Patent Publication Number: US-2022228115-A1

Title: Nucleic acid molecules encoding an engineered antigen receptor and an inhibitory nucleic acid molecule and methods of use thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. application Ser. No. 16/927,452, filed Jul. 13, 2020, which is a Continuation of U.S. application Ser. No. 16/678,600, filed Nov. 8, 2019, which is a Continuation of PCT/US2018/031674 filed May 8, 2018, which International Application was published by the International Bureau in English on Nov. 15, 2018, and application claims priority from U.S. Provisional Patent Application No. 62/503,060, filed May 8, 2017, and U.S. Provisional Patent Application No. 62/579,460, filed Oct. 31, 2017, which applications are hereby incorporated in their entirety by reference in this application. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates to the field of molecular biology and recombinant nucleic acid technology. In particular, the present disclosure relates to nucleic acid molecules encoding an engineered antigen receptor, such as a chimeric antigen receptor or exogenous T cell receptor, and an inhibitory nucleic acid molecule, such as an RNA interference molecule. The present disclosure further relates to nucleic acids, DNA constructs, viral vectors, pharmaceutical compositions, genetically-modified cells, and methods of treatment that utilize the nucleic acid molecule of the invention. 
     REFERENCE TO A SEQUENCE LISTING SUBMITTED AS A TEXT FILE VIA EFS-WEB 
     The instant application contains a Sequence Listing which has been submitted in ASCII format via EFS-Web and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Jul. 14, 2020, is named P89339_1050US_C1_Seq_List, and is 188513 bytes in size. 
     BACKGROUND OF THE INVENTION 
     T cell adoptive immunotherapy is a promising approach for cancer treatment. This strategy utilizes isolated human T cells that have been genetically-modified to enhance their specificity for a specific tumor associated antigen. Genetic modification may involve the expression of a chimeric antigen receptor (CAR) or an exogenous T cell receptor to graft antigen specificity onto the T cell. By contrast to exogenous T cell receptors, CARs derive their specificity from the variable domains of a monoclonal antibody. Thus, T cells expressing CARs induce tumor immunoreactivity in a major histocompatibility complex (MHC) non-restricted manner. To date, T cell adoptive immunotherapy has been utilized as a clinical therapy for a number of cancers, including B cell malignancies (e.g., acute lymphoblastic leukemia (ALL), B cell non-Hodgkin lymphoma (NHL), and chronic lymphocytic leukemia), multiple myeloma, neuroblastoma, glioblastoma, advanced gliomas, ovarian cancer, mesothelioma, melanoma, and pancreatic cancer. 
     Despite its potential usefulness as a cancer treatment, adoptive immunotherapy has been limited, in part, by alloreactivity between host tissues and allogeneic CAR T cells. One cause of alloreactivity arises from the presence of non-host MHC class I molecules on the cell surface of CAR T cells. MHC class I molecules consist of two polypeptide chains, a and β. In humans, the α chain consists of three subunits, α1, α2, and α3, which are encoded by polymorphic human leukocyte antigen (HLA) genes on chromosome 6. The variability of HLA loci, and the encoded α chain subunits, can cause allogeneic CAR T cells to be seen by the host immune system as foreign cells because they bear foreign MHC class I molecules. As a result, CAR T cells administered to a patient can be subject to host versus graft (HvG) rejection, where they are recognized and killed by the host&#39;s cytotoxic T cells. 
     The β chain of MHC class I molecules consists of beta-2 microglobulin, which is encoded by the non-polymorphic beta-2 microglobulin (B2M) gene on chromosome 15 (SEQ ID NO: 1). Beta-2 microglobulin is non-covalently linked to the a3 subunit and is common to all MHC class I molecules. Furthermore, expression of MHC class I molecules at the cell surface requires its association with beta-2 microglobulin. As such, beta-2 microglobulin represents a logical target for suppressing the expression of MHC class I molecules on CAR T cells, which could render the cells invisible to host cytotoxic T cells and reduce alloreactivity. However, complete knockout of beta-2 microglobulin expression may result in NK cell killing of CAR T cells due to the lack of cell surface MHC class I molecules, which could prompt NK cells to recognize them as non-self and initiate cytotoxic action. 
     Another cause of alloreactivity to CAR T cells is the expression of the endogenous T cell receptor on the cell surface. T cell receptors typically consist of variable α and β chains or, in smaller numbers, variable γ and δ chains. The T cell receptor complexes with accessory proteins, including CD3, and functions with cell surface co-receptors (e.g., CD4 and CD8) to recognize antigens bound to MEW molecules on antigen presenting cells. In the case of allogeneic CAR T cells, expression of endogenous T cell receptors may cause the cell to recognize host MHC antigens following administration to a patient, which can lead to the development of graft-versus-host-disease (GVHD). 
     To forestall alloreactivity, clinical trials have largely focused on the use of autologous CAR T cells, wherein a donor&#39;s T cells are isolated, genetically-modified to incorporate a chimeric antigen receptor, and then re-infused into the same subject. An autologous approach provides immune tolerance to the administered CAR T cells; however, this approach is constrained by both the time and expense necessary to produce patient-specific CART cells after a patient&#39;s cancer has been diagnosed. 
     Thus, a need exists in the art for the development of allogeneic CAR T cells which exhibit reduced allogenicity but, at the same time, avoid NK cell killing in vivo. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention provides a nucleic acid molecule comprising: (a) a first expression cassette comprising a nucleic acid sequence encoding an engineered antigen receptor; (b) a second expression cassette comprising a nucleic acid sequence encoding an inhibitory nucleic acid molecule; (c) a 5′ homology arm; and (d) a 3′ homology arm; wherein the 5′ homology arm and the 3′ homology arm have homology to chromosomal regions flanking a nuclease recognition sequence in a gene of interest. 
     In some embodiments, the inhibitory nucleic acid molecule is an RNA interference molecule. In certain embodiments, the RNA interference molecule is a short hairpin RNA (shRNA), a small interfering RNA (siRNA), a hairpin siRNA, a microRNA (miRNA), a precursor miRNA, or an miRNA-adapted shRNA. In particular embodiments, the RNA interference molecule is an shRNA. 
     In some embodiments the engineered antigen receptor is a chimeric antigen receptor. In other embodiments, the engineered antigen receptor is an exogenous T cell receptor. 
     In some embodiments, the nuclease recognition sequence is an engineered meganuclease recognition sequence, a TALEN recognition sequence, a zinc finger nuclease (ZFN) recognition sequence, a CRISPR/Cas recognition sequence, a compact TALEN recognition sequence, or a megaTAL recognition sequence. In certain embodiments, the nuclease recognition sequence is an engineered meganuclease recognition sequence. 
     In some embodiments, the gene of interest is any gene of interest. In certain embodiments, the gene of interest is a human T cell receptor alpha constant region gene. In particular embodiments the nuclease recognition sequence is an engineered meganuclease recognition sequence. In certain embodiments, the engineered meganuclease recognition sequence comprises SEQ ID NO: 1 in a human T cell receptor alpha constant region gene. 
     In some embodiments, the first expression cassette further comprises a promoter which drives expression of the engineered antigen receptor. In certain embodiments, the promoter is a JeT promoter. 
     In some embodiments, the second expression cassette further comprises a promoter which drives expression of the inhibitory nucleic acid molecule. In certain embodiments, the promoter is a U6 promoter. 
     In some embodiments, the first expression cassette comprises a polyadenylation signal to terminate translation of the engineered antigen receptor. In some embodiments, the second expression cassette comprises a central polypurine tract and central terminator sequence (cPPT/CTS) sequence to terminate translation of the inhibitory nucleic acid. 
     In some embodiments, the first expression cassette and the second expression cassette are in the same orientation in the nucleic acid molecule. In certain embodiments, the first expression cassette and the second expression cassette are in a 5′ to 3′ orientation relative to the 5′ and 3′ homology arms. In some such embodiments, the first expression cassette is 5′ upstream of the second expression cassette. In other such embodiments, the second expression cassette is 5′ upstream of the first expression cassette. 
     In some embodiments, wherein the first expression cassette and the second expression cassette are in the same orientation in the nucleic acid molecule, the first expression cassette and the second expression cassette are in a 3′ to 5′ orientation relative to the 5′ and 3′ homology arms. In some such embodiments, the first expression cassette is 5′ upstream of the second expression cassette. In other such embodiments, the second expression cassette is 5′ upstream of the first expression cassette. 
     In some embodiments, the first expression cassette and the second expression cassette are in opposite orientations in the nucleic acid molecule. In some such embodiments, the first expression cassette is in a 3′ to 5′ orientation and the second expression cassette is in a 5′ to 3′ orientation relative to the 5′ and 3′ homology arms. In certain embodiments, the first expression cassette is 5′ upstream of the second expression cassette. In other embodiments, the second expression cassette is 5′ upstream of the first expression cassette. 
     In particular embodiments, wherein the first expression cassette and the second expression cassette are in opposite orientations in the nucleic acid molecule, the first expression cassette is in a 5′ to 3′ orientation and the second expression cassette is in a 3′ to 5′ orientation relative to the 5′ and 3′ homology arms. In some such embodiments, the first expression cassette is 5′ upstream of the second expression cassette. In other such embodiments, the second expression cassette is 5′ upstream of the first expression cassette. 
     In some embodiments, the nucleic acid molecule comprises multiple copies of the second expression cassette. In some such embodiments, the copies are identical. In further embodiments, the copies include a promoter, a coding sequence for the inhibitory nucleic acid molecule, and a sequence, such as a (cPPT/CTS) sequence, to terminate translation of the inhibitory nucleic acid molecule. In some such embodiments, the copies of the second expression cassette are in tandem in the nucleic acid molecule, and can be in the same orientation, or in opposite orientations. In other such embodiments, the copies may not be in tandem, and can be in the same orientation, or in opposite orientations. 
     In some embodiments, the nucleic acid molecule further comprises a 5′ inverted terminal repeat and a 3′ inverted terminal repeat flanking the first expression cassette and the second expression cassette. 
     In some embodiments, the inhibitory nucleic acid molecule is inhibitory against human beta-2 microglobulin. 
     In some embodiments, the inhibitory nucleic acid molecule is inhibitory against a component of the MHC class I molecule. In certain embodiments, the inhibitory molecule is inhibitory against an MHC class I alpha-1 (α1) domain, alpha-2 (α2) domain, alpha-3 (α3) domain, or against beta-2 microglobulin. 
     In some embodiments, the inhibitory nucleic acid molecule is inhibitory against human CD52. 
     In certain embodiments, the inhibitory nucleic acid molecule is an shRNA inhibitory against beta-2 microglobulin, wherein the shRNA has a sequence comprising any one of SEQ ID NOs: 2-4. In particular embodiments, the shRNA has a sequence comprising SEQ ID NO: 2. In some such embodiments, the first expression cassette and the second expression cassette are in a 3′ to 5′ orientation relative to the 5′ and 3′ homology arms, and wherein the first expression cassette is 5′ upstream of the second expression cassette. In some such embodiments, the first expression cassette comprises: (i) a nucleic acid sequence encoding a chimeric antigen receptor or an exogenous T cell receptor; (ii) a JeT promoter which drives expression of the chimeric antigen receptor or the exogenous T cell receptor; and (iii) a polyA sequence; and the second expression cassette comprises: (iv) a nucleic acid sequence encoding the shRNA; (v) a U6 promoter which drives expression of the shRNA; and (vi) a central polypurine tract and central terminator sequence (cPPT/CTS) sequence. 
     In certain embodiments, the inhibitory nucleic acid molecule is an shRNA inhibitory against beta-2 microglobulin, wherein the shRNA has a sequence comprising any one of SEQ ID NOs: 2-4. In particular embodiments, the shRNA has a sequence comprising SEQ ID NO: 2. In some such embodiments, the first expression cassette is in a 3′ to 5′ orientation and the second expression cassette is in a 5′ to 3′ orientation relative to the 5′ and 3′ homology arms, and the first expression cassette is 5′ upstream of the second expression cassette. In some such embodiments, the first expression cassette comprises: (i) a nucleic acid sequence encoding a chimeric antigen receptor or an exogenous T cell receptor; (ii) a JeT promoter which drives expression of the chimeric antigen receptor or the exogenous T cell receptor; and (iii) a polyA sequence; and the second expression cassette comprises: (iv) a nucleic acid sequence encoding the shRNA; (v) a U6 promoter which drives expression of the shRNA; and (vi) a central polypurine tract and central terminator sequence (cPPT/CTS) sequence. In some such embodiments, the nucleic acid molecule comprises a first copy and a second copy of the second expression cassette, wherein the first copy and the second copy are identical, and wherein the first copy and the second copy are in tandem, and further wherein the first copy and the second copy are in the same orientation. 
     In another aspect, the invention provides a recombinant DNA construct comprising any nucleic acid molecule of the invention described herein. 
     In some embodiments, the recombinant DNA construct encodes a viral vector. In certain embodiments, the viral vector is an adenoviral vector, a lentiviral vector, a retroviral vector, or an adeno-associated viral (AAV) vector. In particular embodiments, the viral vector is a recombinant AAV vector. 
     In another aspect, the invention provides a viral vector comprising any nucleic acid molecule of the invention described herein. In certain embodiments, the viral vector is an adenoviral vector, a lentiviral vector, a retroviral vector, or an adeno-associated viral (AAV) vector. In particular embodiments, the viral vector is a recombinant AAV vector. 
     In another aspect, the invention provides a method for producing a genetically-modified eukaryotic cell, the method comprising introducing into a cell any nucleic acid molecule of the invention described herein and: (a) a nucleic acid encoding an engineered nuclease having specificity for the nuclease recognition sequence, wherein the engineered nuclease is expressed in the cell; or (b) an engineered nuclease protein having specificity for the nuclease recognition sequence; wherein the engineered nuclease recognizes and cleaves the nuclease recognition sequence in the genome of the cell to generate a cleavage site, and wherein the nucleic acid molecule of the invention is inserted into the genome of the cell at the cleavage site. 
     In some embodiments of the method, the genetically-modified eukaryotic cell is a human T cell. 
     In some embodiments of the method, the engineered nuclease is an engineered meganuclease, a TALEN, a zinc finger nuclease (ZFN), a CRISPR/Cas, a compact TALEN, or a megaTAL. In certain embodiments of the method, the engineered nuclease is an engineered meganuclease. 
     In some embodiments of the method, the nuclease recognition sequence is in a human T cell receptor alpha constant region gene. 
     In certain embodiments of the method, the nuclease recognition sequence is an engineered meganuclease recognition sequence. In particular embodiments, wherein the engineered meganuclease recognition sequence is within a human T cell receptor alpha constant region, the nuclease recognition sequence comprises SEQ ID NO: 1. 
     In some embodiments of the method, wherein the nuclease recognition sequence is within a human T cell receptor alpha constant region, cell surface expression of an endogenous T cell receptor is reduced compared to a control cell. 
     In some embodiments of the method, the nucleic acid encoding the engineered nuclease is an mRNA. In certain embodiments, the mRNA is a polycistronic mRNA encoding the engineered nuclease and at least one additional polypeptide or nucleic acid molecule. 
     In some embodiments of the method, the nucleic acid molecule of the invention described herein is introduced into the cell using a viral vector. In certain embodiments of the method, the viral vector is an adenoviral vector, a lentiviral vector, a retroviral vector, or an AAV vector. In particular embodiments of the method, the viral vector is a recombinant AAV vector, such as a recombinant AAV vector previously described herein. 
     In some embodiments of the method, the nucleic acid molecule of the invention described herein is introduced into the cell using a recombinant DNA construct. In certain embodiments of the method, the recombinant DNA construct is a recombinant DNA construct previously described herein. 
     In some embodiments of the method, the nucleic acid molecule of the invention described herein is inserted into the genome of the cell at the cleavage site by homologous recombination. 
     In some embodiments of the method, the engineered antigen receptor is a chimeric antigen receptor. In other embodiments of the method, the engineered antigen receptor is an exogenous T cell receptor. 
     In some embodiments of the method, the inhibitory nucleic acid molecule is inhibitory against human beta-2 microglobulin. In certain embodiments of the method, cell surface expression of beta-2 microglobulin is between about 1% and about 50% of cell surface beta-2 microglobulin expression on a control cell. In other embodiments of the method, cell surface expression of beta-2 microglobulin is between about 1% and about 25% of cell surface beta-2 microglobulin expression on a control cell. In other embodiments of the method, cell surface expression of beta-2 microglobulin is between about 1% and about 10% of cell surface beta-2 microglobulin expression on a control cell. In other embodiments of the method, cell surface expression of beta-2 microglobulin is between about 1% and about 5% of cell surface beta-2 microglobulin expression on a control cell. In particular embodiments of the method, a control cell is not genetically-modified to reduce cell surface beta-2 microglobulin expression. 
     In some embodiments of the method, the inhibitory nucleic acid molecule is inhibitory against human beta-2 microglobulin. In certain embodiments of the method, cell surface expression of beta-2 microglobulin is reduced by 10% to 95% compared to cell surface beta-2 microglobulin expression on a control cell. In other embodiments of the method, cell surface expression of beta-2 microglobulin is reduced by 50% to 95% compared to cell surface beta-2 microglobulin expression on a control cell. In other embodiments of the method, cell surface expression of beta-2 microglobulin is reduced by 75% to 95% compared to cell surface beta-2 microglobulin expression on a control cell. In other embodiments of the method, cell surface expression of beta-2 microglobulin is reduced by 90% to 95% compared to cell surface beta-2 microglobulin expression on a control cell. In particular embodiments of the method, a control cell is not genetically-modified to reduce cell surface beta-2 microglobulin expression. 
     In some embodiments of the method, the inhibitory nucleic acid molecule is inhibitory against a component of the MHC class I molecule. In certain embodiments of the method, cell surface expression of MHC class I molecules is between about 1% and about 50% of expression of MHC class I molecules on a control cell. In certain embodiments of the method, cell surface expression of MHC class I molecules is between about 1% and about 25% of expression of MHC class I molecules on a control cell. In certain embodiments of the method, cell surface expression of MHC class I molecules is between about 1% and about 10% of expression of MHC class I molecules on a control cell. In certain embodiments of the method, cell surface expression of MHC class I molecules is between about 1% and about 5% of expression of MHC class I molecules on a control cell. In particular embodiments of the method, a control cell is not genetically-modified to reduce cell surface expression of MHC class I molecules. 
     In some embodiments of the method, the inhibitory nucleic acid molecule is inhibitory against a component of the MHC class I molecule. In certain embodiments of the method, cell surface expression of MHC class I molecules is reduced by 10% to 95% compared to expression of MHC class I molecules on a control cell. In certain embodiments of the method, cell surface expression of MHC class I molecules is reduced by 50% to 95% compared to expression of MHC class I molecules on a control cell. In certain embodiments of the method, cell surface expression of MHC class I molecules is reduced by 75% to 95% compared to expression of MHC class I molecules on a control cell. In certain embodiments of the method, cell surface expression of MHC class I molecules is reduced by 90% to 95% compared to expression of MHC class I molecules on a control cell. In particular embodiments of the method, a control cell is not genetically-modified to reduce cell surface expression of MHC class I molecules. 
     In some embodiments of the method, the inhibitory nucleic acid molecule is inhibitory against human CD52. In certain embodiments of the method, cell surface expression of CD52 is between about 1% and about 50% of cell surface CD52 expression on a control cell. In other embodiments of the method, cell surface expression of CD52 is between about 1% and about 25% of cell surface CD52 expression on a control cell. In other embodiments of the method, cell surface expression of CD52 is between about 1% and about 10% of cell surface CD52 expression on a control cell. In other embodiments of the method, cell surface expression of CD52 is between about 1% and about 5% of cell surface CD52 expression on a control cell. In particular embodiments of the method, a control cell is not genetically-modified to reduce cell surface expression of CD52. 
     In some embodiments of the method, the inhibitory nucleic acid molecule is inhibitory against human CD52. In certain embodiments of the method, cell surface expression of CD52 is reduced by 10% to 95% compared to cell surface CD52 expression on a control cell. In other embodiments of the method, cell surface expression of CD52 is reduced by 50% to 95% compared to cell surface CD52 expression on a control cell. In other embodiments of the method, cell surface expression of CD52 is reduced by 75% to 95% compared to cell surface CD52 expression on a control cell. In other embodiments of the method, cell surface expression of CD52 is reduced by 90% to 95% compared to cell surface CD52 expression on a control cell. In particular embodiments of the method, a control cell is not genetically-modified to reduce cell surface expression of CD52. 
     In another aspect the invention provides a genetically-modified eukaryotic cell made by any of the methods described herein above. 
