Abstract:
This disclosure relates to methods of inducing a natural killer (NK) cell-mediated immune response and increasing NK activity in a mammal for the treatment of tumors and virus infections, comprising isolating peripheral blood mononuclear cells (PBMCs) from a subject, exposing them in vitro to a protein conjugate comprising granulocyte macrophage colony stimulating factor (GM-CSF) covalently linked to a soluble peptide antigen to activate the PBMCs, and administering the activated PBMCs to the subject. The method also relates to assessing NK cell activity of activated PBMCs to determine whether the subject has had a therapeutically effective response to the protein conjugate.

Description:
This patent application is a continuation of U.S. patent application Ser. No. 12/077,823, filed Mar. 21, 2008, now granted as U.S. Pat. No. 8,153,120, which claims priority to U.S. Provisional Patent Application No. 60/896,461 filed on Mar. 22, 2007, which is incorporated herein in its entirety by reference. 
    
    
     REFERENCE TO SEQUENCE LISTING, TABLE OR COMPUTER PROGRAM 
     A Sequence Listing is being submitted with this application in the form of a text file, created 21 Mar. 2012, and named “576368130US01SeqList.txt” (24,576 bytes), the contents of which are incorporated herein by reference in their entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to the fields of biology and immunology. More particularly, it relates to methods for inducing a natural killer (NK) cell-mediated immune response and increasing the NK cell activity of a mammal in order, for example, to treat tumors or viral infections. 
     BACKGROUND OF THE INVENTION 
     The immune system is comprised of many different cell types, factors and organs. These include lymphocytes, monocytes and polymorphonuclear leukocytes, numerous soluble chemical mediators (cytokines and growth factors), the thymus, postnatal bone marrow, lymph nodes, liver and spleen. All of these components work together through a complex communication system to fight against microbial invaders such as bacteria, viruses, fungi and parasites, and against newly arising malignant (tumor) cells. NK cells are bone marrow-derived lymphocytes of the innate arm of the immune system. They are phenotypically defined as expressing the low affinity receptor for the Fc protein of IgG (FcRγIIIA, CD16) and CD 56 in the absence of T cell receptor and its associated CD3 complex (Perussia et al., 2005,  Molecular Immunology  42: 385-395). 
     NK cells have vital importance as a first line of defense against infection and tumor proliferation while the adaptive immune system is being activated (French et al., 2003,  Current Opinion in Immunology  15: 45-51). The primary role of NK cells is to eliminate infected or cancerous cells by direct cellular cytotoxicity (Van der Broek et al., 2000,  Eur. J. Immunology  25: 3514-3516). The recognition mechanism involved does not utilize the major histocompatability class (MHC) I antigen presentation pathway and thus NK cells are neither antigen or MHC restricted and more importantly do not undergo clonal expansion to be effective (Trinchieri, 1989,  Adv. Immunology  47: 176-187). In addition to their cytotoxic actions, NK cells have the ability to modulate the immune system by the production of plietropic cytokines upon cellular activation. 
     The activation of NK cells largely depends on NK triggering receptors, NKG2D, CD16 and the recently identified natural cytoxicity receptors (NCR) (Arnon et al., 2006,  Seminars in Cancer Biology  16: 348-358), which include three members: NKp46, NKp44 and NKp30 (Moretta et al., 2002,  Scand. J. Immunol.  55: 229-232, Bottino et al., 2005,  Trends in Immunology  26: 221-226). The NCR have recently been designated cluster of differentiation notation, with NKp44 designated CD336. 
     CD336 encodes a 44 kDa surface glycoprotein characterized by a protein backbone of approximately 29 kDa (Vitale et al., 1998,  J. Exp. Med.  187: 2065-2072). CD336 is not expressed on resting but only on activated NK cells, thus the surface display of CD336 can be used as a surrogate marker of NK activation (Moretta et al., 2001,  Annu. Rev. Immunol.  19: 197-223). While CD336 is a pertinent marker of cell activation, the hallmark of NK functionality is the ability to lyse target cells, typically NK lytic activity is measured in vitro using a cell line deficient for surface MHC I expression such as the K562 tumor cell line. 
     The present inventors have identified novel methods for inducing an NK cell-mediated immune response, for increasing the activity of NK cells and for assessing and detecting an NK cell response in connection with the treatment of viruses and tumors. 
     BRIEF SUMMARY OF THE INVENTION 
     In a first aspect, this invention provides a method for inducing a cytotoxic NK cell-mediated immune response in a mammalian subject, which comprises the steps of isolating peripheral blood mononuclear cells (PBMCs) from a subject, exposing the PBMCs in vitro to a protein conjugate comprising granulocyte macrophage colony stimulating factor (GM-CSF) covalently linked to a soluble peptide antigen selected from the group consisting of a tumor associated antigen (TAA) and an oncogene product, under conditions effective to activate the PBMCs, wherein the PBMCs are effective in activating NK cells to produce a cytotoxic cellular response that is higher than that produced by the PBMCs which have not been activated by the protein conjugate, and administering the activated PBMCs to the subject. 
     In another aspect, the invention provides a method for increasing NK cell activity, comprising the steps of isolating peripheral blood mononuclear cells (PBMCs) from a subject, exposing the PBMCs in vitro to a protein conjugate comprising granulocyte macrophage colony stimulating factor (GM-CSF) covalently linked to a soluble peptide antigen selected from the group consisting of a tumor associated antigen (TAA) and an oncogene product, under conditions effective to activate the PBMCs, wherein the PBMCs are effective in activating NK cells. 
