes is incubated in co-culture with stromal cells, e.g., macrophages, to increase the removal of nuclear material. 
     In some embodiments, the population of synthetic membrane-receiver complexes is greater than 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, 99.5%, 99.9%, or greater than 99.9% enucleated. 
     In some embodiments, the synthetic membrane-receiver complexes are not co-cultured with support cells, e.g., with an adherent stromal layer. In some embodiments, the population of synthetic membrane-receiver complexes is generated by contacting erythroid cells with a receiver and differentiating the erythroid cells to obtain a population of enucleated cells comprising the receiver. The population of synthetic membrane-receiver complexes is obtained without an enrichment step, such as gravitational separation, magnetic or fluorescent sorting, irradiation, poisoning of nucleated cells, and the like to select for enucleated cells. 
     In some embodiments, the population of synthetic membrane-receiver complexes is comprised of greater than 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 99%, 99.5%, 99.9%, or greater than 99.9% of synthetic membrane-receiver complexes that lack nuclear material as assessed by an assay to detect nuclear material such as those described herein. 
     In some embodiments, the presence, biological activity and/or function of a receiver, such as a receiver polypeptide exhibited by synthetic membrane-receiver complexes is assessed. Many suitable assays are available and known in the art. 
     In one embodiment, the receiver is a polypeptide on the surface of the synthetic membrane-receiver complex. The presence of the receiver can be assessed by assays including but not limited to flow cytometry, western blotting, RT-PCR, Northern blotting, Coombs rosetting, mass spectrometry. In one embodiment, the receiver is a polypeptide in the interior of the synthetic membrane-receiver complex. The presence of the receiver can be assessed by assays including but not limited to Western blotting, RT-PCR, Norther blotting, PCR, Southern blotting, mass spectrometry. 
     In one embodiment, the receiver is a nucleic acid on the surface of the synthetic membrane-receiver complex. The presence of the receiver can be assessed by assays including but not limited to flow cytometry, flow cytometry with a homologous fluorescent probe, southern blotting, northern blotting, PCR. In one embodiment, the receiver is a nucleic acid in the interior of the synthetic membrane-receiver complex. The presence of the receiver can be assessed by assays including but not limited to southern blotting, northern blotting, PCR. 
     In one embodiment, the receiver is a small molecule on the surface of the synthetic membrane-receiver complex. The presence of the receiver can be assessed by assays including but not limited to flow cytometry, mass spectrometry. In one embodiment, the receiver is a small molecule in the interior of the synthetic membrane-receiver complex. The presence of the receiver can be assessed by assays including but not limited to mass spectrometry, fluorescence spectroscopy. 
     In one embodiment, the receiver is a lipid in the membrane of the synthetic membrane-receiver complex. The presence of the receiver can be assessed by assays including but not limited to mass spectrometry, flow cytometry, membrane solubility, fluorescence polarization, spatial light interferences microscopy. 
     In one embodiment, the receiver is fluorescent or is fused to a fluorescent molecule or is co-expressed from an exogenous nucleic acid (e.g., in a vector) with a fluorescent reporter protein like GFP. The presence of the receiver in or on the synthetic membrane-receiver complex can be assessed by assays including but not limited to flow cytometry, fluorescence spectroscopy, absorbance spectroscopy. 
     In one embodiment, the receiver is a gaseous molecule. The presence of the receiver in or on the synthetic membrane-receiver complex can be assessed by assays including but not limited to chemiluminescence assays, mass spectroscopy. 
     The presence of the receiver in or on the synthetic membrane-receiver complex can be assessed by flow cytometry in a quantitative fashion using calibration beads such as commercially available cytometry calibration beads to quantify the number of receivers on an individual complex. Alternatively or in addition, the presence of the receiver in or on the synthetic membrane-receiver complex can be assessed by Western blot in a quantitative fashion using a standard of known concentration that is detectable using the same detection reagents as the receiver, and in this way the number of receivers on an individual complex can be quantified. 
     In some embodiments, the presence of two or more different receivers can be assessed by the same or different methods, either simultaneously, in sequential fashion, or in parallel. For example, in one embodiment a receiver on the surface can be assessed by flow cytometry using an antibody specific to the receiver and a different receiver not on the surface that is fluorescent can be assessed by fluorescent signal using a different channel in flow cytometry. In a different example, a receiver on the surface can be assessed by flow cytometry and a different receiver not on the surface can be assessed by Western blot. 
     In a specific embodiment, the receiver is retained on the synthetic membrane-receiver complex following terminal differentiation of the cell source. For example, the membrane-receiver complex is generated from a cultured erythroid cell and the expression or presence of the receiver is assessed following terminal differentiation of the cell by a suitable method, e.g., by flow cytometry, Western blot, immunoprecipitation, fluorescence spectroscopy, chemiluminescence, Southern blot, Northern blot, or absorbance spectroscopy. 
     In a specific embodiment, the receiver is retained on the synthetic membrane-receiver complex following circulation in vivo after administration of the synthetic membrane-receiver complex to a subject. The synthetic membrane-receiver complex can be injected into a laboratory animal or animal model, such as a mouse intravenously, e.g., via the tail vein, or is injected into a human intravenously. Then blood is drawn and the presence of the receiver on the synthetic membrane-receiver complex is assessed by suitable assay, e.g., by flow cytometry, Western blot, immunoprecipitation, fluorescence spectroscopy, chemiluminescence, Southern blot, Northern blot, or absorbance spectroscopy. 
     In some embodiments, the biological activity of the receiver in or on the synthetic membrane-receiver complex, the overall biological activity of the complex, and the overall activity of a population of complexes can be assessed by in vitro assays. 
     In some embodiments, the activity of the synthetic membrane-receiver complex is rapidly iterated using a model cell line. For example, a library of suitable receivers is expressed in a model cell line, e.g., HEK293T or K562, and the activity is assessed via a suitable assay; then the best receiver candidate, e.g., the one that is expressed at the highest level or one that demonstrates the highest activity in the suitable assay, is expressed, e.g., in cultured erythroid cells to generate synthetic membrane-receiver complexes. 
     In one embodiment, the activity of the synthetic membrane receiver complex is rapidly iterated using a cultured mouse erythroid cell model. For example, a library of suitable receivers is expressed in cultured mouse erythroid cells; activity is assessed in a suitable mouse model of disease or a suitable mouse model system for assessing activity; the best receiver candidate, e.g., the one that is expressed at the highest level or the one that demonstrates the highest activity in the suitable assay, is then expressed, e.g., in cultured erythroid cells to generate synthetic membrane-receiver complex. 
     In some instances, the receiver is an enzyme and the activity of the receiver can be assessed by an enzymatic assay in which the disappearance of a specific substrate molecule is detected or the appearance of a specific product molecule is detected. Such assays include but are not limited to, colorimetric assays, mass spectrometry, HPLC, fluorescent assays. 
     For example, a) the receiver is adenosine deaminase (ADA) and the enzymatic assay detects the conversion of adenosine to inosine; b) the receiver is phenylalanine hydroxylase (PAH) and the assay detects the conversion of phenylalanine to tyrosine; c) the receiver is phenylalanine ammonia lyase (PAL) and the assay detects the conversion of phenylalanine to trans-cinnamic acid; d) the receiver is thymidine phosphorylase (TP) and the assay detects the conversion of thymidine to thymine and 2-deoxy-ribose; e) the receiver is Purine nucleoside phosphorylase (PNP) and the assay detects the conversion of inosine to hypoxanthine, adenosine into adenine, and guanosine into guanine; f) the receiver is homogentisate 1,2-dioxygenase (HDG) and the assay detects the conversion of homogentisate to maleylacetoacetate; g) the receiver is cystathionine beta synthase and the assay detects the conversion of serine and homocysteine to cystathionine; h) the receiver is oxalate oxidase and the assay detects the oxidation of oxalate. 
     In some embodiments, activity of the synthetic membrane-receiver complex is assessed in an animal model, for example a mouse model, and immunodeficient mouse, or an NSG mouse, of a disease, for example a metabolic disease or an enzyme deficiency, or that can demonstrate the effect of the synthetic membrane-receiver complex, for example a mouse into which a substrate is injected and the product of the receiver-mediated conversion measured. 
     In one embodiment, the receiver is complement receptor 1 (CR1) polypeptide, a derivative or functional fragment thereof. The activity of the CR1 receiver can be assessed in several ways including, for example, the specific capture of immune complexes by the CR1 receiver, the efficient transfer of the immune complexes to macrophages, or the in vivo clearance of immune complexes from a mouse. 
     Functionality of erythroid cells overexpressing CR1 receiver may be assessed by one or more processes: capture of immune complexes on the erythroid cell surface comprising CR1 receiver, release of the immune complexes to macrophages while sparing the erythroid cell comprising CR1 receiver, and proper circulation of the erythroid cells comprising CR1 receiver. These three parameters can be assayed in vitro Immune complex capture assays are described in the art, e.g., Oudin et al., J Immunol 2000 and Schifferli et al., J Immunol 1991. For example, labeled immune complexes are incubated with erythroid cells expressing native CR1 or CR1 receiver polypeptide or a fragment thereof and the number of immune complexes captured by the erythroid cells is assayed by flow cytometry. Macrophage transfer assays are described in the art, e.g., Kuhn et al., J Immunol 1998. For example, labeled immune complexes loaded onto erythrocytes expressing native CR1 or CR1 receiver polypeptide or a fragment thereof are incubated with macrophages. The transfer of immune complex from erythrocyte surface to macrophage, and the consumption or sparing of erythrocytes by macrophages, can be measured by flow cytometry. Proper circulation can be predicted by analyzing erythroid cell morphology and deformability. Morphology of erythroid cells expressing native CR1 or CR1 receiver polypeptide or a fragment thereof can be assessed by eye using standard microscopy techniques, as described e.g., by Giarratana et al., Blood 2011 and Repik et al., Clin Exp Immunol 2005. Deformability of erythroid cells expressing native CR1 or CR1 receiver polypeptide or a fragment thereof can be assessed by ektacytometry, also known as laser-assisted optical rotational cell analysis (LORCA), as described e.g., Giarratana et al., Blood 2011. 
     For example, a synthetic membrane-CR1 receiver complex (the complex comprises a CR1 polypeptide receiver) is incubated with immune complexes, such as in vitro generated immune complexes or patient-derived immune complexes. The capture of the immune complexes by the CR1 receiver is assessed by, for example, flow cytometry using a fluorescent marker in the immune complex or by flow cytometry using a secondary detection agent against an element of the immune complex. 
     In one embodiment, the synthetic membrane-CR1 receiver complex is first incubated with immune complexes and then incubated with macrophages, such as primary macrophages, primary monocytes, cultured macrophages, cultured monocytpes, U937 cells, PMA-activated U937 cells, AA9 cells, RAW 264.7 cells, J774 Cells, THP1 cells, KG-1 cells, NR8383 cells, MV-4-11 cells, 3D4/31 cells, MD cells, Fcwf-4 cells, DH82 cells. The macrophages are assayed by, for example, flow cytometry or radiography, for the presence of immune complexes transferred by the synthetic membrane-CR1 receiver complex. The transfer of captured immune complexes from cultured erythroid cells to macrophages is a standard assay in the art, see for example: Repik et al. 2005 Clin Exp Immunol. 140:230; Li et al. 2010 Infection Immunity 78(7):3129. 
     In one embodiment, activity of the synthetic membrane-CR1 receiver complex is assessed in an animal model. For example, a suitable mouse model may be used, such as an immunodeficient mouse, or an NSG mouse. The mouse disease model can be for example an immune complex disease, such as lupus. Mouse models include NZBWF1/J, MRL/MpJ, MRL/MpJ-Fas(1pr), Smn.C3-Fas1/J, NZM2410/Aeg, 129S4-Cd48, Cg-Sle1, NZM-Sle1 Sle2 Sle3/LmoJ, and BXSB.129P2. Alternatively or in addition, a disease phenotype may be introduced into a mouse, e.g., by injection of immune complexes. The synthetic membrane-CR1 receiver complexes may be injected into any suitable mouse (or other animal model) to test one or more biological effects of the complex, e.g., the clearance of the injected immune complexes by the synthetic membrane-CR1 receiver complex. 
     In some embodiments, the synthetic membrane-receiver complex comprising a CR1 receiver is not generated in a mouse and/or are not generated from mouse erythroid cells. In some embodiments, the synthetic membrane-receiver complex comprising a CR1 receiver is not generated in a laboratory animal and/or are not generated from an erythroid cells derived from a laboratory animal. 
     In one embodiment, the receiver is a complement regulatory molecule or has complement regulatory activity. This activity of the receiver can be assessed by both in vitro and in vivo assays. For instance, the activity of the receiver can be assessed by measuring the reduction in an in vitro complement activation assay, e.g., CH50 assay that measures complement-mediated lysis of sensitized sheep erythrocytes, or AH50 assay that measured alternate pathway complement-mediated lysis of non-sensitized rabbit erythrocytes. Alternatively, the activity of the receiver can be assessed by detecting the cleavage or absence of cleavage, which may or may not expose a neoepitope, of a recombinant complement component that has been incubated with the receiver, including but not limited to e.g., the cleavage of recombinant C2 into C2a and C2b, the cleavage of factor B into factor Ba and factor Bb, the cleavage of factor C3b into iC3bH and iC3bL, the cleavage of C3bBb into C3b and Bb, the cleavage of C4bBb into C4b and Bb, or the cleavage of factor C4b into iC4bH and iC4bL. The cleavage or absence of cleavage of a suitable recombinant complement component can be assessed by protein analysis methods known in the art including, but not limited to, e.g., chromatography, gel electrophoresis, ELISA, and western blotting. Suitable in vivo assays for receiver activity include injection of the synthetic membrane-receiver complex into animal, for example a mouse, and examining the deposition of complement factors, for example membrane attack complex, by histological staining. 
     In one embodiment, the receiver is capable of binding or capturing a target and the activity of the receiver can be assessed by detecting the captured target on the receiver in vitro or in vivo. 
     In one embodiment, the synthetic membrane-receiver complex is incubated with the target in vitro, and the capture of the target by the receiver is detected using an in vitro assay including but not limited to, for example, flow cytometry, immunohistochemistry, magnetic separation, radiography, colony-forming assays, microscopy. 
     In one embodiment, the synthetic membrane-receiver complex is incubated with the target in vitro, and the capture of the target by the receiver is detected using an in vitro co-culture assay including but not limited to for example a macrophage consumption assay of opsonized receiver complex, a T cell activation assay, a B cell stimulation assay, a mast cell degranulation assay, an infectious potential assay. 
     In an embodiment, the synthetic membrane-receiver complex is incubated with the target in vitro, and the release or off-rate of the captured target is measured using an in vitro assay including but not limited to, for example, flow cytometry, immunohistochemistry, magnetic separation, radiography, colony-forming assays, microscopy. 
     The capture of the target by the synthetic membrane-receiver complex can be assayed in an in vivo assay, for example in an animal, including a mouse model of diseases in which the target is naturally present in the mouse. Suitable diseases include bacterial infections, viral infections, fungal infections, immune complex diseases, self-antibody diseases, hyperlipidemia, hyperglycemia. In other mouse models, the target is administered to the mouse externally, e.g., by injection or by feeding. In these assays, the capture of the target by the synthetic membrane-receiver complex is assayed either by examining the animal, e.g the plasma, the tissue, for reduction or retention of the target, or by isolating or collecting the receiver complex from the animal, e.g., from the blood, from the plasma, from a tissue, and assaying the presence of the target on the receiver using an in vitro assay including, but not limited to, for example, flow cytometry, immunohistochemistry, magnetic separation, radiography, colony-forming assays, microscopy. 
     In some embodiments, the receiver is capable of binding or capturing a target and substantially increasing the clearance of the target in vivo, or substantially reducing the concentration of the target in circulation. The activity of the receiver on the synthetic membrane-receiver complex can be assessed by detecting the enhanced clearance of the target in vitro or in vivo. 
     In one embodiment, the synthetic membrane-receiver complex is incubated with the target in vitro, and the capture of the target by the receiver is detected using an in vitro assay including but not limited to, for example, flow cytometry, immunohistochemistry, magnetic separation, radiography, colony-forming assays, microscopy. Subsequently, the synthetic membrane-receiver complex is incubated in a co-culture assay with a cell known to promote clearance, for example a macrophage or a monocyte, and the clearance of the target and receiver complex is assessed by, for example, flow cytometry, immunohistochemistry, magnetic separation, radiography, colony-forming assays, microscopy. 
     In one embodiment, the synthetic membrane-receiver complex is incubated with the target in vitro, and the capture of the target by the receiver is detected using an in vitro assay including but not limited to, for example, flow cytometry, immunohistochemistry, magnetic separation, radiography, colony-forming assays, microscopy. Subsequently, the synthetic membrane-receiver complex is incubated in a physical system that mimics the clearance mechanism of the complex in vivo, for example an artificial spleen, a microchannel, a packed column, a resin, a tissue explant, a centrifuge, and the clearance of the target and receiver complex is assessed by, for example, flow cytometry, immunohistochemistry, magnetic separation, radiography, colony-forming assays, microscopy. 
     In one embodiment, the clearance of the target by the synthetic membrane-receiver complex is assayed in an in vivo assay, for example in an animal, including, for example, a mouse model of diseases in which the target is naturally present in the mouse, for example bacterial infection, viral infection, fungal infection, immune complex disease, self-antibody disease, hyperlipidemia, hyperglycemia, or for example, a mouse model in which the target is administered to the mouse externally, e.g., by injection or by feeding. In these assays, the clearance of the target by the receiver complex is assayed either by examining the animal, e.g the plasma, the tissue, for reduction of the target, or by isolating or collecting the synthetic membrane-receiver complex from the animal, e.g., from the blood, from the plasma, from a tissue, and assaying the presence of the target on the receiver using an in vitro assay including, but not limited to, for example, flow cytometry, immunohistochemistry, magnetic separation, radiography, colony-forming assays, microscopy. 
     In some embodiments, the synthetic membrane-receiver complex is capable of delivering a suitable receiver to a specific subcellular compartment, for example a lysosome. 
     For example, a receiver may be delivered to the lysosomal compartment of a target cell, e.g., a macrophage. The successful delivery of the receiver to the lysosomal compartment of a target cell is assessed by microscopy and the detection of punctate spots corresponding to a fluorescent receiver or fluorescent receiver detection agent. Alternatively or in addition, the successful delivery of the receiver to the lysosomal compartment of a target cell is assessed by microscopy and the colocalization of a fluorescent receiver detection agent with a fluorescent detection agent for a known lysosomal marker, e.g., lysotracker, LAMP-1. 
     In some embodiments, the receiver is an enzyme that can degrade toxic components that have built up in the lysosome of a cell exhibiting the genotype or phenotype of, or derived from a patient with, a lysosomal storage disease. For example, the receiver is capable of degrading the toxic material built up in the cell and rescue the cell phenotype, e.g., preventing cell death. 
     The population of synthetic membrane-receiver complexes can be assessed for the inability of the complexes to replicate, the ability of the complexes to circulate safely through the vasculature, and the lack of immunogenicity of the complexes. 
     In some embodiments, the safety of the population of synthetic membrane-receiver complexes is assessed by measuring the replication potential of the population of complexes using a suitable in vitro or in vivo assay. For example, tests for a substantial inability of the synthetic membrane-receiver complexes to self-replicate include: a) a substantial inability to form a tumor when injected into an immunocompromised mouse; b) a substantial inability to form a colony when cultured in soft agar; c) a substantial inability to incorporate thymidine in a thymidine incorporation assay; d) a substantial lack of positive signal upon transfection with DNA encoding a fluorescent reporter, e.g., less than 10%, 1%, 0.1%, 0.01%, 0.001%, 1 ppm, 100 ppb, 10 ppb, 1 ppb, 100 ppt, 10 ppt, 1 ppt, or less than 1 ppt positive signal; e) a substantial lack of positive signal upon staining with a nuclear dye, e.g., less than 10%, 1%, 0.1%, 0.01%; and 0.001%, 1 ppm, 100 ppb, 10 ppb, 1 ppb, 100 ppt, 10 ppt, 1 ppt, or less than 1 ppt positive signal; f) a substantial lack of positive signal upon staining with cell markers of hematological malignancy, e.g., CKIT, CD34, EpCam, e.g., less than 10%, 1%, 0.1%, 0.01%, 0.001%, 1 ppm, 100 ppb, 10 ppb, 1 ppb, 100 ppt, 10 ppt, 1 ppt, or less than 1 ppt positive signal. In certain embodiments, synthetic membrane-receiver complexes are provided that do not contain a substantial amount of a replicating nucleic acid. 
     In some embodiments, the safety of the population of synthetic membrane-receiver complexes is assessed by measuring the ability of an administered complex to circulate in vivo (in the circulatory system of a subject) without causing substantial vascular occlusion or induction of the clotting cascade. Optionally, the circulation pharmacokinetics of the synthetic membrane-receiver complexes may be assessed. 
     In one embodiment, the circulation pharmacokinetics of the synthetic membrane-receiver complexes is assessed by injecting the complex into an animal intravenously, such as a mouse. The mouse can be an NSG (nod-SCID-gamma) immunodeficient mouse. The mouse is depleted of macrophages prior to injection with the complex, e.g., by intraperitoneal injection of human red blood cells, or by intravenous injection with clodronate liposomes. The synthetic membrane-receiver complexes can be labeled with a fluorescent dye, e.g., CFSE. After injection of the complexes, blood is drawn and the number of synthetic membrane-receiver complexes remaining is assessed by, e.g., flow cytometry, western blot, and the clearance rate of the synthetic membrane-receiver complexes is deduced from these data. Human red blood cells can be injected into the same animal model as the synthetic membrane-receiver complexes and the clearance rates of the complexes and human red blood cells are compared. 
     In one embodiment, the risk of activation of the clotting cascade by the synthetic membrane-receiver polypeptide complex is assessed with an in vitro assay. In one embodiment, the synthetic membrane-receiver polypeptide complex is incubated with human blood and clotting cascade activation is assessed by measuring the time required for coagulation in the presence of kaolin, negatively-charged phospholipids, and calcium (activated partial thromboplastin time (aPTT) test), see e.g., Exner and Rickard, Biomedicine 1977 27(2):62, or by measuring the time required for coagulation in the presence of thromboplastin and calcium (prothrombin time (PT) test), see e.g., Jaques and Dunlop 1945, Am J Physiol 145:67. The normal range for the aPTT test is approximately 25-38 seconds. The normal range for the PT test is approximately 10-12 seconds. 
     In one embodiment, any adverse events induced by the synthetic membrane-receiver complexes are assessed by injecting the complex into an animal intravenously and assessing the activation of the clotting cascade. The level of clotting cascade induction is assessed by drawing blood and assessing the levels of clotting cascade components in the plasma by, e.g., Western Blot or ELISA. The clotting cascade components are typically fibrinogen breakdown products, e.g., fibrinopeptide A and fibrinopeptide B. For example, the level of clotting cascade induction is assessed by drawing blood and assessing the levels of clotting activity in the plasma by platelet activation assay, e.g., incubating the plasma with platelets and assessing the activation of the platelets by flow cytometry, e.g., by staining for markers of activation, e.g., by staining for PAC-1, CD62p, or CD40L. 
     In one embodiment, any adverse events induced by the synthetic membrane-receiver complexes are assessed by injecting the complex into an animal intravenously and assessing the activation of inflammatory pathways. The level of inflammation can be assessed by drawing blood and assessing the levels of inflammatory cytokines in the plasma by, e.g., Western Blot or ELISA. In one embodiment, the inflammatory cytokines are interferon gamma, tumor necrosis factor alpha, or IL-12 fragment p70. 
     In one embodiment, any adverse events induced by the synthetic membrane-receiver complexes are assessed by injecting the complex into an animal intravenously and assessing the status of tissues, e.g., liver, spleen, heart, lungs, brain, skin, kidneys. The status of tissue can be assessed by gross necropsy, dissection of the tissue, histological staining, and imaging by microscopy. 
     In one embodiment, the ability of the synthetic membrane-receiver complex to circulate in vivo without causing substantial vascular occlusion or activation of the clotting cascade is assessed by measuring the deformability of the complex. The deformability of the synthetic membrane-receiver complex is assessed using an in vitro assay. For example, the assay is an osmotic fragility assay. Mechanical fragility of the synthetic membrane-receiver complex can be assessed by measuring the structural integrity in response to shear stress in a Couett-type shearing system. In one embodiment, the deformability of the synthetic membrane-receiver complex is assessed using an Ektacytometer. In one embodiment, the deformability of the synthetic membrane-receiver complex is assessed by measuring the elongation index at a defined pressure by laser diffraction using a laser-assisted optical rotational cell analyzer (LORCA) instrument. In one embodiment, the deformability of the synthetic membrane-receiver complex is assessed by measuring the transit time through a series of micron-scale constrictions of defined dimensions at a fixed pressure in a microfluidic device. In one embodiment, the deformability of the synthetic membrane-receiver complex is assessed by measuring the survival rate through a series of micron-scale constrictions of defined dimensions at a fixed pressure in a microfluidic device. The microfluidic device can be selected from one of the following, including but not limited to, a poly dimethyl siloxane (PDMS) chip with micron-scale constrictions (e.g., Hoelzle et al. J Vis Exp 2014 91:e51474); a chip with funnel-shaped constrictions (e.g., Guo et al. Lab Chip 2012 12:1143); a PDMS chip with pillars (e.g., Zhang et al. PNAS 2012 109(46):18707); or an in vitro artificial spleen microbead packed column (Guillaume DePlaine et al., Blood 2011, 117(8)). 
     In one embodiment, the ability of the synthetic membrane-receiver complex to circulate in vivo without causing substantial vascular occlusion or activation of the clotting cascade is assessed by measuring the vascular occlusion of the complex. Vascular occlusion of the synthetic membrane-receiver complex can be assessed using an in vitro assay. For example, the vascular occlusion of the synthetic membrane-receiver complex is assessed using an ex vivo assay. The synthetic membrane-receiver complex is incubated at a 1:1 ratio with reference human red blood cells and induction of multi-cell rosettes are assessed by light microscopy in comparison to a reference assay with Rh-mismatched blood. The vascular occlusion of the synthetic membrane-receiver complex is assessed by measuring the adhesion of the complex to human vascular endothelial cells under flow conditions, see e.g., Kaul D K, Finnegan E, and Barabino G A (2009) Microcirculation 16(1):97-111. Alternatively or in addition, vascular occlusion is assessed by measuring the peripheral resistance unit (PRU) increase in an ex vivo perfusion assay of rat vascular endothelium, see e.g., Kaul, Fabry and Nagel, PNAS 1989, 86:3356. Further, vascular occlusion is assessed by intravital microscopy, see e.g., Zennadi et al. 2007 Blood 110(7):2708. Vascular occlusion may also be assessed by measuring flow rates and adhesion of the complex in vitro graduated height flow chambers, see e.g., Zennadi et al 2004, Blood 104(12):3774. 
     In some embodiments, the safety of the population of synthetic membrane-receiver complexes is assessed by measuring the immunogenicity of the population of complexes using a suitable in vitro or in vivo assay. 
     For example, the population of synthetic membrane-receiver complexes a) does not induce agglutination in a Coombs test using serum from the intended recipient subject or b) does not induce agglutination in a Coombs test using pooled human serum. 
     In one embodiment, the population of synthetic membrane-receiver complexes is derived from a progenitor cell that has been genotyped for the predominant blood group antigens and matched to the blood group antigen genotype of the recipient. 
     In one embodiment, the population of synthetic membrane-receiver complexes comprises a receiver or other exogenous protein that has less than 10%, 1%, 0.1%, 0.01%, 0.001%, or less than 0.001% predicted T cell reactivity by an in silico T cell epitope prediction algorithm. 
     In one embodiment, the population of synthetic membrane-receiver complexes comprises a receiver or other exogenous protein that has less than 10%, 1%, 0.1%, 0.01%, 0.001%, or less than 0.001% reactivity in an in vitro T cell activation assay, e.g., Antitope Inc. EpiScreen assay. 
     For example, synthetic membrane-receiver complexes derived from erythrocytes can be centrifuged and resuspended in appropriate solution (e.g., standard AS-3 solution) for infusion into subjects in need thereof. In some embodiments, the synthetic membrane-receiver complexes to be infused have the same ABO type as that of the recipient to minimize the risk of infusion-associated immune reactions. The synthetic membrane-receiver complexes can also be pretreated to remove blood type-specific antigens or otherwise reduce antigenicities. Methods suitable for this purpose include, but are not limited to, those described in U.S. Patent Application Publication Nos. 20010006772 and 20030207247. 
     Methods of Treatment and Prevention 
     Provided herein are methods of modulating the circulatory concentration of a target to treat or prevent a disease, disorder or condition associated with the presence, absence, elevated or depressed concentration of the target in the circulatory system of a subject. The subject may suffer from the disease, disorder or condition or may be at risk of developing the disease, disorder or condition. The methods provided herein include the administration of a suitable synthetic membrane-receiver polypeptide complex described herein in an amount effective to substantially modulate the circulatory concentration of the target, thereby preventing or treating the disease, disorder or condition. In some embodiments, the synthetic membrane-receiver polypeptide complex is formulated as a pharmaceutical composition. In some embodiments, the pharmaceutical composition is formulated for intravenous injection to the subject. The compositions may be administered once to the subject. Alternatively, multiple administrations may be performed over a period of time. For example, two, three, four, five, or more administrations may be given to the subject. In some embodiments, administrations may be given as needed, e.g., for as long as symptoms associated with the disease, disorder or condition persist. In some embodiments, repeated administrations may be indicated for the remainder of the subject&#39;s life. Treatment periods may vary and could be, e.g., no longer than a year, six months, three months, two months, one month, two weeks, one week, three days, two days, or no longer than one day. 
     In some embodiments, the compositions are administered at least twice over a treatment period such that the disease, disorder or condition is treated, or a symptom thereof is decreased. In some embodiments, the compositions are administered at least twice over a treatment period such that the disease, disorder or condition is treated, or a symptom thereof is prevented. In some embodiments, the pharmaceutical composition is administered a sufficient number of times over a treatment period such that the circulatory concentration of the target is substantially decreased during the treatment period. In some embodiments, the pharmaceutical composition is administered a sufficient number of times over a treatment period such that the circulatory concentration of the target self-antibody is substantially decreased during the treatment period such that one or more symptoms of the self-antibody mediated disease, disorder or condition is prevented, decreased or delayed. In some embodiments, decreasing the circulatory concentration of the target includes decreasing the peak concentration, while in others it includes decreasing the average concentration. In some embodiments, a substantial decrease during the treatment period can be determined by comparing a pretreatment or post-treatment period in the human subject, or by comparing measurements made in a population undergoing treatment with a matched, untreated control population. In some embodiments, the circulatory concentration of the target is decreased by at least about 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or greater than 99.99% during part or the entirety of the treatment period. In some embodiments, the circulatory concentration of the target is decreased by at least about 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 99.99%, or greater than 99.99% within about 1, 5, 10, 15, 20, 30, 40, or 50 minutes, or about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, or 23 hours, or 1, 2, 3, 4, 5, or 6 days or about 1, 2, 3, 4, 5, or 6 weeks of the administration. 
     In some embodiments, the pharmaceutical composition is administered a sufficient number of times over a treatment period such that the circulatory concentration of the target is decreased at a rate greater than i) the endogenous clearance rate of the target \by the human subject, or ii) the endogenous production rate of the target by the human subject, or iii) both i) and ii). In some embodiments, the pharmaceutical composition is administered a sufficient number of times a treatment period such that the circulatory concentration of the target is substantially decreased for at least about one week, two weeks, three weeks, four weeks, one month, two months, three months, four months, five months, six months, or greater than six months. In some embodiments, the pharmaceutical composition is administered a sufficient number of times a treatment period such that the circulatory concentration of the target is substantially decreased for a period of time at least as long as the treatment period. 
     In some embodiments, the pharmaceutical composition is administered at a frequency sufficient to effectively reduce the circulatory concentration of the target below a level that is associated with a symptom of the disease, disorder or condition. 
     In some embodiments, the time interval between administrations within a treatment period is no longer than the period in which the number of synthetic membrane-receiver complexes in circulation is reduced to less than about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95% of the number of synthetic membrane-receiver complexes present in the administered pharmaceutical composition. 
     Diseases, disorders and conditions associated with targets in the circulatory system that may be treated or prevented by administering synthetic membrane-receiver polypeptide complexes are described herein. 
     Diseases, disorders and conditions associated with targets in the circulatory system that may be treated or prevented by administering synthetic membrane-receiver polypeptide complexes include, but are not limited to: self-antibody-mediated diseases, complement dysregulation-associated diseases, immune complex associated diseases, amyloidoses, diseases associated with infectious agents or pathogens (e.g., bacterial, fungal, viral, parasitic infections), disease associated with toxic proteins, diseases associated with the accumulation of lipids, diseases associated with apoptotic, necrotic, aberrant or oncogenic mammalian cells, and metabolic diseases. 
     Provided herein, in some embodiments, are methods for the treatment or prevention of diseases or conditions that are associated with targets (e.g., molecules or entities) that reside, at least in part, in the circulatory system. The methods comprise, in certain embodiments, administering to a subject in need thereof functional erythroid cells comprising a receiver, populations of functional erythroid cells comprising a receiver, or compositions, preferably pharmaceutical compositions comprising functional erythroid cells comprising a receiver, in an amount effective to treat or prevent the disease or condition that is associated with molecules or entities that reside, at least in part, in the circulatory system. 
     Methods are provided for the treatment or prevention of inflammation and diseases associated with inflammation, including sepsis, autoimmune disease, cancer, and microbial infections, the methods comprising, administering to a subject in need thereof an erythrocyte comprising an immune-modulatory receiver in an amount effective to treat or prevent the inflammation or an associated disease. In some embodiments, an erythrocyte comprises an immunomodulatory receiver that comprises a chemokine or cytokine receptor. In a particular embodiment, the chemokine receptor is DARC. 
     Methods are provided for the modulation of chemokine homeostasis at sites of inflammation, the methods comprising, administering to a subject in need thereof an erythrocyte comprising a chemokine—modulatory receiver in an amount effective to modulate chemokine homeostasis at sites of inflammation. In some embodiments, the erythrocyte comprising a chemokine-modulatory receiver comprises a receiver that comprises a chemokine receptor. In a particular embodiment, the chemokine receptor is DARC. In some embodiments, the site of inflammation is vascular. (Darbonne, J Clinical Invet, 1991). 
     Further provided are methods of inducing toxin clearance. The methods include administering to a subject in need thereof a population of functional erythroid cells comprising a receiver that is capable of interacting with a toxin, such as e.g., an antibody, scFv or nanobody receiver, in an amount effective to clear toxins from circulation. Such methods may be employed to sequester the toxin and reduce the amount of tissue damage that would otherwise occur within the vasculature and dissipating its pathogenic effects in a less acute manner. 
     In some embodiments, provided are methods of treating diseases, including, but not limited to, metabolic diseases, cancers, clotting and anti-clotting diseases. The methods include administering to a subject in need thereof a pharmaceutical composition of functional erythroid cells comprising a receiver provided herein in an amount sufficient to treat the metabolic disease, the cancer, the clotting disease or anti-clotting disease of the subject. 
     In certain embodiments, synthetic membrane-receiver polypeptide complexes exhibit one or more receiver polypeptides on their surface, exposed to the environment the circulatory system of the subject. 
     In other embodiments, the synthetic membrane-receiver polypeptide complexes comprise one or more receiver polypeptides facing the unexposed side of the synthetic membrane-receiver polypeptide complex. 
     The receiver polypeptide may interact with targets that are present in the circulatory system. The interaction of the receiver with the target may include, but is not limited to: i) binding of the receiver to the target; ii) degrading the target, iii) cleaving the target; iv) sequestering the target, and/or v) catalytically converting the target. 
     For example, the receiver polypeptide may be an antibody, a single-chain variable fragment, a nanobody, a diabody, a darpin, a lyase, a hydrolase, a protease, or a nuclease. 
     In some embodiments, the synthetic membrane-receiver complex comprises a receiver that is not a polypeptide. In some embodiments, the receiver comprises a carbohydrate (e.g., a GAG), a lipid, DNA, a RNA, a peptide nucleic acid (PNA), or a non-protein ligand, drug or substrate that is capable of interacting with the target. 
     In some embodiments, the interaction between the receiver and the target leads to a direct or indirect reduction of the concentration of the target in the circulatory system. For example, a receiver may directly convert a target into a different product. The receiver may have a catalytic activity toward the target, such as cleaving, degrading, etc. The conversion may be from a target to a degradation product, from a toxic or harmful target to a non-toxic product, etc. The catalytic activity of the receiver may also involve addition of one or more chemical groups to the target. Modification of the target by the receiver may cause, directly or indirectly, e.g., de/phosphorylation, de/ubiquitination, de/methylation, glycosylation, etc. on the target. The receiver may indirectly cause a second modification on the target if the receiver put a first modification that leads to a second modification, e.g., by a different enzyme. Any such modifications may then lead, e.g., to the degradation of the target or to a conversion of the target to a non-harmful or less harmful product. In some embodiments, a decrease in target concentration may be directly or indirectly associated with an increase in a non-target compound. For example, a toxic metabolite may be converted into a non-toxic or less toxic metabolite. In another example, a target may be converted into a product that is lacking or is present in an depressed amount. In this case, a disease, disorder or condition may be associated with the lack of or depressed amount of the non-target compound and conversion of the target, e.g., by a catalytic action of the synthetic membrane-receiver polypeptide complex is capable of increasing the amount of the non-target compound effective to treat the disease, disorder or condition. 
     In other examples, the receiver may bind to the target and keep it sequestered, e.g., being associated with the synthetic membrane-receiver polypeptide complex. The sequestration may inhibit an activity harbored by the target, e.g., a harmful activity, such as that exerted by a self-antibody which may be causative of an autoimmune disease, or a bacterial toxin that may cause sepsis, etc. Alternatively or in addition, upon sequestration or binding of the target the target is redistributed in the circulatory system of the subject according to the distribution of the synthetic membrane-receiver polypeptide complex. This may significantly limit the volume of distribution of the target, and thus potentially its harmful or adverse impact. The target may be degraded or accumulated at a specific site or organ in the body of the subject directed by the turnover or half-life and distribution of the synthetic membrane-receiver polypeptide complex. 
     The administration of the pharmaceutical composition may be sufficient to substantially decrease the concentration or amount of the target molecule in circulation during the treatment period, wherein the substantial decrease can be determined in comparison to a pre-treatment or post-treatment period in the human subject, or via comparison of measurements made in a population undergoing treatment as compared to a matched untreated control population. The substantial decrease of the target molecule can include a substantial decrease of the peak concentration or amount of the target molecule present in a human patient or a substantial decrease in the average concentration or amount of the target molecule present in a human patient. 
     In some embodiments, provided are methods for treating diseases that are marked by periodic flares, wherein a flare is defined as a recurrence of symptoms or an onset of more severe symptoms. Diseases marked by periodic flares include self-antibody mediated diseases, immune complex associated diseases, autoimmune diseases, including for example lupus, rheumatoid arthritis, and goodpasture syndrome. 
     In some embodiments, provided are methods comprising administering the pharmaceutical composition to a patient a sufficient number of times over a treatment period such that the time between flares is reduced compared to an individual who does not receive the pharmaceutical composition. 
     In some embodiments, provided are methods comprising administering the pharmaceutical composition to a patient a sufficient number of times over a treatment period such that the severity of the flares is reduced compared to an individual who does not receive the pharmaceutical composition. 
     In some embodiments, methods of treatment and prevention using synthetic membrane-receiver complexes generated from erythroid cells described herein do not comprise the step of detecting the erythroid cell in vivo, e.g., through a detection agent that is associated with the erythroid cell. 
     In some embodiments, the synthetic membrane-receiver complex is not generated from a human donor pluripotent hematopoietic stem cell. In some embodiments, a population of synthetic membrane-receiver complexes is not expanded in a bioreactor. In some embodiments, the population of synthetic membrane-receiver complexes after expansion and/or differentiation does not comprise a single species of differentiated human blood cells. In some embodiments, the synthetic membrane-receiver complex is not a differentiated, mature human blood cell. In some embodiments, the synthetic membrane-receiver complex is not generated from a blood cell derived from a universal donor, e.g. blood type 0, Rh factor negative. 
     In some embodiments, a synthetic membrane-ADA polypeptide receiver complex is not used to treat severe combined immune deficiency (ADA-SCID). 
     In some embodiments, the methods of treatments described herein do not comprise administering a synthetic membrane-receiver complex generated from an erythroid cell that is contacted with a polypeptide receiver in an amount effective to induce immune tolerance to the polypeptide receiver in a subject. 
     Suitable targets include biological compounds, inorganic or organic compounds. Suitable targets may range in size from less than 100 Da, less than 250 Da, less than 500 Da, less than 1000 Da to targets of more than 1 kDa. Targets can be, e.g., polypeptides, lipids, carbohydrates, nucleic acids, small molecules, metabolites and elements. In some embodiments, the target is an antibody, a complement factor, an immune complex, a serum amyloid protein, a bacterial pathogen, a fungal pathogen, a viral pathogen, or an infected, pathogenic, apoptotic, necrotic, aberrant or oncogenic mammalian cell. 
     Diseases, disorders and conditions associated with targets in the circulatory system that may be treated or prevented by administering synthetic membrane-receiver polypeptide complexes include, but are not limited to: self-antibody-mediated diseases, complement dysregulation-associated diseases, immune complex associated diseases, amyloidoses, diseases associated with infectious agents or pathogens (e.g., bacterial, fungal, viral, parasitic infections), disease associated with toxic proteins, diseases associated with the accumulation of lipids, diseases associated with apoptotic, necrotic, aberrant or oncogenic mammalian cells, and metabolic diseases. 
     In some embodiments, provided are methods of treating diseases, including, but not limited to, metabolic diseases, cancers, clotting and anti-clotting diseases. The methods include administering to a subject in need thereof a pharmaceutical composition of erythrocyte cells comprising a receiver provided herein in an amount sufficient to treat the metabolic disease, the cancer, the clotting disease or anti-clotting disease of the subject. 
     Self-Antibody Mediated Diseases 
     In some embodiment, the synthetic membrane-receiver polypeptide complexes described herein may be used to treat or prevent diseases, disorders or conditions that are associated with self-antibodies. 
     In specific embodiments, methods are provided for reducing the circulatory concentration of a target self-antibody in a subject (e.g., a human) suffering from or at risk of developing a self-antibody mediated disease, disorder or condition. The methods include administering a pharmaceutical composition comprising a synthetic membrane-receiver polypeptide complex described herein. The pharmaceutical composition is administered in an amount effective to substantially reduce the circulatory concentration of the target self-antibody. In certain embodiments, the administration is carried out intravenously. 
     In certain embodiments, synthetic membrane-receiver polypeptide complexes are administered that comprise a receiver that specifically binds and sequesters a target self-antibody that is present in the circulatory system of the subject. 
     In certain embodiments, the pharmaceutical composition will reduce the target self-antibody load in the circulatory system, thereby reducing the burden of the disease, disorder or condition associated with the presence or elevated concentration of the target self-antibody. Diseases associated with target self-antibodies include, but are not limited to, Goodpasture syndrome, membranous glomerulonephropathy, antiphospholipid syndrome (APS), catastrophic antiphospholipid syndrome (CAPS), and those listed in table 6 and table 8. 
     Self-antibody mediated diseases arise from an abnormal immune response of the body against substances and tissues normally present in the body. This may be restricted to certain organs (e.g., in autoimmune thyroiditis) or involve a particular tissue in different places, e.g., Goodpasture syndrome, which may affect the basement membrane in both the lung and the kidney. The treatment of self-antibody mediated diseases typically includes immunosuppressive medications that decrease the immune response, such as cyclophosphamide and rituximab. In certain embodiments, treatment with the pharmaceutical compositions described herein is combined with one or more immunosuppressive medications, and effective agents may be, e.g., co-administered or co-formulated. 
     In healthy subjects, the immune system is able to recognize and ignore the body&#39;s own healthy proteins, cells, and tissues, and does not overreact to non-threatening substances in the environment, such as foods. If the immune system ceases to recognize one or more of the body&#39;s normal constituents as “self” it may produce pathological self-antibodies, i.e. antibodies that recognize “self” antigens. These self-antibodies are directed against the body&#39;s own healthy cells, tissues, and/or organs, and may cause inflammation and tissue damage. 
     In certain embodiments, synthetic membrane-receiver polypeptide complexes are provided that comprise receivers comprising epitopes capable of being recognized by target self-antibodies. For example, the target self-antibody may specifically recognizes glycoprotein (GP Ib-IX, IIb-IIIa, IV, or the NC1 domain of collagen α3 (IV), B2 glycoprotein-1, or phospholipase A2 receptor, and the receiver polypeptide may comprise an antigenic polypeptide selected from the group. 
     Target self-antibodies sequestered by the synthetic membrane-receiver polypeptide complexes may be cleared from circulation, e.g., through the reticulo-endothelial system. Sequestration and/or degradation of the target self-antibody may reduce the degree of inflammation that is normally caused when the self-antibody interacts with “self” tissues. 
     In one embodiment the disease or condition is antiphospholipid syndrome, the receiver is beta2-glycoprotein-1 or fragment thereof, and the target is pathogenic self-antibody against beta2-glycoprotein-1. 
     In one embodiment the disease or condition is catastrophic antiphospholipid syndrome, the receiver is beta2-glycoprotein-1 or fragment thereof, and the target is pathogenic self-antibody against beta2-glycoprotein-1. 
     In one embodiment the disease or condition is cold agglutinin disease, the receiver is I/i antigen or fragment thereof, and the target is pathogenic self-antibody against I/i antigen. 
     In one embodiment the disease or condition is Goodpasture syndrome, the receiver is a3 NC1 domain of collagen (IV) or fragment thereof, and the target is pathogenic self-antibody against a3 NC1 domain of collagen (IV). 
     In one embodiment the disease or condition is immune thrombocytopenia purpura, the receiver is platelet glycoproteins (Ib-IX, IIb-IIIa, IV, Ia-IIa) or fragment thereof, and the target is pathogenic self-antibody against platelet glycoprotein. 
     In one embodiment the disease or condition is membranous nephropathy, the receiver is phospholipase A2 receptor or fragment thereof, and the target is pathogenic self-antibody against phospholipase A2 receptor. 
     In one embodiment the disease or condition is warm antibody hemolytic anemia, the receiver is glycophorin A, glycophorin B, and/or glycophorin C, Rh antigen or fragment thereof, and the target is pathogenic self-antibody against glycophorins and/or Rh antigen. 
     Exemplary self-antibody diseases are Goodpasture syndrome, catastrophic antiphospholipid syndrome, and membranous glomerulopathy. 
     1. Goodpasture Syndrome 
     In some embodiment, subjects may be identified as having received or would benefit from receiving treatment for Goodpasture Syndrome. Subjects suffering from or at risk of developing Goodpasture Syndrome may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising α3IV collagen (COL4A3), or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex. COL4A3 is normally found on kidney cells and presents a target to which self-antibodies associated with Goodpasture syndrome have been shown to bind. 
     COL4A3 is found in air sacs in the lungs and glomeruli of the kidneys. Self-antibodies associated with Goodpasture syndrome are directed against the glomerular basement membrane and can cause kidney damage. Where the disorder is triggered by a viral respiratory infection or by intake of hydrocarbon solvents the resulting immune response can cause bleeding in the air sacs of the lungs and inflammation in the kidney&#39;s glomeruli. 
     2. Catastrophic Antiphospholipid Syndrome (CAPS) 
     In some embodiment, subjects may be identified as having received or would benefit from receiving treatment for antiphospholipid syndrome (APS). Subjects suffering from or at risk of developing APS may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising β2-glycoprotein 1 (b2GPI), or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex. b2GPI is normally found on endothelial cells and presents a target to which self-antibodies associated with APS have been shown to bind. 
     Antiphospholipid syndrome (APS) is a multisystem self-antibody mediated condition characterized by vascular thrombosis and/or pregnancy loss associated with persistently positive antiphospholipid antibodies (aPL). Catastrophic APS (CAPS) is the most severe form of APS with multiple organ involvement developing over a short period of time, usually associated with microthrombosis. ‘Definite’ and ‘probable’ CAPS have been defined based on the preliminary classification criteria; however, aPL-positive patients with multiple organ thromboses and/or thrombotic microangiopathies are encountered who do not fulfill these criteria. Previous APS diagnosis and/or persistent clinically significant aPL positivity is of great importance for the CAPS diagnosis; however, almost half of the patients who develop CAPS do not have a history of aPL positivity. 
     3. Membranous Glomerulopathy (MGN) 
     In some embodiment, subjects may be identified as having received or would benefit from receiving treatment for membranous glomerulopathy (MGN), also called membranous glomerulonephritis membranous nephritis (MN). Subjects suffering from or at risk of developing MGN may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising phospholipase A2 receptor, or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex. Phospholipase A2 receptor is normally found on podocytes and presents a target to which self-antibodies associated with MGN have been shown to bind. 
     The term membranous nephritis, or membranous glomerulonephritis, is used to describe a chronic glomerular disease that on light, immunofluorescence, and electron microscopy study of renal tissue shows a set of distinct morphologic features in glomeruli, including thickened glomerular basement membrane (GBM) and GBM spikes, granular staining for IgG and complement along the periphery of glomerular all capillary loops, and electron-dense subepithelial deposits corresponding to the granular IgG staining. 
     Clinically, most patients present with nephrotic syndrome or have proteinuria detected on a routine urinalysis. Idiopathic MN occurs in all age groups and races and both sexes all over the world and is a leading cause of nephrotic syndrome among Caucasian adults. Spontaneous remission of the disease is common in children but also occurs in adults. Although several immunosuppressive drugs often are used to treat individual patients, with or without treatment, nearly a third of patients progress to end-stage renal disease. 
     Complement Dysregulation-Associated Diseases 
     In some embodiment, the synthetic membrane-receiver polypeptide complexes described herein may be used to treat or prevent diseases, disorders or conditions that are associated with complement dysregulation. 
     In specific embodiments, methods are provided for reducing the circulatory concentration of a target complement protein in a subject (e.g., a human) suffering from or at risk of developing a disease, disorder or condition associated with complement dysregulation. The methods include administering a pharmaceutical composition comprising a synthetic membrane-receiver polypeptide complex described herein. The pharmaceutical composition is administered in an amount effective to substantially reduce the circulatory concentration of the target complement protein. In certain embodiments, the administration is carried out intravenously. 
     In certain embodiments, synthetic membrane-receiver polypeptide complexes are administered that comprise a receiver that specifically binds and sequesters a target complement protein that is present in the circulatory system of the subject. 
     In certain embodiments, the therapeutic compositions of the invention provide functional erythroid cells comprising receivers in compositions that are useful to treat, prevent, or reduce the severity of a disease, disorder or condition associated with complement pathophysiology or improper immune complex clearance. 
     In specific embodiments, methods are provided for reducing the circulatory concentration of a target complement protein in a subject (e.g., a human) suffering from or at risk of developing a disease, disorder or condition associated with complement dysregulation. The methods include administering a pharmaceutical composition comprising a synthetic membrane-receiver polypeptide complex described herein. The pharmaceutical composition is administered in an amount effective to substantially reduce the circulatory concentration of the target complement protein. In certain embodiments, the administration is carried out intravenously. 
     In certain embodiments, synthetic membrane-receiver polypeptide complexes are administered that comprise a receiver that specifically binds and sequesters a target complement protein that is present in the circulatory system of the subject. 
     Provided are therapeutic compositions present in an amount effect to treat a disease or condition associated with complement over-activation such as systemic lupus erythematosus, ischemia reperfusion injury, organ transplantation, myocardial infarction, rheumatoid arthritis, scleroderma, polyarteritis nodosa, serum sickness, arthus reaction, farmer&#39;s lung, Henoch-Schonlein purpura, bacterial endocarditis, vasculitis, and other Type III Hypersensitivity conditions. Further provided are therapeutic compositions present in an amount able to treat an infectious disease in which opsonized pathogen is present in the blood, such as carbapenem-resistant enterobacteriaceae, drug resistant  Neisseria gonorrhoeae , fully resistant  Streptococcus pneumonia , drug resistant tuberculosis, generalized bacterial sepsis, human immunodeficiency virus infection, hepatitis B virus infection, or malaria. In a further embodiment, provided are therapeutic compositions present in an amount effect to treat a complement factor deficiency-associated disease such as cofactor H deficiency, paroxysmal nocturnal hemoglobinuria, factor B deficiency, factor D deficiency, C1q deficiency, C1r deficiency, C4 deficiency, C2 deficiency, C3 deficiency, C5 deficiency, C6 deficiency, C7 deficiency, factor I deficiency, factor D deficiency, MBL deficiency, MASP2 deficiency, CD55 deficiency, CD59 deficiency, and other deficiencies in genes associate with complement activity including but not limited to those listed in table 6 and table 8. 
     In certain embodiments, the pharmaceutical composition will reduce the target complement protein load in the circulatory system, thereby reducing the burden of the disease, disorder or condition associated with the presence or elevated concentration of the target complement protein. Diseases associated with complement dysregulation include, but are not limited to, atypical hemolytic uremic syndrome (aHUS), paroxysmal nocturnal hemoglobinuria (PNH), age-related macular degeneration (AMD), complement factor I (CFI) deficiency and those listed in table 6 and table 8. 
     In certain embodiments, the receiver polypeptide may specifically interact with a complement protein selected from the group consisting of: C1q, C1r, C1s, C2, C3, C3a, C3b, C4, C5, C5a, C5b, C6, C7, C8, and C9, Factor B, Factor D, Properdin, iC3b, C3c, C3dg, C3dk, C3e, Bb, C4a, C4b, and in table 5 and table 10. 
     In certain embodiments, the receiver polypeptide may comprise CD46, CD55, CD59, factor H, CR1, factor I, CR1, CR2, CR3, CR4, C3aR, C3eR, Decay-accelerating factor (DAF), Membrane cofactor protein (MCP), C3 Beta chain Receptor, C1 inhibitor, C4 binding protein, and those listed in table 10. 
     Homologous restriction factormicrobial protein NalP, microbial protein SpeB, microbial protein EspP, a derivative or a functional fragment thereof. Alternatively or in addition, the receiver polypeptide may comprise one or more complement control protein (CCP) modules and/or short consensus repeats (SCR) of different origin. 
     The complement system is composed of more than 32 proteins including 7 serum and 9 membrane regulatory proteins, 1 serosal regulatory protein, and 8 cell membrane receptors that bind complement fragments. Activation of complement occurs with the initiation of an inflammatory reaction, most of which occurs in the intravascular space. The soluble components of complement are present in the circulation and also in body fluids and tissues. In addition to the specific activation induced by antigen-antibody complexes, complement is activated through the pattern recognition receptors, which have the ability to discriminate between self and non-self antigens based on repeating patterns of molecular structure (pathogen-associated molecular patterns) present on the surface of pathogens. Complement-activating pattern recognition receptors include mannose-binding lectin (MBL), ficolins, C-reactive protein, C1q, and natural IgM (IgM). 
     Excessive, deregulated, or chronic inflammation can initiate or contribute to several pathologies. For example, the activation of complement during an inflammatory reaction contributes to inflammation-driven tissue injury, which occurs in the ischemia/reperfusion (I/R) setting, vasculitides of various etiologies, nephritis, and arthritis. A deficiency in complement components may also result in tissue injury, as observed in autoimmune reactions. Further, alterations in the expression of complement regulatory proteins may lead to excessive complement activation and can also contribute to tissue injury. 
     In one embodiment the disease or condition is age-related macular degeneration, the receiver is a suitable complement regulatory protein or fragment thereof, and the target is active complement. 
     In one embodiment the disease or condition is atypical hemolytic uremic syndrome, the receiver is complement factor H, or a suitable complement regulatory protein or fragment thereof, and the target is active complement. 
     In one embodiment the disease or condition is Complement Factor I deficiency, the receiver is Complement Factor I, a suitable complement regulatory protein or fragment thereof, and the target is active complement. 
     In one embodiment the disease or condition is paroxysmal nocturnal hemoglobinuria, the receiver is a suitable complement regulatory protein or fragment thereof, and the target is active complement. 
     In one embodiment the disease or condition is autoimmune hemolytic anemia, the receiver is a suitable complement regulatory molecule or fragment thereof, and the target is active complement. 
     in one embodiment the disease or condition is non-alcoholic steatohepatitis, the receiver is a suitable complement regulatory molecule or fragment thereof, and the target is active complement. 
     1. Paroxysmal Nocturnal Hemoglobinuria (PNH) 
     In some embodiments, subjects may be identified as having received or would benefit from receiving treatment for paroxysmal nocturnal hemoglobinuria (PNH). Subjects suffering from or at risk of developing PNH may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising a complement regulatory protein, such as cofactor H, or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex and may be administered to reduce inflammation. 
     Paroxysmal nocturnal hemoglobinuria is an acquired disorder that leads to the premature death and impaired production of blood cells. The disorder affects erythrocytes, leukocytes), and platelets (thrombocytes). PNH affects both sexes equally and can occur at any age, although it is most often diagnosed in young adulthood. 
     People with paroxysmal nocturnal hemoglobinuria have sudden, recurring episodes of symptoms (paroxysmal symptoms), which may be triggered by stresses on the body, such as infections or physical exertion. During these episodes, red blood cells are prematurely destroyed (hemolysis). Affected individuals may pass dark-colored urine due to the presence of hemoglobin (hemoglobinuria). In many, but not all cases, hemoglobinuria is most noticeable in the morning, upon passing urine that has accumulated in the bladder during the night (nocturnal). 
     The premature destruction of red blood cells results in a deficiency of these cells in the blood (hemolytic anemia), which can cause signs and symptoms such as fatigue, weakness, abnormally pale skin (pallor), shortness of breath, and an increased heart rate. People with PNH may also be prone to infections due to a deficiency of white blood cells. 
     Abnormal platelets associated with PNH can cause problems in the blood clotting process. As a result, people with this disorder may experience abnormal blood clotting (thrombosis), especially in large abdominal veins; or, less often, episodes of severe bleeding (hemorrhage). 
     2. Atypical Hemolytic Uremic Syndrome (aHUS) 
     In some embodiments, subjects may be identified as having received or would benefit from receiving treatment for atypical hemolytic uremic syndrome (aHUS). Subjects suffering from or at risk of developing aHUS may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising a complement regulatory protein, such as cofactor I, or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex and may be administered to reduce inflammation. 
     Atypical hemolytic uremic syndrome (aHUS) is a rare syndrome of hemolysis, thrombocytopenia, and renal insufficiency. Genetic mutations in the alternate pathway of complement is the cause in more than 60% of patients affected by this thrombotic microangiopathy. aHUS may be treated using plasma therapy, complement blockade, and/or liver transplantation. Because aHUS shares many of the presenting characteristics of the other thrombotic microangiopathies, and confirmatory genetic results are not available at the time of presentation, the diagnosis relies heavily on the recognition of a clinical syndrome consistent with the diagnosis in the absence of signs of an alternate cause of thrombotic microangiopathy. 
     3. Age-Related Macular Degeneration (AMD) 
     In some embodiments, subjects may be identified as having received or would benefit from receiving treatment for age related macular degeneration (AMD). Subjects suffering from or at risk of developing AMD may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising a complement regulatory protein, such as CD55 and CD59, or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex and may be administered to reduce inflammation. 
     Age related macular degeneration (AMD) is a common form of blindness in the western world and genetic variations of several complement genes, including the complement regulator Factor H, the central complement component C3, Factor B, C2, and also Factor I confer a risk for the disease. However deletion of a chromosomal segment in the Factor H gene cluster on human chromosome 1, which results in the deficiency of the terminal pathway regulator CFHR1, and of the putative complement regulator CFHR3 has a protective effect for development of AMD. The Factor H gene encodes two proteins Factor H and FHL1 which are derived from alternatively processed transcripts. In particular a sequence variation at position 402 of both Factor H and FHL1 is associated with a risk for AMD. A tyrosine residue at position 402 represents the protective and a histidine residue the risk variant. AMD is considered a chronic inflammatory disease, which can be caused by defective and inappropriate regulation of the continuously activated alternative complement pathway. This activation generates complement effector products and inflammatory mediators that stimulate further inflammatory reactions. Defective regulation can lead to formation of immune deposits, drusen and ultimately translate into damage of retinal pigment epithelial cells, rupture of the interface between these epithelial cells and the Bruch&#39;s membrane and vision loss. 
     Immune Complex-Associated Diseases 
     In some embodiments, the synthetic membrane-receiver polypeptide complexes described herein may be used to treat or prevent diseases, disorders or conditions that are associated with immune complexes or improper immune complex clearance. 
     In specific embodiments, methods are provided for reducing the circulatory concentration of a target immune complex in a subject (e.g., a human) suffering from or at risk of developing a disease, disorder or condition associated with immune complexes. The methods include administering a pharmaceutical composition comprising a synthetic membrane-complement receptor 1 (CR1) receiver complex. The pharmaceutical composition is administered in an amount effective to substantially reduce the circulatory concentration of the target immune complex. In certain embodiments, the administration is carried out intravenously. 
     In certain embodiments, synthetic membrane-complement receptor 1 (CR1) receiver complexes are administered that specifically bind and sequester a target immune complex that is present in the circulatory system of the subject. 
     In some embodiments, functional erythroid cells comprising a receiver that comprises complement receptor 1 (CR1) may be administered to a subject exhibiting immune complexes in circulation. For example, a population of functional erythroid cells comprising a receiver that comprises complement receptor 1 (CR1) can bind C3b within an immune complex and removal and clearance from circulation can occur through the liver. 
     Compositions comprising erythrocyte-bound CR1 receiver, such as a plurality of functional erythroid cells comprising elevated levels of CR1, is preferably administered to a subject having been diagnosed with or being suspected of having a disease state that has resulted from an overabundance of immune complex formation or that has caused a reduction or depletion in the native CR1 level, such as an immune complex-associated disorder or disease. 
     In certain embodiments, the pharmaceutical composition will reduce the target immune complex load in the circulatory system, and/or prevent the deposition of immune complexes in sensitive soft tissue, thereby reducing the burden of the disease, disorder or condition associated with the presence or elevated concentration of the target immune complex. Diseases associated with complement dysregulation include, but are not limited to, systemic lupus erythematosus (SLE), lupus nephritis, IgA nephropathy, Dense Deposit Disease, lupus nephritis, Goodpasture&#39;s syndrome, membranoproliferative glomerulonephritis, immune complex vasculitis, cold agglutinin disease, polymyositis, acute pulmonary hemorrhage, membranous glomerulonephritis, membranous glomerulonephritis, rapidly-progressive glomerulonephritis, post-streptococcal glomerulonephritis, post-staphylococcal glomerulonephritis, Pauci-immune glomerulonephritis, blood hyperviscosity syndrome, and cutaneous leukocytoclastic angiitis and those listed in table 6 and table 8. 
     In certain embodiments, the target immune complex comprises i) IgM or IgG, and ii) C3b and/or C4b. 
     In certain embodiments, the CR1 receiver comprises one or more complement control protein (CCP) modules, short consensus repeats (SCR) and/or long homologous repeats (LHRs). In some embodiments, the CR1 receiver comprises a functional fragment of the full-length CR1 polypeptide. 
     Type III, or immune-complex, reactions are characterized by tissue damage caused by the activation of complement in response to antigen-antibody (immune) complexes (IgG and IgM) that are deposited in tissues. Once the antigen-antibody complexes form, they are deposited in various tissues of the body, especially the blood vessels, kidneys, lungs, skin, and joints. Deposition of the immune complexes causes an inflammatory response, which leads to the release of tissue-damaging enzymes and interleukin-1, which induces fever. Immune complexes underlie many autoimmune diseases, such as systemic lupus erythematosus (an inflammatory disorder of connective tissue), most types of glomerulonephritis (inflammation of the capillaries of the kidney), and rheumatoid arthritis. 
     Type III hypersensitivity reactions can be provoked by inhalation of antigens into the lungs. A number of conditions are attributed to this type of antigen exposure, including farmer&#39;s lung, caused by fungal spores from moldy hay; pigeon fancier&#39;s lung, resulting from proteins from powdery pigeon dung; and humidifier fever, caused by normally harmless protozoans that can grow in air-conditioning units and become dispersed in fine droplets in climate-controlled offices. In each case, the person will be sensitized to the antigen with IgG antibodies to the agent circulating in the blood. Inhalation of the antigen will stimulate the reaction and cause chest tightness, fever, and malaise, symptoms that usually pass in a day or two but recur when the individual is re-exposed to the antigen. Permanent damage is rare unless individuals are exposed repeatedly. Some occupational diseases of workers who handle cotton, sugarcane, or coffee waste in warm countries have a similar cause, with the sensitizing antigen usually coming from fungi that grow on the waste rather than the waste itself. 
     In one embodiment the disease or condition is IgA nephropathy, the receiver is Complement receptor 1 or fragment thereof, and the target is Immune complexes. 
     In one embodiment the disease or condition is lupus nephritis, the receiver is Complement receptor 1 or fragment thereof, and the target is immune complex. 
     In one embodiment the disease or condition is systemic lupus erythematosus, the receiver is Complement receptor 1 or fragment thereof, and the target is immune complex. 
     1. Systemic Lupus Erythematosus (SLE) 
     In some embodiments, subjects may be identified as having received or would benefit from receiving treatment for systemic lupus erythematosus (SLE). Subjects suffering from or at risk of developing SLE may be administered a pharmaceutical composition comprising the synthetic membrane-CR1 receiver complex to treat or prevent disease. 
     In certain embodiments, the CR1 receiver interacts with the target C3b, a constituent of a circulating immune complex. In some embodiments, the immune complex once bound to the synthetic membrane-CR1 receiver complex is degraded through the reticulo-endothelial system. 
     Systemic lupus erythematosus (SLE) is a chronic inflammatory disease that has protean manifestations and follows a relapsing and remitting course. More than 90% of cases of SLE occur in women, frequently starting at childbearing age. SLE is a chronic autoimmune disease that can affect almost any organ system; thus, its presentation and course are highly variable, ranging from indolent to fulminant. In childhood-onset SLE, there are several clinical symptoms more commonly found than in adults, including malar rash, ulcers/mucocutaneous involvement, renal involvement, proteinuria, urinary cellular casts, seizures, thrombocytopenia, hemolytic anemia, fever, and lymphadenopathy. In adults, Raynaud pleuritis and sicca are twice as common as in children and adolescents. A presentation of a triad of fever, joint pain, and rash in a woman of childbearing age should prompt investigation into the diagnosis of SLE. 
     SLE is an autoimmune disorder characterized by multisystem inflammation with the generation of self-antibodies. Self-antibodies may be present for many years before the onset of the first symptoms of SLE. Further, T cells from patients with lupus show defects in both signaling and effector function (e.g., decreased secretion of interleukin (IL)-2). T-cell abnormalities offer targets for therapy, e.g., belimumab, which targets the B-lymphocyte stimulator (B Lys) signaling pathway. 
     Many clinical manifestations of SLE are mediated by circulating immune complexes that form with antigens in various tissues or the direct effects of antibodies to cell surface components. Immune complexes form in the microvasculature, leading to complement activation and inflammation. Moreover, antibody-antigen complexes deposit on the basement membranes of skin and kidneys. In active SLE, this process has been confirmed by demonstration of complexes of nuclear antigens such as DNA, immunoglobulins, and complement proteins at these sites. Self-antibodies (e.g., lupus anticoagulant (LA), and anti-ribosomal P antibodies) can be used as biomarkers to determine future neuropsychiatric events in SLE. 