     In another aspect, the invention provides a genetically-modified eukaryotic cell comprising any nucleic acid molecule of the invention described herein, wherein the engineered antigen receptor and the inhibitory nucleic acid molecule are expressed in the genetically-modified eukaryotic cell. 
     In some embodiments, the genetically-modified eukaryotic cell is a genetically-modified human T cell. 
     In some embodiments, the nucleic acid molecule of the invention is inserted into the genome of the genetically-modified eukaryotic cell at the nuclease recognition sequence. 
     In some embodiments, the gene of interest is a human T cell receptor alpha constant region gene. 
     In some embodiments, the nuclease recognition sequence is an engineered meganuclease recognition sequence, a TALEN recognition sequence, a zinc finger nuclease (ZFN) recognition sequence, a CRISPR/Cas recognition sequence, a compact TALEN recognition sequence, or a megaTAL recognition sequence. In certain embodiments, the nuclease recognition sequence is an engineered meganuclease recognition sequence. 
     In particular embodiments, wherein the nuclease recognition sequence is within a human T cell receptor alpha constant region gene, the nuclease recognition sequence is an engineered meganuclease recognition sequence comprising SEQ ID NO: 1. 
     In some embodiments, cell surface expression of an endogenous T cell receptor is reduced compared to a control cell. 
     In some embodiments, the inhibitory nucleic acid molecule is inhibitory against human beta-2 microglobulin. In certain embodiments, cell surface expression of beta-2 microglobulin is between about 1% and about 50% of cell surface beta-2 microglobulin expression on a control cell. In other embodiments, cell surface expression of beta-2 microglobulin is between about 1% and about 25% of cell surface beta-2 microglobulin expression on a control cell. In other embodiments, cell surface expression of beta-2 microglobulin is between about 1% and about 10% of cell surface beta-2 microglobulin expression on a control cell. In other embodiments, cell surface expression of beta-2 microglobulin is between about 1% and about 5% of cell surface beta-2 microglobulin expression on a control cell. In particular embodiments, a control cell is not genetically-modified to reduce cell surface beta-2 microglobulin expression. 
     In some embodiments, the inhibitory nucleic acid molecule is inhibitory against human beta-2 microglobulin. In certain embodiments, cell surface expression of beta-2 microglobulin is reduced by 10% to 95% compared to cell surface beta-2 microglobulin expression on a control cell. In other embodiments, cell surface expression of beta-2 microglobulin is reduced by 50% to 95% compared to cell surface beta-2 microglobulin expression on a control cell. In other embodiments, cell surface expression of beta-2 microglobulin is reduced by 75% to 95% compared to cell surface beta-2 microglobulin expression on a control cell. In other embodiments, cell surface expression of beta-2 microglobulin is reduced by 90% to 95% compared to cell surface beta-2 microglobulin expression on a control cell. In particular embodiments, a control cell is not genetically-modified to reduce cell surface beta-2 microglobulin expression. 
     In some embodiments, the inhibitory nucleic acid molecule is inhibitory against a component of the MHC class I molecule. In certain embodiments, cell surface expression of MHC class I molecules is between about 1% and about 50% of expression of MHC class I molecules on a control cell. In certain embodiments, cell surface expression of MHC class I molecules is between about 1% and about 25% of expression of MHC class I molecules on a control cell. In certain embodiments, cell surface expression of MHC class I molecules is between about 1% and about 10% of expression of MHC class I molecules on a control cell. In certain embodiments, cell surface expression of MHC class I molecules is between about 1% and about 5% of expression of MHC class I molecules on a control cell. In particular embodiments, a control cell is not genetically-modified to reduce cell surface expression of MHC class I molecules. 
     In some embodiments, the inhibitory nucleic acid molecule is inhibitory against a component of the MHC class I molecule. In certain embodiments, cell surface expression of MHC class I molecules is reduced by 10% to 95% compared to expression of MHC class I molecules on a control cell. In certain embodiments, cell surface expression of MHC class I molecules is reduced by 50% to 95% compared to expression of MHC class I molecules on a control cell. In certain embodiments, cell surface expression of MHC class I molecules is reduced by 75% to 95% compared to expression of MHC class I molecules on a control cell. In certain embodiments, cell surface expression of WIC class I molecules is reduced by 90% to 95% compared to expression of MEW class I molecules on a control cell. In particular embodiments, a control cell is not genetically-modified to reduce cell surface expression of MEW class I molecules. 
     In some embodiments, the inhibitory nucleic acid molecule is inhibitory against human CD52. In certain embodiments, cell surface expression of CD52 is between about 1% and about 50% of cell surface CD52 expression on a control cell. In other embodiments, cell surface expression of CD52 is between about 1% and about 25% of cell surface CD52 expression on a control cell. In other embodiments, cell surface expression of CD52 is between about 1% and about 10% of cell surface CD52 expression on a control cell. In other embodiments, cell surface expression of CD52 is between about 1% and about 5% of cell surface CD52 expression on a control cell. In particular embodiments, a control cell is not genetically-modified to reduce cell surface expression of CD52. 
     In some embodiments, the inhibitory nucleic acid molecule is inhibitory against human CD52. In certain embodiments, cell surface expression of CD52 is reduced by 10% to 95% compared to cell surface CD52 expression on a control cell. In other embodiments, cell surface expression of CD52 is reduced by 50% to 95% compared to cell surface CD52 expression on a control cell. In other embodiments, cell surface expression of CD52 is reduced by 75% to 95% compared to cell surface CD52 expression on a control cell. In other embodiments, cell surface expression of CD52 is reduced by 90% to 95% compared to cell surface CD52 expression on a control cell. In particular embodiments, a control cell is not genetically-modified to reduce cell surface expression of CD52. 
     In another aspect, the invention provides a genetically-modified eukaryotic cell comprising in its genome a nucleic acid sequence encoding an engineered antigen receptor which is expressed by the genetically-modified eukaryotic cell, wherein cell surface expression of beta-2 microglobulin on the genetically-modified eukaryotic cell is reduced by 10% to 95% compared to cell surface beta-2 microglobulin expression on a control cell. In certain embodiments, cell surface expression of beta-2 microglobulin on the genetically-modified eukaryotic cell is reduced between 50% and 95% compared to cell surface beta-2 microglobulin expression on a control cell. In certain embodiments, cell surface expression of beta-2 microglobulin on the genetically-modified eukaryotic cell is reduced between 75% and 95% compared to cell surface beta-2 microglobulin expression on a control cell. In certain embodiments, cell surface expression of beta-2 microglobulin on the genetically-modified eukaryotic cell is reduced between 90% and 95% compared to cell surface beta-2 microglobulin expression on a control cell. In particular embodiments, the control cell is not genetically-modified to reduce cell surface expression of beta-2 microglobulin. 
     In some embodiments, cell surface expression of beta-2 microglobulin is between about 1% and about 50% of cell surface beta-2 microglobulin expression on a control cell. In other embodiments, cell surface expression of beta-2 microglobulin is between about 1% and about 25% of cell surface beta-2 microglobulin expression on a control cell. In other embodiments, cell surface expression of beta-2 microglobulin is between about 1% and about 10% of cell surface beta-2 microglobulin expression on a control cell. In other embodiments, cell surface expression of beta-2 microglobulin is between about 1% and about 5% of cell surface beta-2 microglobulin expression on a control cell. In particular embodiments, a control cell is not genetically-modified to reduce cell surface beta-2 microglobulin expression. 
     In certain embodiments, the genetically-modified eukaryotic cell comprises in its genome a nucleic acid sequence encoding an inhibitory nucleic acid molecule which is inhibitory against beta-2 microglobulin. In particular embodiments, the inhibitory nucleic acid molecule is an RNA interference molecule. In some embodiments, the RNA interference molecule is a short hairpin RNA (shRNA), a small interfering RNA (siRNA), a hairpin siRNA, a microRNA (miRNA), a precursor miRNA, or an miRNA-adapted shRNA. In certain embodiments, the RNA interference molecule is an shRNA. In particular embodiments, the shRNA comprises a sequence of any one of SEQ ID NOs: 2-4. In specific embodiments, the shRNA comprises a sequence of SEQ ID NO: 2. 
     In some embodiments, the nucleic acid sequence encoding the engineered antigen receptor is integrated at the same location within the genome as the nucleic acid sequence encoding the inhibitory nucleic acid molecule. In particular embodiments, the genetically-modified eukaryotic cell comprises in its genome the nucleic acid molecule of the invention. 
     In other embodiments, the nucleic acid sequence encoding the engineered antigen receptor is integrated at a different location within the genome than the nucleic acid sequence encoding the inhibitory nucleic acid molecule. 
     In some embodiments, the genetically-modified eukaryotic cell is less susceptible to endogenous NK cell killing when compared to a control cell, has extended persistence in a subject when compared to a control cell, exhibits enhanced expansion in a subject when compared to a control cell, and/or exhibits reduced allogenicity when compared to a control cell. 
     In some embodiments, the engineered antigen receptor is a chimeric antigen receptor or an exogenous T cell receptor. 
     In some embodiments, the genetically-modified eukaryotic cell is a genetically-modified human T cell. 
     In particular embodiments, the genetically-modified eukaryotic cell is a genetically-modified human T cell, and the engineered antigen receptor is a chimeric antigen receptor or an exogenous T cell receptor. 
     In another aspect, the invention provides a genetically-modified eukaryotic cell comprising in its genome a nucleic acid sequence encoding an engineered antigen receptor which is expressed by the genetically-modified eukaryotic cell, wherein cell surface expression of MHC class I molecules on the genetically-modified eukaryotic cell is reduced by 10% to 95% compared to cell surface expression of MHC class I molecules on a control cell. In certain embodiments, cell surface expression of MHC class I molecules on the genetically-modified eukaryotic cell is reduced by 50% to 95% compared to cell surface expression of MHC class I molecules on a control cell. In certain embodiments, cell surface expression of MHC class I molecules on the genetically-modified eukaryotic cell is reduced by 75% to 95% compared to cell surface expression of MHC class I molecules on a control cell. In certain embodiments, cell surface expression of MHC class I molecules on the genetically-modified eukaryotic cell is reduced by 90% to 95% compared to cell surface expression of MHC class I molecules on a control cell. In particular embodiments, the control cell is not genetically-modified to reduce cell surface expression of a component of the MHC class I molecule. 
     In some embodiments, cell surface expression of MHC class I molecules is between about 1% and about 50% of cell surface MHC class I molecule expression on a control cell. In other embodiments, cell surface expression of MHC class I molecules is between about 1% and about 25% of cell surface MHC class I molecule expression on a control cell. In other embodiments, cell surface expression of MHC class I molecules is between about 1% and about 10% of cell surface MHC class I molecule expression on a control cell. In other embodiments, cell surface expression of MHC class I molecules is between about 1% and about 5% of cell surface MHC class I molecule expression on a control cell. In particular embodiments, a control cell is not genetically-modified to reduce cell surface expression of MHC class I molecules. 
     In certain embodiments, the genetically-modified eukaryotic cell comprises in its genome a nucleic acid sequence encoding an inhibitory nucleic acid molecule which is inhibitory against a component of the MHC class I molecule. In certain embodiments, the inhibitory molecule is inhibitory against an MHC class I alpha-1 (□1) domain, alpha-2 (□2) domain, alpha-3 (□3) domain, or against beta-2 microglobulin. In a particular embodiment, the inhibitory molecule is inhibitory against beta-2 microglobulin. 
     In particular embodiments, the inhibitory nucleic acid molecule is an RNA interference molecule. In some embodiments, the RNA interference molecule is a short hairpin RNA (shRNA), a small interfering RNA (siRNA), a hairpin siRNA, a microRNA (miRNA), a precursor miRNA, or an miRNA-adapted shRNA. In certain embodiments, the RNA interference molecule is an shRNA. 
     In certain embodiments, the inhibitory nucleic acid molecule is an shRNA inhibitory against beta-2 microglobulin, wherein the shRNA has a sequence comprising any one of SEQ ID NOs: 2-4. In particular embodiments, the shRNA has a sequence comprising SEQ ID NO: 2. In some such embodiments, the first expression cassette and the second expression cassette are in a 3′ to 5′ orientation relative to the 5′ and 3′ homology arms, and wherein the first expression cassette is 5′ upstream of the second expression cassette. In some such embodiments, the first expression cassette comprises: (i) a nucleic acid sequence encoding a chimeric antigen receptor or an exogenous T cell receptor; (ii) a JeT promoter which drives expression of the chimeric antigen receptor or the exogenous T cell receptor; and (iii) a polyA sequence; and the second expression cassette comprises: (iv) a nucleic acid sequence encoding the shRNA; (v) a U6 promoter which drives expression of the shRNA; and (vi) a central polypurine tract and central terminator sequence (cPPT/CTS) sequence. 
     In certain embodiments, the inhibitory nucleic acid molecule is an shRNA inhibitory against beta-2 microglobulin, wherein the shRNA has a sequence comprising any one of SEQ ID NOs: 2-4. In particular embodiments, the shRNA has a sequence comprising SEQ ID NO: 2. In some such embodiments, the first expression cassette is in a 3′ to 5′ orientation and the second expression cassette is in a 5′ to 3′ orientation relative to the 5′ and 3′ homology arms, and the first expression cassette is 5′ upstream of the second expression cassette. In some such embodiments, the first expression cassette comprises: (i) a nucleic acid sequence encoding a chimeric antigen receptor or an exogenous T cell receptor; (ii) a JeT promoter which drives expression of the chimeric antigen receptor or the exogenous T cell receptor; and (iii) a polyA sequence; and the second expression cassette comprises: (iv) a nucleic acid sequence encoding the shRNA; (v) a U6 promoter which drives expression of the shRNA; and (vi) a central polypurine tract and central terminator sequence (cPPT/CTS) sequence. In some such embodiments, the nucleic acid molecule comprises a first copy and a second copy of the second expression cassette, wherein the first copy and the second copy are identical, and wherein the first copy and the second copy are in tandem, and further wherein the first copy and the second copy are in the same orientation. 
     In some embodiments, the nucleic acid sequence encoding the engineered antigen receptor is integrated at the same location within the genome as the nucleic acid sequence encoding the inhibitory nucleic acid molecule. In particular embodiments, the genetically-modified eukaryotic cell comprises in its genome the nucleic acid molecule of the invention. 
     In other embodiments, the nucleic acid sequence encoding the engineered antigen receptor is integrated at a different location within the genome than the nucleic acid sequence encoding the inhibitory nucleic acid molecule. 
     In some embodiments, the genetically-modified eukaryotic cell is less susceptible to endogenous NK cell killing when compared to a control cell, has extended persistence in a subject when compared to a control cell, exhibits enhanced expansion in a subject when compared to a control cell, and/or exhibits reduced allogenicity when compared to a control cell. 
     In some embodiments, the engineered antigen receptor is a chimeric antigen receptor or an exogenous T cell receptor. 
     In some embodiments, the genetically-modified eukaryotic cell is a genetically-modified human T cell. 
     In particular embodiments, the genetically-modified eukaryotic cell is a genetically-modified human T cell, and the engineered antigen receptor is a chimeric antigen receptor or an exogenous T cell receptor. 
     In another aspect, the invention provides a pharmaceutical composition comprising a pharmaceutically-acceptable carrier and a therapeutically effective amount of any genetically-modified eukaryotic cell described herein above. 
     In some particular embodiments, the genetically-modified eukaryotic cell of the pharmaceutical composition is a genetically-modified human T cell, the engineered antigen receptor is a chimeric antigen receptor or exogenous T cell receptor, and cell surface expression of beta-2 microglobulin is between about 1% and about 50%, about 1% and about 25%, about 1% and about 10%, or about 1% and about 5% of cell surface beta-2 microglobulin expression on a control cell. 
     In other particular embodiments, the genetically-modified eukaryotic cell of the pharmaceutical composition is a genetically-modified human T cell, the engineered antigen receptor is a chimeric antigen receptor or exogenous T cell receptor, and cell surface expression of beta-2 microglobulin on the genetically-modified human T cell is reduced by 10% to 95%, by 50% to 95%, by 75% to 95%, or by 90% to 95% compared to cell surface expression of beta-2 microglobulin on a control cell. 
     In some particular embodiments, the genetically-modified eukaryotic cell of the pharmaceutical composition is a genetically-modified human T cell, the engineered antigen receptor is a chimeric antigen receptor or exogenous T cell receptor, and cell surface expression of MHC class I molecules is between about 1% and about 50%, about 1% and about 25%, about 1% and about 10%, or about 1% and about 5% of cell surface expression of MHC class I molecules on a control cell. 
     In other particular embodiments, the genetically-modified eukaryotic cell of the pharmaceutical composition is a genetically-modified human T cell, the engineered antigen receptor is a chimeric antigen receptor or exogenous T cell receptor, and cell surface expression of MHC class I molecules on the genetically-modified human T cell is reduced by 10% to 95%, by 50% to 95%, by 75% to 95%, or by 90% to 95% compared to cell surface expression of MHC class I molecules on a control cell. 
     In other particular embodiments, the genetically-modified eukaryotic cell of the pharmaceutical composition is a genetically-modified human T cell, and the engineered antigen receptor is a chimeric antigen receptor, and cell surface expression of CD52 is between about 1% and about 50%, about 1% and about 25%, about 1% and about 10%, or about 1% and about 5% of cell surface CD52 expression on a control cell. 
     In some embodiments, the genetically-modified eukaryotic cell of the pharmaceutical composition is a genetically-modified human T cell, the engineered antigen receptor is a chimeric antigen receptor or exogenous T cell receptor, and cell surface expression of CD52 on the genetically-modified human T cell is reduced by 10% to 95%, by 50% to 95%, by 75% to 95%, or by 90% to 95% compared to cell surface expression of CD52 on a control cell. 
     In certain embodiments, the pharmaceutical composition of the invention is for immunotherapy in the treatment of cancer in a subject in need thereof. 
     In another aspect, the invention provides a population of genetically-modified eukaryotic cells comprising a plurality of any genetically-modified eukaryotic cell described herein. 
     In some embodiments, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or up to 100%, of cells in the population are a genetically-modified eukaryotic cell as described herein. 
     In particular embodiments, the genetically-modified eukaryotic cells of the population are genetically-modified human T cells, or cells derived therefrom, or genetically-modified NK cells, or cells derived therefrom. 
     In certain embodiments, the genetically-modified eukaryotic cells of the population comprise a cell surface chimeric antigen receptor or exogenous T cell receptor. In some of these embodiments, the chimeric antigen receptor or exogenous T cell receptor comprises an extracellular ligand-binding domain having specificity for a tumor-specific antigen. 
     In some embodiments, the genetically-modified eukaryotic cells of the population have no cell surface expression of an endogenous T cell receptor when compared to an unmodified control cell. In some embodiments, the genetically-modified eukaryotic cells of the population have reduced cell surface expression of beta-2 microglobulin, MEW class I molecules, or CD52. 
     In another aspect, the invention provides a method of using immunotherapy to treat a disease in a subject in need thereof, the method comprising administering to the subject a genetically-modified eukaryotic cell described herein; wherein the genetically-modified eukaryotic cell is a genetically-modified human T cell expressing a chimeric antigen receptor or an exogenous T cell receptor; and wherein cell surface expression of beta-2 microglobulin on the genetically-modified human T cell is between about 1% and about 50%, about 1% and about 25%, about 1% and about 10%, or about 1% and about 5% of cell surface beta-2 microglobulin expression on a control cell. 
     In some embodiments of the method, cell surface expression of beta-2 microglobulin on the genetically-modified human T cell is reduced by 10% to 95%, by 50% to 95%, by 75% to 95%, or by 90% to 95% compared to cell surface beta-2 microglobulin expression on a control cell. 
     In some embodiments of the method, endogenous NK cell killing of the genetically-modified human T cell is reduced in the subject when compared to a genetically-modified human T cell having no cell surface beta-2 microglobulin expression. 
     In some embodiments of the method, the subject is administered any pharmaceutical composition described herein in which cell surface beta-2 microglobulin expression is reduced on the genetically-modified human T cell when compared to a control cell. 
     In some embodiments of the method, the genetically-modified human T cell is allogeneic to the subject. 
     In some embodiments of the method, persistence of the genetically-modified human T cell is extended in the subject when compared to a genetically-modified human T cell having no cell surface beta-2 microglobulin expression, or when compared to a genetically-modified human T cell having a wild-type level of cell surface expression of beta-2 microglobulin. 
     In some embodiments of the method, expansion of the genetically-modified human T cell is enhanced in the subject when compared to a genetically-modified human T cell having no cell surface beta-2 microglobulin expression, or when compared to a genetically-modified human T cell having a wild-type level of cell surface expression of beta-2 microglobulin. 
