IMMUNOSTIMULATORY COMPOSITION AND METHOD

Abstract: Disclosed are therapeutic compositions and methods for inducing cytotoxic T cell responses in vitro and in vivo. The therapeutic compositions consist of antigen presenting cells activated by contact with a polypeptide complex constructed by joining together a dendritic cell-binding protein and a polypeptide antigen. Also disclosed are expression vectors and systems for producing the polypeptide complexes.

Description: IMMUNOSTIMULATORY COMPOSITION AND METHOD Field of the Invention The present invention relates to compositions and methods for stimulation of specific cellular immune responses in vivo. More specifically, the invention is concerned with elimination of tumor cells by cytotoxic T-lymphocytes (CTL) activated in vivo or in vitro by exposure to antigen presenting cells exposed to an immunostimulatory polypeptide complex. Background of the Invention The immune response ofthe mammalian immune system is divided into two general types: humoral immunity, mediated largely by circulating antibodies, and cellular immunity mediated by various forms of T-cells. Extracellular antigens stimulate a humoral response, while intracellular antigens such as viruses, stimulate a cellular response. The cellular immune response to virally infected cells and tumor cells is largely mediated by cytotoxic T-lymphocytes (T„ or CTL), when they recognize foreign antigens attached to the host cell surface as part of the Major Histocompatibility Complex (MHC), and more particularly, a common form of MHC known as MHC Class I. In contrast, antigens derived from non-viral pathogens (bacteria, fungi) are generally expressed as part of an MHC Class II complex. A different subpopulation of effector T cells (cell mediated immune cells; CMI) release cytokines that activate the host cell to destroy such pathogens. In experimental systems, tumor-antigen specific CTL are the most powerful immunological mechanism for the elimination of tumors. CTL can be induced ei er in vivo with vaccines or can be generated in vitro and then be re-infused into the tumor-bearing organism. The in vivo induction of CTL is typically accomplished by immunization with live virus or cells (Tanaka, et al. , J.Immunol.. (1991), 141, 3646-52, Wang, et al. , J. Immunol .. (1995), 4685-4692, Torre-Amione, et al., Proc.Natl.Acad.Sci.U.S.A.. (1990), £7, 1486-90). Except for a few special viral proteins such as the SV-40 large T-antigen and the Hepatitis B surface antigen, injection of isolated or soluble proteins does not result in induction of CTL (Schirmbeck, et al., Eur. J.Immunol.. (1993), 23, 1528-34). CTL are induced when a protein enters the class I pathway of antigen processing. To enter this pathway the protein must be present in the cytosol of the APC. There it is degraded into peptides which are then transported into the endoplasmic reticulum, where they associate with nascent HLA class I molecules. These peptides are then displayed together with the class I molecules on the cell surface and can serve as an inducer and target of class I restricted antigen-specific CTL. Physiologically, only proteins that are endogenously synthesized by an APC enter this pathway. Non-cellular-delivery vehicles for proteins, such as pH-sensitive liposomes, can overcome the requirement for endogenous synthesis in vivo (Nair, et al. , J.Exp. Med.. (1992). 175. 609-12, Nair, et al. , J.Virol. (1993), 6 , 4062-9); however, these treatments are also quite toxic to the target cells. Induction of primary HLA class I restricted CTL by pure soluble proteins in vitro has not been reported. The most common tool for ex vivo induction of primary CTL are small (8-11- mer) synthetic peptides (Stauss, et al., Proc.Natl.Acad.Sci.U.S.A. (1992), £2, 7871-5, Carbone, et al., J.Exp.Med. (1988), 167. 