     Other indications include the presence of serum antinuclear antibodies (ANAs) which are found in nearly all individuals with active SLE. Antibodies to native double-stranded DNA (dsDNA) are relatively specific for the diagnosis of SLE. Cytotoxic T cells and suppressor T cells (which would normally down-regulate immune responses) are decreased. The generation of polyclonal T-cell cytolytic activity is impaired. Helper (CD4 + ) T cells are increased. A lack of immune tolerance is observed in animal lupus models. 
     2. IgA Nephropathy 
     In some embodiments, subjects may be identified as having received or would benefit from receiving treatment for IgA nephropathy. Subjects suffering from or at risk of developing IgA nephropathy may be administered a pharmaceutical composition comprising the synthetic membrane-CR1 receiver complex to treat or prevent disease. 
     In certain embodiments, the CR1 receiver interacts with the target C3b, a constituent of a circulating IgA immune complex. In some embodiments, the immune complex once bound to the synthetic membrane-CR1 receiver complex is degraded through the reticulo-endothelial system. 
     IgA nephropathy also known as Berger&#39;s disease is a kidney disease associated with the accumulation of IgA-immune complexes. The presence of the immune complexes triggers a local inflammation that reduces the kidneys&#39; ability to filter waste, excess water and electrolytes from the blood. Kidney damage may be indicated by blood and protein in urine, high blood pressure and swollen feet. 
     IgA nephropathy usually progresses slowly over many years. Some subjects present blood in their urine without developing problems, some eventually achieve complete remission, and others develop end-stage kidney failure. 
     IgA nephropathy is the most common glomerulonephritis worldwide. Clinically, it is characterized by hematuria and proteinuria; about 20-30% of the IgAN patients develop progressive renal failure within 10-20 years from the onset of disease. Histologically, the glomerular mesangium contains deposits of IgA1, the C3 component of complement, and less frequently, IgG and/or IgM. Circulating immune complexes (CICs) composed of IgA1, C3, and IgG are involved in the pathogenesis of the disease. 
     Serum IgA1 from IgAN patients may exhibit alterations in the glycan side chains. Human IgA1 contains N- and O-linked glycans. IgA1 from IgAN patients display altered glycan moieties, usually with a reduced content of galactose (Gal). The Gal-deficient IgA1 may be present in CICs with IgG. IgA1 from sera of IgAN patients exhibit increased binding to lectins specific for a terminal GalNAc, such as  Helix aspersa  (HAA) or  Helix pomatia  (HPO). 
     Amyloidoses 
     In some embodiment, the synthetic membrane-receiver polypeptide complexes described herein may be used to treat or prevent amyloidosis. In some embodiments, membrane-receiver complexes are used that do not contain a receiver polypeptide. The receiver can for example be a glycosaminoglycans (GAG). 
     In specific embodiments, methods are provided for reducing the circulatory concentration of a target serum amyloid protein in a subject (e.g., a human) suffering from or at risk of developing amyloid plaques. The methods include administering a pharmaceutical composition comprising a synthetic membrane-receiver complex described herein. The pharmaceutical composition is administered in an amount effective to substantially reduce the circulatory concentration of the target serum amyloid protein. In certain embodiments, the administration is carried out intravenously. 
     In certain embodiments, synthetic membrane-receiver complexes are administered that comprise a receiver that specifically binds, sequesters and/or degrades a target serum amyloid protein or target amyloid plaque that is present in the circulatory system of the subject. 
     In certain embodiments, the pharmaceutical composition will reduce the target serum amyloid protein or amyloid plaque load in the circulatory system, e.g., preventing their deposition in soft tissue, thereby reducing the burden of the amyloidosis. Amyloidoses include, but are not limited to, AA amyloidosis, light chain (AL) amyloidosis, beta-2 microglobulin amyloidosis and those listed in table 6 and table 8. 
     In certain embodiments, the receiver polypeptide may specifically interact with a target serum amyloid protein selected from the group consisting of: amyloid P protein, amyloid A protein, light chain, misfolded transthyretin, and fibrinogen alpha chain. 
     Amyloidosis is a rare disease associated with amyloid plaques build up. Amyloidosis can affect different organs such as, e.g., the heart, kidneys, liver, spleen, nervous system and digestive tract. Severe amyloidosis can lead to life-threatening organ failure. 
     Acquired systemic amyloidosis is thought to be the cause of death in about 1 in 1,000 persons in Western countries and is most common in the elderly. Systemic AL amyloidosis is the most common and serious type, accounting for over 60% of cases. Dialysis-related β 2 -microglobulin amyloidosis affects about 1 million patients worldwide. Senile transthyretin (ATTR) amyloidosis, which predominantly involves the heart, occurs in about one quarter of persons older than 80 years. 
     In one embodiment the disease or condition is AA amyloidosis, the receiver is an an antibody-like binder to serum amyloid A protein or serum amyloid P component or fragment thereof, and the target is serum amyloid A protein and amyloid placques. 
     In one embodiment the disease or condition is beta2 microglobulin amyloidosis, the receiver is an antibody-like binder to beta-2 microglobulin or serum amyloid P component or fragment thereof, and the target is beta-2 microglobulin or amyloid placques. 
     In one embodiment the disease or condition is light chain amyloidosis, the receiver is an antibody-like binder to light chain, serum amyloid P component or fragment thereof, and the target is antibody light chain or amyloid placques. 
     1. AA Amyloidosis 
     In some embodiments, subjects may be identified as having received or would benefit from receiving treatment for AA amyloidosis. Subjects suffering from or at risk of developing AA amyloidosis may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complexes described herein to treat or prevent disease. 
     AA amyloidosis is a complication of chronic infections and inflammatory diseases or any condition that leads to long-term overproduction of the acute phase reactant SAA. The amyloid fibrils are composed of an N-terminal cleavage fragment of SAA (the AA protein). AA amyloidosis occurs in 1% to 5% of patients with rheumatoid arthritis, juvenile idiopathic arthritis and Crohn&#39;s disease. Tuberculosis and leprosy are also important causes of AA amyloidosis in some parts of the world. Most patients present with proteinuria, and liver and gastrointestinal involvement may occur with time. 
     2. AL Amyloidosis 
     In some embodiments, subjects may be identified as having received or would benefit from receiving treatment for AL amyloidosis. Subjects suffering from or at risk of developing AL amyloidosis may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complexes described herein to treat or prevent disease. 
     Systemic AL occurs in about 2% of people with monoclonal B-cell dyscrasias. AL fibrils are derived from monoclonal immunoglobulin light chains, affecting usually the kidneys, heart, liver and peripheral nerves. 
     3. β2-Microglobulin Amyloidosis 
     In some embodiments, subjects may be identified as having received or would benefit from receiving treatment for β2-Microglobulin amyloidosis. Subjects suffering from or at risk of developing β2-Microglobulin amyloidosis may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complexes described herein to treat or prevent disease. 
     β 2 -Microglobulin amyloid deposition occurs in patients with dialysis-dependent chronic renal failure, mainly affecting articular and periarticular structures. It typically causes arthralgia of the shoulders, knees, wrists and small joints of the hand; joint swelling and carpal tunnel syndrome. The amyloid fibril precursor protein is β 2 -microglobulin, which is the invariant chain of the major histocompatibility complex (MHC) class I molecule and is expressed by all nucleated cells. Since it is normally filtered freely at the glomerulus, reabsorbed and catabolized by proximal tubular cells, decreasing renal function causes a proportionate rise in its concentration. Disease-related amyloidosis (DRA) is present in 20% to 30% of patients within 3 years of starting dialysis for end-stage renal failure. 
     In some embodiments, membrane-receiver complexes that do not contain a receiver polypeptide are used for treatment of an amyloidosis and or for the reduction of a serum amyloid protein or amyloid plaque. In one embodiment, the synthetic membrane-receiver complex comprises a receiver comprising a glycosaminoglycans (GAG), or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver complex and may be administered to bind a circulating amyloidogenic precursors. In certain embodiments, amyloid deposits are prevented from forming. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising a serum amyloid P-component (SAP), or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex and may be administered to prevent amyloids from aggregating. Serum amyloid P-component (protein SAP) has been described to bind in vitro to isolated amyloid fibrils of both primary and secondary types. 
     Infectious Agent-Mediated Diseases and Conditions 
     In some embodiments, the synthetic membrane-receiver polypeptide complexes described herein may be used to treat or prevent diseases, disorders or conditions that are associated with infectious agents. 
     In some embodiments, functional erythroid cells comprising a receiver specific for circulating pathogens are administered to a subject in need thereof in an amount effective to treat an infectious disease in which opsonized pathogen is present in the blood, such as carbapenem-resistant enterobacteriaceae, drug resistant  Neisseria gonorrhoeae , fully resistant  Streptococcus pneumoniae , drug resistant tuberculosis, generalized bacterial sepsis, human immunodeficiency virus infection, hepatitis B virus infection, or malaria. In some embodiments, functional erythroid cells comprise a receiver specific for circulating pathogens that include, but are not limited to, the targets in table 5. 
     In specific embodiments, methods are provided for reducing the circulatory concentration of a target infectious agent in a subject (e.g., a human) suffering from or at risk of developing an infectious disease. The methods include administering a pharmaceutical composition comprising a synthetic membrane-receiver polypeptide complex described herein. The pharmaceutical composition is administered in an amount effective to substantially reduce the circulatory concentration of the target infectious agent. In certain embodiments, the administration is carried out intravenously. 
     In certain embodiments, synthetic membrane-receiver polypeptide complexes are administered that comprise a receiver that specifically binds, sequesters, and/or degrades an infectious agent, such as a bacterium, a virus, a fungus, or a parasite that is present in the circulatory system of the subject. 
     In certain embodiments, synthetic membrane-receiver polypeptide complexes are administered to reduce the plasma titer of the infectious agent, e.g., virus titer. 
     In certain embodiments, synthetic membrane-receiver polypeptide complexes are administered to reduce the ability of the infectious agent to access enough host cells per unit of time. A decrease in the rate of infection of host cells may correlate with an increasing inability of the infectious agent to perpetuate the infection or perpetuate the deleterious effect to the subject host. The infection may be suppressed and/or contained. 
     In certain embodiments, the pharmaceutical composition will reduce the target infectious agent load in the circulatory system, slowing or stopping the infection and aiding the immune system in its defense, thereby reducing the burden of the infectious disease. Infectious diseases include, but are not limited to, Hepatitis A, Hepatitis B, Hepatitis C, HIV, Ebola,  C. difficile, C. botulinum , Anthrax,  E. coli, Mycobacterium tuberculosis, Candida , malaria and those listed in table 6 and table 8. 
     In one embodiment the disease or condition is Anthrax ( B. anthracis ) infection, the receiver is an antibody-like binder to  B. anthracis  surface protein or fragment thereof, and the target is  B. anthracis.    
     In one embodiment the disease or condition is  C. botulinum  infection, the receiver is an antibody-like binder to  C. botulinum  surface protein or fragment thereof, and the target is  C. botulinum.    
     In one embodiment the disease or condition is  C. difficile  infection, the receiver is an antibody-like binder to  C. difficile  surface protein or fragment thereof, and the target is  C. difficile.    
     In one embodiment the disease or condition is  Candida  infection, the receiver is an antibody-like binder to  candida  surface protein or fragment thereof, and the target is  candida.    
     In one embodiment the disease or condition is  E. coli  infection, the receiver is an antibody-like binder to  E. coli  surface protein or fragment thereof, and the target is  E. coli.    
     In one embodiment the disease or condition is Ebola infection, the receiver is an antibody-like binder to Ebola surface protein or fragment thereof, and the target is Ebola. 
     In one embodiment the disease or condition is Hepatitis B (HBV) infection, the receiver is an antibody-like binder to HBV surface protein or fragment thereof, and the target is HBV. 
     In one embodiment the disease or condition is Hepatitis C (HCV) infection, the receiver is an antibody-like binder to HCV surface protein or fragment thereof, and the target is HCV. 
     In one embodiment the disease or condition is Human immunodeficiency virus (HIV) infection, the receiver is an antibody-like binder to HIV envelope proteins or CD4 or CCR5 or fragment thereof, and the target is HIV. 
     In one embodiment the disease or condition is  M. tuberculosis  infection, the receiver is an antibody-like binder to  M. tuberculosis  surface protein or fragment thereof, and the target is  M. tuberculosis.    
     In one embodiment the disease or condition is malaria ( P. falciparum ) infection, the receiver is an antibody-like binder to  P. falciparum  surface protein or fragment thereof, and the target is  P. falciparum.    
     1. Bacterial Infections 
     In some embodiments, subjects may be identified as having received or would benefit from receiving treatment for a bacterial infection. Subjects suffering from or at risk of developing a bacterial infection may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In some embodiments, the target is a bacterium. In certain embodiments, the target comprises a bacterial antigen. In some embodiments, the bacterial antigen comprises a cell surface antigen, a secreted toxin, or a secreted bacterial antigen. 
     Bacteremia is the presence of bacteria in the blood. Gram-negative bacteremia secondary to infection usually originates in the genitourinary system or GI tract, or the skin in patients with decubitus ulcers. Chronically ill and immunocompromised patients have an increased risk of gram-negative bacteremia. They may also develop bacteremia with gram-positive cocci, anaerobes, and fungi. Staphylococcal bacteremia is common in injection drug users.  Bacteroides  bacteremia may develop in patients with infections of the abdomen and the pelvis, particularly the female genital tract. The bacteria most likely to cause bacteremia include members of the  Staphylococcus, Streptococcus, Pseudomonas, Haemophilus , and  Escherichia coli  ( E. coli ) genera. 
     Bacterial infectious diseases that can be treated by the pharmaceutical compositions comprising a synthetic membrane-receiver polypeptide complex described herein include, but are not limited to, Mycobacteria,  Rickettsia, Mycoplasma, Neisseria meningitides, Neisseria gonorrheoeae, Legionella, Vibrio cholerae , Streptococci,  Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, Corynobacteria diphtheriae, Clostridium  spp., enterotoxigenic  Escherichia coli , and  Bacillus anthracis . Other pathogens for which bacteremia has been reported include:  Rickettsia, Bartonella henselae, Bartonella quintana, Coxiella burnetii, chlamydia, Mycobacterium leprae, Salmonella; shigella; Yersinia enterocolitica; Yersinia pseudotuberculosis; Legionella pneumophila; Mycobacterium tuberculosis; Listeria monocytogenes; Mycoplasma  spp.;  Pseudomonas fluorescens; Vibrio cholerae; Haemophilus influenzae; Bacillus anthracis; Treponema pallidum ; Leptospira;  Borrelia; Corynebacterium diphtheriae; Francisella; Brucella melitensis; Campylobacter jejuni; Enterobacter; Proteus mirabilis; Proteus ; and  Klebsiella pneumoniae.    
     In some embodiments, a membrane-receiver polypeptide complex may be used to treat the infectious bacterial disease. A suitable receiver polypeptide may comprise, for example, CD14 or a functional fragment thereof. CD14 is associated with monocyte/macrophages and binds lipopolysaccharide associated with gram negative bacteria as well as lipoteichoic acid associated with the gram positive bacteria  Bacillus subtilis . Other suitable receivers may comprise adenylate cyclase (Bordatella pertussis), Gal alpha 1-4Gal-containing isoreceptors ( E. coli ), glycoconjugate receptors (enteric bacteria), Lewis (b) blood group antigen receptor ( Heliobacter pylori ), CR3 receptor, protein kinase receptor, galactose N-acetylgalactosamine-inhabitable lectin receptor, chemokine receptor ( Legionella ), annexin I ( Leishmania mexicana ), ActA protein ( Listeria monocytogenes ), meningococcal virulence associated Opa receptors (Meningococcus), acute over (05133 integrin ( Mycobacterium avium -M), heparin sulphate proteoglycan receptor, CD66 receptor, integrin receptor, membrane cofactor protein, CD46, GM1, GM2, GM3, and CD3 ( Neisseria gonorrhoeae ), KDEL receptor ( Pseudomonas ), epidermal growth factor receptor ( Samonella typhiurium ), β1 integrin ( Shigella ), nonglycosylated J774 receptor (Streptococci) or combinations or functional fragments thereof. 
     In some embodiments, the synthetic membrane-receiver complex may comprise more than one receiver. One receiver may function to interact with the target, while the other receiver may modify the target, e.g., disrupting the integrity of the target, marking the target for degradation and/or inactivating the target. For example, if the target is a bacterium, one receiver functions to interact with the target bacterium (e.g., through an interaction with an epitope if the receiver comprises an antibody-like function). The other receiver may be capable of breaching the cell membrane of the bacterium. Suitable second receivers include, for example, lysozymes, bacteriocidal permeability increasing peptides, proteases, and other pore forming antimicrobials. For example, a lysozyme receiver may hydrolyse 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in a peptidoglycan and between N-acetyl-D-glucosamine residues in chitodextrins of certain bacteria. 
     Alternatively, a second receiver may comprise a bacteriostatic or bactericidal agent that may be contacted with the bacterium. Yet another alternative is that the synthetic membrane-receiver complex comprises (e.g., through loading) a bacteriostatic or bactericidal agent that may be contacted with the bacterium. Examples of bacteriostatic or bactericidal agents that may be associated with a receiver or the complex include, but are not limited to, beta-lactam compounds (penicillin, methicillin, nafcillin, oxacillin, cloxacillin, dicloxacilin, ampicillin, ticarcillin, amoxicillin, carbenicillin, piperacillin); cephalosporins &amp; cephamycins (cefadroxil, cefazolin, cephalexin, cephalothin, cephapirin, cephradine, cefaclor, cefamandole, cefonicid, cefuroxime, cefprozil, loracarbef, ceforanide, cefoxitin, cefmetazole, cefotetan, cefoperazone, cefotaxime, ceftazidine, ceftizoxine, ceftriaxone, cefixime, cefpodoxime, proxetil, cefdinir, cefditoren, pivoxil, ceftibuten, moxalactam, cefepime); other beta-lactam drugs (aztreonam, clavulanic acid, sulbactam, tazobactam, ertapenem, imipenem, meropenem); cell wall membrane active agents (vancomycin, teicoplanin, daptomycin, fosfomycin, bacitracin, cycloserine); tetracyclines (tetracycline, chlortetracycline, oxytetracycline, demeclocycline, methacycline, doxycycline, minocycline, tigecycline); macrolides (erythromycin, clarithromycin, azithromycin, telithromycin); clindamycin; choramphenicol; quinupristin-dalfopristin; linezolid; aminoglycosides (streptomycin, neomycin, kanamycin, amikacin, gentamicin, tobramycin, sisomicin, netilmicin); spectinomycin; sulfonamides (sulfacytine, sulfisoxazole, silfamethizole, sulfadiazine, sulfamethoxazole, sulfapyridine, sulfadoxine); trimethoprim; pyrimethamine; trimethoprim-sulfamethoxazole; fluoroquinolones (ciprofloxacin, gatifloxacin, gemifloxacin, levofloxacin, lomefloxacin, moxifloxacin, norfloxacin, ofloxacin); colistimethate sodium, methenamine hippurate, methenamine mandelate, metronidazole, mupirocin, nitrofurantoin, and polymyxin B. Examples of anti-mycobacteria drugs include, but are not limited to: isoniazid, rifampin, rifabutin, rifapentine, pyrazinamide, ethambutol, ethionamide, capreomycin, clofazimine, and dapsone. 
     In some embodiments, methods of treatment of bacterial infectious diseases are provided comprising co-administration of one or more bacteriostatic or bactericidal agents and the synthetic membrane-receiver complex described herein, wherein co-administration includes administration of the bacteriostatic or bactericidal agent before, after or concurrent with administration of the synthetic membrane-receiver complex. 
     In some embodiments, methods of treatment of bacterial infectious diseases are provided comprising administration of a pharmaceutical composition comprising one or more bacteriostatic or bactericidal agents and the synthetic membrane-receiver complex described herein. 
     In some embodiments, the receiver may sequester the target bacterium and distribute it in the circulatory system without directly modifying the target. In certain embodiments, the synthetic membrane-receiver complex may subject the associated target bacterium to degradation by the reticulo-endothelial system. 
     2. Fungal Infections 
     In some embodiments, subjects may be identified as having received or would benefit from receiving treatment for a fungal infection. Subjects suffering from or at risk of developing a fungal infection may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In some embodiments, the target is a fungus. In certain embodiments, the target comprises a fungal antigen. In some embodiments, the fungal antigen comprises a cell surface antigen, a secreted toxin, or a secreted fungal antigen. 
     Fungemia (also known as candidemia, candedemia, and invasive candidiasis) is the presence of fungi or yeasts in the blood. The most commonly known pathogen is  Candida albicans , causing roughly 70% of fungemias, followed by  Candida glabrata  with 10%, and  Aspergillus  with 1%. Infections with  T. glabrata, Candida tropicalis, C. krusei , and  C. parapsilosis  may also occur. 
     In some embodiments, a membrane-receiver polypeptide complex may be used to treat the infectious fungal disease. In some embodiments, the synthetic membrane-receiver complex may comprise more than one receiver. One receiver may function to interact with the target, while the other receiver may modify the target, e.g., disrupting the integrity of the target, marking the target for degradation and/or inactivating the target. The second receiver may comprise an antifungal agent that may be contacted with the fungus. In another embodiment, the synthetic membrane-receiver complex comprises (e.g., through loading) an antifungal agent that may be contacted with the fungus. 
     Examples of antifungal agents that may be associated with a receiver or the complex include, but are not limited to, allylamines; terbinafine; antimetabolites; flucytosine; azoles; fluconazole; itraconazole; ketoconazole; ravuconazole; posaconazole; voriconazole; glucan synthesis inhibitors; caspofungin; micafungin; anidulafungin; polyenes; amphotericin B; amphotericin B Lipid Complex (ABLC); amphotericin B Colloidal Dispersion (ABCD); liposomal amphotericin B (L-AMB); liposomal nystatin; and griseofulvin. 
     In some embodiments, methods of treatment of fungal infectious diseases are provided comprising co-administration of one or more antifungal agents and the synthetic membrane-receiver complex described herein, wherein co-administration includes administration of the antifungal agent before, after or concurrent with administration of the synthetic membrane-receiver complex. 
     In some embodiments, methods of treatment of bacterial infectious diseases are provided comprising administration of a pharmaceutical composition comprising one or more antifungal agents and the synthetic membrane-receiver complex described herein. 
     In some embodiments, the receiver may sequester the target fungus and distribute it in the circulatory system without directly modifying the target. In certain embodiments, the synthetic membrane-receiver complex may subject the associated target fungus to degradation by the reticulo-endothelial system. 
     3. Parasite Infections 
     In some embodiments, subjects may be identified as having received or would benefit from receiving treatment for a parasitic infection. Subjects suffering from or at risk of developing a parasitic infection may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In some embodiments, the target is a parasite. In certain embodiments, the target comprises a parasitic antigen. In some embodiments, the parasitic antigen comprises a cell surface antigen, a secreted toxin, or a secreted parasitic antigen. Suitable targets include intestinal or blood-borne parasites, including protazoa. 
     Typically, blood-borne parasites are transmitted through an arthropod vector. Most important arthropod for transmitting parasitic infections are mosquitoes. Mosquitoes carry malaria and filarial nematodes. Biting flies transmit African trypanosomiasis, leishmaniasis and several kinds of filariasis. Examples of parasites include, but are not limited to, trypanosomes; haemoprotozoa and parasites capable of causing malaria; enteric and systemic cestodes including taeniid cestodes; enteric coccidians; enteric flagellate protozoa; filarial nematodes; gastrointestinal and systemic nematodes and hookworms. 
     In some embodiments, a membrane-receiver polypeptide complex may be used to treat the parasitic infection. In some embodiments, the synthetic membrane-receiver complex may comprise more than one receiver. One receiver may function to interact with the target, while the other receiver may modify the target, e.g., disrupting the integrity of the target, marking the target for degradation and/or inactivating the target. The second receiver may comprise an anti-parasitic agent that may be contacted with the fungus. In another embodiment, the synthetic membrane-receiver complex comprises (e.g., through loading) an anti-parasitic agent that may be contacted with the fungus. 
     Examples of anti-parasitic agents that may be associated with a receiver or the complex include, but are not limited to, antiprotozoal agents; eflornithine; furazolidone; melarsoprol; metronidazole; ornidazole; paromomycin sulfate; pentamidine; pyrimethamine; tinidazole; antimalarial agents; quinine; chloroquine; amodiaquine; pyrimethamine; sulphadoxine; proguanil; mefloquine; halofantrine; primaquine; artemesinin and derivatives thereof; doxycycline; clindamycin; benznidazole; nifurtimox; antihelminthics; albendazole; diethylcarbamazine; mebendazole; niclosamide; ivermectin; suramin; thiabendazole; pyrantel pamoate; levamisole; piperazine family; praziquantel; triclabendazole; octadepsipeptides; and emodepside. 
     In some embodiments, methods of treatment of parasitic infectious diseases are provided comprising co-administration of one or more anti-parasitic agents and the synthetic membrane-receiver complex described herein, wherein co-administration includes administration of the anti-parasitic agent before, after or concurrent with administration of the synthetic membrane-receiver complex. 
     In some embodiments, methods of treatment of parasitic infectious diseases are provided comprising administration of a pharmaceutical composition comprising one or more anti-parasitic agents and the synthetic membrane-receiver complex described herein. 
     In some embodiments, the receiver may sequester the target parasite and distribute it in the circulatory system without directly modifying the target. In certain embodiments, the synthetic membrane-receiver complex may subject the associated target parasite to degradation by the reticulo-endothelial system. 
     4. Viral Infections 
     In some embodiments, subjects may be identified as having received or would benefit from receiving treatment for a viral infection. Subjects suffering from or at risk of developing a viral infection may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In some embodiments, the target is a virus. In certain embodiments, the target comprises a viral antigen. In some embodiments, the viral antigen comprises an envelope antigen or a capsid antigen. Suitable viral targets include adenovirus, coxsackievirus, hepatitis a virus, poliovirus, epstein-barr virus, herpes simplex, type 1, herpes simplex, type 2, human cytomegalovirus, human herpesvirus, type 8, varicella-zoster virus, hepatitis B virus, hepatitis C viruses, human immunodeficiency virus (HIV), influenza virus, measles virus, mumps virus, parainfluenza virus, respiratory syncytial virus, papillomavirus, rabies virus, and Rubella virus. Other suitable viral targets include Paramyxoviridae (e.g., pneumovirus, morbillivirus, metapneumovirus, respirovirus or rubulavirus), Adenoviridae (e.g., adenovirus), Arenaviridae (e.g., arenavirus such as lymphocytic choriomeningitis virus), Arteriviridae (e.g., porcine respiratory and reproductive syndrome virus or equine arteritis virus), Bunyaviridae (e.g., phlebovirus or hantavirus), Caliciviridae (e.g., Norwalk virus), Coronaviridae (e.g., coronavirus or torovirus), Filoviridae (e.g., Ebola-like viruses), Flaviviridae (e.g., hepacivirus or flavivirus), Herpesviridae (e.g., simplexvirus, varicellovirus, cytomegalovirus, roseolovirus, or lymphocryptovirus), Orthomyxoviridae (e.g., influenza virus or thogotovirus), Parvoviridae (e.g., parvovirus), Picomaviridae (e.g., enterovirus or hepatovirus), Poxviridae (e.g., orthopoxvirus, avipoxvirus, or leporipoxvirus), Retroviridae (e.g., lentivirus or spumavirus), Reoviridae (e.g., rotavirus), Rhabdoviridae (e.g., lyssavirus, novirhabdovirus, or vesiculovirus), and Togaviridae (e.g., alphavirus or rubivirus). Specific examples of these viruses include human respiratory coronavirus, influenza viruses A-C, hepatitis viruses A to G, and herpes simplex viruses 1-9. 
     In some embodiments, a membrane-receiver polypeptide complex may be used to treat the viral infection. In some embodiments, the synthetic membrane-receiver complex may comprise more than one receiver. One receiver may function to interact with the target, while the other receiver may modify the target, e.g., disrupting the integrity of the target, marking the target for degradation and/or inactivating the target. 
     For example, if the target is a virus, one receiver functions to interact with the target virus (e.g., through an interaction with a viral epitope if the receiver comprises an antibody-like function). The other receiver may be capable of breaching the viral envelope or capsid. Suitable second receivers include, for example, antiviral agents, proteases, nucleases, antisense molecules, ribozymes, RNAi molecules (e.g., siRNA or shRNA), or other molecules that are toxic or detrimental to the virus. 
     The second receiver may comprise an anti-viral agent that may be contacted with the virus. In another embodiment, the synthetic membrane-receiver complex comprises (e.g., through loading) an anti-viral agent that may be contacted with the virus. 
     Examples of anti-viral agents that may be associated with a receiver or the complex include, but are not limited to, thiosemicarbazones; metisazone; nucleosides and nucleotides; acyclovir; idoxuridine; vidarabine; ribavirin; ganciclovir; famciclovir; valaciclovir; cidofovir; penciclovir; valganciclovir; brivudine; ribavirin, cyclic amines; rimantadine; tromantadine; phosphonic acid derivatives; foscarnet; fosfonet; protease inhibitors; saquinavir; indinavir; ritonavir; nelfinavir; amprenavir; lopinavir; fosamprenavir; atazanavir; tipranavir; nucleoside and nucleotide reverse transcriptase inhibitors; zidovudine; didanosine; zalcitabine; stavudine; lamivudine; abacavir; tenofovir disoproxil; adefovir dipivoxil; emtricitabine; entecavir; non-nucleoside reverse transcriptase inhibitors; nevirapine; delavirdine; efavirenz; neuraminidase inhibitors; zanamivir; oseltamivir; moroxydine; inosine pranobex; pleconaril; and enfuvirtide. 
     In some embodiments, methods of treatment of viral infectious diseases are provided comprising co-administration of one or more anti-viral agents and the synthetic membrane-receiver complex described herein, wherein co-administration includes administration of the anti-viral agent before, after or concurrent with administration of the synthetic membrane-receiver complex. 
     In some embodiments, methods of treatment of viral infectious diseases are provided comprising administration of a pharmaceutical composition comprising one or more antiviral agents and the synthetic membrane-receiver complex described herein. 
     In some embodiments, the receiver may sequester the target virus and distribute it in the circulatory system without directly modifying the target. In certain embodiments, the synthetic membrane-receiver complex may subject the associated target virus to degradation by the reticulo-endothelial system. 
     Conditions Associated with Toxins and Poisons 
     In some embodiments, the synthetic membrane-receiver polypeptide complexes described herein may be used to treat or prevent toxic conditions or poisoning caused by toxins or poisons. 
     Sepsis and septic shock, which represent major causes of mortality in modern intensive care medicine, are caused by an inadequate inflammatory and immunological host response to bacterial infection. Evidence suggests that the systemic spread of microbial toxins, rather than bacteremia itself, is the crucial event in the pathogenesis. The endothelium is a main target of bacterial toxins. The resulting endothelial dysfunction is believed to contribute to the underlying pathomechanisms and the collapse of homeostasis of organ function. 
     Bacterial toxins targeting endothelial cells severely alter the behavior of extravascular cells and circulating leukocytes via excessive formation of vasoactive mediators and overexpression of adhesion molecules (Grandel, Crit Rev Immunol, 2003). 
     Pore-forming toxins (PFTs) are one of the most common protein toxins found in nature. These toxins disrupt cells by forming pores in cellular membranes and altering their permeability. In bacterial infections, attack by PFTs is a major virulence mechanism. It has been demonstrated that the inhibition of the pore-forming a-toxin can reduce the severity of  Staphylococcus aureus  infections, and similar PFT-targeted strategies have shown therapeutic potential against other pathogens, including  Escherichia coli, Listeria monocytogenes, Bacillus anthracis  and  Streptococcus pneumoniae . As well as their role in bacterial pathogenesis, PFTs are commonly used in venomous attacks by animals such as sea anemones, scorpions and snakes. Over 80 families of PFTs have been identified, displaying diverse molecular structures and distinctive epitopic targets (Zhang, Nature Nano, 2013). 
     A number of biomolecules show interactions with endotoxins, such as lipopolysaccharide-binding protein (LBP), bactericidal/permeability-increasing protein (BPI), amyloid P component, cationic protein, or the enzyme employed in the biological endotoxin assay (anti-LPS) factor from  Limulus  amebocyte lysate (LAL). These proteins are directly involved in the reaction of many different species upon administration of endotoxin. 
     In one embodiment, functional erythroid cells comprise a receiver that comprises an amino acid sequence derived from lipopolysaccharide binding protein (LBP). A population of functional erythroid cells comprising a receiver that comprises an amino acid sequence derived from lipopolysaccharide binding protein (LBP) may be administered to a subject in need thereof in an amount effective to remove immunogenic lipopolysaccharide that may be in circulation as a result of a microbial infection. 
     Further provided are methods of inducing toxin clearance. The methods include administering to a subject in need thereof a population of functional erythroid cells comprising a receiver that is capable of interacting with a toxin, such as e.g., an antibody, scFv or nanobody receiver, in an amount effective to clear toxins from circulation. The compositions comprising functional erythroid cells that comprise the toxin-specific receiver may be administered to subjects that exhibit levels of toxic metabolites or infectious agents such as anthrax, botulinum, cytokines, sarin, hemolysin, venoms, and including, but not limited to, those in table 5. 
     In one embodiment, functional erythroid cells comprise a receiver that comprises an amino acid sequence derived from the endotoxin receptor CD14. A population of functional erythroid cells comprising a receiver that comprises an amino acid sequence derived from the endotoxin receptor CD14 may be administered to a subject in need thereof in an amount effective to bind to a target endotoxin in circulation. Such methods may be employed to sequester the toxin and reduce the amount of tissue damage that would otherwise occur within the vasculature and dissipating its pathogenic effects in a less acute manner. 
     In one embodiment, the receiver interacts with cell-free circulating DNA. In one embodiment, the functional erythroid cell expresses exogenous gene encoding a receiver comprising an amino acid sequence derived from a DNA-interacting polypeptide, such as, e.g., DNase, a transcription factor DNA binding domain or histone fragments. The DNase, DNA binding domain or histone fragment may be expressed as a fusion protein. In other embodiments, the DNAse, DNA binding domain, histone fragment or another receiver with affinity to circulating DNA is loaded into or onto the erythroid cell. In one embodiment, the receiver is a DNase, DNA binding domain or histone fragment that is localized extracellularly. 
     A hallmark of apoptosis is DNA degradation, in which chromosomal DNA is first cleaved into large fragments (50-300 kb) and subsequently into multiples of nucleosomal units (180-200 bp) (Nagata, Cell Death Differ, 2003). The contents of apoptotic cells are ingested by phagocytes or neighboring cells and the DNA is completely digested by DNase II in lysosomes (Nagata, Cell Death Differ, 2003). Thus, DNA fragments released by apoptosis may be removed before appearing in the circulation. In instances where the engulfment of apoptotic bodies is impaired or cell death is increased an inflammatory response may occur. For example, autoimmunity occurs frequently in cancer and other conditions involving increased circulating DNA (Viorritto, Clin Immunol, 2007). 
     Extracellular DNA, or circulating cell free DNA (cf-DNA), is present in blood plasma. These cf-DNAs, at least part of them, are believed to originate from cancer cells and contain a number of cancer specific entities, including oncogenes, tumor suppressor genes, aberrant microsatellites, aberrant DNA methylation genes, and rearranged chromosomal DNA. The term, ‘genometastasis’ has been proposed to describe the phenomena of an apoptotic body containing DNA that horizontally enters and transforms healthy cells (Garcia-Olmo, Expert Opinion on Bio Therapy, 2012). 
     In certain embodiments, functional erythroid cells comprising a receiver specific for circulating DNA are administered to a subject in need thereof in an amount effective to treat a DNA-driven pathogenesis, such as systemic lupus erythematosus and cancers suspected of genometastasis. In some embodiments, functional erythroid cells comprise an extracellular receiver comprising DNAse fused to the N terminal of glycophorin A such that it is capable of degrading circulating DNA within the vasculature. 
     In specific embodiments, methods are provided for reducing the circulatory concentration of a target toxin or poison in a subject (e.g., a human) suffering from or at risk of developing a toxic condition or poisoning. The methods include administering a pharmaceutical composition comprising a synthetic membrane-receiver polypeptide complex described herein. The pharmaceutical composition is administered in an amount effective to substantially reduce the circulatory concentration of the target toxin or poison. In certain embodiments, the administration is carried out intravenously. 
     In certain embodiments, synthetic membrane-receiver polypeptide complexes are administered that comprise a receiver that specifically binds, sequesters, and/or degrades a toxin or poison, such as a pathogenic toxin, a venom, a prion protein, a cytokine, a metal (e.g., heavy metal), or an alcohol (e.g., methanol) that is present in the circulatory system of the subject. Conditions associated with toxins or poisons include, but are not limited to bacterial toxin-induced shock, spider venom-induced shock, prion diseases, cytokine storm, iron poisoning, copper poisoning, Wilson disease, heavy metal poisoning, methanol poisoning and those listed in table 6 and table 8. 
     Further provided are methods of inducing toxin clearance. In specific embodiments, the methods include administering to a subject in need thereof a pharmaceutical composition of erythrocyte cells comprising a receiver provided herein in an amount sufficient to induce toxin clearance in the subject. The compositions may be administered to subjects that exhibit levels of toxic metabolites or infectious agents such as anthrax, botulinum, cytokines, sarin, hemolysin, venoms, and those included, but not limited to table 5. 
     In one embodiment the disease or condition is alpha hemolysin poisoning, the receiver is an antibody-like binder to alpha hemolysin or fragment thereof, and the target is alpha hemolysin. 
     In one embodiment the disease or condition is antrax toxin poisoning, the receiver is an antibody-like binder to anthrax toxin or fragment thereof, and the target is anthrax toxin. 
     In one embodiment the disease or condition is bacterial toxin-induced shock, the receiver is an antibody-like binder to bacterial toxin or fragment thereof, and the target is bacterial toxin. 
     In one embodiment the disease or condition is botulinum toxin poisoning, the receiver is an antibody-like binder to botulinum toxin or fragment thereof, and the target is botulinum toxin. 
     In one embodiment the disease or condition is prion disease caused by PRP, the receiver is an antibody-like binder to prion protein PRP or fragment thereof, and the target is prion protein PRP. 
     In one embodiment the disease or condition is prion disease caused by PRPc, the receiver is an antibody-like binder to prion protein PRPc or fragment thereof, and the target is prion protein PRPc. 
     In one embodiment the disease or condition is prion disease caused by PRPsc, the receiver is an antibody-like binder to prion protein PRPsc or fragment thereof, and the target is prion protein PRPsc. 
     In one embodiment the disease or condition is prion disease caused by PRPres, the receiver is an antibody-like binder to prion protein PRPres or fragment thereof, and the target is prion protein PRPres. 
     In one embodiment the disease or condition is sepsis or cytokine storm, the receiver is an antibody-like binder to cytokines or duffy antigen receptor of chemokines (DARC) or fragment thereof, and the target is cytokines. 
     Wilson&#39;s disease is caused by a failure of copper metabolism and a buildup of copper in liver, brain, and other organs. Copper chelators are used clinically, for example D-penicillamine, but they suffer from short half-lives that reduce their therapeutic efficacy. In one embodiment, the receiver on the surface of a synthetic membrane-receiver complex is D-penicillamine Administration of the synthetic membrane-receiver complex will allow D-penicillamine to remain in circulation for substantially longer than free D-penicillamine, thus capturing copper for a longer period of time and providing a clinical benefit in Wilson&#39;s disease. 
     In one embodiment the disease or condition is spider venom poisoning, the receiver is an antibody-like binder to spider venom or fragment thereof, and the target is spider venom. 
     1. Toxins 
     In some embodiment, subjects may be identified as having received or would benefit from receiving treatment for botulinum toxin (BTX) poisoning. Subjects suffering from or at risk of developing BTX poisoning may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising an antibody domain or antibody-like domain that binds to BTX of any of the types A-H, or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex. The suitable receiver is capable of binding to BTX and preventing BTX from carrying out its function. 
     BTX is produced by  Clostridium botulinum  and is a potent neurotoxin with an estimated human lethal dose of 1.3-2.1 ng/kg intravenously (Arnon et al. 2001 J Am Med Assoc 285(8):1059). BTX is a protease that attacks one of the fusion proteins (SNAP-25, syntaxin or synaptobrevin) at a neuromuscular junction, preventing vesicles from anchoring to the membrane to release acetylcholine. By inhibiting acetylcholine release, the toxin interferes with nerve impulses and causes flaccid (sagging) paralysis of muscles. 
     2. Prions—Creutzfeldt-Jakob Disease 
     In some embodiment, subjects may be identified as having received or would benefit from receiving treatment for Creutzfeldt-Jakob Disease (CJD) caused by prion protein in the scrapie form (PrPsc). Subjects suffering from or at risk of developing CJD may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising an antibody domain or antibody-like domain that binds to PrPsc or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex. The suitable receiver is capable of binding to PrPsc and preventing PrPsc from carrying out its function. 
     PrPsc is a misfolded form of PrP that call induce normal PrP to misfold in an autocatalytic fashion. PrPsc is protease resistant and forms insoluble aggregates and fibrils that damage cells. In CJD, the PrPsc aggregates and fibrils lead to rapid neurodegeneration, causing the brain tissue to develop holes and take on a sponge-like texture. 
     3. Cytokines 
     In some embodiment, subjects may be identified as having received or would benefit from receiving treatment for sepsis. Subjects suffering from or at risk of developing sepsis poisoning may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises one or more receivers comprising an antibody domain, antibody-like domain, or cytokine receptor domain that bind to one or more of the cytokines tumor necrosis factor alpha (TNFa), interferon gamma (IFNg), or interleukin-2 (IL-2) or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex. The suitable receiver is capable of binding to the cytokine and preventing the cytokine from carrying out its function, e.g., by preventing the cytokine from biding to its native receptor. 
     Cytokines like TNFa, IFNg, and IL-2 are produced by immune cells in response to infection and are powerful inflammatory stimuli for other immune cells. In sepsis, a serious bacterial infection induces whole-body inflammation driven by a storm of cytokines, which triggers multi-organ failure, acute respiratory distress, heart failure, encephalopathy, and edema. 
     Diseases and Conditions Associated with the Accumulation of Lipids or Cholesterols 
     In some embodiments, the synthetic membrane-receiver polypeptide complexes described herein may be used to treat or prevent diseases and conditions associated with the accumulation of lipids or cholesterols. 
     In one embodiment, the receiver interacts with one or more lipids. In one embodiment, the functional erythroid cell expresses a exogenous gene encoding an amino acid sequence derived from a lipase. The lipase may be expressed as a full-length protein or a fragment thereof. The lipase may be expressed as a fusion protein. In other embodiments, the lipase protein receiver or another receiver with affinity to lipids is loaded into or onto the erythroid cell. The lipase protein receiver or the other receiver with affinity to lipids may be localized intracellularly or extracellularly. In one embodiment, the receiver comprises an amino acid sequence derived from lipoprotein lipase. 
     Hyperlipidemia or hyperlipoproteinemia is an excess of lipids, largely cholesterol and triglycerides, in the blood. Lipids travel in the blood attached to proteins to remain dissolved while in circulation. Hyperlipidemia, in general, can be divided into two subcategories; hypercholesterolemia, in which there is a high level of cholesterol and hypertriglyceridemia, in which there is a high level of triglycerides, the most common form of fat. Excess LDL cholesterol contributes to the blockage of arteries, which eventually leads to heart attack. Population studies have shown that the higher the level of LDL cholesterol, the greater the risk of heart disease. 
     Hyperlipidemia usually has no noticeable symptoms and tends to be discovered during routine examination or evaluation for atherosclerotic cardiovascular disease. However, deposits of cholesterol (known as xanthomas) may form under the skin (especially around the eyes or along the Achilles tendon) in individuals with familial forms of the disorder or in those with very high levels of cholesterol in the blood. Individuals with hypertriglyceridemia may develop numerous pimple-like lesions across their body. Extremely high levels of triglycerides may also result in pancreatitis, a severe inflammation of the pancreas that may be life-threatening. 
     In certain embodiments, functional erythroid cells comprise a receiver that is capable of interacting with a lipid, or has affinity to a target lipid or target lipid-associated molecule listed in table 5. In certain embodiments, a population of functional erythroid cells comprising a receiver that is capable of interacting with a lipid or comprising a receiver that comprises an amino acid sequence derived from lipoprotein lipase is administered to a subject in need thereof in an amount effective to treat or prevent hyperlipidemia. 
     In certain embodiments, a population of functional erythroid cells comprising a receiver that is capable of interacting with a lipid or comprising a receiver that comprises an amino acid sequence derived from lipoprotein lipase is administered to a subject in need thereof in an amount effective to remove chylomicrons, which are lipoprotein particles consisting of lipids, protein, and cholesterol, from the blood circulation. In some embodiments, the receiver is lipoprotein lipase and the receiver is localized on the surface of the erythroid cell. In certain embodiments, a population of functional erythroid cells comprising a receiver that comprises an amino acid sequence derived from lipoprotein lipase is administered to a subject in need thereof in an amount effective to treat, alleviate or prevent lipoprotein lipase deficiency. Familial lipoprotein lipase deficiency is a group of rare genetic disorders in which a person lacks the ability to break down lipids, which causes a large amount of fat to build up in the blood. 
     In specific embodiments, methods are provided for reducing the circulatory concentration of a target lipid or cholesterol in a subject (e.g., a human) suffering from or at risk of developing a disease or condition associated with the accumulation of lipids or cholesterols. The methods include administering a pharmaceutical composition comprising a synthetic membrane-receiver polypeptide complex described herein. The pharmaceutical composition is administered in an amount effective to substantially reduce the circulatory concentration of the target lipid or cholesterol. In certain embodiments, the administration is carried out intravenously. 
     In certain embodiments, synthetic membrane-receiver polypeptide complexes are administered that comprise a receiver that specifically binds, sequesters, and/or degrades a target lipid or cholesterol, or a complex or aggregate that comprises a lipid or cholesterol, that is present in the circulatory system of the subject. Reduction in the amount or concentration of circulating lipids or cholesterols and associated complexes therewith may reduce or alleviate cardiovascular and other circulatory problems. Diseases or conditions associated with the accumulation of lipids or cholesterols include, but are not limited to lipoprotein lipase deficiency, hypercholesterolemia, coronary artery disease and those listed in table 6 and table 8. 
     In one embodiment the disease or condition is hypercholesterolemia, the receiver is an antibody-like binder to low-density lipoprotein (LDL), LDL receptor or fragment thereof, and the target is LDL. 
     In one embodiment the disease or condition is hypercholesterolemia, the receiver is an antibody-like binder to high-density lipoprotein (HDL) or HDL receptor or fragment thereof, and the target is HDL. 
     In one embodiment the disease or condition is lipoprotein lipase deficiency, the receiver is lipoprotein lipase or fragment thereof, and the target is chilomicrons and very low density lipoproteins (VLDL). 
     Lipoprotein Lipase Deficiency (Glybera) 
     In some embodiment, subjects may be identified as having received or would benefit from receiving treatment for lipoprotein lipase deficiency. Subjects suffering from or at risk of developing lipoprotein lipase deficiency may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising the enzyme lipoprotein lipase or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex. The suitable receiver is capable of hydrolyzing triglycerides in lipoproteins, such as those found in chylomicrons and very low-density lipoproteins (VLDL), into two free fatty acids and one monoacylglycerol molecule. 
     Lipoprotein lipase deficiency is a rare disorder in which afflicted individuals lack the ability to produce lipoprotein lipase enzymes necessary for effective breakdown of fatty acids. The disorder usually presents in childhood and is characterized by very severe hypertriglyceridemia with episodes of abdominal pain, recurrent acute pancreatitis, eruptive cutaneous xanthomata, and hepatosplenomegaly. Clearance of chylomicrons from the plasma is impaired, causing triglycerides to accumulate in plasma and the plasma to have a milky appearance. Symptoms usually resolve with restriction of total dietary fat to ≤20 grams/day 
     Diseases and Conditions Associated with Infected, Aberrant or Oncogenic Cells 
     In some embodiments, the synthetic membrane-receiver polypeptide complexes described herein may be used to treat or prevent diseases and conditions associated with infected, aberrant or oncogenic cells, such as, e.g., cancer. 
     In one embodiment, the receiver interacts with a cancer stem cell (CSC) or another cancer-associated circulatory cell. In one embodiment, the functional erythroid cell expresses a exogenous gene encoding an antibody, scFv or nanobody specific for a CSC antigen. The antibody, scFv or nanobody may be expressed as a fusion protein. In other embodiments, the antibody, scFv or nanobody receiver or another receiver with affinity to circulating cancer cells is loaded into or onto the erythroid cell. In one embodiment, the receiver is an antibody, scFv or nanobody that is localized extracellularly. In certain embodiments, the antibody, scFv or nanobody receiver is specific for a CSC antigen selected from CD44, CD47, and MET. 
     Cancer stem cells (CSCs), which comprise a small fraction of cancer cells, are believed to constitute the origin of most human tumors. One of the key steps in the metastatic cascade is the migration of tumor cells away from the primary tumor, and CSCs are likely associated with this migration. Most adult tissues maintain some aspect of migratory capacity through the ability to generate an epithelial to mesenchymal transition (EMT)-like process during wound healing, tissue regeneration and organ fibrosis. It has been hypothesized that CSCs may also activate their migration through the process of EMT. 
     A number of studies have linked circulating tumor cells (CTCs) to tumor progression in a variety of solid tumors, and CTC enumeration has begun to be utilized as a prognostic tool in patients with metastatic breast (Cristofanilli et al., 2004), colon (Cohen et al., 2008) and prostate cancer (Danila et al., 2007). Potentially, a fraction of CTCs have CSC activity, and it is hypothesized that CSCs in a primary tumor which enter the circulation become circulating CSCs and remain so until they lodge or home to a target organ. CTCs isolated from patients with melanomas have been found to generate metastases in xenotransplantation models (Ma et al., 2010, Shiozawa, Pharm and Thera, 2013). 
     The vasculature is a powerful conduit for the proliferation of various circulating tumor cells, metastases, and cancer stem cells. In certain embodiments, functional erythroid cells comprising a receiver specific for circulating cancer cells are administered to a subject in need thereof in an amount effective to treat or prevent metastases. In certain embodiments, populations of functional erythroid cells comprising a receiver specific for circulating cancer cells are administered to a subject in need thereof in an amount effective to interact with CSCs or CTCs to clear them from circulation, e.g., by facilitating degradation in the liver. In some embodiments, functional erythroid cells comprise an antibody, scFv, or nanobody receiver specific for CD44, CD47, or MET (three characteristic surface antigens of CTC). Suitable cancer cells that may be cleared by the erythroid cells described herein include, but are not limited to, cells associated with the cancers listed in table 5 and table 8. 
     In specific embodiments, methods are provided for reducing the circulatory concentration of a target cell in a subject (e.g., a human) suffering from or at risk of developing a disease or condition associated with an infected, aberrant or oncogenic cell. The methods include administering a pharmaceutical composition comprising a synthetic membrane-receiver polypeptide complex described herein. The pharmaceutical composition is administered in an amount effective to substantially reduce the circulatory concentration of the target cell. In certain embodiments, the administration is carried out intravenously. 
     In certain embodiments, synthetic membrane-receiver polypeptide complexes are administered that comprise a receiver that specifically binds, sequesters, and/or degrades a target cell, such as an infected, aberrant or oncogenic cell that is present in the circulatory system of the subject. Reduction in the amount or concentration of circulating target cells may reduce or alleviate conditions associated with the infected, aberrant or oncogenic cell, such as, e.g., an infection or cancer. Diseases or conditions associated with infected, aberrant or oncogenic cells include, but are not limited to cancer and those listed in table 6 and table 8. 
     In one embodiment the disease or condition is cancer, the receiver is an antibody-like binder to CD44 or fragment thereof, and the target is a circulating tumor cell. 
     In one embodiment the disease or condition is cancer, the receiver is an antibody-like binder to EpCam or fragment thereof, and the target is a circulating tumor cell. 
     In one embodiment the disease or condition is cancer, the receiver is an antibody-like binder to Her2 or fragment thereof, and the target is a circulating tumor cell. 
     In one embodiment the disease or condition is cancer, the receiver is an antibody-like binder to EGFR or fragment thereof, and the target is a circulating tumor cell. 
     In one embodiment the disease or condition is cancer (B cell), the receiver is an antibody-like binder to CD20 or fragment thereof, and the target is a cancerous B cell. 
     In one embodiment the disease or condition is cancer (B cell), the receiver is an antibody-like hinder to CD19 or fragment thereof, and the target is a cancerous B cell. 
     Circulating Cancer Cell 
     In some embodiment, subjects may be identified as having received or would benefit from receiving treatment for cancer. Subjects suffering from or at risk of developing cancer may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising an antibody domain or antibody-like domain that binds to a circulating cancer cell, e.g., a proliferative B cell, via a cancer cell specific receptor, e.g., CD19, or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex. The suitable receiver is capable of binding to CD19 on the circulating cancer cell and promoting the clearance of the CD19-expressing cancer cell. 
     CD19 is a common receptor to B cells, and is a validated marker for B cell cancers including B cell leukemias and lymphomas (Scheuermann and Racila, (1995) Leukemia and Lymphoma 18 (5): 385-397. It is increasingly understood to play an additional role in the proliferation of B cells in cancer by stabilizing the Myc oncoprotein (Chung et al. 2012, J Clin Invest 122(6):2257). In B cell cancers, proliferative B cells overwhelm lymph nodes and bone marrow. Strategies to target and clear these B cells, including antibody therapy (Rituximab), are accepted as part of the standard of care. 
     Tumor metastasis is the main driver of cancer mortality and therapies targeting metastasis are limited in number, mechanism of action and efficacy. Hematogenous tumor cell spreading (via bloodstream) is a common route for many carcinomas and is a highly complex process involving primary site detachment, migration, transport into the bloodstream, tumor cell adhesion in the vasculature and proliferation at the metastatic site. 
     Diseases and Conditions Associated with a Metabolic Defect 
     In some embodiments, the synthetic membrane-receiver polypeptide complexes described herein may be used to treat or prevent diseases and conditions associated with a metabolic defect. A schematic example of a synthetic membrane-receiver polypeptide complex is shown in  FIG. 13A . 
     As described herein, many small molecule metabolites can diffuse across the membrane of, e.g., erythroid cells comprising a suitable receiver, or are actively transported by defined transmembrane channels (see, e.g., Tunnicliff, Comp. Biochem. Physiol. 1994). Some metabolites, however, may require additional assistance to reach the intracellularly localized receiver enzyme, thus the synthetic membrane-receiver complex may optionally comprise a transporter. 
     In one embodiment, the surface exposed receiver polypepdide may shuttle the substrate across the cell membrane into the synthetic membrane-receiver complex, e.g., an erythroid cell comprising a receiver. The functional erythroid cell comprising a receiver may contain multiple receiver polypeptides, including, but not limited to, the receiver polypeptides listed in Table 7. The receiver polypeptides may increase the cell&#39;s capabilities to transport metabolites or other substrates across the membrane. For example, a Glut1 transporter may be contained in the functional erythroid cell&#39;s membrane in combination with an intracellularly expressed receiver glucokinase, such that the erythroid cell internalizes and phosphorylates an amount of glucose greater than that of a non-modified erythroid cell. Erythroid cells comprising a receiver glucokinase may be used to reduce blood glucose levels. Diabetes mellitus type II is associated with hyperglycemia as a result of insulin resistance and relative lack of insulin. The hyperglycemia may be alleviated by erythroid cells comprising a receiver glucokinase that capture glucose through surface-localized, receiver Glut1 and phosphorylation by an intracellularly localized, receiver glucokinase. Modified glucose may be unable to exit the cell. The synthetic membrane-receiver complex acts as a “buffer” to respond to hyperglycemic conditions. 
     Optionally, a second receiver polypeptide may be present in the functional erythroid cell that exhibits increase transport capabilities. The second receiver polypeptide may be localized intracellularly. The second intracellularly localized receiver polypeptide can enzymatically modify, convert, change or otherwise alter the target substrate that was shuttled into the cell by the first receiver polypeptide localized on the cell surface. 
     In specific embodiments, methods are provided for modulating the circulatory concentration of a target metabolite in a subject (e.g., a human) suffering from or at risk of developing a disease or condition associated with a metabolic defect. The methods include administering a pharmaceutical composition comprising a synthetic membrane-receiver polypeptide complex described herein. The pharmaceutical composition is administered in an amount effective to substantially modulate the circulatory concentration of the target metabolite. In some embodiments, the target metabolite is present or present in elevated levels in circulation and the amount or concentration of the target metabolite is reduced. For example if the level or concentration of a metabolite is toxic, the toxic target metabolite may be degraded or the toxic target metabolite may be converted into another non-toxic product (e.g., by catalytic action of the receiver). In some embodiments, a non-target metabolite is absent or present in depressed levels in circulation and a target metabolite is converted to the non-target metabolite so that its level or concentration is increased. In such embodiments, the absence of depressed levels of the non-target metabolite is associated with the metabolic disease or disorder and conversion of the target metabolite to the non-target metabolite can at least partially restore or replenish the level or concentration of the non-target metabolite, thereby treating or preventing the metabolic disease. In certain embodiments, the administration is carried out intravenously. Diseases or conditions associated with a metabolic defect include, but are not limited to mitochondrial neurogastrointestinal encephalomyopathy (MNGIE), adenosine deaminase (ADA) deficiency, purine nucleoside phosphorylase (PNP) deficiency, phenylketonuria, alkaptonuria, homocystinuria, primary hyperoxaluria and those listed in table 6 and table 8. 
     In specific embodiments, methods of treating a metabolic disease include administering to a subject in need thereof a pharmaceutical composition of erythrocyte cells comprising a receiver provided herein in an amount sufficient to treat the metabolic disease. The compositions may be administered to subjects that exhibit disorders of carbohydrate metabolism, amino acid metabolism, organic acid metabolism, mitochondrial metabolism, fatty acid metabolism, purine-pyrimidine metabolism, steroid metabolism, peroxisomal function, lysosomal storage, or urea cycle. Of these disorders, specific indications include ADA-SCID, primary hyperoxaluria, and phenylketonuria, as well as, but not limited to, the conditions listed in table 6 and table 8. 
     In one embodiment the disease or condition is 3-methylcrotonyl-CoA carboxylase deficiency, the receiver is 3-methylcrotonyl-CoA carboxylase or fragment thereof, and the target is 3-hydroxyvalerylcarnitine, 3-methylcrotonylglycine (3-MCG) and 3-hydroxyisovaleric acid (3-HIVA). 
     In one embodiment the disease or condition is acute intermittent porphyria, the receiver is porphobilinogen deaminase or fragment thereof, and the target is porphobilinogen. 
     In one embodiment the disease or condition is adenine phosphoribosyltransferase deficiency, the receiver is adenine phosphoribosyltransferase or fragment thereof, and the target is insoluble purine 2,8-dihydroxyadenine. 
     In one embodiment the disease or condition is adenosine deaminase deficiency, the receiver is adenosine deaminase or fragment thereof, and the target is adenosine. 
     In one embodiment the disease or condition is alkaptonuria, the receiver is homogentisate oxidase or fragment thereof, and the target is homogentisate. 
     In one embodiment the disease or condition is argininemia, the receiver is ammonia monooxygenase or fragment thereof, and the target is ammonia. 
     In one embodiment the disease or condition is argininosuccinate aciduria, the receiver is ammonia monooxygenase or fragment thereof, and the target is ammonia. 
     In one embodiment the disease or condition is citrullinemia type I, the receiver is ammonia monooxygenase or fragment thereof, and the target is ammonia. 
     In one embodiment the disease or condition is citrullinemia type II, the receiver is ammonia monooxygenase or fragment thereof, and the target is ammonia. 
     In one embodiment the disease or condition is glutaric acidemia type I, the receiver is lysine oxidase or fragment thereof, and the target is 3-hydroxyglutaric and glutaric acid (C5-DC) and lysine. 
     In one embodiment the disease or condition is gout with hyperuricemia, the receiver is uricase or fragment thereof, and the target is uric acid (urate crystals). 
     In one embodiment the disease or condition is hemolytic anemia due to pyrimidine 5′ nucleotidase deficiency, the receiver is pyrimidine 5′ nucleotidase or fragment thereof, and the target is pyrimidines. 
     In one embodiment the disease or condition is homocystinuria, the receiver is Cystathionine B synthase or fragment thereof, and the target is homocysteine. 
     In one embodiment the disease or condition is hyperammonemia/ornithinemia/citrullinemia (ornithine transporter defect), the receiver is ammonia monooxygenase or fragment thereof, and the target is ammonia. 
     In one embodiment the disease or condition is isovaleric acidemia, the receiver is leucine metabolizing enzyme or fragment thereof, and the target is leucine. 
     In one embodiment the disease or condition is Lesch-Nyhan syndrome, the receiver is uricase or fragment thereof, and the target is uric acid. 
     In one embodiment the disease or condition is maple syrup urine disease, the receiver is a leucine metabolizing enzyme or fragment thereof, and the target is leucine. 
     In one embodiment the disease or condition is methylmalonic acidemia (vitamin b12 non-responsive), the receiver is methylmalonyl-CoA mutase or fragment thereof, and the target is methylmalonate. 
     In one embodiment the disease or condition is mitochondrial neurogastrointestinal encephalomyopathy (MNGIE), the receiver is thymidine phosphorylase or fragment thereof, and the target is thymidine. 
     In one embodiment the disease or condition is phenylketonuria, the receiver is phenylalanine hydroxylase, phenylalanine ammonia lyase or fragment thereof, and the target is phenylalanine. 
     In one embodiment the disease or condition is primary hyperoxaluria, the receiver is oxalate oxidase or fragment thereof, and the target is oxalate. 
     In one embodiment the disease or condition is propionic acidemia, the receiver is a propionate convertase or fragment thereof, and the target is proprionyl coA. 
     In one embodiment the disease or condition is purine nucleoside phosphorylase deficiency, the receiver is purine nucleoside phosphorylase or fragment thereof, and the target is Inosine and/or dGTP. 
     In one embodiment the disease or condition is transferase deficient galactosemia (galactosemia type 1), the receiver is galactose dehydrogenase or fragment thereof, and the target is galactose-1-phosphate. 
     In one embodiment the disease or condition is tyrosinemia type 1, the receiver is tyrosine phenol-lyase or fragment thereof, and the target is tyrosine. 
     1. Adenosine Deaminase (ADA) Deficiency 
     In some embodiments, subjects may be identified as having received or would benefit from receiving treatment for adenosine deaminase (ADA) deficiency. Subjects suffering from or at risk of developing ADA deficiency may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising adenosine deaminase (ADA) or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface or on the unexposed side of the synthetic membrane-receiver polypeptide complex and may be administered to convert deoxy-adenosine to deoxy-inosine, thereby preventing the build-up of toxic deoxy-adenosine levels. 
     In certain embodiments, compositions comprising a plurality of functional erythroid cells comprising an adenosine deaminase (ADA) receiver are provided. Such compositions may be used to treat subjects that exhibit ADA-severe combined immunodeficiency (SCID). 
     Subjects that exhibit an ADA-deficiency are experiencing a build-up of deoxy-adenosine in the body&#39;s tissues. The high deoxy-adenosine levels are toxic to immature leukocytes. As a consequence, the subject&#39;s adaptive immune response is impaired, which makes them highly susceptible to infection. ADA is an endogenous enzyme produced by a wide variety of cells, including erythrocytes. ADA is responsible for converting deoxy-adenosine to deoxy-inosine, thereby preventing the build-up of toxic deoxy-adenosine levels. Available enzyme replacement therapies source ADA from bovine intestine. The foreign-sourced ADA is subject to immunogenic reactions and inhibitor development. Inhibitor development may occur when a subject&#39;s immune system develops the ability to clear and/or alter a therapeutic molecule such that its therapeutic effect is decreased. In addition, the emergence of new variant Creutzfeldt-Jakob disease has raised concerns about sourcing ADA from bovine intestine (Booth 2009, Biologics: Targets and Therapy). 
     In certain embodiments, provided herein are compositions comprising a plurality of functional erythroid cells comprising an adenosine deaminase (ADA) receiver which may be administered to ADA-SCID subjects to elevate the level of ADA over that of the endogenous levels of existing wild type cells in the ADA-SCID subject. Most ADA-SCID subjects severely lack a functioning deoxy-adenosine metabolism. The erythroid cells may contain exogenous ADA within their intracellular space. The intracellularly localized exogenous ADA receiver polypeptide may then convert deoxy-adenosine to deoxy-inosine, thereby lowering the levels of deoxy-adenosine. Deoxy-adenosine crosses the cell membrane, is converted to deoxy-inosine, and diffuses back into circulation. This may be sufficient to preserve immature leukocyte populations, thereby treating the disease. In some embodiments, the adenosine deaminase receiver is expressed as a fusion to the C terminus of hemoglobin beta such that the ADA is retained in the functional erythroid cell during enucleation. Alternatively, the ADA gene is fused to the part of the gene encoding the C terminus of glycophorin A such that upon expression it is tethered to the intracellular portion of the transmembrane antigen. 
     2. Phenylketonuria (PKU) 
     In some embodiments, subjects may be identified as having received or would benefit from receiving treatment for phenylketonuria (PKU). Subjects suffering from or at risk of developing PKU may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising phenylalanine ammonia lyase (PAL) or a derivative or functional fragment thereof. 
     In another embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising phenylalanine hydroxylase (PAH) or a derivative or functional fragment thereof. 
     A suitable receiver may be exhibited on the surface or on the unexposed side of the synthetic membrane-receiver polypeptide complex and may be administered to convert phenylalanine to tyrosine, thereby preventing the build-up of toxic phenylalanine levels to treat or prevent PKU. 
     In specific embodiments, compositions comprising a plurality of functional erythroid cells comprising a phenylalanine ammonia lyase (PAL) receiver are provided. Such compositions may be used to treat subjects that exhibit or are diagnosed with phenylketonuria (PKU). 
     Subjects diagnosed with PKU are deficient in phenylalanine ammonia hydroxylase (PAH) activity due to an enzyme mutation or production deficiency. PAH, along with its cofactor tetrahydrobiopterin, is responsible for converting phenylalanine to tyrosine. PAH deficiency leads to phenylalanine accumulation and is associated with several neurological disorders. 
     PAL is an enzyme isolated from plants, yeast, and fungi  chrysanthemi . PAL is a large, 270 kDa enzyme that can elicit a strong immunogenic reaction. It is also quickly cleared from the body, therefore requiring large, frequent infusions. Even in its pegylated form, PAL only remains in circulation for approximately three days. The short half-life makes PAL treatment difficult for patients to adhere to (Gamez, Molecular Therapy 2005). 
     In certain embodiments, provided herein are compositions comprising a plurality of functional erythroid cells comprising a phenylalanine ammonia lyase (PAL) receiver, which may be administered to phenylketonuria (PKU) subjects to treat phenylalanine accumulation. The functional erythroid cells may contain exogenous PAL within their intracellular space. The intracellularly localized exogenous PAL polypeptide may then convert phenylalanine to trans-cinnamic acid, a benign metabolite, thereby lowering the levels of phenylalanine. Phenylalanine crosses the cell membrane, is converted to trans-cinnamic acid, and diffuses back into circulation. This may be sufficient to reduce phenylalanine concentrations in the blood. 
     In specific embodiments, compositions comprising a plurality of functional erythroid cells comprising a phenylalanine hydroxylase (PAH) receiver are provided. Such compositions may be used to treat subjects that exhibit or are diagnosed with phenylketonuria (PKU). PAH is an enzyme that can be isolated from bacteria or mammals. PAH from  Chromobacterium violaceum  is a monomeric ˜30 kDa protein (Yew et al. 2013 Mol Gen Metab 109:339). 
     In certain embodiments, provided herein are compositions comprising a plurality of functional erythroid cells comprising a phenylalanine hydroxylase (PAH) receiver, which may be administered to phenylketonuria (PKU) subjects to treat phenylalanine accumulation. The functional erythroid cells may contain exogenous PAH within their intracellular space. The intracellularly localized exogenous PAH polypeptide may then convert phenylalanine to tyrosine, thereby lowering the levels of phenylalanine. Phenylalanine crosses the cell membrane, is converted to tyrosine, which diffuses back into circulation. This may be sufficient to reduce phenylalanine concentrations in the blood. 
     3. MNGIE 
     In some embodiment, subjects may be identified as having received or would benefit from receiving treatment for Mitochondrial Neurogastrointestinal Encephalopathy (MNGIE). Subjects suffering from or at risk of developing MNGIE may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising the enzyme thymidine phosphorylase (TP) or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex. A suitable receiver may be contained in the interior of the synthetic membrane-receiver polypeptide complex. The suitable receiver is capable of catalyzing the phosphorylation of thymidine or deoxyuridine to thymine or uracil. 
     In MNGIE, aberrant thymidine metabolism leads to impaired replication or maintenance of mtDNA, causing mtDNA depletion, deletion, or both (Nishino et al. 1999 Science 283:689). The disease is characterized by progressive gastrointestinal dysmotility and cachexia manifesting as early satiety, nausea, dysphagia, gastroesophageal reflux, postprandial emesis, episodic abdominal pain and/or distention, and diarrhea; ptosis/ophthalmoplegia or ophthalmoparesis; hearing loss; and demyelinating peripheral neuropathy manifesting as paresthesias (tingling, numbness, and pain) and symmetric and distal weakness more prominently affecting the lower extremities. There is no treatment for MNGIE. Management is supportive and includes attention to swallowing difficulties and airway protection; dromperidone for nausea and vomiting; celiac plexus block with bupivicaine to reduce pain; bolus feedings, gastrostomy, and parenteral feeding for nutritional support; antibiotics for intestinal bacterial overgrowth; morphine, amitriptyline, gabapentin, and phenytoin for neuropathic symptoms; specialized schooling arrangements; and physical and occupational therapy. 
     4. Lysosomal Enzyme Deficiency 
     The synthetic complexes described herein can be useful for the treatment of Lysosomal storage disorders. In one embodiment a synthetic membrane-receiver polypeptide complex comprises a receiver, e.g., an enzyme that is active in cell lysosomes and can degrade accumulated toxic compounds, e.g., proteins, polypeptides, carbohydrates, or lipids, in lysosomes of cells with a deficiency in a lysosomal enzyme. The receiver will act by reducing the amount of toxic compound accumulated in the lysosomes of these cells, thus reducing the burden of the disease. Lysosomal storage disorders include, but are not limited to, mucopolysaccharidosis I, Gaucher Disease, Fabry Disease, Pompe Disease and those listed in table 6 and table 8. 