     In some embodiments of the method, allogenicity of the genetically-modified human T cell is reduced when compared to a genetically-modified human T cell having a wild-type level of cell surface expression of beta-2 microglobulin. 
     In some embodiments of the method, the disease is cancer. 
     In some embodiments of the method, the cancer is selected from the group consisting of a cancer of carcinoma, lymphoma, sarcoma, blastomas, and leukemia. In certain embodiments of the method, the cancer is selected from the group consisting of a cancer of B-cell origin, breast cancer, gastric cancer, neuroblastoma, osteosarcoma, lung cancer, melanoma, prostate cancer, colon cancer, renal cell carcinoma, ovarian cancer, rhabdomyo sarcoma, leukemia, and Hodgkin&#39;s lymphoma. In particular embodiments of the method, the cancer of B-cell origin is selected from the group consisting of B-lineage acute lymphoblastic leukemia, B-cell chronic lymphocytic leukemia, and B-cell non-Hodgkin&#39;s lymphoma. 
     In another aspect, the invention provides a method of using immunotherapy to treat a disease in a subject in need thereof, the method comprising administering to the subject a genetically-modified eukaryotic cell described herein; wherein the genetically-modified eukaryotic cell is a genetically-modified human T cell expressing a chimeric antigen receptor or an exogenous T cell receptor; and wherein cell surface expression of MHC class I molecules on the genetically-modified human T cell is between about 1% and about 50%, about 1% and about 25%, about 1% and about 10%, or about 1% and about 5% of cell surface expression of MHC class I molecules on a control cell. 
     In some embodiments of the method, cell surface expression of MHC class I molecules on the genetically-modified human T cell is reduced by 10% to 95%, by 50% to 95%, by 75% to 95%, or by 90% to 95% compared to cell surface expression of MHC class I molecules on a control cell. 
     In some embodiments of the method, endogenous NK cell killing of the genetically-modified human T cell is reduced in the subject when compared to a genetically-modified human T cell having no cell surface expression of MHC class I molecules. 
     In some embodiments of the method, the subject is administered any pharmaceutical composition described herein in which cell surface expression of MHC class I molecules is reduced on the genetically-modified human T cell when compared to a control cell. 
     In some embodiments of the method, the genetically-modified human T cell is allogeneic to the subject. 
     In some embodiments of the method, persistence of the genetically-modified human T cell is extended in the subject when compared to a genetically-modified human T cell having no cell surface MHC class I molecule expression, or when compared to a genetically-modified human T cell having a wild-type level of cell surface expression of MHC class I molecules. 
     In some embodiments of the method, expansion of the genetically-modified human T cell is enhanced in the subject when compared to a genetically-modified human T cell having no cell surface MHC class I molecule expression, or when compared to a genetically-modified human T cell having a wild-type level of cell surface expression of MHC class I molecules. 
     In some embodiments of the method, allogenicity of the genetically-modified human T cell is reduced when compared to a genetically-modified human T cell having a wild-type level of cell surface expression of MHC class I molecules. 
     In some embodiments of the method, the disease is cancer. 
     In some embodiments of the method, the cancer is selected from the group consisting of a cancer of carcinoma, lymphoma, sarcoma, blastomas, and leukemia. In certain embodiments of the method, the cancer is selected from the group consisting of a cancer of B-cell origin, breast cancer, gastric cancer, neuroblastoma, osteosarcoma, lung cancer, melanoma, prostate cancer, colon cancer, renal cell carcinoma, ovarian cancer, rhabdomyo sarcoma, leukemia, and Hodgkin&#39;s lymphoma. In particular embodiments of the method, the cancer of B-cell origin is selected from the group consisting of B-lineage acute lymphoblastic leukemia, B-cell chronic lymphocytic leukemia, and B-cell non-Hodgkin&#39;s lymphoma. 
     In another aspect, the invention provides a method of using immunotherapy to treat cancer in a subject in need thereof, the method comprising administering to the subject a genetically-modified eukaryotic cell described herein; wherein the genetically-modified eukaryotic cell is a genetically-modified human T cell expressing a chimeric antigen receptor or an exogenous T cell receptor; and wherein cell surface expression of CD52 on the genetically-modified human T cell is between 1% and 50%, 1% and 25%, 1% and 10%, or 1% and 5% of cell surface CD52 expression on a control cell. 
     In some embodiments of the method, cell surface expression of CD52 on the genetically-modified human T cell is reduced by 10% to 95%, by 50% to 95%, by 75% to 95%, or by 90% to 95% compared to cell surface expression of CD52 on a control cell. 
     In some embodiments of the method, the subject is administered a pharmaceutical composition described herein in which cell surface expression of CD52 is reduced on the genetically-modified human T cell when compared to a control cell. 
     In some embodiments of the method, the genetically-modified human T cell is allogeneic to the subject. 
     In some embodiments of the method, the cancer is selected from the group consisting of a cancer of carcinoma, lymphoma, sarcoma, blastomas, and leukemia. In certain embodiments of the method, the cancer is selected from the group consisting of a cancer of B-cell origin, breast cancer, gastric cancer, neuroblastoma, osteosarcoma, lung cancer, melanoma, prostate cancer, colon cancer, renal cell carcinoma, ovarian cancer, rhabdomyo sarcoma, leukemia, and Hodgkin&#39;s lymphoma. In particular embodiments of the method, the cancer of B-cell origin is selected from the group consisting of B-lineage acute lymphoblastic leukemia, B-cell chronic lymphocytic leukemia, and B-cell non-Hodgkin&#39;s lymphoma. 
     In another aspect, the invention provides a method for preparing an enriched population of genetically-modified eukaryotic cells comprising an engineered antigen receptor, the method comprising preparing a population of cells comprising a genetically-modified eukaryotic cell described herein and cells expressing a wild-type level of cell surface CD52, wherein cell surface expression of CD52 on the genetically-modified eukaryotic cell is between about 1% and about 50%, about 1% and about 25%, about 1% and about 10%, or about 1% and about 5% when compared to a control cell, the method comprising: (a) contacting the population of cells with beads conjugated to an anti-CD52 binding molecule, wherein cells expressing a wild-type level of cell surface CD52 are bound to the beads and the genetically-modified eukaryotic cell is not bound to the beads; and (b) removing the beads from the population of cells to produce the enriched population of cells; wherein the enriched population of cells is enriched for the genetically-modified eukaryotic cell. 
     In some embodiments of the method, cell surface expression of CD52 on the genetically-modified eukaryotic cell is reduced by 10% to 95%, by 50% to 95%, by 75% to 95%, or by 90% to 95% when compared to a control cell. 
     In some embodiments of the method, the beads are magnetic beads. In certain embodiments of the method, the magnetic beads are removed from the population of cells by magnetic separation. 
     In some embodiments of the method, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, or up to 100% of cells in the enriched population are the genetically-modified eukaryotic cell. 
     In some embodiments of the method, the genetically-modified eukaryotic cell expresses a chimeric antigen receptor. In other embodiments of the method, the genetically-modified eukaryotic cell expresses an exogenous T cell receptor. 
     In some embodiments of the method, the genetically-modified eukaryotic cell is a genetically-modified human T cell, such as any genetically-modified T cell described herein. 
     In another aspect, the present disclosure provides a genetically-modified eukaryotic cell described herein for use as a medicament. The present disclosure further provides the use of a genetically-modified eukaryotic cell described herein in the manufacture of a medicament for treating a disease in a subject in need thereof. In one such embodiment, the medicament is useful in the treatment of cancer. 
     The foregoing and other aspects and embodiments of the present invention can be more fully understood by reference to the following detailed description and claims. Certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. All combinations of the embodiments are specifically embraced by the present invention and are disclosed herein just as if each and every combination was individually and explicitly disclosed. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. All sub-combinations of features listed in the embodiments are also specifically embraced by the present invention and are disclosed herein just as if each and every such sub-combination was individually and explicitly disclosed herein. Embodiments of each aspect of the present invention disclosed herein apply to each other aspect of the invention mutatis mutandis. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  shows diagrams of various embodiments of the nucleic acid molecule of the invention. The JeT promoter is shown as an example of a promoter driving expression of the engineered antigen receptor. A U6 promoter is shown as an example of a promoter driving expression of the inhibitory nucleic acid molecule. A chimeric antigen receptor (CAR) is shown as an example of an engineered antigen receptor. An shRNA is shown as an example of an inhibitory nucleic acid molecule. A poly-A sequence is shown as an example of a sequence which terminates translation of the engineered antigen receptor. A cPPT/CTS sequence is shown as an example of a sequence which terminates translation of the inhibitory nucleic acid molecule. 5′ and 3′ homology arms are shown flanking the first expression cassette and second expression cassette of each construct. Optional 5′ and 3′ inverted terminal repeats are further shown in each construct. Constructs above the dashed line have first and second expression cassettes in the same orientation, whereas constructs below the dashed line have first and second expression cassettes in opposite orientations. 
         FIG. 2A-2L  shows flow plots which represent NK cell killing of primary human T cells. The indicated ratios represent the ratio of NK cells to T cells (E:T) in each experiment.  FIG. 2A  shows NK cell killing of B2M+ T cells using a 2:1 ratio.  FIG. 2B  shows NK cell killing of B2M+ T cells using a 1:1 ratio.  FIG. 2C  shows NK cell killing of B2M− T cells using a 0.5:1 ratio.  FIG. 2D  shows NK cell killing of B2M− T cells using a 0:1 ratio.  FIG. 2E  shows NK cell killing of B2M- T cells using a 2:1 ratio.  FIG. 2F  shows NK cell killing of B2M- T cells using a 1:1 ratio.  FIG. 2G  shows NK cell killing of B2M+ T cells using a 0.5:1 ratio.  FIG. 2H  shows NK cell killing of B2M− T cells using a 0:1 ratio.  FIG. 2I  shows NK cell killing of Daudi Class I-negative cells using a 2:1 ratio.  FIG. 2J  shows NK cell killing of Daudi Class I-negative cells using a 1:1 ratio.  FIG. 2K  shows NK cell killing of Daudi Class I-negative cells using a 0.5:1 ratio.  FIG. 2L  shows NK cell killing of Daudi Class I-negative cells using a 0:1 ratio. 
         FIG. 3  shows a chart summarizing NK cell killing of B2M+ and B2M− cells at different ratios. 
         FIG. 4  shows percentage knockdown of human B2M in primary human T cells by three candidate B2M shRNAs. 
         FIGS. 5A-5D  show flow diagrams representing NK cell lysis or allogeneic cell lysis of K562 cells or mock-treated primary human T cells.  FIG. 5A  shows NK cell lysis of K562 cells.  FIG. 5B  shows allogeneic cell lysis of K562 cells.  FIG. 5C  shows NK cell lysis of mock-treated primary human T cells.  FIG. 5D  shows allogeneic cell lysis of mock-treated primary human T cells. 
         FIGS. 6A-6D  show flow diagrams representing NK cell lysis or allogeneic cell lysis of primary human T cells treated with B2M shRNAs.  FIG. 6A  shows NK cell lysis of primary human T cells treated with shRNA254.  FIG. 6B  shows allogeneic cell lysis of primary human T cells treated with shRNA254.  FIG. 6C  shows NK cell lysis of primary human T cells treated with shRNA472.  FIG. 6D  shows allogeneic cell lysis of primary human T cells treated with shRNA472. 
         FIGS. 7A-7F  show diagrams of various nucleic acid molecule constructs encoding a chimeric antigen receptor and an shRNA against beta-2 microglobulin.  FIG. 7A  shows construct 7007 (SEQ ID NO: 18).  FIG. 7B  shows construct 7217 (SEQ ID NO: 19).  FIG. 7C  shows construct 7008 (SEQ ID NO: 20).  FIG. 7D  shows construct 7218 (SEQ ID NO: 21).  FIG. 7E  shows construct 7009 (SEQ ID NO: 22).  FIG. 7F  shows construct 7219 (SEQ ID NO: 23). 
         FIG. 8  shows percentage knockdown of human CD52 in primary human T cells by three different candidate CD52 shRNAs. 
         FIG. 9  A-C show knockdown of CD52 using shRNA and magnetic enrichment of the knockdown population of primary human T cells by CD52 magnetic depletion.  FIG. 9A  shows T cells that were mock transduced.  FIG. 9B  shows T cells transduced with an shRNA-568 lentivirus.  FIG. 9C  shows lentivirus-shRNA568 transduced cells that have undergone a CD52 magnetic depletion. 
         FIGS. 10A-10H  shows diagrams of nucleic acid molecule constructs encoding a chimeric antigen receptor and an shRNA against CD52.  FIG. 10A  shows construct 7005 (SEQ ID NO: 10) which encodes a CAR only.  FIG. 10B  shows construct 7002 (SEQ ID NO: 11) which encodes a CAR only.  FIG. 10C  shows construct 7004 (SEQ ID NO: 12).  FIG. 10D  shows construct 7204 (SEQ ID NO: 13).  FIG. 10E  shows construct 7013 (SEQ ID NO: 14).  FIG. 10F  shows construct 7213 (SEQ ID NO: 15).  FIG. 10G  shows construct 7014 (SEQ ID NO: 16).  FIG. 10H  shows construct 7214 (SEQ ID NO: 17). 
         FIG. 11A-11D  shows CD52 knockdown profiles using CAR/CD52 shRNA constructs with different orientations.  FIG. 11A  shows CD52 expression when a CAR is expressed in the absence of a CD52 shRNA.  FIG. 11B  shows CD52 expression when using the 7013 construct.  FIG. 11C  shows CD52 expression when using the 7004 construct.  FIG. 11D  shows CD52 expression when using the 7014 construct. 
         FIG. 12A-12C  shows B2M knockdown on CAR T cells using CAR/B2M shRNA constructs having one or multiple shRNA cassettes.  FIG. 12A  shows B2M expression in CAR T cells expressing no B2M shRNA (7002—shaded curve) or a single B2M shRNA cassette (7008—open curve).  FIG. 12B  shows B2M expression in CAR T cells expressing no B2M shRNA (7002—shaded) or two B2M shRNA cassettes (7029-open).  FIG. 12C  shows B2M expression in CAR-/CD3+(i.e. non-edited) populations from cultures electroporated with 7002, 7008, or 7029. 
         FIG. 13A-13C  shows cell surface expression of beta-2 microglobulin on T cells transfected with linearized DNA to express a control CAR-negative construct (7002), CAR constructs expressing a single shRNA472 copy in a 3′ to 5′ head-to-tail configuration with the CAR (7056), or in a 3′ to 5′/5′ to 3′ tail-to-tail configuration with the CAR (7059), or a CAR construct expressing two shRNA cassette copies in a 3′ to 5′/5′ to 3′ tail-to-tail configuration with the CAR (7060).  FIG. 13A  shows CAR T cells expressing the 7002 and 7056 constructs.  FIG. 13B  shows CAR T cells expressing the 7002 and 7059 constructs.  FIG. 13C  shows CAR T cells expressing the 7002 and 7060 constructs. 
         FIG. 14  A-D shows beta-2 microglobulin expression or HLA-A, B, and C expression (i.e., MHC class I molecule expression) on T cells transduced with an AAV comprising construct 7056 which expresses a single copy of the shRNA472 in a 3′ to 5′ head-to-tail configuration with the CAR.  FIG. 14A  shows the B2M surface levels in CD3−/CAR+ cells compared to meganuclease-edited cells expressing no shRNA from a control culture.  FIG. 14B  shows B2M levels on CD3−/CAR+ versus CD3+/CAR− populations in the same culture.  FIG. 14C  shows HLA-ABC (i.e., MHC class I molecule) surface levels in CD3−/CAR+ cells compared to meganuclease-edited cells expressing no shRNA from a control culture.  FIG. 14D  shows HLA-ABC levels on CD3−/CAR+ versus CD3+/CAR− populations in the same culture. 
       BRIEF DESCRIPTION OF THE SEQUENCES 
       SEQ ID NO: 1 sets forth the nucleic acid sequence of the TRC 1-2 recognition sequence. 
       SEQ ID NO: 2 sets forth the nucleic acid sequence of the anti-beta-2 microglobulin shRNA472. 
       SEQ ID NO: 3 sets forth the nucleic acid sequence of the anti-beta-2 microglobulin shRNA256. 
       SEQ ID NO: 4 sets forth the nucleic acid sequence of the anti-beta-2 microglobulin shRNA254. 
       SEQ ID NO: 5 sets forth the nucleic acid sequence of the anti-CD52 shRNA572. 
       SEQ ID NO: 6 sets forth the nucleic acid sequence of the anti-CD52 shRNA876. 
       SEQ ID NO: 7 sets forth the nucleic acid sequence of the anti-CD52 shRNA568. 
       SEQ ID NO: 8 sets forth the nucleic acid sequence of the anti-CD52 shRNA569. 
       SEQ ID NO: 9 sets forth the nucleic acid sequence of the anti-CD52 shRNA571. 
       SEQ ID NO: 10 sets forth the nucleic acid sequence of the CAR 7005 construct. 
       SEQ ID NO: 11 sets forth the nucleic acid sequence of the CAR 7002 construct. 
       SEQ ID NO: 12 sets forth the nucleic acid sequence of the CAR 7004 construct. 
       SEQ ID NO: 13 sets forth the nucleic acid sequence of the CAR 7204 construct. 
       SEQ ID NO: 14 sets forth the nucleic acid sequence of the CAR 7013 construct. 
       SEQ ID NO: 15 sets forth the nucleic acid sequence of the CAR 7213 construct. 
       SEQ ID NO: 16 sets forth the nucleic acid sequence of the CAR 7014 construct. 
       SEQ ID NO: 17 sets forth the nucleic acid sequence of the CAR 7214 construct. 
       SEQ ID NO: 18 sets forth the nucleic acid sequence of the CAR 7007 construct. 
       SEQ ID NO: 19 sets forth the nucleic acid sequence of the CAR 7217 construct. 
       SEQ ID NO: 20 sets forth the nucleic acid sequence of the CAR 7008 construct. 
       SEQ ID NO: 21 sets forth the nucleic acid sequence of the CAR 7218 construct. 
       SEQ ID NO: 22 sets forth the nucleic acid sequence of the CAR 7009 construct. 
       SEQ ID NO: 23 sets forth the nucleic acid sequence of the CAR 7219 construct. 
       SEQ ID NO: 24 sets forth the nucleic acid sequence of the CAR 7029 construct. 
       SEQ ID NO: 25 sets forth the nucleic acid sequence of the CAR 7056 construct. 
       SEQ ID NO: 26 sets forth the nucleic acid sequence of the CAR 7059 construct. 
       SEQ ID NO: 27 sets forth the nucleic acid sequence of the CAR 7060 construct. 
       SEQ ID NO: 28 sets forth the nucleic acid sequence of the cPPT/CTS sequence. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     1.1 References and Definitions 
     The patent and scientific literature referred to herein establishes knowledge that is available to those of skill in the art. The issued US patents, allowed applications, published foreign applications, and references, including GenBank database sequences, which are cited herein are hereby incorporated by reference to the same extent as if each was specifically and individually indicated to be incorporated by reference. 
     The present disclosure can be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art. For example, features illustrated with respect to one embodiment can be incorporated into other embodiments, and features illustrated with respect to a particular embodiment can be deleted from that embodiment. In addition, numerous variations and additions to the embodiments suggested herein will be apparent to those skilled in the art in light of the instant disclosure, which do not depart from the present disclosure. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. The terminology used in the description of the present disclosure herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. 
     All publications, patent applications, patents, and other references mentioned herein are incorporated by reference herein in their entirety. 
     As used herein, “a,” “an,” or “the” can mean one or more than one. For example, “a” cell can mean a single cell or a multiplicity of cells. 
     As used herein, unless specifically indicated otherwise, the word “or” is used in the inclusive sense of “and/or” and not the exclusive sense of “either/or.” 
     The terms “expression cassette,” “recombinant DNA construct,” “recombinant construct,” “expression construct,” “chimeric construct,” “construct,” and “recombinant DNA fragment” are used interchangeably herein and are nucleic acid fragments. A recombinant construct comprises an artificial combination of nucleic acid fragments, including, without limitation, regulatory and coding sequences that are not found together in nature. For example, a recombinant DNA construct may comprise regulatory sequences and coding sequences that are derived from different sources, or regulatory sequences and coding sequences derived from the same source and arranged in a manner different than that found in nature. Such a construct may be used by itself or may be used in conjunction with a vector. 