     In yet another aspect, the invention provides an improvement for determining whether the individual subject is a candidate for additional treatment by administration of the activated PBMCs by assessing the response of an individual subject to an anti-cancer therapy comprising the steps of (a) isolating PBMCs from a subject; (b) exposing the PBMCs in vitro to a protein conjugate comprising granulocyte macrophage colony stimulating factor (GM-CSF) covalently linked to a soluble peptide antigen selected from the group consisting of a tumor associated antigen (TAA) and an oncogene product, under conditions effective to activate the PBMCs; (c) administering the activated PBMCs to the subject; (d) repeating step (a) and (b) at least 10 days after previous step (c) has occurred, (e) assessing the NK activity of the activated PBMCs from the second isolation; and (f) if the NK activity has increased significantly over the level of NK activity prior to the first administration, classifying the subject as a good candidate for additional treatment by activated PBMC administration. 
     In another aspect, the invention provides a method for determining whether a subject has had a therapeutically effective response to administration of activated PBMCs comprising the steps of (a) isolating PBMCs from a subject; (b) exposing the PBMCs in vitro to a protein conjugate comprising granulocyte macrophage colony stimulating factor (GM-CSF) covalently linked to a soluble peptide antigen selected from the group consisting of a tumor associated antigen (TAA) and an oncogene product, under conditions effective to activate the PBMCs; (c) administering the activated PBMCs to the subject; (d) repeating step (a) and (b) at least 10 days after previous step (c) has occurred, (e) assessing the NK activity of the activated PBMCs from the previous isolation; and (f) determining the change in the NK activity over the level of NK activity of the activated PBMCs prior to the first administration. 
     The methods of the present invention are particularly suited to the treatment of cancers such as, for example, soft tissue sarcomas, lymphomas, and cancers of the brain, esophagus, uterine cervix, bone, lung, endometrium, bladder, breast, larynx, colon/rectum, stomach, ovary, pancreas, adrenal gland and prostate. Exemplified herein are methods for the treatment of prostate and/or breast cancer. 
     In each of the above aspects of the invention, (i) the PBMCs may be antigen presenting cells (APCs); (ii) PBMCs may be dendritic cells (DCs); (iii) for use in treating a tumor, the soluble peptide antigen may be a TAA, including a tissue-specific tumor antigen; (iv) for use in treating a tumor, the soluble peptide antigen may be an oncogene product; (v) the protein conjugate may further include a linker peptide joining the GM-CSF to the soluble peptide antigen; (vi) for use in treating prostate cancer, the tissue-specific tumor antigen may be prostatic acid phosphatase (PAP) having at least 95% sequence identity to the sequence depicted as SEQ ID NO: 1; (vii) the protein conjugate may be a fusion protein having at least 95% sequence identity with the sequence depicted as SEQ ID NO: 5; (vii) for use in treating breast cancer, the oncogene product may be Her2; (viii) the protein conjugate may comprise a fusion protein having at least 95% sequence identity with the sequence depicted as SEQ ID NO: 7; the mammalian subject is a human; and (ix) the protein conjugate may be produced in a baculovirus expression system. 
     Also in aspects of the invention involving the steps of (a) isolating PBMCs from a subject; (b) exposing the PBMCs in vitro to a protein conjugate comprising granulocyte macrophage colony stimulating factor (GM-CSF) covalently linked to a soluble peptide antigen selected from the group consisting of a tumor associated antigen (TAA) and an oncogene product, under conditions effective to activate the PBMCs, and (c) administering the activated PBMCs to the subject; the claimed invention may further comprise repeating steps (a), (b) and (c) at least once with each cycle beginning at least ten days after step (c) has occurred; and steps (a) through (c) may be performed a total of three times and wherein fourteen days has elapsed since the previous step (c) has occurred. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 .  FIG. 1  shows NK cell activity as measured by CD336 surface expression on CD16+ and CD56+ NK cells before and after culture with sipuleucel-T, an investigative immunotherapeutic agent manufactured by Dendreon Corp, Seattle, Wash., at weeks 0, 2 and 4.  FIG. 1  shows that CD336 surface expression on both CD16+ and CD56+ cells is enhanced post-culture. Pre- and post culture cells were surface stained for CD16, CD56 and CD336, and 200,000 events were collected on a Becton Dickinson FACSAria flow cytometer. Gated CD16+ and CD56+ cells were then analyzed for CD336 expression and the percent of CD16+ or CD56+ cells that expressed CD336 then calculated. 
         FIG. 2 .  FIG. 2  shows NK cell activity as measured by CD336 surface expression on CD16+ and CD56+ NK cells from subjects that received a placebo (cells incubated without the GM-CSF fusion protein) in the double-blind, placebo controlled clinical trial for sipuleucel-T.  FIG. 2  shows that CD336 surface expression on both CD16+ and CD56+ cells is not enhanced post-culture. Pre- and post culture cells were surface stained for CD16, CD56 and CD336, and 200,000 events were collected on a Becton Dickinson FACSAria flow cytometer. Gated CD16+ and CD56+ cells were then analyzed for CD336 expression and the percent of CD16+ or CD56+ cells that expressed CD336 then calculated. 
         FIG. 3 .  FIG. 3  shows sipuleucel-T cell lytic activity against the MHC-I deficient cell line K562 at weeks 0, 2 and 4 for several different subjects.  FIG. 2  shows that sipuleucel-T cells generated from the week 2 apheresis from seven different subjects that had received the week 0 treatment, possessed cytotoxic activity as gauged by lysis of the K562 tumor cell line. Sipuleucel-T cells were titrated in triplicate at an effector to target ratio starting at 50:1 against a fixed number of K562 target cells. The cells were incubated at 37° C. for 4 hours after which time the medium was tested in a colorimetric assay for the presence of the intracellular enzyme lactate dehydrogenase (LDH). The degree of lytic activity was thus calculated using the following formula: 
       