     In one embodiment, subjects may be identified as having received or would benefit from receiving treatment for Gaucher&#39;s disease. Subjects suffering from or at risk of developing Gaucher&#39;s disease may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising the enzyme glucocerebrosidase or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex or in the interior of the synthetic membrane-receiver polypeptide complex. The suitable receiver is capable of cleaving by hydrolysis the beta-glucosidic linkage of the chemical glucocerebroside, a sphingolipid. 
     Gaucher&#39;s disease is caused by a hereditary deficiency of the enzyme glucocerebrosidase. When the enzyme is defective, glucocerebroside accumulates in white blood cells, spleen, liver, kidneys, lungs, brain, and bone marrow. The disorder is characterized by bruising, fatigue, anemia, low blood platelets, and enlargement of the liver and spleen. Manifestations may include enlarged spleen and liver, liver malfunction, skeletal disorders and bone lesions that may be painful, severe neurologic complications, swelling of lymph nodes and (occasionally) adjacent joints, distended abdomen, a brownish tint to the skin, anemia, low blood platelets, and yellow fatty deposits on the white of the eye (sclera). Persons affected most seriously may also be more susceptible to infection. 
     Several lysosomal storage disorders are addressable by methods of treatment described herein. For example: In one embodiment the disease or condition is aspartylglucosaminuria (208400), the receiver is N-aspartylglucosaminidase or fragment thereof, and the target is glycoproteins. In one embodiment the disease or condition is cerebrotendinous xanthomatosis (cholestanol lipidosis; 213700), the receiver is sterol 27-hydroxylase or fragment thereof, and the target is lipids, cholesterol, and bile acid. In one embodiment the disease or condition is ceroid lipofuscinosis adult form (CLN4, Kufs&#39; disease; 204300), the receiver is palmitoyl-protein thioesterase-1 or fragment thereof, and the target is lipopigments. In one embodiment the disease or condition is ceroid lipofuscinosis infantile form (CLN1, Santavuori-Haltia disease; 256730), the receiver is palmitoyl-protein thioesterase-1 or fragment thereof, and the target is lipopigments. In one embodiment the disease or condition is ceroid lipofuscinosis juvenile form (CLN3, Batten disease, Vogt-Spielmeyer disease; 204200), the receiver is lysosomal transmembrane CLN3 protein or fragment thereof, and the target is lipopigments. In one embodiment the disease or condition is ceroid lipofuscinosis late infantile form (CLN2, Jansky-Bielschowsky disease; 204500), the receiver is lysosomal pepstatin-insensitive peptidase or fragment thereof, and the target is lipopigments. In one embodiment the disease or condition is ceroid lipofuscinosis progressive epilepsy with intellectual disability (600143), the receiver is transmembrane CLN8 protein or fragment thereof, and the target is lipopigments. In one embodiment the disease or condition is ceroid lipofuscinosis variant late infantile form (CLN6; 601780), the receiver is transmembrane CLN6 protein or fragment thereof, and the target is lipopigments. In one embodiment the disease or condition is ceroid lipofuscinosis variant late infantile form, Finnish type (CLN5; 256731), the receiver is lysosomal transmembrane CLN5 protein or fragment thereof, and the target is lipopigments. In one embodiment the disease or condition is cholesteryl ester storage disease (CESD), the receiver is lisosomal acid lipase or fragment thereof, and the target is lipids and cholesterol. In one embodiment the disease or condition is congenital disorders of N-glycosylation CDG Ia (solely neurologic and neurologic-multivisceral forms; 212065), the receiver is phosphomannomutase-2 or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is congenital disorders of N-glycosylation CDG Ib (602579), the receiver is mannose (Man) phosphate (P) isomerase or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is congenital disorders of N-glycosylation CDG Ic (603147), the receiver is dolicho-P-Glc:Man9GlcNAc2-PP-dolichol glucosyltransferase or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is congenital disorders of N-glycosylation CDG Id (601110), the receiver is dolicho-P-Man:Man5G1cNAc2-PP-dolichol mannosyltransferase or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is congenital disorders of N-glycosylation CDG Ie (608799), the receiver is dolichol-P-mannose synthase or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is congenital disorders of N-glycosylation CDG If (609180), the receiver is protein involved in mannose-P-dolichol utilization or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is congenital disorders of N-glycosylation CDG Ig (607143), the receiver is dolichyl-P-mannose:Man-7-GlcNAc-2-PP-dolichyl-α-6-mannosyltransferase or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is congenital disorders of N-glycosylation CDG Ih (608104), the receiver is dolichyl-P-glucose:Glc-1-Man-9-GlcNAc-2-PP-dolichyl-α-3-glucosyltransferase or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is congenital disorders of N-glycosylation CDG Ii (607906), the receiver is α-1,3-Mannosyltransferase or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is congenital disorders of N-glycosylation CDG IIa (212066), the receiver is mannosyl-α-1,6-glycoprotein-β-1,2-N-acetylglucosaminyltransferase or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is congenital disorders of N-glycosylation CDG IIb (606056), the receiver is glucosidase I or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is congenital disorders of N-glycosylation CDG IIc (Rambam-Hasharon syndrome; 266265, the receiver is GDP-fucose transporter-1 or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is congenital disorders of N-glycosylation CDG IId (607091), the receiver is β-1,4-galactosyltransferase or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is congenital disorders of N-glycosylation CDG He (608779), the receiver is oligomeric golgi complex-7 or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is congenital disorders of N-glycosylation CDG Ij (608093), the receiver is UDP-GlcNAc:dolichyl-P NAcGlc phosphotransferase or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is congenital disorders of N-glycosylation CDG Ik (608540), the receiver is β-1,4-mannosyltransferase or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is congenital disorders of N-glycosylation CDG II (608776), the receiver is α-1,2-mannosyl transferase or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is congenital disorders of N-glycosylation, type 1 (pre-Golgi glycosylation defects), the receiver is α-1,2-mannosyltransferase or fragment thereof, and the target is N-glycosylated protein. In one embodiment the disease or condition is cystinosis, the receiver is cystinosin (lysosomal cystine transporter) or fragment thereof, and the target is cysteine. In one embodiment the disease or condition is Fabry&#39;s disease (301500), the receiver is trihexosylceramide α-galactosidase or fragment thereof, and the target is globotriaosylceramide. In one embodiment the disease or condition is Farber&#39;s disease (lipogranulomatosis; 228000), the receiver is ceramidase or fragment thereof, and the target is lipids. In one embodiment the disease or condition is Fucosidosis (230000), the receiver is α-L-fucosidase or fragment thereof, and the target is fucose and complex sugars. In one embodiment the disease or condition is galactosialidosis (Goldberg&#39;s syndrome, combined neuraminidase and β-galactosidase deficiency; 256540), the receiver is protective protein cathepsin A (PPCA) or fragment thereof, and the target is lipids and glycoproteins. In one embodiment the disease or condition is Gaucher&#39;s disease, the receiver is glucosylceramide β-glucosidase or fragment thereof, and the target is sphingolipids. In one embodiment the disease or condition is glutamyl ribose-5-phosphate storage disease (305920), the receiver is ADP-ribose protein hydrolase or fragment thereof, and the target is glutamyl ribose 5-phosphate. In one embodiment the disease or condition is glycogen storage disease type 2 (Pompe&#39;s disease), the receiver is alpha glucosidase or fragment thereof, and the target is glycogen. In one embodiment the disease or condition is GM1 gangliosidosis, generalized, the receiver is ganglioside β-galactosidase or fragment thereof, and the target is acidic lipid material, gangliosides. In one embodiment the disease or condition is GM2 activator protein deficiency (Tay-Sachs disease AB variant, GM2A; 272750), the receiver is GM2 activator protein or fragment thereof, and the target is gangliosides. In one embodiment the disease or condition is GM2 gangliosidosis, the receiver is Ganglioside β-galactosidase or fragment thereof, and the target is gangliosides. In one embodiment the disease or condition is infantile sialic acid storage disorder (269920), the receiver is Na phosphate cotransporter, sialin or fragment thereof, and the target is sialic acid. In one embodiment the disease or condition is Krabbe&#39;s disease (245200), the receiver is galactosylceramide β-galactosidase or fragment thereof, and the target is sphingolipids. In one embodiment the disease or condition is lysosomal acid lipase deficiency (278000), the receiver is lysosomal acid lipase or fragment thereof, and the target is cholesteryl esters and triglycerides. In one embodiment the disease or condition is metachromatic leukodystrophy (250100), the receiver is arylsulfatase A or fragment thereof, and the target is sulfatides. In one embodiment the disease or condition is mucolipidosis ML II (1-cell disease; 252500), the receiver is N-Acetylglucosaminyl-1-phosphotransfeerase catalytic subunit or fragment thereof, and the target is N-linked glycoproteins. In one embodiment the disease or condition is mucolipidosis ML III (pseudo-Hurler&#39;s polydystrophy), the receiver is N-acetylglucosaminyl-1-phosphotransfeerase or fragment thereof, and the target is N-linked glycoproteins. In one embodiment the disease or condition is mucolipidosis ML III (pseudo-Hurler&#39;s polydystrophy) Type III-A (252600), the receiver is catalytic subunit or fragment thereof, and the target is N-linked glycoproteins. In one embodiment the disease or condition is mucolipidosis ML III (pseudo-Hurler&#39;s polydystrophy) Type III-C(252605), the receiver is substrate-recognition subunit or fragment thereof, and the target is N-linked glycoproteins. In one embodiment the disease or condition is mucopolysaccharidosis MPS I H/S (Hurler-Scheie syndrome; 607015), the receiver is α-1-iduronidase or fragment thereof, and the target is glycosaminoglycans. In one embodiment the disease or condition is mucopolysaccharidosis MPS I-H (Hurler&#39;s syndrome; 607014), the receiver is α-1-iduronidase or fragment thereof, and the target is glycosaminoglycans. In one embodiment the disease or condition is mucopolysaccharidosis MPS II (Hunter&#39;s syndrome; 309900), the receiver is iduronate sulfate sulfatase or fragment thereof, and the target is glycosaminoglycans. In one embodiment the disease or condition is mucopolysaccharidosis MPS III (Sanfilippo&#39;s syndrome) Type III-A (252900), the receiver is Heparan-S-sulfate sulfamidase or fragment thereof, and the target is glycosaminoglycans. In one embodiment the disease or condition is mucopolysaccharidosis MPS III (Sanfilippo&#39;s syndrome) Type III-B (252920), the receiver is N-acetyl-D-glucosaminidase or fragment thereof, and the target is glycosaminoglycans. In one embodiment the disease or condition is mucopolysaccharidosis MPS III (Sanfilippo&#39;s syndrome) Type III-C(252930), the receiver is acetyl-CoA-glucosaminide N-acetyltransferase or fragment thereof, and the target is glycosaminoglycans. In one embodiment the disease or condition is mucopolysaccharidosis MPS III (Sanfilippo&#39;s syndrome) Type III-D (252940), the receiver is N-acetyl-glucosaminine-6-sulfate sulfatase or fragment thereof, and the target is glycosaminoglycans. In one embodiment the disease or condition is mucopolysaccharidosis MPS I-S(Scheie&#39;s syndrome; 607016), the receiver is α-1-iduronidase or fragment thereof, and the target is glycosaminoglycans. In one embodiment the disease or condition is mucopolysaccharidosis MPS IV (Morquio&#39;s syndrome) Type IV-A (253000), the receiver is galactosamine-6-sulfate sulfatase or fragment thereof, and the target is glycosaminoglycans. In one embodiment the disease or condition is mucopolysaccharidosis MPS IV (Morquio&#39;s syndrome) Type IV-B (253010), the receiver is β-galactosidase or fragment thereof, and the target is glycosaminoglycans. In one embodiment the disease or condition is mucopolysaccharidosis MPS IX (hyaluronidase deficiency; 601492), the receiver is hyaluronidase or fragment thereof, and the target is glycosaminoglycans. In one embodiment the disease or condition is mucopolysaccharidosis MPS VI (Maroteaux-Lamy syndrome; 253200), the receiver is N-acetyl galactosamine α-4-sulfate sulfatase (arylsulfatase B) or fragment thereof, and the target is glycosaminoglycans. In one embodiment the disease or condition is mucopolysaccharidosis MPS VII (Sly&#39;s syndrome; 253220), the receiver is β-glucuronidase or fragment thereof, and the target is glycosaminoglycans. In one embodiment the disease or condition is mucosulfatidosis (multiple sulfatase deficiency; 272200), the receiver is sulfatase-modifying factor-1 or fragment thereof, and the target is sulfatides. In one embodiment the disease or condition is Niemann-Pick disease type A, the receiver is sphingomyelinase or fragment thereof, and the target is sphingomyelin. In one embodiment the disease or condition is Niemann-Pick disease type B, the receiver is sphingomyelinase or fragment thereof, and the target is sphingomyelin. In one embodiment the disease or condition is Niemann-Pick disease Type C1/Type D (257220), the receiver is NPC1 protein or fragment thereof, and the target is sphingomyelin. In one embodiment the disease or condition is Niemann-Pick disease Type C2 (607625), the receiver is epididymal secretory protein 1 (HE1; NPC2 protein) or fragment thereof, and the target is sphingomyelin. In one embodiment the disease or condition is prosaposin deficiency (176801), the receiver is prosaposin or fragment thereof, and the target is sphingolipids. In one embodiment the disease or condition is pycnodysostosis (265800), the receiver is cathepsin K or fragment thereof, and the target is kinins. In one embodiment the disease or condition is sandhoffs disease; 268800, the receiver is β-hexosaminidase B or fragment thereof, and the target is gangliosides. In one embodiment the disease or condition is saposin B deficiency (sulfatide activator deficiency), the receiver is saposin B or fragment thereof, and the target is sphingolipids. In one embodiment the disease or condition is saposin C deficiency (Gaucher&#39;s activator deficiency), the receiver is saposin C or fragment thereof, and the target is sphingolipids. In one embodiment the disease or condition is Schindler&#39;s disease Type I (infantile severe form; 609241), the receiver is N-acetyl-galactosaminidase or fragment thereof, and the target is glycoproteins. In one embodiment the disease or condition is Schindler&#39;s disease Type II (Kanzaki disease, adult-onset form; 609242), the receiver is N-acetyl-galactosaminidase or fragment thereof, and the target is glycoproteins. In one embodiment the disease or condition is Schindler&#39;s disease Type III (intermediate form; 609241), the receiver is N-acetyl-galactosaminidase or fragment thereof, and the target is glycoproteins. In one embodiment the disease or condition is sialidosis (256550), the receiver is neuraminidase 1 (sialidase) or fragment thereof, and the target is mucopolysaccharides and mucolipids. In one embodiment the disease or condition is sialuria Finnish type (Salla disease; 604369), the receiver is Na phosphate cotransporter, sialin or fragment thereof, and the target is sialic acid. In one embodiment the disease or condition is sialuria French type (269921), the receiver is UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase, sialin or fragment thereof, and the target is sialic acid. In one embodiment the disease or condition is sphingolipidosis Type I (230500), the receiver is ganglioside β-galactosidase or fragment thereof, and the target is sphingolipids. In one embodiment the disease or condition is sphingolipidosis Type II (juvenile type; 230600), the receiver is ganglioside β-galactosidase or fragment thereof, and the target is sphingolipids. In one embodiment the disease or condition is sphingolipidosis Type III (adult type; 230650), the receiver is ganglioside β-galactosidase or fragment thereof, and the target is sphingolipids. In one embodiment the disease or condition is Tay-Sachs disease; 272800, the receiver is β-hexosaminidase A or fragment thereof, and the target is gangliosides. In one embodiment the disease or condition is Winchester syndrome (277950), the receiver is metalloproteinase-2 or fragment thereof, and the target is mucopolysaccharides. In one embodiment the disease or condition is Wolman&#39;s disease, the receiver is lysosomal acid lipase or fragment thereof, and the target is lipids and cholesterol. In one embodiment the disease or condition is α-mannosidosis (248500), type I (severe) or II (mild), the receiver is α-D-mannosidase or fragment thereof, and the target is carbohydrates and glycoproteins. In one embodiment the disease or condition is β-mannosidosis (248510), the receiver is β-D-mannosidase or fragment thereof, and the target is carbohydrates and glycoproteins. 
     Selective Starvation of Metabolites 
     In some embodiments, the synthetic membrane-receiver polypeptide complexes described herein may be used to treat or prevent cancers. 
     In specific embodiments, methods are provided for reducing the circulatory concentration of a target metabolite, such as an amino acid cell in a subject (e.g., a human) suffering from or at risk of developing a cancer. The target metabolite is essential for survival of the cancer cell but not for survival of a healthy, normal cell. In certain embodiments, the cancer cell is thereby selectively starved of the critical metabolite but healthy normal cells are spared because the metabolite is non-critical for those cells. The methods include administering a pharmaceutical composition comprising a synthetic membrane-receiver polypeptide complex described herein. The pharmaceutical composition is administered in an amount effective to substantially reduce the circulatory concentration of the target metabolite. In certain embodiments, the administration is carried out intravenously. Diseases that benefit from a selective starvation of a target metabolites include cancers such as acute lymphoblastic leukemia, acute myeloblastic leukemia, pancreatic adenocarcinoma, p53-null solid tumors and those listed in table 6 and table 8. 
     In specific embodiments, provided are methods of treating cancer that include administering to a subject in need thereof a pharmaceutical composition of erythrocyte cells that comprise a receiver provided herein in an amount sufficient to treat cancer. The compositions comprising functional erythroid cells that comprise a chemotherapeutic or a receiver polypeptides capable of treating tumors and liquid cancers, may be administered to subjects that exhibit a cancers, including adrenal, anal, bile duct, bladder, bone, central nervous system, breast, leukemia, liver, lung, lymphoma, multiple myeloma, osteosarcoma, pancreatic, and those listed in, but not limited to, table 6 and table 8. 
     In one embodiment the disease or condition is acute lymphoblastic leukemia, the receiver is asparaginase or fragment thereof, and the target is asparagine. 
     In one embodiment the disease or condition is acute myeloblastic leukemia, the receiver is asparaginase or fragment thereof, and the target is asparagine. 
     In one embodiment the disease or condition is p53-null solid tumor, the receiver is serine dehydratase or serine hydroxymethyl transferase or fragment thereof, and the target is serine. 
     In one embodiment the disease or condition is pancreatic adenocarcinoma, the receiver is asparaginase or fragment thereof, and the target is asparagine. 
     Acute Lymphoblastic Leukemia (ALL) 
     In some embodiments, subjects may be identified as having received or would benefit from receiving treatment for acute lymphoblastic leukemia (ALL). Subjects suffering from or at risk of developing ALL may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising asparaginase or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface or on the unexposed side of the synthetic membrane-receiver polypeptide complex and may be administered to reduce the concentration of asparagine in circulation thereby depriving a cancer cell lacking the ability to synthesize L-asparagine and relying on the local environment for the amino acid of asparagine. 
     In specific embodiments, compositions comprising a plurality of functional erythroid cells comprising an asparaginase receiver are provided. Such compositions may be used to treat subjects that exhibit or are diagnosed with acute lymphoblastic leukemia (ALL). 
     Tumor cells lack the ability to synthesize L-asparagine and rely on their local environment for the amino acid. Asparaginase is an enzyme that can be isolated from both  Escherichia coli  and  Erwinia chrysanthemi . The foreign-sourced asparaginase is subject to immunogenic reactions that can generate life-threatening human anti-bacterial antibody responses (Avramis, Anticancer Res., 2009 January; 29(1):299-302). It has provided therapeutic benefit as a stand-alone enzyme replacement therapy, but inhibitor development is a common result of chronic treatment. 
     In specific embodiments, provided herein are compositions comprising a plurality of functional erythroid cells comprising an asparaginase receiver which may be administered to ALL subjects to deprive the cancer cells of asparagine. The functional erythroid cells may contain exogenous asparaginase within their intracellular space. The intracellularly localized exogenous asparaginase polypeptide may then convert asparagine to aspartate, thereby lowering the levels of asparagine. Asparagine crosses the cell membrane, is converted to aspartate, and diffuses back into circulation. This may be sufficient to create a local deficiency in the critical nutrient and starving tumor cells. 
     Diseases and Conditions Associated with Vascular Deficiencies 
     In some embodiments, the synthetic membrane-receiver polypeptide complexes described herein may be used to treat or prevent diseases and conditions associated with vascular deficiencies, e.g., of a vascular protein. A schematic example of this aspect of the invention is shown in  FIG. 13B . 
     In some embodiments, the surface exposed receiver polypepdide may interact with a target substrate and can modify, convert, change or otherwise alter the target substrate. Alternatively, the surface exposed receiver polypepdide is cleaved from the surface of the synthetic membrane-receiver complex in response to a specific microenvironment or molecule. In one embodiment, the receiver&#39;s catalytic activity may be initiated after cleavage. 
     In some embodiments, the synthetic membrane-receiver complexes comprise a receiver and optionally comprise a payload, such as a therapeutic agent, that can be released upon lysis of the synthetic membrane-receiver complex. The payload may be an enzyme, protein, antibody, or small molecule. The lytic event may be triggered by a stimulus in the microenvironment in which the synthetic membrane-receiver complex is present. The stimulus may, for example, recruit membrane-targeting enzymes, trigger the complement system to lyse the synthetic membrane-receiver complex, or mark the complex for destruction. Alternatively, in embodiments in which the synthetic membrane-receiver complex is generated from a cell, e.g., an erythroid cell, the synthetic membrane-receiver complex may be modified to undergo apotosis when exposed to a specific stimulus or once a certain period of time has passed. A schematic example is shown in  FIG. 13C . 
     In specific embodiments, methods are provided for reducing the circulatory concentration of a target vascular protein in a subject (e.g., a human) suffering from or at risk of developing a disease or condition associated with a vascular deficiency. The methods include administering a pharmaceutical composition comprising a synthetic membrane-receiver polypeptide complex described herein. The synthetic membrane-receiver polypeptide complex may comprise a receiver that can degrade, cleave, or convert a vascular protein. In some embodiments, a function of a missing vascular enzyme (a non-target) is restored. In some embodiments, the amount of the target vascular protein is reduced to effectively restore the homeostatic balance of vascular proteins to levels effective to treat or prevent the disease or condition. In certain embodiments, the administration is carried out intravenously. Diseases or conditions associated with vascular deficiencies include, but are not limited to thrombotic thrombocytopenic purpura, hemophilia A, hemophilia B, von Willebrand disease and those listed in table 6 and table 8. 
     In specific embodiments, provided are methods of treating a clotting disease or anti-clotting disease. The methods include administering to a subject in need thereof a pharmaceutical composition of erythrocyte cells that comprise a receiver provided herein in an amount sufficient to treat the clotting disease or anti-clotting disease. The compositions may be administered to subjects that exhibit hemophilia type A, hemophilia type B, hemophilia Type C, von Willebrand disease, Factor II deficiency, Factor V deficiency, Factor VII deficiency, Factor X deficiency, Factor XII deficiency, thrombophilia, pulmonary embolism, stroke, and those disease or deficiencies included in, but not limited to, table 6 and table 8. 
     In one embodiment the disease or condition is hemophilia A, the receiver is factor VIII or fragment thereof, and the target is thrombin (factor II a) or factor X. 
     In one embodiment the disease or condition is hemophilia B, the receiver is factor IX or fragment thereof, and the target is factor XIa or factor X. 
     In one embodiment the disease or condition is thrombotic thrombocytopenic purpura, the receiver is ADAMTS13 or fragment thereof, and the target is ultra-large von Willebrand factor (ULVWF). 
     Hemophilia 
     In some embodiments, subjects may be identified as having received or would benefit from receiving treatment for hemophilia. Subjects suffering from or at risk of developing hemophilia may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising coagulation factor VIII or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex and may be administered to provide factor VIII function to subjects exhibiting hemophilia A. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising coagulation factor IX or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex and may be administered to provide factor IX function to subjects exhibiting hemophilia B. 
     Hemophilia is a common bleeding disorder (occurring in approximately 1:10,000 males) in which causes severe internal bleeding that often leads to death because the patient&#39;s blood doesn&#39;t clot normally. Hemophilia usually is inherited with patients displaying severe uncontrollable bleeding events beginning at birth and re-occurring throughout the individual&#39;s life. Although there are several types of clotting factors that work together with platelets to help the blood coagulate, people with hemophilia usually have quantitative or qualitative defects in the proteins that encode coagulation factor VIII (hemophilia A) or factor IX (hemophilia B) that prevent normal hemostasis. Hemophilia usually occurs in males because Factors VIII and IX are located on the X chromosome (although with rare exceptions females who inherit a defective X chromosome each from an affected father and mother who is a carrier for the disease). About 1 in 10,000 individuals are born with hemophilia each year all over the world. 
     Hemostasis is the complex physiological process that leads to the cessation of bleeding. Platelets, plasma proteins, blood vessels and endothelial cells each play an important role in the events that immediately follow tissue injury and which, under normal circumstances, results in the rapid formation of a clot. Central to this is the coagulation cascade, a series of proteolytic events in which certain plasma proteins (or coagulation factors) are sequentially activated in a “cascade” by another previously activated coagulation factor, leading to the rapid generation of thrombin. The large quantities of thrombin produced in this cascade then function to cleave fibrinogen into the fibrin peptides that are required for clot formation. 
     The coagulation factors circulate as inactive single-chain zymogens, and are activated by cleavage at one or more positions to generate a two-chain activated form of the protein. Factor VII (FVII), a vitamin K-dependent plasma protein, initially circulates in the blood as a zymogen. The FVII zymogen is activated by proteolytic cleavage at a single site, Arg152-IIe153, resulting is a two-chain protease linked by a single disulphide bond (FVIIa). FVIIa binds its cofactor, tissue factor (TF), to form a complex in which FVIIa can efficiently activate factor X (FX) to FXa, thereby initiating the series of events that result in fibrin formation and hemostasis. 
     The blood coagulation pathway, in part, involves the formation of an enzymatic complex of Factor Villa (FVIIIa) and Factor IXa (FIXa) (Xase complex) on the surface of platelets. FIXa is a serine protease with relatively weak catalytic activity without its cofactor FVIIIa. The Xase complex cleaves Factor X (FX) into Factor Xa (FXa), which in turn interacts with Factor Va (FVa) to cleave prothrombin and generate thrombin. 
     About 9 out of 10 people who have hemophilia have type A. Hemophilia A is a bleeding disorder caused by mutations and/or deletions in the Factor VIII (FVIII) gene resulting in a deficiency of FVIII activity. In some cases, patients have reduced levels of FVIII due to the presence of FVIII inhibitors, such as anti-FVIII antibodies. Hemophilia A is characterized by spontaneous hemorrhage and excessive bleeding after trauma. Over time, the repeated bleeding into muscles and joints, which often begins in early childhood, results in hemophilic arthropathy and irreversible joint damage. This damage is progressive and can lead to severely limited mobility of joints, muscle atrophy and chronic pain (Rodriguez-Merchan, E. C., Semin. Thromb. Hemost. 29:87-96 (2003)). 
     The disease can be treated by replacement therapy targeting restoration of FVIII activity to 1 to 5% of normal levels to prevent spontaneous bleeding (see, e.g., Mannucci, P. M., et al., N. Engl. J. Med. 344: 1773-9 (2001), herein incorporated by reference in its entirety). There are plasma-derived and recombinant FVIII products available to treat bleeding episodes on-demand or to prevent bleeding episodes from occurring by treating prophylactically. Based on the half-life of these products (10-12 hr) (White G. C., et al., Thromb. Haemost. 77:660-7 (1997); Morfmi, M., Haemophilia 9 (suppl 1):94-99; discussion 100 (2003)), treatment regimens require frequent intravenous administration, commonly two to three times weekly for prophylaxis and one to three times daily for on-demand treatment (Manco-Johnson, M. J., et al, N. Engl. J. Med. 357:535-544 (2007)), each of which is incorporated herein by reference in its entirety. Such frequent administration is painful and inconvenient. 
     Although on-demand treatment is frequently used, there is a trend toward prophylaxis and the prevention of joint damage (Blanchette P, et al., Haemophilia 2004: 10; 679-683, Manco-Johnson, M J, et al., N. Engl. J. Med. 2007; 357:535-544). Current FVIII products are administered every two to three days for prophylaxis due to the relatively short half-life of 10-12 hr in order to maintain a FVIII:C above 1% in patients (Morfini, M, Haemophilia 2003; 9 (suppl 1):94-99; discussion 100, White G C, et al, Thromb. Haemost. 1997:77:660-7, Blanchette, P, et al, J. Thromb. Haemost. 2008 August; 6(8): 1319-26). Longer-acting FVIII therapies that provide prolonged protection from bleeding would represent an improvement in the quality of life for patients with hemophilia A. 
     Strategies to extend the half-life of clotting factors include pegylation (Roslin J, et al, Bioconj. Chem. 2000; 11:387-96), glycopegylation (Stennicke H R, et al, Thromb. Haemost. 2008; 100:920-8), formulation with pegylated liposomes (Spira J, et al, Blood 2006; 108:3668-3673, Pan J, et al, Blood 2009; 114:2802-2811) and conjugation with albumin (Schulte S., Thromb. Res. 2008; 122 Suppl 4:S14-9). 
     Under normal conditions, activated platelets provide the lipid surface supporting coagulation. Since platelets are activated by thrombin, which is formed at sites of vascular injury, coagulation processes are restricted to the sites of injuries. However, it is undesirable to provide the body with peptides that are general substitutes for procoagulant lipids as this would cause systemic coagulation and ultimately lead to disseminated intravascular coagulation (DIC). 
     U.S. Pat. Nos. 7,109,170 and 6,624,289 disclose regions of the FIXa protease domain that interact with FVIIIa and that comprise the FVIIIa binding site of FIXa. The peptides inhibit binding of FIXa to FVIIIa. The disclosed peptides may be useful as anticoagulants for preventing or treating thrombosis. 
     US20010014456A1 discloses binding molecules for human FVIII and FVIII-like proteins. These polypeptides bind FVIII and/or FVIII-like polypeptides and are useful for the detection and purification of human FVIII and/or FVIII-like polypeptides from solutions such as blood or conditioned media. 
     In U.S. Pat. No. 7,033,590 FIX/FIXa activating antibodies and antibody derivatives are used for increasing the amidolytic activity of FIXa, and for treating blood coagulation disorders such as hemophilia A and hemorrhagic diathesis. 
     U.S. Pat. No. 7,084,109 discloses FVIIa antagonists that are peptides and inhibit FVIIa activity. The peptides may be useful for the prevention of arterial thrombosis in combination with thrombolytic therapy. 
     Hemophilia can be mild, moderate, or severe, depending on how much normal functional clotting factor is present in the blood. About 7 out of 10 people who have hemophilia A have the severe form of the disorder. 
     Hemophilia B (also known as Christmas disease) is one of the most common inherited bleeding disorders in the world. It results in decreased in vivo and in vitro blood clotting activity and requires extensive medical monitoring throughout the life of the affected individual. 
     In the absence of intervention, the afflicted individual may suffer from spontaneous bleeding in the joints, which produces severe pain and debilitating immobility. Bleeding into muscles results in the accumulation of blood in those tissues. Spontaneous bleeding in the throat and neck may cause asphyxiation if not immediately treated. Bleeding into the urine, and severe bleeding following surgery, minor accidental injuries, or dental extractions also are prevalent. 
     Hemophilia B is caused by a deficiency in Factor IX that may result from either the decreased synthesis of the Factor IX protein or a defective molecule with reduced activity. 
     Human FIX, one member of the group of vitamin K-dependent polypeptides, is a single-chain glycoprotein with a molecular weight of 57 kDa, which is secreted by liver cells into the blood stream as an inactive zymogen of 415 amino acids. It contains 12γ-carboxy-glutamic acid residues localized in the N-terminal Gla-domain of the polypeptide. The Gla residues require vitamin K for their biosynthesis. Following the Gla domain there are two epidermal growth factor domains, an activation peptide, and a trypsin-type serine protease domain. Further posttranslational modifications of FIX encompass hydroxylation (Asp 64), N-(Asn157 and Asn167) as well as O-type glycosylation (Ser53, Ser61, Thr159, Thr169, and Thr172), sulfation (Tyr155), and phosphorylation (Ser158). FIX is converted to its active form, Factor IXa, by proteolysis of the activation peptide at Arg145-A1a146 and Arg180-Va1181 leading to the formation of two polypeptide chains, an N-terminal light chain (18 kDa) and a C-terminal heavy chain (28 kDa), which are held together by one disulfide bridge. Activation cleavage of Factor IX can be achieved in vitro e.g., by Factor XIa or Factor VIIa/TF. Factor IX is present in human plasma in a concentration of 5-10 μg/ml. Terminal plasma half-life of Factor IX in humans was found to be about 15 to 18 hours (White G C et al. 1997. Recombinant factor IX. Thromb Haemost. 78: 261-265; Ewenstein B M et al. 2002. Pharmacokinetic analysis of plasma-derived and recombinant F IX concentrates in previously treated patients with moderate or severe hemophilia B. Transfusion 42: 190-197). 
     The treatment of hemophilia B occurs by replacement of the missing clotting factor by exogenous factor concentrates highly enriched in Factor IX. However, generating such a concentrate from blood is difficult. Purification of Factor IX from plasma (plasma derived Factor IX; pdFIX) almost exclusively yields active Factor IX. However, such purification of FIX from plasma is very difficult because FIX is only present in low concentration in plasma (Andersson, Thrombosis Research 7: 451 459 (1975). Further, purification from blood requires the removal or inactivation of infectious agents such as HIV and HCV. In addition, pdFIX has a short half-life and therefore requires frequent dosing. Recombinant FIX (rFIX) is also available, but suffers from the same short half-life and need for frequent dosing (e.g., 2-3 times per week for prophylaxis) as pdFIX. 
     A recombinant FVIIa product is marketed by Novo Nordisk (NovoSeven). Recombinant FVIIa has been approved for the treatment of hemophilia A or B patients that have inhibitors to FVIII or FIX, and is used to stop bleeding episodes or prevent bleeding associated with trauma and/or surgery, as well as being approved for the treatment of patients with congenital FVII deficiency. FVIIa therapy leaves significant unmet medical need, because an average of 3 doses of FVIIa over a 6 hour time period are required to manage acute bleeding episodes in hemophilia patients. 
     Complications of replacement therapy include developing antibodies response to the normal therapeutic protein that is foreign to the patient&#39;s immune system (known as inhibitor formation), which ultimately leads to inactivation or destruction of the clotting factor and uncontrolled bleeding in about 30% of patients, developing viral infections from human clotting factors (from blood contaminated with HIV or Hepatitis from infected blood donors especially in third world countries), very expensive costs of the replacement protein which has a very short half-life (days) which requires frequent re-administration to subside a severe vascular injury and damage to joints, muscles, or other parts of the body resulting from delays in treatment. 
     In specific embodiments, provided herein are platelets comprising a receiver polypeptide capable of treating or preventing clotting diseases, including hemophilia. Suitable receiver polypeptides include clotting factors, e.g., Factor VIII and/or Factor IX. Human Factor VIII has the accession number NM 000132.3 and Human Factor IX has the accession number NM 000133.3. 
     In some embodiments, methods of treatment of hemophilia are provided comprising co-administration of one or more recombinant factors (e.g., recombinant FIX, FIXa, FVIII, and FVIIa) and the synthetic membrane-receiver complex described herein, wherein co-administration includes administration of the recombinant factor before, after or concurrent with administration of the synthetic membrane-receiver complex. 
     In some embodiments, methods of treatment of viral infectious diseases are provided comprising administration of a pharmaceutical composition comprising one or more recombinant factors (e.g., recombinant FIX, FIXa, FVIII, and FVIIa) and the synthetic membrane-receiver complex described herein. 
     In some embodiments, a single treatment is utilized to provide long-term protection against episodes of bleeding. In some embodiments that treat hemophilia, treatment is performed on a regular basis (e.g., weekly, monthly, yearly, once every 2, 3, 4, 5 or more years, and the like) in order to prevent episodes of bleeding. In some embodiments, treatment is only administered when episodes of abnormal bleeding occur (e.g., following accidents, prior to or following surgery, etc.). In some embodiments, maintenance therapy is administered in combination with extra therapy when episodes of abnormal bleeding occur. 
     Thrombotic Thrombocytopenic Purpura 
     In some embodiment, subjects may be identified as having received or would benefit from receiving treatment for Thrombotic Thrombocytopenic Purpura (TTP). Subjects suffering from or at risk of developing TTP may be administered a pharmaceutical composition comprising the synthetic membrane-receiver polypeptide complex described herein to treat or prevent disease. 
     In one embodiment, the synthetic membrane-receiver polypeptide complex comprises a receiver comprising the protease ADAMTS13 or a derivative or functional fragment thereof. A suitable receiver may be exhibited on the surface of the synthetic membrane-receiver polypeptide complex. The suitable receiver is capable of cleaving ultra-large von Willebrand Factor (UL-VWF) multimers into smaller multimers. 
     Circulating multimers of UL-VWF increase platelet adhesion to areas of endothelial injury, particularly at arteriole-capillary junctions. Red blood cells passing the microscopic clots are subjected to shear stress which damages their membranes, leading to intravascular hemolysis, which in turn leads to anaemia and schistocyte formation. Reduced blood flow due to thrombosis and cellular injury results in end organ damage. Current therapy is based on support and plasmapheresis to replenish blood levels of the enzyme. 
     The present disclosure also describes the following embodiments, set out in numbered paragraphs.
     A1. An isolated erythroid cell population comprising at least 80% enucleated erythroid cells each comprising at least 1,000 copies of a cytosolic exogenous polypeptide.   A2. The erythroid cell population of paragraph A1 comprising at least 85%, 90%, 95%, 97%, 98% or at least 99% enucleated erythroid cells.   A3. The erythroid cell population of embodiment A1, wherein each erythroid cell comprises at least 5,000, 10,000, 25,000, 50,000, 100,000, 250,000, 500,000, or 1,000,000, 2,500,000, 5,000,000, 10,000,000, 25,000,000, or 50,000,000 copies of the cytosolic exogenous polypeptide.   A4. The erythroid cell population of any one of embodiments A1-A3, wherein the cytosolic exogenous polypeptide is fused to a membrane-anchored polypeptide.   A5. The erythroid cell population of embodiment A4, wherein the membrane-anchored polypeptide is a transmembrane polypeptide.   A6. The erythroid cell population of embodiment A4, wherein fusion of the cytosolic exogenous polypeptide to the membrane-anchored polypeptide generates a chimeric fusion polypeptide.   A7. The erythroid cell population of any one of embodiments A4-A6, wherein the membrane-anchored polypeptide is an exogenous polypeptide or an endogenous polypeptide.   A8. The erythroid cell population of any one of embodiments A1-A7, wherein the erythroid cell is an erythrocyte.   A9. The erythroid cell population of any one of embodiments A1-A7, wherein the erythroid cell is a platelet.   A10. The erythroid cell population of any one of the preceding embodiments, wherein the cytosolic exogenous polypeptide has enzymatic activity.   A11. The erythroid cell population of embodiment A10, wherein the enzymatic activity is specific to a toxin or a metabolite.   A12. The erythroid cell population of any one of embodiments A1 to A10, wherein the cytosolic exogenous polypeptide is capable of binding, sequestering and/or degrading an anti-drug antibody.   A13. The erythroid cell population of any one of the preceding embodiments, wherein the population has an osmotic fragility of less than 50% cell lysis at 0.3%, 0.35%, 0.4%, 0.45%, or 0.5% NaCl.   A14. The erythroid cell population of any one of the preceding embodiments, wherein the population has hemoglobin levels of at least 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 pg.   A15. The erythroid cell population of any one of the preceding embodiments, wherein the population has a phosphatidylserine content as measured by Annexin V staining of less than 15%.   A16. The erythroid cell population of any one of the preceding embodiments, wherein the erythroid cells are immunologically omnicompatible.   A17. The erythroid cell population of any one of the preceding embodiments, wherein the erythroid cells lack one or more antigen selected from Diego, RHAG, Kx, GLOB, I, Ch/Rg, Colton, Kidd, Rhesus (RhD, RhCE), Kell, Yt, Scianna, Dombrock, LW, H, Cromer, Knops, Indian, OK, JMH, GIL, ABO, Lewis, P, Raph, Xg, Lutheran, MNS, Gerbich, and Duffy, or any combination thereof.   A18. The erythroid cell population of any one of the preceding embodiments, wherein the erythroid cells have a reduced glycosylation level of less than 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.25%, or of less than 0.1% compared to a control erythroid cell.   A19. The erythroid cell population of any one of the preceding embodiments, wherein the erythroid cells:
       i) do not comprise a MHC antigen, or   ii) comprise no more than one type of MHC antigen, wherein the cells arise from a population of homozygous or hemizygous progenitor cells.   
       A20. A pharmaceutical composition comprising the erythroid cell population of any one of embodiments A1-A19 and a pharmaceutically acceptable excipient.   A21. The pharmaceutical composition of embodiment A20 further comprising one anti-coagulant.   A22. The pharmaceutical composition of embodiment A20 provided in a storage container that does not comprise DEHP plasticizer.   A23. The pharmaceutical composition of embodiment A20, wherein the erythroid cell population in the storage container is substantially purged of oxygen and/or is contacted with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere.   A24. A dosage form comprising the pharmaceutical composition of embodiment A20, wherein the dosage form is formulated as a liquid suspension.   A25. The dosage form of embodiment A24, wherein the liquid suspension is formulated for intravenous administration to a subject.   A26. The dosage form of embodiment A24 or A25, wherein the liquid suspension comprises at least 1×10 5  erythroid cells provided in a volume of between 10 nl and 500 ml.   A27. The dosage form of embodiment A23, wherein the liquid suspension comprises at least 1×10 6 , 1×10 7 , 1×10 8 , 1×10 9 , or at least 1×10 10  erythroid cells.   A28. A method of producing the isolated erythroid cell population of any one of embodiments A1-A19, the method comprising:
       providing erythroid cells,   introducing an exogenous nucleic acid encoding the cytosolic exogenous polypeptide into the erythroid cells,   culturing the erythroid cells,   inducing enucleation of the erythroid cells, and   purifying the enucleated erythroid cells to produce a population of at least 80% enucleated erythroid cells comprising the cytosolic exogenous polypeptide, wherein during enucleation the cytosolic exogenous polypeptide is retained by the enucleated erythroid cell whereas the exogenous nucleic acid is not retained by the enucleated erythroid cell.   
       A29. The method of embodiment A28, further comprising the step of expanding the erythroid cells after the cytosolic exogenous polypeptide is introduced.   A30. The method of embodiment A29, wherein the erythroid cells are expanded by at least 5,000-fold, 10,000-fold, 20,000-fold, 30,000-fold, 40,000-fold, or by at least 50,000-fold.   A31. The method of embodiment A30, wherein expansion is not carried out by co-culturing of the erythroid cells with an adherent stromal layer.   A32. The method of embodiment A28, wherein the purifying step comprises one or more, 2, 3, 4, 5, or more passage of the erythroid cell population through a de-leukocyting filter.   A33. The method of embodiment A28 further comprising rendering the erythroid cells immunologically omnicompatible.   A34. The method of embodiment A33, wherein rendering the erythroid cells immunologically omnicompatible comprises:
       i) reducing the number of antigenic glycans,   ii) reducing the number of antigenic polypeptides, or   iii) both reducing the number of antigenic glycans and reducing the number of antigenic polypeptides, on the surface of the cells, thereby reducing their immunogenicity.   
       A35. The method of embodiment A34, wherein the reducing the number of antigenic glycans comprises contacting the cells with an enzyme capable of glycan trimming for a time sufficient to detach the antigenic glycans and then removing the detached glycans from the cells.   A36. The method of embodiment A34, wherein the reducing the number of antigenic polypeptides comprises contacting the cells with an enzyme capable of cleaving polypeptides for a time sufficient to detach the antigenic polypeptides and then removing the detached polypeptides from the cells.   A37. The method of embodiment A34, wherein the reducing the number of antigenic glycans comprises contacting the cells with an exogenous nucleic acid encoding an agent capable of repressing glycan biosynthesis or processing.   A38. The method of embodiment A34, wherein the reducing the number of antigenic polypeptides comprises contacting the cells with an exogenous nucleic acid encoding an agent capable of repressing polypeptide biosynthesis or processing.   A39. The method of embodiment A37 or A38, wherein the agent is CRISPR/Cas9 or a short interfering RNA.   A40. The method of embodiment A37 or A38, wherein the agent acts on a gene encoding a fucosyltransferase or a glycosyltransferase.   A41. The method of embodiment A37 or A38, wherein the agent is transiently active in the erythroid cell and is not maintained after enucleation.   A42. The method of embodiment A28, further comprising the step of irradiating the erythroid cell population.   A43. The method of embodiment A28, wherein the provided erythroid cells are erythroid precursors.   A44. The method of embodiment A28, wherein the enucleated erythroid cells are erythrocytes.   A45. The method of embodiment A28, wherein the enucleated erythroid cells are platelets.   A46. The method of any one of embodiments A28-A45, wherein culturing comprises contacting the erythroid cells with one or more culturing factors selected from the group consisting of stem cell factor, IL-3, IL-6, insulin, transferrin, erythropoietin, hydrocortisone, and estrogen.   A47. The method of embodiment A46, wherein the erythroid cell population is cultured in a bioreactor.   A48. A method of preserving the isolated erythroid cell population of any one of embodiments A1-A19, the method comprising:
       providing the erythroid cell population,   contacting the erythroid cell population with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere, and   storing the contacted erythroid cell population.   
       A49. The method of embodiment A48, wherein the erythroid cell population is stored in an atmosphere comprising the inert or noble gas.   A50. The method of embodiment A48, wherein the erythroid cell population is stored at a refrigerated temperature above the freezing point.   A51. The method of embodiment A48, wherein oxygen residing in the erythroid cell population is purged.   A52. The method of embodiment A48, wherein the inert or noble gas is selected from the group consisting of helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe).   A53. The method of embodiment A48, wherein hemolysis of the erythroid cell population is less than 5%, 4%, 3%, 2% or less than 1% after storage of at least 10 days, 15 days, 20 days, 25 days, 30 days, 35 days, 40 days, or at least 45 days.   A54. A method of transporting an erythroid cell population according to any of embodiments A1-A19, comprising:
       providing an erythroid cell population according to any of embodiments A1-A19, wherein the erythroid cell population is in contact with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere, and wherein optionally the erythroid cell population is at a refrigerated temperature above the freezing point, and transporting the erythroid cell population to a recipient.   
       A55. A method of receiving an erythroid cell population to any of embodiments A1-A19, comprising:
       receiving an erythroid cell population according to any of embodiments A1-A19, wherein the erythroid cell population is in contact with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere, and wherein optionally the erythroid cell population is at a refrigerated temperature above the freezing point, and   optionally putting the erythroid cell population in contact with naturally occurring atmosphere or an atmosphere typical of a cell incubator, and   optionally raising the temperature of the erythroid cell population, e.g., to room temperature or body temperature.   
       B1. An isolated erythroid cell population comprising at least 80% enucleated erythroid cells each comprising a high-density target substrate interaction surface, wherein the high-density target substrate interaction surface comprises at least 10,000 copies of polypeptide receiver on the plasma membrane of the erythroid cell, wherein the polypeptide receiver comprises a first polypeptide domain that is surface exposed and has an enzymatic activity, and a second polypeptide domain that is associated with the membrane of the erythroid cell, wherein the first and second polypeptide domain are not of the same natural origin, wherein the domain that has enzymatic activity is not naturally found membrane-associated, and wherein the domain that has enzymatic activity is capable of interacting and modifying the target substrate.   B2. The erythroid cell population of embodiment B 1, comprising at least 85%, 90%, 95%, 97%, 98% or at least 99% enucleated erythroid cells.   B3. The erythroid cell population of embodiment B 1, wherein each erythroid cell comprises at least 25,000 copies, 50,000 copies, or at least 100,000 copies of the polypeptide receiver.   B4. The erythroid cell population of any one of embodiments B1-B3, wherein the second polypeptide domain is a transmembrane polypeptide.   B5. The erythroid cell population of any one of embodiments B1-B3, wherein the target substrate is a self-antibody.   B6. The erythroid cell population of any one of embodiments B1-B3, wherein the target substrate is a complement cascade factor.   B7. The erythroid cell population of any one of embodiments B1-B3, wherein the target substrate is a clotting cascade factor.   B8. The erythroid cell population of any one of embodiments B1-B3, wherein the target substrate is an immune complex.   B9. The erythroid cell population of any one of embodiments B1-B3, wherein the target substrate is a serum amyloid protein.   B10. The erythroid cell population of any one of embodiments B1-B3, wherein the target substrate is a toxin or a metabolite.   B11. The erythroid cell population of any one of embodiments B1-B3, wherein the target molecule is an anti-drug antibody.   B12. The erythroid cell population of any one of embodiments B1-B11, wherein the erythroid cell is an erythrocyte.   B13. The erythroid cell population of any one of embodiments B1-B11, wherein the erythroid cell is a platelet.   B14. The erythroid cell population of embodiment B12, wherein the population has an osmotic fragility of less than 50% cell lysis at 0.3%, 0.35%, 0.4%, 0.45%, or 0.5% NaCl.   B15. The erythroid cell population of embodiment B12, wherein the population has a phosphatidylserine content as measured by Annexin V staining of less than 15%.   B16. The erythroid cell population of any one of embodiments B1-B15, wherein the erythroid cells are immunologically omnicompatible.   B17. The erythroid cell population of any one embodiments B1-B16, wherein the erythroid cells lack one or more antigen selected from Diego, RHAG, Kx, GLOB, I, Ch/Rg, Colton, Kidd, Rhesus (RhD, RhCE), Kell, Yt, Scianna, Dombrock, LW, H, Cromer, Knops, Indian, OK, JMH, GIL, ABO, Lewis, P, Raph, Xg, Lutheran, MNS, Gerbich, and Duffy, or any combination thereof.   B18. The erythroid cell population of any one of any one embodiments B1-B17, wherein the erythroid cells have a reduced glycosylation level of less than 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.25%, or of less than 0.1% compared to a control erythroid cell.   B19. The erythroid cell population of any one of any one embodiments B1-B18, wherein the erythroid cells:
       i) do not comprise a MHC antigen, or   ii) comprise no more than one type of MHC antigen, wherein the cells arise from a population of homozygous or hemizygous progenitor cells.   
       B20. The erythroid cell population of any one of embodiments B1-B19, wherein the method does not comprise introducing a nucleic acid into the cell by performing chemical disruption of the cell membrane.   B21. The erythroid cell population of any one of embodiments B1-B15, wherein the high-density target substrate interaction surface has one or more of the following properties:
       i) has a K off  rate, with respect to the target substrate, that is substantially lower than (e.g., less than 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.25%, of 0.1% lower than) that of a surface with a lower number of binding sites or a single binding site,   ii) has a dissociation constant (Kd), with respect to the target substrate, that is substantially lower than (e.g., less than 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.25%, of 0.1% lower than) that provided by a surface with a lower number of binding sites or a single binding site,   iii) has an affinity, with respect to the target substrate, that is substantially higher than (e.g., at least 10%, 20%, 50%, 2-fold, 5-fold, 10-fold, 20-fold, 50-fold, 100-fold, 200-fold, 500-fold, or 1,000-fold higher than) that provided by a surface with a lower number of binding sites or a single binding site,   iv) has an avidity, with respect to the target substrate, that is substantially higher than (e.g., at least 10%, 20%, 50%, 2-fold, 5-fold, 10-fold, 20-fold, 50-fold, 100-fold, 200-fold, 500-fold, or 1,000-fold higher than) that provided by a surface with a lower number of binding sites or a single binding site,   v) results in a local concentration of the target substrate that is substantially higher than (e.g., at least 10%, 20%, 50%, 2-fold, 5-fold, 10-fold, 20-fold, 50-fold, 100-fold, 200-fold, 500-fold, or 1,000-fold higher than) that resulting from a surface with a lower number of binding sites or a single binding site.   
       B22. The erythroid cell of embodiment B21, wherein the surface with a lower number of binding sites has less than 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.25%, of 0.1% the number of binding sites on the high-density target substrate interaction surface.   B23. The erythroid cell of embodiment B22, wherein the high-density target substrate interaction surface has one or more of the following properties:
       i) a k off  rate of less than 5×10 −2  s −1 , 2×10 −2  s −1 , 1×10 −2  s −1 , 5×10 −3  s −1 , 2×10 −3  s −1 , 1×10 −3  s −1 , 5×10 −4  s −1 , 2×10 4  s −1 , 1×10 4  s −1 , 5×10 −5  s −1 , 2×10 −5  s −1 , 1×10 −5  s −1 , 5×10 −6  s −1 , 2×10 −6  s −1 , 1×10 −6  s −1 , with respect to the target substrate, or   ii) a K d  of less than 10 mM, 5 mM, 2 mM, 1 mM, 500 μM, 200 μM, 100 μM, 50 μM, 20 μM, 10 μM, 5 μM, 2 μM, 1 μM, 500 nM, 200 nM, 100 nM, 50 nM, 20 nM, 10 nM, 5 nM, 2 nM, 1 nM, 500 pM, 200 pM, 100 pM, 50 pM, 20 pM, 10 pM, 5 pM, 2 pM, or 1 pM with respect to the target substrate,   iii) or both i) and ii).   
       B24. A pharmaceutical composition comprising the erythroid cell population of any one of embodiments B1-A19 and a pharmaceutically acceptable excipient.   B25. The pharmaceutical composition of embodiment B24 further comprising one anti-coagulant.   B25. The pharmaceutical composition of embodiment B24 provided in a storage container that does not comprise DEHP platicizer.   B27. The pharmaceutical composition of embodiment B24, wherein the erythroid cell population in the storage container is substantially purged of oxygen and/or is contacted with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere.   B28. A dosage form comprising the pharmaceutical composition of embodiment B24, wherein the dosage form is formulated as a liquid suspension.   B29. The dosage form of embodiment B28, wherein the liquid suspension is formulated for intravenous administration to a subject.   B30. The dosage form of embodiment B28 or B29, wherein the liquid suspension comprises at least 1×10 5  erythroid cells provided in a volume of between 10 nl and 500 ml.   B31. The dosage form of embodiment B28, wherein the liquid suspension comprises at least 1×10 6 , 1×10 7 , 1×10 8 , 1×10 9 , or at least 1×10 10  erythroid cells.   B32. A method of producing the isolated erythroid cell population of any one of embodiments B1-B23, the method comprising:
       providing erythroid cells,   introducing an exogenous nucleic acid encoding the cytosolic exogenous polypeptide into the erythroid cells,   culturing the erythroid cells,   inducing enucleation of the erythroid cells, and   purifying the enucleated erythroid cells to produce a population of at least 80% enucleated erythroid cells comprising the cytosolic exogenous polypeptide, wherein during enucleation the cytosolic exogenous polypeptide is retained by the enucleated erythroid cell whereas the exogenous nucleic acid is not retained by the enucleated erythroid cell.   
       B33. The method of embodiment B32 further comprising the step of expanding the erythroid cells after the cytosolic exogenous polypeptide is introduced.   B34. The method of embodiment B33, wherein the erythroid cells are expanded by at least 5,000-fold, 10,000-fold, 20,000-fold, 30,000-fold, 40,000-fold, or by at least 50,000-fold.   B35. The method of embodiment B34, wherein expansion is not carried out by co-culturing of the erythroid cells with an adherent stromal layer.   B36. The method of embodiment B32, wherein the purifying step comprises one or more, 2, 3, 4, 5, or more passages of the erythroid cell population through a de-leukocyting filter.   B37. The method of embodiment B32 further comprising rendering the erythroid cells immunologically omnicompatible.   B38. The method of embodiment B37, wherein rendering the erythroid cells immunologically omnicompatible comprises:
       i) reducing the number of antigenic glycans,   ii) reducing the number of antigenic polypeptides, or   iii) both reducing the number of antigenic glycans and reducing the number of antigenic polypeptides,   on the surface of the cells, thereby reducing their immunogenicity.   
       B39. The method of embodiment B38, wherein the reducing the number of antigenic glycans comprises contacting the cells with an enzyme capable of glycan trimming for a time sufficient to detach the antigenic glycans and then removing the detached glycans from the cells.   B40. The method of embodiment B38, wherein the reducing the number of antigenic polypeptides comprises contacting the cells with an enzyme capable of cleaving polypeptides for a time sufficient to detach the antigenic polypeptides and then removing the detached polypeptides from the cells.   B41. The method of embodiment B38, wherein the reducing the number of antigenic glycans comprises contacting the cells with an exogenous nucleic acid encoding an agent capable of repressing glycan biosynthesis or processing.   B42. The method of embodiment B38, wherein the reducing the number of antigenic polypeptides comprises contacting the cells with an exogenous nucleic acid encoding an agent capable of repressing polypeptide biosynthesis or processing.   B43. The method of embodiment B41 or B42, wherein the agent is CRISPR/Cas9 or a short interfering RNA.   B44. The method of embodiment B41 or B42, wherein the agent acts on a gene encoding a fucosyltransferase or a glycosyltransferase.   B45. The method of embodiment B41 or B42, wherein the agent is transiently active in the erythroid cell and is not maintained after enucleation.   B46. The method of embodiment B32, further comprising the step of irradiating the erythroid cell population.   B47. The method of embodiment B32, wherein the provided erythroid cells are erythroid precursors.   B48. The method of embodiment B32, wherein the enucleated erythroid cells are erythrocytes.   B49. The method of embodiment B32, wherein the enucleated erythroid cells are platelets.   B50. The method of any one of embodiments B32-B49, wherein culturing comprises contacting the erythroid cells with one or more culturing factors selected from the group consisting of stem cell factor, IL-3, IL-6, insulin, transferrin, erythropoietin, hydrocortisone, and estrogen.   B51. The method of embodiment B50, wherein the erythroid cell population is cultured in a bioreactor.   B52. A method of preserving the isolated erythroid cell population of any one of embodiments B1-B23, the method comprising:
       providing the erythroid cell population,   contacting the erythroid cell population with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere, and   storing the contacted erythroid cell population.   
       B53. The method of embodiment B52, wherein the erythroid cell population is stored in an atmosphere comprising the inert or noble gas.   B54. The method of embodiment B52, wherein the erythroid cell population is stored at a refrigerated temperature above the freezing point.   B55. The method of embodiment B52, wherein oxygen residing in the erythroid cell population is purged.   B56. The method of embodiment B52, wherein the inert or noble gas is selected from the group consisting of helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe).   B57. The method of embodiment B52, wherein hemolysis of the erythroid cell population is less than 5%, 4%, 3%, 2% or less than 1% after storage of at least 10 days, 15 days, 20 days, 25 days, 30 days, 35 days, 40 days, or at least 45 days.   B48. A method of reducing the circulatory concentration of a target anti-drug antibody, the method comprising: administering to a human subject suffering from or at risk of developing an anti-drug antibody mediated disease, disorder or condition, a pharmaceutical composition comprising an erythroid cell as described herein, e.g., an erythroid cell population of any of embodiments B1-B23, wherein the pharmaceutical composition is administered in an amount effective to substantially reduce the circulatory concentration of the target anti-drug antibody.   B49. A method of transporting an erythroid cell population according to any of embodiments B1-B23, comprising:
       providing an erythroid cell population according to any of embodiments B1-B23, wherein the erythroid cell population is in contact with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere, and wherein optionally the erythroid cell population is at a refrigerated temperature above the freezing point, and   transporting the erythroid cell population to a recipient.   
       B50. A method of receiving an erythroid cell population to any of embodiments B 1-B23, comprising:
       receiving an erythroid cell population according to any of embodiments B1-B23, wherein the erythroid cell population is in contact with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere, and wherein optionally the erythroid cell population is at a refrigerated temperature above the freezing point, and   optionally putting the erythroid cell population in contact with naturally occurring atmosphere or an atmosphere typical of a cell incubator (e.g., an atmosphere with CO 2  levels elevated above naturally occurring atmospheric CO 2  levels), and   optionally raising the temperature of the erythroid cell population, e.g., to room temperature or body temperature.   
       C1. An enucleated, synthetic erythroid cell comprising on its surface at least about 1,000 copies of an exogenous docking polypeptide comprising a high-affinity acceptor site, wherein the docking polypeptide is less than about 50 kDa, and wherein the acceptor site has an affinity for a donor molecule of about 100 picomolar or less in 1× phosphate buffered saline (PBS) on ice.   C2. The erythroid cell of embodiment C1, wherein the docking polypeptide is expressed from an exogenous nucleic acid, and wherein during enucleation the docking polypeptide is retained by the erythroid cell whereas the exogenous nucleic acid is not retained.   C3. The erythroid cell of embodiment C1, wherein the erythroid cell comprises at least 5,000, 10,000, 25,000, 50,000, 100,000, 500,000, 1,000,000, 5,000,000, 10,000,000, 25,000,000, or 50,000,000, copies of the docketing polypeptide.   C4. The erythroid cell of embodiment C1, wherein the docking polypeptide comprises a membrane-anchored polypeptide.   C5. The erythroid cell of embodiment C4, wherein the membrane-anchored polypeptide is a transmembrane polypeptide.   C6. The erythroid cell of embodiment C4, wherein the docketing polypeptide is a chimeric fusion polypeptide with a first part comprising the high-affinity acceptor site and a second part comprising the membrane-anchored polypeptide being from different origin.   C7. The erythroid cell of any one of embodiments C1-C6, wherein the erythroid cell is an erythrocyte.   C8. The erythroid cell of any one of embodiments C1-C6, wherein the erythroid cell is a platelet.   C9. The erythroid cell of any one of embodiments C1-C8, wherein the acceptor site has an affinity to a donor molecule selected from the group consisting of biotin, digoxin, and FITC.   C10. The erythroid cell of any one of embodiments C1-C8, wherein the docking polypeptide comprises scFv.   C11. The erythroid cell of any one of embodiments C1-C8, wherein the acceptor site has an affinity for the donor molecule of about 50 picomolar, 20 picomolar, 10 picomolar, 5 picomolar, 2 picomolar, 1 picomolar, 500 femtomolar, 250 femtomolar, 100 femtomolar, 50 femtomolar, 25 femtomolar, or about 10 femtomolar or less.   C12. The erythroid cell of any one of embodiments C1-C11, wherein the docking polypeptide is less than about 45 kDa, 40 kDa, 35 kDa, 30 kDa, or less than about 25 kDa.   C13. The erythroid cell of any one of embodiments C1-C12 further comprising a receiver polypeptide, wherein the receiver polypeptide binds to the high affinity acceptor site of the docking polypeptide.   C14. The erythroid cell of embodiment C13, wherein the receiver polypeptide is conjugated to a donor molecule that hinds to the acceptor site, thereby attaching the receiver polypeptide to the erythroid cell.   C15. The erythroid cell of embodiment C13 or C14, wherein the receiver polypeptide is capable of interacting with a target molecule.   C16. The erythroid cell of embodiment C15, wherein the target molecule is a self-antibody.   C17. The erythroid cell of embodiment C15, wherein the target molecule is a complement cascade factor.   C18. The erythroid cell of embodiment C15, wherein the target molecule is a clotting cascade factor.   C19. The erythroid cell of embodiment C15, wherein the target molecule is an immune complex.   C20. The erythroid cell of embodiment C15, wherein the target molecule is a serum amyloid protein.   C21. The erythroid cell of embodiment C15, wherein the target molecule is a toxin.   C22. The erythroid cell of embodiment C15, wherein the target molecule is a metabolite.   C23. The erythroid cell of embodiment C15, wherein the target molecule is an anti-drug antibody.   C24. The erythroid cell population of any one of embodiments C1-C23, wherein the erythroid cells are immunologically omnicompatible.   C25. The erythroid cell population of any one embodiments C1-C24, wherein the erythroid cells lack one or more antigen selected from Diego, RHAG, Kx, GLOB, I, Ch/Rg, Colton, Kidd, Rhesus (RhD, RhCE), Kell, Yt, Scianna, Dombrock, LW, H, Cromer, Knops, Indian, OK, JMH, GIL, ABO, Lewis, P, Raph, Xg, Lutheran, MNS, Gerbich, and Duffy, or any combination thereof.   C26. The erythroid cell population of any one of embodiments C1-C25, wherein the erythroid cells have a reduced glycosylation level of less than 90%, 80%, 70%, 60%, 50%, 40%, 30%, 20%, 10%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.25%, or of less than 0.1% compared to a control erythroid cell.   C27. The erythroid cell population of any one of embodiments C1-C26, wherein the erythroid cells:
       i) do not comprise a MHC antigen, or   ii) comprise no more than one type of MHC antigen, wherein the cells arise from a population of homozygous or hemizygous progenitor cells.   
       C28. A pharmaceutical composition comprising a population of erythroid cells of any one of embodiments C1-C27 and a pharmaceutically acceptable excipient.   C29. The pharmaceutical composition of embodiment C28, provided in a storage container.   C30. The pharmaceutical composition of embodiment C29, wherein the erythroid cell population in the storage container is substantially purged of oxygen and/or is contacted with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere.   C31. A dosage form comprising the pharmaceutical composition of embodiment C28, wherein the dosage form is formulated as a liquid suspension.   C32. The dosage form of embodiment C31, wherein the liquid suspension is formulated for intravenous administration to a subject.   C33. The dosage form of embodiment C31 or C32, wherein the liquid suspension comprises at least 1×10 5  erythroid cells provided in a volume of between 10 nl and 500 ml.   C34. The dosage form of embodiment C33, wherein the liquid suspension comprises at least 1×10 6 , 1×10 7 , 1×10 8 , 1×10 9 , or at least 1×10 10  erythroid cells.   C35. A method of producing a population of enucleated synthetic erythroid cells, the method comprising:
       providing isolated erythroid cells,   introducing an exogenous nucleic acid encoding a docking polypeptide comprising a high-affinity acceptor site into the erythroid cells,   culturing the erythroid cells,   inducing enucleation of the erythroid cells to obtain a population of enucleated erythroid cells comprising a docking polypeptide, wherein the docking polypeptide is less than about 50 kDa, wherein the acceptor site has an affinity for a donor molecule of about 100 picomolar or less in 1× phosphate buffered saline (PBS) on ice, and wherein during enucleation at least 1,000 copies of the docking polypeptide are retained by the erythroid cell whereas the exogenous nucleic acid is not retained.   
       C36. The method of embodiment C35, wherein the acceptor site has an affinity for the donor molecule of about 50 picomolar, 20 picomolar, 10 picomolar, 5 picomolar, 2 picomolar, 1 picomolar, 500 femtomolar, 250 femtomolar, 100 femtomolar, 50 femtomolar, 25 femtomolar, or about 10 femtomolar or less.   C37. The method of embodiment C35, further comprising the step of expanding the erythroid cells after the docking polypeptide is introduced.   C38. The method of embodiment C37, wherein the erythroid cells are expanded by at least 5,000-fold, 10,000-fold, 20,000-fold, 30,000-fold, 40,000-fold, or by at least 50,000-fold.   C39. The method of embodiment C37 or 31, wherein expansion is not carried out by co-culturing of the erythroid cells with an adherent stromal layer.   C40. The method of any one of embodiments C35-C37, further comprising contacting the erythroid cells with a receiver polypeptide comprising a donor molecule with affinity to the acceptor site of the docking polypeptide.   C41. The method of any one of embodiments C35-C38 further comprising purifying the enucleated erythroid cells to produce a population of at least 80% enucleated erythroid cells.   C42. The method of embodiment C41, wherein the purifying step comprises one or more, 2, 3, 4, 5, or more passage of the erythroid cell population through a de-leukocyting filter.   C43. The method of any one of embodiments C35-C42 further comprising rendering the erythroid cells immunologically omnicompatible.   C44. The method of embodiment C43, wherein rendering the erythroid cells immunologically omnicompatible comprises:
       i) reducing the number of antigenic glycans,   ii) reducing the number of antigenic polypeptides, or   iii) both reducing the number of antigenic glycans and reducing the number of antigenic polypeptides,   on the surface of the cells, thereby reducing their immunogenicity.   
       C45. The method of embodiment C44, wherein the reducing the number of antigenic glycans comprises contacting the cells with an enzyme capable of glycan trimming for a time sufficient to detach the antigenic glycans and then removing the detached glycans from the cells.   C46. The method of embodiment C44, wherein the reducing the number of antigenic polypeptides comprises contacting the cells with an enzyme capable of cleaving polypeptides for a time sufficient to detach the antigenic polypeptides and then removing the detached polypeptides from the cells.   C47. The method of embodiment C44, wherein the reducing the number of antigenic glycans comprises contacting the cells with an exogenous nucleic acid encoding an agent capable of repressing glycan biosynthesis or processing.   C48. The method of embodiment C44, wherein the reducing the number of antigenic polypeptides comprises contacting the cells with an exogenous nucleic acid encoding an agent capable of repressing polypeptide biosynthesis or processing.   C49. The method of embodiment C47 or C48, wherein the agent is CRISPR/Cas9 or an interfering RNA   C50. The method of embodiment C47 or C48, wherein the agent acts on a gene encoding a fucosyltransferase or a glycosyltransferase.   C51. The method of embodiment C50, wherein the fucosyltransferase is FUT1 or FUT2.   C52. The method of embodiment C50, wherein the glycosyltransferase is an ABO gene.   C53. The method of embodiment C47 or C48, wherein the agent is transiently active in the erythroid cell and is not maintained after enucleation.   C54. The method of any one of embodiments C35-053 further comprising the step of irradiating the erythroid cells.   C55. The method of embodiment C35, wherein the provided isolated erythroid cells are erythroid precursors.   C56. The method of embodiment C35, wherein the enucleated erythroid cells are erythrocytes.   C57. The method of embodiment C35, wherein the enucleated erythroid cells are platelets.   C58. The method of any one of embodiments C35-057, wherein culturing comprises contacting the erythroid cells with one or more culturing factors selected from the group consisting of stem cell factor, IL-3, IL-6, insulin, transferrin, erythropoietin, hydrocortisone, and estrogen.   C59. The method of embodiment C57, wherein the erythroid cells are cultured in a bioreactor.   C60. The method of any one of embodiments C35-50 further comprising contacting the erythroid cells with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere and storing the contacted erythroid cell population.   C61. The method of embodiment C60, wherein the erythroid cells are stored in an atmosphere comprising the inert or noble gas.   C62. The method of embodiment C60, wherein the erythroid cells are stored at a refrigerated temperature above the freezing point.   C63. The method of embodiment C60, further comprising purging the oxygen residing in the erythroid cells.   C64. The method of embodiment C60, wherein the inert or noble gas is selected from the group consisting of helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe).   C65. The method of embodiment C60, wherein hemolysis of the erythroid cells is less than 5%, 4%, 3%, 2% or less than 1% after storage of at least 10 days, 15 days, 20 days, 25 days, 30 days, 35 days, 40 days, or at least 45 days.   C66. The method of embodiment C40, wherein contacting the receiver polypeptide comprising the donor molecule results in binding of the receiver polypeptide to the acceptor site, thereby attaching the receiver polypeptide to the erythroid cell.   C67. The method of embodiment C66, wherein the receiver polypeptide is capable of interacting with a target molecule.   C68. The method of embodiment C67, wherein the target molecule is a self-antibody.   C69. The method of embodiment C67, wherein the target molecule is a complement cascade factor.   C70. The method of embodiment C67, wherein the target molecule is a clotting cascade factor.   C71. The method of embodiment C67, wherein the target molecule is an immune complex.   C72. The method of embodiment C67, wherein the target molecule is a serum amyloid protein.   C73. The method of embodiment C67, wherein the target molecule is a toxin.   C74. The method of embodiment C67, wherein the target molecule is a metabolite.   C75. The erythroid cell of embodiment C67, wherein the target molecule is an anti-drug antibody.   C76. A method of transporting an erythroid cell according to any of embodiments C1-C27, comprising:
       providing an erythroid cell according to any of embodiments C1-C27, wherein the erythroid cell is in contact with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere, and wherein optionally the erythroid cell is at a refrigerated temperature above the freezing point, and   transporting the erythroid cell to a recipient.   
       C77. A method of receiving an erythroid cell to any of embodiments C1-C27, comprising:
       receiving an erythroid cell according to any of embodiments C1-C27, wherein the erythroid cell is in contact with an inert or noble gas at a concentration that is greater than what naturally occurs in the atmosphere, and wherein optionally the erythroid cell is at a refrigerated temperature above the freezing point, and   optionally putting the erythroid cell in contact with naturally occurring atmosphere or an atmosphere typical of a cell incubator, and   optionally raising the temperature of the erythroid cell, e.g., to room temperature or body temperature.   
       