     As used herein, a “vector” or “recombinant DNA vector” may be a construct that includes a replication system and sequences that are capable of transcription and translation of a polypeptide-encoding sequence in a given host cell. If a vector is used then the choice of vector is dependent upon the method that will be used to transform host cells as is well known to those skilled in the art. Vectors can include, without limitation, plasmid vectors and recombinant lentiviral or recombinant AAV vectors, or any other vector known in that art suitable for delivering a gene encoding a co-stimulatory domain of the present disclosure to a target cell. The skilled artisan is well aware of the genetic elements that must be present on the vector in order to successfully transform, select and propagate host cells comprising any of the isolated nucleotides or nucleic acid sequences of the present disclosure. 
     As used herein, a “vector” can also refer to a viral vector. Viral vectors can include, without limitation, retroviral vectors, lentiviral vectors, adenoviral vectors, and adeno-associated viral vectors (AAV). 
     As used herein, the term “operably linked” is intended to mean a functional linkage between two or more elements. For example, an operable linkage between a nucleic acid sequence encoding a nuclease as disclosed herein and a regulatory sequence (e.g., a promoter) is a functional link that allows for expression of the nucleic acid sequence encoding the nuclease. Operably linked elements may be contiguous or non-contiguous. When used to refer to the joining of two protein coding regions, by operably linked is intended that the coding regions are in the same reading frame. 
     As used herein, the term “RNA interference” or “RNAi” refers to a phenomenon in which the introduction of double-stranded RNA (dsRNA) into a diverse range of organisms and cell types causes degradation of the complementary mRNA. In the cell, long dsRNAs are cleaved into short 21-25 nucleotide small interfering RNAs, or siRNAs, by a ribonuclease known as Dicer. The siRNAs subsequently assemble with protein components into an RNA-induced silencing complex (RISC), unwinding in the process. Activated RISC then binds to complementary transcript by base pairing interactions between the siRNA antisense strand and the mRNA. The bound mRNA is cleaved and sequence specific degradation of mRNA results in gene silencing. See, for example, U.S. Pat. No. 6,506,559. 
     The term “siRNA” as used herein refers to small interfering RNA, also known as short interfering RNA or silencing RNA. siRNAs can be, for example, 18 to 30, 20 to 25, 21 to 23 or 21 nucleotide-long double-stranded RNA molecules. An “shRNA” as used herein is a short hairpin RNA, which is a sequence of RNA that makes a tight hairpin turn that can also be used to silence gene expression via RNA interference. shRNA can by operably linked to the U6 promoter expression. The shRNA hairpin structure is cleaved by the cellular machinery into siRNA. shRNA disclosed herein can comprise a sequence complementary to at least 13 nucleotides, at least 14 nucleotides, at least 15 nucleotides, at least 16 nucleotides, at least 17 nucleotides, at least 18 nucleotides, at least 19 nucleotides, at least 20 nucleotides, at least 21 nucleotides, at least 22 nucleotides, or 23 nucleotides of the mRNA a target protein. 
     As used herein, an “engineered antigen receptor” refers to an exogenous receptor introduced into a cell, such as a chimeric antigen receptor or exogenous T cell receptor, which induces an activating signal in the cell upon stimulation/binding to a ligand or antigen (e.g., a tumor-specific antigen). 
     As used herein, a “chimeric antigen receptor” or “CAR” refers to an engineered receptor that grafts specificity for an antigen or other ligand or molecule onto an immune effector cell (e.g., a T cell or NK cell). A chimeric antigen receptor typically comprises at least an extracellular ligand-binding domain or moiety and an intracellular domain that comprises one or more signaling domains and/or co-stimulatory domains. 
     In some embodiments, the extracellular ligand-binding domain or moiety is in the form of a single-chain variable fragment (scFv) derived from a monoclonal antibody, which provides specificity for a particular epitope or antigen (e.g., an epitope or antigen preferentially present on the surface of a cell, such as a cancer cell or other disease-causing cell or particle). In some embodiments, the scFv is attached via a linker sequence. In some embodiments, the extracellular ligand-binding domain is specific for any antigen or epitope of interest. In some embodiments, the scFv is humanized. In some embodiments, the extracellular domain of a chimeric antigen receptor comprises an autoantigen (see, Payne et al. (2016)  Science, Vol.  353 (6295): 179-184), which is recognized by autoantigen-specific B cell receptors on B lymphocytes, thus directing T cells to specifically target and kill autoreactive B lymphocytes in antibody-mediated autoimmune diseases. Such CARs can be referred to as chimeric autoantibody receptors (CAARs), and the incorporation of one or more co-stimulatory domains described herein into such CAARs is encompassed by the present disclosure. 
     The extracellular domain of a chimeric antigen receptor can also comprise a naturally-occurring ligand for an antigen of interest, or a fragment of a naturally-occurring ligand which retains the ability to bind the antigen of interest. 
     Intracellular signaling domains are cytoplasmic domains which transmit an activation signal to the cell following binding of the extracellular domain. An intracellular signaling domain can be any intracellular signaling domain of interest that is known in the art. Such cytoplasmic signaling domains can include, without limitation, CD3 ξ. 
     In some embodiments, the intracellular domain also includes one or more intracellular co-stimulatory domains, such as those described herein, which transmit a co-stimulatory signal which promotes cell proliferation, cell survival, and/or cytokine secretion after binding of the extracellular domain. As used herein, a “co-stimulatory domain” refers to a polypeptide domain which transmits an intracellular proliferative and/or cell-survival signal upon activation. Activation of a co-stimulatory domain may occur following homodimerization of two co-stimulatory domain polypeptides. Activation may also occur, for example, following activation of a construct comprising the co-stimulatory domain (e.g., a chimeric antigen receptor or an inducible regulatory construct). Generally, a co-stimulatory domain can be derived from a transmembrane co-stimulatory receptor, particularly from an intracellular portion of a co-stimulatory receptor. Such intracellular co-stimulatory domains can be any of those known in the art and can include, without limitation, CD27, CD28, CD8, 4-1BB (CD137), OX40, CD30, CD40, PD-1, ICOS, lymphocyte function-associated antigen-1 (LFA-1), CD2, CD7, LIGHT, NKG2C, B7-H3 and a ligand that specifically binds with CD83, N1, N6, or any combination thereof. 
     As used herein, a “co-stimulatory signal” refers to an intracellular signal induced by a co-stimulatory domain that promotes cell proliferation, expansion of a cell population in vitro and/or in vivo, promotes cell survival, modulates (e.g., upregulates or downregulates) the secretion of cytokines, and/or modulates the production and/or secretion of other immunomodulatory molecules. In some embodiments, a co-stimulatory signal is induced following homodimerization of two co-stimulatory domain polypeptides. In some embodiments, a co-stimulatory signal is induced following activation of a construct comprising the co-stimulatory domain (e.g., a chimeric antigen receptor or an inducible regulatory construct). 
     A chimeric antigen receptor can further include additional structural elements, including a transmembrane domain that is attached to the extracellular ligand-binding domain via a hinge or spacer sequence. The transmembrane domain can be derived from any membrane-bound or transmembrane protein. For example, the transmembrane polypeptide can be a subunit of the T-cell receptor (i.e., an α, β, γ or ξ, polypeptide constituting CD3 complex), IL2 receptor p55 (a chain), p75 (β chain) or y chain, subunit chain of Fc receptors (e.g., Fcy receptor III) or CD proteins such as the CD8 alpha chain. Alternatively the transmembrane domain can be synthetic and can comprise predominantly hydrophobic residues such as leucine and valine. 
     The hinge region refers to any oligo- or polypeptide that functions to link the transmembrane domain to the extracellular ligand-binding domain. For example, a hinge region may comprise up to 300 amino acids, preferably 10 to 100 amino acids and most preferably 25 to 50 amino acids. Hinge regions may be derived from all or part of naturally occurring molecules, such as from all or part of the extracellular region of CD8, CD4 or CD28, or from all or part of an antibody constant region. Alternatively, the hinge region may be a synthetic sequence that corresponds to a naturally occurring hinge sequence, or may be an entirely synthetic hinge sequence. In particular examples, a hinge domain can comprise a part of a human CD8 alpha chain, FcyRIIIa receptor or IgGl. 
     As used herein, the term “activation” refers to the state of a cell (e.g., a T cell) that has been sufficiently stimulated to induce detectable effector function. In some embodiments, activation is associated with induced cytokine production and/or induced cell proliferation and expansion. 
     As used herein, an “exogenous T cell receptor” or “exogenous TCR” refers to a TCR whose sequence is introduced into the genome of an immune effector cell (e.g., a human T cell) that may or may not endogenously express the TCR. Expression of an exogenous TCR on an immune effector cell can confer specificity for a specific epitope or antigen (e.g., an epitope or antigen preferentially present on the surface of a cancer cell or other disease-causing cell or particle). Such exogenous T cell receptors can comprise alpha and beta chains or, alternatively, may comprise gamma and delta chains. Exogenous TCRs useful in the invention may have specificity to any antigen or epitope of interest. 
     As used herein, with respect to a protein, the term “engineered” or “recombinant” means having an altered amino acid sequence as a result of the application of genetic engineering techniques to nucleic acids which encode the protein, and cells or organisms which express the protein. With respect to a nucleic acid, the term “recombinant” means having an altered nucleic acid sequence as a result of the application of genetic engineering techniques. Genetic engineering techniques include, but are not limited to, PCR and DNA cloning technologies; transfection, transformation and other gene transfer technologies; homologous recombination; site-directed mutagenesis; and gene fusion. In accordance with this definition, a protein having an amino acid sequence identical to a naturally-occurring protein, but produced by cloning and expression in a heterologous host, is not considered recombinant. 
     As used herein, the term “wild-type” refers to the most common naturally occurring polynucleotide or polypeptide sequence responsible for a given phenotype. Whereas a wild-type allele or polypeptide can confer a normal phenotype in an organism, a mutant or variant allele or polypeptide can, in some instances, confer an altered phenotype. 
     As used herein with respect to recombinant proteins, the term “modification” means any insertion, deletion or substitution of an amino acid residue in the recombinant sequence relative to a reference sequence (e.g., a wild-type or a native sequence). 
     As used herein, the term “meganuclease” refers to an endonuclease that binds double-stranded DNA at a recognition sequence that is greater than 12 base pairs. In some embodiments, the recognition sequence for a meganuclease of the present disclosure is 22 base pairs. A meganuclease can be an endonuclease that is derived from I-CreI, and can refer to an engineered variant of I-CreI that has been modified relative to natural I-CreI with respect to, for example, DNA-binding specificity, DNA cleavage activity, DNA-binding affinity, or dimerization properties. Methods for producing such modified variants of I-CreI are known in the art (e.g. WO 2007/047859). A meganuclease as used herein binds to double-stranded DNA as a heterodimer. A meganuclease may also be a “single-chain meganuclease” in which a pair of DNA-binding domains are joined into a single polypeptide using a peptide linker. The term “homing endonuclease” is synonymous with the term “meganuclease.” Meganucleases of the present disclosure are substantially non-toxic when expressed in cells, particularly in human T cells, such that cells can be transfected and maintained at 37° C. without observing deleterious effects on cell viability or significant reductions in meganuclease cleavage activity when measured using the methods described herein. 
     As used herein, the term “single-chain meganuclease” refers to a polypeptide comprising a pair of nuclease subunits joined by a linker. A single-chain meganuclease has the organization: N-terminal subunit—Linker—C-terminal subunit. The two meganuclease subunits will generally be non-identical in amino acid sequence and will recognize non-identical DNA sequences. Thus, single-chain meganucleases typically cleave pseudo-palindromic or non-palindromic recognition sequences. A single-chain meganuclease may be referred to as a “single-chain heterodimer” or “single-chain heterodimeric meganuclease” although it is not, in fact, dimeric. For clarity, unless otherwise specified, the term “meganuclease” can refer to a dimeric or single-chain meganuclease. 
     As used herein, the term “linker” refers to an exogenous peptide sequence used to join two meganuclease subunits into a single polypeptide. A linker may have a sequence that is found in natural proteins, or may be an artificial sequence that is not found in any natural protein. A linker may be flexible and lacking in secondary structure or may have a propensity to form a specific three-dimensional structure under physiological conditions. A linker can include, without limitation, any of those encompassed by U.S. Pat. Nos. 8,445,251 and 9,434,931. 
     As used herein, the term “zinc finger nuclease” or “ZFN” refers to a chimeric protein comprising a zinc finger DNA-binding domain fused to a nuclease domain from an endonuclease or exonuclease, including but not limited to a restriction endonuclease, homing endonuclease, Si nuclease, mung bean nuclease, pancreatic DNAse I, micrococcal nuclease, and yeast HO endonuclease. Nuclease domains useful for the design of zinc finger nucleases include those from a Type IIs restriction endonuclease, including but not limited to FokI, FoM, and StsI restriction enzyme. Additional Type IIs restriction endonucleases are described in International Publication No. WO 2007/014275, which is incorporated by reference in its entirety. The structure of a zinc finger domain is stabilized through coordination of a zinc ion. DNA binding proteins comprising one or more zinc finger domains bind DNA in a sequence-specific manner. The zinc finger domain can be a native sequence or can be redesigned through rational or experimental means to produce a protein which binds to a pre-determined DNA sequence—18 basepairs in length, comprising a pair of nine basepair half-sites separated by 2-10 basepairs. See, for example, U.S. Pat. Nos. 5,789,538, 5,925,523, 6,007,988, 6,013,453, 6,200,759, and International Publication Nos. WO 95/19431, WO 96/06166, WO 98/53057, WO 98/54311, WO 00/27878, WO 01/60970, WO 01/88197, and WO 02/099084, each of which is incorporated by reference in its entirety. By fusing this engineered protein domain to a nuclease domain, such as FokI nuclease, it is possible to target DNA breaks with genome-level specificity. The selection of target sites, zinc finger proteins and methods for design and construction of zinc finger nucleases are known to those of skill in the art and are described in detail in U.S. Publications Nos. 20030232410, 20050208489, 2005064474, 20050026157, 20060188987 and International Publication No. WO 07/014275, each of which is incorporated by reference in its entirety. Cleavage by a zinc finger nuclease can create a blunt end or a 5′ overhand of variable length (frequently four basepairs). 
     As used herein, the term “TALEN” refers to an endonuclease comprising a DNA-binding domain comprising a plurality of TAL domain repeats fused to a nuclease domain or an active portion thereof from an endonuclease or exonuclease, including but not limited to a restriction endonuclease, homing endonuclease, S1 nuclease, mung bean nuclease, pancreatic DNAse I, micrococcal nuclease, and yeast HO endonuclease. See, for example, Christian et al. (2010) Genetics 186:757-761, which is incorporated by reference in its entirety. Nuclease domains useful for the design of TALENs include those from a Type IIs restriction endonuclease, including but not limited to FokI, FoM, StsI, HhaI, HindIII, Nod, BbvCI, EcoRI, BglI, and AlwI. Additional Type IIs restriction endonucleases are described in International Publication No. WO 2007/014275. In some embodiments, the nuclease domain of the TALEN is a FokI nuclease domain or an active portion thereof. TAL domain repeats can be derived from the TALE (transcription activator-like effector) family of proteins used in the infection process by plant pathogens of the  Xanthomonas  genus. TAL domain repeats are 33-34 amino acid sequences with divergent 12th and 13th amino acids. These two positions, referred to as the repeat variable dipeptide (RVD), are highly variable and show a strong correlation with specific nucleotide recognition. Each base pair in the DNA target sequence is contacted by a single TAL repeat, with the specificity resulting from the RVD. In some embodiments, the TALEN comprises 16-22 TAL domain repeats. DNA cleavage by a TALEN requires two DNA recognition regions flanking a nonspecific central region (i.e., the “spacer”). The term “spacer” in reference to a TALEN refers to the nucleic acid sequence that separates the two nucleic acid sequences recognized and bound by each monomer constituting a TALEN. The TAL domain repeats can be native sequences from a naturally-occurring TALE protein or can be redesigned through rational or experimental means to produce a protein which binds to a pre-determined DNA sequence (see, for example, Boch et al. (2009) Science 326(5959):1509-1512 and Moscou and Bogdanove (2009) Science 326(5959):1501, each of which is incorporated by reference in its entirety). See also, U.S. Publication No. 20110145940 and International Publication No. WO 2010/079430 for methods for engineering a TALEN to recognize a specific sequence and examples of RVDs and their corresponding target nucleotides. In some embodiments, each nuclease (e.g., FokI) monomer can be fused to a TAL effector sequence that recognizes a different DNA sequence, and only when the two recognition sites are in close proximity do the inactive monomers come together to create a functional enzyme. 
     As used herein, the term “compact TALEN” refers to an endonuclease comprising a DNA-binding domain with one or more TAL domain repeats fused in any orientation to any portion of the I-TevI homing endonuclease or any of the endonucleases listed in Table 2 in U.S. Application No. 20130117869 (which is incorporated by reference in its entirety), including but not limited to MmeI EndA, End1, I-BasI, I-TevII, I-TevIII, I-TwoI, MspI, MvaI, NucA, and NucM. Compact TALENs do not require dimerization for DNA processing activity, alleviating the need for dual target sites with intervening DNA spacers. In some embodiments, the compact TALEN comprises 16-22 TAL domain repeats. 
     As used herein, the term “CRISPR” refers to a caspase-based endonuclease comprising a caspase, such as Cas9, and a guide RNA that directs DNA cleavage of the caspase by hybridizing to a recognition site in the genomic DNA. The caspase component of a CRISPR is an RNA-guided DNA endonuclease. In certain embodiments, the caspase is a class II Cas enzyme. In some of these embodiments, the caspase is a class II, type II enzyme, such as Cas9. In other embodiments, the caspase is a class II, type V enzyme, such as Cpfl. The guide RNA comprises a direct repeat and a guide sequence (often referred to as a spacer in the context of an endogenous CRISPR system), which is complementary to the target recognition site. In certain embodiments, the CRISPR further comprises a tracrRNA (trans-activating CRISPR RNA) that is complementary (fully or partially) to a direct repeat sequence (sometimes referred to as a tracr-mate sequence) present on the guide RNA. In particular embodiments, the caspase can be mutated with respect to a corresponding wild-type enzyme such that the enzyme lacks the ability to cleave one strand of a target polynucleotide, functioning as a nickase, cleaving only a single strand of the target DNA. Non-limiting examples of caspase enzymes that function as a nickase include Cas9 enzymes with a D10A mutation within the RuvC I catalytic domain, or with a H840A, N854A, or N863A mutation. 
     As used herein, the term “megaTAL” refers to a single-chain nuclease comprising a transcription activator-like effector (TALE) DNA binding domain with an engineered, sequence-specific homing endonuclease. 
     As used herein, the term “recognition sequence” refers to a DNA sequence that is bound and cleaved by an endonuclease. In the case of a meganuclease, a recognition sequence comprises a pair of inverted, 9 basepair “half sites” which are separated by four basepairs. In the case of a single-chain meganuclease, the N-terminal domain of the protein contacts a first half-site and the C-terminal domain of the protein contacts a second half-site. Cleavage by a meganuclease produces four basepair 3′ “overhangs”. “Overhangs”, or “sticky ends” are short, single-stranded DNA segments that can be produced by endonuclease cleavage of a double-stranded DNA sequence. In the case of meganucleases and single-chain meganucleases derived from I-CreI, the overhang comprises bases 10-13 of the 22 basepair recognition sequence. In the case of a compact TALEN, the recognition sequence comprises a first CNNNGN sequence that is recognized by the I-Teel domain, followed by a non-specific spacer 4-16 basepairs in length, followed by a second sequence 16-22 bp in length that is recognized by the TAL-effector domain (this sequence typically has a 5′ T base). Cleavage by a Compact TALEN produces two basepair 3′ overhangs. In the case of a CRISPR, the recognition sequence is the sequence, typically 16-24 basepairs, to which the guide RNA binds to direct cleavage. Full complementarity between the guide sequence and the recognition sequence is not necessarily required to effect cleavage. Cleavage by a CRISPR can produce blunt ends (such as by a class II, type II caspase) or overhanging ends (such as by a class II, type V caspase), depending on the caspase. In those embodiments wherein a Cpfl caspase is utilized, cleavage by the CRISPR complex comprising the same will result in 5′ overhangs and in certain embodiments, 5 nucleotide 5′ overhangs. Each caspase enzyme also requires the recognition of a PAM (protospacer adjacent motif) sequence that is near the recognition sequence complementary to the guide RNA. The precise sequence, length requirements for the PAM, and distance from the target sequence differ depending on the caspase enzyme, but PAMs are typically 2-5 base pair sequences adjacent to the target/recognition sequence. PAM sequences for particular caspase enzymes are known in the art (see, for example, U.S. Pat. No. 8,697,359 and U.S. Publication No. 20160208243, each of which is incorporated by reference in its entirety) and PAM sequences for novel or engineered caspase enzymes can be identified using methods known in the art, such as a PAM depletion assay (see, for example, Karvelis et al. (2017) Methods 121-122:3-8, which is incorporated herein in its entirety). In the case of a zinc finger, the DNA binding domains typically recognize an 18-bp recognition sequence comprising a pair of nine basepair “half-sites” separated by 2-10 basepairs and cleavage by the nuclease creates a blunt end or a 5′ overhang of variable length (frequently four basepairs). 