         
           
             
               
                 % 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 Cytotxicity 
               
               = 
               
                 100 
                 ⁢ 
                 
                     
                 
                 × 
                 
                   
                     A 
                     - 
                     B 
                     - 
                     C 
                   
                   
                     D 
                     - 
                     C 
                   
                 
               
             
           
         
           
           A=LDH from test cell mixture (effector cells+target cells) 
           B=spontaneous LDH from effector cells 
           C=spontaneous LDH from target cells 
           D=maximal LDH from target cells 
         
      
         FIG. 4 .  FIG. 4  shows sipuleucel-T cell lytic activity against the MHC-I deficient cell line K562 at weeks 0, 2 and 4 from two subjects that received a placebo (cells incubated without the GM-CSF fusion protein) in the double bind, placebo cotrolled clinical trial for sipuleucel-T.  FIG. 4  shows that cells generated from the week 2 apheresis from two subjects who had received the week 0 placebo, did not possess cytotoxic activity as gauged by lysis of the K562 tumor cell line. Sipuleucel-T cells were titrated in triplicate at an effector to target ratio starting at 50:1 against a fixed number of K562 target cells. The cells were incubated at 37° C. for 4 hours after which time the medium was tested in a colorimetric assay for the presence of the intracellular enzyme lactate dehydrogenase (LDH). The degree of lytic activity was thus calculated using the following formula: 
       
         
           
             
               
                 % 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 Cytotxicity 
               
               = 
               
                 100 
                 × 
                 
                   
                     A 
                     - 
                     B 
                     - 
                     C 
                   
                   
                     D 
                     - 
                     C 
                   
                 
               
             
           
         
           
           A=LDH from test cell mixture (effector cells+target cells) 
           B=spontaneous LDH from effector cells 
           C=spontaneous LDH from target cells 
           D=maximal LDH from target cells 
         
      
         FIG. 5 .  FIG. 5  is a diagrammatic representation of a portion of a 96 well V-bottomed plate on which the major histocompatability complex (MHC) I negative cell line K562 (also referred to as “target cells”) and sipuleucel-T cells (also referred to as “effector cells”) were used to assess the NK lytic activity of sipuleucel-T. 
     
    
    