     EXAMPLES 
     Example 1: Gene Assembly 
     DNA encoding the following genes—glycophorin A (Uniprot ID P02724), Kell (Uniprot ID P23276), antibody scFv against hepatitis B surface antigen (Bose et al. 2003 Mol Immunol 40(9):617, GenBank ID AJ549501.1), adenosine deaminase (Uniprot ID P00813), phenylalanine hydroxylase from  Chromobacterium violaceum  (GenBank ID AF146711.1), complement receptor 1 (Uniprot ID P17927), CD46 (GenBank: BAA12224.1), CD55 (Uniprot ID P08174), CD59 (Uniprot ID P13987), green fluorescent protein (Uniprot ID P42212), thymidine phosphorylase (Uniprot ID P19971), glucocerebrosidase (Uniprot ID P04062), beta2 glycoprotein 1 (Uniprot ID P02749), phospholipase a2 receptor (Uniprot ID Q13018), collagen alpha-3(IV) (Uniprot ID Q01955), serum amyloid P (Uniprot ID P02743), lipoprotein lipase (Uniprot ID P06858), asparaginase (Uniprot ID P00805), factor IX (Uniprot ID F2RM35), ADAMTS13 (Uniprot ID Q76LX8)—were purchased as cDNA from Dharmacon (GE Life Sciences) or synthesized de novo by DNA2.0 and Genscript. 
     1. Single Gene Cloning (CR1) 
     Genes were assembled into expression vectors by standard molecular biology methods known in the art. The gene for complement receptor 1 (CR1) was synthesized by a commercial vendor (DNA2.0) and supplied in a standard cloning vector (pJ series). The gene was amplified out of the pJ vector by polymerase chain reaction (PCR) using oligos with non-homologous terminal sequences to prepare for insertion into the mammalian expression vector (System Biosciences, pM series): the upstream oligo consisted of 25 nt homologous to the upstream pM insertion site and 25 nt homologous to the start of CR1; the downstream oligo consisted of 25 nt homologous to the downstream pM insertion site and 25 nt homologous to the end of CR1. The amplified product was purified by gel electrophoresis (Qiagen). The pM vector was linearized by PCR with tail-to-tail oligos homologous to the upstream and downstream insertion sites and purified by PCR purification (Qiagen). The CR1 amplicon was ligated into the linearized pM vector by Gibson assembly, described in detail in Gibson 2011, Methods Enzymology Vol 498, p. 394. Sequences were confirmed by Sanger sequencing. 
     2. Fusion of Two Genes (Membrane Kell-scFv) 
     The gene for Kell was purchased as cDNA and supplied in a standard cloning vector (pJ series). The gene for an antibody scFv specific to hepatitis B surface antigen (scFv, described in Bose 2003, Molecular Immunology 40:617) was synthesized by a commercial vendor (DNA2.0) and supplied in a standard cloning vector (pJ series). The genes was amplified out of the pJ vectors by polymerase chain reaction (PCR) using oligos with non-homologous terminal sequences to prepare for insertion into the mammalian expression vector (System Biosciences, pM series). Kell was amplified with an upstream oligo consisting of 25 nt homologous to the upstream pM insertion site and 25 nt homologous to the 5′ terminus of Kell, and a downstream oligo consisting of 25 nt homologous to the 5′ terminus of scFv and 25 nt homologous to the 3′ terminus of Kell. scFv was amplified with an upstream oligo consisting of 25 nt homologous to the 3′ terminus of Kell insertion site and 25 nt homologous to the 5′ terminus of scFv, and a downstream oligo consisting of 25 nt homologous to the downstream pM insertion site and 25 nt homologous to the 3′ terminus of scFv. The amplified products were purified by gel electrophoresis (Qiagen). The pM vector was linearized by PCR with tail-to-tail oligos homologous to the upstream and downstream insertion sites and purified by PCR purification (Qiagen). The Kell and scFv amplicons were ligated into the linearized pM vector by one-pot Gibson assembly, described in detail in Gibson 2011, Methods Enzymology Vol 498, p. 394. Sequences were confirmed by Sanger sequencing. 
     3. Linker-Assembly Between Genes (Kell-Scfv) 
     The gene for Kell was purchased as cDNA and supplied in a standard cloning vector (pJ series). The gene for an antibody scFv specific to hepatitis B surface antigen (scFv, described in Bose 2003, Molecular Immunology 40:617) was synthesized by a commercial vendor (DNA2.0) and supplied in a standard cloning vector (pJ series). The genes was amplified out of the pJ vectors by polymerase chain reaction (PCR) using oligos with non-homologous terminal sequences to prepare for insertion into the mammalian expression vector (System Biosciences, pM series). Kell was amplified with an upstream oligo consisting of 25 nt homologous to the upstream pM insertion site and 25 nt homologous to the 5′ terminus of Kell; and a downstream oligo consisting of 25 nt homologous to the 5′ terminus of scFv, 24 nt encoding a (GlyGlyGlySer)×2 (SEQ ID NO: 23) spacer, and 25 nt homologous to the 3′ terminus of Kell. scFv was amplified with an upstream oligo consisting of 25 nt homologous to the 3′ terminus of Kell insertion site, 24 nt encoding a (GlyGlyGlySer)×2_(SEQ ID NO: 23) spacer, and 25 nt homologous to the 5′ terminus of scFv; and a downstream oligo consisting of 25 nt homologous to the downstream pM insertion site and 25 nt homologous to the 3′ terminus of scFv. The amplified products were purified by gel electrophoresis (Qiagen). The pM vector was linearized by PCR with tail-to-tail oligos homologous to the upstream and downstream insertion sites and purified by PCR purification (Qiagen). The Kell and scFv amplicons were ligated into the linearized pM vector by one-pot Gibson assembly, described in detail in Gibson 2011, Methods Enzymology Vol 498, p. 394. Sequences were confirmed by Sanger sequencing. 
     4. Epitope Tag Attachment (Kell-scFv) 
     The gene for Kell was purchased as cDNA and supplied in a standard cloning vector (pJ series). The gene for an antibody scFv specific to hepatitis B surface antigen (scFv, described in Bose 2003, Molecular Immunology 40:617) was synthesized by a commercial vendor (DNA2.0) and supplied in a standard cloning vector (pJ series). The genes was amplified out of the pJ vectors by polymerase chain reaction (PCR) using oligos with non-homologous terminal sequences to prepare for insertion into the mammalian expression vector (System Biosciences, pM series). Kell was amplified with an upstream oligo consisting of 25 nt homologous to the upstream pM insertion site and 25 nt homologous to the 5′ terminus of Kell; and a downstream oligo consisting of 25 nt homologous to the 5′ terminus of scFv, 24 nt encoding a (GlyGlyGlySer)×2 (SEQ ID NO: 23) spacer, and 25 nt homologous to the 3′ terminus of Kell. scFv was amplified with an upstream oligo consisting of 25 nt homologous to the 3′ terminus of Kell insertion site, 24 nt encoding a (GlyGlyGlySer)×2 (SEQ ID NO: 23) spacer, and 25 nt homologous to the 5′ terminus of scFv; and a downstream oligo consisting of 25 nt homologous to the downstream pM insertion site, the 27 nt sequence tacccctatgacgtgcccgactatgcc (Seq. ID No. 8) encoding an HA epitope tag, and 25 nt homologous to the 3′ terminus of scFv. The amplified products were purified by gel electrophoresis (Qiagen). The pM vector was linearized by PCR with tail-to-tail oligos homologous to the upstream and downstream insertion sites. The downstream primer additionally contained the 27 nt sequence tacccctatgacgtgcccgactatgcc (Seq. ID No. 8) encoding an HA epitope tag. The linearized vector was purified by PCR purification (Qiagen). The Kell and scFv amplicons were ligated into the linearized pM vector by one-pot Gibson assembly, described in detail in Gibson 2011, Methods Enzymology Vol 498, p. 394. Sequences were confirmed by Sanger sequencing. 
     5. Fusion of Two Genes (Reporter Assembly) (GPA-HA) 
     The genes for complement receptor 1 (CR1) and green fluorescent protein (GFP) were synthesized by a commercial vendor (DNA2.0) and supplied in standard cloning vectors (pJ series). The CR1 gene was amplified out of the pJ vector by polymerase chain reaction (PCR) using oligos with non-homologous terminal sequences to prepare for insertion into the mammalian expression vector (System Biosciences, pM series): the upstream oligo consisted of 25 nt homologous to the upstream pM insertion site and 25 nt homologous to the start of CR1; the downstream oligo consisted of 54 nt homologous to the viral-derived T2A sequence gagggcagaggaagtcttctaacatgcggtgacgtggaggsgsstcccggccct (Seq. ID No. 7). The GFP gene was amplified out of the pJ vector by polymerase chain reaction (PCR) using oligos with non-homologous terminal sequences to prepare for insertion into the mammalian expression vector (System Biosciences, pM series): the upstream oligo consisted of 54 nt homologous to the viral-derived T2A sequence gagggcagaggaagtcttctaacatgcggtgacgtggaggsgsstcccggccct (Seq. ID No. 7) and 25 nt homologous to the start of GFP; the downstream oligo consisted of 25 nt homologous to the downstream pM insertion site and 25 nt homologous to the end of GFP. The amplified products were purified by gel electrophoresis (Qiagen). The pM vector was linearized by PCR with tail-to-tail oligos homologous to the upstream and downstream insertion sites and purified by PCR purification (Qiagen). The CR1 and GFP amplicons were ligated together and into the linearized pM vector by Gibson assembly, described in detail in Gibson 2011, Methods Enzymology Vol 498, p. 394. Sequences were confirmed by Sanger sequencing. 
     Example 2: mRNA Assembly 
     A gene of interest is cloned into the multiple cloning site of the pSP64 vector (Promega) using standard molecular biology methods. The vector is digested with EcoRI (NEB) to generate a linearized dsDNA vector containing the SP6 promoter, gene of interest, and 30 nucleotide long poly-A tail. mRNA is synthesized by reaction with SP6 RNA polymerase (Promega) according to manufacturer&#39;s instructions, including recommended concentrations of 5′ cap analog (ARCA) to synthesize capped mRNA transcript. The reaction mixture is then treated with DNAse to digest the template vector (Riboprobe from Promega) and the mRNA is purified using the EZNA MicroElute RNA Clean-Up kit (Omega). 
     Example 3: Cell Culture 
     1. Human Red Blood Cells (RBCs) 
     CD34 cells are isolated from peripheral blood by supermagnetic microbead selection by the use of Mini-MACS columns (Miltenyi Biotec; 94%+/−3% purity). The cells are cultured in erythroid differentiation medium (EDM) on the basis of IMDM supplemented with stabilized glutamine, 330 μg/mL holo-human transferrin, 10 μg/mL recombinant human insulin, 2 IU/mL heparin, and 5% solvent/detergent virus-inactivated plasma. The expansion procedure comprises 3 steps. In the first step (day 0 to day 7), 10{circumflex over ( )}4/mL CD34+ cells are cultured in EDM in the presence of 1 μM hydrocortisone, 100 ng/mL SCF, 5 ng/mL IL-3, and 3 IU/mL EPO. On day 4, 1 volume of cell culture is diluted in 4 volumes of fresh medium containing SCF, IL-3, EPO, and hydrocortisone. In the second step (day 7 to day 11), the cells are resuspended at 10″5/mL in EDM supplemented with SCF and EPO. In the third step (day 11 to day 18), the cells are cultured in EDM supplemented with EPO alone. Cell counts are adjusted to 7.5×10{circumflex over ( )}5 to 1×10{circumflex over ( )}6 and 5-10×10{circumflex over ( )}6 cells/mL on days 11 and 15, respectively. Beyond day 18, the culture medium containing EPO is renewed twice a week. The cultures are maintained at 37° C. in 5% CO2 in air. 
     2. Mouse Red Blood Cells 
     Methods of culturing mouse erythroid cells from mouse fetal liver erythroid progenitors are known in the art, see e.g., Shi et al. 2014, PNAS 2014 111(28):10131. 
     Mouse erythroid progenitors are isolated from fetal livers. Fetal livers are purchased from Charles River Labs. Livers are put in 1 ml PBS on ice. Pipette up and down to get a single-cell suspension solution and pass by a 70 um strainer (BD Falcon 35-2235). Rinse the mesh with 1 ml PBS. Combine the flow through (1 ml per embryo). Pellet the cells at 1.5 k RPM for 5 min, re-suspend with red cell lysis buffer (Ammonium Chloride Solution from Stemcell), and incubate on ice for 10 mins. Pellet the cells at 1.5 k RPM for 5 min, remove the lysis buffer, and re-suspend with 10 ml PBS-2% FBS. Add chromPure Rat IgG (Jackson ImmunoResearch, #012-000-003) at 50 ul/mouse and incubate at 4 C for 5 min. Add Biotinylated anti-mouse TER119 (BD Pharmingen, #553672) at (at 1 ul/1*10{circumflex over ( )}6 cells) and incubate at 4 C for 15 min. Add Ms Lineage Panel (Fisher Scientific (Thermo Fisher Scientific) #BDB559971) to the cells at (2 ul/1*10{circumflex over ( )}6 cells) and incubate at 4 C for 15 min. Washing once with 10× volume of PBS/and Spin the cells with 1.5 k RPM for 5 min at 4 degree. Add Streptavidin Particles Plus—DM (magnetic beads) (BD Pharmigen, #557812) (5 ul/1*10{circumflex over ( )}6 cells) and incubate at 4 C for 30 min. Prepare 2-4 FACS tubes on a magnetic holder. Aliquot 2 ml cells into each tube (4 ml in total), and carefully take the cells out of the tube and put into the other tube on the other side avoiding the disruption of the magnetic stick beads. Repeat the same procedure and take the Ter119 negative and linkage negative cells to a new tube. Concentrate the cells, and resuspend the cells with 50-100 ul PBS (2% FBS). 
     Purified erythroid progenitors are cultured in differentiation medium comprising (for 40 mL): IMDM: 29 ml, FBS (Stem Cell): 6 ml (Final 15%), 10% BSA in IMDM (Stem Cell): 4 ml (Final 1%), 10 mg/ml Holo-transferrin: 2000 ul (Final: 500 ug/ml), 100*L-Glutamine: 400 ul, 100*penicillin streptomycin: 400 ul, 10 U/ul Epo: 2 ul (Final: 0.5 U/ml), 10 mg/ml Insulin: 40 ul (Final: 10 ug/ml). Culture 2*10{circumflex over ( )}5 cells/ml in the differentiation medium in 24 wells plate at 37 C. After a total culture of 44-48 hours, analyses are performed, for example by flow cytometry as performed herein. Enucleated red blood cells are gated out using (Hoechst stain) for differentiation profile analysis. A successful culture will yield 16 fold increase. 
     3. Platelets 
     Donated CD34+ cells are acquired from the Fred Hutchinson Cancer Research Center. The CD34+ enriched cells are plated in a serum-free medium at 2-4×10{circumflex over ( )}4 cells/mL and medium refreshment is done on day 4 by adding an equal volume of media. On day 6, cells are counted and analyzed: 1.5×10{circumflex over ( )}5 cells are washed and placed in 1 mL of the same medium supplemented with a cytokine cocktail consisting of TPO 30 ng/mL, SCF 1 ng/mL, interleukin (1L)-6 7.5 ng/mL and 1L-9 13.5 ng/mL┘ to induce megakaryocyte differentiation. At day 10, ½-¼ of the suspension culture is replaced with fresh medium. All cytokines are purchased from Peprotech. The cultures are incubated in a humidified atmosphere (10% CO2) at 39° C. for the first 6 days of culture and 37° C. for the last 8 days. Viable nucleated cells are counted with a hemocytometer (0.4% trypan blue; Invitrogen, Burlington, ON, Canada). 
     Clonogenic progenitor cells (CPC) are assayed using MethoCult H4436 for myeloid CPC, and MegaCult-C for colony-forming unit—megakaryocyte (CFU-Mk), according to manufacturer&#39;s instructions (StemCell Technologies, Vancouver, BC, Canada). To assess differentiation, cells are stained with antibodies against CD61m CD42b, CD41, CD61, and CD49b by flow cytometry using a FACS-Calibur (Becton Dickinson). For cell cycle analysis, cells are rinsed with phosphate-buffered saline (PBS), fixed with formaldehyde 2% (Sigma, St Louis, Mo., USA) for 5 min and permeabilized with 0.1% of Triton X-100 (Bio-Rad, Hercules, Calif., USA). Cells are then marked with mAb-Ki-67-FITC (BD Bioscience, San Jose, Calif., USA), washed and resuspended in 0.5 mL PBS-1% fetal bovine serum (FBS)-0.01% azide 7-amino-actinomycin D (7-AAD) following the manufacturer&#39;s instructions (BD Biosciences). 
     Example 4: Cell Isolation 
     1. Primary RBCs 
     Whole blood is collected using aseptic techniques in tubes containing low molecular weight heparin, dalteparin sodium (9 units/mL blood). Blood is centrifuged at 5000×g for 5 minutes and after removal of plasma and buffy coat (both can be retained for later use), the erythrocytes are washed twice in cold (4 C) phosphate buffered saline (PBS) with centrifugation. The resultant red blood cell population is stored at 4 C in CPDA-1 anticoagulant or a glycerol solution for long-term preservation. 
     2. Primary Platelets 
     Whole blood (40 ml) is collected in 3.8% sodium citrate (1:9 citrate to blood vol/vol) from healthy individuals under an appropriate IRB protocol. Blood is centrifuged at 200 g for 15 minutes to isolate platelet-rich plasma (PRP). Platelets are then washed in modified Tyrode&#39;s buffer (containing 138 mM NaCl, 5.5 mM dextrose, 12 mM NaHCO 3 , 0.8 mM CaCl2, 0.4 mM MgCl2, 2.9 mM KCl2, 0.36 mM Na2HPO4 and 20 mM Hepes, pH 7.4) in presence of 1 μM prostaglandin 12, and resuspended in the same buffer. 
     Example 5: Irradiation of Primary or Cultured Cell 
     Irradiation of a population of synthetic membrane-receiver complexes can be performed to ensure that they are incapable of replication. Such protocols are similar to those known in the art for irradiating cells, e.g., primary red blood cells. Briefly, one unit (350 ml) of whole blood is taken and divided into two aliquots of 175 ml each, 10 such units are thus divided into 20 aliquots. One aliquot (175 ml) from each unit of blood is subjected to gamma irradiation of 25 Gy, and not exceeding 50 Gy, by a self-contained gamma cell irradiator (GammaCell 1000, Theratronics). The blood is then stored at 4 C under conventional blood banking conditions. Sampling is done from these 10 irradiated and 10 non-irradiated blood bags on days 0, 7, 14, and 21 with the help of sampling site coupler (Fenwal, USA). Tests for cell proliferation are conducted, including a thymidine incorporation assay to quantify any mitotic potential. Supernatant is assayed for free hemoglobin by absorbance spectroscopy, and for free lactate dehydrogenase by colorimetric assay (Pierce) to evaluate levels of cell lysis. 
     Example 6: Enucleation of Erythroid Cells 
     Erythroid cells are grown to semiconfluence (1 to 4×10{circumflex over ( )}4 cells per cm2) on 12-mm diameter coverslips coated with collagen in IMDM medium supplemented with 100 units/mi of penicillin and 100 units/ml of streptomycin. The collagen is necessary to prevent all the cells from falling off the coverslip during centrifugation. Cells are grown to monolayers (5×104 cells per cm2) on coverslips either in the same medium or in Dulbecco&#39;s modified Eagle&#39;s medium with 10% calf serum. It is not necessary to coat the cell coverslips with collagen. In order to enucleate the cells, the coverslips are inverted (cell side down) and placed into the bottom of 15-ml Corex centrifuge tubes containing 2-5 ml of medium with 10 g of cytochalasin B per ml. The centrifuge tubes with the coverslips are placed immediately into a Sorvall RC-2 centrifuge that has been warmed to 37 C by spinning the (SS 34) rotor with the head in place for about 1 hr at 10,000 rpm (with the temperature regulator set at 37-39°). The length of time and speed of centrifugation are crucial factors for successful enucleation. Cells are spun at 9000 rpm for 1 hr at 37±20 and cells are spun at 6500 rpm for 50 min at 37±−20. After centrifugation, the coverslips are removed from the centrifuge and placed cell side up into 35-mm (Falcon) tissue culture dishes (Biolquest) containing 3 ml of medium without cytochalasin B. Within 30-60 min at 370, the cells are morphologically normal and 90-99% lacked nuclei. Enucleated cells are removed from the coverslips by treatment with trypsin-EDTA (Grand Island Biological Co.) and the cells are suspended in normal medium. The enucleated cells are then replated in small drops on 22-mm2 coverslips kept in 35-mm tissue culture dishes and placed in an incubator. At time intervals after replating, the coverslips are mounted on slides (12) and observations on the enucleates are made with Zeiss phase contrast, polarized light, and Nomarski optics. 
     Example 7: Contacting of Cells 
     1. Nucleic Acid—Transfection 
     The nucleic acid of interest is scaled up to provide approximately 5 ug nucleic acid per 10{circumflex over ( )}5 complexes to be loaded, e.g., a cell, such as an erythroid cell, a platelet, or a hematopoietic precursor cell. The nucleic acid is diluted in Opti-MEM Medium (Life Technologies) at a ratio of 1 ug to 50 uL medium. The diluted nucleic is then combined with a transfection reagent (Trans-IT for DNA, Trans-IT mRNA for mRNA, Trans-IT siRNA for siRNA, Mirus Bio) at a 1:1 volume ratio and allowed to form complexes for 5 minutes at room temperature. The nucleic acid complex is added to cells for 12-24 hours. Optionally, after this period of time, the media can be exchanged with fresh media such that the transfection reagents are no longer present. 
     2. Nucleic Acid—Viral Transduction 
     The gene of interest is cloned into the multiple cloning site of lentivirus vector pCDH with the MSCV promoter sequence from System Biosciences. 
     Lentivirus is produced in 293T cells by transfecting the cells with lipofectamine. 5×10{circumflex over ( )}6 293T cells (Lenti-X 293T Cell Line, Clontech catalog #632180) are plated in a P10 petri dish the day before transfection. Cell confluency should be around 70%. One plate is transfected per construct. 20 μl (10 μg) pPACKH1 (System Biosciences) plasmid mix+2 μg lenti construct+20 μl Plus reagent (LifeTechnologies, Catalog #11514-015) are combined in 400 μl Optimem and incubated 15 min at RT. 30 μl of LF2000 (LifeTechnologies, Catalog #11668-019) is diluted into 400 μl Optimem, added dropwise to DNA mix, and incubated for 15 min RT. DNA mix is added to cells (cells are in 9 ml of Optimem). Cells are incubated for 6 hours and then the medium is changed to DMEM/10% FBS. The virus supernatant is collected 48 hours post-transfection by centrifugation at 1,500 rpm for 5 minutes. The supernatant is collected and frozen in 1 ml aliquots at −80° C. 
     Target cells are transduced at day 3-7 of the culture process described herein. 5×10{circumflex over ( )}5 cultured cells are plated in 500 μL of medium containing 20 μg/mL polybrene in a 24-well plate. For each virus, cells are transduced in triplicate wells. Virus supernatant is added in another 500 μL of medium and the sample is mixed by pipetting. Infection is achieved by spinoculation, spinning the plate at 2000 rpm for 90 minutes at room temperature. After spinoculation, the cells are incubated at 37 C overnight, and the next day 1 mL of fresh IMDM medium with appropriate cytokines is added. 
     3. Nucleic Acid—Cationic Polymer 
     An mRNA encoding the transgene of interest, and including an upstream promoter sequence and a downstream poly A tail, can be purchased from multiple commercial vendors (e.g., IDT-DNA, Coralville Iowa). RNA transfections are carried out using RNAIMax (Invitrogen, Carlsbad, Calif.) or TRANSIT-mRNA (Mims Bio, Madison, Wis.) cationic lipid delivery vehicles. RNA and reagent are first diluted in Opti-MEM basal media (Invitrogen, Carlsbad, Calif.). 100 ng/uL RNA is diluted 5× and 5 μL, of RNAIMax per μg of RNA is diluted 10×. The diluted components are pooled and incubated 15 minutes at room temperature before they are dispensed to culture media. For TRANSIT-mRNA transfections, 100 ng/uL RNA is diluted 10× in Opti-MEM and BOOST reagent is added (at a concentration of 2 μL, per μg of RNA), TRANSIT-mRNA is added (at a concentration of 2 μL, per μg of RNA), and then the RNA-lipid complexes are delivered to the culture media after a 2-minute incubation at room temperature. RNA transfections are performed in Nutristem xenofree hES media (STEMGENT®, Cambridge, Mass.) or Opti-MEM plus 2% FBS. Successful introduction of the mRNA transcript into host cells can be monitored using various known methods, such as a fluorescent label or reporter protein, such as Green Fluorescent Protein (GFP). Successful transfection of a modified mRNA can also be determined by measuring the protein expression level of the target polypeptide by e.g., Western Blotting or immunocytochemistry Similar methods may be followed for large volume scale-up to multi-liter (5-10,000 L) culture format following similar RNA-lipid complex ratios. 
     4. Nucleic Acid—Electroporation 
     mRNA encoding the transgene of interest, and including an upstream promoter sequence and a downstream poly A tail, can be purchased from multiple commercial vendors (e.g., IDT-DNA, Coralville Iowa). Electroporation parameters are optimized by transfecting erythroid lineage cells with mRNA transcripts and measuring transfection efficiency by quantitative RT-PCR with primers designed to specifically detect the exogenous transcripts. For certain cells preparations, discharging a 150 uF capacitor into 2.5×10{circumflex over ( )}6 cells suspended in 50 μl of Opti-MEM (Invitrogen, Carlsbad, Calif.) in a standard electroporation cuvette with a 2 mm gap is sufficient for repeated delivery in excess of 10,000 copies of modified mRNA transcripts per cell, as determined using the standard curve method, while maintaining high viability (&gt;70%). Cell density may vary from 1×10{circumflex over ( )}6 cell/50 μl to a density of 2.5×10{circumflex over ( )}6 cells/500 and require from 110V to 145V to transfect cells with similar efficiencies measured in transcript copies per cell. Large multi-liter (5-10,000 L) electroporation may be performed similar to large volume flow electroporation strategies similar to methods described with the above described constraints (Li et al., 2002; Geng et al., 2010). 
     5. Polypeptide—Liposome 
     Cells, including primary terminally-differentiated cells e.g., erythrocytes, can be loaded with exogenous protein on their surface and in their cytoplasm. The loading of proteins can be performed using liposomes. 
     Lipids (Pro-Ject reagent, Pierce) in organic solvent were dried under nitrogen into a thin film in glass scintillation vial. Approximately 2 uL lipids were used per 10{circumflex over ( )}5 cells. Polyclonal mouse IgG (Abeam) was labeled with Dylight-650 (Pierce) per manufacturer&#39;s instructions. Protein solution at 0.1 mg/mL in PBS was added to the dried lipid mixture. The solution was pipetted several times, incubated for 5 minutes at room temperature, then vortexed vigorously to generate encapsulating liposomes. Serum-free medium was added to bring the total volume to 500 uL per 10{circumflex over ( )}5 cells. The liposomal mixture was then incubated with the cells for 3-4 hours at 37 C. 
       FIG. 1A-1F  show the loading of an exogenous protein, in this case fluorescently-labeled IgG, into primary erythrocytes with liposomes. The loading is measured by flow cytometry. The loading is dose-dependent, as 0.06% of cells are fluorescent without liposomes, ˜60% of cells are fluorescent at a low liposome dose, and ˜85% of cells are fluorescent at a high liposome dose. The data in  FIG. 1A-1F  is strong proof that exogenous proteins can be loaded into erythroid cells with liposomes. 
     6. Polypeptide—Mechanical Disruption 
     Cells may be loaded using a microfluidic device containing 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 10 μm wide channels that transiently porate the cells, allowing a payload to enter when the cells are pressured through the system. 
     The silicon-based devices are fabricated at the Massachusetts Institute of Technology microfabrication facility using photolithography and deep reactive ion etching techniques. In this process, 6″ silicon wafers with a 450-μm thickness are treated with hexamethyldisilazane, spin coated with photoresist (OCG934; FujiFilm) for 60 s at 3,000 rpm, exposed to UV light (EV1; EVG) through a chrome mask with the constriction channel design, and developed in AZ405 (AZ Electronic Materials) solution for 100 s. After 20 min of baking at 90° C., the wafer is etched by deep reactive ion etching (SPTS Technologies) to the desired depth (typically 15 μm). The process is repeated on the opposite side of the wafer (i.e., the one not containing the etched channels) using a different mask, which contains the access hole patterns, and using a thicker photoresist AZ9260 (AZ Electronic Materials). Wet oxidation is then used to grow 100-200 nm of silicon oxide before the wafer is anodically bonded to a Pyrex wafer and diced into individual devices. Before each experiment, devices are visually inspected and mounted onto a holder with inlet and outlet reservoirs (all designed in-house and produced by Firstcut). These reservoirs interface with the device using Buna-N O-rings (McMaster-Carr) to provide proper sealing. The inlet reservoir is connected to a home-made pressure regulator system using Teflon tubing to provide the necessary driving force to push material through the device. A population of erythroid cells is first suspended in the desired delivery buffer [growth medium, PBS, or PBS supplemented with 3% FBS and 1% F-68 Pluronics (Sigma)], mixed with the desired delivery material, and placed in the device&#39;s inlet reservoir. This reservoir is connected to a compressed air line controlled by a regulator, and the selected pressure (0-70 psi) is used to drive the fluid through the device. Treated cells are then collected from the outlet reservoir. Cells are incubated at room temperature in the delivery solution for 5-20 min after treatment to ensure hole closure before being subjected to any further treatment. To deliver fluorescently labeled phenylalanine ammonia hydroxylase (PAH), the experiments are conducted as described above such that the delivery buffer contained 0.1-0.3 mg/mL PAH. GFP knockdown is measured as the percentage reduction in a cell population&#39;s average fluorescence intensity relative to untreated controls. 
     7. Polypeptide—Surface Conjugation 
     The cell surface is treated with Traut&#39;s reagent (2-iminothiolane HCl, Pierce) to thiolate primary amines Traut&#39;s reagent is dissolved in Tris buffer pH 8 with EDTA to prevent oxidation of sulfhydryls. Approximately 1 pmol Traut&#39;s reagent is used to treat 10{circumflex over ( )}6 cells. Incubate Traut&#39;s reagent with cells for 1 hour at room temperature. Remove excess or unreacted reagent by centrifugation and washing the cells. The number of available sulfhydryl groups can be measured using Ellman&#39;s Reagent. In the meantime, treat suitable receiver polypeptide with amine-to-sulfhydryl crosslinker, such as SMCC (Pierce) according to manufacturer&#39;s instructions. Excess crosslinking reagent is removed by desalting. The maleimide-functionalized protein is then incubated with the thiolated cells for several hours. Unreacted protein is separated from the conjugated cells by centrifugation and washing. 
     8. Polypeptide—Non-Covalent Surface Attachment 
     The gene for an antibody scFv against hepatitis B surface antigen (scFv, described in Bose 2003, Molecular Immunology 40:617) is fused to a 6-histidine (SEQ ID NO: 27) affinity tag and to the gene encoding the polypeptide sequence that binds mouse glycophorin A, HWMVLPWLPGTLDGGSGCRG (SEQ ID NO: 28), in a mammalian expression vector (Genlantis). The full fusion protein is produced by transient transfection of HEK-293T cells using standard methods and purified on a Ni-NTA affinity resin (Pierce) according to manufacturer&#39;s instructions. The purified fusion protein is incubated with mouse erythrocytes at &gt;100 nM concentration to allow for rapid equilibration and binding of the peptide to glycophorin A. 
     9. Polypeptide—Lipid Insertion into Membrane 
     Traut&#39;s reagent (Thermo Fisher) is used to generate sulfhydryl groups on an amine-containing suitable receiver polypeptide molecule following manufacturer&#39;s protocol. The reaction mixture is incubated for 1 h at room temperature (RT) on a shaker and washed through a spin desalting column (Zeba, MWCO 7K, Thermo Scientific) following the manufacturer&#39;s instructions to remove the unreacted Traut&#39;s reagent. The generation of sulfhydryl groups on the modified polypeptide is quantified using Ellman&#39;s Reagent (Pierce) based on the manufacturer&#39;s protocol. 
     DSPE-PEG 3400 -mal (1×10{circumflex over ( )}−3 M in PBS, 4 μL, molar ratio lipid:Polypeptide=1:1) (all lipids purchased from Avanti Polar Lipids and stored as chloroform solution under argon at −20 C) are added to the desalted polypeptide solution and incubated at RT on a shaker. After 1 h, the sample solution is filtered using a centrifugal filter device (Microcon, Millipore Co.) at 14 000 g for 15 min at 4° C. to remove the small molecules and suspended in 600 μL PBS (1 mg/mL polypeptide). 
     200 μL of whole blood is suspended in 1000 μL PBS and spun at 1500 g for 30 s, repeated four times. Finally, the RBCs are suspended in 800 μL PBS. The conjugation of RBC/DSPE-PEG-Polypeptide is prepared by mixing the above RBCs suspensions and various amounts of DSPE-PEG-Polypeptide solution (1 mg per mL) followed by incubation for 15-30 min at 37° C. The mixture is kept for 5 min at room temperature, then washed three times in PBS and resuspended to a final RBC concentration of 5×10{circumflex over ( )}8 per mL. An automated cell counter (Countess, Invitrogen) is used to measure the cell concentration. 
     10. Polypeptide—Hypotonic Loading 
     A suitable receiver polypeptide, in this instance mouse IgG, was purchased from Abeam and was added at 0.25 mg/mL to a RBC suspension in isotonic solution at a hematocrit (Hct) of 70%. The suspension was dialyzed in 250 mL of a hypotonic solution containing 10 mM sodium phosphate pH 7.4, 10 mM sodium bicarbonate, and 20 mM glucose, stirred at 15 rpm for 1 hour at 4 C. The cells were then isotonically resealed by adding 1/10 volume of resealing solution comprising 5 mM adenine, 100 mM inosine, 100 mM sodium pyruvate, 100 mM sodium phosphate, 100 mM glucose, 12% (w/v) NaCl at pH 7.4. Cells were then incubated at 37 C for 30 minutes. 
     11. Polypeptide—Cell-Penetrating Peptide 
     The manufacture of protamine-conjugated polypeptide is known in the art, see e.g., Kwon et al. 2009 J Contr Rel 139(3):182. 5 mg/ml of Low Molecular Weight Protamine (LMWP) in 50 mM HEPES buffer (pH 8) is mixed with the heterobifunctional cross-linker 3-(2-pyridyldithio)propionic acid N-hydroxysuccinimide (SPDP, Sigma-Aldrich) at a 1:10 molar ratio in DMSO and shaken for 1 h at room temperature. The reaction mixture is then treated with 50 mM dithiothreitol (DTT, Sigma-Aldrich) and the thiolated LMWP is purified by HPLC on a heparin affinity column. The product is collected by ultrafiltration, lyophilized, and stored at −20° C. until further use. 
     For conjugation, 5 mg/ml suitable receiver polypeptide is mixed with SPDP (40 μl of 0.1 M SPDP in ethanol to 1 ml protein solution) in phosphate buffer, and stirred at room temperature for 1 h. Unreacted SPDP is removed by rapid desalting and buffer exchange by FPLC with 0.1 M phosphate buffer (pH 7.4). Activated polypeptide is then conjugated with a 10-fold molar excess of the above-prepared LMWP-SH for 24 h at 4° C. The LMWP-polypeptide conjugates are isolated by ion-exchange chromatography using a heparin affinity column followed by five rounds of centrifugal filtration (molecular weight cut-off: 5,000 Da). Pooled LMWP-polypeptide conjugates are concentrated, and the degree of conjugation determined by MALDI-TOF mass spectroscopy. 
     For uptake experiments, fresh sheep erythrocytes (MP Biomedicals, Solon, Ohio) are suspended in Hank&#39;s balanced salt solution (HBSS) at a density of 5×10{circumflex over ( )}8 cells/ml, and are then incubated with a 0.5 mg/ml solution of the LMWP-polypeptide conjugates for 30 min at room temperature under gentle shaking. RBCs are then washed with HBSS and stored at 2-8 C. 
     12. Polypeptide—Chemical Permeability 
     3×10{circumflex over ( )}8 RBCs were preincubated for 30 mM with chlorpromazine (Sigma Aldrich) at 200 μM in Ringer&#39;s solution. Afterwards, the suitable receiver polypeptide was added in Ringer&#39;s solution (1 to 4 μM) to a final volume of 400 μl and incubated for 30 min at room temperature under mild agitation. After incubation, cells were washed twice, resuspended in Ringer and collected for analysis. 
     13. Polypeptide—Enzymatic Conjugation 
     Cell surface enzymatic conjugations with sortase are known in the art, see e.g., Shi et al PNAS 2014 111(28):10131. To label the GPA N terminus with polypeptide, 30 uL of 500 uM  S aureus  sortase and 1 mM polypeptide with LPETGG (SEQ ID NO: 29) at the C terminus is preincubated in 50 mM Tris pH 7.5, 150 mM NaCl, on ice for 15 minutes and added to 5×10{circumflex over ( )}7 RBCs in DMEM. The sortase and cell mixture is incubated on ice for 30 min with occasional gentle mixing, then spun at 500×g for 2 mM at 4 C to remove buffer/DMEM, then washed three times with 1 mL of ice-cold PBS. 
     14. Gas 
     The following steps are taken to load erythroid cells with nitric oxide (NO). To avoid oxidative side reactions or S-nitrosylation of erythrocytic proteins other than Hb by S-nitrocysteine (CSNO), S-nitrosothiol (SNO)Hb is synthesized in intact RBCs by (i) addition of aqueous NO to fully deoxygenated RBCs to yield Fe-nitrosylHb [HbFe(II)NO]; (ii) washing under anaerobic conditions; and (iii) reoxygenation, effecting intraerythrocytic intramolecular transfer of NO from heme [Fe(II)NO] to Cys-B93. Sulfanilamide [SA; 3.4% (wt_vol)] in 0.4MHCl is prepared with and without 1% (wt/vol) HgCl2, as is 0.1% (wt/vol) of N-(1-naphthyl)ethylenediamine (NED). Equal volumes of SNOHb are added to SA with or without HgCl2 and then reacted with NED. [SNO] is determined from the difference in absorbance (540 nm) using colorimetry. 
     15. Small Molecule (Cytoplasm) 
     Liposomal ProJect reagent (Pierce) is dried under nitrogen into a thin film in glass scintillation vials. Approximately 2 uL reagent is needed per 10{circumflex over ( )}5 cells. Solution of small molecule of interest in PBS is added to the dried liposome reagent. The solution is pipetted several times, incubated for 5 minutes at room temperature, then vortexed vigorously to generate encapsulating liposomes. Serum-free medium is added to bring the total volume to 500 uL per 10{circumflex over ( )}5 cells. The liposomal mixture is incubated with the cells for 3-4 hours at 37° C. 
     16. Small Molecule (Surface) 
     The conjugation of small molecules to the surface of cells using chemical functionalities is well known in the art, see e.g., Hermanson G T, Bioconjugation Techniques 2 nd  Ed, ISBN 978-0123705013. Briefly, the small molecule of interest is provided with an amine-reactive functional group, such as NHS ester, for example NHS ester biotin (Pierce). The small molecule of interest is stored in organic solvent to prevent hydrolysis of the NHS ester functional group. The small molecule of interest is incubated with cells in aqueous medium in large molar excess (at least 10 pmol for 10{circumflex over ( )}6 cells) to drive conjugation to primary amines on the cell surface. After 1 hr incubation, the excess unreacted molecule is removed by centrifugation and washing of the cells. 
     Example 8: Assessment of Polypeptide Presence 
     1. Fluorescent Transgene 
     Erythroid cells were cultured as described herein. A transgene encoding glycophorin A with an HA tag on the C-terminus fused to GFP with an intervening viral T2A peptide was constructed by Gibson assembly as described herein. The transgene was introduced into the erythroid cells by lentiviral transduction as described herein. Two days after transduction, cells were collected, washed in PBS buffer, and analyzed on a flow cytometer (Attune, Life Technologies). Transduction efficiency was assessed as the percentage of GFP-positive cells in the population. 
     2. Cell Surface Proteins 
     For cell surface proteins, the level of protein expression can be detected as early as 2 days after transfection by flow cytometry with antibodies specific for the protein or for a co-expressed epitope tag. Erythroid cells were cultured as described herein. A transgene encoding glycophorin A with an HA tag at the N-terminus was constructed by Gibson assembly as described herein. The transgene was introduced into the erythroid cells by lentiviral transduction as described herein. Two days after transduction, cells were collected, washed in PBS buffer, and stained with 1:50 dilution of mouse anti-HA antibody (Abcam) for 1 hr. Cells were washed and then stained with a 1:100 dilution of alexa 488-labeled goat anti-mouse secondary antibody (Life Technologies) for 30 minutes on ice. Cells were washed and analyzed on a flow cytometer (Attune, Life Technologies). Transduction efficiency was assessed as the percentage of alexa 488-positive cells in the population. 
     3. Intracellular Proteins 
     For intracellular proteins, the level of protein expression can be detected as early as 8-12 hours after transfection by Western Blot. Erythroid cells were cultured as described herein. A transgene encoding adenosine deaminase with an HA tag at the C-terminus was constructed by Gibson assembly as described herein. The transgene was introduced into the erythroid cells by lentiviral transduction as described herein. Two days after transduction, cells were collected, washed in PBS buffer, and lysed in RIPA cell lysis buffer (Pierce). Cell lysate was denatured by boiling in 100 mM DTT, then loaded onto a NuPage SDS-PAGE pre-cast gel. After electrophoresis and transfer to nitrocellulose membrane, protein bands were developed by staining with 1:5000 dilution of mouse anti-HA antibody (Abcam) followed by 1:5000 dilution of goat anti-mouse HRP (Pierce), and subsequent treatment with HRP substrate (SuperSignal, Pierce). Images were captured using an Amersham imager (GE healthcare). 
     Example 9: Assessment of Small Molecule Presence 
     Eyrthrocytes from a normal human donor were purchased (Research Blood Components). Cells were then biotinylated with NHS-biotin (Sigma) per manufacturer&#39;s instructions using 0.02× volumes of 2 mM stock biotin reagent for 30 minutes at room temperature. Anti-biotin antibody (Abcam) was fluorescently labeled with Dylight 650 (Pierce). Labeling efficiency of the cells was assessed by flow cytometry as described herein using the labeled anti-biotin antibody as a detection marker. 
     Example 10: Assessment of Gas Level 
     A standard protocol is used to determine NO2- and NO3-levels in the three blood components, see e.g., Yang et al. 2003, Free Radic Res 37(1):1. Briefly, a “stop solution” (K3Fe(CN)6, N-ethylmaleimide, water, NP40) is added to blood to maintain nitrite levels until sample analysis. A 1:4 dilution of “stop solution” to blood is vortexed and placed on dry ice. At the time of sample analysis, a 1:1 dilution of 99.9% pure methanol and thawed sample is centrifuged for 2 min at 13,000 rpm; the supernatant is immediately injected into the chemiluminescent nitric oxide analyzer (NOA, Sievers, Model 280 NO analyzer, Boulder, Colo.) using helium as the carrier gas. The triiodide (I3−) ozone-based chemiluminescent assay is used to analyze nitrite levels. To analyze nitrate, deionized water (Millipore CQ-Gard, Bedford, Mass.) is added to blood to lyse cells. A 9:1 dilution of deionized water to blood is vortexed and placed on dry ice. At the time of sample analysis, a 3:1 dilution of pure HPLC grade ethanol and thawed sample is centrifuged, and the supernatant is immediately analyzed using a Vanadium(III)chloride chemiluminescent assay, see e.g., Ewing and Janero, 1998 Free Radic Biol Med 25(4-5):621. The VCl3 reaction solution is maintained at 90° C. with helium as the carrier gas. 1 μM nitrite and nitrate solutions are used to generate standard curves for comparisons and adjustments of sample nitrite and nitrate concentrations. 
     A thiol-stabilization solution (NEM-DPTA; K3Fe(CN)6, N-ethylmaleimide, Diethylenetriaminepenta acetic acid, NP40, water) is added to blood to maintain SNOHb and HbNO levels by inhibiting additional thiol reactions. A 4:1 dilution of NEM-DPTA to blood is vortexed and placed on dry ice. A 9:1 dilution of sample and 5% acid sulfanilamide (AS) is incubated for 5 min; half is injected into the NOA (I3− assay) to give combined SNOHb and HbNO levels. The remaining sample is incubated with 50 mM HgCl2, then incubated again with 5% AS, and injected into the NOA to give HbNO levels. 
     Example 11: Assessment of Expression and Activity 
     The expression of exogenous proteins in and on cultured cells can be assessed quantitatively by flow cytometry (if the protein is expressed on the surface) or by Western blot (for proteins expressed in the cytoplasm). 
     1. Quantitative Flow Cytometry 
     Anti-mouse Fc-binding quantitative flow cytometry beads (Simply Cellular Calibration) were purchased from Bangs Labs. Fluorescently labeled mouse antibodies against relevant cell surface receptors—glycophorin A, Ckit, and transferrin receptor—were purchased from BioLegend. Fluorescently labeled mouse antibody against the HA epitope tag was purchased from Life Technologies. Erythroid cells were cultured as described herein. A transgene encoding glycophorin A with an HA tag at the N-terminus was constructed by Gibson assembly as described herein. The transgene was introduced into the erythroid cells by lentiviral transduction as described herein. At least two days after transduction, 2×10{circumflex over ( )}5 cells were collected, washed in PBS buffer, and stained with 1:100 dilution of one of the above-listed antibodies for 1 hr. Cells were washed and analyzed on a flow cytometer (Attune, Life Technologies). The protocol was repeated for each of the four antibodies listed above. Quantification was performed according to manufacturer&#39;s instructions. Briefly, one drop of each of the five bead samples was incubated with 1:100 dilution of an above-listed antibody. The beads were incubated for 1 hr, washed in PBS, and analyzed on a flow cytometer (Attune, Life Technologies). The protocol was repeated for each of the four antibodies listed above. Calibration curves were fit using the manufacturer&#39;s provided excel spreadsheets, from which quantification of fluorescence intensity for the cell-based signals was derived. 
     2. Quantitative Western Blot 
     Erythroid cells were cultured as described herein. A transgene encoding adenosine deaminase with an HA tag at the C-terminus was constructed by Gibson assembly as described herein. The transgene was introduced into the erythroid cells by lentiviral transduction as described herein. Two days after transduction, cells were collected, washed in PBS buffer, and lysed in RIPA cell lysis buffer (Pierce). 
     The transgene was introduced into HEK293T cells by transient transfection using lipofectamine 2000 (Life technologies). Cells were cultured for one week and the supernatant was harvested. Recombinant protein was purified on an HA affinity column (Pierce) according to manufacturer&#39;s instructions. Protein concentration was assessed by absorbance at 280 nm. 
     Western blotting was performed as described herein. In addition to the cell lysate samples, known amounts of the recombinant adenosine deaminase were run on the same gel. Following image collection, the intensity of the recombinant bands were used to generate a standard curve to quantify the amount of protein present in the cell samples. 
     The robust expression of transgenes at high levels has important implications for the therapeutic capacity of the final cell population.  FIG. 2  quantifies the expression of three surface proteins indicative of differentiation and one exogenous transgene by quantitative flow cytometry, and demonstrates that the transgene is robustly expressed at a high level. 
     Erythroid cells in culture were collected at seven time points during a four-stage in vitro differentiation process. At the first time point (“Expand D6”) the cells are nucleated hematopoietic precursors. By the final time point (“Diff 3 D8”) the cells are predominantly enucleated erythroid cells. GPA (solid triangles), a canonical marker of erythroid cells, starts low in the precursor cells and rapidly reaches &gt;1×10{circumflex over ( )}6 copies per cell. CKIT (dashed squares), a receptor for stem cell factor, starts high then decreases to &lt;1×10{circumflex over ( )}4 copies per cell as differentiation ensues. TR (dotted diamonds), necessary for the transport of iron into erythroid cells, increases initially then gradually declines to &lt;1×10{circumflex over ( )}5 copies per cell. The transgene (open circles) is introduced at the end of the second differentiation stage (“Diff 1”) and is steadily expressed at approximately 1×10{circumflex over ( )}5 copies per cell throughout differentiation. The above data demonstrate that transgenes are robustly expressed in cultured cells. 
     The expression of exogenous proteins in and on cultured cells can be assessed by flow cytometry (if the protein is expressed on the surface) as described herein, or by Western blot (for proteins expressed in the cytoplasm) as described herein. In instances where an exogenous gene is in a single-transcript construct that contains a downstream fluorescent reporter protein, the fluorescence of the reporter protein can be used as a proxy for expression of the upstream gene, and assessed by flow cytometry as described herein. 
       FIG. 3A - FIG. 3N  shows the exogenous expression of surface and cytoplasmic proteins on enucleated cultured erythroid cells. The above data conclusively demonstrate that multiple protein classes—including cytoplasmic, surface, intact, fusions to type I membrane proteins, fusions to type II membrane proteins, fusions to GPI-linked membrane proteins, intracellular fusions, overexpressed, and de novo expressed—can be expressed on multiple cell types including cultured enucleated erythroid cells, cultured nucleated erthyroid precursor cells, and K562 erythroleukemia cells. 
       FIG. 3B  and  FIG. 3D  demonstrate the simultaneous expression of two exogenous proteins in an enucleated cultured cell. 
     In  FIG. 3B , Erythroid cells were cultured as described herein. A transgene construct encoding glycophorin A signal sequence, an HA epitope tag, glycophorin A coding sequence, viral T2A cleavable sequence and GFP was assembled by Gibson assembly as described herein. The transgene was introduced into the erythroid cells by lentiviral transduction as described herein. The cells were cultured to terminal differentiation as described herein. Cells were analyzed by flow cytometry as described herein, using a fluorescent anti-HA antibody and GFP fluorescence to detect expression of both transgenes. 
     In  FIG. 3D , Erythroid cells were cultured as described herein. A transgene construct encoding glycophorin A signal sequence, antibody scFv specific to hepatitis B surface antigen, HA epitope tag, glycophorin A coding sequence, viral T2A cleavable sequence and GFP was assembled by Gibson assembly as described herein. The transgene was introduced into the erythroid cells by lentiviral transduction as described herein. The cells were cultured to terminal differentiation as described herein. Cells were analyzed by flow cytometry as described herein, using a fluorescent anti-HA antibody and GFP fluorescence to detect expression of both transgenes. 
     Example 12: Expression of Protein from mRNA in Platelets 
     The expression in platelets of exogenous proteins translated from exogenous transfected mRNA was measured by flow cytometry. In brief, platelet-enriched serum was centrifuged at 190 g for 15 minutes to remove erythrocytes and leukocytes. The supernatant was then spun for an additional 5 minutes at 2500 g to pellet platelets. Platelets were resuspended in 5 mL of Tyrode&#39;s buffer with 1 uM prostaglandin, washed, and resuspended in 750 uL of Tyrode&#39;s buffer with 1 uM prostaglandin. mRNA encoding the gene of interest, in this example GFP, was mixed with lipofectamine at a 1:1 mg/mL ratio. The mixture was incubated for 5 minutes, then added to the washed platelet population. The combination was incubated for 24 hours at room temperature with slow rocking. Platelet expression of the transgene was assayed by flow cytometry measuring GFP fluorescence. Surface proteins can also be assayed by flow cytometry. Cytoplasmic or other intracellularly-expressed proteins can also be assayed by Western blot. 
     There is therapeutic relevance to introducing exogenous proteins into and onto platelets. Since platelets do not possess a nucleus or RNA transcription machinery, DNA transfection is not a viable means of inducing exogenous protein expression in platelets. However, mRNA transfection and translation is a way of introducing exogenous proteins into cells. It is thought that platelets contain mRNA translation machinery, but until now it was not known whether they are able to accept and translate exogenous mRNA into protein. 
       FIGS. 4A-4C  is a collection of flow cytometry plots that demonstrate the translation of exogenous mRNA encoding a transgene, in this case GFP, by platelets. The GFP is detected by fluorescence in the FL1 channel after excitation with a 488 nm laser. ( FIG. 4A ) Untransfected platelets (1.7% GFP+). ( FIG. 4B ) Platelets transfected with 3 ug GFP mRNA (8.6% GFP+). ( FIG. 4C ) Platelets transfected with 6.8 ug GFP mRNA (3.3% GFP+). 
     The data conclusively demonstrate, for the first time, the translation of exogenous mRNA into exogenous protein by platelets. 
     Example 13: Activity of Enzymes 
       FIGS. 5A-5D  demonstrate the activity for enzymes contained on erythroid cells. Biochemical activity of cytoplasmic enzymes was assessed by Western blot for retention of a protein over the course of differentiation. Biological activity of cytoplasmic enzymes was assessed by in vitro enzymatic activity assay. 
       FIGS. 5A-5D  show the activity of two different intracellular enzymes expressed in cultured erythroid cells. 
     1. Adenosine Deaminase. 
     A transgene encoding adenosine deaminase with an HA tag at the C-terminus was constructed by Gibson assembly as described herein. The transgene was introduced into HEK-293T cells by lipofectamine transfection (Life Technologies) as described herein. Enzymatic activity is assayed using a protocol derived from Helenius 2012, Biochim Biophys Acta 1823(10):1967, in which a specific mixture of enzymes convert purines into uric acid and H2O2 followed by fluorometric detection of the generated H2O2. In brief, two days after transfection, cells were collected, media aspirated, and Krebs Ringer phosphate glucose (KRPG; comprising: 145 mM NaCl, 5.7 mM sodium phosphate, 4.86 mM KCl, 0.54 mM CaCl2, 1.22 mM MgSO4, and 5.5 mM glucose; pH 7.35) added to the cells at 2×10{circumflex over ( )}5 cells/mL. Adenosine was added at 50 uM. After reaction for 6 hours, supernatant was collected and heat inactivated for 5 minutes at 60 C. Aliquots of supernatant were transferred to wells in a white 96-well microplate containing 0.25 U/ml bacterial purine nucleoside phosphorylase (PNP) and 0.15 U/ml microbial xanthine oxidase (XO), both from Sigma. After 20 min incubation at RT, 30 μl of H2O2-detecting mixture containing HRP (final concentration 1 U/ml, Sigma) and Amplex Red reagent (60 μM, Invitrogen, Molecular Probes) was added to the microwells, followed by measurement of the fluorescence intensity at the emission and excitation wavelengths of 545 and 590 nm, respectively (Tecan Infinite M200). 
     2. Phenylalanine Hydroxylase 
     Erythroid cells were cultured as described herein. A transgene encoding phenylalanine hydroxylase with an HA tag at the C-terminus was constructed by Gibson assembly as described herein. The transgene was introduced into the erythroid cells by lentiviral transduction as described herein. Two days after transduction, cells were collected, washed in PBS buffer, and lysed in RIPA cell lysis buffer (Pierce). Cell lysates (64 ug total protein) were added to 1 mL reaction buffer containing 100 mM Tris-HCl, pH 7.5, 4 mM DTT, 4 mM Phenylalanine, 33 pg catalase, and 0.4 mM DMPH4 (all from Sigma). Reactions were run overnight at 37 C. After incubation, samples were de-proteinized by centrifugal filtration in an Amicon Ultra-4 Centrifugal Filter 10 KD (Millipore UFC801024) spinning at 3700 rpm for 10 min Samples were collected and assayed for tyrosine concentration by absorbance at 540 nm. 
     Both of these exogenous proteins were retained through the end of terminal differentiation, a non-trivial feat given that it is well-known in the field that erythroid cells undergo a rigorous program of elimination of proteins unnecessary for basic function (Liu J et al. (2010) Blood 115(10):2021-2027, Lodish H F et al. (1975) Developmental Biology 47(1):59). In  FIG. 5A , the exogenously over-expressed protein adenosine deaminase is detected by anti-HA Western blot at various time points over the course of differentiation, from nucleated precursor cells (“Diff I D5”) through to enucleated erythroid cells (“Diff III D8”). In  FIG. 5C , the exogenously expressed microbial protein phenylalanine hydroxylase is detected by anti-HA Western blot at various time points over the course of differentiation, from nucleated precursor cells (“Diff I D5”) through to enucleated erythroid cells (“Diff III D8”). 
     Additionally, both of these enzymes maintained their ability to enzymatically convert substrate into product.  FIG. 5B  shows the enzymatic conversion of adenosine to inosine by intact adenosine deaminase-expressing 293T cells.  FIG. 5D  shows the enzymatic conversion of phenylalanine to tyrosine by lysates of cultured phenylalanine hydroxylase-expressing enucleated erythroid cells. 
     These data conclusively demonstrate that exogenous enzymes are retained on erythroid cells throughout the culture process and that they are enzymatically active in erythroid cells, which has profound therapeutic implications. 
     Example 14: Activity of CR1 
       FIGS. 6A-6B  show both biochemical and biological activity for complement receptor 1 (CR1) over-expressed on the surface of cultured erythroid cells. Biochemical activity of CR1 was assessed by flow cytometry for binding to an immune complex. Biological activity of CR1 was assessed by transfer of immune complexes to macrophages in a co-culture assay. 
     1. Immune Complex Binding of CR1-Expressing Cells. 
     Erythroid cells were cultured as described herein. A transgene construct encoding complement receptor 1 (CR1) was constructed by Gibson assembly as described herein. The transgene was introduced into the erythroid cells by lentiviral transduction as described herein. Transgene expression levels were assessed by flow cytometry as described herein using an anti-CR1 antibody (Abcam). The cells were cultured to terminal differentiation as described herein. 
     Dylight 650-labeled bovine serum albumin (BSA-650) was incubated with polyclonal rabbit anti-BSA (Abcam) in an excess of antibody for 30 minutes at room temp. The complexes were then mixed with human serum at a 1:1 volume ratio for 30 minutes at 37 C. Control complexes were either not mixed with human serum or mixed with heat-inactivated human serum. 
     Complexes were incubated with the CR1-expressing cells for 30 minutes at 37 C. Cells were washed and analyzed by flow cytometry for capture of immune complexes by detecting Dylight 650 fluorescence. 
     2. Immune Complex Transfer to Macrophages 
     Cultured U937 monocytes were activated by incubation with 100 nM phorbol myristate acetate (PMA) for 24 hours at 37 C. Cells coated with immune complexes (see above) were incubated with activated U937 macrophages for 30 minutes at 37 C. The co-culture was analyzed by flow cytometry. Macrophages were identified by FSC/SSC gating. Presence of immune complex on macrophages was analyzed by detecting Dylight 650 fluorescence in the macrophage population. 
       FIGS. 6A-6B  shows the biochemical and biological activity of complement receptor 1 (CR1) exogenously over-expressed on cultured erythroid cells. 
       FIG. 6A  shows the biochemical activity of CR1, defined as the capture of immune complexes in vitro. The black histogram shows the capture of BSA-based immune complexes by CR1 over-expressed on cultured erythroid cells. The shaded histogram shows the minimal background binding to complexes of BSA and IgG that lack human complement, demonstrating that the binding event is CR1-mediated. 
       FIG. 6B  shows the biological activity of CR1, defined as the transfer of captured immune complexes from cultured erythroid cells to macrophages. This is a standard assay in the field, see: Repik et al. 2005 Clin Exp Immunol. 140:230; Li et al. 2010 Infection Immunity 78(7):3129. Transfer is assessed by flow cytometry and measured as the intensity of labeled immune complex-derived fluorescence on macrophages. In this assay, macrophages that are incubated with no immune complexes (black bars) do not become fluorescent. Macrophages that are incubated with complexes of BSA and IgG that lack complement (and therefore do not bind CR1) take up only a small amount of immune complex (solid gray bars), independent of the presence of cultured CR1-overexpressing erythroid cells. This uptake is likely due to Fc-gamma receptors on the U937 cells interacting with the Fc regions of the IgG molecules. Macrophages that are incubated with immune complexes (BSA+IgG+ complement) in the absence of CR1-overexpressing cells (hashed bar, left) take up the same amount of immune complex as in the absence of complement, likely by the same Fc-gamma mediated method. However, the macrophages that are incubated with immune complexes in the presence of CR1-overexpressing cells (hashed bar, right) take up nearly double the number of immune complexes as measured by fluorescence. 
     These data conclusively demonstrate that CR1 overexpression on cultured erythroid cells enables the capture of immune complexes on said erythroid cells, facilitates the transfer of immune complexes from erythoroid cells to macrophages, and significantly increases the rate and number of immune complexes taken up by macrophages. 
     Example 15: Activity of scFv 
       FIG. 7A-7B  show the biochemical and biological activity of antibody scFv exogenously expressed on the surface of cultured erythroid cells as a fusion to the transmembrane protein GPA. 
     Erythroid cells were cultured as described herein. A transgene construct encoding the leader sequence of glycophorin A, an antibody scFv specific to hepatitis B surface antigen (scFv, described in Bose 2003, Molecular Immunology 40:617), an HA epitope tag, a [Gly-3-Ser]2 flexible linker, and the body of glycophorin A was assembled by Gibson assembly as described herein. The transgene was introduced into the erythroid cells by lentiviral transduction as described herein. Transgene expression was assessed by flow cytometry as described herein using an anti-HA antibody (Abcam). The cells were cultured to terminal differentiation as described herein. Biochemical activity of the antibody scFv was assessed by flow cytometry for binding to the target protein, in this case hepatitis B surface antigen (HBsAg). Recombinant HBsAg protein (Abcam) was labeled with Dylight-650 fluorophore (Pierce). scFv-expressing cells were incubated with 100 nM labeled protein, washed in PBS, and analyzed for Dylight 650 fluorescence by flow cytometry as described herein. 
     Biological activity of the antibody scFv was assessed by in vivo capture of HBsAg detected by flow cytometry. Recombinant HBsAg protein (Abcam) was labeled with Dylight-650 fluorophore (Pierce). scFv-expressing cells were fluorescently labeled with CFSE (Sigma) Immunocompromised NSG mice (Jackson labs) were injected with ˜400 pmol of the labeled HBsAg into the tail vein. A few minutes later, the same mice were injected with 2×10{circumflex over ( )}7 scFv-expressing cells. Blood was collected by submandibular puncture at regular intervals in an EDTA-containing tube. Collected blood cells were washed and analyzed by flow cytometry as described herein. Human cells were identified as those that were CFSE positive. Capture of HBsAg was detected as Dylight 650 fluorescence on the human cells. 
       FIGS. 7A-7B  show the biochemical activity of antibody scFv, defined as the binding of its cognate antigen, hepatitis B surface antigen (HBsAg). In  FIG. 7A , cells that express (black) or do not express (gray shaded) the antibody scFv are incubated with 450 nM HBsAg and stained with biotinylated anti-HBsAg antibody and fluorescent streptavidin. Cells that express the antibody scFv (˜45% of the cells in this culture) bind to the antigen. In  FIG. 7B , cells that express the antibody scFv are incubated with various concentrations of HBsAg and stained as above, showing that the binding event is dose-dependent with an affinity of approximately 10 nM. 
       FIGS. 7C-7D  show the biological activity of antibody scFv, defined as the capture of cognate antigen HBsAg while in circulation in a mouse. In this experiment, immunocompromised NSG mice were injected with ˜400 pmol fluorescently-labeled HBsAg via the tail vein. Five minutes later, cultured enucleated erythroid cells ( FIG. 7C ) or cultured enucleated erythroid cells that expressed exogenous antibody scFv ( FIG. 7D ) were injected via the tail vein. Prior to injection, all cultured cells were labeled with CFSE fluorescent dye. Blood was collected 6 hours later, analyzed on a flow cytometer, and gated on CFSE+ human cells. Bare cultured cells did not bind to HBsAg ( FIG. 7C ), whereas antibody scFv-expressing cells do bind to HBsAg ( FIG. 7D ). Consistently with the biochemical activity experiment, approximately 45% of the cells in this culture express antibody-scFv. 
     These data demonstrate that the antibody scFv is biochemically active when expressed on the surface of cultured erythroid cells and that the antibody scFv on the erythroid cell is able to bind its target in vivo when in circulation. This has profound implications for therapeutic approaches in which the capture, sequestration, and clearance of a substance in circulation is desired. 
     Example 16: Activity—Circulating Clearance 
       FIGS. 8A-8D  show both biochemical and biological activity for surface molecule capture agents used for circulating clearance of a target. 
     Biochemical activity of the capture agents, in this case HA polypeptide and biotin, was assessed by flow cytometry for binding to the target protein, in this case anti-HA antibody and anti-biotin antibody. Biological activity of the capture agents was assessed by in vivo capture and clearance of target protein as detected by flow cytometry and plasma protein quantification. 
     1. Capture of Anti-Biotin Antibody by Chemically-Modified Cells 
     Eyrthrocytes from a normal human donor were purchased (Research Blood Components). Cells were labeled with CFSE (Sigma) per manufacturer&#39;s instructions for 20 minutes at 37 C. Cells were then biotinylated with NHS-biotin (Sigma) per manufacturer&#39;s instructions using 0.02 volumes of 2 mM stock biotin reagent for 30 minutes at room temperature. Anti-biotin antibody (Abcam) was fluorescently labeled with Dylight 650 (Pierce). Labeling efficiency of the cells was assessed by flow cytometry using the labeled anti-biotin antibody and CFSE fluorescence as detection markers. 250 ug labeled antibody was injected into an NSG mouse (Jackson Labs) intravenously via the tail vein. Four hours later 1×10{circumflex over ( )}8 biotinylated cells were injected intravenously via the tail vein. Blood was collected by submandibular puncture at regular intervals in an EDTA-containing tube. Collected blood cells were washed and analyzed by flow cytometry as described herein. Human cells were identified as those that were CFSE positive. Capture of anti-biotin antibody was detected as Dylight 650 fluorescence on the human cells. Plasma from the blood draw was analyzed by ELISA using a biotin-coated microplate (Pierce) per manufacturer&#39;s instructions to detect the level of antibody in circulation. 
     2. Capture of Anti-HA Antibody by Transgenic Cultured Cells 
     Erythroid cells were cultured as described herein. A transgene construct encoding glycophorin A signal sequence, an HA epitope tag, glycophorin A coding sequence, viral T2A cleavable sequence and GFP was assembled by Gibson assembly as described herein. The transgene was introduced into the erythroid cells by lentiviral transduction as described herein. The cells were cultured to terminal differentiation as described herein. Cells were analyzed by flow cytometry as described herein, using an anti-HA antibody (Life Technologies) fluorescently labeled with Dylight 650 (Pierce) and GFP fluorescence to detect expression of both transgenes. 250 ug labeled anti-HA antibody was injected into an NSG mouse (Jackson Labs) intravenously via the tail vein. Four hours later 1×10{circumflex over ( )}8 cultured cells were injected intravenously via the tail vein. Blood was collected by submandibular puncture at regular intervals in an EDTA-containing tube. Collected blood cells were washed and analyzed by flow cytometry as described herein. Human cells were identified as those that were CFSE positive. Capture of anti-HA antibody was detected as Dylight 650 fluorescence on the human cells. Plasma from the blood draw was analyzed by ELISA using an HA peptide-coated microplate (Pierce) per manufacturer&#39;s instructions to detect the level of antibody in circulation. 
       FIGS. 8A-8D  show biochemical and biological activity of ( FIG. 8A-8B ) the polypeptide HA expressed on the surface of cultured erythroid cells as a fusion to GPA and of ( FIG. 8C-8D ) biotin chemically conjugated to the surface of primary erythrocytes. Biochemical activity is defined as the capture of a target protein in vitro. Biological activity is defined as the enhanced clearance of a target protein in vitro. 
     In  FIG. 8A , the HA polypeptide, expressed as a fusion to the N terminus of GPA, captures a mouse anti-HA antibody in vivo. NSG mice were injected with fluorescently-labeled mouse anti-HA antibody, followed by injection of cultured human erythroid cells that either do not (left) or do (right) express HA epitope tag on their surface as a fusion to GPA. Blood was drawn and cells analyzed on the flow cytometer. The x-axis measures CFSE fluorescence. The y-axis measures anti-HA antibody Dylight 650 fluorescence. CFSE-positive cultured human erythrocytes are observed in both samples, but only the cells expressing the HA epitope tag are able to capture circulating anti-HA antibody. 
     In  FIG. 8B , mice were injected with anti-HA antibody then then optionally with cultured human erythroid cells that either do not or do express HA peptide on their surface as a fusion to GPA. Plasma was collected at multiple time points and the level of anti-HA antibody in plasma was assessed by ELISA using an HA peptide-coated plate as a substrate. Mice injected with anti-HA antibody alone (open circles, solid line—this mouse died after 120 minutes of causes unrelated to treatment) or with anti-HA antibody followed by cells that do not express HA peptide on their surface (dashed line) have significant antibody in circulation out to 24 hours post injection of cells. In contrast, mice injected with anti-HA antibody followed by cells that express HA peptide on their surface are depleted of target antibody within minutes. This data conclusively demonstrates that the target antibody is rapidly and specifically cleared from circulation by cultured erythroid cells that express receiver polypeptide on their surface. 
     In  FIG. 8C , the biotin molecule, conjugated to the surface of erythroid cells by amine functionalization chemistry, captures a mouse anti-biotin antibody. In both of these cases capture was assessed by flow cytometry. Cells that are CFSE labeled and biotinylated show up as double positive when stained with a fluorescent anti-biotin antibody (lower dot plot), whereas CFSE-labeled cells that are not biotinylated only show up as single positive (upper dot plot). 
     In  FIG. 8D , mice were injected with anti-biotin antibody then then optionally with cultured human erythroid cells that either are not or are conjugated to biotin on their surface. Plasma was collected at multiple time points and the level of anti-biotin antibody in plasma was assessed by ELISA using a biotin-coated plate as a substrate. Mice injected with anti-biotin antibody alone (open circles, solid line) or with anti-biotin antibody followed by cells that are not conjugated to biotin on their surface (dashed line) have significant antibody in circulation out to 24 hours post injection of cells. In contrast, mice injected with anti-biotin antibody followed by cells that are conjugated to biotin on their surface are depleted of target antibody within minutes. This data conclusively demonstrates that target antibodies are rapidly and specifically cleared from circulation by cultured erythroid cells that contain receiver polypeptide on their surface. 
     Together the data conclusively demonstrate that suitable receivers on membrane-receiver complexes are able to bind their target molecules in vivo and mediate rapid circulating clearance of target molecules when in circulation, which has profound therapeutic implications. 
     Example 17: Activity of Complement Regulators 
     The complement regulatory activity of the synthetic membrane-receiver complexes is assessed by standard CH50 and AH50 assays known in the art (see e.g., Kabat et al. 1961 Exp Immunochem pp. 133-239 and Platts-Mills et al. 1974 J Immunol 113:348). 
     Briefly, the CH50 assay utilizes sheep erythrocytes (SRBC) as target cells. Briefly, a suspension containing 1×10{circumflex over ( )}9 SRBC/ml is prepared in the GVB(2+) buffer (gelatin/Veronal-buffered saline with Ca2+ and Mg2+), pH 7.35. Hemolysin (rabbit anti-sheep antiserum) is titrated to determine the optimal dilution to sensitize SRBC. Diluted hemolysin (1:800) is mixed with an equal volume of SRBC (1×109 SRBC/ml), and the whole is incubated at 37° C. for 15 minutes. This results in 5×10{circumflex over ( )}8/ml antibody-coated erythrocytes (EA). EA (100 μl) are incubated with 100 μl of five serial twofold dilutions (1:20, 1:40, 1:80, 1:160, and 1:320) of the normal human serum (NHS) or similar dilution of the mixture of NHS and the membrane-receiver complex at 37° C. for 1 hour. NHS incubated with GVB2+ buffer is used as the control. Background control is obtained by incubating EA with buffer alone (serum is not added), and total lysis (100% hemolysis) is determined by adding distilled water to EA. The reaction is stopped using 1.2 ml of ice-cold 0.15 M NaCl, the mixture is spun to pellet the unlysed cells, and the optical density of the supernatant is determined spectrophotometrically (412 nm). The percentage of hemolysis is determined relative to the 100% lysis control. Complement activity is quantitated by determining the serum dilution required to lyse 50% of cells in the assay mixture. The results are expressed as the reciprocal of this dilution in CH50 units/ml of serum. 
     Briefly, the AH50 assay depends on lysis of unsensitized rabbit erythrocytes (Erab) by human serum by activation of the alternative pathway. Activation of the calcium-dependent classical pathway is prevented by addition of the calcium chelator ethylene glycol tetraacetic acid (EGTA) to the assay buffer, and magnesium, necessary for both pathways, is added to the buffer. Briefly, a cell suspension of rabbit RBC (2×10{circumflex over ( )}8 cell/ml) is prepared in the GVB-Mg2+-EGTA buffer. A serial 1.5-fold dilution (1:4, 1:6, 1:9, 1:13.5, and 1:20.25) of normal human serum (NHS) or similar dilution of the mixture of NHS and the membrane-receiver complex are prepared in GVB-Mg2+-EGTA buffer, and 100 μl of each serum dilution is added to 50 μl of standardized Erab. NHS incubated with GVB-Mg2+-EGTA buffer is used as the control. The mixture is then incubated at 60 minutes at 37° C. in a shaking water bath to keep cells in suspension, and 1.2 ml of ice-cold NaCl (0.15 M) is used to stop the reaction. The tubes are spun at 1250 g, at 4° C., for 10 minutes to pellet the cells, and the optical density of the supernatant is determined spectrophotometrically (412 nm). Background control has 100 μl GVB-Mg2+-EGTA buffer, and 50 μl Erab and does not exceed 10% of the total lysis. In the total lysis control tube 100 μl of distilled water is added to 50 μl Erab suspension, and the percentage of hemolysis is determined relative to 100% lysis control. The results of the assay are calculated and complement activity is quantitated by determining the serum dilution required to lyse 50% of cells in the assay mixture. The results are expressed as the reciprocal of this dilution in AH50 units/ml of serum. 
     Example 18: Activity of Platelet-Loaded Thymidine Phosphorylase 
     A transgene encoding thymidine phosphorylase with an HA tag at the C-terminus is constructed by Gibson assembly as described herein. Platelets are cultured from precursor cells as described herein. The transgene is introduced into the cultured platelet precursor cells by lentiviral transduction as described herein. Expression of thymidine phosphorylase within the cultured platelets is assessed by Western blotting using an anti-HA detection antibody, as described herein. 
     Thymidine phosphorylase activity is determined in platelet samples by quantifying the rate of conversion of thymidine to thymine. Preliminary experiments are conducted to determine the linear metabolite formation kinetics with respect to time and enzyme dilution; the method is shown to be linear for up to 16 min, over a thymine phosphorylase range of 4.0-719 nmol/min/ml (corresponding to a sample dilution range of 10-9088). Lysates of pre-dialysis samples cultured platelet and control platelet samples are prepared by diluting thawed samples 1:710 with 125 mM Tris-HCl, pH 7.4. Twenty-five ul of the platelet lysate is then added to 100 ul sodium phosphate buffer (100 mM, pH 6.5) and 25 ul thymidine standard (10 mM), mixed and incubated at 37 C for 10 min. The reaction is terminated with 25 ul of 40% TCA. Assay blanks are prepared by adding TCA to the sodium phosphate buffer/thymidine incubation mixture prior to adding the platelet lysate. Samples are centrifuged at 13,400×g for 2 min, and the supernatant washed twice with water-saturated diethyl ether with 2 min on a shaker to extract the TCA. To avoid ether interfering with HPLC separation, effective removal is achieved by exposing the matrix to the air for 5 min to allow evaporation of the ether. A sample volume of 10 ul is injected into the HPLC. 
     Chromatographic separation of substrate and product is achieved using reversed phase chromatography with isocratic elution using a Waters Alliance HPLC 2795 system. A pre-packed C18 column (Spherisorb ODS 125 mm×4.6 mm ID, 5 um particle size, Waters) is used as the stationary stage. Analytes are eluted using a mobile phase of ammonium acetate (40 mM) with the ion-pairing agent tetrabutyl ammonium hydrogen sulphate (5 mM) adjusted to pH 2.70 with HCl, delivered at a flow rate of 1.0 ml/min, with a run time of 8 min UV detection is at 254 nm and 0.1 absorbance units full scale. Metabolites are identified by comparing spectra with pure standards. 
     Example 19: Activity of Platelet-Displayed Goodpasture Antigen 
     A transgene encoding collagen alpha-3(IV) (COL4A3) NC1 domain antigen fused to the N terminus of CD42b (GP1B, genbank AAH27955.1) with an intervening HA tag is constructed by Gibson assembly as described herein. Platelets are cultured from precursor cells as described herein. The transgene is introduced into the cultured platelet precursor cells by lentiviral transduction as described herein. Expression of the exogenous antigen on the cultured platelets is assessed by flow cytometry using an anti-HA detection antibody as described herein. 
     Serum is collected from a patient suffering from Goodpasture&#39;s syndrome, and the serum is tested for anti-COL4A3 antibodies by commercial ELISA (MyBioSource COL4A3 ELISA Kit). The binding capacity of the antigen-expressing platelets is assessed by flow cytometry as described herein, using this anti-COL4A3 serum as the primary detection antibody and fluorescent anti-human IgG as the secondary detection antibody. 
     Platelet-facilitated clearance of a circulating antigen in vivo is modeled in a mouse using the antigen-expressing platelets. NSG mice are injected with 100 uL of mouse anti-human COL4A3 antibody (Creative BioMart) fluorescently labeled with Dylight 650 dye. CFSE-labeled cultured platelets (10{circumflex over ( )}8 per mouse) that express the exogenous antigen are then injected via the tail vein. Blood is drawn from a submandibular location at 10 min, 30 min, 2 h, 12 h, and 24 h. Blood is centrifuged to collect the platelet-rich fraction, which is then stained and analyzed by flow cytometry as described herein. Antibody capture by platelets is determined by tracking the CFSE-Dylight 650 double positive population. 
     Example 20: Activity In Vivo (Mouse) 
     Mouse erythroid cells are cultured as described herein. Erythroid precursor cells are transduced with a suitable receiver polypeptide transgene, e.g., encoding complement receptor 1 (CR1) using a lentivirus as described herein. Cells are cultured to terminal differentiation as described herein. The presence of the exogenous protein in the cells is assessed by flow cytometry as described herein. The cells are labeled with a fluorescent die, e.g., CFSE (Sigma Aldrich) per manufacturer&#39;s instructions to aid in their detection. The cells are injected into a NZBWF1/J mouse model of lupus, or other appropriate model of disease or activity corresponding to the suitable receiver polypeptide, approximately 1×10{circumflex over ( )}8 cells injected via the tail vein. Blood is collected at multiple time points by submandibular puncture. Immune complex levels in the plasma are detected by Raji cell assay, see e.g., Theofilopoulos et al. 976, J Clin Invest 57(1):169. Pharmacokinetics of the cultured cells are assessed by flow cytometry as described herein, by tracking the percentage of CFSE fluorescent cells in the drawn blood sample. Mouse overall health is assessed by gross necropsy, including histology of kidney tissue to track reduction of immune complex deposition and inflammation-mediated damage. 
     Example 21: Rapid Screening 
     Cell lines, e.g., 293T and K562, have shorter expression and culturing cycles (˜1 day) compared to cultured erythroid cells (days-weeks). These cell lines can be used to rapidly iterate through a gene library encoding suitable receiver polypeptides to identify the receiver polypeptide with the highest expression or activity. 
     A library of suitable receiver polypeptide transgenes, e.g., full-length and shorter variants of complement receptor 1 (CR1), are constructed by polymerase chain reaction and Gibson assembly as described herein. The library of transgenes is transfected into HEK293T cells in a parallel fashion in a inicrotiter plate using lipofectamine as described herein and transduced into K562 cells using lentivirus as described herein. The expression of the receivers is assessed by flow cytometry as described herein after 24-48 hours. The activity of each of the receivers in the library is assessed by capture of fluorescent immune complex detected with flow cytometry as described herein, and by the transfer of fluorescent immune complexes to cultured monocytes detected with flow cytometry as described herein. The receivers from the library that are most functional—e.g., are highest expressed, capture most immune complexes, or best transfer immune complexes to monocytes—are then individually transduced into parallel erythroid cell cultures as described herein using lentivirus as described herein. The expression of each receiver on cultured erythroid cells is assessed by flow cytometry as described herein. The activity of each receiver on cultured erythroid cells is assessed by capture of fluorescent immune complex detected with flow cytometry as described herein, and by the transfer of fluorescent immune complexes to cultured monocytes detected with flow cytometry as described herein. 
     Example 22: Assessment of Clearance Rate of RBC In Vivo 
     The clearance rate of erythroid cells was assessed in vivo in an immunocompromised mouse model. NSG mice were treated at day −1 with 100 uL of clordonate liposome (Clodrosomes.com) solution to selectively deplete macrophages. Cells were labeled with the fluorescent tag CFSE and approximately 1×10{circumflex over ( )}8 cells were injected into each mouse via the tail vein. At regular intervals blood was collected by submandibular puncture and blood cells were collected. Cells were co-stained with anti-human GPA antibodies and analyzed by flow cytometry. Human erythroid cells were distinguished from mouse erythroid cells by CFSE signal and by human GPA signal. 
     For therapeutic applications, it is important that cultured erythroid cells and cultured erythroid cells containing exogenous protein either intracellularly or on the surface circulate normally in vivo. This is shown in  FIGS. 9A-9B  using a standard immunocompromised mouse model. In  FIG. 9A , blood collected from an injected mouse is analyzed on the flow cytometer. Cultured human erythroid cells are identified in the top right quadrant of the plot, double-positive for CFSE and human-GPA. In  FIG. 9B , mice were injected with human red blood cells (solid circles), cultured enucleated erythroid cells (dashed diamonds), cultured enucleated erythroid cells that express an intracellular exogenous protein (dotted squares) and cultured enucleated erythroid cells that express a surface exogenous protein (open triangles). The clearance rate of the human cells is measured as the percentage of CFSE+ cells remaining over time, scaled to the initial time point (20 minutes post injection). There is no significant difference in clearance rate between the four samples. 
     These data clearly demonstrates that cultured enucleated erythroid cells have substantially similar circulation to normal human red blood cells. Furthermore, exogenous proteins expressed either in the intracellular space or on the surface of the cells do not substantially affect the circulation behavior of these cells. This is an important result for therapeutic translation of the technology. 
     Example 23: Assessment of Adverse Circulatory Events 
     The incidence of adverse events caused by cultured eyrthroid cells in circulation were assessed by detection of fibrinogen breakdown products in blood and histology in animals injected with cultured erythroid cells. 
     Detection of Fibrinogen Breakdown Products. Mice were injected with cultured erythroid cells as described herein. Blood was collected from mice by submandibular puncture in an EDTA-containing tube. Cells were separated by centrifugation and plasma was collected. The levels of fibrinogen breakdown products fibrinopeptide A and fibrinopeptide B were measured in mouse plasma by ELISA (MyBiosource) following manufacturer&#39;s instructions. 
     Histology. Tissue samples from the same mice were collected following necropsy. Tissues were trimmed, embedded in paraffin wax, and sectioned. Tissue sections were stained by H&amp;E staining and trichrome staining. Microscope images were taken at 10× and 20× magnification. 
     For therapeutic applications, it is important that cultured erythroid cells and cultured erythroid cells that contain exogenous proteins (either intracellularly or on the surface) not induce adverse events, such as activation of the clotting cascade and tissue thrombus formation. 
       FIGS. 10A and 10B  show the levels of fibrinopeptide A and B in mouse plasma for mice injected with (1) human red blood cells, (2) cultured enucleated erythroid cells, (3) cultured enucleated erythroid cells expressing an intracellular exogenous protein, (4) cultured enucleated erythroid cells expressing a surface exogenous protein, and (5) recombinant protein alone. The levels of fibrinopeptide A and B, a marker of fibrinogen breakdown and activation of the clotting cascade, are substantially similar for all samples. 
       FIGS. 10C and 10D  show histologically stained sections of spleen for a mouse injected with cultured enucleated erythroid cells ( FIG. 10C ) and recombinant protein ( FIG. 10D ). There is no substantial difference between the tissue, and no identifiable tissue damage in spleen, liver, lung, brain, heart, and kidney was observed between any of the samples. 
     These data conclusively demonstrate that cultured erythroid cells, with or without exogenous protein, do not induce any adverse events while in circulation in mice. 
     Example 24: Assessment of Exogenous Protein Retention in Circulation 
     The retention of exogenous proteins in and on cultured enucleated erythroid cells was assessed by flow cytometry and Western blotting. 
     1. Retention of Exogenous Protein Assessed by Flow Cytometry 
     Erythroid cells were cultured as described herein. A transgene construct encoding glycophorin A signal sequence, antibody scFv specific to hepatitis B surface antigen, HA epitope tag, and glycophorin A coding sequence was assembled by Gibson assembly as described herein. The transgene was introduced into the erythroid cells by lentiviral transduction as described herein. The cells were cultured to terminal differentiation as described herein. Cells were fluorescently labeled with CFSE and injected into an immunocompromised NSG mouse (Jackson Labs) via the tail vein (1×10{circumflex over ( )}8 cells per mouse). At regular intervals blood was collected by submandibular puncture. Collected cells were stained with a fluorescent anti-HA antibody (Abeam), and analyzed by flow cytometry. Human cells were identified as CFSE+ cells, and exogenous protein retention was assessed by the fraction of CFSE+ cells that also stained positive for the epitope tag. 
     2. Retention of Exogenous Protein Assessed by Western Blot 
     Erythroid cells were cultured as described herein. A transgene construct encoding adenosine deaminase and an HA epitope tag was assembled by Gibson assembly as described herein. The transgene was introduced into the erythroid cells by lentiviral transduction as described herein. The cells were cultured to terminal differentiation as described herein. Cells were fluorescently labeled with CFSE and injected into an immunocompromised NSG mouse (Jackson Labs) via the tail vein (1×10{circumflex over ( )}8 cells per mouse). At regular intervals blood was collected by submandibular puncture. Collected cells were washed, lysed, and analyzed by Western blot as described herein with a detection antibody against the HA epitope tag. 
     For therapeutic applications, it is important that cultured erythroid cells that contain exogenous proteins either intracellularly or on the surface retain these transgenes when in circulation. This feat is non-trivial given that it is widely hypothesized in the field that erythroid cells undergo a rigorous program of maturation and elimination of proteins unnecessary for basic function when in circulation as they mature (Liu J et al. (2010) Blood 115(10):2021-2027, Lodish H F et al. (1975) Developmental Biology 47(1):59). 
       FIG. 11A-11B  show that exogenous proteins expressed in and on cultured enucleated erythroid cells were retained in circulation. In  FIG. 11A , mice were injected with cultured enucleated erythroid cells that expressed antibody scFv on their surface. The percentage of antibody scFv-positive cells began and remained steadily at approximately 50% through the duration of the multi-day circulation study. In  FIG. 11B , mice were injected either with cultured enucleated erythroid cells that expressed a cytoplasmic enzyme with an HA tag or with recombinant enzyme with an HA tag. When analyzed by Western blot, it is clear that the enzyme retained within the cultured cell for the duration of the experiment. The decrease in band intensity is attributable to the clearance of cells during the experiment, not from the removal of exogenous enzyme from said cells. 
     The data clearly demonstrate that exogenous proteins expressed in and on culture enucleated erythroid cells are retained in and on the cells in circulation, which has tremendous and unprecedented implications for therapeutic relevance. 
     Example 25: Assessment of Half-Life Extension In Vivo 
     Erythroid cells were cultured as described herein. A transgene construct encoding adenosine deaminase and an HA epitope tag was assembled by Gibson assembly as described herein. The transgene was introduced into the erythroid cells by lentiviral transduction as described herein. The cells were cultured to terminal differentiation as described herein. Cells were fluorescently labeled with CFSE and injected into an immunocompromised NSG mouse (Jackson Labs) via the tail vein (1×10{circumflex over ( )}8 cells per mouse). At regular intervals blood was collected by submandibular puncture. Collected cells were washed, lysed, and analyzed by Western blot as described herein with a detection antibody against the HA epitope tag. 
     A transgene encoding adenosine deaminase with an HA tag at the C-terminus was constructed by Gibson assembly as described herein. The transgene was introduced into HEK-293T cells by lipofectamine transfection (Life Technologies) as described herein. The protein was purified from the cell culture supernatant after 7 days using an HA affinity resin (Pierce) according to manufacturer&#39;s instructions. Protein concentration was assessed by absorbance of light at 280 nm. Protein (40 ug) was injected into an immunocompromised NSG mouse (Jackson Labs) via the tail vein. At regular intervals blood was collected by submandibular puncture. Plasma was analyzed by Western blot as described herein with a detection antibody against the HA epitope tag. 
     In  FIG. 11B , mice were injected either with cultured enucleated erythroid cells that expressed a cytoplasmic enzyme with an HA tag or with recombinant enzyme with an HA tag. When analyzed by Western blot, it is clear that the enzyme&#39;s circulating half-life is significantly extended when expressed within a circulating cell compared to when injected in soluble form. 
     Example 26: Assessment of Clearance Rate In Vivo—Platelets 
     A population of exogenous thymidine phosphorylase expressing platelets is cultured using the herein detailed procedure and is labeled with CFSE and injected into an NSG mouse via the tail vein. A population of native human-sourced platelets is similarly labeled with CFSE and injected into another mouse. Samples are taken from both mice at 10 min, 1 h, 4 h, 8 h, 24 h, and 48 h and flow cytometry is used to quantify platelet circulation levels. The half-life of natural vs cultured platelets is compared. 
     Example 27: Assessment of Adverse Circulatory Events—Platelets 
     For therapeutic applications, it is important that cultured platelets and cultured platelets that contain exogenous proteins (either intracellularly or on the surface) not induce adverse events, such as activation of the clotting cascade and tissue thrombus formation. Upon injection of cultured platelets into an NSG mouse via the tail vein, fibrinogen breakdown products fibrinopeptide A and fibrinopeptide B are detected in mouse plasma by ELISA following manufacturer&#39;s protocol (MyBiosource). Tissue samples from NSG mice are collected following necropsy. Tissues are trimmed, embedded in paraffin wax, and sectioned. Tissue sections are stained by H&amp;E staining and trichrome staining. Microscope images are taken at 10× and 20× magnification and assessed by a trained pathologist for any pathogenic features. 
     Example 28: Assessment of Exogenous Protein Retention in Circulation—Platelets 
     The retention of exogenous proteins in and on cultured platelets is assessed by flow cytometry and Western blotting. 
     CFSE labeled platelets that contain intracellular exogenous protein are injected into a mouse via the tail vein. At regular intervals blood is collected by submandibular puncture. Blood is centrifuged to isolate the platelet-rich plasma, which is then lysed, and analyzed by Western blot with staining for an epitope tag present on the exogenous protein. 
     Example 29: Acquisition of Donor Cells for Production 
     After obtaining informed consent, healthy CD34+ stem cell donors receive rhG-CSF (Granocyte or Neupogen), 10 ug/kg/day s.c., for 5 days for peripheral blood stem cell mobilization and then undergo apheresis for 2 consecutive days to collect mobilized CD34+ HSC. Mononuclear cells (MNC) are isolated from mobilized peripheral blood by Ficoll density gradient centrifugation and are split in two parts. One part is used to purify CD34+ cells by using anti-CD34-coated magnetic beads (Miltenyi Biotec, Inc., Germany), relative to Miltenyi protocol. The purity of the CD34+ fractions is controlled. CD34+-enriched HSC are then used immediately in the two-step culture method or frozen until use in the one-step culture method. 
     Complete medium (CM) used is RPMI 1640 (Eurobio, France), supplemented with 2 mM L-glutamine and 100 IU/ml penicillin-streptomycin (Gibco, Grand Island, N.Y., USA) and 10% heat-inactivated FBS (Gibco). IMDM (Gibco), supplemented with 10% heat-inactivated FBS, is used for expansion. Recombinant human stem cell factor (rhSCF), thrombopoietin (TPO), fetal liver tyrosine kinase 3 ligand (Flt-3L), GM-CSF, and TNF-alpha are purchased from R&amp;D Systems (Minneapolis, Minn., USA). 
     Example 30: Scale-Up for Production 
     Erythroid cells are scaled up in volume progressively, maintaining the cells at a density of between 1×10{circumflex over ( )}5 and 2×10{circumflex over ( )}6 cells/mL in static culture. Expansion stage is seeded at 10{circumflex over ( )}5/ml and includes 3-7 progressive volume transfers; 100 ml, 500 ml, 1 L, 10L, SOL, 100L, 100L. During the course of production the cell media includes a combination of IMDM, FBS, BSA, holotransferrin, insulin, glutamine, dexamethasone, beta estradiol, IL-3, SCF, and erythropoietin. When the cells reach a volume appropriate for seeding the production bioreactor, they are transferred to the production bioreactor for final scale-up and differentiation. 
     Example 31: Culturing Cells in a Bioreactor (Wave) 
     The WAVE Bioreactor 2/10 system is set up according to the operator manual. In brief, the Cellbag is assembled on the rocking unit, which is placed on the perfusion module. After inflating the bag with air, the weight is set to zero. Subsequently, the bag is filled with the appropriate amount of culturing media and incubated for at least two hours, allowing the media to reach 37 C. The media and cells are transferred to the bag via a transfer flask, a special designed DURAN glass bottle with two ports. In the upper part of the flask, a filter is connected to the port. In the other port, by the bottom of the flask, a tube is assembled. The tube one the transfer flask is coupled with the feed connection on the Cellbag. The transfer flask is maintained in a LAF hood, to decrease the risk of contamination. 
     Before perfusion is started, tubing and containers for harvest and feed are connected to the Cellbag. Tubing is prepared as follows; a 50 or 70 cm long Saniflex ASTP-ELP silicone tubing (Gore/Saniflex AB), with an inner and outer diameter of 3.2 respectively 6.4 mm, is equipped with male luer lock connections in both ends. The silicone tubing is connected to one end of a C-Flex tube, via a female luer lock. At the other end of the C-Flex tube a male luer lock is assembled and tubings are thereafter autoclaved. Luer locks are held in place with zip-ties on all tubes. Prior to perfusion, the silicone part is connected to the Cellbag and the C-Flex part to a 5 L container (Hyclone Labtainer) for both feed and harvest. All connections are performed in a laminar airflow cabinet. 
     Control of environmental and metabolic factors can alter the expression or activity of transcription factors and gene regulatory proteins of erythroid cells in culture, see e.g., Csaszar et al., 2009 Biotechnol Bioeng 103(2):402; Csaszar et al. 2012 Cell Stem Cell 10(2):218. To provide control over inputs and outputs in the reactor a micro-volume delivery system is created, a key component of which is a 60-80 cm long fused silica capillary (#TSP100375, Polymicro Technologies) with an internal diameter of 100 urn. At the input end, the capillary is fed with a luer-lok tip stock syringe (#309585 BD) connected via a PEEK luer to a MicroTight adapter (#P-662, Upchurch Scientific). The stock syringe is loaded on a Model 33 Twin Syringe Pump (#553333, Harvard Apparatus), kept in a refrigerator at 4 C. At the output end, the capillary enters the bioreactor: a two port FEP cell culture bag (#2PF-0002, VueLife) placed on an orbital shaker in a cell culture incubator at 37 C with 5% CO2. The capillary is fed through a self-sealing rubber septa (#B-IIS, InterLink) with a needle, into the midpoint of the bioreactor. The opposing connector on the bioreactor is replaced with an additional self-sealing rubber septa. Stock syringes and delivery capillaries are blocked overnight before use with a solution of PBS with 10% fetal bovine serum to prevent protein adhesion to syringe and capillary walls. 
     National Instruments LabVIEW 7.1 is used to create a program to control the syringe pump&#39;s injections. The program&#39;s basic dosing strategy is an initial injection to concentration L1 followed by wait time t1 and subsequent injections, each to concentration L2 and followed by wait time t2, repeated for n times. The user inputs the flow rate, the stock concentration, the initial culture volume, the desired concentration after injections, the time between injections, and the total number of injections. 
     Example 32: Assess Expansion and Differentiation of Cultured Erythroid Cells 
     It is important to assess the expansion, differentiation, and enucleation in vitro differentiated cells to ensure that the introduction of a transgene does not negatively affect the quality of the cells in culture. Expansion is assessed by cell counting. Differentiation is assessed by flow cytometry, Western blot, and RT-PCR. Enucleation is assessed by flow cytometry. 
     Assessing Expansion Rate by Cell Counting. Erythroid cells are cultured as described herein. At various time points, cells are collected, washed with PBS, and counted using a Countess Automatic Cell Counter instrument (Life Technologies). The expansion rate of the cells is determined by the growth in number of cells over time. 
     Assessing Differentiation by Flow Cytometry. Erythroid cells are cultured as described herein. At various time points, cells are collected, washed with PBS, and stained with 1:100 dilutions of fluorescent antibodies against the cell surface markers GPA (CD235a), CKIT (CD117), and TR (CD71), purchased from Life Technologies. Labeled cells were analyzed by flow cytometry as described herein. 
     Assessing Differentiation by Western Blot. Erythroid cells are cultured as described herein. At various time points, cells are collected, washed with PBS, lysed with RIPA buffer, and analyzed by Western Blot as described herein using antibodies for differentiation markers GATA1, GATA2, Band3, CD44, and actin (Abcam). 
     Assessing Enucleation by Flow Cytometry. Erythroid cells are cultured as described herein. At various time points, cells are collected, washed with PBS, and stained with a fluorescent antibody against glycophorin A (Life Technologies) and the nucleic acid stain DRAQ5 (Pierce) at manufacturer-recommended dilutions, and analyzed on an Attune flow cytometer as described herein. 
     Assessing Enucleation by Microscopy (Benzidine-Giemsa). Erythroid cells were cultured as described herein. At various time points, cells were collected, washed with PBS, and spun onto slides using a Cytospin (Thermo Scientific). Cells were fixed cells after cytospin with −20 C methanol for 2 min at room temp, rinsed with water, and air-dried. A benzidine tablet (Sigma #D5905) was dissolved with 10 mL PBS, to which 10 μL of H2O2 was added. The solution was filtered with a 0.22 urn syringe filter. The cell spot on the slide was covered with 300-500 uL of benzidine solution, incubated at room temperature for 1 hr, then washed with water. Giemsa stain was diluted (Sigma #GS500) 1:20 with water. The cell spot on the slide was covered with 300-500 uL Giemsa solution, incubated at room temperature for 40 minutes, washed with water, and air-dried. Slides were then mounted and sealed before imaging on a microscope. 
       FIG. 12A  shows the expansion rate of erythroid cells in culture during a seven day window of expansion and differentiation for cells that contain transgenes (dashed line and dotted line) and cells that do not contain a transgene (solid line). Of note, the expansion rate of cultured cells that contain a transgene is indistinguishable from that of cells that do not contain a transgene. 
       FIG. 12B  is a collection of flow cytometry plots for cells stained with antibodies against the cell surface differentiation markers GPA and CKIT. At this particular stage of differentiation, the culture is losing its CKIT expression and increasing its GPA expression as the cells approach terminal maturation. Of note, cultured cells that contain a transgene are indistinguishable from those that do not contain a transgene by this metric of differentiation. 
       FIG. 12C  is a collection of flow cytometry plots for cells stained with an antibody against the surface marker GPA and a fluorescent DNA stain. Three cell populations are evident: (1) cells that are GPA-high and DNA-low, comprising enucleated erythroid cells; (2) cells that are GPA-high and DNA-high, comprising erythroid cells that still contain genetic material; and (3) cells that are GPA-low and DNA-high, comprising pyrenocytes or the membrane-encapsulated ejected nuclei from enucleated cells. Of note, cultured cells that contain a transgene are indistinguishable from those that do not contain a transgene by this metric of enucleation. 
     The introduction of a transgene into cell culture does not noticeably affect the rate of expansion, the differentiation, or the rate of enucleation of the cells in culture. 
     Example 33: Assess Hemoglobin Content 
     1. Total Hemoglobin 
     Erythrocyte hemoglobin content was determined by Drabkin&#39;s reagent (Sigma-Aldrich, product D5941) per manufacturer&#39;s instructions. Briefly, blood cells were combined with the reagent in an aqueous buffer, mixed thoroughly, and absorbance of light at a wavelength of 540 nm was measured using a standard spectrophotometer. A soluble hemoglobin standard curve was used to quantify the hemoglobin content in the cells. 
     2. Hemoglobin Typing by RT-PCR 
     Cells were lysed and total RNA is collected. Reverse Transcription was carried out with the SuperScript First-Strand Synthesis System for RT-PCR (Life Technologies) according to manufacturer&#39;s protocol. Briefly, total RNA (5 ug) was incubated with 150 ng random hexamer primer and 10 nmol dNTP mix in 10 uL H2O for five minutes at 65 C then 1 minute on ice. The reaction master mixture was prepared with 2 uL 10× RT buffer, 4 uL of 25 mM MgCl2, 2 uL of 0.1 M DTT, and 1 uL of RNAseOUT. The reaction mixture was added to the RNA/primer mixture, mixed briefly, and then placed at room temperature for 2 min. 1 uL (50 units) of SuperScript II RT was added to each tube, mixed, and incubated at 25□C for 10 min. The reaction was incubated at 42 C for 50 min, heat inactivated at 70 C for 15 min, then stored on ice. 1 uL RNase H was added and incubated at 37 C for 20 min. This reaction product, the 1 st  strand cDNA, was then stored at −20 C until needed for RT-PCR reaction. 
     Primers to amplify the different hemoglobin genes and control genes were purchased from IDT-DNA. The primers were as follows: hHBB_F-tcctgaggagaagtctgccgt (Seq. ID No. 9); hHBB_R-ggagtggacagatccccaaag (Seq. ID No. 10); hHBA_F1-tctcctgccgacaagaccaa (Seq. ID No. 11); hHBA_R1-gcagtggcttagcttgaagttg (Seq. ID No. 12); hHBA_F2-caacttcaagctaagccactgc (Seq. ID No. 13); hHBA_R2-cggtgctcacagaagccag (Seq. ID No. 14); hHBD_F-gactgctgtcaatgccctgt (Seq. ID No. 15); hHBD_R-aaaggcacctagcaccttctt (Seq. ID No. 16); hHBG2_F-cactggagctacagacaagaaggtg (Seq. ID No. 17); hHBG2_R-tctcccaccatagaagataccagg (Seq. ID No. 18); hHBE_F-aagagcctcaggatccagcac (Seq. ID No. 19); hHBE_R-tcagcagtgatggatggacac (Seq. ID No. 20); h18S-RNA-F-cgcagctaggaataatggaatagg (Seq. ID No. 21); h18S-RNA-R-catggcctcagttccgaaa (Seq. ID No. 22). 
     An RT PCR reaction mix was prepared with 25 uL SYBR Green Mix (2×) (Applied Biosystems), 0.5 uL 1 st  strand cDNA, 2 uL forward/reverse primer pair mix (each primer at 5 pmol/uL), in a total volume of 50 uL H2O. Reactions were run in an ABI Prism SDS 7000 instrument (applied biosystems) using the following amplification cycle: 50 C 2 min, 1 cycle; 95 C 10 min, 1 cycle; 95 C 15 s→60 C 30 s→72 C 30 s, 40 cycles; 72 C 10 min, 1 cycle. Dissociation curve analysis and RT-PCR results was performed with the SDS 7000 instrument. 
     Example 34: Assess Differentiation of Cultured Platelets—FACS 
     The differentiation state of platelets in culture can be assessed by flow cytometry. Megakaryocytes (MKs) represent a distinct cellular morphology that precedes terminal platelet differentiation. To determine the extent of maturation toward MKs, 1×10{circumflex over ( )}6 cultured cells (LAMA-84 and CD34+ cells) are washed and then labeled with (a) anti-CD41-FITC (GpIIb/IIIa; BD Bioscience, San Jose, Calif., USA) or anti CD71-FITC or (b) anti-CD33-FITC, anti-CD41-PE, anti-CD45-PerCp and CD34-APC (Beckman Coulter, Fullerton, Calif., USA), and analyzed for the percentage of CD41 cells generated. 
     To determine the amount of ploidy, differentiated LAMA-84 cells are fixed overnight in 75% ethanol at 4° C. and labeled with propidium iodide (PI, 50 μg/ml) and analyzed using the FACScalibur (Becton Dickinson), whereas day 14 differentiated CD34+ cells are analyzed quantitatively under a microscope after May-Grunwald/Giemsa staining by quantitating the number of nuclei per cell and specific morphology of MKs with this stain. Only cells with MK morphology are analyzed. The presence of multinucleated cells in the cytospin preparation is indicative of the presence of polyploid MKs. Differentiated CD34+ cells are assessed for the presence of multinucleated mature MKs by morphology. 
     Example 35: Assess Differentiation of Cultured Platelets—qPCR 
     The differentiation state of platelets in culture can be assessed by quantitative PCR. Platelet RNA is extracted to further characterize the cultured cells. Total RNA is extracted using TRIzol reagent (Invitrogen). The purity of each platelet preparation is assessed by PCR analysis of platelet (GPIIIa) and leukocyte (CD45) markers. The integrity of platelet RNA is assessed using Bioanalyzer 2100 (Agilent) prior to further analyses. 
     Total RNA is collected from cell lysate and a cDNA library is generated using a commercial synthesis kit (Clontech). The labeled cDNAs are quantified with the Quant-iT PicoGreen dsDNA Kit (Invitrogen) and diluted to 3 pM for loading into a single lane and sequencing on an Illumina 1G Genome Analyzer (Solexa). 
     Raw sequences are filtered through serial quality control criteria. First, the presence of at least 6 nt of the 3′ Solexa adapter is verified. The sequence reads that did not comply with this criterion are discarded, whereas the others are trimmed to remove the adapter sequence harbored at the 3′ end. The remaining tags are further filtered regarding their length (&gt;10 nt), copy number (&gt;4 reads) and readability (&lt;9 non-identified nucleotides, annotated N). Reads complying with all those criteria are subsequently defined as usable reads. 