1767-79). These synthetic peptides associate with class I molecules on the cell surface without the requirement for endogenous processing. When presented on the surface of an appropriate APC (such as a dendritic cell) they can then induce a primary CTL response. However, frequently these CTL do not protect against challenge with pathogens that endogenously synthesize the protein from which the peptide was derived because of their low T-cell receptor avidity (Speiser, et al., J.Immunol. (1992), 142, 972-80) and because they induce reactivity with a single epitope of the target antigen. GM-CSF is a cytokine that has pleiotropic function both in hematopoiesis as well as in immunology. GM-CSF has been shown to promote differentiation and survival of dendritic cells. GM-CSF can be used as an systemic adjuvant (Jones, et al., Eur.J.Clin.Microbiol. Infect.Dis. (1994), 13., S47-53). It is well known that immunization with soluble proteins can result in a significant antibody response. However, since class II restricted antigen presentation or direct B-cell stimulation is responsible for this effect, antibody induction has no predictive value for the stimulation of class I mediated induction of CTL. Most proteins uiat induce antibodies in vivo fail to induce CTL. GM-CSF fusion proteins have been shown to induce in vivo antibody responses in a lymphoma mouse model (Levy, R. and Tao, M.-H. (1993) Nature 362: 755-758; Chen, et al., J.Immunol. (1995), 3105-3117). In this study, tumor idiotype fused to GM-CSF was found to be superior to the mixture of both molecules and to other conventional adjuvants for the induction of antibody responses. In contrast to other solid tumors, antibody responses are believed to be the effector mechanism for tumor protection and for tumor therapy in lymphoma. Moreover, in vitro induction of immunity is generally much more difficult to achieve for both cellular and humoral responses. For example, viral antigen-transfected fibroblasts induce Class I restricted CTL in vivo in mice but fail to do so in vitro (Kundig, et al., Science (1995), 268. 1343-1347). Therefore, an antibody induction study with GM-CSF fusion proteins in vivo does not imply any of its in vitro utilities, and is particularly unpredictive of CTL induction in vitro or in vivo. Other methods that have been used for in vitro induction of primary protein-derived CTL are osmotic shock of dendritic cells and the use of pH-sensitive liposomes (Nair, et al., J.Exp. Med. (1992), .175, 609-12). However, such methods have been shown to be inherently ineffec¬ tive and toxic to APC 's, because they disrupt cellular membranes by physical and chemical force in order to release the protein antigen into the cytoplasm. These limitations are overcome by the discovery encompassed by the present invention. It is the discovery of the present invention that a T-cell response, and specifically, an MHC- Class I mediated T-cell response, can be stimulated by an isolated or soluble protein, when it is presented to the immune system as part of a complex with a dendritic cell binding protein, and more particularly GM-CSF. It is the further discovery of the present invention that such a response can be stimulated in vitro. As discussed above, in vitro stimulation of such a response has not previously been demonstrated using a full-length soluble antigen. The present invention provides for induction by isolated or soluble proteins of cellular immunity in vitro by presenting a specific antigen to an antigen presenting cell (APC), such as a dendritic cell, as part of an immunogenic fusion protein. An important aspect of the present invention is the choice of fusion partner protein: a dendritic cell binding protein, such as granulocyte-macrophage colony stimulating protein (GM- CSF). Without relying on any particular mechanistic theory, it is believed that the protein antigen is transported over the plasma membrane of the APC in a receptor-mediated, non-disruptive fashion. It is further believed that the dendritic cell binding portion of the fusion protein serves to preserve the viability and functionality of the APC. An additional aspect of the invention relates to the choice of target antigen. Although several tumor related antigens have been shown to serve as targets for T-cell mediated immunity in vivo, in vitro induction by isolated soluble polypeptide antigens has not been demonstrated. (Fisk, et al., J.Exp.Med. (1995), 181, 2109-2117). In experiments carried out in support ofthe present invention, it has now been demonstrated that tumor associated proteins not previously shown to be target antigens for CTL can become such targets by priming CTL with GM-CSF fusion derivatives in vitro. Summary of the Invention In one aspect, the invention is directed to a therapeutic composition for stimulating a cellular immune response. The composition is an isolated, stimulated potent antigen presenting cell, such as an activated