     SEQ ID NO: 1 is the amino acid sequence of human prostatic acid phosphatase (huPAP) as encoded by the cDNA sequence depicted in SEQ ID NO: 2. 
     SEQ ID NO: 2 is the nucleotide sequence of a cDNA encoding human prostatic acid phosphatase (huPAP) as depicted in SEQ ID NO: 1. 
     SEQ ID NO: 3 is the amino acid sequence of a human granulocyte-macrophage colony stimulating factor (huGM-CSF) as encoded by the cDNA sequence depicted in SEQ ID NO: 4. 
     SEQ ID NO: 4 is the nucleotide sequence of a cDNA encoding human granulocyte-macrophage colony stimulating factor (huGM-CSF) as depicted in SEQ ID NO: 3. 
     SEQ ID NO: 5 is the amino acid sequence of a human prostatic acid phosphatase/human granulocyte-macrophage colony stimulating factor (huPAP/huGM-CSF) fusion protein as encoded by the cDNA sequence depicted in SEQ ID NO: 6, 
     SEQ ID NO: 6 is the nucleotide sequence of a cDNA encoding human prostatic acid phosphatase/human granulocyte-macrophage colony stimulating factor (huPAP/huGM-CSF) fusion protein as depicted in SEQ ID NO: 5. 
     SEQ ID NO: 7 is the amino acid sequence of a HER500-human granulocyte-macrophage colony stimulating factor (HER500-huGM-CSF) fusion protein as encoded by the cDNA sequence depicted in SEQ ID NO: 8. 
     SEQ ID NO: 8 is the nucleotide sequence of a cDNA encoding a HER500-human human granulocyte-macrophage colony stimulating factor (HER500-huGM-CSF) fusion protein as depicted in SEQ ID NO: 7. 
     DETAILED DESCRIPTION OF THE INVENTION 
     As described above, the invention provides a method for inducing a cytotoxic NK cell-mediated immune response in a mammalian subject, which comprises the steps of isolating peripheral blood mononuclear cells (PBMCs) from a subject, exposing the PBMCs in vitro to a protein conjugate comprising a GM-CSF having at least 95% sequence identity with the sequence depicted in SEQ ID NO: 3 (GM-CSF), covalently linked to a soluble peptide antigen selected from the group consisting of a tumor associated antigen and an oncogene product, under conditions effective to activate the PBMCs, wherein the PBMCs are effective in activating NK cells to produce a cytotoxic cellular response that is higher than that produced by the PBMCs when not activated by the protein conjugate, and administering the activated PBMCs to the subject. 
     In another aspect, the invention provides a method for increasing NK cell activity, comprising the steps of isolating peripheral blood mononuclear cells (PBMCs) from a subject, exposing the PBMCs in vitro to a protein conjugate comprising GM-CSF covalently linked to a soluble peptide antigen selected from the group consisting of a tumor associated antigen (TAA) and an oncogene product, under conditions effective to activate the PBMCs, wherein the PBMCs are effective in activating NK cells. 
     In yet another aspect, the invention provides an improvement for determining whether the individual subject is a candidate for additional treatment by administration of the activated PBMCs by assessing the response of an individual subject to an anti-cancer therapy comprising the steps of (a) isolating PBMCs from a subject; (b) exposing the PBMCs in vitro to a protein conjugate comprising GM-CSF covalently linked to a soluble peptide antigen selected from the group consisting of a tumor associated antigen (TAA) and an oncogene product, under conditions effective to activate the PBMCs; (c) administering the activated PBMCs to the subject; (d) repeating step (a) and (b) at least 10 days after previous step (c) has occurred, (e) assessing the NK activity of the activated PBMCs from the second isolation; and (f) if the NK activity has increased significantly over the level of NK activity prior to the first administration, classifying the subject as a good candidate for additional treatment by activated PBMC administration. 
     In another aspect, the invention provides a method for determining whether a subject has had a therapeutically effective response to administration of activated PBMCs comprising the steps of (a) isolating PBMCs from a subject; (b) exposing the PBMCs in vitro to a protein conjugate comprising GM-CSF covalently linked to a soluble peptide antigen selected from the group consisting of a tumor associated antigen (TAA) and an oncogene product, under conditions effective to activate the PBMCs; (c) administering the activated PBMCs to the subject; (d) repeating step (a) and (b) at least 10 days after previous step (c) has occurred, (e) assessing the NK activity of the activated PBMCs from the previous isolation; and (f) determining the change in the NK activity over the level of NK activity of the activated PBMCs prior to the first administration. 
     In each of the aspects of the invention, (i) the PBMCs may be antigen presenting cells (APCs); (ii) PBMCs may be dendritic cells (DCs); (iii) for use in treating a tumor, the soluble peptide antigen may be a TAA, including a tissue-specific tumor antigen; (iv) for use in treating a tumor, the soluble peptide antigen may be an oncogene product; (v) the protein conjugate may further include a linker peptide joining the GM-CSF to the soluble peptide antigen; (vi) for use in treating prostate cancer, the tissue-specific tumor antigen may be prostatic acid phosphatase (PAP) having at least 95% sequence identity to the sequence depicted as SEQ ID NO: 1; (vii) the protein conjugate may be a fusion protein having at least 95% sequence identity with the sequence depicted as SEQ ID NO: 5; (vii) for use in treating breast cancer, the oncogene product may be Her2; (viii) the protein conjugate may comprise a fusion protein having at least 95% sequence identity with the sequence depicted as SEQ ID NO: 7; the mammalian subject is a human; and (ix) the protein conjugate may be produced in a baculovirus expression system. 