     All the usable reads are aligned to pre-microRNAs extracted from miRBase database. Sequence tags that matched perfectly to more than one precursor are distributed equally among them. In order to account for Drosha and Dicer imperfect cleavage, any sequence tag that perfectly matched the pre-microRNA in the mature microRNA region, allowing up to 4 nt shift as compared to the reference mature microRNA position, is considered as a mature microRNA. The microRNA expression level is defined as the number of reads mapping each mature microRNA normalized to the total number of usable reads, considering that the overall number of small RNAs is invariant. The relative abundance of each microRNA is defined as the number of reads mapping each microRNA compared to the total number of reads mapping mature microRNAs. 
     Example 36: Purification by Centrifugation 
     Cultured cell fractions can be purified and separated from nuclei and contaminating alternate-density cell types via centrifugation. Cells are centrifuged at 200 g for 15 minutes to isolate an erythrocyte and reticulocyte rich fraction. The supernatant is pipetted off and the desirable cell fraction is then washed in modified Tyrode&#39;s buffer (containing 138 mM NaCl, 5.5 mM dextrose, 12 mM NaHCO3, 0.8 mM CaCl2, 0.4 mM MgCl2, 2.9 mM KCl2, 0.36 mM Na2HPO4 and 20 mM Hepes, pH 7.4) in presence of 1 μM prostaglandin 12, and resuspended in the same buffer. 
     Example 37: Purification by Chemical Enucleation 
     Enucleation of cultured cells can be stimulated by chemical additives to the culture, which can help increase the enucleated fraction of cells prior to purification. Erythroid cells are cultured as described herein. 48 hours prior to collection, cells are incubated with 210 mM Me2SO. Cells are then collected by centrifugation at 350×g for 5 min at room temperature, resuspended at a level of 3×105 cells per ml in fresh medium containing 210 mM Me2SO and 5 ug/mL of cytochalasin B (or other actin or nucleus manipulating molecule, ie. p38 MAPK, psoralens) and incubated at 37 C. The proportion of cells without nuclei is assessed by flow cytometry as described herein, using DRAQ5 as a nucleic acid stain and antibodies against glycophorin A as an erythroid surface marker of differentiation. 
     Example 38: Purification by Acoustophoresis 
     Several mechanical separation systems may be used to obtain a uniform cell population. Free flow acoustophoresis represents one mechanical separation method (Petersson 2007, American Chemical Society). While suspended in saline solution (0.9 mg/mL) with nutrient additives, including CsCl (0.22 g/mL), is added to the saline solution. A sample suspension containing cultured erythroid cells is processed using an acoustopheresis chip (Cell-Care) with two active outlets (flow rate 0.10 mL/min per outlet). 
     Syringe pumps (WPI SP260P, World Precision Instruments Inc., Sarasota, Fla.) are used to control the flow rates in the chip. All outlets are individually connected to high-precision glass syringes (1005 TLL and 1010 TLL, Hamilton Bonaduz AG, Bonaduz, Switzerland) via the injectors using Teflon tubing, allowing independent control of the outlet flow rates. The clean fluid inlet is connected to a syringe pump and the cell suspension inlet to a 50-mm-long piece of Teflon tubing (0.3-mm i.d.) with its other end submerged in a beaker from which the sample suspension is aspirated at a rate defined by the difference between the net outlet flow and the clean fluid inlet flow. 
     The ultrasound used to induce the standing wave between the walls of the separation channel is generated using a 20×20 mm piezoelectric ceramic (Pz26, Ferroperm Piezoceramics AS, Kvistgard, Denmark) attached to the back side of the chip. Ultrasonic gel (Aquasonic Clear, Parker Laboratories Inc., Fairfield, N.J.) ensures a good acoustic coupling between the two. The piezoelectric ceramic is actuated via a power amplifier (model 75A250, Amplifier Research, Souderton, Pa.) connected to a function generator (HP 3325A, Hewlett-Packard Inc., Palo Alto, Calif.). Even though the acoustic waves enter the chip from the back side, a standing wave is induced between the side walls of the separation channel as a result of the coupling of the mechanical vibrations along the three axes of the crystal structure. 
     The separation process is monitored using a standard microscope and a wattmeter (43 Thruline Wattmeter, Bird Electronic Corp., Cleveland, Ohio). The process can subsequently be controlled by tuning the signal frequency, the actuation power, and the flow rates. 
     The cell size distributions in the samples are analyzed using a Coulter counter (Multisizer 3, Beckman Coulter Inc., Fullerton, Calif.). Each sample is mixed with an electrolyte (Isoton II, Beckman Coulter Inc.) and analyzed using a 100-um aperture. The level of hemolysis, i.e., the concentration of free hemoglobin from damaged red cells, is measured using a photometer (Plasma/low HB Photometer, HemoCue AB, Angelholm, Sweden). 
     Example 39: Purification by Ex Vivo Maturation 
     Erythroid cells that are not fully mature can be driven to maturity by ex vivo incubation in a system that mimics the natural in vivo maturation triggers. 
     1. Co-Culture with Stromal Cells 
     In the final stage of culture, erythroid cells are cultured on an adherent stromal layer in fresh medium without cytokines. The cultures are maintained at 37 C in 5% CO2 in air. The adherent cell layer consists of either the MS-5 stromal cell line or mesenchymal stromal cells (MSCs) established from whole normal adult bone marrow (see Prockop, D J (1997) Science 276:71) in RPMI (Invitrogen) supplemented with 10% fetal calf serum. Adherent MSCs are expanded and purified through at least two successive passages prior to use in co-culture. 
     2. Culture in Fibronectin-Coated Plates 
     In the final stage of culture, erythroid cells are cultured in plates adsorbed with human fibronectin. To produce these plates, fibronectin (Sigma Aldrich) is reconstituted with 1 mL sterile H2O/mg of protein and allowed to dissolve for at least 30 minutes at 37° C. A small amount of undissolved material may remain. This will not affect product performance. The fibronectin solution is diluted 100× in sterile balanced salt solution and added to the culture surface with a minimal volume. The culture surface is allowed to air dry for at least 45 minutes at room temperature. Excess fibronectin is removed by aspiration. 
     Example 40: Purification by Magnetophoresis 
     Strategies for separating, enriching, and/or purifying erythroid cells by magnetophoresis are known in the art, see e.g., Zborowski et al., 2003, Biophys J 84(4) 2638 and Jin &amp; Chalmers 2012, PLOS One 2012 7(8):e39491. A commercial magnetic separation system (QuadroMACS™ Separator combining four MidiMACS™ separation units and LD columns, Miltenyi Biotec, Auburn, Calif.) is used for magnetic erythrocyte enrichment from HSC-derived erythrocyte cultures. Cells are deoxygenated in a Glove-Bag™ inflatable glove chamber (Cole Parmer, Vernon Hills, Ill.), filled with nitrogen (Medipure™ nitrogen, concentration &gt;99%, Praxair, Inc., Danbury, Conn.). Before deoxygenation, all materials and equipment including the separation system, degassed sterile buffer (PBS+2 mM EDTA+0.5% BSA), and sterile collection tubes are placed in the glove bag, which is then tightly sealed. Deoxygenated cultures are loaded directly into a MACS® LD column which was placed in the QuadroMACS™ separator kept under anoxic conditions inside an inflatable glove chamber filled with N2 gas. Cells which pass through the column contained within the magnet are labeled as negative fraction and they are expected to be “non-magnetic”, including HSCs and erythroid cells before final maturation. The cells retained in the separation column are labeled as positive fraction, which is “magnetic” and consist of maturing RBC-like cells nearly full of functional hemoglobin. They are eluted from LD column after its removal from the magnet. Once separation is finished, oxygenated cells are reversibly recovered by exposing the collected cells to air. 
     Example 41: Purification by FACS 
     A population of erythroid cultured cells is sorted using a Becton-Dickinson Aria Hu cell sorter. Prior to sorting, cells are collected, washed with PBS, and stained with a fluorescent antibody against glycophorin A (Life Technologies) and the nucleic acid stain DRAQ5 (Pierce) at manufacturer-recommended dilutions. A 100 μm nozzle is used with a drop drive frequency of 28,000 drops/second. The sample threshold rate is approximately 4000 events/second. The temperature control option is used to maintain sample and collection tubes at 4° C. the entire duration of sorting. Additionally, the sample agitation feature is used at 200 rpm to prevent the sample from sedimenting throughout the sort. The sample is sorted in aliquots of approximately 750 μl dispensed from the syringe. Meanwhile, during these pauses the collection tubes are kept at 4° C., protected from the light, and gently mixed prior to resuming sort. The sorted samples are collected into a 12×75 mm borosilicate glass collection tube containing 250 μl DMEM supplemented with 10% FCS. 
     Example 41B: Purification by Enzymatic Treatment of Cells 
     Allogeneic erythrocyte sourcing may benefit from A and B antigen removal to generate a universally compatible product. This may be facilitated by a set of enzymes capable of selectively cleaving the galactose groups, rendering the erythroid cells more immunogenically favorable. 
     Two types of recombinant proteins of endo-β-galactosidase, which are originally identified from  Clostridium perfringens , are produced in  E. coli  BL-21 using standard cloning methods. ABase is prepared for releasing A/B Ag and endo-β-galactosidase C (EndoGalC) for releasing Galα1-3Galβ1-4G1cNAc (Gal Ag), which is known to be highly immunogenic in xenotransplantation, and has a carbohydrate structure resembling the A/B Ag. ABase cleaves Ga1β1-4G1cNAc linkage in blood type A [Ga1NAcα1-3(Fucα1-2) Ga1β1-4G1cNAc] and in blood type B [Ga1α1-3(Fucα1-2) Ga1β1-4G1cNAc]. 
     Briefly, after cloning of ABase, an expression plasmid with a C-terminal His tag is constructed in the pET-15b vector eabC without signal peptide. This exogenous gene is transformed into  E. coli  BL-21 cells. The enzyme produced in the cells as a soluble protein fraction is purified over a nickel-nitrilotriacetic acid column (QIAGEN GmbH, Hilden, Germany). Finally, 5 mL of purified recombinant ABase is obtained at the concentration of 3.6 mg/mL with the specific activity of 1500 U/mg. One unit of the enzymatic activity is defined as the amount of the enzyme required to hydrolyze 1 μmol of the substrate per min. 
     The effect of ABase treatment on Ag presence, Ab binding and complement activation is examined Human A/B RBC are digested with ABase and subjected to flow cytometric analysis after incubation with cross-reactive (anti-A or anti-B or anti-A and B containging; type B, type A or type O respectively) human sera. The mean fluorescence intensity (MFI) is used to quantitate the expression level of blood type A, B and Gal Ag. Digestion level is expressed as a percentage of blood type A or B Ag expressed on RBC after incubation in the absence of ABase. 
     Fresh blood type O sera are pooled from three healthy human volunteers and frozen at −80° C. to preserve endogenous complement activity until used. Heat-inactivated (for 30 min at 56° C.) sera are used for analysis of Ab binding. RBC with and without enzyme (ABase) digestion are incubated with 50% blood type O sera (100 μL) diluted with phosphate-buffered saline containing 0.2% bovine serum albumin (PBS/BSA) for 30 min at 37° C. After washing, RBC are reacted with FITC-labeled anti-human IgG/IgM (DAKO, Glostrup, Denmark) (×30, 100 μL) for 30 min at 4° C. and then subjected to flow cytometric analysis. 
     The inhibitory effect of enzyme treatment on complement activation is also evaluated by the change of C3d deposition. After RBC are incubated with 50% human sera in the presence of complement activity for 15 min at 37° C., RBC are reacted with FITC-labeled rabbit anti-human C3d Ab (DAKO, Glostrup, Denmark) (×100, 100 μL) for 30 min at 4° C. and then applied to flow cytometric analysis. The percentage of the control level (in the absence of enzyme) is calculated based on MFI to evaluate the inhibitory effect of enzyme treatment on Ab binding and C3d deposition. 
     Example 42: Purification of Platelets by Centrifugation 
     Platelets can be purified from mixed cell suspensions by centrifugation. Some 40 ml of whole blood is distributed in blood collection tubes with sodium citrate at 3.2% used as an anticoagulant. The tubes are centrifuged at 400×g for 10 min. After this stage, three layers are clearly demarcated: plasma, red blood cells, and an intermediate zone. The plasma is at the top with the platelets, the red blood cells are at the bottom because of their heavier density; and the fine, whitish intermediate zone consists of larger platelets and leukocytes and is called the buffy coat. Using a Jelco 18G needle, the upper portion of plasma with platelets is drawn off, and the buffy coat is placed into two other tubes, this time with no additives: one tube to produce plasma (P tube) and the other to produce thrombin (T tube). Only 1.5 ml of plasma is used to produce thrombin, to which 0.5 ml of calcium gluconate at 10% is added, with 15 min in a double boiler at 37° C. The two tubes are then centrifuged again, this time at 800×g, for the same length of time (T=10 min). After this final centrifugation, the T tube contains a thrombin-rich liquid while the P tube contains the platelet sedimentation and some red blood cells (erythrocyte-platelet clump). The volume is reduced at this stage by removing two-thirds of the total plasma volume. The portion removed is platelet poor, while the remaining portion with the sedimented platelets (that are easily dispersible by stirring) is platelet rich. 
     Example 43: Thymidine Incorporation 
     Self-replication potential of a cell population can be assessed using a thymidine incorporation assay known in the art, see e.g., Harkonen et al. 1991 Exp Cell Res 186L288 and Tanaka et al. 1992 PNAS 89:8928. 
     Briefly, uniformly 13C- and 15N-enriched thymidine [U-13C, 15N-TdR] is obtained from Martek Biosciences (Columbia, Md.), and 3 H-TdR (80 Ci/mmol) is purchased from ICN Radiochemicals (Irvine, Calif.). Media and buffers are obtained from Fisher Scientific (Pittsburgh, Pa.). All enzymes except phosphodiesterase are from Boehinger Mannheim (Indianapolis, Ind.). Phosphodiesterase II is obtained from Worthington Biochemical Corporation (Lakewood, N.J.). High-performance liquid chomatography (HPLC) solvents are from EM Science (Gibbstown, N.J.) and contained &lt;0.1 ppm evaporation residue. 
     Erythroid cells are cultured as described herein. Following the culture, cells are collected for use in the thymidine incorporation assay. 
     Cells are labeled with [U-13C, 15N]-TdR at L6 μg/ml for 18 h, with the addition of unenriched thymidine to achieve a final thymidine concentration of 1 μM. After they are washed with phosphate-buffered saline, the cells are cultured in supplemented DMEM for 6 h more before 3 H-TdR is added at the indicated concentrations (0.1-10 μCi/ml) for another 18-h incubation. Unlabeled thymidine is added to the samples to bring the final thymidine concentration to 0.13 μM, which is equivalent to the concentration of 3 H-TdR in the samples receiving 10 μCi radiolabel/ml. After removal of 3 H-TdR, the cells are incubated in supplemented DMEM for an additional 6-54 h before isolation of DNA. 
     DNA is extracted using the modified Puregene DNA isolation kit (Gentra Systems, Minneapolis, Minn.). Based on the number of cells in the sample, a scale-up/scale-down procedure is used to determine the added reagent volumes. For example, when 1×10{circumflex over ( )}7 cells are used, 21 μl containing 328 μg of proteinase K is added to 3 ml of cell lysis solution. After mixing, the sample is left overnight at room temperature. The following day, 10 μg of RNase is added and the sample is mixed and incubated for 2 h at 37 C. Protein precipitation solution (1 ml) is added, and the sample is incubated on ice for 5 min. After centrifugation for 10 min at 2000 g, the supernatant containing DNA is mixed with 3 ml 100% 2-propanol and gently inverted 50 times or until white threads of DNA became visible. The sample is then centrifuged at 2000 g for 5 min. The resultant DNA pellet is dried for 5 min before washing in 3 ml of 70% ethanol and recentrifugation for 5 min at 2000 g. The final pellet is air-dried and then rehydrated in deionized H2O and quantitated by absorption at 260 nm. The same procedure is applied to CD34+ stem cells as a control for replicative ability. 
     Any DNA is denatured by boiling for 3 min, then chilled rapidly on ice. The enzymatic hydrolysis procedure is carried out with a DNA concentration of 0.5 mg/ml. The following protocol describes volume of reagent added per milliliter of DNA solution. DNA is hydrolyzed with 10 μl of nuclease P1 (0.5 U/μ1) and 5 μl of DNase I (4 U/μ1) in 10 μl of buffer containing 200 mM MgCl2, 100 mM ZnCl2, and 1 M Tris, pH 7.2, for 2 h at 45° C., followed by addition of 20 μl phosphodiesterase (4 mU/μl) and further incubation for 2 h at 37° C. Finally, 5 μl of 10 M ammonium acetate (pH 9.0) and 10 μl of alkaline phosphatase (1 U/μl) are added, and the samples incubated for another 2 h at 37° C. 
     The digested DNA sample is filtered with a 0.22-μm nylon filter. This sample is analyzed with the HPLC/CRI/IRMS system, using a 4.6×250 mm Supelcosil LC-18-S HPLC column (Supelco, Bellefonte, Pa.). The same solvent system is used at 1 ml/min and a linear gradient of 5% to 25% B in 15 min. 
     After separation by HPLC, the deoxynucleosides are analyzed using chemical reaction interface mass spectrometry (CRIMS). In this process, the deoxynucleosides flow into a nebulization and desolvation system driven by a stream of helium, where they emerge as a dry particle beam. The 13CO2/12CO2 abundances from this in-line generated CO2 are determined with a Finnigan/MAT Delta S isotope ratio mass spectrometer (ThermoFinnigan, San Jose, Calif.) and its accompanying Isodat data system. 5-Fluorodeoxyuridine (Sigma) is used as an internal isotope ratio standard. 
     Isotope ratios (IR in equation that follows) for three nucleosides are obtained from each sample: T, dA, and dG. The enrichment of CO2 evolved from each DNA-derived deoxynucleoside is computed by the equation (13)CO2 (per mil)=1000× (IR experimental −IR std)/IRstd. To maintain the highest level of internal consistency and avoid any interexperimental drift, the isotope ratio for dG is subtracted across all experiments from the isotope ratio for T. The data from the end of the stable-isotope labeling period (day 0) to the end of the washout (day 3) are evaluated. 
     Example 44: Quantification of Nuclear Material 
     The number of cells in a mixed population that contain DNA is assessed by flow cytometry using the DNA stain DRAQ5 (Pierce). Cells are incubated with the stain per manufacturer&#39;s instructions and analyzed on a flow cytometer, e.g., an Attune cytometer (Life Technologies). The percentage of cells above a predefined threshold of nuclear material content is quantified. 
     Example 45: Tumorigenicity assay in vitro 
     To assess the replication potential of cells, a soft agar colony formation assay can be performed. In brief, a base agar layer is made by making a 0.5% Agar+1×RPMI+10% FCS solution, all components warmed to 40 C, and adding 1.5 mL of the solution to a 35 mm petri dish. The agar is allowed to solidify for 30 min at room temp before use. 
     The top agarose layer is prepared by melting 0.7% agarose in a microwave and cooling to 40 C. A 2×RPMI+20% FCS solution is heated to 40 C. Cells are counted and prepared for plating at 5000 cells per plate at a density of 200,000 cells per mL. 0.1 mL of cell suspension is added to 10 mL tubes, followed by 3 mL of the warm 0.7% Agarose and 3 mL of the warm RPMI/FCS solution. The solution is mixed gently by swirling and added (1.5 mL) to each of three or four replicate base agar plates. 
     Plates are incubated at 37 C in a humidified incubator for 10-30 days. Cells are fed 1-2 times per week with cell culture media, 0.75 mL/plate. 
     To assess colony formation, plates are stained with 0.5 mL of 0.005% Crystal Violet for &gt;1 hr. Colonies are counted using a dissecting microscope. 
     Example 46: Tumorigenicity Assay In Vivo 
     Terminally-differentiated cultured erythroid cells are implanted in various animal models to evaluate the potential for tumorigenicity. Several tissues are collected from the various models and analyzed with histological, immunochemical, and fluorescent assays to quantify tumorigenicity. 
     Animals receive daily intraperitoneal injections of CsA (10 mg/kg, Sandimmune, Novatis Pharma, Nürnberg) starting two days before grafting. For the depletion of NK cells, some rats receive, in addition to CsA intraperitoneal injections of the monoclonal antibody (mAb), anti-NKR-P1A (clone 10/78, mouse IgG 1 , BD Biosciences, Heidelberg, Germany) or the respective isotype control (clone PPV-06, mouse IgG 1 , Exbio, Prague, Czech Republic). The anti-NKR-P1A mAb (clone 10/78) is directed against the same epitope as the mAb (clone 3.2.3). One mg of the respective antibodies are given one day before the injection of erythroid cells followed by 0.5 mg at day 4 after cell transplantation. 
     Blood samples are taken before starting these experiments, at day 0 and 4 days after erythroid cell transplantation, and at autopsy (day 92) in order to determine the proportion of NK cells in the blood by flow cytometry. For the analysis of subcutaneous tumor growth erythroid cells are injected in 100 μl phosphate-buffered saline (PBS) into the flank of the animals. Tumor growth is monitored every second day by palpation and size is recorded using linear calipers. Animals are sacrificed before day 100 when a tumor volume of 1 cm 3  in mice and 5 cm 3  in rats is reached, when a weight loss of more than 10% occurs, or when any behavioral signs of pain or suffering are observable. Autopsies of all animals are performed. 
     Murine tissue near the site of injection is immediately frozen in liquid nitrogen or placed in phosphate-buffered 4% formalin for 16 h and then embedded in paraffin. Spleens and lymph nodes are removed for subsequent immunological analyses. The transplantation of erythroid cells into the striatum of unilaterally 6-OHDA-lesioned rats is performed. These animals are sacrificed 6 weeks after transplantation. 
     Animal tissue is analyzed by flow cytometry. Appropriate fluorescent and PE-conjugated antibodies against established cancer cell biomarkers of CD133, CD3, CD, CD16, CD19, CD20, CD56, CD44, CD24, and CD133 are added to the excised tissues samples and analyzed to quantify tumorigenic potential. 
     Example 47: Deformability by EKTA 
     Erythroid cells cultured as described herein are assessed for deformability characteristics relative to natural erythrocyte samples via ektacytometry. 
     The ektacytometer consists of a Couette-type viscometer combined with a helium-neon laser used to produce a diffraction image of red cells suspended in a viscous fluid between the two cylinders. When the viscometer rotates, normal red cells elongate in the shear field, causing the diffraction image to become elliptical. The ellipticity of the image is measured by quantifying the light intensity along the major (A) and minor (B) axes of the diffraction pattern and expressing this as a ratio (A−B)/(A+B), the deformability index (DI) or elongation index (EI). The viscosity of the medium is chosen to be greater than the internal viscosity of the densest erythroid cells. A 31 g/liter solution of polyvinylpyrrolidone (PVP), mw=360,000, in a phosphate buffer of 0.04 M composed of K2HP04 and KH2P04 in distilled water yields a viscosity of 0.20 poise at 25° C. and 12 poise at 37 C. 
     Osmolarity is adjusted with NaCl to the desired level and measured in a Roebling freezing-point osmometer. The final pH is varied by using small additions of 1-M solutions of NaOH and HCl and is measured in a Technicon BG II blood gas analyzer. Sodium azide is added as a preservative to stock solutions to obtain 0.4 g/l. 
     The ektacytometer collects three primary metrics from the erythroid cell samples and compares them to native erythrocytes; Osmolality minimum (O min ), deformability index (Di max ), and the osmolality at which the DI reaches half of its maximum value (O hyp ). 
     O min  is related to the surface area to volume ratio of the cell and has been found to equal the 50% hemolysis point in the classical osmotic fragility test. 
     Di max  is the maximum value of the deformability index, normally reached at 290 mosmol (the physiologic osmolality value). This indicates the maximum deformability of the cell under shear stress and is related to a number of factors, such as surface area, volume, internal viscosity, and mechanical properties of the cell membrane. 
     O hyp  is the osmolality at which the DI reaches half of its maximum value. This gives an indication of the position of the hypertonic part of the curve, which is related to the internal viscosity of the cell as well as mechanical properties of the membrane, such as how it will bend under force (stiffness). 
     The parameters obtained for the cultured erythroid cells are compared to the same values for primary erythroid cells. 
     Example 48: Deformability by LORCA 
     The deformability of purified cRBC populations is measured by a laser diffraction technique (LORCA, laser-assisted optical rotational cell analyzer, R&amp;R Mechanotrics). In brief, a highly diluted suspension of cells is sheared in a Couette system with a gap of 0.3 mm between 2 cylinders, one of which is able to rotate to induce shear stresses. A laser beam is passed through the suspension, and the diffraction pattern is measured at 37° C. At low shear stress, the cells are circular disks, whereas at high shear stress, the cells become elliptical. The cell deformability is expressed in terms of the elongation index (EI), which depends on the ellipticity of the deforming cells. Aliquots containing 12.5 uL of pelleted RBC pellets are diluted in 5 mL of polyvinylpyrrolidone solution (molecular weight 360 000). The EI values at 30 Pa (referred to as EImax) and 3 Pa are selected as representative values of the deformability for easy comparison between samples at various shear stresses. 
     Example 49: Assessment of Vascular Occlusion—Ex Vivo Rat Vasculature 
     The potential for vascular occlusion of erythroid cells can be assessed with isolated artificially perfused rat vasculature using methods known in the art, see e.g., Kaul et al. 1983, J Clin Invest 72:22. Briefly, in anesthetized (sodium pentabarbitol 30 mg/kg) rats of the Wistar strain, 120-150 g, the right ileocolic artery and vein are cannulated with heparinized (100 uL/mL) silastic tubing at a site 3 cm distant from the ileocolic junction. Under a steady-state perfusion with Ringer&#39;s containing 1% bovine serum albumin, the ascending colon and terminal ileum (3 cm each) are sectioned between ties. After hemostatic ties of all vascular connections is achieved, the tissue is isolated. The isolated mesoappendix is gently spread on an optically clear Lucite block on a microscope stage. The entire preparation is covered with a plastic saran wrap except for outlets of cannulas and the microscope objective. 
     The control arterial perfusion pressure (Ppa) and venous outflow pressures (Pv) are kept constant at 80 and 3.8 mmHg, respectively, and monitored via Statham-Gould P-50 pressure transducers (Stathan Instruments Inc, Oxnard Calif.). The venous outflow (Fv) rate is monitored using a photoelectric dropcounter and expressed in mL/min A lapse of 10-12 min is allowed for tissue equilibration and stabilization of Fv. Only preparations exhibiting mesoappendix microvasculature free of host blood cells and with a steady Fv of 4.6+/−0.5 (mean+/−SD) are used. The experiments are done at 37 C. 
     Erythroid cells are isolated as described herein. After control measurements of Ppa and Fv, erythroid cells (0.2 mL, Hct 30%) are gently delivered via an injection port 15 cm distal to site of arterial cannulation, and the changes in Ppa and Fv are recorded on the strip chart of a Grass polygraph (Grass Instrument Co, Quincy Mass.). The tissue preparations are perfused for 10-15 min before the infusion of samples with Ringer&#39;s solution to allow stabilization of the tissue and clear the vasculature of the remaining blood cells of the host animal. The resulting obstruction after the infusion of cells can be cleared and the flow restored by briefly (2-3 min) perfusing the vasculature with fully-oxygenated Ringer&#39;s solution at high pressure (100 mmHg). 
     At the end of each experiment the entire tissue preparation (free of cannulas and luminal content) is weighed. Peripheral resistance units (PRU) are calculated and expressed as PRU=ΔP/Q=mmHg/mL/(min-g) where ΔP (mmHg) is the arteriovenous pressure difference and Q (mL/min-g) is the rate of venous outflow per gram of tissue. 
     In each experiment, pressure-flow recovery time (Tpf) is determined following the bolus infusion of samples. Tpf is defined as the time (seconds) required for Ppa and Fv to return to their base-line levels following the delivery of a given sample, and it represents total transit time throughout the mesoappendix vasculature. The parameter values obtained for cultured erythroid cells are compared to the values obtained for primary erythroid cells. 
     Example 50: Assessment of Vascular Occlusion—In Vitro Flow Chamber 
     Methods to assess vascular occlusion of erythroid cells using in vitro graduated height flow chambers are known in the art, see e.g., Zennadi et al 2004, Blood 104(12):3774. 
     Briefly, graduated height flow chambers are used to quantitate the adhesion of erythroid cells to endothelial cells (ECs). Slides coated with ECs are washed with Hanks balanced saline solution (HBSS) with 1.26 mM Ca2+, 0.9 mM Mg2+(Gibco, Grand Island, N.Y.) warmed previously to 37° C. and then fit into a variable height flow chamber. The flow chamber is mounted on the stage of an inverted phase contrast microscope (Diaphot; Nikon, Melville, N.Y.) connected to a thermoplate (Tokai Hit, Fujinomiya-shi, Japan) set at 37° C. Cells are observed using a video camera (RS Photometrics, Tucson, Ariz.) attached to the microscope and connected to a Macintosh G4 computer (Apple, Cupertino, Calif.). Erythroid cells are cultured as described herein, and labeled with fluorescent dye PKH 26 red fluorescent cell linker kit (Sigma) following the manufacturer&#39;s instructions. Cells (3 mL) suspended at 0.2% (vol/vol) in HBSS with Ca2+, Mg2+ are infused into the flow chamber and allowed to adhere to the slide for 15 minutes without flow. Before exposure to flow, a minimum of 3 fields at each of 7 different locations along a line oriented normal to future flow are examined for the total number of fluorescent cells. Fluid flow (HBSS with Ca2+, Mg2+) is then started using a calibrated syringe pump. After exposure to flow, the fields are again examined and the number of adherent cells counted. The fraction of adherent cells is presented as follows: Number of cells attached after exposure to flow/Cells present per field before flow. The wall shear stress is calculated as follows: τw=(6 μQ)/(wH[×]2), in which τw indicates wall shear stress (dyne/cm2); Q, volumetric flow rate (cm3/s); μ, media viscosity; w, width of the flow channel; and H(x), height of the flow chamber as a function of position along the microscope slide. 
     Example 51: Assessment of Vascular Occlusion—Intravital Microscopy 
     Methods to assess vascular occlusion of erythroid cells using intravital microscopy are known in the art, see e.g., Zennadi et al. 2007 Blood 110(7):2708. 
     Briefly, general anesthesia of a test animal is achieved by intraperitoneal injection of 100 mg/kg ketamine (Abbott Laboratory, Chicago, Ill.) and 10 mg/kg xylazine (Bayer, Shawnee Mission, Kans.). A double-sided titanium frame window chamber is surgically implanted into the dorsal skin fold under sterile conditions using a laminar flow hood. Surgery involves carefully removing the epidermal and dermal layers of one side of a dorsal skin fold, exposing the blood vessels of the subcutaneous tissue adjacent to the striated muscles of the opposing skin fold, and then securing the 2 sides of the chamber to the skin using stainless steel screws and sutures. A glass window is placed in the chamber to cover the exposed tissue and secured with a snap ring. Subsequently, animals are kept at 32° C. to 34° C. until in vivo studies were performed 3 days after surgery. 
     Anesthetized animals with window chambers are placed on the stage of an Axoplan microscope (Carl Zeiss, Thornwood, N.Y.); temperature is maintained at 37° C. using a thermostatically controlled heating pad. All infusions are through the dorsal tail vein. Erythroid cells are cultured as described herein. Cells are then labeled with Di1 or DiO (Molecular Probes, Eugene, Oreg.) dyes per manufacturer&#39;s instructions. Labeled cells (300 μL; hematocrit [Hct] 0.50 [50%] in PBS with Ca2+ and Mg2+) are infused, and RBC adhesion and blood flow dynamics are observed in subdermal vessels for at least 30 minutes using LD Achroplan 20×/0.40 Korr and Fluar 5×/0.25 objectives. Microcirculatory events and cell adhesion are simultaneously recorded using a Trinitron Color video monitor (PVM-1353 MD; Sony, Tokyo, Japan) and JVC video cassette recorder (BR-S3784; VCR King, Durham, N.C.) connected to a digital video camera C2400 (Hamamatsu Photonics KK, Hamamatsu City, Japan). Thirty segments of venules are examined for each set of conditions. Arterioles are distinguished from venules based on (1) observation of divergent flow as opposed to convergent flow; (2) birefringent appearance of vessel walls using transillumination, which is characteristic of arteriolar vascular smooth muscle; and (3) relatively straight vessel trajectory without evidence of tortuosity. 
     Measurement of red cell flux and adhesion is performed by examining videotapes produced using ×20 magnification. Cell adherence is quantitated by considering cells attached to the vessel walls and immobile for 1 minute. The percentage of the length of vessels with diameters up to 25 μm or more than 25 μm, occupied by SS RBCs, is quantified as follows: % venular length occupied by SS RBCs=(length of vessel wall with adherent cells/total length of the vessel segments analyzed)×100. Changes in RBC flux are calculated as follows: flux=number of circulating fluorescent human RBCs crossing a single point marked on vessels less than 50 μm in diameter per minute. 
     Example 52: Assessment of Vascular Occlusion—Platelets 
     Methods to assess vascular occlusion of platelets using human vascular endothelial cells (HUVECs) can be adapted from similar methods for eythroctyes. Briefly, a 2-mL volume of 0.05% hematocrit suspension is added to confluent HUVECs on tissue culture Petri dish. The cone-and-plate apparatus is assembled within 1 min after addition of platelets and placed on a Nikon Diaphot-TMD inverted-phase contrast microscope (Southern Micro Instruments, Atlanta, Ga.). The motor is started to turn the cone, and adherence is continuously monitored at 0.1 or 1 dyne/cm2 shear stress for 30 min Temperature is maintained constant at 37° C. by an air curtain incubator (Nicholson Precision Instruments, Inc., Bethesda, Md.) blowing on the adhesion apparatus. Platelet adherence is visualized and recorded every 5 min by focusing on 8 different fields of view for 20 sec per field for each time point. The entire experiment is viewed under 400× total magnification through a CCD-72 series camera (Dage-MTI, Inc., Michigan City, Ind.) and recorded on videotape with a SVO 2000 video cassette recorder (Sony Electronics, San Jose, Calif.). Adherence is quantified off-line at the end of each experiment by counting individual adherent cells during manual playback of recorded video images. The cell counts in 8 fields for each time point are averaged and normalized to adherent red cells per square millimeter of endothelium. 
     Example 53: Assessment of Mass/Volume/Density with Resonator 
     A dual suspended microchannel resonator (SMR) system is used to characterize the mass, volume, and density of a population of terminally-differentiated erythroid cells based on Bryan et al,  LabChip,  2014. At the start of a cell density measurement, the system is first flushed with filtered Percoll media, which serves as the high density fluid. Next, the sample bypass is filled with a dilute cell sample, and the vial heights at the sample inlet and outlet are adjusted to direct fluid flow into the first SMR. Pressure at the high density fluid inlet is used to set the density of Fluid 2, and pressure at the waste outlet controls the overall flow speed in the device. To minimize the likelihood of size biasing due to heavier cells settling at the bottom of the sample vial or tubing, a fresh sample is introduced at regular intervals by flushing the sample bypass channel Data is acquired via LabVIEW and processed with MATLAB. 
     Cell concentration is monitored using a Coulter counter. Cell measurements are performed on cultures grown to 5×10{circumflex over ( )}5-1×10{circumflex over ( )}6 cells/ml. High density fluid introduced for measurement in the second SMR is formulated as a solution of 50% (v/v) Percoll (Sigma), 1.38% (w/v) powdered L15 media (Sigma), 0.4% (w/v) glucose, 100 IU penicillin, and 100 μg mL—1 streptomycin. Media pH is adjusted to 7.2. This Percoll media is stored at 4° C. and filtered immediately prior to use in the dual SMR. 
     Example 54: Assessment of Phosphatidyl Serine Content by Annexin V 
     Erythroid cells are cultured as described herein. 50 μL cell suspension is washed in Ringer solution containing 5 mM CaCl 2  and then stained with Annexin-V-FITC (1:200 dilution; ImmunoTools, Friesoythe, Germany) in this solution at 37° C. for 20 min under protection from light. Cells are washed and stained by flow cytometry as described herein, and annexin-V fluorescence intensity is measured with an excitation wavelength of 488 nm and an emission wavelength of 530 nm. Relative phosphatidyl serine exposure is assessed from annexin-V fluorescence. 
     Example 55: Assessment of Lipid Content by Chromatography 
     Lipids are extracted from washed synthetic membrane-receiver complexes by three extractions with methanol-chloroform 1:1 at room temperature in the presence of the antioxidant BHT (Sigma Aldrich). The pooled extracts are washed with 0.05 M KCl in the method of Folch, Lees and Sloane Stanley 1957, J Biol Chem 226:497. Briefly, for the first extraction, 15 mL methanol containing 0.05 mg/mL BHT are added to the washed complexes in a centrifuge tube and allowed to stand for 30 min with occasional stirring to break up sediment. 15 mL of chloroform is then added and the mixture is allowed to stand for 30 min with occasional stirring to break up clumps. The tubes are centrifuged for 5 minutes at 1500 g and the supernatant fractions decanted into separatory funnels fitted with Teflon stopcocks. The second and third extractions are performed similarly with 15 mL of the methanol-BHT added to the residue followed by 15 mL of chloroform, except the extracts stand for only 10 minutes with occasional stirring after each addition. After centrifugation, the supernatant fractions are pooled in a separatory funnel then 48 mL of chloroform and 28 mL of 0.05 M KCl are added and mixed. The mixture is allowed to stand overnight in darkness at 4 C for phase separation. After being rewarmed to room temperature, the lower of the two clear phases is collected and evaporated to dryness in vacuo at 40 C in a rotary vacuum evaporator. The lipid is transferred quantitatively to a 10 mL volumetric flask with chloroform and stored at −22 C. 
     The concentration of free cholesterol in the lipid extract is determined as follows. The lipid extract is chromatographed on a 0.5 mm layer of Silica Gel HR (Brinkmann Instruments, Inc., Westbury, N.Y.) in hexane-diethyl ether-glacial acetic acid 80:20:1, the TLC plate is stained by spraying with 2,7-dichlorofluorescein solution (see below), the free cholesterol spot is scraped into a conical centrifuge tube and extracted once with 2.0 ml and three times with 1.0 ml of chloroform, the extract is evaporated to dryness in vacuo at 40° C. in a rotary vacuum evaporator, and the cholesterol is estimated by the ferric chloride method of Mann 1961 Clin Chem 7:275 without saponification. A free cholesterol standard, prepared from a commercial certified reagent grade material by isolation through the dibromide derivative (see e.g., Fieser J Amer Chem Soc 1953 75:5421), is taken through the chromatographic procedure and estimated with each set of determinations. The values for free cholesterol are corrected in each determination for the recovery of the standard, which averaged 95%. The TLC is necessary to remove the BHT, which otherwise interferes with the ferric chloride method by producing a brown product that absorbed at 560 nm. 
     The phospholipid distribution is determined in triplicate by TLC of aliquots of the total lipid extract at 4° C. on Silica Gel HR, 0.5 mm thick, in chloroformmethanol-glacial acetic acid-water 25:15:4:2 to which is added BHT at a concentration of 50 mg/100 ml to prevent autoxidation during chromatography; the TLC plates are prepared with water (“neutral” plates). Use of a “wedged-tip technique” for applying the lipid sample at the origin of the plate (see e.g., Stahl 1965 Thin-Layer Chromatography, Academic Press Inc.) results in excellent separations of the individual phospholipids. In particular, the method provides complete separation between phosphatidyl ethanolamine (PE), phosphatidyl serine (PS), lecithin, and sphingomyelin; a discrete spot migrates between PS and lecithin that is identified as phosphatidyl inositol (PI). The spots are made visible in UV light by spraying with a solution of 2,7-dichlorofluorescein (33.3 mg/100 ml of aqueous 2 mM NaOH) and then scraping directly into Kramer-Gittleman tubes, where the phospholipids are digested at 190° C. for 60 min with 1.0 ml of 70% perchloric acid. The remainder of the procedure is performed as described above, except that after color development, the silica gel is removed by centrifugation at 3000 g for 5 min and the absorbency is determined on the clear supernatant solution. Corrections are made for the absorbency of corresponding areas of blank lanes. 
     Gas-liquid chromatography is performed on hexane-dissolved samples with a Barber-Colman instrument, model 5000, equipped with paired 8-ft columns of EGSS-X (an ethylene glycol succinate polyester combined with a silicone) 8% on Gas-Chrom P, 100-120 mesh (Applied Science Laboratories Inc.) and dual flame ionization detectors. The nitrogen flow rate is 50 ml/min at the inlet. The column temperature is maintained at 1650 C for 10 min after injection of the sample, then increased at 2 C/min to 200° C. 
     Example 56: Assessment of Membrane Viscosity 
     The membrane viscosity of a population of cells can be assessed by fluorescence photobleaching assay. A 0.5-ml sample of erythroid cells is collected and washed once in HEPES-buffered saline (132 mM NaCl, 4.7 mM KCl, 2.0 mM CaCl2, 1.2 mM MgSO4, 20 mM HEPES, adjusted to pH 7.4). The packed cells are then washed once in 145 mM NaCl-10 mM NaHCO 3 , pH 9.5, and resuspended in the same buffer with 1 mg/ml DTAF (obtained from Research Organics, Cleveland, Ohio). The cells are incubated on ice for 1 h, then washed twice in 50 mM glycine—95 mM NaCl-10 mM NaHCO 3 , pH 9.5, to remove any dye that has not bound covalently to protein. Finally, the cells are washed twice and resuspended to −2% hematocrit in HEPES-buffered saline with 1 mg/ml bovine serum albumin. The same treatment is applied to control native erythrocytes. 
     The flow chamber is mounted on the stage of a Leitz Diavert (Rockleigh, N.J.) inverted microscope equipped for incident-light fluorescence microscopy. The dichroic mirror and excitation/emission filters are the standard combination for use with fluorescein dyes (Leitz designation 12), with excitation wavelength in the range 450-490 nm. The objective is an oil immersion type with 100× magnification and 1.25 numerical aperture. A 100 watt high pressure mercury arc lamp (Osram, Munich) with an appropriate power supply and housing (Oriel, Stamford, Conn.) serves as the fluorescence excitation source. 
     A computer-controlled electronic shutter (Vincent Associates, Rochester, N.Y.) limits the exposure duration and is synchronized with a photon-counting electronic system for measuring fluorescence intensity. The field diaphragm of the incident light illuminator is used to limit excitation to a circular area of diameter 20-40 urn. At regular intervals, an output pulse from the computer causes the shutter to open for a typical duration of 20 ms. Light from the brief fluorescent image is split with a series of prisms so that half the light is directed to a low-light-level SIT video camera (Model 66-SIT, Dage-MTI, Michigan City, Ind.) and half to a photomultiplier tube (Model 8850, RCA, Harrison, N.J.) enclosed in an ambient temperature housing. During the time that the electronic shutter is open, a video image processor (Model 794, Hughes Aircraft, Carlsbad, Calif.) is triggered to acquire the fluorescent image, providing a video snapshot that can be monitored to ensure that the subject remains in focus and that no foreign object intrudes into the field of view. Distances on the video screen are measured with a video caliper and calibrated by comparison with the video image of a stage micrometer. Also during the time the shutter is open, the photomultiplier signal is processed with the photon-counting technique. An amplifier/discriminator (Model AD6, Pacific Instruments, Concord, Calif.) generates a digital logic pulse for each signal pulse above a given magnitude, and those digital pulses are counted on a 100-MHz gated counter (Model 770, EG&amp;G Ortec, Oak Ridge, Tenn.). The microcomputer controls the gating, resetting, and recording of the photon count. 
     A typical experiment consists of a number of preliminary fluorescence measurements made during brief (20 ms) pulses of excitation light, followed by an extended period of illumination (typically 30 s) during which the samples cells are bleached, followed by another series of brief exposures, every 15-30 s, until the fluorescence appears to have completed its recovery. 
     The recovery time and other parameter values obtained for cultured erythroid cells are compared to the same values obtained for primary erythroid cells. 
     Example 57: Assessment of Mean Corpuscular Volume with Advia Hematology Analyzer 
     The Mean corpuscular volume (MCV) of the cultured erythroid cells is measured using electrical impedance in an Advia 120 hematology analyzer (Siemens Healthcare). The results are compared to that of natural human erythrocytes. 
     Example 58: Pathogen Testing of Cultured Erythroid Cells 
     RT-PCR is used to quantify adventitious virus presence in cultured erythroid cell populations and confirm non-contamination (Assay No. 003000.BSV, BioReliance). Sterility testing of unprocessed and final bulk, final vials, prebanking cells, and cell and virus banks is performed by directly inoculating the erythroid population into 2 different types of media that support the growth of aerobic and anaerobic bacteria respectively. Samples are incubated for 14 days followed by testing for microbial contaminants per BioReliance Sterility Testing protocol USP 71. 
     Example 59: Assessment of Osmotic Fragility 
     Osmotic fragility is evaluated to measure the resistance of the erythroid cells to lysis when exposed to hypotonic solutions. Solutions of NaCl in water were made at concentrations spanning 0% to 1%. Cells were incubated in each of the salt solutions for 15 minutes. The samples were centrifuged to pellet intact cells. Supernatant was assayed for hemoglobin content by absorption of light at 540 nm using a spectrophotometer. The point at which 50% hemolysis occurs is calculated and compared to the value obtained for primary erythrocytes. 
     Example 60: Assessment of Rosetting/Immunogenicity 
     The direct antiglobulin test, also known as Coombs test, assesses the agglutination or resetting of erythroid cells caused by the binding of polyclonal antibodies from serum to surface antigens on the cell. It can be performed with pooled human serum for general allogeneic immunogenicity assessment, or with serum from the intended recipient for specific immunogenicity prediction. 
     In brief, add 1-2 drops of cells stored in an EDTA tube to a reaction tube. Wash this tube three times with isotonic saline. After the third wash, prepare a 3% suspension from the washed cells. Label 2 tubes A and B. Add one drop of the washed 3% suspension to each tube. Wash these tubes one more time. When decanting, position the tubes so that the cell button is on top. This will prevent too many cells from being lost in the washing process. Drain well, and blot dry with a biowipe Immediately add one drop human test serum to both tubes, and shake to mix. Allow the B tube to incubate at room temperature 5 minutes. Centrifuge the A tube for the time calibrated for the Coombs spin on the serofuge. Immediately resuspend gently and examine for agglutination using the lighted agglutination viewer (Beckton Dickinson). If the A tube is positive, it is not necessary to read the B tube nor is it necessary to examine the A tube microscopically. If the A tube is negative by lighted agglutination viewer, examine for agglutination under the microscope. If the A tube was negative through the microscopic reading, centrifuge the B tube after its incubation period and repeat steps 2-4 with the B tube sample. If the B tube is negative as well, add one drop of IgG-coated Coombs Control Cells (Check Cells) to the tube and centrifuge. Examine for agglutination. Agglutination should be present in this step, or the test is invalid. 
     If there is no agglutination in any of the steps before addition of the check cells (ccc), the test is interpreted as negative. If agglutination is observed in any of the steps before addition of the check cells, the test is interpreted as positive. 
     Example 61: Assessment of Oxygen-binding capacity 
     Equilibrium oxygen binding curves at 37° C. are determined in a tonometer linked to a 1-cm path length cuvette. Spectral measurements are performed with a spectrophotometer (Cary 50; Variant Inc), and the temperature is controlled with a Peltier module. Analyses are performed in 50 mM bis-Tris buffer (pH 7.2) containing 140 mM NaCl and 2 mM glucose. After thorough deoxygenation under nitrogen, the red cell suspensions are equilibrated at different partial pressures of oxygen by injection of known volumes of pure oxygen into the tonometer through a rubber cap with a Hamilton syringe. The fractional saturation is estimated by simulation of the absorption spectra in the visible and Soret regions as a linear combination of the fully deoxygenated and oxygenated spectra of the RBC suspension by least squares regression. 
     Example 62: Assessment of Metabolic State of Cells 
     The erythroid cell population may be verified as metabolically active using a variety of different enzyme based assays to quantify important metabolic end products. Active glycolysis is a crucial metabolic pathway to assess and may be measured with the following assay (Glycolysis cell-based assay kit, Cayman Chemical, Item 600450). 
     450 ul of assay buffer is aliquoted into a test tube, followed by 50 uL of the L-Lactic acid standard and mixed thoroughly. A titration curve is constructed using the lactic acid concentration standard, beginning with a 1 mM dilution. 
     Cells are added to a 96 well plate and centrifuged at 1000 RPM for 5 minutes. 100 uL of the standards are transferred into a separate 96 well plate. 90 uL of assay buffer is then added to each well. 10 ul of supernatant in each cell well is then transferred to corresponding new wells. Add 100 ul of reaction solution to each well using a repeating pipettor. The plates are then incubated on an orbital shaker for 30 minutes at RT. The absorbance is read at 490 nm with a plate reader. Results are compared to natural cells to identify any metabolic differences. 
     Example 63: Assessment of Platelet Aggregation 
     Aggregation propensity of cultured or primary sourced platelets can be monitored. Platelets are submitted to swirling analysis by shaking them in front of a light source, with the results expressed as presence or absence of birefringence. The units of platelet concentrates produced with a volume of 50-70 mL are left to rest for one hour and placed in a linear shaker (C-Mar®) at 70 rpm at a controlled temperature of 22±2° C. (71.6±3.6° F.). 
     The tests of platelets concentrates (platelet count, platelet aggregation and pH) are carried out on days 1, 3 and 5 after processing; a leukocyte count is performed only on day 1 and the microbiological control is performed only on the 5th day of storage. In order to obtain aliquots from samples of platelet concentrates, a sterile connection (Haemonetics®) is used which ensured the integrity of the environment. Platelet aggregation is achieved using the turbidimetric aggregometry technique using a dual-channel Chronolog (Crono-Log Corporation®) within four hours of blood collection. For this, the cells are initially obtained through light centrifugation at 1000 rpm for five minutes, and then centrifuged at 3000 rpm for fifteen minutes (Eppendorf®). Samples are subjected to a platelet count in an automatic counter (Human Count®). 
     After adjusting the platelet concentration, aggregation is evaluated using different concentrations of inducing agonists: collagen 2.0 μg/mL and ADP 7.0 μg/mL (Crono-Log Corporation®). For each test, 400 μL of PRP and 400 μL of PPP are used, each one in a different cuvette after waiting for spontaneous aggregation. The aggregation curve is observed after five minutes of stimulation by inducing agonists, and soon after, aggregation is measured and expressed as a percentage according to the curves formed during the tests. The result of the test is commonly expressed as a percentage of aggregation by the quantity of light transmitted through the test solution; aggregation is classified as normal, low or high. 
     Example 64: Autologous Culture Process 
     The culture of erythroid cells using autologously sourced progenitor CD34+ cells is done to optimize cell immunocompatibility for patients. CD34+ cells from the bone marrow are mobilized to the periphery in a patient using GM-CSF as described herein. Between 10{circumflex over ( )}6-10{circumflex over ( )}8 CD34+ cells are collected and cultured using the aforementioned 22 day protocol using defined media. During Day 4 the cells are transfected with a lentiviral vector containing a gene that codes for the expression of a therapeutic agent. Upon completion of the culturing protocol, the cells are purified and assessed across several quality control metrics including physical properties that correlate with circulation viability, immunogenicity, replicative potential, purity, and therapeutic dose. The cells are then stored in appropriate stabilizing solution and formulated in a syringe or appropriate delivery vehicle. The cells are then infused into the same patient that donated the initial CD34+ cells. 
     Example 65: Autologous Loading Process 
     For the preparation of therapeutic erythroid cells loaded with a suitable receiver, autologously sourced erythrocytes can be used to optimize cell immunocompatibility for patients. Blood is drawn from the patient and centrifuged at 5000 g for 20 minutes. The huffy coat is removed and the remaining red cells are re-suspended in anticoagulant buffer at a density of 10{circumflex over ( )}8 cells/ml, giving a total of 10{circumflex over ( )}10 cells. The cells are loaded with a therapeutic receiver of interest by one of the methods described above. Upon completion of the loading protocol, the cells are purified and assessed across several quality control metrics including physical properties that correlate with circulation viability, immunogenicity, replicative potential, purity, and therapeutic dose. The cells are then stored in appropriate stabilizing solution and formulated in a syringe or appropriate delivery vehicle. The cells are infused into the same patient that donated the initial erythrocytes. 
     Example 66: Allogeneic Culture Process 
     To create a scalable, universal therapeutic, erythroid cells can be cultured from an allogeneic source. The culture of erythroid cells using allogeneically sourced progenitor CD34+ cells is done to streamline the process and culture a volume of therapeutic capable of treating patients at scale. Donors are blood-typed for major blood antigens, including A, B, Rh to identify universal donors (e.g., 0 Rh— or Bombay Rh—). CD34+ cells from the bone marrow are mobilized to the periphery in a suitable donor using GM-CSF as described herein. Between 10{circumflex over ( )}6-10{circumflex over ( )}8 CD34+ cells are collected and cultured using the aforementioned 22 day protocol using defined media. During Day 4 the cells are transfected with a lentiviral vector containing a gene that codes for the expression of a therapeutic agent. Upon completion of the culturing protocol, the cells are purified and assessed across several quality control metrics including physical properties that correlate with circulation viability, immunogenicity, replicative potential, purity, and therapeutic dose. The cells are then stored in appropriate stabilizing solution and formulated in a syringe or appropriate delivery vehicle. The cells are then infused into patients irrespective of their major blood groups. 
     Example 67: Allogeneic Loading Process 
     The culture of erythroid cells using allogeneically sourced progenitor CD34+ cells is done to streamline the process to prepare larger volumes of therapeutic cells capable of treating patients at scale. Donors are blood-typed for major blood antigens, including A, B, Rh to identify universal donors (e.g., O Rh— or Bombay Rh—). The cells are loaded with a therapeutic receiver of interest by one of the methods described above. Upon completion of the loading protocol, the cells are purified and assessed across several quality control metrics including physical properties that correlate with circulation viability, immunogenicity, replicative potential, purity, and therapeutic dose. The cells are then stored in appropriate stabilizing solution and formulated in a syringe or appropriate delivery vehicle. The cells are then infused into patients irrespective of their major blood groups. 
     Example 68: Storage 
     1. Storage in Refrigerated Buffer Solution 
     Standard protocols for the storage of red blood cells are known in the art, see e.g., Meryman and Hornblower 1986, Transfusion 26(6):500. The standard protocol for the storage of red blood cells (for up to 42 days) is the collection of blood into anticoagulant solutions (citrate-dextrose-phosphate). Erythroid cells are cultured as described herein. Red cell concentrates are prepared by the removal of plasma by centrifugation. The cells are stored at 4±2° C. in a slightly hypertonic additive solution, SAGM (sodium, adenine, glucose, mannitol, 376 mOsm/L). 
     2. Storage in Frozen Buffer Solution 
     Methods for glycerolization, freezing, and thawing of erythroid cells are known in the art, see e.g., Meryman and Hornblower 1977 Transfusion 17(5):4348. Human blood in citrate phosphate dextrose is glycerolized and frozen within 4 days of collection. To prepare glycerolized RBCs, approximately 10 mL of whole blood is first centrifuged at 1,400 g for 10-15 min, and the plasma is removed. The resulting packed cells are then glycerolized in two steps using an aqueous glycerol solution with the following composition: 57.1 g glycerol, 0.03 g potassium chloride, 0.085 g magnesium chloride hexahydrate, 0.08 g disodium phosphate, and 1.6 g sodium lactate in a total volume of 100 mL, adjusted to a pH of 6.8.42 In the first step, 1.5 mL of this glycerol solution is added drop-wise to the packed cells with gentle agitation over a period of 3 min. The mixture is then allowed to equilibrate undisturbed for at least 5 min. In the second glycerolization step, 5 mL of the glycerol solution is added drop-wise while the mixture is gently agitated over a 3-min period, yielding a final glycerol composition of ˜40% w/v. The entire glycerolization process is carried out at room temperature. The glycerolized RBCs are then divided into aliquots of 0.6-1.1 mL in cryogenic vials, placed in a NalgeneVR Cryo “Mr. Frosty” freezing container (Thermo Scientific, NC), and stored in a −80 C freezer for at least 12 h and up to 10 years. Frozen RBCs are thawed by placing the cryogenic vial in a 37 C water bath for 1 min. All glycerolized blood samples are used in deglycerolization experiments within 2 h of thawing. 
     3. Formulation as Syringe 
     The cell population may be intravenously administered via a syringe. The therapeutic cells are diluted to a density of 10{circumflex over ( )}7 cells/ml using standard saline buffer at 37 C such that 100 ml of volume, or 10{circumflex over ( )}9 cells, are delivered. The cell solution is loaded into a 150 cc syringe, 20 gauge needle and injected into the patient through the basilic vein at 5 cc/min. During injection the patient&#39;s vitals are monitored for any immunogenic or clotting reactions. 
     4. Formulation as Bag 
     The cell population may be intravenously administered via syringe connected to a bag and drip chamber (i.e. an IV drip). The therapeutic cells are diluted to a density of 10{circumflex over ( )}7 cells/ml using standard saline buffer at 37 C such that 100 ml of volume, or 10{circumflex over ( )}9 cells, are delivered. The cell solution is loaded into a 1L plastic bag, connected to a catheter and allowed to drain via gravity into the patient through the basilic vein. During infusion the patient&#39;s vitals are monitored for any immunogenic or clotting reactions. 
     Example 69: CAPS Catastrophic Antiphospholipid Syndrome 
     Cells are cultured in the presence of a lentivirus encoding the exogenous transgene β2-Glycoprotein I (b2GPI) (GenBank: X53595.1) fused to the N-terminus of glycophorin A such that the final cell product expresses &gt;1×10{circumflex over ( )}5 copies of the b2GPI receiver on the surface per cell. To ensure that the receiver is functionally expressed, in vitro activity is assessed by flow cytometry. Briefly, cells are incubated with serum from patients with Antiphospholipid Syndrome that have previously tested positive for anti-b2GPI antibodies by ELISA. The cells are washed and labeled with secondary antibodies to detect human primary antibodies bound to their surface and analyzed by flow cytometry for presence of the fluorophore. 
     The cultured erythroid cell population that over expresses beta-2 glycoprotein I is provided as a treatment for antiphospholipid syndrome in an early phase clinical trial. 
     A patient diagnosed as having antiphospholipid autoantibodies in circulation is intravenously administered single doses of 10{circumflex over ( )}9-10{circumflex over ( )}11 cells once a month for 6-12 months. During the course of treatment patients&#39; thymidine and thymine levels are monitored with daily blood tests and relevant APS symptoms such as thrombotic events and bleeding are documented. 
     A population of 10{circumflex over ( )}11 erythroid cells expressing between 10K and 100K copies of Beta-2 glycoprotein 1 per cell is stored in a transfusion bag with CPDA-1 and glycerol and stored at −80 C for up to 10 years. Upon treatment, the bag is thawed, centrifuged, and the cells removed and resuspended in saline for administration to a patient. Cells are intravenously administered with a 50 gauge needle at 5 ml/min at 37 C. 
     Example 70: Goodpasture Disease 
     Cells are cultured in the presence of a lentivirus encoding the non-collagenous C-terminal domain of the exogenous transgene COL4A3, NC1-COL4A3 (ID: NM_000091.4) fused to the N-terminus of glycophorin A such that the final cell product expresses &gt;1×10{circumflex over ( )}5 copies of the NC1-COL4A3 receiver on the surface per cell as assessed by flow cytometry. To ensure that the receiver is functionally expressed, in vitro activity is assessed by flow cytometry. Briefly, cells are incubated with serum from patients with Goodpasture Syndrome that have previously tested positive for anti-NC1-COL4A3 antibodies by ELISA. The cells are washed and labeled with secondary antibodies to detect human primary antibodies bound to their surface and analyzed by flow cytometry for presence of the fluorophore. 
     Example 71: Membranous GN 
     Cells are cultured in the presence of a lentivirus encoding the 4 th -6 th  extracellular domains of the exogenous transgene phospholipase A2 receptor (PLA2R) (ID: MGC:178179) fused to the N-terminus of glycophorin A such that the final cell product expresses &gt;1×10{circumflex over ( )}5 copies of the PLA2R receiver on the surface per cell as assessed by flow cytometry. To ensure that the receiver is functionally expressed, in vitro activity is assessed by flow cytometry. Briefly, cells are incubated with serum from patients with Membranous Glomerulonephritis (MGN) that have previously tested positive for anti-PLA2R antibodies by ELISA. The cells are washed and labeled with secondary antibodies to detect human primary antibodies bound to their surface and analyzed by flow cytometry for presence of the fluorophore. 
     Example 72: IgA Nephropathy 
     Cells are cultured in the presence of a lentivirus encoding the extracellular domain of exogenous transgene complement receptor 1 (CR1) (SEQ ID 2) fused to the N terminus of glycophorin A such that the final cell product expresses &gt;1×10{circumflex over ( )}5 copies of CR1 ectodomain receiver per cell as assessed by flow cytometry. To ensure that the receiver is functionally expressed, the cell is assayed for its ability to bind immune complexes and transfer those complexes to macrophages. 
     Dylight 650-labeled bovine serum albumin (BSA-650) is incubated with polyclonal rabbit anti-BSA (Abcam) in an excess of antibody for 30 minutes at room temp to generate complexes. The complexes are then mixed with human serum at a 1:1 volume ratio for 30 minutes at 37 C to form immune complexes. Control complexes are either not mixed with human serum or mixed with heat-inactivated human serum. The complexes are then incubated with cells for 30 minutes at 37 C. Cells are washed and analyzed by flow cytometry for capture of immune complexes by detecting Dylight 650 fluorescence. 
     Cultured U937 monocytes are activated by incubation with 100 nM phorbol myristate acetate (PMA) for 24 hours at 37 C. Cells coated with immune complexes (see above) are incubated with activated U937 macrophages for 30 minutes at 37 C. The co-culture is analyzed by flow cytometry. Macrophages are identified by FSC/SSC gating. Presence of immune complex on macrophages is analyzed by detecting Dylight 650 fluorescence in this cell population. 
     Example 73: Systemic Lupus Erythematosus 
     Cells are cultured in the presence of a lentivirus encoding the extracellular domain of exogenous transgene complement receptor 1 (CR1) (SEQ ID 2) fused to the N terminus of glycophorin A such that the final cell product expresses &gt;1×10{circumflex over ( )}5 copies of CR1 ectodomain receiver per cell as assessed by flow cytometry. To ensure that the receiver is functionally expressed, the cell is assayed for its ability to bind immune complexes and transfer those complexes to macrophages. 
     Dylight 650-labeled bovine serum albumin (BSA-650) is incubated with polyclonal rabbit anti-BSA (Abcam) in an excess of antibody for 30 minutes at room temp to generate complexes. The complexes are then mixed with human serum at a 1:1 volume ratio for 30 minutes at 37 C to form immune complexes. Control complexes are either not mixed with human serum or mixed with heat-inactivated human serum. The complexes are then incubated with cells for 30 minutes at 37 C. Cells are washed and analyzed by flow cytometry for capture of immune complexes by detecting Dylight 650 fluorescence. 
     Cultured U937 monocytes are activated by incubation with 100 nM phorbol myristate acetate (PMA) for 24 hours at 37 C. Cells coated with immune complexes (see above) are incubated with activated U937 macrophages for 30 minutes at 37 C. The co-culture is analyzed by flow cytometry. Macrophages are identified by FSC/SSC gating. Presence of immune complex on macrophages is analyzed by detecting Dylight 650 fluorescence in this cell population. 
     Example 74: Paroxysmal Nocturnal Hemoglobinuria 
     Cells are cultured in the presence of a lentivirus encoding the exogenous transgene CD59 (NCBI Reference Sequence: NM_203330.2) with an N-terminal epitope tag such that the final cell product expresses &gt;1×10{circumflex over ( )}5 copies of CD59 receiver per cell as assessed by flow cytometry. To ensure that the receiver is functionally expressed, the cell is assayed for its ability to inhibit membrane attack complex on sheep erythrocytes in co-culture. 
     Briefly, fresh sheep erythrocytes in 10% solution of 1× veronal buffered saline (VBS) are sensitized with polyclonal rabbit anti-sheep RBC antibody (haemolysin) for 30 minutes at 30 C. Serial dilutions of cultured cells are added to sensitized sheep erythrocytes. Human serum is added at serial dilutions to each well, starting with 1:4 dilution in VBS. Incubate at 37° C. for 30 minutes, mixing after 15 minutes. Centrifuge the samples at 1,500 g for 5 minutes to sediment the RBCs. Transfer 100 ul of supernatant from each tube to a well in a 96 well flat bottom plate. Add 100 ml of distilled water to each well. Read the absorbance of the samples at 540 nm using a plate spectrophotometer. % lysis is calculated as OD540 (test)−OD540 (blank)/OD540 (total lysis)−OD540 (blank)*100. 
     Example 75: Atypical Hemolytic Uremic Syndrome 
     Cells are cultured in the presence of a lentivirus encoding the exogenous transgene CD59 (NCBI Reference Sequence: NM_203330.2) with an N-terminal epitope tag such that the final cell product expresses &gt;1×10{circumflex over ( )}5 copies of CD59 receiver per cell as assessed by flow cytometry. To ensure that the receiver is functionally expressed, the cell is assayed for its ability to inhibit membrane attack complex on sheep erythrocytes in co-culture. 
     Briefly, fresh sheep erythrocytes in 10% solution of 1× veronal buffered saline (VBS) are sensitized with polyclonal rabbit anti-sheep RBC antibody (haemolysin) for 30 minutes at 30 C. Serial dilutions of cultured cells are added to sensitized sheep erythrocytes. Human serum is added at serial dilutions to each well, starting with 1:4 dilution in VBS. Incubate at 37° C. for 30 minutes, mixing after 15 minutes. Centrifuge the samples at 1,500 g for 5 minutes to sediment the RBCs. Transfer 100 ul of supernatant from each tube to a well in a 96 well flat bottom plate. Add 100 ml of distilled water to each well. Read the absorbance of the samples at 540 nm using a plate spectrophotometer. % lysis is calculated as OD540 (test)−OD540 (blank)/OD540 (total lysis)−OD540 (blank)*100. 
     Example 76: Age-Related Macular Degeneration 
     Cells are cultured in the presence of a lentivirus encoding the exogenous transgene CD59 (NCBI Reference Sequence: NM_203330.2) with an N-terminal epitope tag such that the final cell product expresses &gt;1×10{circumflex over ( )}5 copies of CD59 receiver per cell as assessed by flow cytometry. To ensure that the receiver is functionally expressed, the cell is assayed for its ability to inhibit membrane attack complex on sheep erythrocytes in co-culture. 
     Briefly, fresh sheep erythrocytes in 10% solution of 1× veronal buffered saline (VBS) are sensitized with polyclonal rabbit anti-sheep RBC antibody (haemolysin) for 30 minutes at 30 C. Serial dilutions of cultured cells are added to sensitized sheep erythrocytes. Human serum is added at serial dilutions to each well, starting with 1:4 dilution in VBS. Incubate at 37° C. for 30 minutes, mixing after 15 minutes. Centrifuge the samples at 1,500 g for 5 minutes to sediment the RBCs. Transfer 100 ul of supernatant from each tube to a well in a 96 well flat bottom plate. Add 100 ml of distilled water to each well. Read the absorbance of the samples at 540 nm using a plate spectrophotometer. % lysis is calculated as OD540 (test)−OD540 (blank)/OD540 (total lysis)−OD540 (blank)*100. 
     Example 77: B Cell Acute Lymphoblastic Leukemia 
     An antibody scFv is generated based on a full-length anti-CD20 antibody. Splice overlap extension PCR (SOE-PCR) are used to create fully synthetic anti-CD20 variable (V) genes based on the V gene sequences of the murine 2B8 (U.S. Pat. No. 5,736,137). Full-length 2B8 VL and VH genes are then assembled by SOE-PCR to produce a single chain Fv (scFv) with 18-residue long linker (Whitlow 218 linker; GSTSGSGKPGSGEGSTKG (SEQ ID NO: 30)) in VL-VH orientation. Following SOE-PCR which also includes a signal peptide to the 5′-end (upstream) to enable secretion, the construct is cloned into pCR®-2.1-TOPO vector (Invitrogen Corp., Carlsbad, Calif.) and confirmed by sequencing. 
     Cells are cultured in the presence of a lentivirus encoding the exogeneous anti-CD20 antibody scFv anti-CD20 (Olafsen et al., J Nucl Med 2009, 50(9):1500) fused to the N-terminus of glycophorin A such that the final cell product expresses &gt;1×10{circumflex over ( )}5 copies of anti-CD20 scFv receiver per cell as assessed by flow cytometry. To ensure that the receiver is functionally expressed, in vitro activity is assessed by flow cytometry. Briefly, cells are incubated with soluble CD20 target protein (Abcam) at a range of concentrations. The target proteins are directly labeled with a fluorophore. Incubated cells are washed and analyzed by flow cytometry for presence of the fluorophore. 
     Example 78: Light Chain Amyloidosis 
     Cells are cultured in the presence of a lentivirus encoding the exogenous transgene Serum Amyloid P (SAP) component (GenBank: D00097.1) fused to the N terminus of glycophorin A such that the final cell product expresses &gt;1×10{circumflex over ( )}5 copies of SAP receiver per cell as assessed by flow cytometry. To ensure that the receiver is functionally expressed, in vitro activity is assessed by flow cytometry. Briefly, cells are incubated with serum from patients with light chain amyloidosis that are positive for amyloid plaques by anti-Light Chain ELISA. Binding of light chain amyloid plaques to the SAP-displaying cells is detected by secondary labeling with anti-lambda light chain antibodies (Abcam) that are directly labeled with fluorophore. Incubated cells are washed and analyzed by flow cytometry for presence of the fluorophore. 
     Example 79: Hepatitis B 
     Cells are cultured in the presence of a lentivirus encoding the exogenous transgene antibody scFv against hepatitis B surface antigen (HBsAg) (SEQ ID No. 1) such that the final cell product expresses &gt;1×10{circumflex over ( )}5 copies of antibody scFv receiver per cell as assessed by flow cytometry. To ensure that the receiver is functionally expressed, in vitro activity is assessed by flow cytometry. Briefly, cells are incubated with target protein HBsAg (Abcam) that is directly labeled with Dylight 650 fluorophore at a range of concentrations. Incubated cells are washed and analyzed by flow cytometry for presence of the fluorophore. 
     Example 80: ADA-SCID 
     Adenosine deaminase activity is monitored in vitro using HPLC protocol to detect adenosine and inosine levels. Approximately 10{circumflex over ( )}5 erythroid cells expressing an exogenous, intracellular adenosine deaminase, produced using the aforementioned transfection protocol, are aliquoted into 1 ml wells. 1 mM of adenosine is administered to each well and incubated for 1 hr. The cells are centrifuged and soluble protein is removed from the supernatant using cold methanol precipitation. The supernatant samples are then run on an Agilent 1100 HPLC using a standard inosine and adenosine curve to determine the relative amounts of nucleoside and intracellular enzymatic activity compared to natural cells. 
     Adenosine deaminase activity is monitored in vivo using HPLC protocol to detect adenosine and inosine levels. An ADA-SCID mouse model is treated with clodronate for 3 days prior to cell therapy administration. 100 ul of 10{circumflex over ( )}8 ADA expressing human erythroid cells are administered via tail vein injection to the mouse model and blood samples are taken via a submandibular bleed at 10 min, 12 h, 24, h, 48 h, 72 h. The samples are analyzed using HPLC and inosine and adenosine levels are tracked over time. 
     A population of 10{circumflex over ( )}8 cultured erythroid cells expressing 10K to 100K copies of ADA per cell is administered via tail vein injection to a cohort of NOD-SCID mice. Prior to injection adenosine and inosine circulation levels are documented. Cells are allowed to circulated for 1 week and blood samples are taken at 10 min, 1 h, 6, h, 12 h, 24, h, 48 h, 96 h, 144 h. Adenosine and inosine levels are tracked. 
     A patient diagnosed with ADA-SCID is confirmed via genotyping and found to be deficient for ADA activity. Relevant clinical symptoms used in the diagnosis include lymphocyte count, adenosine levels, and infection frequency. The patient is intravenously administered 10{circumflex over ( )}11 erythroid cells cultured from a blood-type matched donor and expressing exogenous ADA diluted in 500 ml of saline solution via gravity drain over the course of 1 hr. The procedure is repeated monthly for 6 months. Patient lymphocyte counts are tracked using immunofluorescence analysis of specific CD antigens, adenosine and inosine levels are monitored using HPLC, and infection rate recorded over the duration of the treatment. Immunogenic response to the transfusion is closely monitored. 
     The cultured erythroid cell population that over expresses adenosine deaminase is provided as a treatment for ADA-SCID. 
     A patient diagnosed as deficient for adenosine deaminase is intravenously administered single doses of 10{circumflex over ( )}9-10{circumflex over ( )}11 cells once a month for 6-12 months. During the course of treatment patients&#39; adenosine and inosine levels are monitored with daily blood tests and relevant ADA-SCID symptoms such as lymphocyte counts, infections, and skin rashes are documented. 
     A population of 10{circumflex over ( )}11 erythroid cells expressing between 10 K and 100 K copies of ADA per cell is stored in a transfusion bag with CPDA-1 and glycerol and stored at −80 C for up to 10 years. Upon treatment, the bag is thawed, centrifuged, and the cells removed and resuspended in saline for administration to a patient. Cells are intravenously administered with a 50 gauge needle at 5 ml/min at 37 C. 
     Example 81: MNGIE 
     Thymidine phosphorylase (TP) activity is monitored in vitro using HPLC protocol to detect thymidine and thymine levels. Approximately 10{circumflex over ( )}5 erythroid cells expressing an exogenous, intracellular thymidine phosphorylase, produced using the aforementioned transfection protocol, are aliquoted into 1 ml wells. 1 mM of thymidine is administered to each well and incubated for 1 hr. The cells are centrifuged and soluble protein is removed from the supernatant using cold methanol precipitation. The supernatant samples are then run on an Agilent 1100 HPLC using a standard thymidine and thymine curve to determine the relative amounts of nucleoside and intracellular enzymatic activity compared to natural cells. 
     Thymidine phosphorylase activity is monitored in vivo using HPLC protocol to detect thymidine and thymine levels. A TP deficient mouse model is treated with clodronate for 3 days prior to cell therapy administration (Haragushi, Mol. Cell Biol 2002). 100 ul of 10{circumflex over ( )}8 TP expressing erythroid cells are administered via tail vein injection to the mouse model and blood samples are taken via a submandibular bleed at 10 min, 12 h, 24, h, 48 h, 72 h. The samples are analyzed using HPLC and thymidine and thymine levels are tracked over time. 
     A patient diagnosed with MNGIE is confirmed via genotyping and found to be deficient for TYMP. Relevant clinical symptoms used in the diagnosis include gastrointestinal motility, early satiety, cachexia, and nausea. The patient is intravenously administered 10{circumflex over ( )}11 erythroid cells cultured from a blood-type matched donor and expressing exogenous TP diluted in 500 ml of saline solution via gravity drain over the course of 1 hr. The procedure is repeated monthly for 6 months. The patient&#39;s symptoms are monitored over the duration of the treatment, including thymidine and thymine levels using HPLC. 
     The cultured erythroid cell population that over expresses thymidine phosphorylase is provided as a treatment for MNGIE. 
     A patient diagnosed as deficient for thymidine phosphorylase is intravenously administered single doses of 10{circumflex over ( )}9-10{circumflex over ( )}11 cells once a month for 6-12 months. During the course of treatment patients&#39; thymidine and thymine levels are monitored with daily blood tests and relevant MNGIE symptoms such as gastrointestinal behavior and cachexia are documented. 
     A population of 10{circumflex over ( )}11 erythroid cells expressing between 10K and 100K copies of thymidine phosphorylase per cell is stored in a transfusion bag with CPDA-1 and glycerol and stored at −80 C for up to 10 years. Upon treatment, the bag is thawed, centrifuged, and the cells removed and resuspended in saline for administration to a patient. Cells are intravenously administered with a 50 gauge needle at 5 ml/min at 37 C. 
     Example 82: Gaucher Disease 
     An in vitro assay is conducted to demonstrate the delivery of β-glucocerebrosidase (GC) to macrophages using GC-loaded, or expressing, erythroid cells. Successful delivery is indicative of potential mechanistic action as a treatment for Gaucher&#39;s disease. Primary cultures of macrophages are prepared using a U937 cell line. Erythroid cells are loaded with GC and CFSE using transgene expression methods and standard protocol for small molecule loading, washed with Alsever&#39;s solution and added to the macrophages on coverslips at a ratio of 10:1. Plates are centrifuged at 2600 g for 5 min and incubated at 37 C for 30 min. Non-phagocytosed erythroid cells are lysed with hypotonic buffer. Macrophages are washed with PBS and stained with benzidine and Giemsa. The macrophages are then analyzed with FACS for internalized GC and CFSE, as well as accumulated ceramide levels using a diacylglycerol (DAG) kinase assay. 
     Erythroid cells from mice are washed with Alsever&#39;s solution and stained with PKH26 (Sigma Aldrich). Labeled, GC-loaded cells are injected into mice intraperitoneally. Four days after injection spleens are prepared for microscopy and 12 micron sections are visualized using a fluorescent microscope. PKH26 is observed and quantified. In addition, GC-loaded erythroid cells are administered and after 7 days circulating macrophage cell levels are quantified using FACS of respective CD antigens and compared to levels in control mice. Ceramide levels in the macrophage population are quantified using the DAG kinase assay. 
     A patient is diagnosed with Gaucher&#39;s disease according to characteristic symptoms such as; enlarged liver, anemia, thrombocytopenia, lung disease, arthritis, and genetic typing that identifies associated mutant genes. The patient is administered 10{circumflex over ( )}11 erythroid cells either loaded with or expressing GC. The cells are diluted in 500 ml of saline solution and are administered via gravity drain over the course of 1 hr. The procedure is repeated monthly for 6 months. The patient&#39;s symptoms are monitored over the duration of the treatment, including macrophage counts, bleeding and thrombotic events, and macrophage ceramide levels. 
     Example 83: ALL-Asparaginase 
     Asparaginase activity is monitored in vitro using HPLC protocol to detect L-asparagine and aspartic acid levels. Approximately 10{circumflex over ( )}5 erythroid cells expressing an exogenous, intracellular asparaginase, produced using the standard transfection protocol, are aliquoted into 1 ml wells. 1 mM of asparagine is administered to each well and incubated for 1 hr. The cells are centrifuged and soluble protein is removed from the supernatant using cold methanol precipitation. The supernatant samples are then run on an Agilent 1100 HPLC using a standard asparagine and aspartic acid curve to determine the relative amounts of amino acid and intracellular enzymatic activity compared to natural cells. 
     Asparaginase activity is monitored in vivo using HPLC protocol to detect asparagine and aspartic acid levels. An acute lymphocytic leukemia mouse model created via insertion of a mutant NOTCH1 gene is treated with clodronate for 3 days prior to cell therapy administration (Haragushi, Mol. Cell Biol 2002). 100 ul of 10{circumflex over ( )}8 asparaginase expressing erythroid cells are administered via tail vein injection to the mouse model and blood samples are taken via a submandibular bleed at 10 min, 12 h, 24, h, 48 h, 72 h. The samples are analyzed using HPLC and asparagine and aspartic acid levels are tracked over time as well as with T cell proliferation behavior demonstrative of leukemia progression. 
     A patient diagnosed with ALL according to standard symptoms and somatic mutation analysis, including NOTCH1, RAS/PI3K/AKT deregulated signaling is intravenously administered 10{circumflex over ( )}11 erythroid cells cultured from a blood-type matched donor. The cells express exogenous, intracellular asparaginase diluted in 500 ml of saline solution and are administered via gravity drain over the course of 1 hr. The procedure is repeated monthly for 6 months. The patient&#39;s symptoms are monitored over the duration of the treatment, including asparagine and aspartic acid levels using HPLC. Proliferative leukemic cells are quantified using immunofluorescence of blood samples. 
     Example 84: Thrombotic Thrombocytopenic Purpura 
     An in vitro assay is conducted to demonstrate the activity of ADAMTS13 expressed on a cultured erythroid cell&#39;s membrane. The ADAMTS13 assay is a FRET-inducible system that relies on a synthetic 73-amino-acid peptide, FRETS-VWF73. Cleavage of this substrate between two modified residues relieves the fluorescence quenching in the intact peptide. Incubation of FRETS-VWF73 with cultured erythroid cells, compared to native erythrocytes, demonstrates quantitatively increased fluorescence over time. Quantitative analysis is achieved within a 1-h period using a 96-well format in commercial plate readers with common filters (Kokame, Br J Haematol, 2005). 
     The mechanistic ability of an ADAMTS13 expressing cultured erythroid cell is demonstrated using an NSG mouse model that is administered clodronate for macrophage depletion. Recombinant, human Von Willebrand factor (VWF) is injected at 10 mM via the tail vein. 10{circumflex over ( )}8 human erythroid cells expressing ADAMTS13 is subsequently injected and blood samples are taken at 10 min, 1 hr, 4 hr, 8 hr, 24 hr. The serum is assayed for VWF cleavage using gel electrophoresis. Cleavage of the VWF by ADAMTS13 takes place leading to a reduction in multimer sizes. This reduction is visualized by agarose gel electrophoresis followed by Western blotting with a peroxidase-conjugated anti-VWF antibody. The concentration of ADAMTS13 activity in the test sample is established by reference to a series of diluted normal plasma samples. 
     A patient is diagnosed with thrombotic thrombocytopenia purpura according to characteristic symptoms such as; thrombocytopenia, microangiopathic hemolytic anemia, neurologic symptoms, kidney failure, and genetic typing that identifies associated mutant genes. The patient is administered 10{circumflex over ( )}11 erythroid cells expressing ADAMTS13 on the surface. The cells are diluted in 500 ml of saline solution and are administered via gravity drain over the course of 1 hr. The procedure is repeated monthly for 6 months. The patient&#39;s symptoms are monitored over the duration of the treatment, including VWF multimer levels, bleeding, and thrombotic events. 
     Example 85: Hemophilia B (FIX) 
     An in vitro assay is conducted to demonstrate the activity of Factor IX (FIX) expressed on a cultured erythroid cell&#39;s membrane. The Factor IXa assay protocol (activated Factor IX, BIOPHEN Factor IXa, Ref. A221812) is used to provide a quantitative chromogenic read out of a sample of erythroid cells. FIXa activity of the erythroid cells is compared to that of both native erythrocytes and human plasma. 
     A mouse model of hemophilia B (Jackson Laboratories, B6.129P2-F9 trn1Dws /J) is immunosuppressed with cyclophosphamide and cleared of macrophages with clodronate. The mouse is then injected with 10{circumflex over ( )}8 human erythroid cells expressing human FIX on the surface. The mouse is bled daily for 2 weeks via the tail vein and clotting time is recorded. Results are compared to a negative control mouse model and a positive control model that receives a single dose of soluble FIX. 
     A patient is diagnosed with hemophilia B according to characteristic symptoms such as; spontaneous bleeding, gastrointestinal tract hemorrhage, bruising, low circulating Factor IX levels, and genotyping that confirms mutation in the X-linked gene. The patient is administered 10{circumflex over ( )}11 erythroid cells expressing FIX on the surface. The cells are diluted in 500 ml of saline solution and are administered via gravity drain over the course of 1 hr. The procedure is repeated monthly for 6 months. The patient&#39;s symptoms are monitored over the duration of the treatment, including FIXa levels, spontaneous bleeding, and thrombotic events. 
     Example 85B: Acute Lymphoblastic Leukemia 
     Erythroid cells expressing scFv against the leuekemic antigen, Wilms&#39; tumor (WT1), are assayed in vitro for rosetting with primary sourced, WT1 positive, leukemia cells. Cells are cultivated at 3% hematocrit using McCoy&#39;s 5A medium enriched with 20% homologous serum, using the method described by Russell et al. 2011 Blood 118(13):e74. The presence of rosettes is detected and quantified using a novel Giemsa subvital staining methodology, modified from techniques applied in van Driessche, Leukemia 2005. The sampled culture suspension is stained with Giemsa (the final stain concentration is 5%) for 15 minutes. A small volume of this suspension (7.5 W) is used to make a wet mount with 22×32 mm (0.17 mm thickness) glass cover slip. The wet mount is examined immediately with light microscope under oil immersion magnification. The rosetting rate is determined by examining erythroid cells in McCoy&#39;s 5A medium enriched with 20% homologous serum. 
     An NSG mouse model is treated with clodronate to eliminate its macrophage population. The mouse is injected with 10{circumflex over ( )}8 leukemic cells that are positive for WT1. A population of erythroid cells expressing multiple copies of a scFv against WT1 on its surface is injected shortly thereafter and blood samples are taken at 10 min, 1 hr, 4 hr, 12 hr, 24 hr, 48 hr time points. Samples are analyzed using FACS and erythroid-B cell binding is quantified and compared to that of a positive control erythrocyte infused mouse. 
     A patient diagnosed with acute lymphoblastic leukemia according to characteristic symptoms such as; fatigue, fever loss of weight, anemia, abnormal white blood cell count, and positive bone marrow biopsy. The patient is administered 10{circumflex over ( )}11 erythroid cells expressing anti-WT1 scFv on the surface. The cells are diluted in 500 ml of saline solution and are administered via gravity drain over the course of 1 hr. The procedure is repeated monthly for 6 months. The patient&#39;s symptoms are monitored over the duration of the treatment, including leukemic white blood cell counts. 
     Example 86: ADAMTS13 Expression and Activity 
       FIG. 15  shows expression of ADAMTS13 fused to the extracellular domain of GPA in the erythroleukemia cell line K562. The ADAMTS13-GPA construct contains an HA epitope tag, which is detected with an anti-HA antibody by flow cytometry (a) and Western blot (b).  FIG. 16  shows the activity of ADAMTS13-GPA expressed on the erythroleukemia cell line K562, as measured by the enzymatic cleavage of vWF subdomain A2 detected by Western blot. Importantly, the cell-expressed ADAMTS13 (lane 4) appears more active than the recombinant ADAMTS13 (lane 2), despite the fact that there is 6× less cell-expressed ADAMTS13 (13 ng) than recombinant ADAMTS13 (75 ng) in the assay. This suggests that by virtue of being on the cell surface the enzyme is more active, likely through avidity effects or a local increase in concentration at the cell surface. 
     Example 87: Complement Factor I Expression 
       FIG. 17  shows expression of CFI fused to the extracellular domain of GPA in (a) the erythroleukemia cell line K562 and in (b) primary erythroid cells cultured from hematopoietic progenitors. The CFI-GPA construct contains an HA epitope tag, which is detected with an anti-HA antibody by flow cytometry (in a) or the entire construct is detected with an anti-CFI antibody by flow cytometry (in b). Figure C1 (c) shows the activity of CFI-GPA expressed on the erythroleukemia cell line K562, as measured by the enzymatic cleavage of recombinant complement factor C3b by Western blot. 
     Example 88: Phenylketonuria and Cell Proliferation Disorders 
     In  FIG. 18 , cultured erythroid cells expressing cytoplasmic free PAH (a) or PAH conjugated to the cytoplasmic C-terminus of glycophorin A (b) are shown at various stages of differentiation, from precursor to terminal cells. The protein is detected by Western blot against an HA epitope tag present on the constructs. The free PAH is quantified compared to recombinant PAH by Western blot (c) and found to be present at 5.3 ng PAH/ug total protein, which equates to approximately 300 fg PAH per cell, or approximately 5.6×10{circumflex over ( )}6 molecules of PAH per cell. The activity of PAH in cultured erythroid cells is shown in (d), measured as the production of tyrosine from phenylalanine in the presence of BH4 co-factor and measured by colorimetric readout (Biovision Inc. Milpitas Calif.). 
     Levels of exogenous protein were also measured in two other cultured erythroid cell samples: cells expressing PAL (phenylalanine ammonia lyase, e.g., for phenylketonuria) and MGL (methionine gamma lyase, e.g., for tumor starvation). Protein levels were measured using quantitative Western blot with an anti-HA antibody, and are shown in Table 16 herein. 
     Example 89: Cell Volume and Hemoglobin Concentration 
     The cell volume of cultured erythroid cells was determined by running the cells on a Moxi Z Coulter Counter instrument (Orflo Technologies, Ketchum Id.) using a size S-chip per manufacturer&#39;s instructions. Primary red blood cells (RBC), cultured erythroid cells (cRBC), and a commercial reticulocyte standard (Retic) used to calibrate hematology instruments (Liquichek, Bio-Rad, Hercules Calif.) were analyzed ( FIG. 27A ). As is apparent, reticulocytes are larger than mature erythrocytes—known in the literature—and there is substantial overlap in both size and distribution between the cultured erythroid cell population and the reticulocyte population. By the Coulter counter, RBCs have a volume range of approximately 37-232 fL and cultured erythroid cells have a volume range of 62-412 IL. A more detailed analysis of the populations in  FIG. 27B  demonstrates that approximately 9% of cultured erythroid cells have a volume that falls within the range of 70% of RBCs (&lt;100 fL), approximately 15% of cultured erythroid cells have a volume that falls within the range of 80% of RBCs (&lt;113 fL), approximately 32% of cultured erythroid cells have a volume that falls within the range of 90% of RBCs (&lt;135 fL), approximately 46% of cultured erythroid cells have a volume that falls within the range of 95% of RBCs (&lt;156 fL), and approximately 71% of cultured erythroid cells have a volume that falls within the range of 99% of RBCs (&lt;202 fL). 
     In another experiment, erythroid cells were observed to have a mean corpuscular hemoglobin of 26.0 pg, which is comparable with known hemoglobin content of isolated naturally occurring reticulocytes. 
     Next, the volume of six types of erythrocytes was measured. The types are untreated control cells, hypotonically treated and resealed erythrocytes, hypotonically treated, loaded, and resealed erythrocytes, human RBC, cultured untransfected erythrocytes, and cultured HA-GPA expressing erythrocytes. The untreated control cells, hypotonically treated and resealed erythrocytes, hypotonically treated, loaded, and resealed erythrocytes, were prepared from cells purchased from a healthy donor. Loaded red blood cells were produced essentially as described in Rossi et al. 2003, using a 0.5 ml 70% hematocrit solution. “Human RBC” cells are internal control cells analyzed in isotonic saline. Cell volume was measured in a Moxi Z Coulter counter using a Type S cassette, and diameter was calculated based on the volume measurement. Cells were measured at a concentration of about 3×10 3 −2.5×10 6  cells/ml. The cells were found to have the volume and diameter listed in Table 17 herein. 
     Cell volume was analyzed in populations of cells, and the volume distribution of the six cell types is shown in  FIGS. 28A and 28B . The data show that the transfected or untransfected cultured cells have a markedly larger cell volume than the four other cell types. 
     Example 90: Osmotic Fragility 
     Osmotic fragility of cultured erythroid cells, with or without expression of a receiver polypeptide in the cell cytoplasm, was compared to primary RBCs and primary RBCs that had been loaded by hypotonic dialysis (HD-RBCs).  FIG. 29  shows the osmotic fragility of the samples analyzed. Cultured erythroid cells, with or without expression of a receiver polypeptide, have an osmotic fragility (salt concentration at which 50% of cells are lysed) between 0.35-0.5% NaCl. Primary RBCs have an osmotic fragility between 0.45-0.55% NaCl. In contrast, HD-RBCs have an osmotic fragility between 0.6-0.8% NaCl. These data suggest that cultured erythroid cells comprising a receiver polypeptide maintain a key characteristic of red blood cells (osmotic fragility) close to that of naturally occurring RBCs. 
     Example 91: Phosphatidylserine Exposure 
     Phosphatidylserine (PS) is a phospholipid typically expressed in the inner leaflet of the plasma membrane of erythrocytes that, as the cell ages, is exposed on the cell surface. PS engages macrophages and thus, exposure of PS increases the likelihood that the cells will be phagocytosed. PS exposure is a known mechanism by which ejected nuclei are cleared, see e.g. Mankelow et al., Blood 2013, 122(21); Yoshida et al., Nature 2005, 437(7059):754-8. It is desirable to limit PS exposure on the surface of erythroid cells to improve long-term circulation in a human subject. PS exposure can be assessed by staining for Annexin-V-FITC, which binds preferentially to PS, and measuring FITC fluorescence by flow cytometry.  FIG. 30  shows Annexin-V staining of cultured erythroid cells. The cell population is gated by forward- and side-scatter to separate nucleated and enucleated cells from ejected nuclei known to be PS-high (gate R1). This population has low level of Annexin-V staining, statistically equivalent to cultured erythroid cells that do not express the receiver polypeptide.  FIG. 31  shows Annexin-V staining of primary RBCs and primary RBCs that have been loaded by hypotonic dialysis (HD-RBCs). The HD treatment damages the cells as can be seen by the introduction of a new cell population by forward and side-scatter analysis. Gating on the entire population or on any of the sub-populations shows that HD-RBCs have significantly more PS exposure than untreated RBCs, ranging from 36-69%. 
     Next, PS exposure was measured in nucleated cells, enucleated cells, and nuclei within a single population in order to characterize the difference between sub-populations of cells. A sample of cultured erythrocytes contains nucleated cells, enucleated cells, and ejected nuclei, as seen in  FIG. 32A  where the cells and nuclei are distinguished using Syto16 (a DNA dye which detects nuclei and nucleated cells) and FSC (forward scatter, which is low for nuclei and enucleated cells but high for nucleated cells).  FIG. 32A  shows that 39% of the cells in this population are enuclated.  FIG. 32B  shows that the prevalence of nucleated cells, enucleated cells, and nuclei is essentially the same in the presence of Annexin V (37%, compared to 39% in  FIG. 32A ). The level of Annexin V staining of each sub-population was then assayed.  FIG. 32C  shows that the ejected nuclei are high in Annexin-V staining (75% of ejected nuclei have staining over a threshold of about 3×10 4 ) and therefore high in exposed PS.  FIG. 32D  shows that in nucleated cells, Annexin-V stains at a moderate level (33% of cells have staining over a threshold of about 3×10 4 ).  FIG. 32E  shows that in enucleated cells, Annexin-V stains at a much lower level (only 7% of cells have staining over a threshold of about 3×10 4 ). This experiment indicates that enucleated erythrocytes described herein have low levels of exposed PS. 
     Furthermore, transduction of the erythrocytes does not change the low PS exposure levels observed. As shown in  FIG. 33A , a sample of cultured erythrocytes comprises nucleated cells, enucleated cells, and ejected nuclei, where enucleated cells make up about 39% of the cell population. After filtering, a level of about 99% enucleated cells is achieved ( FIG. 33B ), and nuclei and nucleated cells are depleted. When PS levels are assayed in filtered, enuclated cells, a low level of Annexin-V staining (7% of cells have staining over a threshold of about 3×10 4 ) was observed in untransduced cells ( FIG. 33C ) and cells transduced with HA-GPA ( FIG. 33D ). 
     The mean and median Annexin-V binding levels of three enucleated cell populations above was calculated and is shown in Table 18 herein. 
     Example 92: Non-Viral Delivery Methods 
     For lentivirally transduced K562 cells the expression of an epitope tag (HA tag) contained on the transgene is inversely correlated to the provirus length, with an approximately 1-log decrease in percent of cells expressing the HA tag for provirus constructs larger than approximately 6 kb (see  FIG. 21 ). While not intending to be bound by any particular theory, it is believed that the reason for the decrease in transduction efficiency has to do with the reduced packaging efficiency of longer provirus sequences within lentiviruses. A set of lentivirus constructs of provirus lengths ranging from 3.6 kb to 8.2 kb were tested (see  FIG. 22 ). The number of lentivirus particles produced was quantified using the number of p24 capsid proteins measured by ELISA. The number of copies of provirus RNA was measured by quantitative polymerase chain reaction (qPCR). Normalization provides a quantification of RNA copies per microgram p24 capsid protein as a function of provirus length. In the experiments, for provirus length &lt;5 kb about 3×10 9  RNA copies per microgram p24 could be seen. For constructs &gt;6 kb no virus preparation exhibited more than about 8×10 8  RNA copies per microgram p24 capsid. A size-dependent difference between RNA-containing and RNA-deficient virus preparations can be observed leading to a reduction in transduction efficiency. 
     Electroporation by a single pulse of 260V/150 μF of K562 cells and cultured erythroid cells (from primary cells) with mRNA encoding for green fluorescent protein (GFP) was performed (see,  FIG. 23 ). Successful gene transfer was measured by reading the fluorescence from the GFP, which requires that the mRNA successfully enter the cell and then be successfully translated into protein. The conditions from the literature that lead to successful electroporation of K562 cells (Van Tendeloo et al., Blood 2001 98(1):49-56) are insufficient for the effective delivery of exogenous nucleic acids to cultured erythroid cells (derived from primary progenitors). More than 50 different conditions for electroporation of cultured erythroid cells from primary progenitors were tested. Transfection efficiencies generally ranged from 0.1% transfected cells to more than 85% transfected cells (see,  FIG. 24 ).  FIG. 24  shows the translation of GFP from mRNA following electroporation of cultured erythroid cells from primary progenitors at day 8 of differentiation for 12 different conditions. Viability was measured using LIVE/DEAD stain from Life Technologies, in which cells that were negative for the stain were considered viable. Condition 1 corresponds to the untransfected control (0.21% GFP, 97.39% viability). Depending on the electroporation conditions used, cells had very good uptake of mRNA (86.9%) and high viability (92.6%), e.g. condition 2, or poor uptake of mRNA (30.9%) and poor viability (42.7%), e.g. condition 9. 
     As the cells continue to differentiate, different electroporation conditions are required to achieve good transgene uptake and expression while maintaining high viability. Greater than 50 conditions were tested on cells over the course of an approximately 20 day differentiation culture to identify conditions that were conducive to good transfection and good viability.  FIG. 25  shows the successful transfection of cells with GFP mRNA by electroporation at three different time points—day 8, day 13, and day 15. Suitable conditions are summarized in Tables 11 to 13. Cultured erythroid cells were also transfected with GFP mRNA by electroporation on day 10 and day 12 of differentiation, resulting in GFP expression (data not shown). 
     It was also observed, that electroporation under the conditions disclosed herein of erythroid cells cultured from primary progenitors did not appear to damage the cells&#39; ability to terminally differentiate. Cells that had been electroporated once were re-electroporated and again successfully took up and translated the transgene.  FIG. 26  shows a population of erythroid cells cultured from primary progenitors that were electroporated at day 9, allowed to divide for four days during which the amount of GFP fluorescence decreased—likely because of dilution of the mRNA and protein through cell division—and then re-electroporated at day 13. 
     Cultured erythroid cells were electroporated with GFP mRNA on day 4 of differentiation, which is during the expansion phase where the cells are relatively undifferentiated. On day 8 of differentiation, the cells showed GFP fluorescence and high viability by 7AAD staining, as shown in Table 19. In Table 19, P1 indicates the percentage of the main population that constitutes cells (e.g., high P1 values mean low levels of debris); % GFP indicates the percent of cells in P1 that show GFP fluorescence, MFI is the mean fluorescent intensity of the GFP+ cells, and % AAD-indicates the percent of cells that are AAD negative, where viable cells are AAD negative. 
     Example 93: ELISA 
     P24 protein was quantified using a commercial kit (Clontech) following manufacturer&#39;s protocol. Briefly, viral supernatants were dispensed into tubes with 20 uL lysis buffer and incubated at 37 C for 60 minutes, then transferred to a microtiter plate. The microtiter plate was washed and incubated with 100 μl of Anti-p24 (Biotin conjugate) detector antibody at 37 C for 60 minutes. Following a wash, the plate was incubated with 100 μl of Streptavidin-HRP conjugate at room temperature for 30 minutes, then washed again. 12. Substrate Solution was added to the plate and incubated at room temperature (18-25° C.) for 20 (±2) minutes. The reaction was topped with stop solution, and colorimetric readout detected by absorbance at 450 nm. 
     Example 94: qPCR 
     Viral RNA copies were quantified using a commercial lentivector qRT-PCR kit (Clontech) following manufacturer&#39;s protocol. Briefly, an RNA virus purification kit was used to extract RNA from lentiviral supernatant. The PCR reaction was performed with standard lentivirus primers (forward and reverse) that recognize conserved sequences on the viral genome and are not dependent on the specific transgene encoded by the vector. The RT reaction was performed with a 42 C 5 min incubation followed by a 95° C. 10 sec incubation, followed by 40 cycles of 95 C for 5 sec and 60 C for 30 sec. The instrument used was a Life Technologies QuantStudio. 
     Example 95: Production of mRNA by In Vitro Transcription 
     Kits for in vitro production of mRNA are available commercially, e.g. from Life Technologies MAxiscript T7 kit. Briefly, a gene of interest is cloned into an appropriate T7 promoter-containing plasmid DNA by standard molecular biology techniques. The transcription reaction is set up with 1 ug DNA template, 2 uL 10× transcription buffer, 1 uL each of 10 mM ATP, CTP, GTP, and UTP, 2 uL of T7 polymerase enzyme mix, in a total volume of 20 uL. The reaction is mixed thoroughly and incubated for 1 hr at 37 C. To remove contaminating residual plasmid DNA, 1 uL turbo DNAse is added and the reaction incubated for 15 minutes at 37 C. The reaction is stopped by the addition of 1 uL 0.5 M EDTA. The transcript is purified by gel electrophoresis or spin column purification. 
     Example 96: Electroporation 
     Cells were washed in RPMI buffer, loaded into a Life Technologies Neon electroporation instrument at a density of 1×10{circumflex over ( )}7 cells/mL in a total volume of 10 uL, and electroporated with the following conditions: 1 pulse of 1000 V, 50 ms pulse width. 
     Example 97: Electroporation with chemically modified mRNA 
     Chemically modified mRNA encoding GFP was purchased from TriLink. The RNA contains pseudo-uridine and 5-methyl cytosine. Differentiating erythroid cells were electroporated at day 4, 8, 10, or 12 of differentiation. On all days of differentiation tested, and under different electroporation conditions tested, GFP fluorescence was observed. Table 20 indicates the GFP fluorescence levels observed when cells were electroporated on day 4 and observed on day 8. Table 21 indicates GFP fluorescence levels observed when cells were electroporated on day 12 and observed on day 15. GFP fluorescence was also observed in cells electroporated at day 8 or 10 of differentiation (data not shown). 
     Cell viability and proliferation ability were measured in electroporated cells, using trypan blue staining. The cells were electroporated at day 8 of differentiation with unmodified GFP mRNA or TriLink chemically modified RNA comprising pseudo-uridine and 5-methyl cytosine. On day 9, GFP fluorescence was observed in the cells receiving unmodified or modified RNA (data not shown). Also on day 9, the total number of cell, number of live cells, and cell viability were measured. In the samples electroporated with unmodified mRNA, the number of live cells was lower than the number of live cells in the control cells that were electroporated without adding exogenous nucleic acid (see Table 22). This decline was partially reversed when modified RNA was used (Table 22). This indicates that electroporation with unmodified RNA may reduce cell growth or viability, and use of modified RNA can at least partially rescue growth or viability. 
     Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be readily apparent to one of ordinary skill in the art in light of the teachings of this invention that certain changes and modifications can be made thereto without departing from the spirit or scope of the appended claims. 
     Tables 
       