     As used herein, the term “target site” or “target sequence” refers to a region of the chromosomal DNA of a cell comprising a recognition sequence for a nuclease. 
     As used herein, the term “homologous recombination” or “HR” refers to the natural, cellular process in which a double-stranded DNA-break is repaired using a homologous DNA sequence as the repair template (see, e.g. Cahill et al. (2006), Front.  Biosci.  11:1958-1976). The homologous DNA sequence may be an endogenous chromosomal sequence or an exogenous nucleic acid that was delivered to the cell. 
     As used herein, the term “non-homologous end-joining” or “NHEJ” refers to the natural, cellular process in which a double-stranded DNA-break is repaired by the direct joining of two non-homologous DNA segments (see, e.g. Cahill et al. (2006),  Front. Biosci.  11:1958-1976). 
     As used herein, the term “reduced” refers to any reduction in the symptoms or severity of a disease or any reduction in the proliferation or number of cancerous cells. In either case, such a reduction may be up to 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or up to 100%. Accordingly, the term “reduced” encompasses both a partial reduction and a complete reduction of a disease state. 
     As used herein, the term “reduced” can also refer to a decrease in the cell surface expression of a polypeptide when compared to an appropriate control cell. In the present context, a reduction is distinct from knockout of polypeptide expression, wherein expression is reduced by 100%. Rather, in the present invention, a reduction indicates that expression is decreased but not completely eliminated. Such as a reduction can be, for example, a reduction in cell surface beta-2 microglobulin, MHC class I molecule, or CD52 expression when compared to a control cell which has not been genetically-modified to reduce beta-2 microglobulin, MHC class I molecules, or CD52, respectively. A reduction in expression can be between about 10% and about 99% or any number or range therein. For example, a reduction can be between about 10% and 95%, about 50% and about 95%, about 75% and about 95%, or about 90% and about 95%, when compared to a control cell. A reduction can also be by about 10%, 20%, 30%, 40%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or 99% when compared to a control cell. 
     As used herein, the term “MHC class I molecule” refers to a major histocompatibility complex (MHC) found on the cell surface which displays peptide fragments of non-self proteins. MHC class I molecules consist of two polypeptide chains. The alpha chain consists of 3 polypeptides referred to as the alpha-1 (□1), alpha-2 (□2), and alpha-3 (□3) domains. The alpha chain is linked non-covalently via the □3 domain to a beta chain which consists of beta-2 microglobulin (B2M). The alpha chain is polymorphic and is encoded by the HLA gene (i.e., HLA-A, HLA-B, and HLA-C), whereas beta-2 microglobulin is not polymorphic and it encoded by the B2M gene. 
     As used herein, the term “beta-2 microglobulin” refers to the beta chain component of MHC class I molecules. Human beta-2 microglobulin is encoded by the B2M gene (e.g., NCBI Gene ID 567). Expression of beta-2 microglobulin is necessary for assembly and function of MHC class I molecules on the cell surface. 
     As used herein, the term “CD52” refers to the polypeptide encoded by the human CD52 gene (e.g., NCBI gene ID 1043) which is also referred to as cluster of differentiation 52. 
     As used herein, the term “anti-tumor activity” or “anti-tumor effect” refers to a biological effect which can be manifested by a decrease in tumor volume, a decrease in the number of tumor cells, a decrease in the number of metastases, an increase in life expectancy, or amelioration of various physiological symptoms associated with the cancerous condition. An “anti-tumor effect” can also be manifested by the ability of the genetically-modified cells of the present disclosure in prevention of the occurrence of tumor in the first place. 
     The term “effective amount” or “therapeutically effective amount” refers to an amount sufficient to effect beneficial or desirable biological and/or clinical results. The therapeutically effective amount will vary depending on the therapeutic (e.g., genetically-modified cell, CAR T cell, etc.) formulation or composition, the disease and its severity, and the age, weight, physical condition and responsiveness of the subject to be treated. In specific embodiments, an effective amount of a cell comprising a co-stimulatory domain disclosed herein or pharmaceutical compositions disclosed herein reduces at least one symptom or the progression of a disease. 
     As used herein, the term “treat” or “treatment” means to reduce the frequency or severity of at least one sign or symptom of a disease or disorder experienced by a subject. 
     As used herein, the term “cancer” should be understood to encompass any neoplastic disease (whether invasive or metastatic) which is characterized by abnormal and uncontrolled cell division causing malignant growth or tumor. 
     As used herein, the term “carcinoma” refers to a malignant growth made up of epithelial cells. 
     As used herein, the term “leukemia” refers to malignancies of the hematopoietic organs/systems and is generally characterized by an abnormal proliferation and development of leukocytes and their precursors in the blood and bone marrow. 
     As used herein, the term “sarcoma” refers to a tumor which is made up of a substance like the embryonic connective tissue and is generally composed of closely packed cells embedded in a fibrillary, heterogeneous, or homogeneous substance. 
     As used herein, the term “melanoma” refers to a tumor arising from the melanocytic system of the skin and other organs. 
     As used herein, the term “lymphoma” refers to a group of blood cell tumors that develop from lymphocytes. 
     As used herein, the term “blastoma” refers to a type of cancer that is caused by malignancies in precursor cells or blasts (immature or embryonic tissue). 
     As used herein, “transfected” or “transformed” or “transduced” or “nucleofected” refers to a process by which exogenous nucleic acid is transferred or introduced into the host cell. A “transfected” or “transformed” or “transduced” cell is one which has been transfected, transformed or transduced with exogenous nucleic acid. The cell includes the primary subject cell and its progeny. 
     As used herein, a “human T cell” or “T cell” refers to a T cell isolated from a human donor. Human T cells, and cells derived therefrom, include isolated T cells that have not been passaged in culture, T cells that have been passaged and maintained under cell culture conditions without immortalization, and T cells that have been immortalized and can be maintained under cell culture conditions indefinitely. 
     As used herein, a “human natural killer cell” or “human NK cell” or “natural killer cell” or “NK cell” refers to a type of cytotoxic lymphocyte critical to the innate immune system. The role NK cells play is analogous to that of cytotoxic T-cells in the vertebrate adaptive immune response. NK cells provide rapid responses to virally infected cells and respond to tumor formation, acting at around 3 days after infection. 
     As used herein, a “control” or “control cell” refers to a cell that provides a reference point for measuring changes in genotype or phenotype of a genetically-modified cell. A control cell may comprise, for example: (a) a wild-type cell, i.e., of the same genotype as the starting material for the genetic alteration which resulted in the genetically-modified cell; (b) a cell of the same genotype as the genetically-modified cell but which has been transformed with a null construct (i.e., with a construct which has no known effect on the trait of interest); or, (c) a cell genetically identical to the genetically-modified cell but which is not exposed to conditions, stimuli, or further genetic modifications that would induce expression of altered genotype or phenotype. In particular embodiments, a control cell is otherwise identical to a genetically-modified cell but has not been genetically-modified to reduce cell surface expression of a particular polypeptide (e.g., beta-2 microglobulin, MHC class I molecules, CD52). 
     As used herein with respect to both amino acid sequences and nucleic acid sequences, the terms “percent identity,” “sequence identity,” “percentage similarity,” “sequence similarity,” and the like, refer to a measure of the degree of similarity of two sequences based upon an alignment of the sequences which maximizes similarity between aligned amino acid residues or nucleotides, and which is a function of the number of identical or similar residues or nucleotides, the number of total residues or nucleotides, and the presence and length of gaps in the sequence alignment. A variety of algorithms and computer programs are available for determining sequence similarity using standard parameters. As used herein, sequence similarity is measured using the BLASTp program for amino acid sequences and the BLASTn program for nucleic acid sequences, both of which are available through the National Center for Biotechnology Information (www.ncbi.nlm.nih.gov), and are described in, for example, Altschul et al. (1990),  J. Mol. Biol.  215:403-410; Gish and States (1993),  Nature Genet.  3:266-272; Madden et al. (1996),  Meth. Enzymol. 266:131-141; Altschul et al. (1997),  Nucleic Acids Res.  25:33 89-3402); Zhang et al. (2000),  J. Comput. Biol.  7(1-2):203-14. As used herein, percent similarity of two amino acid sequences is the score based upon the following parameters for the BLASTp algorithm: word size=3; gap opening penalty=−11; gap extension penalty=−1; and scoring matrix=BLOSUM62. As used herein, percent similarity of two nucleic acid sequences is the score based upon the following parameters for the BLASTn algorithm: word size=11; gap opening penalty=−5; gap extension penalty=−2; match reward=1; and mismatch penalty=−3. 
     As used herein with respect to modifications of two proteins or amino acid sequences, the term “corresponding to” is used to indicate that a specified modification in the first protein is a substitution of the same amino acid residue as in the modification in the second protein, and that the amino acid position of the modification in the first proteins corresponds to or aligns with the amino acid position of the modification in the second protein when the two proteins are subjected to standard sequence alignments (e.g., using the BLASTp program). Thus, the modification of residue “X” to amino acid “A” in the first protein will correspond to the modification of residue “Y” to amino acid “A” in the second protein if residues X and Y correspond to each other in a sequence alignment, and despite the fact that X and Y may be different numbers. 
     As used herein, the recitation of a numerical range for a variable is intended to convey that the present disclosure may be practiced with the variable equal to any of the values within that range. Thus, for a variable which is inherently discrete, the variable can be equal to any integer value within the numerical range, including the end-points of the range. Similarly, for a variable which is inherently continuous, the variable can be equal to any real value within the numerical range, including the end-points of the range. As an example, and without limitation, a variable which is described as having values between 0 and 2 can take the values 0, 1 or 2 if the variable is inherently discrete, and can take the values 0.0, 0.1, 0.01, 0.001, or any other real values and ≥0 and ≤2 if the variable is inherently continuous. 
     2.1 Principle of the Invention 
     The present disclosure is based, in part, on the observation that knockdown of cell surface beta-2 microglobulin, and consequently MHC class I molecules, can reduce allogenicity of genetically-modified cells, such as CAR T cells. Importantly, the inventors have discovered that an incomplete knockdown of beta-2 microglobulin and MEW class I molecules (i.e., to a low percentage of wild-type expression, but not complete knockout) not only reduces allogenicity of genetically-modified cells, but also serves to dramatically reduce killing by NK cells, which can recognize cells that are B2M-negative as non-self and induce a cytotoxic action. 
     The present invention is also based, in part, on the inventors&#39; discovery that a population of CAR-positive T cells can be enriched by an advantageous negative-selection method when the CAR-encoding construct includes a coding sequence for an RNA interfering molecule against CD52. In this manner, a population of CAR T cells can be contacted with beads conjugated to an anti-CD52 antibody in order to capture CD52-positive cells. Separation of the beads, and thus the CD52-positive cells, results in an enriched population of CAR-positive cells having reduced cell surface expression of CD52. 
     Accordingly, a nucleic acid molecule is provided comprising a first expression cassette which encodes an engineered antigen receptor, such as a chimeric antigen receptor, and a second expression cassette which encodes an inhibitory nucleic acid molecule, such as an RNA interfering molecule. Further, the nucleic acid molecule is flanked by 5′ and 3′ homology arms to promote targeted insertion of the nucleic acid into the genome of a cell at a double-strand break, such as a cleavage site produced by an engineered nuclease. In certain embodiments of the invention, the inhibitory nucleic acid molecule can be against human beta-2 microglobulin, a component of the MEW class I molecule, or CD52. 
     Further disclosed herein are recombinant DNA constructs and viral vectors comprising the nucleic acid molecule, genetically-modified cells comprising the nucleic acid molecule, and pharmaceutical compositions comprising such cells. Also disclosed are genetically-modified cells expressing an engineered antigen receptor (e.g., a CAR or exogenous TCR) which have reduced cell-surface expression of beta-2 microglobulin, MEW class I molecules, or CD52, and may or may not express the particular nucleic acid molecule of the invention. 
     In some embodiments, administration of genetically-modified cells of the invention reduces the symptoms or severity of diseases, such cancers, which can be targeted by genetically-modified cells of the present disclosure. 
     Also disclosed herein are methods of immunotherapy for treating cancer in a subject in need thereof comprising administering to the subject a pharmaceutical composition comprising a genetically-modified cell disclosed herein and a pharmaceutically acceptable carrier. In such methods, wherein a CAR is expressed and cell surface beta-2 microglobulin and/or MHC class I molecules is reduced, incomplete knockout leads to a reduction in both allogenicity of the cells and killing of the cells by NK cells. 
     Further disclosed are methods for producing an enriched population of genetically-modified cells, wherein a CAR is expressed and cell surface CD52 is reduced by RNA interference, allowing for negative selection of CAR-positive cells having reduced CD52 expression. 
     2.2 Nucleic Acid Molecules 
     In certain embodiments, the invention provides a nucleic acid molecule comprising: (a) a first expression cassette comprising a nucleic acid sequence encoding an engineered antigen receptor; (b) a second expression cassette comprising a nucleic acid sequence encoding an inhibitory nucleic acid molecule; (c) a 5′ homology arm; and (d) a 3′ homology arm. The 5′ homology arm and the 3′ homology arm can be engineered at any suitable length to have homology to chromosomal regions flanking a nuclease recognition sequence in a gene of interest, which can be any desired gene in a target cell in which a suitable recognition sequence is present. 
     The nucleic acid molecule of the invention can have any number of orientations. Some non-limiting examples illustrated in  FIG. 1 . In particular embodiments, the first and second expression cassettes can be in the same orientation. This orientation can be either 5′ to 3′ relative to the homology arms or, alternatively, 3′ to 5′. In either case, the first expression cassette may be 5′ to the second cassette, or the second cassette may be 5′ to the first cassette. In other embodiments, the first and second expression cassettes can be in different orientations in the nucleic acid molecule. For example, the first expression cassette may be oriented 5′ to 3′, whereas the second expression cassette may be oriented 3′ to 5′. Alternatively, the first expression cassette may be oriented 3′ to 5′ and the second expression cassette may be oriented 5′ to 3′. 
     In embodiments wherein the expression cassettes are in opposite orientations, they may be oriented in a “tail-to-tail” configuration, such that the first expression cassette is oriented 3′ to 5′ and is positioned 5′ to the second expression cassette, which is oriented 5′ to 3′. In a similar tail-to-tail embodiment, the second expression cassette is oriented 3′ to 5′ and is positioned 5′ to the first expression cassette, which is oriented 5′ to 3′. 
     In other embodiments wherein the expression cassettes are in opposite orientations, they may be oriented in a “head-to-head” configuration, such that the first expression cassette is oriented 5′ to 3′ and is positioned 5′ to the second expression cassette, which is oriented 3′ to 5′. In a similar head-to-head embodiment, the second expression cassette is oriented 5′ to 3′ and is positioned 5′ to the first expression cassette, which is oriented 3′ to 5′. 
     In some embodiments, the nucleic acid molecule can comprise multiple copies of the second expression cassette. The copies of the second expression cassette can be identical or vary from one another. In some cases, the copies can include a promoter, a coding sequence for the inhibitory nucleic acid molecule, and a sequence, such as a (cPPT/CTS) sequence, to terminate translation of the inhibitory nucleic acid molecule. The copies of the second expression cassette can be in tandem to one another in the nucleic acid molecule, and can be in the same orientation, or in opposite orientations. Alternatively, the copies may not be in tandem, and can be in the same orientation, or in opposite orientations. 
     The expression cassettes of the nucleic acid molecule can include various promoters which drive expression of the engineered antigen receptor and/or the inhibitory nucleic acid molecule. One example of a suitable promoter is the immediate early cytomegalovirus (CMV) promoter sequence. This promoter sequence is a strong constitutive promoter sequence capable of driving high levels of expression of any polynucleotide sequence operatively linked thereto. Another example of a suitable promoter is Elongation Growth Factor-1α (EF-1α). However, other constitutive promoter sequences may also be used, including, but not limited to the simian virus 40 (SV40) early promoter, mouse mammary tumor virus (MMTV), human immunodeficiency virus (HIV) long terminal repeat (LTR) promoter, MoMuLV promoter, an avian leukemia virus promoter, an Epstein-Barr virus immediate early promoter, a Rous sarcoma virus promoter, as well as human gene promoters such as, but not limited to, the actin promoter, the myosin promoter, the hemoglobin promoter, and the creatine kinase promoter. Further, the present disclosure should not be limited to the use of constitutive promoters. Inducible promoters are also contemplated as part of the present disclosure. The use of an inducible promoter provides a molecular switch capable of turning on expression of the polynucleotide sequence which it is operatively linked when such expression is desired, or turning off the expression when expression is not desired. Examples of inducible promoters include, but are not limited to a metallothionine promoter, a glucocorticoid promoter, a progesterone promoter, and a tetracycline promoter. 
     Synthetic promoters are also contemplated as part of the present disclosure. For example, in particular embodiments, the promoter driving expression of the engineered antigen receptor is a JeT promoter (see, WO/2002/012514). 
     In some embodiments, the promoters are selected based on the desired outcome. It is recognized that different applications can be enhanced by the use of different promoters in the expression cassettes to modulate the timing, location and/or level of expression of the polynucleotides disclosed herein. Such expression constructs may also contain, if desired, a promoter regulatory region (e.g., one conferring inducible, constitutive, environmentally- or developmentally-regulated, or cell- or tissue-specific/selective expression), a transcription initiation start site, a ribosome binding site, an RNA processing signal, a transcription termination site, and/or a polyadenylation signal. 
     Promoters particularly useful for driving expression of an RNA interference molecule are well known in the art and can include, without limitation, pol III promoters, such as U6 or H1. 
     The 5′ and 3′ homology arms of the nucleic acid molecule have sequence homology to corresponding sequences 5′ upstream and 3′ downstream of the nuclease recognition sequence in the genome. The homology arms promote insertion of the nucleic acid molecule into the cleavage site generated by the nuclease. In general, homology arms can have a length of at least 50 base pairs, preferably at least 100 base pairs, and up to 2000 base pairs or more, and can have at least 90%, preferably at least 95%, or more, sequence homology to their corresponding sequences in the genome. 
     In order to assess the expression of an engineered antigen receptor (e.g. a CAR or exogenous T cell receptor) in a genetically-modified cell, the nucleic acid molecule of the invention can optionally comprise an epitope which can be used to detect the presence of the encoded cell surface protein. In some examples described herein, a CAR coding sequence may include a QBend10 epitope which allows for detection using an anti-CD34 antibody (see, W02013/153391). 
     In other examples, an expression cassette can also contain either a selectable marker gene or a reporter gene, or both, to facilitate identification and selection of expressing cells from the population of cells sought to be transfected or infected through viral vectors. In other aspects, the selectable marker may be carried on a separate piece of DNA and used in a co-transfection procedure. Both selectable markers and reporter genes may be flanked with appropriate regulatory sequences to enable expression in the host cells. Useful selectable markers include, for example, antibiotic-resistance genes and fluorescent marker genes. 
     Expression may also be assessed by determining protein expression of the polypeptide targeted by the inhibitory nucleic acid sequence. For example, expression of beta-2 microglobulin and CD52 can be detected on the cell surface by a number of techniques known in the art. Expression can also be determined by positive or negative selection procedures which purify particular populations of cells expressing, or lacking expression, of the cell surface polypeptides. 
     Also provided herein are vectors comprising the nucleic acid molecules of the present disclosure. In some embodiments, the nucleic acid molecule is cloned into a vector including, but not limited to a plasmid, a phagemid, a phage derivative, an animal virus, or a cosmid. Vectors of particular interest include expression vectors, replication vectors, probe generation vectors, and sequencing vectors. 
     In other embodiments, nucleic acid molecules of the invention are provided on viral vectors, such as retroviral vectors, lentiviral vectors, adenoviral vectors, and adeno-associated viral (AAV) vectors. Viral vector technology is well known in the art and is described, for example, in Sambrook et al. (2001, Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, New York), and in other virology and molecular biology manuals. Viruses, which are useful as vectors include, but are not limited to, retroviruses, adenoviruses, adeno-associated viruses, herpes viruses, and lentiviruses. In general, a suitable vector contains an origin of replication functional in at least one organism, a promoter sequence, convenient restriction endonuclease sites, and one or more selectable markers, (e.g., WO 01/96584; WO 01/29058; and U.S. Pat. No. 6,326,193). Where the nucleic acid of the invention is provided in a viral vector that promotes random integration into the genome, and does not require the presence of 5′ and 3′ homology arms for homologous recombination, the nucleic acid of the invention can be provided without 5′ and 3′ homology arms. 