     Immunotherapeutic Compositions 
     Within certain embodiments, the present invention provides that the PBMCs are isolated antigen presenting cells (APCs) obtained from a subject. In certain embodiments, the APCs are stimulated by exposure in vitro to a tumor-associated antigen (TAA). The tumor-associated antigen may be a tissue-specific tumor antigen. As used herein, The tumor-associated antigen and/or the tissue-specific tumor antigen are a component of an immunotherapeutic composition that comprises a protein conjugate wherein the protein conjugate comprises an N-terminal moiety and a C-terminal moiety, wherein the C-terminal moiety has at least 95% sequence identity with the sequence depicted as SEQ ID NO: 3 (huGM-CSF or GM-CSF). In certain preferred embodiments, the APCs are stimulated with a protein conjugate comprising an N-terminal moiety, having at least 95% sequence identity with the sequence depicted in SEQ ID NO: 1 (huPAP or PAP) or an active fragment, derivative, or variant of huPAP. In an especially preferred embodiment the subject&#39;s APCs are stimulated by a protein conjugate comprising the sequence depicted in SEQ ID NO: 5 (PAP/GM-CSF) 
     In other embodiments, the APCs are stimulated in vitro by exposure to a protein conjugate comprising a C-terminal moiety comprising GM-CSF and an N-terminal moiety comprising an oncogene product. The oncogene product is a component of an immunotherapeutic composition that comprises a protein conjugate wherein the protein conjugate comprises an N-terminal moiety and a C-terminal moiety, wherein the C-terminal moiety is GM-CSF. In a preferred embodiment, the N-terminal moiety having at least 95% sequence identity with the sequence depicted in SEQ ID NO: 7 (HER500-hGM-CSF). The immunotherapeutic compositions described herein are effective in inducing an NK cell-mediated immune response against the protein conjugate. The NK cell-mediated immune response is higher than that produced by APCs when not exposed to the protein conjugate. Specific preferred embodiments provide that the APCs are dendritic cells (DCs). 
     APCs and DCs 
     As used herein, the term “antigen presenting cells” or “APCs” refers to cells that are capable of inducing an NK cell-mediated immune response, and include, but are not limited to certain macrophages, B cells, and, most preferable, dendritic cells (DCs). “Dendritic cells” or “DCs” are members of a diverse population of morphologically similar cell types found in lymphoid or non-lymphoid tissues. These cells are characterized by their distinctive morphology and high levels of surface MHC class II expression (Steinman et al., 1991,  Ann. Rev. Immunol.  9: 271). 
     APCs and DCs may be isolated from a number of tissue sources, and conveniently from peripheral blood. APCs and DCs may be isolated by routine methodologies that are readily available in the art. An exemplary suitable methodology for isolation of DCs is disclosed in U.S. Pat. Nos. 5,976,546, 6,080,409, and 6,210,662, each of these patents is incorporated herein by reference. Briefly, buffy coat cells may be prepared from peripheral blood. Cells may be harvested from leukopacs, layered over columns of organosilanized colloidal silica (OCS) separation medium (prepared as described by Dorn in U.S. Pat. No. 4,927,749, incorporated herein by reference) at a density 1.0770 g/ml, pH 7.4, 280 mOsm/kg H 2 O) in centrifuge tubes or devices. The OCS medium is preferable prepared by reacting and thus blocking the silanol groups of colloidal silica (approximately 10-20 nm diameter particles) with an alkyl tri-methoxy silane reagent. 
     In one embodiment, the OCS density gradient material is diluted to an appropriate specific density in a physiological salt solution supplemented with polyvinylpyrolidone (PVP). The tubes are centrifuged and the PBMCs present at the interface, are harvested. 
     PBMC are resuspended and centrifuged again to remove platelets and may optionally be spun through columns of OCS (density 1.0650 g/ml, 280 mOsm/kg H 2 O). The resulting interface and PBMCs are harvested and washed with D-PBS by centrifugation. The pellet fraction is resuspended in cell culture medium and cultured with the protein conjugate in a humidified 5% CO 2  incubator for approximately 40 hours. Following incubation, the cells are harvested. 
     In a preferred embodiment, sipuleucel-T, an investigative immunotherapeutic agent manufactured by Dendreon Corp, (Seattle, Wash.) is generated from a subject&#39;s own blood cells using an apheresis. The subject&#39;s apheresis cells are centrifuged to remove autologous plasma, they are then resuspended in 0.9% sodium chloride USP solution and passed through a buoyant density solution (BDS) of 1.077 g/ml gravity. The interface cells are collected and washed in 0.9% sodium chloride USP solution after which they are then passed over a BDS 1.065 g/ml gravity separation solution. The cells that pass through the density solution are then collected and washed in 0.9% sodium chloride USP solution. These cells, termed BDS65 cells are cultured in AIM-V® culture medium for up to 44 hours with PA2024, a fusion protein comprising human prostatic acid phosphatase fused to human GM-CSF. The cultured cells are then washed out of the culture medium and resuspended in lactated ringers solution and are re-infused back into the subject. This process is performed three times, with each cycle of apheresis and culture being conducted two weeks apart. 