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Erythroid Polypeptides and Non-Receiver Polypeptides 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 ABO blood groups 
                 Stomatin 
                 Peters 
                 DAF Cromer 
               
               
                 Aquaporin 3 
                 Tropomyosin 
                 Rasmussen 
                 Gerbich (GYPC) 
               
               
                 Aubergers 
                 Glucose transporter 
                 Reid 
                 CD47 
               
               
                 Band 3 
                 Adducin 
                 REIT 
                 Glycophorin A, B, C 
               
               
                 Basigin 
                 Rabphilin 
                 SARA 
                 Band 3 (AE3) 
               
               
                 C41 
                 C1 tetrahydrofolate 
                 Rhesus blood D group 
                 GYPB Ss 
               
               
                   
                 synthase 
               
               
                 CD44 
                 Vel group 
                 Aldolase 
                 C4A, C4B Chido, 
               
               
                   
                   
                   
                 Rodgers C4 component 
               
               
                   
                   
                   
                 of complement 
               
               
                 Cis AB 
                 Lan antigen 
                 Tropomodulin 
                 HLA Bg HLA class I 
               
               
                 Diego (Di) 
                 At antigen 
                 Arginase 
                 RHAG Rh-associated 
               
               
                   
                   
                   
                 Ammonium transport 
               
               
                 Colton antigen 
                 Jr antigen 
                 Creatine kinase 
                 glycoprotein 
               
               
                 Complement 
                 AnWj antigen 
                 B-Cam protein 
                 Colton (Co) Water 
               
               
                 Component 4 
                   
                   
                 channel protein 
               
               
                 alpha(1,3) 
                 Sd antigen 
                 Rap1A 
                 ACHE Cartwright (Yt) 
               
               
                 fucosyltransferase 
                   
                   
                 Acetylcholinesterase 
               
               
                 CR1 
                 Batty 
                 Bennett-Goodspeed 
                 Glutathione transferase 
               
               
                 DAF 
                 Bilkes 
                 P antigen system 
                 Glycophorin C 
               
               
                 Diego 
                 Wright (Wr) 
                 Rh blood group 
                 Aquaporin 
               
               
                 Duffy 
                 Box 
                 Xg antigen system 
                 Erythroblast associated 
               
               
                   
                   
                   
                 membrane protein 
               
               
                 Hh/Bombay antigen 
                 Christiansen 
                 XK protein 
                 CD44 
               
               
                 ii antigen 
                 alpha(1,2) 
                 Yt/Cartwright antigen 
                 Synaptobrevin 2 
               
               
                   
                 fucosyltransferase 
                 system 
               
               
                 Indian blood group 
                 HJK 
                 CD58 
                 Ribonuclease 
               
               
                 Kell 
                 HOFM 
                 Rh 
                 ABO glycosyl 
               
               
                   
                   
                   
                 transferases 
               
               
                 Kidd 
                 JFV 
                 AnWj Adhesion 
                 CD59 
               
               
                   
                   
                 receptor 
               
               
                 Lewis antigen 
                 JONEs 
                 Scianna 
                 CD44 
               
               
                 Lutheran antigen 
                 Jensen 
                 Radin 
                 MER2 
               
               
                 MNS antigen system 
                 Katagiri 
                 Duodenal cytochrome B 
                 DOK Dombrock ADP- 
               
               
                   
                   
                   
                 ribosyltransferase 
               
               
                 Cost group 
                 Livesay 
                 DARC (Duffy) 
                 SEMA7A JMH 
               
               
                   
                   
                   
                 Putative adhesion 
               
               
                   
                   
                   
                 receptor 
               
               
                 Er group 
                 Milne 
                 CR1 Knops-McCoy 
                 UMOD Sda Tamm- 
               
               
                   
                   
                   
                 Horsfall protein 
               
               
                   
                   
                   
                 (uromodulin) 
               
               
                 Dematin 
                 Oldeide 
                 FP Family 
                 Anion exchanger 
               
               
                   
                   
                   
                 channel protein (band 
               
               
                   
                   
                   
                 3, AE1) 
               
               
                 Indian (In) 
                 Annexin Family 
                 Tweety Family 
                 CTL Family 
               
               
                 Kidd (Jk) Urea 
                 Bcl-2 Family 
                 UT Family 
                 DAACS Family 
               
               
                 transporter 
               
               
                 FUT3 Lewis (Le) 
                 Bestrophin Family 
                 VIC Family 
                 DASS family 
               
               
                 Adenosine deaminase 
                 BNip3 Family 
                 AAAP Family 
                 DMT family 
               
               
                 OK Oka Neurothelin, 
                 CD20 Family 
                 transferrin receptor 
                 ENT Family 
               
               
                 putative adhesion 
               
               
                 molecule 
               
               
                 LW Adhesion receptor 
                 CLIC Family 
                 c-KIT 
                 GPH Family 
               
               
                 FUT2 Secretor (Se) 
                 Connexin Family 
                 Insulin receptors 1 &amp; 2 
                 GUP Family 
               
               
                 FUT1 Hh alpha 
                 CRAC-C Family 
                 Estrogen receptor 
                 LCT Family 
               
               
                 LU Lutheran (Lu) 
                 Ctr Family 
                 Dexamethasone 
                 MC family 
               
               
                 Adhesion receptor 
                   
                 receptor 
               
               
                 P1 Glycosyltransferase 
                 E-CIC Family 
                 JAK2 kinase 
                 MET Family 
               
               
                 XK Kx Putative 
                 ENaC Family 
                 ABC family 
                 MFS Family 
               
               
                 neurotransmitter 
               
               
                 transporter 
               
               
                 XG Xg formerly called 
                 GIC Family 
                 ArsAB family 
                 MOP Family 
               
               
                 PBDX 
               
               
                 MIC2 
                 ICC Family 
                 F-ATPase Family 
                 MTC Family 
               
               
                 Hemoglobin 
                 Innexin Family 
                 IISP Family 
                 NCS2 Family 
               
               
                 Ankyrin 
                 IRK-C Family 
                 MPT Family 
                 Nramp Family 
               
               
                 Spectrin 
                 LIC Family 
                 P-ATPase Family 
                 NSS Family 
               
               
                 KEL Kell (K, k, Kp, Js) 
                 MIP Family 
                 AE family 
                 OAT Family 
               
               
                 Metalloproteinase 
               
               
                 Torkildsen 
                 MIT family 
                 APC Family 
                 OST Family 
               
               
                 Rab 35 
                 NSCC2 Family 
                 ArsB Family 
                 Oxa1 Family 
               