dendritic cell, that is able to activate T-cells to produce a multivalent cellular immune response against a selected antigen. In general, the measured T-cell response is substantially higher than a T-cell response produced by such potent antigen presenting cells stimulated by the selected antigen alone. In a preferred embodiment of the invention, the potent antigen presenting cell is stimulated by exposing the cell in vitro to a polypeptide complex that consists essentially of a dendritic cell-binding protein and a polypeptide antigen. Preferably, the polypeptide antigen is either a tissue-specific tumor antigen or an oncogene gene product. However, it is appreciated that other antigens, such as viral antigens can be used in such combination to produce immunostimulatory responses. In another preferred embodiment, the dendritic cell-binding protein that forms part of the immunostimulatory polypeptide complex is GM-CSF. In a further preferred embodiment, the polypeptide antigen that forms part of the complex is the tumor-specific antigen prostatic acid phosphatase. In still further preferred embodiments, the polypeptide antigen may be any one of the oncogene product peptide antigens Her2, p21RAS, and p53. The polypeptide complex may also contain, between the dendritic cell-binding protein and the polypeptide antigen, a linker peptide. In a related aspect, the invention includes a method of activating an isolated antigen presenting cell in vitro. According to the method, the activation includes contacting an isolated antigen presenting cell with a polypeptide complex. The polypeptide complex used in this method is as described above; that is, it consists essentially of a dendritic cell-binding protein covalently linked to a polypeptide antigen, in any of the embodiments described above. According to the method, the activated antigen presenting cell is effective to activate a T-cell to produce a multivalent cellular immune response that is substantially higher than that produced by antigen presenting cells contacted with the selected polypeptide antigen alone. In a preferred embodiment, the antigen presenting cell is a dendritic cell, isolated as described herein. In yet another related aspect, the invention includes a method of inducing a cytotoxic T-cell response in a vertebrate subject. According to this aspect ofthe invention an isolated dendritic cell is contacted with an immunostimulatory polypeptide complex according to any of the embodiments described above for a period of time effective to activate the antigen presenting cell. The antigen presenting cell is then injected into the mammalian subject. In a preferred embodiment, the antigen presenting cell that is activated and injected is a dendritic cell. In further related aspects, the invention also includes the polypeptide complexes formed as described above. As described above, such polypeptide complexes are preferably formed from a dendritic cell binding protein, preferably GM-CSF, and a polypeptide antigen. The polypeptide antigen is preferably a tissue-specific tumor antigen such as prostatic acid phosphatase (PAP), or an oncogene product, such as Her2, p21RAS, and p53; however, other embodiments, such as viral antigen antigens, are also within the contemplation ofthe invention. In further related aspects, the invention also includes expression vectors and expression systems for producing the above-described immunostimulatory fusion proteins, as well as substantially purified nucleic acid molecules that encode such fusion proteins. In preferred embodiments, the nucleic acid molecules code for fusion proteins consisting essentially of GM¬ CSF and prostatic acid phosphatase or of GM-CSF and Her2. The invention also includes a novel prostate carcinoma cell line, HLA A2.1 cells, that can be used a target cell for testing tumor cell killing, as described herein. Brief Description of the Figures FIG. 1 shows nucleic acid (SEQ ID NO: 1) and deduced amino acid sequence (SEQ ID NO: 2) of PAP-GM-CSF fusion protein having as a peptide linker gly-ser resulting from the Bam HI linker (underlined); FIG. 2 shows the amino acid sequence of the fusion protein Human Prostatic Acid Phosphatase/Human GM-CSF, with the PAP signal sequence not present in the mature protein shown in small caps, potential N-glycosylation sites marked "C" , and potential disulfide bridges marked "S-S"; FIGS. 