     Protein Conjugates 
     Preferred protein conjugates comprise an N-terminal moiety which includes at least a portion of a tumor associated antigen or an oncogene product and a C-terminal moiety which includes the dendritic cell binding protein, GM-CSF. 
     As used herein, the term “tumor-associated antigen” refers to an antigen that is characteristic of a tissue type, including specific tumor tissues. An example of a tumor-associated antigen expressed by a tumor tissue is the antigen prostatic acid phosphatase (PAP), which is present on over 90% of all prostate tumors. The term “tissue specific tumor antigen” can be characterized as (i) inclusive of antigens that are common to a specific type of tumor and (ii) exclusive of antigens that are specific only to an individual tumor. The term “oncogene product” refers to any protein encoded by a gene associated with cellular transformation. Examples of oncogene products include, for example, Her2, p21RAS, and p53. 
     The terms “antigen presenting cell binding protein” and “dendritic cell binding protein” refer to any protein for which receptors are expressed on an APC or a DC, respectively. Examples of antigen presenting cell binding proteins and dendritic cell binding proteins include, but are not limited to, GM-CSF, IL-1, TNF, IL-4, CD40L, CTLA4, CD28, and FLT-3 ligand. 
     “Protein conjugates,” as disclosed herein, refer to covalent complexes formed between the N-terminal moiety and the C-terminal moiety. Protein conjugates between tumor associated antigens/tumor-specific antigens/oncogene products and antigen presenting cell binding proteins/dendritic cell binding proteins may be complexed either chemically or as a fusion protein. 
     The exemplary PAP/GM-CSF protein conjugate disclosed herein was previously described within U.S. Pat. Nos. 5,976,546, 6,080,409, and 6,210,662, each of which is incorporated herein by reference and is presented herein as SEQ ID NO: 5. This protein conjugate is a fusion protein between a 386 amino acid portion of PAP at the N-terminus and a 127 amino acid portion of GM-CSF at the C-terminus. In addition, the PAP/GM-CSF fusion protein further comprises, between the N-terminal moiety and the C-terminal moiety, a two amino acid peptide linker having the sequence gly-ser. The fusion protein is manufactured in a Baculovirus expression system using sf21 insect cells. 
     As described above, the PAP/GM-CSF protein conjugate is exposed to a subject&#39;s PBMCs under conditions effective to activate the PBMCs and the activated PBMCs are administered to the subject to induce a cytotoxic NK cell-mediated immune response. 
     The term “administration” or “administering” refers to various methods of contacting a substance with a mammal, especially a human. Modes of administration may include, but are not limited to, methods that involve contacting the substance intravenously, intraperitoneally, intranasally, transdermally, topically, subcutaneously, parentally, intramuscularly, orally, or systemically, and via injection, ingestion, inhalation, implantation, or adsorption by any other means. One exemplary means of administration of the protein conjugates or fusion proteins of this invention is via intravenous delivery, where the protein conjugate or fusion protein can be formulated as an aqueous solution, a suspension, or an emulsion, etc. Other means for delivering the protein conjugates or fusion proteins of this invention includes intradermal injection, subcutaneous injection, intramuscular injection or transdermal application as with a patch. 
     Another exemplary protein conjugate disclosed herein is the HER500-hGM-CSF fusion protein that was previously described within U.S. Pat. Nos. 5,976,546, 6,080,409, 6,210,662, and 7,060,279 each of which is incorporated herein by reference and is presented herein as SEQ ID NO: 7. This protein conjugate is a fusion protein that is composed of 289 amino acids from the N-terminal extra-cellular domain and 217 amino acids from the C-terminal intra-cellular domain of Her2 fused to 127 amino acids of human GM-CSF at the C-terminus. The fusion protein is manufactured in a Baculovirus expression system using sf21 insect cells. 
     In a preferred embodiment, the invention provides a method of inducing a cytotoxic NK cell-mediated immune response in a human subject comprising the steps of (a) isolating APCs from the subject; (b) exposing the APCs in vitro to a protein conjugate comprising GM-CSF covalently linked to PAP, under conditions effective to activate APCs; (c) administering the activated APCs to the subject; and (d) repeating steps (a)-(c) at least once with each cycle beginning at least 10 days after step (c) has occurred. In an especially preferred embodiment, steps (a)-(c) are repeated one time with step (a) occurring 14 days after step (c). 
     In another aspect, the invention provides a method for increasing NK cell activity in a patient, comprising the steps of (a) isolating APCs from the patient; (b) exposing the APCs in vitro to a protein conjugate comprising GM-CSF covalently linked to PAP, under conditions effective to activate APCs; (c) administering the activated APCs to the patient; and (d) repeating steps (a)-(c) at least once with each cycle beginning at least 10 days after step (c) has occurred. In an especially preferred embodiment, steps (a)-(c) are repeated one time with step (a) occurring 14 days after step (c). 