     2.3 Chimeric Antigen Receptors (CARs) 
     Provided herein are genetically-modified cells expressing an engineered antigen receptor. In some embodiments, the engineered antigen receptor is a chimeric antigen receptor (CAR). Generally, a CAR of the present disclosure will comprise at least an extracellular domain and an intracellular domain. In some embodiments, the extracellular domain comprises a target-specific binding element otherwise referred to as a ligand-binding domain or moiety. In some embodiments, the intracellular domain, or cytoplasmic domain, comprises at least one co-stimulatory domain and one or more signaling domains. In other embodiments, the CAR may only comprise a signaling domain, such as CD3□, and the cell may comprise one or more co-stimulatory domains on another construct expressed in the cell. 
     In some embodiments, a CAR comprises an extracellular, target-specific binding element otherwise referred to as a ligand-binding domain or moiety. The choice of ligand-binding domain depends upon the type and number of ligands that define the surface of a target cell. For example, the ligand-binding domain may be chosen to recognize a ligand that acts as a cell surface marker on target cells associated with a particular disease state. Thus, examples of cell surface markers that may act as ligands for the ligand-binding domain in the CAR of the present disclosure can include those associated with viral, bacterial and parasitic infections, autoimmune disease, and cancer cells. In some embodiments, the CAR of the present disclosure is engineered to target a tumor antigen of interest by way of engineering a desired ligand-binding moiety that specifically binds to an antigen on a tumor cell. In the context of the present disclosure, “tumor antigen” refers to antigens that are common to specific hyperproliferative disorders such as cancer. 
     In some embodiments, the extracellular ligand-binding domain of the CAR is specific for any antigen or epitope of interest, particularly any tumor antigen or epitope of interest. As non-limiting examples, in some embodiments the antigen of the target is a tumor-associated surface antigen, such as ErbB2 (HER2/neu), carcinoembryonic antigen (CEA), epithelial cell adhesion molecule (EpCAM), epidermal growth factor receptor (EGFR), EGFR variant III (EGFRvIII), CD19, CD20, CD22, CD30, CD40, CLL-1, disialoganglioside GD2, ductal-epithelial mucine, gp36, TAG-72, glycosphingolipids, glioma-associated antigen, B-human chorionic gonadotropin, alphafetoprotein (AFP), lectin-reactive AFP, thyroglobulin, RAGE-1, MN-CA IX, human telomerase reverse transcriptase, RU1, RU2 (AS), intestinal carboxyl esterase, mut hsp70-2, M-CSF, prostase, prostase specific antigen (PSA), PAP, NY-ESO-1, LAGA-la, p53, prostein, PSMA, surviving and telomerase, prostate-carcinoma tumor antigen-1 (PCTA-1), MAGE, ELF2M, neutrophil elastase, ephrin B2, insulin growth factor (IGFI)-1, IGF-II, IGFI receptor, mesothelin, a major histocompatibility complex (MHC) molecule presenting a tumor-specific peptide epitope, 5T4, ROR1, Nkp30, NKG2D, tumor stromal antigens, the extra domain A (EDA) and extra domain B (EDB) of fibronectin and the Al domain of tenascin-C (TnC Al) and fibroblast associated protein (fap); a lineage-specific or tissue specific antigen such as CD3, CD4, CD8, CD24, CD25, CD33, CD34, CD38, CD123, CD133, CD138, CTLA-4, B7- 1 (CD80), B7-2 (CD86), endoglin, a major histocompatibility complex (MHC) molecule, BCMA (CD269, TNFRSF 17), CS1, or a virus-specific surface antigen such as an HIV-specific antigen (such as HIV gp120); an EBV-specific antigen, a CMV-specific antigen, a HPV-specific antigen such as the E6 or E7 oncoproteins, a Lasse Virus-specific antigen, an Influenza Virus-specific antigen, as well as any derivate or variant of these surface markers. In a particular embodiment of the present disclosure, the ligand-binding domain is specific for CD19. 
     In some embodiments, the extracellular domain of a chimeric antigen receptor further comprises an autoantigen (see, Payne et al. (2016)  Science,  Vol. 353 (6295): 179-184), which can be recognized by autoantigen-specific B cell receptors on B lymphocytes, thus directing T cells to specifically target and kill autoreactive B lymphocytes in antibody-mediated autoimmune diseases. Such CARs can be referred to as chimeric autoantibody receptors (CAARs), and the incorporation of one or more co-stimulatory domains described herein into such CAARs is encompassed by the present disclosure. 
     In some embodiments, the extracellular domain of a chimeric antigen receptor can comprise a naturally-occurring ligand for an antigen of interest, or a fragment of a naturally-occurring ligand which retains the ability to bind the antigen of interest. 
     In some embodiments, a CAR comprises a transmembrane domain which links the extracellular ligand-binding domain or autoantigen with the intracellular signaling and co-stimulatory domains via a hinge or spacer sequence. The transmembrane domain can be derived from any membrane-bound or transmembrane protein. For example, the transmembrane polypeptide can be a subunit of the T-cell receptor (i.e., an α, β, γ or ξ, polypeptide constituting CD3 complex), IL2 receptor p55 (a chain), p75 (β chain) or γ chain, subunit chain of Fc receptors (e.g., Fcy receptor III) or CD proteins such as the CD8 alpha chain. Alternatively the transmembrane domain can be synthetic and can comprise predominantly hydrophobic residues such as leucine and valine. In particular examples, the transmembrane domain is a CD8□ transmembrane polypeptide. 
     The hinge region refers to any oligo- or polypeptide that functions to link the transmembrane domain to the extracellular ligand-binding domain. For example, a hinge region may comprise up to 300 amino acids, preferably 10 to 100 amino acids and most preferably 25 to 50 amino acids. Hinge regions may be derived from all or part of naturally occurring molecules, such as from all or part of the extracellular region of CD8, CD4 or CD28, or from all or part of an antibody constant region. Alternatively, the hinge region may be a synthetic sequence that corresponds to a naturally occurring hinge sequence, or may be an entirely synthetic hinge sequence. In particular examples, a hinge domain can comprise a part of a human CD8 alpha chain, FcyRIIIa receptor or IgGl. 
     The intracellular signaling domain of a CAR of the present disclosure is responsible for activation of at least one of the normal effector functions of the cell in which the CAR has been placed and/or activation of proliferative and cell survival pathways. The term “effector function” refers to a specialized function of a cell. Effector function of a T cell, for example, may be cytolytic activity or helper activity including the secretion of cytokines. An intracellular signaling domain, such as CD3 , can provide an activation signal to the cell in response to binding of the extracellular domain. As discussed, the activation signal can induce an effector function of the cell such as, for example, cytolytic activity or cytokine secretion. 
     The intracellular domain of the CAR can include one or more intracellular co-stimulatory domains which transmit a co-stimulatory signal to promote cell proliferation, cell survival, and/or cytokine secretion after binding of the extracellular domain. Such intracellular co-stimulatory domains include those known in the art such as, without limitation, CD27, CD28, CD8, 4-1BB (CD137), OX40, CD30, CD40, PD-1, ICOS, lymphocyte function-associated antigen-1 (LFA-1), CD2, CD7, LIGHT, NKG2C, B7-H3 and a ligand that specifically binds with CD83, N1, or N6. 
     The CAR can be specific for any type of cancer cell. Such cancers can include, without limitation, carcinoma, lymphoma, sarcoma, blastomas, leukemia, cancers of B cell origin, breast cancer, gastric cancer, neuroblastoma, osteosarcoma, lung cancer, melanoma, prostate cancer, colon cancer, renal cell carcinoma, ovarian cancer, rhabdomyosarcoma, leukemia, and Hodgkin&#39;s lymphoma. In certain embodiments, cancers of B cell origin include, without limitation, B lineage acute lymphoblastic leukemia, B cell chronic lymphocytic leukemia, B cell non-Hodgkin&#39;s lymphoma, and multiple myeloma. 
     2.4 Methods for Producing Recombinant Viral Vectors 
     In some embodiments, the present disclosure provides recombinant AAV vectors for use in the methods of the present disclosure. Recombinant AAV vectors are typically produced in mammalian cell lines such as HEK-293. Because the viral cap and rep genes are removed from the vector to prevent its self-replication to make room for the therapeutic gene(s) to be delivered (e.g. the endonuclease gene), it is necessary to provide these in trans in the packaging cell line. In addition, it is necessary to provide the “helper” (e.g. adenoviral) components necessary to support replication (Cots D, Bosch A, Chillon M (2013)  Curr. Gene Ther.  13(5): 370-81). Frequently, recombinant AAV vectors are produced using a triple-transfection in which a cell line is transfected with a first plasmid encoding the “helper” components, a second plasmid comprising the cap and rep genes, and a third plasmid comprising the viral ITRs containing the intervening DNA sequence to be packaged into the virus. Viral particles comprising a genome (ITRs and intervening gene(s) of interest) encased in a capsid are then isolated from cells by freeze-thaw cycles, sonication, detergent, or other means known in the art. Particles are then purified using cesium-chloride density gradient centrifugation or affinity chromatography and subsequently delivered to the gene(s) of interest to cells, tissues, or an organism such as a human patient. Accordingly, methods are provided herein for producing recombinant AAV vectors comprising the nucleic acid molecules of the invention described herein. 
     In some embodiments, genetic transfer is accomplished via lentiviral vectors. Lentiviruses, in contrast to other retroviruses, in some contexts may be used for transducing certain non-dividing cells. Non-limiting examples of lentiviral vectors include those derived from a lentivirus, such as Human Immunodeficiency Virus 1 (HIV-1), HIV-2, an Simian Immunodeficiency Virus (SIV), Human T-lymphotropic virus 1 (HTLV-1), HTLV-2 or equine infection anemia virus (E1AV). For example, lentiviral vectors have been generated by multiply attenuating the HIV virulence genes, for example, the genes env, vif, vpr, vpu and nef are deleted, making the vector safer for therapeutic purposes. Lentiviral vectors are known in the art, see Naldini et al., (1996 and 1998); Zufferey et al., (1997); Dull et al., 1998, U.S. Pat. Nos. 6,013,516; and 5,994,136). In some embodiments, these viral vectors are plasmid-based or virus-based, and are configured to carry the essential sequences for incorporating foreign nucleic acid, for selection, and for transfer of the nucleic acid into a host cell. Known lentiviruses can be readily obtained from depositories or collections such as the American Type Culture Collection (“ATCC”; 10801 University Blvd., Manassas, Va. 20110-2209), or isolated from known sources using commonly available techniques. 
     In specific embodiments, lentiviral vectors are prepared using a first plasmid encoding the gag, pol, tat, and rev genes cloned from human immunodeficiency virus (HIV) and a second plasmid encoding the envelope protein from vesicular stomatitis virus (VSV-G) used to pseudotype viral particles. A transfer vector, such as the pCDH-EF1-MCS vector, can be used with a suitable promoter. All three plasmids can then be transfected into lentivirus cells, such as the Lenti-X-293T cells, and lentivirus can then be harvested, concentrated and screened after a suitable incubation time. Accordingly, methods are provided herein for producing recombinant lentiviral vectors comprising the nucleic acid molecule of the invention described herein. 
     2.5 Genetically-Modified Cells 
     Provided herein are cells genetically-modified to comprise the nucleic acid molecule of the invention described herein. Further provided are genetically-modified cells (e.g., human T cells expressing a CAR or exogenous TCR) with reduced cell-surface expression of beta-2 microglobulin, MHC class I molecules, and or CD52, which do not necessarily comprise the particular nucleic acid molecule of the invention. 
     In different variations of the present disclosure, a nucleic acid molecule of the invention is present within the genome of the genetically-modified cell or, alternatively, is not integrated into the genome of the cell. In particular embodiments, the nucleic acid molecule of the invention is inserted into the genome of a cell by targeted insertion at a cleavage site produced by a double-strand break, such as that produced by an engineered nuclease. The presence of 5′ and 3′ homology arms flanking the first and second expression cassettes of the nucleic acid molecule promote homologous recombination of the nucleic acid molecule into the cleavage site, resulting in targeted insertion. 
     In some embodiments where the nucleic acid molecule is not integrated into the genome, the nucleic acid molecule can be present in the genetically-modified cell in a recombinant DNA construct, in an mRNA, in a viral genome, or other nucleic acid which is not integrated into the genome of the cell. 
     In specific embodiments, the cells comprising the nucleic acid molecule of the invention, and other genetically-modified cells of the invention, are eukaryotic cells. In particular embodiments, such cells are T cells or NK cells, particularly human T cells or NK cells. In some embodiments, the cells are primary T cells or primary NK cells. 
     T cells and NK cells can be obtained from a number of sources, including peripheral blood mononuclear cells, bone marrow, lymph node tissue, cord blood, thymus tissue, tissue from a site of infection, ascites, pleural effusion, spleen tissue, and tumors. In certain embodiments of the present disclosure, any number of T cell and NK cell lines available in the art may be used. In some embodiments of the present disclosure, T cells and NK cells are obtained from a unit of blood collected from a subject using any number of techniques known to the skilled artisan. In one embodiment, cells from the circulating blood of an individual are obtained by apheresis. 
     Genetically-modified cells comprising the nucleic acid molecule disclosed herein, and other genetically-modified cells of the invention, can exhibit a number of functional properties dependent upon which polypeptide is reduced in the cell and/or targeted by the inhibitory nucleic acid molecule. For example, in some genetically-modified cells of the invention, beta-2 microglobulin is reduced, or the inhibitory nucleic acid molecule is against human beta-2 microglobulin, and cell surface beta-2 microglobulin expression is reduced, to a small percentage of wild-type expression. Such genetically-modified cells can be less susceptible to endogenous NK cell killing, have extended persistence time in a subject, exhibit enhanced expansion in a subject, and/or have reduced allogenicity than cells with wild-type levels of B2M or cells which are completely B2M-negative. Reductions in beta-2 microglobulin consequently result in a reduction in cell surface expression of MHC class I molecules, because beta-2 microglobulin is necessary for their assembly and function. Therefore, the same properties are also applicable to genetically-modified cells of the invention which have reduced cell surface expression of MHC class I molecules. 
     Susceptibility to NK cell killing can be determined by methods known in the art such as those described further herein. Reductions in NK cell killing can be by about 5%, 10%, 20%, 30%, 40%, 50% 55%, 60%, 65%, 70%, 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93% 94%, 95%, 96, 97%, 98%, 99%, or up to 100% when compared to a control cell. 
     The genetically-modified cells of the invention are capable of expansion in a subject following administration. Here, expansion is considered an increase in cell number resulting from proliferation and division in vivo. The degree of expansion depends, in part, on the subject&#39;s response to the cells; for example, if the cells are identified as allogeneic and/or non-self, the subject&#39;s immune system may reduce the ability of the cells to expand and further reduce persistence of the cells post-administration. Thus, in some examples, genetically-modified cells of the invention can exhibit an increase in expansion in a subject that is about 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100% 150%, 200%, 250%, 200%, 350%, 400%, 450%, 500%, up to 1000%, or more, when compared to a control cell. Expansion in vivo can be determined post-administration by any method known in the art. Persistence time of a genetically-modified cell in a subject can be considered, for example, as the amount of time post-administration of the cell that it can be detected in the subject by any method known in the art. In some examples, a genetically-modified cell of the invention will have an increase in persistence time that is up to about 1 week, 2 weeks, 3, weeks, 4 weeks, 5 weeks, 6 weeks, 7 weeks, 2 months, 3 months, 4 months, 5 months, 6 months, 1 year, or more, longer than a control cell. 
     Allogenicity can be determine by any method known in the art, such as those methods described further herein. The genetically-modified cells of the invention can exhibit a reduction in allogenicity of about 5%, 10%, 20%, 30%, 40%, 50% 55%, 60%, 65%, 70%, 75%, 80%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93% 94%, 95%, 96, 97%, 98%, 99%, or up to 100% when compared to a control cell. 
     2.6 Methods for Producing Genetically-Modified Cells 
     The present disclosure provides methods for producing genetically-modified cells comprising the nucleic acid molecule of the invention described herein. In specific embodiments, methods are provided for modifying the cell to comprise the nucleic acid molecule. In different aspects of the present disclosure, the nucleic acid molecule is integrated into the genome of the cell or, alternatively, is not integrated into the genome of the cell. 
     In some embodiments, the nucleic acid molecule is introduced into a cell using any technology known in the art. In specific embodiments, vectors or expression cassettes comprising the nucleic acid molecule disclosed herein is introduced into a cell using a viral vector. Such vectors are known in the art and include lentiviral vectors, adenoviral vectors, and adeno-associated virus (AAV) vectors (reviewed in Vannucci, et al. (2013  New Microbiol.  36:1-22). Recombinant AAV vectors useful in the present disclosure can have any serotype that allows for transduction of the virus into the cell and insertion of the nuclease gene into the cell and, in particular embodiments, into the cell genome. In particular embodiments, recombinant AAV vectors have a serotype of AAV2, AAV6, or AAV8. Recombinant AAV vectors can also be self-complementary such that they do not require second-strand DNA synthesis in the host cell (McCarty, et al. (2001)  Gene Ther.  8:1248-54). 
     In some embodiments, nucleic acid molecules disclosed herein are delivered into a cell in the form of DNA (e.g., circular or linearized plasmid DNA or PCR products) and/or via a viral vector. In some embodiments, the nucleic acid molecule disclosed herein is coupled covalently or non-covalently to a nanoparticle or encapsulated within such a nanoparticle using methods known in the art (Sharma, et al. (2014)  Biomed Res Int.  2014). A nanoparticle is a nanoscale delivery system whose length scale is &lt;1 □m, preferably &lt;100 nm. Such nanoparticles may be designed using a core composed of metal, lipid, polymer, or biological macromolecule, and multiple copies of the nucleic acid molecules can be attached to or encapsulated with the nanoparticle core. This increases the copy number of the DNA that is delivered to each cell and, so, increases the intracellular expression to maximize the likelihood that the encoded products will be expressed. The surface of such nanoparticles may be further modified with polymers or lipids (e.g., chitosan, cationic polymers, or cationic lipids) to form a core-shell nanoparticle whose surface confers additional functionalities to enhance cellular delivery and uptake of the payload (Jian et al. (2012)  Biomaterials.  33(30): 7621-30). Nanoparticles may additionally be advantageously coupled to targeting molecules to direct the nanoparticle to the appropriate cell type and/or increase the likelihood of cellular uptake. Examples of such targeting molecules include antibodies specific for cell surface receptors and the natural ligands (or portions of the natural ligands) for cell surface receptors. 
     In some embodiments, the nucleic acid molecule disclosed herein can be encapsulated within liposomes or complexed using cationic lipids (see, e.g., LIPOFECTAMINE, Life Technologies Corp., Carlsbad, Calif.; Zuris et al. (2015) Nat  Biotechnol.  33: 73-80; Mishra et al. (2011)  J Drug Deliv.  2011:863734). The liposome and lipoplex formulations can protect the payload from degradation, and facilitate cellular uptake and delivery efficiency through fusion with and/or disruption of the cellular membranes of the cells. 
     In some embodiments, the nucleic acid molecule disclosed herein can be encapsulated within polymeric scaffolds (e.g., PLGA) or complexed using cationic polymers (e.g., PEI, PLL) (Tamboli et al. (2011)  Ther Deliv.  2(4): 523-536). In some embodiments, the nucleic acid molecule disclosed herein can be combined with amphiphilic molecules that self-assemble into micelles (Tong et al. (2007)  J Gene Med.  9(11): 956-66). Polymeric micelles may include a micellar shell formed with a hydrophilic polymer (e.g., polyethyleneglycol) that can prevent aggregation, mask charge interactions, and reduce nonspecific interactions outside of the cell. 
     In some embodiments, the nucleic acid molecule disclosed herein can be formulated as an emulsion for delivery to the cell. The term “emulsion” refers to, without limitation, any oil-in-water, water-in-oil, water-in-oil-in-water, or oil-in-water-in-oil dispersions or droplets, including lipid structures that can form as a result of hydrophobic forces that drive apolar residues (e.g., long hydrocarbon chains) away from water and polar head groups toward water, when a water immiscible phase is mixed with an aqueous phase. These other lipid structures include, but are not limited to, unilamellar, paucilamellar, and multilamellar lipid vesicles, micelles, and lamellar phases. Emulsions are composed of an aqueous phase and a lipophilic phase (typically containing an oil and an organic solvent). Emulsions also frequently contain one or more surfactants. Nanoemulsion formulations are well known, e.g., as described in US Patent Application Nos. 2002/0045667 and 2004/0043041, and U.S. Pat. Nos. 6,015,832, 6,506,803, 6,635,676, and 6,559,189, each of which is incorporated herein by reference in its entirety. 