3A and 3B show schematic representations of PAP-GM expression vectors pCEP4 PAPGM (3 A) and PAPHGM-BAC (3B) used in mammalian (293 cells) and insect (SF21) cell lines, respectively; FIG. 4 shows a graph of GM-CSF bioactivity of mammalian and baculovirus-derived PAP- GM-CSF fusion proteins; FIG. 5 shows a graph of acid phosphatase bioactivity of PAP-GM-CSF fusion proteins; FIG. 6 shows a graph of lysis of prostate carcinoma cells by CTL primed with PAP-GM- CSF and stimulated with PAP-GM-CSF pulsed antigen presenting cells; FIG. 7 shows a bar graph depicting blockade by HLA-class I blocking antibody of lysis of prostate carcinoma cells by PAP-GM-CSF primed CTL; FIG. 8 shows the nucleic acid (SEQ ID NO: 3) and amino acid (SEQ ID NO: 4) sequences of a GM-CSF-Her2 fusion protein in accordance with the present invention; FIG.9 shows titration of GM-CSF activity in crude Baculovirus Insect Cell (BVIC) culture supernatants from ratPAP or ratPAP-mouseGM-CSF infected Sf21 cultures as compared to recombinant mouseGM-CSF and resultant proliferative response of rodent GM-CSF-dependent cell line GM-NFS-60; FIG. 10 shows an immunization scheme of COP rats wkh purified dendritic cells pulsed with ratPAP-ratGM-CSF; FIG. 11 shows nucleic acid and deduced protein sequence of the p53-GM-CSF fusion gene, where the Xba I linker that codes for serine and arginine is boxed; and FIG. 12 shows the amino acid sequence of p53-GM-CSF fusion protein with the synthetic serine-arginine linker printed in boldface and underlined. Detailed Description of the Invention I. Definitions As used herein, the term "tissue-specific antigen" refers to an antigen that is characteristic of a tissue type, including specific tumor tissues. An example of a tissue-specific antigen expressed by a tumor tissue is the antigen prostatic acid phosphatase, which is present in over 90% of all prostate tumors. By way of contrast, B-cell lymphomas produce immunoglobulin antigens that are particular to the individual tumor. Such particular tumor antigens are not considered to fall within the definition of the term "tissue-specific antigen." The term "oncogene product" refers to any protein coded for by a gene associated with cellular transformation. Examples of oncogene products include, for example, Her2, p21RAS, and p53. "Antigen presenting cells" (APC) are cells that are capable of activating T cells, and include, but are not limited to, certain macrophages, B cells and dendritic cells. "Potent antigen presenting (PAP) cells" are cells which, after being pulsed with an antigen, can activate naive CD8 + cytotoxic T-lymphocytes (CTL) in a primary immune response. The term "dendritic cell" refers to any member of a diverse population of morphologically similar cell types found in lymphoid or non-lymphoid tissues. These cells are characterized by their distinctive morphology, high levels of surface MHC-class II expression (Steinman, et al., Ann. Rev. Immunol. 9: 271 (1991); incorporated herein by reference for its description of such cells). These cells can be isolated from a number of tissue sources, and conveniently, from peripheral blood, as described herein. The term "dendritic cell binding protein" refers to any protein for which receptors are expressed on a dendritic cell. Examples include GM-CSF, IL-1, TNF, IL-4, CD40L, CTLA4, CD28, and FLT-3 ligand. II. Immunostimulatory Polypeptide Complexes A. Selection of Components of the Polypeptide Complex An immunogenic polypeptide formed in accordance with the present invention is generally characterized as an isolated polypeptide antigen which is covalently linked to a dendritic cell- binding protein. 1. Polypeptide Antigens As stated above, isolated polypeptide antigens do not generally stimulate activation of T-cells in vivo or in vitro. It is the discovery of the present invention that certain types of polypeptide antigens, when coupled to a dendritic cell-binding proteins, such as those discussed below, stimulate T-cell activation. The present invention identifies as particularly useful in this capacity (1) tissue-specific tumor antigens and (2) oncogene product peptide antigens. In the context of the present invention, the term "tissue-specific tumor antigens" refers to antigens that are common to specific tumor types. By way of contrast, antigens that are specific to a particular individual tumor, such as the B cell