     In another aspect, the invention provides a method of detecting in a subject a cytotoxic NK cell-mediated immune response comprising the steps of (a) isolating APCs from the subject; (b) exposing the APCs in vitro to a protein conjugate comprising GM-CSF covalently linked to a soluble peptide antigen selected from the group consisting of a tissue-specific tumor antigen and an oncogene product, under conditions effective to activate the APCs; (c) administering the activated APCs to the subject; (d) repeating steps (a) and (b); and (e) detecting an NK cell response in the activated PBMCs. In certain embodiments of the invention, the NK cell response is detected in vitro by CD336 surface expression. In other embodiments of the invention, the NK cell response is detected in vitro by lysis of the K562 tumor line. 
     Evaluation of NK Cell Activation 
     In one embodiment of the invention, NK cell activation is evaluated by flow cytometry of CD336 surface expression. APCs are obtained from subjects as described above and evaluated before and after culture with the protein conjugates described above. Pre- and post culture cells were surface stained for CD16, CD56 and CD336, and data were collected on a Becton Dickinson FACSAria flow cytometer. Gated CD16+ and CD56+ cells are then analyzed for CD336 expression and the percent of CD16+ or CD56+ cells that expressed CD336 then calculated. The results, as shown in  FIG. 1 , show that NK cell activity is enhanced post-culture with a PAP/GM-CSF protein conjugate and subsequent administration to the subject. 
     In another embodiment of the invention, NK cell activation is evaluated by lysis of the K562 tumor cell line. The K562 cell line is widely used as a target for NK activity as it is MHC class I negative and therefore cannot present either autologous or antigen derived peptides (Ortaldo et al., 1977,  J. Natl. Cancer Inst.  59: 77-82). The details of material and methods used for the NK lytic cell assay are described below in Example 2. The results, as shown in  FIG. 2 , show that APCs generated from the week 2 apheresis from subjects undergoing treatment with sipuleucel-T possessed cytotoxic activity as gauged by lysis of the K562 cell line. 
     EXAMPLES 
     The following examples are provided by way of illustration only and not by way of limitation. Those of skill in the art will readily recognize a variety of non-critical parameters that could be changed or modified to yield essentially similar results. 
     Example 1 
     Materials and Methods 
     PA2024 is a proprietary recombinant fusion protein containing PAP and GM-CSF sequences manufactured by Dendreon Corporation (Seattle, Wash.) for the investigational cellular immunotherapy sipuleucel-T. PA2024 is expressed in a baculovirus system. 
     All subject and healthy donor specimens were collected according to investigator sponsored protocols approved by the appropriate Investigational Review Board. After receiving informed consent, white blood cells were collected by apheresis and prepared for transport and/or processing. The subject&#39;s apheresis cells were centrifuged to remove autologous plasma, they are then resuspended in 0.9% sodium chloride USP solution and passed through a buoyant density solution (BDS) of 1.077 g/ml gravity. The interface cells were collected and washed in 0.9% sodium chloride USP solution after which they were then passed over a BDS 1.065 g/ml gravity separation solution. The cells that pass through the density solution were then collected and washed in 0.9% sodium chloride USP solution. These cells, termed BDS65 cells were cultured in AIM-V® culture medium for up to 44 hours with PA2024, a fusion protein comprising human prostatic acid phosphatase fused to human GM-CSF. The cultured cells were then washed out of the culture medium and resuspended in lactated ringers solution and were re-infused back into the subject. This process was performed three times, with each cycle of apheresis and culture being conducted two weeks apart. 
     1×10 7  pre-culture and post-culture cells were pelletted by centrifugation and then resuspended in 1 ml of Dulbeccos Phosphate Buffered Saline (D-PBS) containing 10% normal mouse serum (NMS) and incubated at room temperature for 10 minutes. After this time the cells were then centrifuged again and the supernatant was aspirated and the cells were resuspended in 1 ml of staining buffer (D-PBS containing 2% Bovine Serum Albumin—BSA). Aliquots of 1×10 6  cells were then stained with the following combination of antibodies in the wells of a 96 well round bottom staining plate: Fluoroisothiocyanate (FITC) labeled murine IgG1 together with Phycoerythrin (PE) labeled murine IgG1 and Phycoerythrin-Cyanate 5 (PE-Cy5) labeled murine IgG1, FITC labeled murine anti-human CD16 together with PE labeled murine anti-human CD336 and PE-Cy5 labeled murine anti-human CD56. The cells were incubated in the dark at 4° C. for 20 minutes after which time 100 μl of staining buffer was added and the plate was centrifuged for 5 minutes, the supernatant was aspirated off and the cells were then resuspended in a total volume of 200 μl of D-PBS containing 1% parformaldehyde. Fixed cells were then acquired on a Becton Dickinson FACSAria where a total of 200,000 gated events were collected. Flow data was then analyzed using Beckman Coulter CXP software; the cells stained with FITC labeled murine IgG1, PE labeled murine IgG1 and PECy5 labeled murine IgG1 were used to establish non specific staining. To define the CD16+ and CD56+ NK cell populations, the signals for these surface markers had to be greater than the signal from the FITC or PECy5 labeled murine IgG1 stained cells. Gated CD16+ and CD56+ NK cells were then assessed for CD336 staining, with positive staining for CD336 being a signal that was greater than that detected by staining with PE labeled murine IgG1 and the number of CD16+ or CD56+ cells positive for CD336 were expressed as a percentage of the CD16+ or CD56+ NK cell populations. 