               
                 Ral A binding protein 
                 PCC Family 
                 BASS Family 
                 PiT Family 
               
               
                 Zona pellucida binding 
                 Plamolipin Family 
                 CaCA Family 
                 PNaS Family 
               
               
                 protein 
               
               
                 Lyn B protein 
                 PLB Family 
                 CCC Family 
                 POT Family 
               
               
                 KIaa1741 protein 
                 PLM Family 
                 CDF Family 
                 RFC Family 
               
               
                 DC38 
                 Presenilin Family 
                 CIC Family 
                 RND Family* 
               
               
                 Calciums transporting 
                 RIR-CaC Family 
                 CNT Family 
                 SSS Family 
               
               
                 ATPase 
               
               
                 ACC Family 
                 TRIC Family 
                 CPA1 Family 
                 STRA6 Family 
               
               
                 Amt Family 
                 TRP-CC Family 
                 CPA2 Family 
                 SulP Family 
               
               
                 ZIP Family 
                 HCC Family 
                 NIPA Family 
                 N-MDE Family 
               
               
                 ATP-E Family 
                 LPI Family 
                 PPI Family 
                 Epo receptor 
               
               
                 dsRNA-T Family 
                 MagT1 Family 
                 PPI2 Family 
                 MgtE Family 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Erythroid Cells 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                 Embryonic stem cells (ESC) 
                 Blastocyte colony-forming cells 
               
               
                 Cord blood stem cell (CD-SC) 
                 Burst-forming unit erythroid (BFU-E) 
               
               
                 CD34+ cells 
                 Megakaryocyte-erythroid progenitor (MEP) cell 
               
               
                 Hematopoietic stem cells (HSC) 
                 Erythroid forming colony unit (CFU-E) 
               
               
                 Spleen colony forming unit (CFU-S) 
                 Reticulocytes 
               
               
                 Common myeloid progenitor (CMP) cells capable 
                 Erythrocytes 
               
               
                 of forming a granulocyte, erythrocyte, monocyte, 
               
               
                 or megakaryocyte (CFU-GEMM) 
               
               
                 Any cell of myeloid lineage 
                 Induced pluripotent stem cells (iPSC) 
               
               
                 Proerythroblast 
                 Mesenchymal stem cell 
               
               
                 Polychromatophilic erythrocyte 
                 Polychromatic normoblasts 
               
               
                 Normoblast 
                 Orthochromatic normoblasts 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Erythroid Promoters 
               
            
           
           
               
               
               
            
               
                   
                 Promoter 
                 Gene 
               
               
                   
                   
               
               
                   
                 beta globin promoter 
                 beta globin 
               
               
                   
                 3′ beta-globin enhancer 
                 beta globin 
               
               
                   
                 beta globin locus control region 
                 beta globin 
               
               
                   
                 GATA-1 promoter 
                 GATA-1 
               
               
                   
                 GYPA promoter 
                 Glycophorin A 
               
               
                   
                 HK1 promoter 
                 Hexokinase 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
               
                   
               
               
                 Sequences of Complement Receptor 1 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 4A. CR1 isoform S precursor,  Homo   sapiens  NCBI Reference Sequence 
               
               
                 No. NP_000642.3 
               
            
           
           
               
               
            
               
                 1 
                 mgassprspe pvgppapglp fccggsllav vvllalpvaw gqcnapewlp farptnitde 
               
               
                 61 
                 fefpigtyln yecrpgysgr pfsiiclkns vwtgakdrcr rkscrnppdp vngmvhvikg 
               
               
                 121 
                 iqfgsqikys ctkgyrligs ssatciisgd tviwdnetpi cdripcglpp titngdfist 
               
               
                 181 
                 nrenfhygsv vtyrcnpgsg grkvfelvge psiyctsndd qvgiwsgpap qciipnkctp 
               
               
                 241 
                 pnvengilvs dnrslfslne vvefrcqpgf vmkgprrvkc qalnkwepel pscsrvcqpp 
               
               
                 301 
                 pdvlhaertq rdkdnfspgq evfyscepgy dlrgaasmrc tpqgdwspaa ptcevkscdd 
               
               
                 361 
                 fmgqllngry lfpvnlqlga kvdfvcdegf qlkgssasyc vlagmeslwn ssvpvccqif 
               
               
                 421 
                 cpsppvipng rhtgkplevf pfgktvnytc dphpdrgtsf dligestirc tsdpqgngvw 
               
               
                 481 
                 sspaprcgil ghcqapdhfl faklktqtna sdfpigtslk yecrpeyygr pfsitcldnl 
               
               
                 541 
                 vwsspkdvck rkscktppdp vngmvhvitd iqvgsrinys cttghrligh ssaecilsgn 
               
               
                 601 
                 aahwstkppi cqripcglpp tiangdfist nrenfhygsv vtyrcnpgsg grkvfelvge 
               
               
                 661 
                 psiyctsndd qvgiwsgpap qciipnkctp pnvengilvs dnrslfslne vvefrcqpgf 
               
               
                 721 
                 vmkgprrvkc qalnkwepel pscsrvcqpp pdvlhaertq rdkdnfspgq evfyscepgy 
               
               
                 781 
                 dlrgaasmrc tpqgdwspaa ptcevkscdd fmgqllngry lfpvnlqlga kvdfvcdegf 
               
               
                 841 
                 qlkgssasyc vlagmeslwn ssvpvceqif cpsppvipng rhtgkplevf pfgktvnytc 
               
               
                 901 
                 dphpdrgtsf dligestirc tsdpqgngvw sspaprcgil ghcqapdhfl faklktqtna 
               
               
                 961 
                 sdfpigtslk yecrpeyygr pfsitcldnl vwsspkdvck rkscktppdp vngmvhvitd 
               
               
                 1021 
                 iqvgsrinys cttghrligh ssaecilsgn aahwstkppi cqripcglpp tiangdfist 
               
               
                 1081 
                 nrenthygsv vtyrcnpgsg grkvfelvge psiyctsndd qvgiwsgpap qciipnkctp 
               
               
                 1141 
                 pnvengilvs dnrslfslne vvefrcqpgf vmkgprrvkc qalnkwepel pscsrvcqpp 
               
               
                 1201 
                 pdvlhaertq rdkdnfspgq evfyscepgy dlrgaasmrc tpqgdwspaa ptcevkscdd 
               
               
                 1261 
                 fmgqllngry lfpvnlqlga kvdfvcdegf qlkgssasyc vlagmeslwn ssvpvceqif 
               
               
                 1321 
                 cpsppvipng rhtgkplevf pfgkavnytc dphpdrgtsf dligestirc tsdpqgngvw 
               
               
                 1381 
                 sspaprcgil ghcqapdhfl faklktqtna sdfpigtslk yecrpeyygr pfsitcldnl 
               
               
                 1441 
                 vwsspkdvck rkscktppdp vngmvhvitd iqvgsrinys cttghrligh ssaecilsgn 
               
               
                 1501 
                 tahwstkppi cqripcglpp tiangdfist nrenfhygsv vtyrcnlgsr grkvfelvge 
               
               
                 1561 
                 psiyctsndd qvgiwsgpap qciipnkctp pnvengilvs dnrslfslne vvefrcqpgf 
               
               
                 1621 
                 vmkgprrvkc qalnkwepel pscsrvcqpp peilhgehtp shqdnfspgq evfyscepgy 
               
               
                 1681 
                 dlrgaaslhc tpqgdwspea prcavkscdd flgqlphgry lfpinlqlga kvsfvcdegf 
               
               
                 1741 
                 rlkgssyshc vlvgmrslwn nsvpvcehif cpnppailng rhtgtpsgdi pygkeisytc 
               
               
                 1801 
                 dphpdrgmtf nligestirc tsdphgngvw sspaprcels vraghcktpe qfpfasptip 
               
               
                 1861 
                 indfefpvgt slnyecrpgy fgkmfsiscl enlvwssved ncrrkscgpp pepfngmvhi 
               
               
                 1921 
                 ntdtqfgstv nyscnegfrl igspsttclv sgnnvtwdkk apiceiisce ppptisngdf 
               
               
                 1981 
                 ysnnrtsfhn gtvvtyqcht gpdgeqlfel vgersiycts kddqvgvwss ppprcistnk 
               
               
                 2041 
                 ctapevenai rvpgnrsfft lteiirfrcq pgfvmvgsht vqcqtngrwg pklphcsrvc 
               
               
                 2101 
                 qpppeilhge htlshqdnfs pgqevfysce psydlrgaas lhctpqgdws peaprctvks 
               
               
                 2161 
                 cddflgqlph grvllpinlq lgakvsfvcd egfrlkgrsa shcvlagmka lwnssvpvce 
               
               
                 2221 
                 qifcpnppai lngrhtgtpf gdipygkeis yacdthpdrg mtfnligess irctsdpqgn 
               
               
                 2281 
                 gvwsspaprc elsvpaacph ppkiqnghyi gghvslylpg mtisyicdpg yllvgkgfif 
               
               
                 2341 
                 ctdqgiwsql dhyckevncs fplfmngisk elemkkvyhy gdyvtlkced gytlegspws 
               
               
                 2401 
                 qcqaddrwdp plakctsrth dalivgtlsg tiffilliif lswiilkhrk gnnahenpke 
               
               
                 2461 
                 vaihlhsqgg ssvhprtlqt neensrvlp (Seq. ID No. 1) 
               
               
                   
               
            
           
           
               
            
               
                 4B. CR1 isoform F precursor,  Homo   sapiens  NCBI Reference 
               
               
                 Sequence No. NP_000564.2 
               
            
           
           
               
               
            
               
                 1 
                 mgassprspe pvgppapglp fccggsllav vvllalpvaw gqcnapewlp farptnitde 
               
               
                 61 
                 fefpigtyln yecrpgysgr pfsiiclkns vwtgakdrcr rkscrnppdp vngmvhvikg 
               
               
                 121 
                 iqfgsqikys ctkgyrligs ssatciisgd tviwdnetpi cdripcglpp titngdfist 
               
               
                 181 
                 nrenfhygsv vtyrcnpgsg grkvfelvge psiyctsndd qvgiwsgpap qciipnkctp 
               
               
                 241 
                 pnvengilvs dnrslfslne vvefrcqpgf vmkgprrvkc qalnkwepel pscsrvcqpp 
               
               
                 301 
                 pdvlhaertq rdkdnfspgq evfyscepgy dlrgaasmrc tpqgdwspaa ptcevkscdd 
               
               
                 361 
                 fmgqllngry lfpvnlqlga kvdfvcdegf qlkgssasyc vlagmeslwn ssvpvceqif 
               
               
                 421 
                 cpsppvipng rhtgkplevf pfgktvnytc dphpdrgtsf dligestirc tsdpqgngvw 
               
               
                 481 
                 sspaprcgil ghcqapdhfl faklktqtna sdfpigtslk yecrpeyygr pfsitcldnl 
               
               
                 541 
                 vwsspkdvck rkscktppdp vngmvhvitd iqvgsrinys cttghrligh ssaecilsgn 
               
               
                 601 
                 aahwstkppi cqripcglpp tiangdfist nrenfhygsv vtyrcnpgsg grkvfelvge 
               
               
                 661 
                 psiyctsndd qvgiwsgpap qciipnkctp pnvengilvs dnrslfslne vvefrcqpgf 
               
               
                 721 
                 vmkgprrvkc qalnkwepel pscsrvcqpp pdvlhaertq rdkdnfspgq evfyscepgy 
               
               
                 781 
                 dlrgaasmrc tpqgdwspaa ptcevkscdd fmgqllngrv lfpvnlqlga kvdfvcdegf 
               
               
                 841 
                 qlkgssasyc vlagmeslwn ssvpvceqif cpsppvipng rhtgkplevf pfgkavnytc 
               
               
                 901 
                 dphpdrgtsf dligestirc tsdpqgngvw sspaprcgil ghcqapdhfl faklktqtna 
               
               
                 961 
                 sdfpigtslk yecrpeyygr pfsitcldnl vwsspkdvck rkscktppdp vngmvhvitd 
               
               
                 1021 
                 iqvgsrinys cttghrligh ssaecilsgn tahwstkppi cqripcglpp tiangdfist 
               
               
                 1081 
                 nrenfhygsv vtyrcnIgsr grkvfelvge psiyctsndd qvgiwsgpap qciipnkctp 
               
               
                 1141 
                 pnvengilvs dnrslfslne vvefrcqpgf vmkgprrvkc qalnkwepel pscsrvcqpp 
               
               
                 1201 
                 peilhgehtp shqdnfspgq evfyscepgy dlrgaaslhc tpqgdwspea prcavkscdd 
               
               
                 1261 
                 flgqlphgry lfpinlqlga kvsfvcdegf rlkgssyshc vlvgmrslwn nsvpvcehif 
               
               
                 1321 
                 cpnppailng rhtgtpsgdi pygkeisytc dphpdrgmtf nligestirc tsdphgngvw 
               
               
                 1381 
                 sspaprcels vraghcktpe qfpfasptip indfefpvgt slnyecrpgy fgkmfsiscl 
               
               
                 1441 
                 enlvwssved ncrrkscgpp pepfngmvhi rudtqfgstv nyscnegfrl igspsttclv 
               
               
                 1501 
                 sgnnvtwdkk apiceiisce ppptisngdf ysnnrtsfhn gtvvtyqcht gpdgeqlfel 
               
               
                 1561 
                 vgersiycts kddqvgvwss ppprcistnk ctapevenai rvpgnrsfft lteiirfrcq 
               
               
                 1621 
                 pgfvmvgsht vqcqtngrwg pklphcsrvc qpppeilhge htlshqdnfs pgqevfysce 
               
               
                 1681 
                 psydlrgaas lhctpqgdws peaprctvks cddflgqlph grvllpinlq lgakvsfvcd 
               
               
                 1741 
                 egfrIkgrsa shcvlagmka lwnssvpvce qifcpnppai lngrhtgtpf gdipygkeis 
               
               
                 1801 
                 yacdthpdrg mtfnligess irctsdpqgn gvwsspaprc elsvpaacph ppkiqnghyi 
               
               
                 1861 
                 gghvslylpg mtisyicdpg yllvgkgfif ctdqgiwsql dhyckevncs fplfmngisk 
               
               
                 1921 
                 elemkkvyhy gdyvtlkced gytlegspws qcqaddrwdp plakctsrth dalivgtlsg 
               
               
                 1981 
                 tiffilliif lswiilkhrk gnnahenpke vaihlhsqgg ssvhprtlqt neensrvlp 
               
               
                   
                 (Seq. ID No. 2) 
               
               
                   
               
            
           
           
               
            
               
                 4C. Predicted CR1 isoform X1,  Homo   sapiens , NCBI Reference Sequence 
               
               
                 No. XP_005273121.1 
               
            
           
           
               
               
            
               
                 1 
                 mclgrmgass prspepvgpp apglpfccgg sllavvvlla lpvawgqcna pewlpfarpt 
               
               
                 61 
                 nitdefefpi gtylnyecrp gysgrpfsii clknsvwtga kdrcrrkscr nppdpvngmv 
               
               
                 121 
                 hvikgiqfgs qikysctkgy rligsssatc iisgdtviwd netpicdrip cglpptitng 
               
               
                 181 
                 dfistnrenf hygsvvtyrc npgsggrkvf elvgepsiyc tsnddqvgiw sgpapqciip 
               
               
                 241 
                 nkctppnven gilvsdnrsl fslnevvefr cqpgfvmkgp rrvkcqalnk wepelpscsr 
               
               
                 301 
                 vcqpppdvlh aertqrdkdn fspgqevfys cepgydlrga asmrctpqgd wspaaptcev 
               
               
                 361 
                 kscddfmgql lngrvlfpvn lqlgakvdfv cdegfqlkgs sasycvlagm eslwnssvpv 
               
               
                 421 
                 ceqifcpspp vipngrhtgk plevfpfgkt vnytcdphpd rgtsfdlige stirctsdpq 
               
               
                 481 
                 gngvwsspap rcgilghcqa pdhflfaklk tqtnasdfpi gtslkyecrp eyygrpfsit 
               
               
                 541 
                 cldnlvwssp kdvckrksck tppdpvngmv hvitdiqvgs rinyscttgh rlighssaec 
               
               
                 601 
                 ilsgnaahws tkppicqrip cglpptiang dfistnrenf hygsvvtyrc npgsggrkvf 
               
               
                 661 
                 elvgepsiyc tsnddqvgiw sgpapqciip nkctppnven gilvsdnrsl fslnevvefr 
               
               
                 721 
                 cqpgfvmkgp rrvkcqalnk wepelpscsr vcqpppdvlh aertqrdkdn fspgqevfys 
               
               
                 781 
                 cepgydlrga asmrctpqgd wspaaptcev kscddfmgql lngrvlfpvn lqlgakvdfv 
               
               
                 841 
                 cdegfqlkgs sasycvlagm eslwnssvpv ceqifcpspp vipngrhtgk plevfpfgkt 
               
               
                 901 
                 vnytcdphpd rgtsfdlige stirctsdpq gngvwsspap rcgilghcqa pdhflfaklk 
               
               
                 961 
                 tqtnasdfpi gtslkyecrp eyygrpfsit cldnlvwssp kdvckrksck tppdpvngmv 
               
               
                 1021 
                 hvitdiqvgs rinyscttgh rlighssaec ilsgnaahws tkppicqlcq pppdvlhaer 
               
               
                 1081 
                 tqrdkdnfsp gqevfyscep gydlrgaasm rctpqgdwsp aaptcevksc ddfmgqllng 
               
               
                 1141 
                 rvlfpvnlql gakvdfvcde gfqlkgssas ycvlagmesl wnssvpvceq ifcpsppvip 
               
               
                 1201 
                 ngrhtgkple vfpfgkavny tcdphpdrgt sfdligesti rctsdpqgng vwsspaprcg 
               
               
                 1261 
                 ilghcqapdh flfaklktqt nasdfpigts lkyecrpeyy grpfsitcld nlvwsspkdv 
               
               
                 1321 
                 ckrkscktpp dpvngmvhvi tdiqvgsrin yscttghrli ghssaecils gntahwstkp 
               
               
                 1381 
                 picqripcgl pptiangdfi stnrenfhyg svvtyrcnlg srgrkvfelv gepsiyctsn 
               
               
                 1441 
                 ddqvgiwsgp apqciipnkc tppnvengil vsdnrslfsl nevvefrcqp gfvmkgprry 
               
               
                 1501 
                 kcqalnkwep elpscsrvcq pppeilhgeh tpshqdnfsp gqevfyscep gydlrgaasl 
               
               
                 1561 
                 hctpqgdwsp eaprcavksc ddflgqlphg rvlfpinlql gakvsfvcde gfrlkgssys 
               
               
                 1621 
                 hcvlvgmrsl wnnsvpvceh ifcpnppail ngrhtgtpsg dipygkeisy tcdphpdrgm 
               
               
                 1681 
                 tfnligesti rctsdphgng vwsspaprce lsvraghckt peqfpfaspt ipindfefpv 
               
               
                 1741 
                 gtslnyecrp gyfgkmfsis clenlvwssv edncrrkscg pppepfngmv hintdtqfgs 
               
               
                 1801 
                 tvnyscnegf rligspsttc lvsgnnvtwd kkapiceiis ceppptisng dfysnnrtsf 
               
               
                 1861 
                 hngtvvtyqc htgpdgeqlf elvgersiyc tskddqvgvw ssppprcist nkctapeven 
               
               
                 1921 
                 airvpgnrsf ftlteiirfr cqpgfvmvgs htvqcqtngr wgpklphcsr vcqpppeilh 
               
               
                 1981 
                 gehtlshqdn fspgqevfys cepsydlrga aslhctpqgd wspeaprctv kscddflgql 
               
               
                 2041 
                 phgrvllpin lqlgakvsfv cdcgfrlkgr sashcvlagm kalwnssvpv ceqifcpnpp 
               
               
                 2101 
                 ailngrhtgt pfgdipygke isyacdthpd rgmtfnlige ssirctsdpq gngvwsspap 
               
               
                 2161 
                 rcelsvpaac phppkiqngh yigghvslyl pgmtisyicd pgyllvgkgf ifctdqgiws 
               
               
                 2221 
                 qldhyckevn csfplfmngi skelemkkvy hygdyvtlkc edgytlegsp wsqcqaddrw 
               
               
                 2281 
                 dpplakctsr thdalivgtl sgtiffilli iflswiilkh rkgnnahenp kevaihlhsq 
               
               
                 2341 
                 ggssvhprtl qtneensrvl p (Seq. ID No. 3) 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 5 
               
               
                   
               
               
                 Targets 
               
               
                   
               
             
            
               
                 General Classes of Targets 
               
            
           
           
               
               
               
               
            
               
                 Microbes 
                 Polypeptides 
                 DNA 
                 Amino Acids 
               
               
                 Fungi 
                 Toxins 
                 RNA 
                 Prions 
               
               
                 Bacteria 
                 Lipids 
                 Parasites 
                 Cytokines 
               
               
                 Virus 
                 Cells 
                 Cellular debris 
                 Complement-associated 
               
               
                   
                   
                   
                 molecules 
               
            
           
           
               
            
               
                 Complement-Related Targets 
               
            
           
           
               
               
               
               
            
               
                 Immune complexes 
                 C3dg 
                 C4a 
                 C6 
               
               
                 Factor B 
                 C3dk 
                 C4b 
                 C7 
               
               
                 Factor D 
                 C3e 
                 C2 
                 C8 
               
               
                 Properdin 
                 Bb 
                 C4bp 
                 C9 
               
            
           
           
               
               
               
            
               
                 C3 
                 membrane attack complex 
                 Mannose-Binding Lectin (MBL) 
               
               
                 C3a 
                 C1q 
                 MBL-Associated Serine Protease 1 (MASP1) 
               
               
                 C3b 
                 C1r 
                 MBL-Associated Serine Protease 2 (MASP2) 
               
            
           
           
               
               
               
               
            
               
                 iC3b 
                 C1s 
                 C5 
                   
               
               
                 C3c 
                 C4 
                 C5a 
               
            
           
           
               
            
               
                 Infectious Disease-Related Targets 
               
            
           
           
               
               
               
               
            
               
                 Lipopolysaccharides 
                 Cell invasion 
                 Intermedilysin 
                 Secreted effector protein 
               
               
                   
                 protein 
                   
                 sptP 
               
               
                 Zona occludens toxin 
                 Cholera enterotoxin 
                 Invasion protein 
                 Seeligeriolysin 
               
               
                   
                   
                 sipA 
               
               
                 Actin polymerization protein 
                 Cysteine protease 
                 Iota toxin 
                 Serine protease 
               
               
                 RickA 
                   
                 component Ia 
               
               
                 Actin polymerization protein 
                 Cytolethal 
                 Ivanolysin 
                 Shiga toxin 
               
               
                 RickA 
                 distending toxin 
               
               
                 Adenosine monophosphate- 
                 Cytolysin 
                 LepB 
                 Sphingomyelinase 
               
               
                 protein transferase vopS 
               
               
                 adenylate cyclase 
                 Cytotoxic 
                 Lethal factor 
                 Staphylokinase 
               
               
                   
                 necrotizing factor 
               
               
                 Adenylate cyclase ExoY 
                 Cytotoxin 
                 Leukotoxin 
                 Streptokinase 
               
               
                 ADP-ribosyltransferase 
                 Dermonecrotic 
                 Listeriolysin 
                 Streptolysin 
               
               
                 enzymatic component 
                 toxin 
               
               
                 Aerolysin 
                 Deubiquitinase 
                 Microbial 
                 Streptopain 
               
               
                   
                   
                 collagenase 
               
               
                 Alpha-toxin 
                 Diphtheria toxin 
                 Outer membrane 
                 Suilysin 
               
               
                   
                   
                 protein IcsA 
               
               
                   
                   
                 autotransporter 
               
               
                 Alveolysin 
                 Enterohemolysin 
                 Panton-Valentine 
                 Superantigen 
               
               
                   
                   
                 Leucocidin F 
               
               
                 Alveolysin 
                 Enterotoxin 
                 Perfringolysin 
                 T3SS secreted effector 
               
               
                   
                   
                   
                 EspF 
               
               
                 Anthrolysin O 
                 Epidermal cell 
                 Pertussis toxin 
                 Tetanus toxin 
               
               
                   
                 differentiation 
               
               
                   
                 inhibitor 
               
               
                 Arp2/3 complex-activating 
                 Exoenzyme 
                 Phospholipase 
                 Tir 
               
               
                 protein rickA 
               
               
                 Binary ADP- 
                 Exotoxin 
                 Plasminogen 
                 TolC 
               
               
                 ribosyltransferase CDT toxin 
                   
                 activator 
               
               
                 Botulinum neurotoxin 
                 G-nucleotide 
                 Pneumolysin 
                 Toxic shock syndrome 
               
               
                   
                 exchange factor 
                   
                 toxin 
               
               
                 C2 toxin, component II 
                 Guanine nucleotide 
                 Protective antigen 
                 Zink-carboxypeptidase 
               
               
                   
                 exchange factor 
               
               
                   
                 sopE 
               
               
                 CagA 
                 Heat stable 
                 Protein kinase 
                 Zink-carboxypeptidase 
               
               
                   
                 enterotoxin 
               
               
                 Calmodulin-sensitive 
                 IgA-specific serine 
                 Pyolysin 
                 Zn-dependent peptidase 
               
               
                 adenylate cyclase 
                 endopeptidase 
               
               
                   
                 autotransporter 
               
               
                 Cell cycle inhibiting factor 
                 Inositol phosphate 
                 RTX toxin 
               
               
                   
                 phosphatase sopB 
               
            
           
           
               
            
               
                 Other Molecular Targets 
               
            
           
           
               
               
               
               
            
               
                 G-CSF 
                 IL3 
                 IL10 
                 MIP1a 
               
               
                 GM-CSF 
                 IL4 
                 IL12 
                 MIP1b 
               
               
                 M-CSF 
                 IL5 
                 IFNa 
                 TGFb 
               
               
                 IL1a 
                 IL6 
                 IFNb 
                 TNFa 
               
               
                 IL1b 
                 IL7 
                 IFNg 
                 TNFb 
               
               
                 IL2 
                 IL8 
                 Self-antibodies 
                 Non-self antibodies 
               
               
                 PRP 
                 PRPc 
                 PRPsc 
                 PRPres 
               
            
           
           
               
            
               
                 Lipid &amp; Cell Targets 
               
            
           
           
               
               
               
               
            
               
                 Circulating tumor cells 
                 very low density 
                 triglycerides 
                 Fatty acids 
               
               
                   
                 lipid (VLDL) 
               
               
                 Metastases 
                 high density 
                 chylomicrons 
                 Cholesterol 
               
               
                   
                 lipoprotein 
               
            
           
           
               
               
               
            
               
                 Eukaryotic cells 
                 low density 
                 apolipoproteins 
               
               
                   
                 lipoprotein 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 6 
               
               
                   
               
               
                 Diseases and Conditions 
               
               
                   
               
             
            
               
                 Cancers 
               
            
           
           
               
               
               
               
            
               
                 Acute 
                 Colorectal cancer 
                 Macroglobulinemia, 
                 Pleuropulmonary 
               
               
                 lymphoblastic 
                   
                 Waldenström 
                 Blastoma, 
               
               
                 leukaemia (ALL) 
                   
                   
                 Childhood 
               
               
                 Acute myeloid 
                 Craniopharyngioma, 
                 Male Breast Cancer 
                 Pregnancy and 
               
               
                 leukaemia (AML) 
                 Childhood 
                   
                 Breast Cancer 
               
               
                 Adrenocortical 
                 Cutaneous T-Cell Lymphoma 
                 Malignant Fibrous 
                 Primary Central 
               
               
                 Carcinoma 
                   
                 Histiocytoma of Bone 
                 Nervous System 
               
               
                   
                   
                 and Osteosarcoma 
                 (CNS) Lymphoma 
               
               
                 AIDS-Related 
                 Ductal Carcinoma In Situ 
                 Melanoma 
                 Prostate Cancer 
               
               
                 Kaposi Sarcoma 
                 (DCIS) 
               
               
                 AIDS-Related 
                 Embryonal Tumors, 
                 Merkel Cell Carcinoma 
                 Rare cancers 
               
               
                 lymphoma 
                 Childhood 
               
               
                 Anal Cancer 
                 Endometrial Cancer 
                 Mesothelioma 
                 Rectal Cancer 
               
               
                 Appendix Cancer 
                 Ependymoma, Childhood 
                 Metastatic Squamous 
                 Renal cell 
               
               
                   
                   
                 Neck Cancer with 
                 carcinoma 
               
               
                   
                   
                 Occult Primary 
               
               
                 Astrocytomas, 
                 Epithelial cancer 
                 Midline Tract 
                 Renal Pelvis and 
               
               
                 Childhood 
                   
                 Carcinoma 
                 Ureter, Transitional 
               
               
                   
                   
                 Involving NUT Gene 
                 Cell Cancer 
               
               
                 Atypical 
                 Esophageal Cancer 
                 Molar pregnancy 
                 Retinoblastoma 
               
               
                 Teratoid/Rhabdoid 
               
               
                 Tumor, Childhood 
               
               
                 Basal Cell 
                 Esthesioneuroblastoma, 
                 Mouth and 
                 Rhabdomyosarcoma 
               
               
                 Carcinoma 
                 Childhood 
                 oropharyngeal cancer 
               
               
                 Bile duct cancer 
                 Ewing sarcoma 
                 Multiple Endocrine 
                 Salivary Gland 
               
               
                   
                   
                 Neoplasia Syndromes, 
                 Cancer 
               
               
                   
                   
                 Childhood 
               
               
                 Bladder cancer 
                 Extragonadal Germ Cell 
                 Multiple 
                 Sarcoma 
               
               
                   
                 Tumor 
                 Myeloma/Plasma Cell 
               
               
                   
                   
                 Neoplasm 
               
               
                 Bone cancer 
                 Extrahepatic Bile Duct Cancer 
                 Mycosis Fungoides 
                 Secondary cancers 
               
               
                 Bowel cancer 
                 Eye Cancer 
                 Myelodysplastic 
                 Sézary Syndrome 
               
               
                   
                   
                 Syndromes 
               
               
                 Brain Stem 
                 Gallbladder Cancer 
                 Myelodysplastic/ 
                 Skin Cancer 
               
               
                 Glioma, 
                   
                 Myeloproliferative 
               
               
                 Childhood 
                   
                 Neoplasms 
               
               
                 Brain tumours 
                 Gastric cancer 
                 Myeloproliferative 
                 Skin cancer (non 
               
               
                   
                   
                 Disorders, Chronic 
                 melanoma) 
               
               
                 Breast cancer 
                 Gastrointestinal Carcinoid 
                 Nasal Cavity and 
                 Small Cell Lung 
               
               
                   
                 Tumor 
                 Paranasal Sinus Cancer 
                 Cancer 
               
               
                 Bronchial Tumors, 
                 Germ Cell Tumor 
                 Nasopharyngeal cancer 
                 Small Intestine 
               
               
                 Childhood 
                   
                   
                 Cancer 
               
               
                 Burkitt 
                 Gestational trophoblastic 
                 Neuroblastoma 
                 Soft Tissue Sarcoma 
               
               
                 Lymphoma 
                 tumours (GTT) 
               
               
                 Cancer of 
                 Glioma 
                 Non-Hodgkin 
                 Squamous Cell 
               
               
                 unknown primary 
                   
                 Lymphoma 
                 Carcinoma 
               
               
                 Cancer spread to 
                 Hairy cell leukaemia 
                 Non-Small Cell Lung 
                 Squamous Neck 
               
               
                 bone 
                   
                 Cancer 
                 Cancer with Occult 
               
               
                   
                   
                   
                 Primary, Metastatic 
               
               
                 Cancer spread to 
                 Head and neck cancer 
                 Oesophageal cancer 
                 Stomach (Gastric) 
               
               
                 brain 
                   
                   
                 Cancer 
               
               
                 Cancer spread to 
                 Heart Cancer, Childhood 
                 Oral Cancer 
                 Stomach cancer 
               
               
                 liver 
               
               
                 Cancer spread to 
                 Hepatocellular (Liver) Cancer 
                 Oral Cavity Cancer 
                 T-Cell Lymphoma, 
               
               
                 lung 
                   
                   
                 Cutaneous - see 
               
               
                   
                   
                   
                 Mycosis Fungoides 
               
               
                   
                   
                   
                 and Sézary Syndrome 
               
               
                 Carcinoid Tumor 
                 Histiocytosis, Langerhans Cell 
                 Oropharyngeal Cancer 
                 Testicular cancer 
               
               
                 Carcinoma of 
                 Hodgkin Lymphoma 
                 Osteosarcoma (Bone 
                 Throat Cancer 
               
               
                 Unknown Primary 
                   
                 Cancer) 
               
               
                 Cardiac (Heart) 
                 Hypopharyngeal Cancer 
                 Osteosarcoma and 
                 Thymoma and 
               
               
                 Tumors, Childhood 
                   
                 Malignant Fibrous 
                 Thymic Carcinoma 
               
               
                   
                   
                 Histiocytoma 
               
               
                 Central Nervous 
                 Intraocular Melanoma 
                 Ovarian Cancer 
                 Thyroid Cancer 
               
               
                 System Atypical 
               
               
                 Teratoid/Rhabdoid 
               
               
                 Tumor, Childhood 
               
               
                 Central Nervous 
                 Islet Cell Tumors, Pancreatic 
                 Pancreatic Cancer 
                 Transitional Cell 
               
               
                 System Embryonal 
                 Neuroendocrine Tumors 
                   
                 Cancer of the Renal 
               
               
                 Tumors, Childhood 
                   
                   
                 Pelvis and Ureter 
               
               
                 Central Nervous 
                 Kidney cancer 
                 Pancreatic 
                 Unknown primary 
               
               
                 System, Childhood 
                   
                 Neuroendocrine Tumors 
                 cancer 
               
               
                   
                   
                 (Islet Cell Tumors) 
               
               
                 Cervical cancer 
                 Langerhans Cell Histiocytosis 
                 Papillomatosis, 
                 Ureter and Renal 
               
               
                   
                   
                 Childhood 
                 Pelvis, Transitional 
               
               
                   
                   
                   
                 Cell Cancer 
               
               
                 Chordoma, Childhood 
                 Laryngeal Cancer 
                 Paraganglioma 
                 Urethral Cancer 
               
               
                 Choriocarcinoma 
                 Leukemia 
                 Parathyroid Cancer 
                 Uterine Cancer, 
               
               
                   
                   
                   
                 Endometrial 
               
               
                 Chronic 
                 Lip and Oral Cavity Cancer 
                 Penile Cancer 
                 Uterine Sarcoma 
               
               
                 Lymphocytic 
               
               
                 Leukemia (CLL) 
               
               
                 Chronic myeloid 
                 Liver cancer 
                 Pharyngeal Cancer 
                 Vaginal cancer 
               
               
                 leukaemia (CML) 
               
               
                 Chronic 
                 Lobular Carcinoma In Situ 
                 Pheochromocytoma 
                 Vulvar Cancer 
               
               
                 Myeloproliferative 
                 (LCIS) 
               
               
                 Disorders 
               
               
                 Colon cancer 
                 Low Malignant Potential 
                 Pituitary Tumor 
                 Waldenström 
               
               
                   
                 Tumor 
                   
                 Macroglobulinemia 
               
               
                 Lymphoma 
                 Lung Cancer 
                 Plasma Cell 
                 Wilms Tumor 
               
               
                   
                   
                 Neoplasm/Multiple 
               
               
                   
                   
                 Myeloma 
               
            
           
           
               
            
               
                 Complement and Immune Complex-Related Diseases 
               
            
           
           
               
               
               
               
            
               
                 Age-related 
                 ANCA-associated vasculitis 
                 Glomerulonephritis - 
                 MYH9-related 
               
               
                 macular 
                 (Includes Pauci-immune) 
                 sparse hair - 
                 disease 
               
               
                 degeneration 
                   
                 telangiectasis 
               
               
                 Atypical 
                 Anti-glomerular basement 
                 Goodpasture&#39;s sndrome 
                 Nail-patella 
               
               
                 hemolytic uremic 
                 membrane disease 
                   
                 syndrome 
               
               
                 syndrome 
                 (Goodpasture&#39;s) 
               
               
                 Autoimmune 
                 Arthus Reaction 
                 Granulomatosis with 
                 Nail-patella-like 
               
               
                 hemolytic anemia 
                   
                 polyangiitis (ANCA and 
                 renal disease 
               
               
                   
                   
                 Wegeners) 
               
               
                 C1 inhibitor 
                 Asthma 
                 Guillain-Barre 
                 Nephritis 
               
               
                 deficiency 
                   
                 syndrome 
               
               
                 C1q deficiency 
                 Atypical hemolytic uremic 
                 Hemolytic angioedema 
                 Non-amyloid 
               
               
                   
                 syndrome 
                 (HAE) 
                 monoclonal 
               
               
                   
                   
                   
                 immunoglobulin 
               
               
                   
                   
                   
                 deposition disease 
               
               
                 C1r deficiency 
                 Autoimmune inner ear disease 
                 Henoch-Schonlein 
                 Pauci-immune 
               
               
                   
                 (AIED) Sensorineural hearing 
                 purpura 
                 glomerulonephritis 
               
               
                   
                 loss 
               
               
                 C1s deficiency 
                 Autoimmune uveitis 
                 HIVICK 
                 Pediatric systemic 
               
               
                   
                   
                   
                 lupus erythematosus 
               
               
                 C2 deficiency 
                 Autosomal dominant 
                 Hypersensitivty 
                 Pierson syndrome 
               
               
                   
                 intermediate Charcot-Marie- 
                 vasculitis 
               
               
                   
                 Tooth disease type E 
               
               
                 C3 deficiency 
                 Behçet disease 
                 Hypocomplementemic 
                 Polyarteritis 
               
               
                   
                   
                 urticarial vasculitis 
               
               
                 C4 deficiency 
                 Berger (IgA) Nephropathy 
                 Idiopathic membranous 
                 polyarteritis nodosa 
               
               
                   
                   
                 glomerulonephritis 
               
               
                 C5 deficiency 
                 Buergers disease 
                 Idiopathic nephrotic 
                 Polymyalgia 
               
               
                   
                   
                 syndrome 
                 rheumatica 
               
               
                 C6 deficiency 
                 Central nervous system 
                 IgA nephropathy 
                 Polymyositis 
               
               
                   
                 vasculitis 
                 (Berger&#39;s disease) 
               
               
                 C7 deficiency 
                 Choroiditis 
                 IgA nephropathy/vasculitis 
                 Polymyositis/ 
               
               
                   
                   
                 (Henoch-Schonlein 
                 dermatomyositis 
               
               
                   
                   
                 purpura) 
               
               
                 C8 deficiency 
                 Chronic demyelinating 
                 Immune 
                 Poststaphilococcal 
               
               
                   
                 polyneuropathy (CIDP) 
                 thrombocytopenia 
                 glomerulonephritis 
               
               
                 C9 deficiency 
                 Churg-strauss syndrome 
                 Immunobullous diseases 
                 Poststeptococcal 
               
               
                   
                   
                   
                 glomerulonephritis 
               
               
                 CD55 deficiency 
                 Cogan&#39;s syndrome 
                 Immunotactoid or 
                 Primary 
               
               
                   
                   
                 fibrillary 
                 membranoproliferative 
               
               
                   
                   
                 glomerulopathy 
                 glomerulonephritis 
               
               
                 CD59 deficiency 
                 Collagen type III 
                 Infection-related 
                 Rapidly progressive 
               
               
                   
                 glomerulopathy 
                 glomerulonephritis 
                 glomerulonephritis 
               
               
                   
                   
                   
                 (Crescentic) 
               
               
                 Complement 
                 Congenital and infantile 
                 Inflammatory 
                 Rapidly progressive 
               
               
                 Factor I 
                 nephrotic syndrome 
                 myopathies 
                 glomerulonephritis 
               
               
                 deficiency 
                   
                   
                 (RPGN) 
               
               
                 Complement 
                 Congenital membranous 
                 Juvenile 
                 Rasmussen 
               
               
                 factor-H related 
                 nephropathy due to maternal 
                 dermatomyositis 
                 syndrome 
               
               
                 1(CFHR1) 
                 anti-neutral endopeptidase 
               
               
                 deficiency 
                 alloimmunization 
               
               
                 Complement 
                 Cryoglobulinaemia/Cold 
                 Juvenile polymyositis 
                 Reactive arthritis 
               
               
                 factor-H related 
                 agglutinin diease 
               
               
                 3(CFHR3) 
               
               
                 deficiency 
               
               
                 CR3/CR4 
                 Cryoglobulinemic vasculitis 
                 Kawasaki disease 
                 Relapsing 
               
               
                 defieciency 
                   
                   
                 polychondritis 
               
               
                 (leukocyte 
               
               
                 adhesion 
               
               
                 deficiency 1) 
               
               
                 Factor B 
                 Cutaneous vasculitis 
                 Lipoprotein 
                 Renal amyloidosis 
               
               
                 deficiency 
                   
                 glomerulopathy 
               
               
                 Factor D 
                 Demyelinating myopathies 
                 Lupus nephritis 
                 Reynolds syndrome 
               
               
                 deficiency 
                 (paraprotein associated) 
               
               
                 Factor H 
                 Denys-Drash syndrome 
                 Lupus nephropathy 
                 Rheumatoid arthritis 
               
               
                 deficiency 
               
               
                 Factor I 
                 Dermatomyositis 
                 May Hegglin anomaly 
                 Sarcoidosis (Nesnier 
               
               
                 deficiency 
                   
                   
                 Boeck Schuamann 
               
               
                   
                   
                   
                 Disease) 
               
               
                 Ficolin 3 
                 Dermatomyositis 
                 Membranoglomerular 
                 Schimke 
               
               
                 deficiency 
                   
                 nephritis 
                 immunoosseous 
               
               
                   
                   
                   
                 dysplasia 
               
               
                 MASP2 
                 Diabetic nephropathy 
                 Membranoproliferative 
                 Scleroderma 
               
               
                 deficiency 
                   
                 glomerulonephritis 
               
               
                 MBL deficiency 
                 Drug-induced immune 
                 Membranoproliferative 
                 Sebastian syndrome 
               
               
                   
                 complex vasculitis 
                 glomerulonephritis Type 
               
               
                   
                   
                 I (MPGN Type I) 
               
               
                 Non-alcoholic 
                 Eosinophilic granulomatosis 
                 Membranoproliferative 
                 Secondary 
               
               
                 steatohepatitis 
                 with polyangiitis (Churgg- 
                 glomerulonephritis Type 
                 amyloidosis 
               
               
                   
                 Strauss) 
                 II (Dense Deposit 
               
               
                   
                   
                 Disease, MPGN Type II) 
               
               
                 Paroxysmal 
                 Epstein Syndrome 
                 Membranoproliferative 
                 Severe or recurring 
               
               
                 nocturnal 
                   
                 glomerulonephritis Type 
                 C diff colitis 
               
               
                 hemoglobinuria 
                   
                 III (MPGN Type III) 
               
               
                 Properdin 
                 Essential mixed 
                 Membranouse 
                 Sjogren&#39;s syndrome 
               
               
                 deficency 
                 cryoglobulinemia 
                 glomerulonephritis 
               
               
                 Action 
                 Familial Mediterranean fever 
                 Menieres disease 
                 Staphylococcal or 
               
               
                 myoclonus - renal 
                   
                   
                 streptococcal sepsis 
               
               
                 failure syndrome 
               
               
                 Acute respiratory 
                 Familial renal amyloidosis 
                 Microscopic polyangiitis 
                 Stiff person 
               
               
                 disease syndrome 
                   
                   
                 syndrome 
               
               
                 (ARDS)/Severe 
               
               
                 acute respiratory 
               
               
                 syndrome (SARS) 
               
               
                 Acute serum 
                 Familial steroid-resistant 
                 Minimal change disease 
                 Systemic lupus 
               
               
                 sickness 
                 nephrotic syndrome with 
                   
                 erythematosus 
               
               
                   
                 sensorineural deafness 
               
               
                 Adult-onset Still 
                 Farmer&#39;s lung 
                 Mixed connective tissue 
                 Systemic sclerosis 
               
               
                 disease 
                   
                 disease 
               
               
                 Age-related 
                 Fechtner Syndrome 
                 Mostly large vessel 
                 Takayasu arteritis 
               
               
                 macular 
                   
                 vasculitis 
               
               
                 degeneration 
               
               
                 AL amyloidosis 
                 Fibronectin glomerulopathy 
                 mostly mediu m vessel 
                 Toxic epidermal 
               
               
                   
                   
                 vasculitis 
                 necrolysis (Stevens 
               
               
                   
                   
                   
                 Johnson syndrome) 
               
               
                 Alport&#39;s 
                 Fibrosing alveolitis 
                 Mostly small vessel 
                 Transplantation/reper- 
               
               
                 syndrome 
                   
                 vsculitis 
                 fusion (solid organ) 
               
               
                 Alzheimer&#39;s 
                 Focal segmental glomerular 
                 Muckle-Wells syndrome 
                 Vasculitis 
               
               
                 disease 
               
               
                 Amyloidosis (AL, 
                 Focal segmental 
                 Myasthenia gravis 
                 Wegener&#39;s 
               
               
                 AA, MIDD, Other) 
                 glomerulosclerosis 
                   
                 granulomatosis 
               
            
           
           
               
               
               
            
               
                 Giant cell arteritis 
                 Frasier syndrome 
                 Galloway-Mowat syndrome 
               
            
           
           
               
               
               
               
            
               
                 Type 1 diabetes 
                 Myasthenia gravis 
                 Graves&#39; disease 
                 Pernicious anemia 
               
               
                 Crohn&#39;s disease 
                 alopecia areata 
                 thrombocytopenic 
                 Primary biliary 
               
               
                   
                   
                 purpura 
                 cirrhosis 
               
               
                 Ulcerative colitis 
                 autoimmune hepatitis 
                 Guillain-Barre 
                 Psoriasis 
               
               
                   
                   
                 syndrome 
               
               
                 Inflammatory 
                 autoimmune deramtomyositis 
                 Autoimmune 
                 Rheumatoid arthritis 
               
               
                 bowel syndrome 
                   
                 myocarditis 
               
               
                 Multiple sclerosis 
                 Juvenile idiopathic arthritis 
                 Autoimmune pemphigus 
                 Vitiligo 
               
            
           
           
               
            
               
                 Enzyme Deficiencies &amp; Vascular Diseases 
               
            
           
           
               
               
               
               
            
               
                 2,4-dienoyl-CoA 
                 Fabry disease (1:80,000 to 
                 Isobutyryl-CoA 
                 Peripheral 
               
               
                 reductase 
                 1:117,000) 
                 dehydrogenase 
                 neuropathy 
               
               
                 deficiency 
               
               
                 2-Methyl-3- 
                 Familial hypercholesterolemia 
                 Isovaleric acidemia 
                 Peroxisomal 
               
               
                 hydroxy butyric 
                 (1:500) 
                   
                 disorders (1:50,000; 
               
               
                 aciduria 
                   
                   
                 e.g., Zellweger 
               
               
                   
                   
                   
                 syndrome, neonatal 
               
               
                   
                   
                   
                 adrenoleukodystrophy, 
               
               
                   
                   
                   
                 Refsum&#39;s disease) 
               
               
                 2-methylbutyryl- 
                 Familial myocardial 
                 Lactase deficiency 
                 Phenylketonuria 
               
               
                 CoA dehydrogenase 
                 infarct/stroke 
                 (common) 
               
               
                 3-hydroxy-3- 
                 Fatty acid oxidation disorders 
                 Lesch-Nyhan syndrome 
                 Primary 
               
               
                 methylglutaryl 
                 (1:10,000) 
                   
                 hyperoxaluria 
               
               
                 (HMG) aciduria 
               
               
                 3-methylglutaconic 
                 Galactokinase deficiency 
                 Lipoprotein lipase 
                 Propionic acidemia 
               
               
                 aciduria 
                   
                 deficiency (rare) 
               
               
                 3-oxothiolase 
                 Galactose epimerase 
                 long-chain 1-3- 
                 Recurrent emesis 
               
               
                 deficiency 
                   
                 hdroxyacyl-CoA 
               
               
                 (1:100,000) 
                   
                 dehydrogenase 
               
               
                 4-hydroxybutyric 
                 Galactosemia 
                 Lysinuric protein 
                 Short-chain acyl- 
               
               
                 aciduria 
                   
                 intolerance (rare) 
                 CoA dehydrogenase 
               
               
                 5,10- 
                 Galactosemia (1:40,000) 
                 Lysinuric protein 
                 Sucrase-isomaltase 
               
               
                 methylenetetrahydrofolate 
                   
                 intolerance (rare) 
                 deficiency (rare) 
               
               
                 reductase 
               
               
                 deficiency (common) 
               
               
                 5-Oxoprolinuria 
                 Gaucher&#39;s disease 
                 Malonic acidemia 
                 Symptoms of 
               
               
                 (pyroglutamic 
                   
                   
                 pancreatitis 
               
               
                 aciduria) 
               
               
                 Abetalipoproteinemia 
                 Glutaric acidemia type I 
                 Maple syrup urine 
                 Transferase deficient 
               
               
                 (rare) 
                   
                 disease 
                 galactosemia 
               
               
                   
                   
                   
                 (Galactosemia type 1) 
               
               
                 Acute 
                 Glutaric acidemia Type II 
                 Medium chain acyl-CoA 
                 Trifunctional protein 
               
               
                 Intermittent 
                   
                 dehydrogenase 
                 deficiency 
               
               
                 Porphyria 
               
               
                 Alkaptonuria 
                 Glutathione Synthetase 
                 Medium/short chain L- 
                 Tyrosinemia type 1 
               
               
                   
                 Deficiency w/5-oxoprolinuria 
                 3-hydroxy acyl-CoA 
               
               
                   
                   
                 dehydrogenase 
               
               
                 Argininemia 
                 Glutathione Synthetase 
                 Medum-chain ketoacyl- 
                 Tyrosinemia type 2 
               
               
                   
                 Deficiency w/o 5- 
                 coA thiolase 
               
               
                   
                 oxoprolinuria 
               
               
                 argininosuccinate 
                 Glycogenolysis disorders 
                 Metachromatic 
                 Tyrosinemia type 3 
               
               
                 aciduria 
                 (1:20,000) 
                 leukodystrophy 
               
               
                   
                   
                 (1:100,000) 
               
               
                 Benign 
                 Glycogenosis, type I 
                 Metachromatic 
                 Upward gaze 
               
               
                 hyperphenylalaninemia 
                 (1:70,000) 
                 leukodystrophy 
                 paralysis 
               
               
                   
                   
                 (1:100,000) 
               
               
                 beta ketothiolase 
                 Hemolytic anemia due to 
                 Methylmalonic acidemia 
                 Very long chain 
               
               
                 deficiency 
                 adenylate kinase deficiency 
                 (Cbl C) 
                 acyl-CoA 
               
               
                   
                   
                   
                 dehydrogenase 
               
               
                 Biopterin cofactor 
                 Hemolytic anemia due to 
                 Methylmalonic acidemia 
                 Wilson Disease 
               
               
                 biosynthesis 
                 deficiency in Glucose 6 
                 (Cbl D) 
               
               
                 defects 
                 phosphate dehydrogenase 
               
               
                 Biopterin cofactor 
                 Hemolytic anemia due to 
                 Methylmalonic acidemia 
                 Aicardi-Goutieres 
               
               
                 regeneration 
                 diphosphoglycerate mutase 
                 (vitamin b12 non- 
                 Syndrome (may be an 
               
               
                 defects 
                 deficiency 
                 responsive) 
                 allelic form of CLE) 
               
               
                 biotin- 
                 Hemolytic anemia due to 
                 Methylmalonic acidemia 
                 Cutaneous lupus 
               
               
                 unresponsive 3- 
                 erythrocyte adenosine 
                 w/0 homocystinuria 
                 erythematosus 
               
               
                 methylcrotonyl- 
                 deaminase overproduction 
               
               
                 CoA carboxylase 
               
               
                 deficiency 
               
               
                 Carbamoyl 
                 Hemolytic anemia due to 
                 Methylmalonic aciduria 
                 Dermatitis 
               
               
                 phosphate 
                 glucophosphate isomerase 
                 and homocystinuria 
                 herpetiformis 
               
               
                 synthetase 
                 deficiency 
               
               
                 Carnitine 
                 Hemolytic anemia due to 
                 Mitochondrial disorders 
                 hemophilia A 
               
               
                 acylcarnitine 
                 glutathione reductase 
                 (1:30,000) 
               
               
                 translocase 
                 deficiency 
               
               
                 Carnitine 
                 Hemolytic anemia due to 
                 Mitochondrial disorders 
                 hemophilia B 
               
               
                 palmitoyltransferase 
                 glyceraldehyde-3-phosphate 
                 (1:30,000; e.g., 
               
               
                 I 
                 dehydrogenase deficiency 
                 cytochrome-c oxidase 
               
               
                   
                   
                 deficiency; MELAS 
               
               
                   
                   
                 syndrome; Pearson&#39;s 
               
               
                   
                   
                 syndrome [all rare]) 
               
               
                 Carnitine 
                 Hemolytic anemia due to 
                 Mitochondrial disorders 
                 Idiopathic steroid 
               
               
                 palmitoyltransferase 
                 pyrimidine 5′ nucleotidase 
                 (1:30,000; e.g., Leigh 
                 sensitive nephrotic 
               
               
                 II 
                 deficiency 
                 disease, Kearns-Sayre 
                 syndrome (same as 
               
               
                   
                   
                 syndrome [rare]) 
                 focal segmental 
               
               
                   
                   
                   
                 glomerulaosclerosis) 
               
               
                 Carnitine uptake 
                 Hemolytic anemia due to red 
                 Mitochondrial disorders 
                 Immune 
               
               
                 defect 
                 cell pyruvate kinase deficiency 
                 (1:30,000; e.g., 
                 thrombocytopenic 
               
               
                   
                   
                 lipoamide 
                 purpura 
               
               
                   
                   
                 dehydrogenase 
               
               
                   
                   
                 deficiency [rare]) 
               
               
                 citrullinemia 
                 HHH syndrome (rare) 
                 Mitochondrial disorders 
                 Myasthenia gravis 
               
               
                 type I 
                   
                 (1:30,000; e.g., 
               
               
                   
                   
                 Pearson&#39;s syndrome 
               
               
                   
                   
                 [rare]) 
               
               
                 Citrullinemia 
                 homocysteinuria 
                 Multiple carboxylase 
                 Oligoarticular 
               
               
                 type II 
                   
                 (holocarboxylase 
                 juvenile arthritis 
               
               
                   
                   
                 synthetase) 
               
               
                 Congenital 
                 Homocystinuria (1:200,000) 
                 Multiple carboxylase 
                 Scleroderma 
               
               
                 disorders of 
                   
                 deficiency (e.g., 
               
               
                 glycosylation (rare) 
                   
                 holocarboxylase 
               
               
                   
                   
                 synthetase [rare]) and 
               
               
                   
                   
                 biotinidase deficiencies 
               
               
                   
                   
                 (1:60,000) 
               
               
                 D-2- 
                 hyperammonemia/ornithinemia/ 
                 Muscle 
                 Solar urticaria 
               
               
                 hydroxyglutaricaciduria 
                 citrullinemia (ornithine 
                 cramps/spasticity 
                 (maybe protophyria 
               
               
                   
                 transporter defect) 
                   
                 erythema) 
               
               
                 D-2- 
                 Hyperlipoproteinemia, types I 
                 Myoadenylate 
                 Thrombotic 
               
               
                 hydroxyglutaricaciduria 
                 and IV (rare) 
                 deaminase deficiency 
                 thrombocytopenic 
               
               
                 (rare) 
                   
                 (1:100,000) 
                 purpura 
               
               
                 Enteropeptidase 
                 Hypermethioninemia due to 
                 Niemann-Pick disease, 
                 Tubulointerstitial 
               
               
                 deficiency (rare) 
                 glycine N-methyltransferase 
                 type C (rare) 
                 nephritis with 
               
               
                   
                 deficiency 
                   
                 Uveitis/ATIN 
               
               
                 Ethylmalonic 
                 Hypermethioninemia 
                 Nonketotic 
                 Von willebrand 
               
               
                 encephalopathy 
                 encephalopathy due to 
                 hyperglycinemia 
                 disease 
               
               
                   
                 adenosine kinase deficiency 
               
            
           
           
               
               
               
            
               
                   
                 Hyperprolinemia 
                   
               
            
           
           
               
            
               
                 Infectious Diseases &amp; agents 
               
            
           
           
               
               
               
               
            
               
                 Acinetobacter 
                 Dengue haemorrhagic fever 
                 Infection-induced 
                 Sepsis 
               
               
                   
                   
                 immune complex 
               
               
                   
                   
                 vasculitis 
               
               
                 Arcobacter butzleri 
                 Disseminated infection with 
                 Klebsiella 
                 Serratia 
               
               
                 infection - 
                 
                   mycobacterium avium 
                 
               
               
                 blood infection 
                 complex - blood infection 
               
               
                 Arcobacter cryaerophilus 
                 
                   E. coli 
                 
                 Leprosy/Hansen&#39;s 
                 
                   Staphylococcus Aureus 
                 
               
               
                 infection - blood 
                   
                 disease 
               
               
                 infection 
               
               
                 Arcobacter 
                 Enterobacter 
                 Malaria 
                 Stenotrophomonas 
               
               
                 infection - blood 
                   
                   
                 maltophilia - blood 
               
               
                 infection 
                   
                   
                 infection 
               
               
                 Bacteremia 
                 Enterococcus 
                 Meningococcus 
                 Streptococcal Group 
               
               
                   
                   
                   
                 A invasive disease - 
               
               
                   
                   
                   
                 blood infection 
               
               
                 Bacterial 
                 Glanders - blood infection 
                 Methicillin Resistant 
                 
                   Streptococcus 
                 
               
               
                 endocarditis 
                   
                 
                   Staphylococcus Aureus 
                 
                 
                   pneumoniae 
                 
               
               
                 Campylobacter 
                 Gonorrhea 
                 Pseudomonas 
                 
                   Streptococcus 
                 
               
               
                 fetus infection - 
                   
                   
                 
                   pyogenes 
                 
               
               
                 blood infection 
               
               
                 Campylobacter 
                 Hepatitis 
                 Rhodococcus equi - 
                 Trypanosomiasis 
               
               
                 jejuni infection - 
                   
                 blood infection 
               
               
                 blood infection 
               
               
                 Candida 
                 Human Immunodeficiency 
                 Salmonella 
                 Yellow fever 
               
               
                   
                 Virus 
               
            
           
           
               
            
               
                 Coagulase-negative  Staphylococcus   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 7 
               
               
                   
               
               
                 Receivers 
               
               
                   
               
             
            
               
                 General Classes of Receivers 
               
            
           
           
               
               
               
            
               
                 Ankyrin repeat proteins 
                 Fibronectins 
                 Lyases 
               
            
           
           
               
               
               
               
            
               
                 Antibodies 
                 Complement receptors 
                 GPI-linked 
                 Nanobodies 
               
               
                   
                   
                 polypeptides 
               
               
                 Aptamers 
                 Cyclic peptides 
                 HEAT repeat proteins 
                 Nucleic Acids 
               
               
                 ARM repeat proteins 
                 DARPins 
                 Hydrolases 
                 Polypeptides 
               
               
                 Carbohydrates 
                 DNAses 
                 Kinases 
                 Single-chain variable 
               
               
                   
                   
                   
                 fragments (scFv) 
               
               
                 Cell surface receptors 
                 Enzymes 
                 Lipoproteins 
                 Tetratricopeptide 
               
               
                   
                   
                   
                 repeat proteins 
               
            
           
           
               
            
               
                 Complement-Related Receivers 
               
            
           
           
               
               
               
               
            
               
                 C1 inhibitor 
                 C4 binding protein 
                 CR3 
                 Factor I 
               
               
                 C3 Beta chain 
                 CD59 
                 CR4 
                 Homologous restriction 
               
               
                 Receptor 
                   
                   
                 factor 
               
               
                 C3aR 
                 CR1 
                 Decay-accelerating 
                 Membrane cofactor 
               
               
                   
                   
                 factor (DAF) 
                 protein (MCP) 
               
               
                 C3eR 
                 CR2 
                 Factor H 
                 PRELP 
               
            
           
           
               
            
               
                 Enzymes 
               
            
           
           
               
               
               
               
            
               
                 triacylglycerol lipase 
                 bile-acid-CoA hydrolase 
                 feruloyl esterase 
                 phosphatidate 
               
               
                   
                   
                   
                 phosphatase 
               
               
                 (S)-methylmalonyl- 
                 bis(2- 
                 formyl-CoA hydrolase 
                 phosphatidylglycero- 
               
               
                 CoA hydrolase 
                 ethylhexyl)phthalate 
                   
                 phosphatase 
               
               
                   
                 esterase 
               
               
                 [acyl-carrier-protein] 
                 bisphosphoglycerate 
                 fructose- 
                 phosphatidylinositol 
               
               
                 phosphodiesterase 
                 phosphatase 
                 bisphosphatase 
                 deacylase 
               
               
                 [phosphorylase] 
                 Carboxylic-Ester 
                 fumarylacetoacetase 
                 phosphodiesterase I 
               
               
                 phosphatase 
                 Hydrolases 
               
               
                 1,4-lactonase 
                 carboxymethylenebutenolidase 
                 fusarinine-C 
                 phosphoglycerate 
               
               
                   
                   
                 ornithinesterase 
                 phosphatase 
               
               
                 11-cis-retinyl- 
                 cellulose-polysulfatase 
                 galactolipase 
                 phosphoglycolate 
               
               
                 palmitate hydrolase 
                   
                   
                 phosphatase 
               
               
                 1-alkyl-2- 
                 cephalosporin-C 
                 gluconolactonase 
                 phosphoinositide 
               
               
                 acetylglycerophospho- 
                 deacetylase 
                   
                 phospholipase C 
               
               
                 choline esterase 
               
               
                 2′-hydroxybiphenyl-2- 
                 cerebroside-sulfatase 
                 glucose-1- 
                 phospholipase A1 
               
               
                 sulfinate desulfinase 
                   
                 phosphatase 
               
               
                 2-pyrone-4,6- 
                 cetraxate benzylesterase 
                 glucose-6- 
                 phospholipase A2 
               
               
                 dicarboxylate 
                   
                 phosphatase 
               
               
                 lactonase 
               
               
                 3′,5′-bisphosphate 
                 chlorogenate hydrolase 
                 glutathione 
                 phospholipase C 
               
               
                 nucleotidase 
                   
                 thiolesterase 
               
               
                 3-hydroxyisobutyryl- 
                 chlorophyllase 
                 glycerol-1- 
                 phospholipase D 
               
               
                 CoA hydrolase 
                   
                 phosphatase 
               
               
                 3′-nucleotidase 
                 cholinesterase 
                 glycerol-2- 
                 phosphonoacetaldehyde 
               
               
                   
                   
                 phosphatase 
                 hydrolase 
               
               
                 3-oxoadipate enol- 
                 choline-sulfatase 
                 glycerophosphocholine 
                 phosphonoacetate 
               
               
                 lactonase 
                   
                 phosphodiesterase 
                 hydrolase 
               
               
                 3-phytase 
                 choloyl-CoA hydrolase 
                 Glycosidases, i.e. 
                 phosphonopyruvate 
               
               
                   
                   
                 enzymes that 
                 hydrolase 
               
               
                   
                   
                 hydrolyse O- and S- 
               
               
                   
                   
                 glycosyl compounds 
               
               
                 4-hydroxybenzoyl- 
                 chondro-4-sulfatase 
                 glycosulfatase 
                 phosphoprotein 
               
               
                 CoA thioesterase 
                   
                   
                 phosphatase 
               
               
                 4-methyloxaloacetate 
                 chondro-6-sulfatase 
                 Glycosylases 
                 Phosphoric-diester 
               
               
                 esterase 
                   
                   
                 hydrolases 
               
               
                 4-phytase 
                 citrate-lyase deacetylase 
                 histidinol-phosphatase 
                 Phosphoric-monoester 
               
               
                   
                   
                   
                 hydrolases 
               
               
                 4-pyridoxolactonase 
                 cocaine esterase 
                 hormone-sensitive 
                 Phosphoric-triester 
               
               
                   
                   
                 lipase 
                 hydrolases 
               
               
                 5′-nucleotidase 
                 cutinase 
                 Hydrolysing N- 
                 phosphoserine 
               
               
                   
                   
                 glycosyl compounds 
                 phosphatase 
               
               
                 6-acetylglucose 
                 cyclamate 
                 Hydrolysing S- 
                 poly(3- 
               
               
                 deacetylase 
                 sulfohydrolase 
                 glycosyl compounds 
                 hydroxybutyrate) 
               
               
                   
                   
                   
                 depolymerase 
               
               
                 6- 
                 Cysteine endopeptidases 
                 hydroxyacylglutathione 
                 poly(3- 
               
               
                 phosphogluconolactonase 
                   
                 hydrolase 
                 hydroxyoctanoate) 
               
               
                   
                   
                   
                 depolymerase 
               
               
                 a-amino-acid esterase 
                 Cysteine-type 
                 hydroxybutyrate- 
                 polyneuridine-aldehyde 
               
               
                   
                 carboxypeptidases 
                 dimer hydrolase 
                 esterase 
               
               
                 a-Amino-acyl-peptide 
                 D-arabinonolactonase 
                 hydroxymethylglutaryl- 
                 protein-glutamate 
               
               
                 hydrolases 
                   
                 CoA hydrolase 
                 methylesterase 
               
               
                 acetoacetyl-CoA 
                 deoxylimonate A-ring- 
                 iduronate-2-sulfatase 
                 quorum-quenching N- 
               
               
                 hydrolase 
                 lactonase 
                   
                 acyl-homoserine 
               
               
                   
                   
                   
                 lactonase 
               
               
                 acetoxybutynylbithiophene 
                 dGTPase 
                 inositol-phosphate 
                 retinyl-palmitate 
               
               
                 deacetylase 
                   
                 phosphatase 
                 esterase 
               
               
                 acetylajmaline esterase 
                 dihydrocoumarin 
                 juvenile-hormone 
                 Serine dehyrdatase or 
               
               
                   
                 hydrolase 
                 esterase 
                 serine hydroxymethyl 
               
               
                   
                   
                   
                 transferase 
               
               
                 acetylalkylglycerol 
                 Dipeptidases 
                 kynureninase 
                 Serine endopeptidases 
               
               
                 acetylhydrolase 
               
               
                 acetylcholinesterase 
                 Dipeptide hydrolases 
                 L-arabinonolactonase 
                 serine- 
               
               
                   
                   
                   
                 ethanolaminephosphate 
               
               
                   
                   
                   
                 phosphodiesterase 
               
               
                 acetyl-CoA hydrolase 
                 Dipeptidyl-peptidases 
                 limonin-D-ring- 
                 Serine-type 
               
               
                   
                 and tripeptidyl- 
                 lactonase 
                 carboxypeptidases 
               
               
                   
                 peptidases 
               
               
                 acetylesterase 
                 Diphosphoric-monoester 
                 lipoprotein lipase 
                 S-formylglutathione 
               
               
                   
                 hydrolases 
                   
                 hydrolase 
               
               
                 acetylpyruvate 
                 disulfoglucosamine-6- 
                 L-rhamnono-1,4- 
                 sialate O-acetylesterase 
               
               
                 hydrolase 
                 sulfatase 
                 lactonase 
               
               
                 acetylsalicylate 
                 dodecanoyl-[acyl- 
                 lysophospholipase 
                 sinapine esterase 
               
               
                 deacetylase 
                 carrier-protein] 
               
               
                   
                 hydrolase 
               
               
                 acetylxylan esterase 
                 Endodeoxyribonucleases 
                 mannitol-1- 
                 Site specific 
               
               
                   
                 producing 3′- 
                 phosphatase 
                 endodeoxyribonucleases: 
               
               
                   
                 phosphomonoesters 
                   
                 cleavage is not 
               
               
                   
                   
                   
                 sequence specific 
               
               
                 acid phosphatase 
                 Endodeoxyribonucleases 
                 Metallocarboxypeptidases 
                 Site-specific 
               
               
                   
                 producing 5′- 
                   
                 endodeoxyribonucleases 
               
               
                   
                 phosphomonoesters 
                   
                 that are specific for 
               
               
                   
                   
                   
                 altered bases. 
               