     In some embodiments, the nucleic acid molecule disclosed herein can be covalently attached to, or non-covalently associated with, multifunctional polymer conjugates, DNA dendrimers, and polymeric dendrimers (Mastorakos et al. (2015)  Nanoscale.  7(9): 3845-56; Cheng et al. (2008)  J Pharm Sci.  97(1): 123-43). The dendrimer generation can control the payload capacity and size, and can provide a high payload capacity. Moreover, display of multiple surface groups can be leveraged to improve stability and reduce nonspecific interactions. 
     Methods of introducing and expressing genes into a cell are known in the art. In the context of an expression vector, the vector can be readily introduced into a host cell, e.g., mammalian, bacterial, yeast, or insect cell by any method in the art. For example, the expression vector can be transferred into a host cell by physical, chemical, or biological means. Physical methods for introducing a polynucleotide into a host cell include calcium phosphate precipitation, lipofection, particle bombardment, microinjection, electroporation, and the like. Methods for producing cells comprising vectors and/or exogenous nucleic acids are well-known in the art. See, for example, Sambrook et al. (2001, Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory, New York). A preferred method for the introduction of a polynucleotide into a host cell is calcium phosphate transfection. Biological methods for introducing a polynucleotide of interest into a host cell include the use of DNA and RNA vectors. Viral vectors, and especially retroviral vectors, have become the most widely used method for inserting genes into mammalian, e.g., human cells. Other viral vectors can be derived from lentivirus, poxviruses, herpes simplex virus I, adenoviruses and adeno-associated viruses, and the like. See, for example, U.S. Pat. Nos. 5,350,674 and 5,585,362. Chemical means for introducing a polynucleotide into a host cell include colloidal dispersion systems, such as macromolecule complexes, nanocapsules, microspheres, beads, and lipid-based systems including oil-in-water emulsions, micelles, mixed micelles, and liposomes. An exemplary colloidal system for use as a delivery vehicle in vitro and in vivo is a liposome (e.g., an artificial membrane vesicle). 
     2.7 Pharmaceutical Compositions 
     In some embodiments, the present disclosure provides a pharmaceutical composition comprising a genetically-modified cell, or a population of genetically-modified cells, of the present disclosure and a pharmaceutically-acceptable carrier. Such pharmaceutical compositions can be prepared in accordance with known techniques. See, e.g., Remington,  The Science And Practice of Pharmacy  (21st ed. 2005). In the manufacture of a pharmaceutical formulation according to the present disclosure, cells are typically admixed with a pharmaceutically acceptable carrier and the resulting composition is administered to a subject. The carrier must, of course, be acceptable in the sense of being compatible with any other ingredients in the formulation and must not be deleterious to the subject. In some embodiments, pharmaceutical compositions of the present disclosure further comprises one or more additional agents useful in the treatment of a disease in the subject. In additional embodiments, where the genetically-modified cell is a genetically-modified human T cell or NK cell (or a cell derived therefrom), pharmaceutical compositions of the present disclosure further include biological molecules, such as cytokines (e.g., IL-2, IL-7, IL-15, and/or IL-21), which promote in vivo cell proliferation and engraftment. Pharmaceutical compositions comprising genetically-modified cells of the present disclosure can be administered in the same composition as an additional agent or biological molecule or, alternatively, can be co-administered in separate compositions. 
     In some embodiments, the pharmaceutical compositions of the present disclosure are useful for treating any disease state that can be targeted by T cell adoptive immunotherapy. In a particular embodiment, the pharmaceutical compositions of the present disclosure are useful as immunotherapy in the treatment of cancer. Such cancers can include, without limitation, carcinoma, lymphoma, sarcoma, blastomas, leukemia, cancers of B-cell origin, breast cancer, gastric cancer, neuroblastoma, osteosarcoma, lung cancer, melanoma, prostate cancer, colon cancer, renal cell carcinoma, ovarian cancer, rhabdomyo sarcoma, leukemia, and Hodgkin&#39;s lymphoma. In certain embodiments, cancers of B-cell origin include, without limitation, B-lineage acute lymphoblastic leukemia, B-cell chronic lymphocytic leukemia, and B-cell non-Hodgkin&#39;s lymphoma. Non-limiting examples of cancer which may be treated with the pharmaceutical compositions and medicaments of the present disclosure are carcinomas, lymphomas, sarcomas, melanomas, blastomas, leukemias, and germ cell tumors, including but not limited to cancers of B-cell origin, neuroblastoma, osteosarcoma, prostate cancer, renal cell carcinoma, rhabdomyosarcoma, liver cancer, gastric cancer, bone cancer, pancreatic cancer, skin cancer, cancer of the head or neck, breast cancer, lung cancer, cutaneous or intraocular malignant melanoma, renal cancer, uterine cancer, ovarian cancer, colorectal cancer, colon cancer, rectal cancer, cancer of the anal region, stomach cancer, testicular cancer, uterine cancer, carcinoma of the fallopian tubes, carcinoma of the endometrium, carcinoma of the cervix, carcinoma of the vagina, carcinoma of the vulva, non-Hodgkin&#39;s lymphoma, cancer of the esophagus, cancer of the small intestine, cancer of the endocrine system, cancer of the thyroid gland, cancer of the parathyroid gland, cancer of the adrenal gland, sarcoma of soft tissue, cancer of the urethra, cancer of the penis, solid tumors of childhood, lymphocytic lymphoma, cancer of the bladder, cancer of the kidney or ureter, carcinoma of the renal pelvis, neoplasm of the central nervous system (CNS), primary CNS lymphoma, tumor angiogenesis, spinal axis tumor, brain stem glioma, pituitary adenoma, Kaposi&#39;s sarcoma, epidermoid cancer, squamous cell cancer, environmentally induced cancers including those induced by asbestos, multiple myeloma, Hodgkin lymphoma, non-Hodgkin&#39;s lymphomas, acute myeloid lymphoma, chronic myelogenous leukemia, chronic lymphoid leukemia, immunoblastic large cell lymphoma, acute lymphoblastic leukemia, mycosis fungoides, anaplastic large cell lymphoma, and T-cell lymphoma, and any combinations of said cancers. In certain embodiments, cancers of B-cell origin include, without limitation, B-lineage acute lymphoblastic leukemia, B-cell chronic lymphocytic leukemia, B-cell lymphoma, diffuse large B cell lymphoma, pre-B ALL (pediatric indication), mantle cell lymphoma, follicular lymphoma, marginal zone lymphoma, Burkitt&#39;s lymphoma, and B-cell non-Hodgkin&#39;s lymphoma. 
     In some of these embodiments wherein cancer is treated with the presently disclosed genetically-modified cells, the subject administered the genetically-modified cells is further administered an additional therapeutic, such as radiation, surgery, or a chemotherapeutic agent. 
     The invention further provides a population of genetically-modified cells comprising a plurality of genetically-modified cells described herein. Such genetically-modified cells can comprise in their genome a nucleic acid molecule encoding an engineered antigen receptor, such as a chimeric antigen receptor or exogenous T cell receptor, and an inhibitory nucleic acid molecule, such as an RNA interference molecule. Such genetically-modified cells can also comprise in their genome a nucleic acid molecule encoding an engineered antigen receptor, such as a chimeric antigen receptor or exogenous T cell receptor, and have reduced cell surface expression of beta-2 microglobulin, MHC class I molecules, or CD52, without necessarily comprising the particular nucleic acid molecule of the invention. Thus, in various embodiments of the invention, a population of genetically-modified cells is provided wherein at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or up to 100%, of cells in the population are a genetically-modified cell described herein. 
     2.8 Methods of Administering Genetically-Modified Cells 
     Another aspect disclosed herein is the administration of the genetically-modified cells of the present disclosure to a subject in need thereof. In particular embodiments, the pharmaceutical compositions described herein are administered to a subject in need thereof. For example, an effective amount of a genetically-modified cell or population of genetically-modified cells of the invention which express a cell surface chimeric antigen receptor or exogenous T cell receptor, can be administered to a subject having a disease. In particular embodiments, the disease can be cancer, such as a cancer of B-cell origin. Thus, the present disclosure also provides a method for providing a T cell-mediated immune response to a target cell population or tissue in a mammal, comprising the step of administering to the mammal a CAR T cell, wherein the CAR comprises an extracellular ligand-binding domain that specifically interacts with a predetermined target, such as a tumor antigen, and an intracellular domain that comprises at least one signaling domain, such as CD3ξ, and optionally one or more co-stimulatory signaling domains. The administered CAR T cells are able to reduce the proliferation, reduce the number, or kill target cells in the recipient. Unlike antibody therapies, genetically-modified cells of the present disclosure are able to replicate and expand in vivo, resulting in long-term persistence that can lead to sustained control of a disease. 
     In examples wherein the inhibitory nucleic acid molecule is against human beta-2 microglobulin or a component of the MHC class I molecule, or wherein beta-2 microglobulin or MHC class I molecules are otherwise reduced, expansion and/or persistence of such CAR T cells can be enhanced in the subject when compared to a CAR T cell having wild-type levels of beta-2 microglobulin or MHC class I molecules, or no cell surface beta-2 microglobulin or MHC class I expression. Further, allogenicity of the CAR T cell can be reduced when compared to a CAR T cell having a wild-type level of cell surface expression of beta-2 microglobulin and MHC class I molecules. These advantageous characteristics result from the incomplete reduction of cell surface beta-2 microglobulin (and consequently MHC class I molecules) to a small percentage of wild-type expression, which allows for reduced allogenicity but avoidance of NK cells which would otherwise target a beta-2 microglobulin-negative cell. 
     Examples of possible routes of administration include parenteral, (e.g., intravenous (IV), intramuscular (IM), intradermal, subcutaneous (SC), or infusion) administration. Moreover, the administration may be by continuous infusion or by single or multiple boluses. In specific embodiments, one or both of the agents is infused over a period of less than about 12 hours, 6 hours, 4 hours, 3 hours, 2 hours, or 1 hour. In still other embodiments, the infusion occurs slowly at first and then is increased over time. 
     In some embodiments, a genetically-modified eukaryotic cell or population thereof of the present disclosure targets a tumor antigen for the purposes of treating cancer. Such cancers can include, without limitation, carcinoma, lymphoma, sarcoma, blastomas, leukemia, cancers of B cell origin, breast cancer, gastric cancer, neuroblastoma, osteosarcoma, lung cancer, melanoma, prostate cancer, colon cancer, renal cell carcinoma, ovarian cancer, rhabdomyosarcoma, leukemia, and Hodgkin&#39;s lymphoma. In specific embodiments, cancers and disorders include but are not limited to pre-B ALL (pediatric indication), adult ALL, mantle cell lymphoma, diffuse large B cell lymphoma, salvage post allogenic bone marrow transplantation, and the like. These cancers can be treated using a combination of CARS that target, for example, CD19, CD20, CD22, and/or ROR1. In some non-limiting examples, a genetically-modified eukaryotic cell or population thereof of the present disclosure targets carcinomas, lymphomas, sarcomas, melanomas, blastomas, leukemias, and germ cell tumors, including but not limited to cancers of B-cell origin, neuroblastoma, osteosarcoma, prostate cancer, renal cell carcinoma, rhabdomyosarcoma, liver cancer, gastric cancer, bone cancer, pancreatic cancer, skin cancer, cancer of the head or neck, breast cancer, lung cancer, cutaneous or intraocular malignant melanoma, renal cancer, uterine cancer, ovarian cancer, colorectal cancer, colon cancer, rectal cancer, cancer of the anal region, stomach cancer, testicular cancer, uterine cancer, carcinoma of the fallopian tubes, carcinoma of the endometrium, carcinoma of the cervix, carcinoma of the vagina, carcinoma of the vulva, non-Hodgkin&#39;s lymphoma, cancer of the esophagus, cancer of the small intestine, cancer of the endocrine system, cancer of the thyroid gland, cancer of the parathyroid gland, cancer of the adrenal gland, sarcoma of soft tissue, cancer of the urethra, cancer of the penis, solid tumors of childhood, lymphocytic lymphoma, cancer of the bladder, cancer of the kidney or ureter, carcinoma of the renal pelvis, neoplasm of the central nervous system (CNS), primary CNS lymphoma, tumor angiogenesis, spinal axis tumor, brain stem glioma, pituitary adenoma, Kaposi&#39;s sarcoma, epidermoid cancer, squamous cell cancer, environmentally induced cancers including those induced by asbestos, multiple myeloma, Hodgkin lymphoma, non-Hodgkin&#39;s lymphomas, acute myeloid lymphoma, chronic myelogenous leukemia, chronic lymphoid leukemia, immunoblastic large cell lymphoma, acute lymphoblastic leukemia, mycosis fungoides, anaplastic large cell lymphoma, and T-cell lymphoma, and any combinations of said cancers. In certain embodiments, cancers of B-cell origin include, without limitation, B-lineage acute lymphoblastic leukemia, B-cell chronic lymphocytic leukemia, B-cell lymphoma, diffuse large B cell lymphoma, pre-B ALL (pediatric indication), mantle cell lymphoma, follicular lymphoma, marginal zone lymphoma, Burkitt&#39;s lymphoma, multiple myeloma, and B-cell non-Hodgkin&#39;s lymphoma. 
     When an “effective amount” or “therapeutic amount” is indicated, the precise amount of the compositions of the present disclosure to be administered can be determined by a physician with consideration of individual differences in age, weight, tumor size (if present), extent of infection or metastasis, and condition of the patient (subject). In some embodiments, a pharmaceutical composition comprising the genetically-modified cells described herein is administered at a dosage of 104 to 109 cells/kg body weight, including all integer values within those ranges. In further embodiments, the dosage is 105 to 106 cells/kg body weight, including all integer values within those ranges. In some embodiments, cell compositions are administered multiple times at these dosages. The cells can be administered by using infusion techniques that are commonly known in immunotherapy (see, e.g., Rosenberg et al., New Eng. J. of Med. 319:1676, 1988). The optimal dosage and treatment regime for a particular patient can readily be determined by one skilled in the art of medicine by monitoring the patient for signs of disease and adjusting the treatment accordingly. 
     In some embodiments, administration of genetically-modified cells of the present disclosure reduce at least one symptom of a target disease or condition. For example, administration of genetically-modified cells of the present disclosure can reduce at least one symptom of a cancer, such as cancers of B-cell origin. Symptoms of cancers, such as cancers of B-cell origin, are well known in the art and can be determined by known techniques. 
     EXPERIMENTAL 
     This disclosure is further illustrated by the following examples, which should not be construed as limiting. Those skilled in the art will recognize, or be able to ascertain, using no more than routine experimentation, numerous equivalents to the specific substances and procedures described herein. Such equivalents are intended to be encompassed in the scope of the claims that follow the examples below. 
     EXAMPLE 1 
     NK Cell Killing of B2M Knockout Primary Human T Cells 
     1. Methods and Materials 
     Primary human T cells were stimulated for 3 days using ImmunoCult anti-CD2/CD3/CD28 (StemCell Technologies) in the presence of IL-2 (Gibco) in XVIVO-15 medium (Lonza) supplemented with 5% fetal bovine serum. RNA encoding B2M13-1433 479 nuclease was introduced into the T cells using the 4D Nucleofector (Lonza). Cells were cultured in the presence of IL-2 for 6 days before magnetic depletion of remaining B2M +  cells using biotinylated anti-human B2M (BioLegend) and a Biotin Selection Kit (StemCell Technologies). NK cells were isolated from PBMC samples of the same donor using a CD56 positive selection kit (StemCell Technologies). Daudi cells were purchased from ATCC. Daudi cells are naturally B2M −  and are reported to be highly sensitive to NK cytolysis. All target cells were labeled with 1 uM CellTrace Violet (LifeTechnologies) to distinguish them from effectors in mixed cultures. Isolated NK cells were mixed with either autologous B2M +  T cell targets (negative control for NK cytolysis), Daudi targets (positive control for NK cytolysis), or autologous B2M KO T cell targets (experimental sample) at effector:target ratios of 2:1, 1:1, 0.5:1, and 0:1. Killing was assessed after 2h of co-culture. Killing by NK cells was measured by staining with CaspACE—VAD-FMK (Promega). 
     2. Results 
     NK cells elicited only dim VAD-FMK signals in autologous B2M +  targets, indicating low levels of apoptosis induction by active caspases ( FIGS. 2A-2D  Daudi cells (71-83%,  FIGS. 2I-2L ), indicating extensive caspase cascade activation. Similarly, B2M −  autologous T cells returned high VAD-FMK signals in response to NK encounter (19-47%,  FIG. 2  E-H), indicative of caspase-mediated apoptosis induction. A graphical summary of these results appears in  FIG. 3 . 
     3.Conclusions 
     Complete knockout of cell surface B2M using engineered meganucleases sensitizes primary human T cells to NK cell attack and killing. 
     EXAMPLE 2 
     Characterization of Candidate shRNAs Against B2M and Effect of B2M Knockdown on NK Cell Killing of Primary Human T Cells 
     1. Materials and Methods 
     Five Mission-shRNA lentiviral transfer plasmids encoding different B2M targeting sequences were purchased from Sigma-Aldrich. Second-generation lentiviral vectors were produced in-house using Lenti-X 293T cells (ClonTech) and a triple transfection method (Lipofectamine 2000—Thermo-Fisher). T cells were prepared for lentiviral transduction by stimulating for 3 days with ImmunoCult anti-CD2/CD3/CD28 as in Example 1. Transduction was carried out in the presence of 5 uM polybrene (Sigma-Aldritch) and transduced cells were selected with puromycin (InVivoGen) beginning at 48 h post-transduction and concluding 72h following drug addition. Selected cells were expanded for 5 days in IL-2 supplemented medium before a flow cytometric analysis of B2M surface expression to determine the extent of knockdown. Cultures receiving B2M shRNAs were used as targets in NK and CTL killing assays. The NK killing assays were carried out as described in Example 1, but the K562 cell line was used as the positive control for NK cytolysis. For the CTL killing assay, CD8+ T cells from a donor unrelated to the donor of the target cells were isolated and used as effectors. The NK killing assay was carried out for 2 h and the CTL assay was carried out for 6 h. For both assays, target cells were labeled with 1 uM CellTrace Violet (Life Technologies), and killing was measured using CaspACE-VAD-FMK (Promega). 
     2. Results 
     Five shRNAs were screened in human T cells for interference with B2M expression. Two sequences did not reduce the mean fluorescence intensity of B2M in a cytometric analysis (not shown). Three shRNA sequences did reduce the 1MFI of B2M expression, with sequence 254 and 255 reducing MFI by approximately 50% and sequence 472 reducing the MFI by approximately 95% ( FIG. 4 ). 
     CTL and NK killing of targets exhibiting altered B2M expression was next measured. NK cells, but not CTLs induced caspase activation (measured by VAD-FMK signal) in Class I deficient K562 cells (46% vs. 5%— FIGS. 5A and 5B ). Conversely, CTLs induced caspase activation (32%) in mismatched B2M +  T cells while NK cells induced a signal in a lower frequency of mismatched T cells (14%) ( FIGS. 5C and 5D ). In T cell targets exhibiting a 50% reduction in B2M antigen density, NK cells elicited caspase activity in 17% of targets while mismatched CTLs did so in 36% of targets ( FIGS. 6A and 6B ). In T cell targets exhibiting a 95% knockdown of B2M levels, NK cells elicited caspase activation in 16% of targets, while mismatched CTLs did so in 20.8% of targets ( FIGS. 5  C and D). 
     3. Conclusions 
     B2M expression can be effectively knocked down using shRNA delivered by a viral vector. Using caspase (VAD-FMK) activity to measure apoptosis induction in target cells by NK cells or CTLs, it was determined that B2M knockdown does not alter a target&#39;s susceptibility to NK cytolysis, as both B2M knockdown targets exhibited the same VAD-FMK frequency as un-manipulated targets, and less VAD-FMK signal than K562 targets. In addition, B2M knockdown confers some protection against CTL cytolysis, as the frequency of VAD-FMK+targets in the shRNA 472 group was approximately half the frequency observed in the positive control. In fact, there was a direct relationship between the degree of knockdown and the degree of protection against CTL activity from NK cells. 