     Results 
     The results, as presented in  FIG. 1 , show that CD336 surface expression on both CD16+ and CD56+ cells is enhanced post-culture with sipuleucel-T. The results, as presented in  FIG. 2 , also show that CD336 expression is not enhanced for the subjects that did not receive sipuleucel-T. 
     Example 2 
     Materials and Methods 
     PA2024 is a proprietary recombinant fusion protein containing PAP and GM-CSF sequences manufactured by Dendreon Corporation (Seattle, Wash.) for the investigational cellular immunotherapy sipuleucel-T. PA2024 is expressed in a baculovirus system. 
     All subject and healthy donor specimens were collected according to investigator sponsored protocols approved by the appropriate Investigational Review Board. After receiving informed consent, white blood cells were collected by apheresis and prepared for transport and/or processing. The subject&#39;s apheresis cells were centrifuged to remove autologous plasma, they are then resuspended in 0.9% sodium chloride USP solution and passed through a buoyant density solution (BDS) of 1.077 g/ml gravity. The interface cells were collected and washed in 0.9% sodium chloride USP solution after which they were then passed over a BDS 1.065 g/ml gravity separation solution. The cells that pass through the density solution were then collected and washed in 0.9% sodium chloride USP solution. These cells, termed BDS65 cells were cultured in AIM-V® culture medium for up to 44 hours with PA2024, a fusion protein comprising human prostatic acid phosphatase fused to human GM-CSF. The cultured cells were then washed out of the culture medium and resuspended in lactated ringers solution and were re-infused back into the subject. This process was performed three times, with each cycle of apheresis and culture being conducted two weeks apart. 
     NK lytic activity of sipuleucel-T was determined by assessing the degree of lysis of the major histocompatability complex (MHC) I negative cell line K562, also referred to as target cells, by use of a Non-Radioactive Cytotoxicity Assay (Promega Cat#G1780, Instructions Part #TB163). K562 cells were maintained in log phase culture in standard RPMI1640 media supplemented with 10% Fetal Bovine Serum (FBS) and on the day of use were washed out of the RPMI/10% FBS medium by centrifugation. K562 cells were then resuspended in RPMI1640 medium supplemented with 5% Human Serum (HS) at a concentration of 2.5×10 5 /ml. 15×10 6  sipuleucel-T cells, also referred to as effector cells, were washed and also resuspended in 600 μl of RPMI/5% HS and 100 μl of the effector cells were dispensed in triplicate into the wells of a 96 well V-bottomed plate, in the first column of the Experimental and Effectors only section of the plate, as detailed in  FIG. 5 . 
     The first column of cells represents the highest effector: target ratio, 100 μl of RPMI/5% HS was then dispensed into every triplicate set of wells of the Experimental, Effectors only, T max , (Target maximal release), T Spont (Target spontaneous release), and media sets. The plate was then centrifuged and the Effector cells were then serially diluted down the Experimental and Effectors only by transferring 100 μl of volume across the plate of the two aforementioned sets. 2.5×10 4  target cells were then dispensed in triplicate into the wells of the Experimental, T Spont  and T Max . sets and a further 100 μl of RPMI/5% HS was added to the Media wells. The plate was then incubated for 3.5 hours at 37° C., 5% CO 2  after which time 20 μl of 10× lysis buffer was added to the T Max  wells and the plate was then incubated for a further 30 minutes. The plate was then centrifuged for 4 minutes at 250G. 50 μl of supernatant was then transferred from each well to a 96 well black walled flat bottomed plate and an equal volume of substrate buffer was added to each well and the plate incubated at room temperature for 30 minutes. After this time 50 μl of stop solution was added and the optical density of each well was determined on an ELISA plate reader at a wavelength of 490 nm. The degree of lytic activity was the calculated using the following formula: 
               %   ⁢           ⁢   Cytotxicity     =       Experimental   -     Effector   ⁢           ⁢   Spontaneous     -     Target   ⁢           ⁢   Spontaneous                 Target   ⁢           ⁢   Maximum     -               Target   ⁢           ⁢   Spontaneous                   
Results
 
     The results, as presented in  FIG. 3 , show that sipuleucel-T cells generated from the week 2 apheresis of treated subjects possessed cytotoxic activity as gauged by lysis of the K562 tumor cell line. The results, as presented in  FIG. 4 , also show that NK lytic activity is not generated at week 2 in the placebo subjects. 
     All patents, patent applications, and other publications cited in this application, including published amino acid or polynucleotide sequences, are incorporated by reference in the entirety for all purposes.