lymphoma tumor-associated idiotype antigen, are distinguishable from tissue-specific tumor antigens in that they have a characteristic epitope that varies from individual to individual. Such antigens are less useful in the context of the present invention, since a immunostimulatory reagents must be tailored to the individual tumor, and consequently do not form part of the invention. Malignant tumors express a number of proteins that can serve as target antigens for an immune attack. These molecules include but are not limited to tissue-specific antigens such as MART-1, tyrosinase and GP 100 in melanoma and prostatic acid phosphatase (PAP) and prostate-specific antigen (PSA) in prostate cancer. Other target molecules belong to the group of transformation-related molecules such as the oncogene HER-2/Neu/ErbB-2. Yet another group of target antigens are onco-fetal antigens such as carcinoembryonic antigen (CEA). In B-cell lymphoma the tumor-specific idiotype immunoglobulin constitutes a truly tumor-specific immunoglobulin antigen that is unique to the individual tumor. B-cell differentiation antigens such as CD 19, CD20 and CD37 are other candidates for target antigens in B-cell lymphoma. Some of these antigens (CEA, HER-2, CD 19, CD20, idiotype) have been used as targets for passive immunotherapy with monoclonal antibodies wid limited success. Thus, examples of tissue-specific tumor antigens include, but are not limited to prostatic acid phosphatase (PAP; associated with prostatic tumors), Melan-A/MART-1 (associated with melanoma; Coulie et al., 1994, J.Exp.Med. 1SQ:35, Hawakami et al., 1994, PNAS £1:3515, Bakker et al., 1994, J.Exp.Med. 179:1005), tyrosinase/albino (associated with melanoma; Kawakami et al., 1994, J.Exp.Med.). CD19, CD20 and CD37 (associated with lymphoma). Likewise, oncogene product peptide antigens have been identified that are common to specific tumor types. These polypeptides can be incorporated into polypeptide complexes of the present invention as reagents that can be used generally to stimulate T-cell responses effective to react wi i tumors bearing such antigens. Oncogene product peptide antigens include but are not limited to ΗER-2/neu (Beckmann et al., 1992, Eur.J. Cancer 28:322) associated with human breast and gynecological cancers, and carcinoembryonic antigen (CEA) associated with cancer of the pancreas. A variety of tumor markers are known in the art or are commercially available and include, but are not limited to the tissue-specific antigens that include cytokeratins, prostate- specific antigen (Wang et al. , 1977), gplSlbrown (Brichard et al. , 1993, J.Exp.Med. 178:489) associated with melanoma, melanotransferrin (Real etal., 1984, J.Exp.Med. 160:1219). MUC1 (Barnd, 1989, PNAS USA £6_:7159 and Vijayasaradhi et al., 1990, J.Exp.Med. 121:1375) associated with pancreas and breast cancer; oncogene/tumor suppressor genes that include EGF- R (Osborne et al., 1980), estrogen receptor, progesterone receptor, retinoblastoma gene product, myc associated with lung cancer, ras, p53, nonmutant associated with breast tumors, MAGE-1,3 (van der Bruggen et al., 1991, Science 254:1643 and Gaugler et al., 1994, J.Exp. Med. 122:921) associated with melanoma, lung, and other cancers. Isolated viral antigens may include HIV antigens gρl20, gp41, gag, RT, NEF, VIF; influenza antigens HA, core and matrix,; EBV antigens: EBNA, BFLF1, BOLF1, BGLF2, LMP2a, LMP2b, BBRF1, BBRF2, and P11L27; and human papilloma virus. Polypeptide antigens such as those described above can be isolated, synthesized or recombinantly expressed according to methods known in the art. In most cases, DNA coding sequences have been identified for these molecules. In addition, many of the so-called "tumor markers" are available commercially. Such isolated antigens can be complexed with a dendritic cell binding protein chemically, as discussed below, or fusion protein constructs may be produced recombinantly, according to methods well known in the art. As an example of the foregoing, prostatic acid phosphatase (PAP) is the prostate-specific isozyme of the ubiquitous enzyme acid phosphatase. PAP is a secreted molecule that has been identified as a serum tumor marker that is specific for prostate cancer. (Vihko, et al. , FEBS Lett. (1988), 22£, 275-281, Solin, et al., Biochem.Biophvs.Acta (1990), lfi48_, 72-77). There is no evidence from the literature