     EXAMPLE 3 
     Production and Characterization of CAR T Cells Utilizing shRNA to Reduce Cell Surface Expression of B2M 
     1. Materials and Methods 
     A number of constructs were prepared comprising an anti-CD19 CAR coding sequence and an shRNA against B2M. These are illustrated in  FIG. 7A -7F and are provided in SEQ ID NOs: 18-23. CAR constructs 7007 and 7217 (SEQ ID NOs: 18 and 19) comprise the CAR coding sequence and the shRNA472 sequence in the same 5′ to 3′ orientation. CAR constructs 7008 and 7218 (SEQ ID NOs: 20 and 21) comprise the CAR coding sequence in the 3′ to 5′ orientation, and shRNA472 sequence in the 5′ to 3′ orientation (i.e., tail-to-tail). CAR constructs 7009 and 7219 (SEQ ID NOs: 22 and 23) comprise both the CAR coding sequence and the shRNA472 sequence in the 3′ to 5′ orientation. The 5′ and 3′ homology arms flanking the CAR coding sequence and the shRNA472 sequence have homology to regions upstream and downstream of the TRC 1-2 recognition sequence in the TRAC locus. 
     CAR T cells will be prepared using primary donor human T cells transduced with recombinant AAV vectors comprising one of the CAR/shRNA constructs above, with simultaneous nucleofection of mRNA encoding the TRC 1-2x.87EE to induce a double-strand break at the TRC 1-2 recognition sequence and promote targeted insertion of the construct into the genome of the T cells. Beta-2 microglobulin expression will be determined as described above to determine which orientation of the first and second expression cassettes will result in the highest and/or the most consistent CAR expression, along with the most consistent level of B2M knockdown on the cell surface. 
     CAR T cells produced with certain constructs will be evaluated in both the allogenicity and NK cell killing assays previously described above. Further, CAR T cells produced using the disclosed constructs will be evaluated in various stress tests, in which the CAR T cells are repeatedly exposed to antigen in order to determine changes in cell proliferation/expansion and cytotoxic potential. CAR T cells produced using the disclosed constructs will also be utilized with in vivo tumor models to determine their ability to clear tumor cells in an animal and to evaluate their ability to persist in vivo. It is expected, based on the Examples described herein, that CAR T cells having a reduced but incomplete knockdown of cell surface beta-2 microglobulin will have greater persistence and/or enhanced expansion in vivo when compared to CAR T cells which are completely B2M-negative and may be susceptible to NK cell killing. 
     In a particular study, CAR T cells were prepared that are TCR-negative, CAR-positive, and have reduced cell surface expression of B2M. CAR T cells were prepared using donor templates that comprise a promoter-driven CAR coding sequence, a T2A element, and one or multiple promoter-driven B2M shRNA cassettes. In this study, an apheresis sample was drawn from a healthy, informed, and compensated donor, and the T cells were enriched using the CD3 positive selection kit II in accord with the manufacturer&#39;s instructions (Stem Cell Technologies). T cells were activated using ImmunoCult T cell stimulator (anti-CD2/CD3/CD28—Stem Cell Technologies) in X-VIVO 15 medium (Lonza) supplemented with 5% fetal bovine serum and 10 ng/ml IL-2 (Gibco). After 3 days of stimulation, cells were collected and samples of 1e6 cells were electroporated with the following mixture of nucleic acid species using the Lonza 4D NucleoFector.
         1 μg mRNA encoding the TRC 1-2x.87EE meganuclease which produces a double-strand break in Exon 1 of the T cell receptor alpha constant region gene   1.5 μl of 100 mM siRNA specific for TMEM173 (STING)   1 μg of linearized plasmid DNA comprising a donor template In this experiment, three different CAR constructs were analyzed for their ability to knock down B2M surface expression. All three constructs use homology to genomic regions flanking the TRC 1-2x.87EE binding site (referred to as the TRC 1-2 recognition site) to direct targeted insertion into the T cell receptor alpha constant region locus, and they all express a CAR that comprises a CD34 epitope tag (for detection). Construct 7002 (SEQ ID NO: 11) does not encode an shRNA gene. Construct 7008 (SEQ ID NO: 20) encodes one copy of shRNA472. Construct 7029 (SEQ ID NO: 24) encodes two copies of this shRNA cassette. Expression from each shRNA cassette is driven by a U6 promoter.       

     Cell cultures were maintained for 10 additional days in X-VIVO15 medium supplemented with 5% FBS and 30 ng/m1 of IL-2. On d4, 7, and 10 post-nucleofection, the cultures were sampled and analyzed for surface expression of CD3 (anti-CD3-BV711, BioLegend), CD34 (anti-CD34-PE, LifeTechnologies), and B2M (anti-B2M-APC, BioLegend). Flow cytometry data were acquired on a Beckman-Coulter CytoFLEX-LX. 
     2. Results 
     B2M surface levels were measured in samples nucleofected with a control CAR construct (7002) or with CAR constructs expressing one (7008) or two (7029) copies of B2M-specific shRNA ( FIG. 12 ). When comparing the CD3-/CD34+ populations in 7002 (control) and 7008 (single shRNA) expressing cells, 7008 expressing cells were observed to display slightly lower levels of surface B2M ( FIG. 12A ). Notably, cells nucleofected with construct 7029 (two shRNA copies) displayed approximately half of the amount of B2M displayed on the surface of control cells (7002) ( FIG. 12B ). This observation was specific to the CD3-/CD34+ population, but was not observed in the CD3-/CD34− population ( FIG. 12C ). 
     3. Conclusions 
     A pre-screened B2M-targeting shRNA can knock down B2M expression levels on the surface of cells into which the construct has been delivered (via targeted insertion into the T cell receptor alpha constant region locus). Due to the high abundance of B2M transcripts, these data suggest that a single shRNA copy can be sufficient for low levels of B2M knockdown, whereas multiple copies of the shRNA cassette may be required to achieve more significant knockdown. 
     EXAMPLE 4 
     Production and Characterization of CAR T Cells Utilizing shRNA to Reduce Cell Surface Expression of B2M 
     1. Materials and Methods 
     A number of constructs were prepared comprising an anti-CD19 CAR coding sequence and an shRNA against B2M. These are illustrated in  FIG. 7A-7F  and are provided in SEQ ID NOs: 18-23. CAR constructs 7007 and 7217 (SEQ ID NOs: 18 and 19) comprise the CAR coding sequence and the shRNA472 sequence in the same 5′ to 3′ orientation. CAR constructs 7008 and 7218 (SEQ ID NOs: 20 and 21) comprise the CAR coding sequence in the 3′ to 5′ orientation, and shRNA472 sequence in the 5′ to 3′ orientation (i.e., tail-to-tail). CAR constructs 7009 and 7219 (SEQ ID NOs: 22 and 23) comprise both the CAR coding sequence and the shRNA472 sequence in the 3′ to 5′ orientation. CAR constructs 7056, 7059, and 7060 contain modified versions of the U6-shRNA gene cassette. A cloning site that was located between the U6 promoter and the hairpin sequence in constructs 7007-7009, and in 7217-7219 was removed. Construct 7056 comprises the CAR coding sequence and the shRNA472 sequence in the 3′ to 5′ orientation. Construct 7056 comprises the CAR coding sequence in 3′ to 5′ orientation, and the shRNA472 sequence in the 5′ to 3′ orientation (tail-to-tail). Construct 7060 comprises the CAR coding sequence in 3′ to 5′ orientation and two copies of the U6-shRNA472 sequence in 5′ to 3′ orientation. The 5′ and 3′ homology arms flanking the CAR coding sequence and the shRNA472 sequence have homology to regions upstream and downstream of the TRC 1-2 recognition sequence in the T cell receptor alpha constant locus. 
     In a particular study, CAR T cells were prepared that are TCR-negative, CAR-positive, and have reduced cell surface expression of B2M. CAR T cells were prepared using donor templates that comprise a promoter-driven CAR coding sequence, and one or multiple promoter-driven B2M shRNA cassettes. In this study, an apheresis sample was drawn from a healthy, informed, and compensated donor, and the T cells were enriched using the CD3 positive selection kit II in accord with the manufacturer&#39;s instructions (Stem Cell Technologies). T cells were activated using ImmunoCult T cell stimulator (anti-CD2/CD3/CD28—Stem Cell Technologies) T cells were activated using ImmunoCult T cell simulator (anti-CD2/CD3/CD28—Stem Cell Technologies( in X-VIVO 15 medium (Lonza) supplemented with 5% fetal bovine serum and 10 ng/ml IL-2 (Gibco). After 3 days of stimulation, cells were collected and samples of le6 cells were electroporated with the following mixture of nucleic acid species using the Lonza 4D NucleoFector.
         1 μg mRNA encoding the TRC 1-2x.87EE meganuclease which produces a double-strand break in Exon 1 of the T cell receptor alpha constant region gene   1.5 μl of 100 mM siRNA specific for TMEM173 (STING)   1 μg of linearized plasmid DNA comprising a donor template
 
In this experiment, four different CAR constructs were analyzed for their ability to knock down B2M surface expression. All four constructs use homology to genomic regions flanking the TRC 1-2x.87EE recognition site to direct targeted insertion into the T cell receptor alpha constant region locus, and they all express a CAR that comprises a CD34 epitope tag (for detection). Construct 7002 (SEQ ID NO: 11) does not encode an shRNA gene. Construct 7056 (SEQ ID NO: 25) encodes one copy of shRNA472, and both cassettes are in the 3′ to 5′ orientation (head-to-tail). Construct 7059 (SEQ ID NO: 26) encodes one copy of this shRNA cassette, with the CAR expression cassette in a 3′ to 5′ orientation, and the shRNA472 cassette in a 5′ to 3′ orientation (tail-to-tail). Construct 7060 (SEQ ID NO: 27) is in the same orientation as construct 7059 but encodes two copies of the shRNA472 cassette (tail-to-tail). Expression from each shRNA cassette is driven by a U6 promoter. Cell cultures were maintained for up to 10 additional days in X-VIVO15 medium supplemented with 5% FBS and 30 ng/m1 of IL-2. On d4, 7, and/or 10 post-nucleofection, the cultures were sampled and analyzed for surface expression of CD3 (anti-CD3-BV711, BioLegend), CD34 (anti-CD34-PE, or APC, LifeTechnologies), B2M (anti-B2M-APC, or PE, BioLegend), and/or HLA-A, B, and C (clone W6/32, BV605). Flow cytometry data were acquired on a Beckman-Coulter CytoFLEX-LX.
       

     2. Results 
     B2M surface levels were measured in samples nucleofected with a control CAR construct (7002) or with CAR constructs expressing one (7056 or 7059) or two (7060) copies of B2M-specific shRNA in either head-to-tail (7056) or tail-to-tail (7059, 7060) configurations. A restriction digest site that was present in previous constructs between the U6 promoter and the shRNA sequence was been removed from these shRNA472 vectors. It was hypothesized that the palindromic restriction digest site interfered with the efficacy of the constructs and the ability of the shRNA to knock down B2M. 
     When comparing the CD3−/CD34+ populations in 7002 (control) and 7056 (single shRNA) expressing cells, 7056 expressing cells were observed to display lower levels of surface B2M (77% knockdown) ( FIG. 13A ). Cells nucleofected with 7059 (single copy, tail-to-tail) displayed a 90.1% knockdown of B2M relative to 7002 control cells ( FIG. 13B ), while 7060 nucleofection (two copies, tail-to-tail) resulted in a 92% knockdown relative to 7002 controls ( FIG. 13C ). 
     3. Conclusions 
     A pre-screened B2M-targeting shRNA can knock down B2M expression levels on the surface of cells into which the construct has been delivered (via targeted insertion into the T cell receptor alpha constant region locus). Removing the cloning site between the U6 promoter and the hairpin sequence improves the efficiency with which B2M is knocked down. 7008 (tail-to-tail, one shRNA472 cassette— FIG. 12A ) supports minimal B2M knockdown while 7059 (one cassette, tail-to-tail— FIG. 13B ) supports greater than 90% knockdown. As was observed using a CD52-specific shRNA, superior knockdown was observed when the CAR promoter and the shRNA promoter were oriented in different directions (tail-to-tail configuration). Adding a second shRNA sequence did not provide any noticeable benefit (92% versus 90.1% knockdown). 
     EXAMPLE 5 
     Production and Characterization of CAR T Cells Utilizing shRNA to Reduce Cell Surface Expression of B2M 
     1. Materials and Methods 
     In this study, an apheresis sample was drawn from a healthy, informed, and compensated donor, and the T cells were enriched using the CD3 positive selection kit II in accord with the manufacturer&#39;s instructions (Stem Cell Technologies). T cells were activated using ImmunoCult T cell stimulator (anti-CD2/CD3/CD28—Stem Cell Technologies) in X-VIVO 15 medium (Lonza) supplemented with 5% fetal bovine serum and 10 ng/ml IL-2 (Gibco). After 3 days of stimulation, cells were collected and samples of 1e6 cells were electroporated with lug of RNA encoding the TRC 1-2L.1592 meganuclease, which recognizes and cleaves the TRC 1-2 recognition sequence in the T cell receptor alpha constant locus, and were transduced with AAV packaged with construct 7056 at an MOI of 25000 viral genomes/cell. 
     Cell cultures were maintained for up to 10 additional days in X-VIVO15 medium supplemented with 5% FBS and 30 ng/ml of IL-2. On day 4, 7, and/or 10 post-nucleofection, the cultures were sampled and analyzed for surface expression of CD3 (anti-CD3-PE, BioLegend), (anti-FMC63 anti-CAR clone VM16 conjugated to AlexaFluor488), B2M (anti-B2M-APC, or PE, BioLegend), and HLA-A, B, and C (clone W6/32, BV605). Flow cytometry data were acquired on a Beckman-Coulter CytoFLEX-LX. 
     2. Results 
     B2M and HLA-ABC levels were measured in samples expressing construct 7056 and control populations.  FIG. 14A  shows the B2M surface levels in CD3-/CAR+ cells compared to TRAC-edited cells expressing no shRNA from a control culture.  FIG. 14B  shows B2M levels on CD3-/CAR+ versus CD3+/CAR− populations in the same culture.  FIG. 14C  and 14D make the same respective comparisons in displays of HLA-ABC surface levels. The CD3-/CAR+ fraction of cells transduced with AAV-7056 displayed levels of B2M and HLA-ABC that are reduced by greater than 90% compared to control populations. 
     3. Conclusions 
     A pre-screened B2M-targeting shRNA can knock down B2M expression levels on the surface of cells into which the construct has been delivered (via targeted insertion into the T cell receptor alpha constant region locus). This effect is specific to CAR+ populations (i.e., cells in which targeted integration into the TRAC locus has occurred). This experiment demonstrates that B2M can be efficiently knocked down using a single copy of shRNA472 co-delivered to the TRAC locus with the CAR gene on the same AAV template. 
     EXAMPLE 6 
     Characterization of Candidate shRNAs Against CD52 in Primary Human T Cells 
     1. Materials and Methods 
     Five Mission-shRNA lentiviral transfer plasmids encoding different CD52 targeting sequences were purchased from Sigma-Aldrich. Second-generation lentiviral vectors were produced in-house using Lenti-X 293T cells (ClonTech) and a triple transfection method (Lipofectamine 2000—Thermo-Fisher). T cells were prepared for lentiviral transduction by stimulating for 3 days with ImmunoCult anti-CD2/CD3/CD28 as in Example 1. Transduction was carried out in the presence of 5 uM polybrene (Sigma-Aldritch) and transduced cells were expanded for 5 days in IL-2 supplemented medium before a flow cytometric analysis of CD52 surface levels. Cells were not selected with puromycin because a heterogeneous population was desired for downstream attempts at magnetic depletion of CD52Hi cells. Cells transduced with a lentivirus encoding shRNA 568 were labeled with biotinylated anti-CD52 (Miltenyi Biotec), and magnetic separation was performed using a Biotin Positive Selection Kit (StemCell Technologies). A post-separation analysis of surface CD52 was performed. 
     2. Results 
     Of the 5 shRNA sequences screened, 3 (shRNA568, shRNA572, and shRNA876) interfered with CD52 expression. CD52 surface expression profiles are displayed in  FIG. 8 . Levels of CD52 displayed on the surface of T cells are shown in  FIG. 9  for mock transduced T cells (9A), T cells transduced with an shRNA-568 lentivirus (9B), and LV-shRNA568 transduced cells that have undergone a CD52 magnetic depletion (9C). 
     3. Conclusions 
     CD52 antigen density on the surface of cells can be reduced using shRNA delivered by a viral vector. Sequence 568 exhibited the highest degree of CD52 knockdown. Knockdown of CD52 using this shRNA sequence was sufficient to allow for magnetic depletion of non-transduced CD52 Hi cells. 
     EXAMPLE 7 
     CD52 Knockdown Profiles Using CAR/CD52 Constructs with Different Orientations 
     1. Materials and Methods 
     T cells were stimulated for 3 days using ImmunoCult anti-CD2/CD3/CD28 as described in EXAMPLE 1. After 3 days, TRC 1-2x.87EE mRNA, STING siRNA, and linearized AAV transfer vector encoding different CAR constructs ( FIG. 10 ) were delivered to the T cells using the 4-D Nucleofector (Lonza). Cultures of nucleofected T cells were carried for 10 days in medium supplemented with IL-2 prior to flow cytometric analyses of CD3, CAR (CD34 epitope-tagged), and CD52. 
     2. Results 
     To demonstrate un-manipulated levels of CD52 surface display on TRAC-edited CAR T cells, a TRC 1-2x.87EE nuclease and a CD34-tagged CAR construct encoding no shRNA sequence were delivered. CD52 levels on TCR KO cells, TCR KO CAR+ cells and nonedited cells are overlaid in the histogram in  FIG. 11A . Three CAR constructs encoding a U6 promoter-controlled CD52 shRNA were evaluated for ability to knock down CD52 when integrated into the TRAC locus. When the CAR gene and the shRNA cassette are both in forward orientation, CD52 antigen density is reduced by approximately 50% ( FIG. 11C ; construct 7004). Reversing the transcriptional orientation of the CAR gene alone (i.e., a tail-to-tail configuration) reduces the amount of CD52 displayed on the surface by approximately 95% ( FIG. 11B ; construct 7013), while reversing the orientation of both the CAR gene and the U6-shRNA element reduces the CD52 signal by approximately 90% ( FIG. 11D ; construct 7014). 
     3. Conclusions 
     The CD52 specific shRNA sequence 568 can interfere with CD52 expression when only one copy is delivered by targeted insertion into the TRAC locus. Altering the transcriptional orientation of either the CAR gene only (i.e., tail-to-tail configuration) or both the CAR and shRNA genes can influence the efficiency of target gene knockdown. Reversing only the CAR gene&#39;s orientation resulted in the most efficient knockdown. 
     4. Further Studies 
     A number of constructs were prepared comprising an anti-CD19 CAR coding sequence and an shRNA against CD52. These are illustrated in  FIG. 10A-10H  and are provided in SEQ ID NOs: 10-17. As described above, CAR constructs 7004 (SEQ ID NO: 12), 7013 (SEQ ID NO: 14), and 7014 (SEQ ID NO: 16) were previously evaluated for their ability to reduce CD52 expression while expressing a CAR. The 5′ and 3′ homology arms flanking the CAR coding sequence and the shRNA sequence have homology to regions upstream and downstream of the TRC 1-2 recognition sequence in the TRAC locus. 
     In additional studies, CAR T cells will be prepared using primary donor human T cells transduced with recombinant AAV vectors comprising one of the CAR/shRNA constructs above, with simultaneous nucleofection of mRNA encoding the TRC 1-2x.87EE to induce a double-strand break at the TRC 1-2 recognition sequence and promote targeted insertion of the construct into the genome of the T cells. CD52 expression will be determined as described above to determine which orientation of the first and second expression cassettes will result in the highest and/or the most consistent CAR expression, along with the most consistent level of CD52 knockdown on the cell surface. 
     CAR T cells produced with certain constructs will be evaluated in both the allogenicity and NK cell killing assays previously described above. Further, CAR T cells produced using the disclosed constructs will be evaluated in various stress tests, in which the CAR T cells are repeatedly exposed to antigen in order to determine changes in cell proliferation/expansion and cytotoxic potential. CAR T cells produced using the disclosed constructs will also be utilized with in vivo tumor models to determine their ability to clear tumor cells in an animal and to evaluate their ability to persist in vivo. It is expected, based on the Examples described herein, that enriched populations of CAR T cells can be produced for in vivo use by an advantageous negative-selection for CAR T cells having reduced cell surface expression of CD52.