               
                 Acting on acid 
                 Endopeptidases of 
                 Metalloendopeptidases. 
                 Site-specific 
               
               
                 anhydrides to catalyse 
                 unknown catalytic 
                   
                 endodeoxyribonucleases: 
               
               
                 transmembrane 
                 mechanism 
                   
                 cleavage is sequence 
               
               
                 movement of 
                   
                   
                 specific 
               
               
                 substances 
               
               
                 Acting on acid 
                 Endoribonucleases 
                 methylphosphothioglyc- 
                 sphingomyelin 
               
               
                 anhydrides to facilitate 
                 producing 3′- 
                 erate phosphatase 
                 phosphodiesterase 
               
               
                 cellular and subcellular 
                 phosphomonoesters 
               
               
                 movement 
               
               
                 Acting on GTP to 
                 Endoribonucleases 
                 methylumbelliferyl- 
                 S-succinylglutathione 
               
               
                 facilitate cellular and 
                 producing 5′- 
                 acetate deacetylase 
                 hydrolase 
               
               
                 subcellular movement 
                 phosphomonoesters 
               
               
                 Acting on phosphorus- 
                 Endoribonucleases that 
                 monoterpene e- 
                 steroid-lactonase 
               
               
                 nitrogen bonds 
                 are active with either 
                 lactone hydrolase 
               
               
                   
                 ribo- or 
               
               
                   
                 deoxyribonucleic acids 
               
               
                   
                 and produce 3′- 
               
               
                   
                 phosphomonoesters 
               
               
                 Acting on sulfur- 
                 Endoribonucleases that 
                 N- 
                 sterol esterase 
               
               
                 nitrogen bonds 
                 are active with either 
                 acetylgalactosamine- 
               
               
                   
                 ribo- or 
                 4-sulfatase 
               
               
                   
                 deoxyribonucleic acids 
               
               
                   
                 and produce 5′- 
               
               
                   
                 phosphomonoesters 
               
               
                 actinomycin lactonase 
                 Enzymes acting on acid 
                 N- 
                 steryl-sulfatase 
               
               
                   
                 anhydrides 
                 acetylgalactosamine- 
               
               
                   
                   
                 6-sulfatase 
               
               
                 acylcarnitine hydrolase 
                 Enzymes Acting on 
                 N- 
                 succinyl-CoA 
               
               
                   
                 carbon-carbon bonds 
                 acetylgalactosaminoglycan 
                 hydrolase 
               
               
                   
                   
                 deacetylase 
               
               
                 acyl-CoA hydrolase 
                 Enzymes acting on 
                 N-acetylglucosamine- 
                 sucrose-phosphate 
               
               
                   
                 carbon-nitrogen bonds, 
                 6-sulfatase 
                 phosphatase 
               
               
                   
                 other than peptide bonds 
               
               
                 acylglycerol lipase 
                 Enzymes acting on 
                 N-sulfoglucosamine 
                 sugar-phosphatase 
               
               
                   
                 carbon-phosphorus 
                 sulfohydrolase 
               
               
                   
                 bonds 
               
               
                 acyloxyacyl hydrolase 
                 Enzymes acting on 
                 oleoyl-[acyl-carrier- 
                 Sulfuric-ester 
               
               
                   
                 carbon-sulfur bonds 
                 protein] hydrolase 
                 hydrolases 
               
               
                 acylpyruvate hydrolase 
                 Enzymes Acting on 
                 Omega peptidases 
                 tannase 
               
               
                   
                 ether bonds 
               
               
                 ADAMTS13 
                 Enzymes acting on 
                 orsellinate-depside 
                 Thioester hydrolases 
               
               
                   
                 halide bonds 
                 hydrolase 
               
               
                 Adenosine deaminase 
                 Enzymes acting on 
                 oxaloacetase 
                 Thioether and 
               
               
                   
                 peptide bonds 
                   
                 trialkylsulfonium 
               
               
                   
                 (peptidases) 
                   
                 hydrolases 
               
               
                 adenylyl-[glutamate- 
                 Enzymes acting on 
                 palmitoyl[protein] 
                 Threonine 
               
               
                 ammonia ligase] 
                 phosphorus-nitrogen 
                 hydrolase 
                 endopeptidases 
               
               
                 hydrolase 
                 bonds 
               
               
                 ADP-dependent 
                 Enzymes acting on 
                 palmitoyl-CoA 
                 thymidine 
               
               
                 medium-chain-acyl- 
                 sulfur-nitrogen bonds 
                 hydrolase 
                 phosphorylase 
               
               
                 CoA hydrolase 
               
               
                 ADP-dependent short- 
                 Enzymes acting on 
                 pectinesterase 
                 trehalose-phosphatase 
               
               
                 chain-acyl-CoA 
                 sulfur-sulfur bonds 
               
               
                 hydrolase 
               
               
                 ADP- 
                 Ether hydrolases. 
                 Peptidyl peptide 
                 triacetate-lactonase 
               
               
                 phosphoglycerate 
                   
                 hydrolases 
               
               
                 phosphatase 
               
               
                 alkaline phosphatase 
                 Exodeoxyribonucleases 
                 Peptidyl-amino-acid 
                 Triphosphoric- 
               
               
                   
                 producing 5′- 
                 hydrolases 
                 monoester hydrolases 
               
               
                   
                 phosphomonoesters 
               
               
                 all-trans-retinyl- 
                 Exonucleases that are 
                 Peptidylamino-acid 
                 trithionate hydrolase 
               
               
                 palmitate hydrolase 
                 active with either ribo- 
                 hydrolases or 
               
               
                   
                 or deoxyribonucleic 
                 acylamino-acid 
               
               
                   
                 acids and produce 3′- 
                 hydrolases 
               
               
                   
                 phosphomonoesters 
               
               
                 aminoacyl-tRNA 
                 Exonucleases that are 
                 Peptidyl-dipeptidases 
                 tropinesterase 
               
               
                 hydrolase 
                 active with either ribo- 
               
               
                   
                 or deoxyribonucleic 
               
               
                   
                 acids and produce 5′- 
               
               
                   
                 phosphomonoesters 
               
               
                 Aminopeptidases 
                 Exoribonucleases 
                 phenylacetyl-CoA 
                 ubiquitin thiolesterase 
               
               
                   
                 producing 3′- 
                 hydrolase 
               
               
                   
                 phosphomonoesters 
               
               
                 arylesterase 
                 Exoribonucleases 
                 Phenylalanine 
                 UDP-sulfoquinovose 
               
               
                   
                 producing 5′- 
                 ammonia lyase 
                 synthase 
               
               
                   
                 phosphomonoesters. 
               
               
                 arylsulfatase 
                 Factor IX 
                 Phenylalanine 
                 uricase 
               
               
                   
                   
                 hydroxylase 
               
               
                 Asparaginase 
                 Factor VIII 
                 pheophorbidase 
                 uronolactonase 
               
               
                 Aspartic 
                 fatty-acyl-ethyl-ester 
                 phloretin hydrolase 
                 wax-ester hydrolase 
               
               
                 endopeptidases 
                 synthase 
               
            
           
           
               
               
               
            
               
                 b-diketone hydrolase 
                 phorbol-diester 
                 xylono-1,4-lactonase 
               
               
                   
                 hydrolase 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Selected Diseases, Receivers and Targets 
               
            
           
           
               
               
               
               
            
               
                 Category 
                 Disease 
                 Receiver 
                 Target 
               
               
                   
               
               
                 Amyloidoses 
                 AA Amyloidosis 
                 an an antibody-like binder to 
                 Serum amyloid A 
               
               
                   
                   
                 serum amyloid A protein or 
                 protein and amyloid 
               
               
                   
                   
                 serum amyloid P component 
                 placques 
               
               
                 Amyloidoses 
                 beta2 microglobulin 
                 an an antibody-like binder to 
                 Beta2 microglobulin or 
               
               
                   
                 amyloidosis 
                 beta-2 microglobulin or serum 
                 amyloid placques 
               
               
                   
                   
                 amyloid P component 
               
               
                 Amyloidoses 
                 Light chain amyloidosis 
                 an an antibody-like binder to 
                 Antibody light chain or 
               
               
                   
                   
                 light chain, serum amyloid P 
                 amyloid placques 
               
               
                   
                   
                 component 
               
               
                 Cell 
                 Cancer 
                 an an antibody-like binder to 
                 a circulating tumor cell 
               
               
                 clearance 
                   
                 CD44 
               
               
                 Cell 
                 Cancer 
                 an an antibody-like binder to 
                 a circulating tumor cell 
               
               
                 clearance 
                   
                 EpCam 
               
               
                 Cell 
                 Cancer 
                 an an antibody-like binder to 
                 a circulating tumor cell 
               
               
                 clearance 
                   
                 Her2 
               
               
                 Cell 
                 Cancer 
                 an an antibody-like binder to 
                 a circulating tumor cell 
               
               
                 clearance 
                   
                 EGFR 
               
               
                 Cell 
                 Cancer (B cell) 
                 an an antibody-like binder to 
                 a cancerous B cell 
               
               
                 clearance 
                   
                 CD20 
               
               
                 Cell 
                 Cancer (B cell) 
                 an an antibody-like binder to 
                 a cancerous B cell 
               
               
                 clearance 
                   
                 CD19 
               
               
                 Clearance 
                 Antiphospholipid 
                 beta2-glycoprotein-1 
                 pathogenic self- 
               
               
                 Ab 
                 syndrome 
                   
                 antibody against beta2- 
               
               
                   
                   
                   
                 glycoprotein-1 
               
               
                 Clearance 
                 Catastrophic 
                 beta2-glycoprotein-1 
                 pathogenic self- 
               
               
                 Ab 
                 antiphospholipid 
                   
                 antibody against beta2- 
               
               
                   
                 syndrome 
                   
                 glycoprotein-1 
               
               
                 Clearance 
                 Cold agglutinin disease 
                 I/i antigen 
                 Pathogenic self- 
               
               
                 Ab 
                   
                   
                 antibody against I/i 
               
               
                   
                   
                   
                 antigen 
               
               
                 Clearance 
                 Goodpasture syndrome 
                 a3 NC1 domain of collagen 
                 pathogenic self- 
               
               
                 Ab 
                   
                 (IV) 
                 antibody against a3 
               
               
                   
                   
                   
                 NC1 domain of 
               
               
                   
                   
                   
                 Collagen (IV) 
               
               
                 Clearance 
                 Immune 
                 Platelet Glycoproteins (Ib-IX, 
                 pathogenic self- 
               
               
                 Ab 
                 thrombocytopenia 
                 IIb-IIIa, IV, Ia-IIa) 
                 antibody against 
               
               
                   
                 purpura 
                   
                 platelet glycoprotein 
               
               
                 Clearance 
                 Membranous 
                 Phospholipase A2 receptor 
                 pathogenic self- 
               
               
                 Ab 
                 Nephropathy 
                   
                 antibody against 
               
               
                   
                   
                   
                 phospholipase A2 
               
               
                   
                   
                   
                 receptor 
               
               
                 Clearance 
                 Warm antibody 
                 Glycophorin A, glycophorin B, 
                 pathogenic self- 
               
               
                 Ab 
                 hemolytic anemia 
                 and/or glycophorin C, Rh 
                 antibody against 
               
               
                   
                   
                 antigen 
                 glycophorins and/or Rh 
               
               
                   
                   
                   
                 antigen 
               
               
                 Complement 
                 Age-related macular 
                 a suitable complement 
                 active complement 
               
               
                   
                 degeneration 
                 regulatory protein 
               
               
                 Complement 
                 Atypical hemolytic 
                 complement factor H, or a 
                 active complement 
               
               
                   
                 uremic syndrome 
                 suitable complement regulatory 
               
               
                   
                   
                 protein 
               
               
                 Complement 
                 Autoimmune hemolytic 
                 a suitable complement 
                 active complement 
               
               
                   
                 anemia 
                 regulatory molecule 
               
               
                 Complement 
                 Complement Factor I 
                 Complement factor I, a suitable 
                 active complement 
               
               
                   
                 deficiency 
                 complement regulatory protein 
               
               
                 Complement 
                 Non-alcoholic 
                 a suitable complement 
                 active complement 
               
               
                   
                 steatohepatitis 
                 regulatory molecule 
               
               
                 Complement 
                 Paroxysmal nocturnal 
                 a suitable complement 
                 active complement 
               
               
                   
                 hemoglobinuria 
                 regulatory protein 
               
               
                 Enzyme 
                 3-methylcrotonyl-CoA 
                 3-methylcrotonyl-CoA 
                 3-hydroxyvalerylcarnitine, 
               
               
                   
                 carboxylase deficiency 
                 carboxylase 
                 3-methylcrotonylglycine 
               
               
                   
                   
                   
                 (3-MCG) and 3- 
               
               
                   
                   
                   
                 hydroxyisovaleric acid 
               
               
                   
                   
                   
                 (3-HIVA) 
               
               
                 Enzyme 
                 Acute Intermittent 
                 Porphobilinogen deaminase 
                 Porphobilinogen 
               
               
                   
                 Porphyria 
               
               
                 Enzyme 
                 Acute lymphoblastic 
                 Asparaginase 
                 Asparagine 
               
               
                   
                 leukemia 
               
               
                 Enzyme 
                 Acute lymphocytic 
                 Asparaginase 
                 Asparagine 
               
               
                   
                 leukemia, acute myeloid 
               
               
                   
                 leukemia 
               
               
                 Enzyme 
                 Acute myeloblastic 
                 Asparaginase 
                 Asparagine 
               
               
                   
                 leukemia 
               
               
                 Enzyme 
                 Adenine 
                 adenine 
                 Insoluble purine 2,8- 
               
               
                   
                 phosphoribosyltransferase 
                 phosphoribosyltransferase 
                 dihydroxyadenine 
               
               
                   
                 deficiency 
               
               
                 Enzyme 
                 Adenosine deaminase 
                 Adenosine deaminase 
                 Adenosine 
               
               
                   
                 deficiency 
               
               
                 Enzyme 
                 Afibrinogenomia 
                 FI 
                 enzyme replacement 
               
               
                 Enzyme 
                 Alcohol poisoning 
                 Alcohol dehydrogenase/oxidase 
                 Ethanol 
               
               
                 Enzyme 
                 Alexander&#39;s disease 
                 FVII 
                 enzyme replacement 
               
               
                 Enzyme 
                 Alkaptonuria 
                 homogentisate oxidase 
                 homogentisate 
               
               
                 Enzyme 
                 Argininemia 
                 Ammonia monooxygenase 
                 ammonia 
               
               
                 Enzyme 
                 argininosuccinate 
                 Ammonia monooxygenase 
                 ammonia 
               
               
                   
                 aciduria 
               
               
                 Enzyme 
                 citrullinemia type I 
                 Ammonia monooxygenase 
                 ammonia 
               
               
                 Enzyme 
                 Citrullinemia type II 
                 Ammonia monooxygenase 
                 ammonia 
               
               
                 Enzyme 
                 Complete LCAT 
                 Lecithin-cholesterol 
                 Cholesterol 
               
               
                   
                 deficiency, Fish-eye 
                 acyltransferase (LCAT) 
               
               
                   
                 disease, atherosclerosis, 
               
               
                   
                 hypercholesterolemia 
               
               
                 Enzyme 
                 Cyanide poisoning 
                 Thiosulfate-cyanide 
                 Cyanide 
               
               
                   
                   
                 sulfurtransferase 
               
               
                 Enzyme 
                 Diabetes 
                 Hexokinase, glucokinase 
                 Glucose 
               
               
                 Enzyme 
                 Factor II Deficiency 
                 FII 
                 enzyme replacement 
               
               
                 Enzyme 
                 Familial hyperarginemia 
                 Arginase 
                 Arginine 
               
               
                 Enzyme 
                 Fibrin Stabilizing factor 
                 FXIII 
                 enzyme replacement 
               
               
                   
                 Def. 
               
               
                 Enzyme 
                 Glutaric acidemia type I 
                 lysine oxidase 
                 3-hydroxyglutaric and 
               
               
                   
                   
                   
                 glutaric acid (C5-DC), 
               
               
                   
                   
                   
                 lysine 
               
               
                 Enzyme 
                 Gout 
                 Uricase 
                 Uric Acid 
               
               
                 Enzyme 
                 Gout - hyperuricemia 
                 Uricase 
                 Uric acid (Urate 
               
               
                   
                   
                   
                 crystals) 
               
               
                 Enzyme 
                 Hageman Def. 
                 FXII 
                 enzyme replacement 
               
               
                 Enzyme 
                 Hemolytic anemia due to 
                 pyrimidine 5′ nucleotidase 
                 pyrimidines 
               
               
                   
                 pyrimidine 5′ 
               
               
                   
                 nucleotidase deficiency 
               
               
                 Enzyme 
                 Hemophilia A 
                 Factor VIII 
                 Thrombin (factor II a) 
               
               
                   
                   
                   
                 or Factor X 
               
               
                 Enzyme 
                 Hemophilia B 
                 Factor IX 
                 Factor XIa or Factor X 
               
               
                 Enzyme 
                 Hemophilia C 
                 FXI 
                 enzyme replacement 
               
               
                 Enzyme 
                 Hepatocellular 
                 Arginine deiminase 
                 Arginine 
               
               
                   
                 carcinoma, melanoma 
               
               
                 Enzyme 
                 Homocystinuria 
                 Cystathionine B synthase 
                 homocysteine 
               
               
                 Enzyme 
                 hyperammonemia/ 
                 Ammonia monooxygenase 
                 Ammonia 
               
               
                   
                 ornithinemia/citrullinemia 
               
               
                   
                 (ornithine transporter 
               
               
                   
                 defect) 
               
               
                 Enzyme 
                 Isovaleric acidemia 
                 Leucine metabolizing enzyme 
                 leucine 
               
               
                 Enzyme 
                 Lead poisoning 
                 d-aminolevulinate 
                 lead 
               
               
                   
                   
                 dehydrogenase 
               
               
                 Enzyme 
                 Lesch-Nyhan syndrome 
                 Uricase 
                 Uric acid 
               
               
                 Enzyme 
                 Maple syrup urine 
                 Leucine metabolizing enzyme 
                 Leucine 
               
               
                   
                 disease 
               
               
                 Enzyme 
                 Methylmalonic acidemia 
                 methylmalonyl-CoA mutase 
                 methylmalonate 
               
               
                   
                 (vitamin b12 non- 
               
               
                   
                 responsive) 
               
               
                 Enzyme 
                 Mitochondrial 
                 thymidine phosphorylase 
                 thymidine 
               
               
                   
                 neurogastrointestinal 
               
               
                   
                 encephalomyopathy 
               
               
                 Enzyme 
                 Mitochondrial 
                 Thymidine phosphorylase 
                 Thymidine 
               
               
                   
                 neurogastrointestinal 
               
               
                   
                 encephalomyopathy 
               
               
                   
                 (MNGIE) 
               
               
                 Enzyme 
                 Owren&#39;s disease 
                 FV 
                 enzyme replacement 
               
               
                 Enzyme 
                 p53-null solid tumor 
                 Serine dehyrdatase or serine 
                 serine 
               
               
                   
                   
                 hydroxymethyl transferase 
               
               
                 Enzyme 
                 Pancreatic 
                 Asparaginase 
                 asparagine 
               
               
                   
                 adenocarcinoma 
               
               
                 Enzyme 
                 Phenylketonuria 
                 Phenylalanine hydroxylase, 
                 Phenylalanine 
               
               
                   
                   
                 phenylalanine ammonia lyase 
               
               
                 Enzyme 
                 Primary hyperoxaluria 
                 Oxalate oxidase 
                 Oxalate 
               
               
                 Enzyme 
                 Propionic acidemia 
                 Propionate conversion enzyme? 
                 Proprionyl coA 
               
               
                 Enzyme 
                 Purine nucleoside 
                 Purine nucleoside 
                 Inosine, dGTP 
               
               
                   
                 phosphorylase deficiency 
                 phosphorylase 
               
               
                 Enzyme 
                 Stuart-Power Def. 
                 FX 
                 enzyme replacement 
               
               
                 Enzyme 
                 Thrombotic 
                 ADAMTS13 
                 ultra-large von 
               
               
                   
                 Thrombocytopenic 
                   
                 willebrand factor 
               
               
                   
                 Purpura 
                   
                 (ULVWF) 
               
               
                 Enzyme 
                 Transferase deficient 
                 galactose dehydrogenase 
                 Galactose-1-phosphate 
               
               
                   
                 galactosemia 
               
               
                   
                 (Galactosemia type 1) 
               
               
                 Enzyme 
                 Tyrosinemia type 1 
                 tyrosine phenol-lyase 
                 tyrosine 
               
               
                 Enzyme 
                 von Willebrand disease 
                 vWF 
                 enzyme replacement 
               
               
                 IC clearance 
                 IgA Nephropathy 
                 Complement receptor 1 
                 Immune complexes 
               
               
                 IC clearance 
                 Lupus nephritis 
                 Complement receptor 1 
                 immune complex 
               
               
                 IC clearance 
                 Systemic lupus 
                 Complement receptor 1 
                 immune complex 
               
               
                   
                 erythematosus 
               
               
                 Infectious 
                 Anthrax ( B. anthracis ) 
                 an an antibody-like binder to 
                 B. anthracis 
               
               
                   
                 infection 
                   B. anthracis  surface protein 
               
               
                 Infectious 
                   C. botulinum  infection 
                 an an antibody-like binder to 
                 C. botulinum 
               
               
                   
                   
                   C. botulinum  surface protein 
               
               
                 Infectious 
                   C. difficile  infection 
                 an antibody-like binder to 
                 C. difficile 
               
               
                   
                   
                   C. difficile  surface protein 
               
               
                 Infectious 
                   Candida  infection 
                 an antibody-like binder to 
                 candida 
               
               
                   
                   
                   candida  surface protein 
               
               
                 Infectious 
                   E. coli  infection 
                 an antibody-like binder to 
                 
                   E. coli 
                 
               
               
                   
                   
                   E. coli  surface protein 
               
               
                 Infectious 
                 Ebola infection 
                 an antibody-like binder to 
                 Ebola 
               
               
                   
                   
                 Ebola surface protein 
               
               
                 Infectious 
                 Hepatitis B (HBV) 
                 an antibody-like binder to HBV 
                 HBV 
               
               
                   
                 infection 
                 surface protein 
               
               
                 Infectious 
                 Hepatitis C (HCV) 
                 an antibody-like binder to HCV 
                 HCV 
               
               
                   
                 infection 
                 surface protein 
               
               
                 Infectious 
                 Human 
                 an antibody-like binder to HIV 
                 HIV 
               
               
                   
                 immunodeficiency virus 
                 envelope proteins or CD4 or 
               
               
                   
                 (HIV) infection 
                 CCR5 or 
               
               
                 Infectious 
                 M. tuberculosis infection 
                 an antibody-like binder to 
                 M. tuberculosis 
               
               
                   
                   
                 M. tuberculosis surface protein 
               
               
                 Infectious 
                 Malaria (P. falciparum) 
                 an antibody-like binder to 
                 P. falciparum 
               
               
                   
                 infection 
                 P. falciparum surface protein 
               
               
                 Lipid 
                 Hepatic lipase 
                 Hepatic lipase (LIPC) 
                 Lipoprotein, 
               
               
                   
                 deficiency, 
                   
                 intermediate density 
               
               
                   
                 hypercholesterolemia 
                   
                 (IDL) 
               
               
                 Lipid 
                 Hyperalphalipoproteinemia 1 
                 Cholesteryl ester transfer 
                 Lipoprotein, high 
               
               
                   
                   
                 protein(CETP) 
                 density (HDL) 
               
               
                 Lipid 
                 hypercholesterolemia 
                 an antibody-like binder to low- 
                 LDL 
               
               
                   
                   
                 density lipoprotein (LDL), LDL 
               
               
                   
                   
                 receptor 
               
               
                 Lipid 
                 hypercholesterolemia 
                 an antibody-like binder to high- 
                 HDL 
               
               
                   
                   
                 density lipoprotein (HDL) or 
               
               
                   
                   
                 HDL receptor 
               
               
                 Lipid 
                 lipoprotein lipase 
                 lipoprotein lipase 
                 chilomicrons and very 
               
               
                   
                 deficiency 
                   
                 low density 
               
               
                   
                   
                   
                 lipoproteins (VLDL) 
               
               
                 Lipid 
                 Lipoprotein lipase 
                 lipoprotein lipase (LPL) 
                 Lipoprotein, very low 
               
               
                   
                 deficiency, disorders of 
                   
                 density (VLDL) 
               
               
                   
                 lipoprotein metabolism 
               
               
                 Lysosomal 
                 Aspartylglucosaminuria 
                 N-Aspartylglucosaminidase 
                 glycoproteins 
               
               
                 storage 
                 (208400) 
               
               
                 Lysosomal 
                 Cerebrotendinous 
                 Sterol 27-hydroxylase 
                 lipids, cholesterol, and 
               
               
                 storage 
                 xanthomatosis 
                   
                 bile acid 
               
               
                   
                 (cholestanol lipidosis; 
               
               
                   
                 213700) 
               
               
                 Lysosomal 
                 Ceroid lipofuscinosis 
                 Palmitoyl-protein thioesterase-1 
                 lipopigments 
               
               
                 storage 
                 Adult form (CLN4, Kufs&#39; 
               
               
                   
                 disease; 204300) 
               
               
                 Lysosomal 
                 Ceroid lipofuscinosis 
                 Palmitoyl-protein thioesterase-1 
                 lipopigments 
               
               
                 storage 
                 Infantile form (CLN1, 
               
               
                   
                 Santavuori-Haltia 
               
               
                   
                 disease; 256730) 
               
               
                 Lysosomal 
                 Ceroid lipofuscinosis 
                 Lysosomal transmembrane 
                 lipopigments 
               
               
                 storage 
                 Juvenile form (CLN3, 
                 CLN3 protein 
               
               
                   
                 Batten disease, Vogt- 
               
               
                   
                 Spielmeyer disease; 
               
               
                   
                 204200) 
               
               
                 Lysosomal 
                 Ceroid lipofuscinosis 
                 Lysosomal pepstatin-insensitive 
                 lipopigments 
               
               
                 storage 
                 Late infantile form 
                 peptidase 
               
               
                   
                 (CLN2, Jansky- 
               
               
                   
                 Bielschowsky disease; 
               
               
                   
                 204500) 
               
               
                 Lysosomal 
                 Ceroid lipofuscinosis 
                 Transmembrane CLN8 protein 
                 lipopigments 
               
               
                 storage 
                 Progressive epilepsy 
               
               
                   
                 with intellectual 
               
               
                   
                 disability (600143) 
               
               
                 Lysosomal 
                 Ceroid lipofuscinosis 
                 Transmembrane CLN6 protein 
                 lipopigments 
               
               
                 storage 
                 Variant late infantile 
               
               
                   
                 form (CLN6; 601780) 
               
               
                 Lysosomal 
                 Ceroid lipofuscinosis 
                 Lysosomal transmembrane 
                 lipopigments 
               
               
                 storage 
                 Variant late infantile 
                 CLN5 protein 
               
               
                   
                 form, Finnish type 
               
               
                   
                 (CLN5; 256731) 
               
               
                 Lysosomal 
                 Cholesteryl ester storage 
                 lisosomal acid lipase 
                 lipids and cholesterol 
               
               
                 storage 
                 disease (CESD) 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 Phosphomannomutase-2 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation CDG Ia 
               
               
                   
                 (solely neurologic and 
               
               
                   
                 neurologic-multivisceral 
               
               
                   
                 forms; 212065) 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 Mannose (Man) phosphate (P) 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation CDG Ib 
                 isomerase 
               
               
                   
                 (602579) 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 Dolicho-P-Glc: Man9GlcNAc2- 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation CDG Ic 
                 PP-dolichol glucosyltransferase 
               
               
                   
                 (603147) 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 Dolicho-P-Man: 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation CDG Id 
                 Man5GlcNAc2-PP- 
               
               
                   
                 (601110) 
                 dolichol mannosyltransferase 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 Dolichol-P-mannose synthase 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation CDG Ie 
               
               
                   
                 (608799) 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 Protein involved in mannose-P- 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation CDG If 
                 dolichol utilization 
               
               
                   
                 (609180) 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 Dolichyl-P-mannose: Man-7- 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation CDG Ig 
                 GlcNAc-2-PP-dolichyl-α-6- 
               
               
                   
                 (607143) 
                 mannosyltransferase 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 Dolichyl-P-glucose: Glc-1-Man- 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation CDG Ih 
                 9-GlcNAc-2-PP-dolichyl-α-3- 
               
               
                   
                 (608104) 
                 glucosyltransferase 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 α-1,3-Mannosyltransferase 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation CDG Ii 
               
               
                   
                 (607906) 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 Mannosyl-α-1,6-glycoprotein- 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation CDG IIa 
                 β-1,2-N- 
               
               
                   
                 (212066) 
                 acetylglucosminyltransferase 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 Glucosidase I 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation CDG IIb 
               
               
                   
                 (606056) 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 GDP-fucose transporter-1 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation CDG IIc 
               
               
                   
                 (Rambam-Hasharon 
               
               
                   
                 syndrome; 266265 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 β-1,4-Galactosyltransferase 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation CDG IId 
               
               
                   
                 (607091) 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 Oligomeric Golgi complex-7 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation CDG IIe 
               
               
                   
                 (608779) 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 UDP-GlcNAc: dolichyl-P 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation CDG Ij 
                 NAcGlc phosphotransferase 
               
               
                   
                 (608093) 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 β-1,4-Mannosyltransferase 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation CDG Ik 
               
               
                   
                 (608540) 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 α-1,2-Mannosyltransferase 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation CDG Il 
               
               
                   
                 (608776) 
               
               
                 Lysosomal 
                 Congenital disorders of 
                 α-1,2-Mannosyltransferase 
                 N-glycosylated protein 
               
               
                 storage 
                 N-glycosylation, type I 
               
               
                   
                 (pre-Golgi glycosylation 
               
               
                   
                 defects) 
               
               
                 Lysosomal 
                 Cystinosis 
                 Cystinosin (lysosomal cystine 
                 Cysteine 
               
               
                 storage 
                   
                 transporter) 
               
               
                 Lysosomal 
                 Fabry&#39;s disease (301500) 
                 Trihexosylceramide α- 
                 globotriaosylceramide 
               
               
                 storage 
                   
                 galactosidase 
               
               
                 Lysosomal 
                 Farber&#39;s disease 
                 Ceramidase 
                 lipids 
               
               
                 storage 
                 (lipogranulomatosis; 
               
               
                   
                 228000) 
               
               
                 Lysosomal 
                 Fucosidosis (230000) 
                 α-L-Fucosidase 
                 fucose and complex 
               
               
                 storage 
                   
                   
                 sugars 
               
               
                 Lysosomal 
                 Galactosialidosis 
                 Protective protein/cathepsin A 
                 lysosomal content 
               
               
                 storage 
                 (Goldberg&#39;s syndrome, 
                 (PPCA) 
               
               
                   
                 combined neuraminidase 
               
               
                   
                 and β-galactosidase 
               
               
                   
                 deficiency; 256540) 
               
               
                 Lysosomal 
                 Gaucher&#39;s disease 
                 Glucosylceramide β- 
                 sphingolipids 
               
               
                 storage 
                   
                 glucosidase 
               
               
                 Lysosomal 
                 Glutamyl ribose-5- 
                 ADP-ribose protein hydrolase 
                 glutamyl ribose 5- 
               
               
                 storage 
                 phosphate storage 
                   
                 phosphate 
               
               
                   
                 disease (305920) 
               
               
                 Lysosomal 
                 Glycogen storage disease 
                 alpha glucosidase 
                 glycogen 
               
               
                 storage 
                 type 2 (Pompe&#39;s disease) 
               
               
                 Lysosomal 
                 GM1 gangliosidosis, 
                 Ganglioside β-galactosidase 
                 acidic lipid material, 
               
               
                 storage 
                 generalized 
                   
                 gangliosides 
               
               
                 Lysosomal 
                 GM2 activator protein 
                 GM2 activator protein 
                 gangliosides 
               
               
                 storage 
                 deficiency (Tay-Sachs 
               
               
                   
                 disease AB variant, 
               
               
                   
                 GM2A; 272750) 
               
               
                 Lysosomal 
                 GM2 gangliosidosis 
                 Ganglioside β-galactosidase 
                 gangliosides 
               
               
                 storage 
               
               
                 Lysosomal 
                 Infantile sialic acid 
                 Na phosphate cotransporter, 
                 sialic acid 
               
               
                 storage 
                 storage disorder 
                 sialin 
               
               
                   
                 (269920) 
               
               
                 Lysosomal 
                 Krabbe&#39;s disease 
                 Galactosylceramide β- 
                 sphingolipids 
               
               
                 storage 
                 (245200) 
                 galactosidase 
               
               
                 Lysosomal 
                 Lysosomal acid lipase 
                 Lysosomal acid lipase 
                 cholesteryl 
               
               
                 storage 
                 deficiency (278000) 
                   
                 esters and triglycerides 
               
               
                 Lysosomal 
                 Metachromatic 
                 Arylsulfatase A 
                 sulfatides 
               
               
                 storage 
                 leukodystrophy (250100) 
               
               
                 Lysosomal 
                 Mucolipidosis ML II (I- 
                 N-Acetylglucosaminyl-1- 
                 N-linked glycoproteins 
               
               
                 storage 
                 cell disease; 252500) 
                 phosphotransfeerase catalytic 
               
               
                   
                   
                 subunit 
               
               
                 Lysosomal 
                 Mucolipidosis ML III 
                 N-acetylglucosaminyl-1- 
                 N-linked glycoproteins 
               
               
                 storage 
                 (pseudo-Hurler&#39;s 
                 phosphotransfeerase 
               
               
                   
                 polydystrophy) 
               
               
                 Lysosomal 
                 Mucolipidosis ML III 
                 Catalytic subunit 
                 N-linked glycoproteins 
               
               
                 storage 
                 (pseudo-Hurler&#39;s 
               
               
                   
                 polydystrophy) Type III- 
               
               
                   
                 A (252600) 
               
               
                 Lysosomal 
                 Mucolipidosis ML III 
                 Substrate-recognition subunit 
                 N-linked glycoproteins 
               
               
                 storage 
                 (pseudo-Hurler&#39;s 
               
               
                   
                 polydystrophy) Type III- 
               
               
                   
                 C (252605) 
               
               
                 Lysosomal 
                 Mucopolysaccharidosis 
                 α-1-Iduronidase 
                 glycosaminoglycans 
               
               
                 storage 
                 MPS I H/S (Hurler- 
               
               
                   
                 Scheie syndrome; 
               
               
                   
                 607015) 
               
               
                 Lysosomal 
                 Mucopolysaccharidosis 
                 α-1-Iduronidase 
                 glycosaminoglycans 
               
               
                 storage 
                 MPS I-H (Hurler&#39;s 
               
               
                   
                 syndrome; 607014) 
               
               
                 Lysosomal 
                 Mucopolysaccharidosis 
                 Iduronate sulfate sulfatase 
                 glycosaminoglycans 
               
               
                 storage 
                 MPS II (Hunter&#39;s 
               
               
                   
                 syndrome; 309900) 
               
               
                 Lysosomal 
                 Mucopolysaccharidosis 
                 Heparan-S-sulfate sulfamidase 
                 glycosaminoglycans 
               
               
                 storage 
                 MPS III (Sanfilippo&#39;s 
               
               
                   
                 syndrome) Type III-A 
               
               
                   
                 (252900) 
               
               
                 Lysosomal 
                 Mucopolysaccharidosis 
                 N-acetyl-D-glucosaminidase 
                 glycosaminoglycans 
               
               
                 storage 
                 MPS III (Sanfilippo&#39;s 
               
               
                   
                 syndrome) Type III-B 
               
               
                   
                 (252920) 
               
               
                 Lysosomal 
                 Mucopolysaccharidosis 
                 Acetyl-CoA-glucosaminide N- 
                 glycosaminoglycans 
               
               
                 storage 
                 MPS III (Sanfilippo&#39;s 
                 acetyltransferase 
               
               
                   
                 syndrome) Type III-C 
               
               
                   
                 (252930) 
               
               
                 Lysosomal 
                 Mucopolysaccharidosis 
                 N-acetyl-glucosaminine-6- 
                 glycosaminoglycans 
               
               
                 storage 
                 MPS III (Sanfilippo&#39;s 
                 sulfate sulfatase 
               
               
                   
                 syndrome) Type III-D 
               
               
                   
                 (252940) 
               
               
                 Lysosomal 
                 Mucopolysaccharidosis 
                 α-1-Iduronidase 
                 glycosaminoglycans 
               
               
                 storage 
                 MPS I-S (Scheie&#39;s 
               
               
                   
                 syndrome; 607016) 
               
               
                 Lysosomal 
                 Mucopolysaccharidosis 
                 Galactosamine-6-sulfate 
                 glycosaminoglycans 
               
               
                 storage 
                 MPS IV (Morquio&#39;s 
                 sulfatase 
               
               
                   
                 syndrome) Type IV-A 
               
               
                   
                 (253000) 
               
               
                 Lysosomal 
                 Mucopolysaccharidosis 
                 β-Galactosidase 
                 glycosaminoglycans 
               
               
                 storage 
                 MPS IV (Morquio&#39;s 
               
               
                   
                 syndrome) Type IV-B 
               
               
                   
                 (253010) 
               
               
                 Lysosomal 
                 Mucopolysaccharidosis 
                 Hyaluronidase deficiency 
                 glycosaminoglycans 
               
               
                 storage 
                 MPS IX (hyaluronidase 
               
               
                   
                 deficiency; 601492) 
               
               
                 Lysosomal 
                 Mucopolysaccharidosis 
                 N-Acetyl galactosamine α-4- 
                 glycosaminoglycans 
               
               
                 storage 
                 MPS VI (Maroteaux- 
                 sulfate sulfatase (arylsulfatase 
               
               
                   
                 Lamy syndrome; 
                 B) 
               
               
                   
                 253200) 
               
               
                 Lysosomal 
                 Mucopolysaccharidosis 
                 β-Glucuronidase 
                 glycosaminoglycans 
               
               
                 storage 
                 MPS VII (Sly&#39;s 
               
               
                   
                 syndrome; 253220) 
               
               
                 Lysosomal 
                 Mucosulfatidosis 
                 Sulfatase-modifying factor-1 
                 sulfatides 
               
               
                 storage 
                 (multiple sulfatase 
               
               
                   
                 deficiency; 272200) 
               
               
                 Lysosomal 
                 Niemann-Pick disease 
                 Sphingomyelinase 
                 sphingomyelin 
               
               
                 storage 
                 type A 
               
               
                 Lysosomal 
                 Niemann-Pick disease 
                 Sphingomyelinase 
                 sphingomyelin 
               
               
                 storage 
                 type B 
               
               
                 Lysosomal 
                 Niemann-Pick disease 
                 NPC1 protein 
                 sphingomyelin 
               
               
                 storage 
                 Type C1/Type D 
               
               
                   
                 ((257220) 
               
               
                 Lysosomal 
                 Niemann-Pick disease 
                 Epididymal secretory protein 1 
                 sphingomyelin 
               
               
                 storage 
                 Type C2 (607625) 
                 (HE1; NPC2 protein) 
               
               
                 Lysosomal 
                 Prosaposin deficiency 
                 Prosaposin 
                 sphingolipids 
               
               
                 storage 
                 (176801) 
               
               
                 Lysosomal 
                 Pycnodysostosis 
                 Cathepsin K 
                 kinins 
               
               
                 storage 
                 (265800) 
               
               
                 Lysosomal 
                 Sandhoff&#39;s disease; 
                 β-Hexosaminidase B 
                 gangliosides 
               
               
                 storage 
                 268800 
               
               
                 Lysosomal 
                 Saposin B deficiency 
                 Saposin B 
                 sphingolipids 
               
               
                 storage 
                 (sulfatide activator 
               
               
                   
                 deficiency) 
               
               
                 Lysosomal 
                 Saposin C deficiency 
                 Saposin C 
                 sphingolipids 
               
               
                 storage 
                 (Gaucher&#39;s activator 
               
               
                   
                 deficiency) 
               
               
                 Lysosomal 
                 Schindler&#39;s disease Type 
                 N-Acetyl-galactosaminidase 
                 glycoproteins 
               
               
                 storage 
                 I (infantile severe form; 
               
               
                   
                 609241) 
               
               
                 Lysosomal 
                 Schindler&#39;s disease Type 
                 N-Acetyl-galactosaminidase 
                 glycoproteins 
               
               
                 storage 
                 II (Kanzaki disease, 
               
               
                   
                 adult-onset form; 
               
               
                   
                 609242) 
               
               
                 Lysosomal 
                 Schindler&#39;s disease Type 
                 N-Acetyl-galactosaminidase 
                 glycoproteins 
               
               
                 storage 
                 III (intermediate form; 
               
               
                   
                 609241) 
               
               
                 Lysosomal 
                 Sialidosis (256550) 
                 Neuraminidase 1 (sialidase) 
                 mucopolysaccharides 
               
               
                 storage 
                   
                   
                 and mucolipids 
               
               
                 Lysosomal 
                 Sialuria Finnish type 
                 Na phosphate cotransporter, 
                 sialic acid 
               
               
                 storage 
                 (Salla disease; 604369) 
                 sialin 
               
               
                 Lysosomal 
                 Sialuria French type 
                 UDP-N-acetylglucosamine-2- 
                 sialic acid 
               
               
                 storage 
                 (269921) 
                 epimerase/N- 
               
               
                   
                   
                 acetylmannosamine kinase, 
               
               
                   
                   
                 sialin 
               
               
                 Lysosomal 
                 Sphingolipidosis Type I 
                 Ganglioside β-galactosidase 
                 sphingolipids 
               
               
                 storage 
                 (230500) 
               
               
                 Lysosomal 
                 Sphingolipidosis Type II 
                 Ganglioside β-galactosidase 
                 sphingolipids 
               
               
                 storage 
                 (juvenile type; 230600) 
               
               
                 Lysosomal 
                 Sphingolipidosis Type 
                 Ganglioside β-galactosidase 
                 sphingolipids 
               
               
                 storage 
                 III (adult type; 230650) 
               
               
                 Lysosomal 
                 Tay-Sachs disease; 
                 β-Hexosaminidase A 
                 gangliosides 
               
               
                 storage 
                 272800 
               
               
                 Lysosomal 
                 Winchester syndrome 
                 Metalloproteinase-2 
                 mucopolysaccharides 
               
               
                 storage 
                 (277950) 
               
               
                 Lysosomal 
                 Wolman&#39;s disease 
                 lysosomal acid lipase 
                 lipids and cholesterol 
               
               
                 storage 
               
               
                 Lysosomal 
                 α-Mannosidosis 
                 α-D-Mannosidase 
                 carbohydrates and 
               
               
                 storage 
                 (248500), type I (severe) 
                   
                 glycoproteins 
               
               
                   
                 or II (mild) 
               
               
                 Lysosomal 
                 β-Mannosidosis 
                 β-D-Mannosidase 
                 carbohydrates and 
               
               
                 storage 
                 (248510) 
                   
                 glycoproteins 
               
               
                 Toxic 
                 alpha hemolysin 
                 an antibody-like binder to alpha 
                 alpha hemolysin 
               
               
                 Molecule 
                 poisoning 
                 hemolysin 
               
               
                 Toxic 
                 antrax toxin poisoning 
                 an antibody-like binder to 
                 anthrax toxin 
               
               
                 Molecule 
                   
                 anthrax toxin 
               
               
                 Toxic 
                 bacterial toxin-induced 
                 an antibody-like binder to 
                 bacterial toxin 
               
               
                 Molecule 
                 shock 
                 bacterial toxin 
               
               
                 Toxic 
                 botulinum toxin 
                 an antibody-like binder to 
                 botulinum toxin 
               
               
                 Molecule 
                 poisoning 
                 botulinum toxin 
               
               
                 Toxic 
                 Hemochromatosis (iron 
                 iron chelator 
                 molecular iron 
               
               
                 Molecule 
                 poisoning) 
               
               
                 Toxic 
                 Methanol poisoning 
                 Methanol dehdrogenase 
                 Methanol 
               
               
                 Molecule 
               
               
                 Toxic 
                 Nerve gas poisoning 
                 Butyryl cholinesterase 
                 Sarin 
               
               
                 Molecule 
               
               
                 Toxic 
                 Prion disease caused by 
                 an antibody-like binder to prion 
                 Prion protein PRP 
               
               
                 Molecule 
                 PRP 
                 protein PRP 
               
               
                 Toxic 
                 Prion disease caused by 
                 an antibody-like binder to prion 
                 Prion protein PRPc 
               
               
                 Molecule 
                 PRPc 
                 protein PRPc 
               
               
                 Toxic 
                 Prion disease caused by 
                 an antibody-like binder to prion 
                 Prion protein PRPsc 
               
               
                 Molecule 
                 PRPsc 
                 protein PRPsc 
               
               
                 Toxic 
                 Prion disease cuased by 
                 an antibody-like binder to prion 
                 Prion protein PRPres 
               
               
                 Molecule 
                 PRPres 
                 protein PRPres 
               
               
                 Toxic 
                 Sepsis or cytokine storm 
                 an antibody-like binder to 
                 cytokines 
               
               
                 Molecule 
                   
                 cytokines or Duffy antigen 
               
               
                   
                   
                 receptor of chemokines 
               
               
                   
                   
                 (DARC) 
               
               
                 Toxic 
                 spider venom poisoning 
                 an antibody-like binder to 
                 spider venom 
               
               
                 Molecule 
                   
                 spider venom 
               
               
                 Toxic 
                 Wilson disease 
                 copper chelator 
                 molecular copper 
               
               
                 Molecule 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 9A 
               
               
                   
               
               
                 Conjugation methods 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 Zero-length x-linker 
               
               
                   
                 EDC 
               
               
                   
                 EDC plus sulfo NHS 
               
               
                   
                 CMC 
               
               
                   
                 DCC 
               
               
                   
                 DIC 
               
               
                   
                 Woodward&#39;s reagent K 
               
               
                   
                 N,N′-carbonyldiimidazole 
               
               
                   
                 Schiff base + reductive amination 
               
               
                   
                 Homobifunctional NHS esters 
               
               
                   
                 DSP 
               
               
                   
                 DTSSP 
               
               
                   
                 DSS 
               
               
                   
                 BS{circumflex over ( )}3 
               
               
                   
                 DST 
               
               
                   
                 Sulfo-DST 
               
               
                   
                 BSOCOES 
               
               
                   
                 Sulfo-BSOCOES 
               
               
                   
                 EGS 
               
               
                   
                 Sulfo-EGS 
               
               
                   
                 DSG 
               
               
                   
                 DSC 
               
               
                   
                 Homobifunctional Imidoesters 
               
               
                   
                 DMA 
               
               
                   
                 DMP 
               
               
                   
                 DMS 
               
               
                   
                 DTBP 
               
               
                   
                 Sulfhydryl reactive x-linkers 
               
               
                   
                 DPDPB 
               
               
                   
                 BMH 
               
               
                   
                 Difluorobenzene derivatives 
               
               
                   
                 DFDNB 
               
               
                   
                 DFDNPS 
               
               
                   
                 Photoreactive x-linker 
               
               
                   
                 BASED 
               
               
                   
                 Homobifunctional aldehydes 
               
               
                   
                 Formaldehyde 
               
               
                   
                 Glutaraldehyde 
               
               
                   
                 bis-epoxide 
               
               
                   
                 1,4-butanediol diglycidyl ether 
               
               
                   
                 Homobifunctional hydrazides 
               
               
                   
                 adipic acid dihydrazide 
               
               
                   
                 carbohydrazide 
               
               
                   
                 Bis-diazonium derivative 
               
               
                   
                 o-tolidine diazotized 
               
               
                   
                 Bis-diazotized benzidine 
               
               
                   
                 Amine-sulfhydryl x-linker 
               
               
                   
                 SPDP, LC-SPDP, sulfo-LC-SPDP 
               
               
                   
                 SMPT and sulfo-LC-SMPT 
               
               
                   
                 SMCC and sulfo-SMCC 
               
               
                   
                 MBS and sulfo-MBS 
               
               
                   
                 SIAB and sulfo-SIAB 
               
               
                   
                 SMPB and sulfo-SMPB 
               
               
                   
                 GMBS and sulfo-GMBS 
               
               
                   
                 SIAX and SIAXX 
               
               
                   
                 SIAC and SIACX 
               
               
                   
                 NPIA 
               
               
                   
                 Carbonyl-sulfydryl x-linker 
               
               
                   
                 MPBH 
               
               
                   
                 M2C2H 
               
               
                   
                 PDPH 
               
               
                   
                 amine-photoreactive x-linker 
               
               
                   
                 NHS-ASA, Sulfo-NHS-ASA 
               
               
                   
                 Sulfo-NHS-LC-ASA 
               
               
                   
                 SASD 
               
               
                   
                 HSAB and sulfo-HSAB 
               
               
                   
                 SANPAH and sulfo-SANPAH 
               
               
                   
                 ANB-NOS 
               
               
                   
                 SAND 
               
               
                   
                 SADP and sulfo-SADP 
               
               
                   
                 Sulfo-SAPB 
               
               
                   
                 SAED 
               
               
                   
                 Sulfo-SAMCA 
               
               
                   
                 p-Nitrophenyl diazopyruvate 
               
               
                   
                 PNP-DTP 
               
               
                   
                 sulfhydryl-photoreactive x-linker 
               
               
                   
                 ASIB 
               
               
                   
                 APDP 
               
               
                   
                 Benzophenone-4-iodoacetamide 
               
               
                   
                 Benzophenone-4-maleimide 
               
               
                   
                 Carbonyl-photoreactive x-linker 
               
               
                   
                 ABH 
               
               
                   
                 Carboxylate-photoreactive x-linker 
               
               
                   
                 ASBA 
               
               
                   
                 arginine-photoreactive x-linker 
               
               
                   
                 APG 
               
               
                   
                 Bioorthogonal reactions 
               
               
                   
                 Diels-alder reagent pairs 
               
               
                   
                 Hydrazine-aldehyde reagent pairs 
               
               
                   
                 Boronic acid salicylhydroxamate 
               
               
                   
                 Click chemistry 
               
               
                   
                 Staudinger ligation 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 9B 
               
               
                   
               
               
                 Enzymatic conjugation methods 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 Sortase 
               
               
                   
                 DD-transpeptidase 
               
               
                   
                 Peptidyl transferase 
               
               
                   
                 G-glutamyl transpeptidase 
               
               
                   
                 D-glutamyl transpeptidase 
               
               
                   
                 Farnesyltransferase 
               
               
                   
                 Prenyltranferase 
               
               
                   
                 Dimethylallyltrans-transferase 
               
               
                   
                 Geranylgeranyl pyrophosphate synthase 
               
               
                   
                 Dehydrodolichol diphosphate synthase 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 9C 
               
             
            
               
                   
               
               
                 Chemistry of reactive groups 
               
            
           
           
               
               
               
               
            
               
                 Amine reactions 
                 Thiol reactions 
                 Hydroxyl reactions 
                 Active hydrogen reactions 
               
               
                   
               
               
                 Isothyocyantes 
                 Haloacetyl and alkl 
                 Epoxides and oxiranes 
                 Diazonium derivatives 
               
               
                   
                 halide derivatives 
               
               
                 Isocyanates 
                 Maleimides 
                 Carbonyldiimidazole 
                 Mannich condensation 
               
               
                 Acyl azides 
                 Aziridines 
                 N,N′0disuccinimidyl 
                 Iodination reactions 
               
               
                   
                   
                 carbonate 
               
               
                 NHS esters 
                 Acryloyl derivatives 
                 N-hydroxysuccinimidyl 
               
               
                   
                   
                 chloroformate 
               
               
                 Sulfonyl chlorides 
                 Arylating agents 
                 Oxidation with periodate 
               
               
                 Aldehydes and 
                 Thil-disulfide exchange 
                 Enzymatic oxidation 
                 Cycloaddition reactions 
               
               
                 glyoxals 
                 reagents 
               
               
                 Epoxides and oxiranes 
                 Vinylsulfone derivatives 
                 Alkyl halogens 
                 Diels-Alder reaction 
               
               
                 Carbonates 
                 Metal-thiol dative bonds 
                 Isocyanates 
                 Complex formation with 
               
               
                   
                   
                   
                 boronic acid derivatives 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 10 
               
               
                   
               
               
                 Complement &amp; Complement Regulatory Molecules 
               
               
                 Soluble molecules 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 Alternative Pathway 
               
               
                   
                 Factor B 
               
               
                   
                 Factor D 
               
               
                   
                 Properdin 
               
               
                   
                 C3 
               
               
                   
                 C3a 
               
               
                   
                 C3b 
               
               
                   
                 iC3b 
               
               
                   
                 C3c 
               
               
                   
                 C3dg 
               
               
                   
                 C3dk 
               
               
                   
                 C3e 
               
               
                   
                 Bb 
               
               
                   
                 Factor I 
               
               
                   
                 Classical Pathway 
               
               
                   
                 C1q 
               
               
                   
                 C1r 
               
               
                   
                 C1s 
               
               
                   
                 C4 
               
               
                   
                 C4a 
               
               
                   
                 C4b 
               
               
                   
                 C2 
               
               
                   
                 C4bp 
               
               
                   
                 Lectin Pathway 
               
               
                   
                 Mannose-Binding Lectin (MBL) 
               
               
                   
                 MBL-Associated Serine Protease 1 (MASP1) 
               
               
                   
                 MBL-Associated Serine Protease 2 (MASP2) 
               
               
                   
                 Late Components 
               
               
                   
                 C5 
               
               
                   
                 C5a 
               
               
                   
                 C6 
               
               
                   
                 C7 
               
               
                   
                 C8 
               
               
                   
                 C9 
               
               
                   
                 Receptors 
               
               
                   
                 CR1 
               
               
                   
                 CR2 
               
               
                   
                 CR3 
               
               
                   
                 CR4 
               
               
                   
                 C3aR 
               
               
                   
                 C3eR 
               
               
                   
                 Decay-accelerating factor (DAF) 
               
               
                   
                 Membrane cofactor protein (MCP) 
               
               
                   
                 CD59 
               
               
                   
                 C3 Beta chain Receptor 
               
               
                   
                 Homologous restriction factor 
               
               
                   
                 Control Proteins 
               
               
                   
                 C1 inhibitor 
               
               
                   
                 C4 binding protein 
               
               
                   
                 Factor I 
               
               
                   
                 Factor H 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 11 
               
             
            
               
                   
               
               
                 Electroporation Conditions (Day 8-9) 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Pulse 
                 Pulse 
                 Pulse 
                   
                 Cell 
               
               
                 Sample 
                 Voltage 
                 width 
                 number 
                 % GFP 
                 viability 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 1 
                 No electroporation 
                   
                   
                 0.21 
                 97.39 
               
               
                 2 
                 1400 
                 20 
                 1 
                 86.9 
                 92.6 
               
               
                 3 
                 1500 
                 20 
                 1 
                 79.5 
                 85.7 
               
               
                 4 
                 1600 
                 20 
                 1 
                 68.2 
                 78.5 
               
               
                 5 
                 1700 
                 20 
                 1 
                 41.4 
                 52.3 
               
               
                 6 
                 1100 
                 30 
                 1 
                 79 
                 96 
               
               
                 7 
                 1200 
                 30 
                 1 
                 83.6 
                 91.9 
               
               
                 8 
                 1300 
                 30 
                 1 
                 77.6 
                 86.6 
               
               
                 9 
                 1400 
                 30 
                 1 
                 30.9 
                 42.7 
               
               
                 10 
                 1000 
                 40 
                 1 
                 65.3 
                 92.4 
               
               
                 11 
                 1100 
                 40 
                 1 
                 69.3 
                 86.9 
               
               
                 12 
                 1200 
                 40 
                 1 
                 65.8 
                 79.9 
               
               
                 13 
                 1100 
                 20 
                 2 
                 81.3 
                 92.8 
               
               
                 14 
                 1200 
                 20 
                 2 
                 82.1 
                 91.2 
               
               
                 15 
                 1300 
                 20 
                 2 
                 78.2 
                 86.3 
               
               
                 16 
                 1400 
                 20 
                 2 
                 79.3 
                 88.1 
               
               
                 17 
                 850 
                 30 
                 2 
                 32.4 
                 95.9 
               
               
                 18 
                 950 
                 30 
                 2 
                 59.5 
                 93.8 
               
               
                 19 
                 1050 
                 30 
                 2 
                 72 
                 90.8 
               
               
                 20 
                 1150 
                 30 
                 2 
                 74.8 
                 84.8 
               
               
                 21 
                 1300 
                 10 
                 3 
                 88.3 
                 94.2 
               
               
                 22 
                 1400 
                 10 
                 3 
                 88.7 
                 93.3 
               
               
                 23 
                 1500 
                 10 
                 3 
                 86.5 
                 90.3 
               
               
                 24 
                 1600 
                 10 
                 3 
                 83.3 
                 87.7 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 12 
               
             
            
               
                   
               
               
                 Electroporation Conditions (Day 12-13) 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Pulse 
                 Pulse 
                 Pulse 
                   
                 Cell 
               
               
                 Sample 
                 Voltage 
                 width 
                 number 
                 % GFP 
                 viability 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 1 
                 No electroporation 
                   
                   
                 0.58 
                 96.7 
               
               
                 2 
                 1400 
                 20 
                 1 
                 42.5 
                 94.9 
               
               
                 3 
                 1500 
                 20 
                 1 
                 54.8 
                 91.8 
               
               
                 4 
                 1600 
                 20 
                 1 
                 56.9 
                 91.6 
               
               
                 5 
                 1700 
                 20 
                 1 
                 61.5 
                 88.7 
               
               
                 6 
                 1100 
                 30 
                 1 
                 13.5 
                 95.6 
               
               
                 7 
                 1200 
                 30 
                 1 
                 29 
                 95.5 
               
               
                 8 
                 1300 
                 30 
                 1 
                 43.8 
                 94.3 
               
               
                 9 
                 1400 
                 30 
                 1 
                 44.5 
                 92.9 
               
               
                 10 
                 1000 
                 40 
                 1 
                 6.5 
                 95.3 
               
               
                 11 
                 1100 
                 40 
                 1 
                 21.7 
                 94.8 
               
               
                 12 
                 1200 
                 40 
                 1 
                 33.2 
                 92.3 
               
               
                 13 
                 1100 
                 20 
                 2 
                 18 
                 95.8 
               
               
                 14 
                 1200 
                 20 
                 2 
                 29.3 
                 95.2 
               
               
                 15 
                 1300 
                 20 
                 2 
                 42 
                 94.5 
               
               
                 16 
                 1400 
                 20 
                 2 
                 51.5 
                 91.8 
               
               
                 17 
                 850 
                 30 
                 2 
                 2.7 
                 95.9 
               
               
                 18 
                 950 
                 30 
                 2 
                 7.3 
                 95.3 
               
               
                 19 
                 1050 
                 30 
                 2 
                 13.5 
                 94.5 
               
               
                 20 
                 1150 
                 30 
                 2 
                 20.7 
                 94.7 
               
               
                 21 
                 1300 
                 10 
                 3 
                 27.3 
                 95.9 
               
               
                 22 
                 1400 
                 10 
                 3 
                 38.8 
                 95.3 
               
               
                 23 
                 1500 
                 10 
                 3 
                 55 
                 94.1 
               
               
                 24 
                 1600 
                 10 
                 3 
                 62.6 
                 93.3 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 13 
               
             
            
               
                   
               
               
                 Electroporation Conditions (Day 14-16) 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Pulse 
                 Pulse 
                 Pulse 
                   
                 Cell 
               
               
                 Sample 
                 Voltage 
                 width 
                 number 
                 % GFP 
                 viability 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 0 
                 No electroporation 
                   
                   
                 1.1 
                 5.2 
               
               
                 1 
                 1700 
                 20 
                 1 
                 44.7 
                 7.7 
               
               
                 2 
                 1700 
                 20 
                 2 
                 44.1 
                 15.5 
               
               
                 3 
                 1700 
                 20 
                 3 
                 42.7 
                 25 
               
               
                 4 
                 1600 
                 10 
                 3 
                 37.6 
                 7.6 
               
               
                 5 
                 1600 
                 10 
                 6 
                 34.9 
                 19.1 
               
               
                 6 
                 1600 
                 10 
                 8 
                 20.1 
                 47.8 
               
               
                 7 
                 1600 
                 20 
                 1 
                 36.7 
                 5.7 
               
               
                 8 
                 1600 
                 20 
                 2 
                 37.2 
                 14.6 
               
               
                 9 
                 1600 
                 20 
                 3 
                 40.2 
                 13 
               
               
                 10 
                 1700 
                 10 
                 1 
                 21.7 
                 4.9 
               
               
                 11 
                 1700 
                 10 
                 2 
                 43 
                 9.7 
               
               
                 12 
                 1700 
                 10 
                 3 
                 24.9 
                 33.9 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 14 
               
             
            
               
                   
               
               
                 Gene Names and Identification Numbers 
               
            
           
           
               
               
               
               
            
               
                   
                 Name 
                 Gene ID 
                 Prot ID 
               
               
                   
                   
               
               
                   
                 ADAMTS13 
                 11093  
                 Q76LX8 
               
               
                   
                 CFI 
                 3426 
                 P05156 
               
               
                   
                 Factor V 
                 2153 
                 P12259 
               
               
                   
                 Factor VII 
                 2155 
                 P08709 
               
               
                   
                 Factor VIII 
                 2157 
                 P00451 
               
               
                   
                 Factor IX 
                 2158 
                 P00740 
               
               
                   
                 Factor X 
                 2159 
                 P00742 
               
               
                   
                 PAH 
                 5053 
                 P00439 
               
               
                   
                 cPAH 
                 2827919   
                 P30967 
               
               
                   
                 (chromobact. 
               
               
                   
                 violaceum) 
               
               
                   
                 PAL 
                 3758891   
                 Q3M5Z3 
               
               
                   
                 PBGD/HMBS 
                 3145 
                 P08397 
               
               
                   
                 FXI 
                 2160 
                 P03951 
               
               
                   
                 FXII 
                 2161 
                 P00748 
               
               
                   
                 FXIII 
                   2162 a 
                 P00488 a 
               
               
                   
                   
                   2165 b 
                 P05160 b 
               
               
                   
                 FIII (Tissue 
                 2152 
                 P13726 
               
               
                   
                 Factor) 
               
               
                   
                 FII (thrombin) 
                 2147 
                 P00734 
               
               
                   
                 MGL (Pp or 
                 1041604   
                 P13254 
               
               
                   
                 At) 
                 AT1G64660 
                 Q9SGU9 
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 15 
               
             
            
               
                   
               
               
                 Coagulation Cascade and Factors 
               
            
           
           
               
               
               
            
               
                 Number and/or Name 
                 Function 
                 Related Genetic Disorder 
               
               
                   
               
               
                 I (fibrinogen) 
                 Forms clot (fibrin) 
                 Congenital 
               
               
                   
                   
                 afibrinogenemia, Familial renal 
               
               
                   
                   
                 amyloidosis 
               
               
                 II (prothrombin) 
                 Its active form (IIa) activates I, V, 
                 Prothrombin 
               
               
                   
                 VII, VIII, XI, XIII, protein 
                 G20210A, Thrombophilia 
               
               
                   
                 C, platelets 
               
               
                 III (tissue factor or tissue 
                 Co-factor of VIIa (formerly known as 
               
               
                 thromboplastin) 
                 factor III) 
               
               
                 IV Calcium 
                 Required for coagulation factors to 
               
               
                   
                 bind to phospholipid (formerly 
               
               
                   
                 known as factor IV) 
               
               
                 V (proaccelerin, labile 
                 Co-factor of X with which it forms 
                 Activated protein C resistance 
               
               
                 factor) 
                 the prothrombinase complex 
               
               
                 VI 
                 Unassigned - old name of Factor Va 
               
               
                 VII (stable factor, 
                 Activates IX, X 
                 congenital proconvertin/factor 
               
               
                 proconvertin) 
                   
                 VII deficiency 
               
               
                 VIII (Antihemophilic 
                 Co-factor of IX with which it forms 
                 Haemophilia A 
               
               
                 factor A) 
                 the tenase complex 
               
               
                 IX (Antihemophilic factor 
                 Activates X: forms tenase complex 
                 Haemophilia B 
               
               
                 B or Christmas factor) 
                 with factor VIII 
               
               
                 X (Stuart-Prower factor) 
                 Activates II: 
                 Congenital Factor X deficiency 
               
               
                   
                 forms prothrombinase complex with 
               
               
                   
                 factor V 
               
               
                 XI (plasma 
                 Activates IX 
                 Haemophilia C 
               
               
                 thromboplastin 
               
               
                 antecedent) 
               
               
                 XII (Hageman factor) 
                 Activates factor XI, VII and 
                 Hereditary angioedema type III 
               
               
                   
                 prekallikrein 
               
               
                 XIII (fibrin-stabilizing 
                 Crosslinks fibrin 
                 Congenital Factor XIIIa/b 
               
               
                 factor) 
                   
                 deficiency 
               
               
                 von Willebrand factor 
                 Binds to VIII, mediates platelet 
                 von Willebrand disease 
               
               
                   
                 adhesion 
               
               
                 prekallikrein (Fletcher 
                 Activates XII and prekallikrein; 
                 Prekallikrein/Fletcher Factor 
               
               
                 factor) 
                 cleaves HMWK 
                 deficiency 
               
               
                 high-molecular-weight 
                 Supports reciprocal activation of XII, 
                 Kininogen deficiency 
               
               
                 kininogen (HMWK) 
                 XI, and prekallikrein 
               
               
                 (Fitzgerald factor) 
               
               
                 fibronectin 
                 Mediates cell adhesion 
                 Glomerulopathy with fibronectin 
               
               
                   
                   
                 deposits 
               
               
                 antithrombin III 
                 Inhibits IIa, Xa, and other proteases 
                 Antithrombin III deficiency 
               
               
                 heparin cofactor II 
                 Inhibits IIa, cofactor for heparin 
                 Heparin cofactor II deficiency 
               
               
                   
                 and dermatan sulfate (“minor 
               
               
                   
                 antithrombin”) 
               
               
                 protein C 
                 Inactivates Va and VIIIa 
                 Protein C deficiency 
               
               
                 protein S 
                 Cofactor for activated protein C 
                 Protein S deficiency 
               
               
                   
                 (APC, inactive when bound to C4b- 
               
               
                   
                 binding protein) 
               
               
                   
                 Mediates thrombin adhesion to 
               
               
                 protein Z 
                 phospholipids and stimulates 
                 Protein Z deficiency 
               
               
                   
                 degradation of factor X by ZPI 
               
               
                 Protein Z-related protease 
                 Degrades factors X (in presence of 
               
               
                 inhibitor (ZPI) 
                 protein Z) and XI (independently) 
               
               
                 plasminogen 
                 Converts to plasmin, lyses fibrin and 
                 Plasminogen deficiency, type I 
               
               
                   
                 other proteins 
                 (ligneous conjunctivitis) 
               
               
                 alpha 2-antiplasmin 
                 Inhibits plasmin 
                 Antiplasmin deficiency 
               
               
                 tissue plasminogen 
                 Activates plasminogen 
                 Familial hyperfibrinolysis and 
               
               
                 activator (tPA) 
                   
                 thrombophilia 
               
               
                 urokinase 
                 Activates plasminogen 
                 Quebec platelet disorder 
               
               
                 plasminogen activator 
                 Inactivates tPA &amp; urokinase 
                 Plasminogen activator inhibitor- 
               
               
                 inhibitor-1 (PAI1) 
                 (endothelial PAI) 
                 1 deficiency 
               
               
                 plasminogen activator 
                 Inactivates tPA &amp; urokinase 
               
               
                 inhibitor-2 (PAI2) 
                 (placental PAI) 
               
               
                 cancer procoagulant 
                 Pathological factor X activator linked 
               
               
                   
                 to thrombosis in cancer 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 16 
               
             
            
               
                   
               
               
                 Exogenous protein levels in erythroid cells 
               
            
           
           
               
               
               
            
               
                   
                 Construct/Enzyme 
                 Copies of enzyme per cell 
               
               
                   
                   
               
               
                   
                 PAL-HA 
                 7.4 × 10 5  ± 2.7 × 10 5   
               
               
                   
                   
                 (3 independent experiments) 
               
               
                   
                 MGL-HA 
                 6.2 × 10 5   
               
               
                   
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 17 
               
             
            
               
                   
               
               
                 Cell size measurements 
               
            
           
           
               
               
               
            
               
                   
                 Mean 
                 Mean 
               
               
                 Cell 
                 diameter (um) 
                 volume (fL) 
               
               
                   
               
            
           
           
               
               
               
            
               
                 Untreated control 
                 5.867 
                 106 
               
               
                 Hypotonically treated 
                 5.768 
                 100 
               
               
                 Hypotonically treated and loaded 
                 5.612 
                 93 
               
               
                 with mIgG-FITC 
               
               
                 Human RBC 
                 5.532 
                 89 
               
               
                 Cultured, untransfected (filtered) 
                 6.583 
                 149 
               
               
                 Cultured, expressing HA-GPA 
                 6.553 
                 147 
               
               
                 (filtered) 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 18 
               
             
            
               
                   
               
               
                 Mean and median Annexin-V binding levels 
               
            
           
           
               
               
               
            
               
                   
                 Mean Annexin-V 
                 Median Annexin-V 
               
               
                 Sample: 
                 binding (in FL4-H) 
                 binding (in FL4-H) 
               
               
                   
               
            
           
           
               
               
               
            
               
                 Untransfected, unfiltered 
                 154,111 
                 63,018 
               
               
                 enucleated cells 
               
               
                 Untransfected, filtered 
                 107,190 
                 60,826 
               
               
                 enucleated cells 
               
               
                 HA-GPA transfected, filtered 
                 76,503 
                 62,212 
               
               
                 enucleated cells 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 19 
               
             
            
               
                   
               
               
                 GFP fluorescence of electroporated Day 4 cells. 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 % GFP+ 
                   
                   
               
               
                   
                 % P1 
                 cells 
                 MFI 
                 % AAD− 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Non-electroporated control 
                 87.3 
                 0.85 
                 2,678 
                 98.6 
               
               
                 Electroporated, condition 
                 79 
                 91.6 
                 121,279 
                 98.6 
               
               
                 A, trial 1 
               
               
                 Electroporated, condintion 
                 80.8 
                 90.6 
                 105,741 
                 98.5 
               
               
                 A, trial 2 
               
               
                 Electroporated, condition 
                 83.5 
                 58.8 
                 25,482 
                 98.4 
               
               
                 B, trial 1 
               
               
                 Electroporated, condition 
                 85.9 
                 19.6 
                 10,709 
                 98.7 
               
               
                 B, trial 2 
               
               
                 Electroporated, condition 
                 87 
                 35 
                 17,086 
                 98.7 
               
               
                 C, trial 1 
               
               
                 Electroporated, condition 
                 86.3 
                 13.1 
                 8,114 
                 98.8 
               
               
                 C, trial 2 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 20 
               
             
            
               
                   
               
               
                 GFP fluorescence of Day 4 cells electroporated 
               
               
                 with chemically modified RNA 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 % GFP+ 
                   
                   
               
               
                   
                 % P1 
                 cells 
                 MFI 
                 % AAD− 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Non-electroporated control 
                 87.3 
                 0.85 
                 2,678 
                 98.6 
               
               
                 Electroporated, condition 
                 87.2 
                 96.6 
                 75,393 
                 98.0 
               
               
                 A, trial 1 
               
               
                 Electroporated, condintion 
                 87.4 
                 96.3 
                 75,853 
                 98.5 
               
               
                 A, trial 2 
               
               
                 Electroporated, condition 
                 88.4 
                 60.8 
                 23,097 
                 98.9 
               
               
                 B, trial 1 
               
               
                 Electroporated, condition 
                 87.6 
                 57.8 
                 21,759 
                 98.7 
               
               
                 B, trial 2 
               
               
                 Electroporated, condition 
                 88.7 
                 61 
                 24,857 
                 98.8 
               
               
                 C, trial 1 
               
               
                 Electroporated, condition 
                 88.4 
                 50.9 
                 20,358 
                 98.5 
               
               
                 C, trial 2 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 21 
               
             
            
               
                   
               
               
                 GFP fluorescence of Day 12 cells electroporated 
               
               
                 with chemically modified RNA 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 % GFP+ 
                   
                   
               
               
                   
                 % P1 
                 cells 
                 MFI 
                 % AAD− 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Non-electroporated control 
                 92.2 
                 0.86 
                 3,754 
                 95 
               
               
                 Electroporated, trial 1 
                 93.7 
                 55.2 
                 22,748 
                 98 
               
               
                 Electroporates, trial 2 
                 90.7 
                 90 
                 107,091 
                 94 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 22 
               
             
            
               
                   
               
               
                 Evaluation of cell viability and proliferation ability 
               
               
                 by trypan blue staining after electroporation 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Day 8 
                 Day 9 
                 Day 9 
                   
               
               
                   
                 Total 
                 Total 
                 Live 
                 Day 9 
               
               
                   
                 cells 
                 Cells 
                 Cells 
                 Cell 
               
               
                   
                 (M) 
                 (M) 
                 (M) 
                 viability 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
            
               
                 Electroporated without 
                 0.21 
                 0.441 
                 0.441 
                 100 
               
               
                 exogenous nucleic acid 
               
               
                 Electroporated with 
                 0.2 
                 0.376 
                 0.37 
                 99 
               
               
                 unmodified GFP mRNA, 1 ug 
               
               
                 Electroporated with 
                 0.2 
                 0.354 
                 0.332 
                 94 
               
               
                 unmodified GFP mRNA, 2 ug 
               
               
                 Electroporated with 
                 0.2 
                 0.414 
                 0.381 
                 92 
               
               
                 modified GFP mRNA, 1 ug