that PAP by itself might serve as an inducer and target of CTL. As is demonstrated below, the present invention shows that PAP can serve both as an inducer of CTL and as a target in prostate cancer cells, when combined with the dendritic cell binding protein GM-CSF and used to stimulate antigen presenting cells (exemplified by dendritic cells) that are then used to prime CTL. 2. Dendritic cell binding proteins The second component of the polypeptide complex of the present invention is a dendritic cell binding protein. As mentioned above, without relying on any particular mechanistic theory, it is believed that the presence of such a molecule in covalent complex with a protein antigen facilitates transport of die antigen over the plasma membrane of the antigen presenting cell, and more particularly, the dendritic cell, in a receptor-mediated, non-disruptive way. It is further believed that the dendritic cell binding portion of uie fusion protein serves to preserve the viability and functionality of the APC. An example of a dendritic cell binding protein is granulocyte-macrophage colony stimulating factor (GM-CSF). This glycoprotein, which has an apparent molecular weight of about 23-33,000 by SDS-PAGE, is a cytokine tiiat has pleiotropic function both in hema- topoiesis as well as in immunology. Both human and murine GM-CSF are synthesized with a 17-amino acid hydrophobic leader sequence that is proteolytically cleaved during secretion. The mature proteins are 127 (human) or 124 (murine) amino acids, and have core polypeptide molecular weights of 14,700 and 14,400, respectively, but share only 52% amino acid identity. The factor has been found to play a stimulatory role in the differentiation and survival of dendritic cells and is active in both glycosylated and de-glycosylated forms. Human and murine GM-CSF have been shown to bind to both high affinity (K D = 20-60 pM) and low affinity (K D = l-6 nM) binding sites on cells of the monocyte-macrophage, neutrophil and eosinophil cell lineages. Competition for binding by another member of the hemopoietic colony stimulating factors, Multi-CSF, has been shown when the binding is carried out at 37°. Binding of GM-CSF to high affinity receptors results in rapid internal ization and degradation of GM-CSF (Metcalf, D. and Nicola, N.A. (1995) The Hemopoietic Colony- Stimulating Factors. Cambridge University Press, NY.). These properties may be used to serve as a guide to the selection of additional dendritic cell binding proteins useful in forming immunostimulatory polypeptide complexes in accordance with the present invention. B. Formation of Polypeptide Complexes Polypeptide complexes can be formed by chemical means, such as by conventional coupling techniques known in the art. For example, the peptides can be coupled using a dehydrating agent such as dicyclohexylcarbodiimide (DCCI) to form a peptide bond between the two peptides. Alternatively, linkages may be formed through sulfhydryl groups, epsilon amino groups, carboxyl groups or other reactive groups present in the polypeptides, using commercially available reagents. (Pierce Co., Rockford, IL). Polypeptide complexes can also be formed recombinantly as fusion proteins according to methods known in the art. Example 1 details the methods used to produce a GM-CSF-PAP fusion protein in accord with the present invention. Briefly, human PAP was cloned from a prostate carcinoma cell line according to methods known in the art. The stop codon at the 3' end ofthe sequence was mutated away, and a Bam HI site inserted in its place, to fuse the PAP cDNA to GM-CSF DNA. GM-CSF DNA was cloned from a PBMNC library according to standard methods. A Bam HI site was inserted at the 5' end of the DNA, and an Xbal cloning site was inserted at the 3' end, along with an in-frame stop codon. PCR-generated cDNA's were digested with appropriate restriction enzymes and cloned into restriction vectors for transfection into specific mammalian or insect cell lines. FIG. 1 shows nucleic acid and deduced amino acid sequences ofthe PAP-GM-CSF fusion polypeptide having a gly-ser peptide linker. FIG. 2 further illustrates the fusion protein sequence with potential glycosylation sites indicated as "C" and probable disulfide bridges shown as "S-S." FIGS. 3A and 3B show schematic representations of the PAP-GM-CSF expression vectors used for transfecting mammalian (293) and insect (SF21) cell lines, respectively. The fusion expression vectors were used to transfect COS cells (transient expression) as well as mammalian 293-EBNA cells (Invitrogen) and insect SF21 cells (Clontech, Palo Alto, CA). Fusion protein products were recovered from the tissue culture supernatants, and affinity purified by passage over an anti-human PAP monoclonal antibody immunoaffinity column. Analysis by SDS-PAGE revealed protein bands migrating at 75 kD and 64 kD as products from mammalian and insect cells, respectively. The 75 Kd band corresponds to a size that is approximately 19.5 Kd larger than the predicted size of the PAP-GM-CSF polypeptide backbone which is 55.5 Kd. This can be explained by the presence of 5 potential N-glycosyla¬ tion sites in the sequence, glycosylation at which would increase the apparent M r ofthe protein, and is consistent with the fact that 293-EBNA cells contain fully functional human glycosylation machinery. The insect cell-derived fusion protein was approximately 8.5 Kd larger than the PAP-GM-CSF peptide backbone. These data are consistent with the known glycosylation patterns in Sf21 cells, which are reported to utilize N-glycosylation sites but which only add truncated carbohydrates that typically end with the addition of a single mannose residue. The fusion molecules were tested for PAP and GM-CSF bioactivities in appropriate assays, detailed in Example 2. Both insect and mammalian cell-derived fusion proteins exhibited GM- CSF activity, as evidenced by their ability to support growth of GM-CSF dependent cell lines (FIG. 4). Similarly, both products exhibited PAP activity (FIG. 5). Fusion proteins constructed to incorporate oncogene product antigens are exemplified by incorporation ofthe oncogene product Her2. Her2 is a growth factor receptor belonging to the EGF-R family of receptors. It is over-expressed by breast cancer cells, ovarian cancer cells and a variety of other cancer cells. The cDNA coding for the extracellular domain of Her2 is cloned from a breast cancer cell line and fused to the GM-CSF cDNA, essentially as detailed for PAP-GM-CSF, above. Production of the soluble protein can be verified using Her2- specific monoclonal antibodies in an ELISA test, according to methods well-known in the art. The fusion protein includes the sequences for the extracellular domain (amino acids 1-652) of Her2 (GenBank) and GM-CSF (FIG. 8). In this particular fusion protein the two proteins are linked by a leucine/glutamic acid linker which is generated by inserting a XHO I site. The cellular tumor suppressor gene p53 is cloned and fused to GM-CSF, as described in Example 7. The sequence of the recombinant fusion gene is shown in FIG. 11, and the sequence of the produced polypeptide p53-GM-CSF is shown in FIG. 12. The p53-GM-CSF fusion protein is used to generate anti-p53 immunity as described for the induction of anti-PAP immunity by PAP-GM-CSF in Examples 3, 4 and 6. Other oncogene product antigens are similarly incorporated into fusion proteins according to the methods described herein, using published sequences. In addition, other antigens, such as viral antigens, may be part of a fusion construct, according to the methods described herein. While the foregoing description describes particular embodiments ofthe present invention, it will be appreciated that persons skilled in the art can substitute different antigens, vectors and expression cell lines, according to known methods, to prepare immunostimulatory polypeptide complex compositions in accordance with the principles described above. In addition, it is appreciated that the invention may also be practiced by inserting between the dendritic cell binding protein and the polypeptide antigen, a linker peptide or protein such as ubiquitin, according to recombinant methods known in the art. III. Stimulation of T-cells An important aspect of the present invention is the utility of the above-described polypeptide complex constructions in a method to target the antigen protein partner to Antigen Presenting Cells (APC), such as the cell type known as the "dendritic cell", described above. In accordance with the invention, the targeting occurs in a manner that results in entry into the class I pathway of antigen processing. The APC is then used to prime CTL ex vivo and in vivo, according to the methods discussed below. Dendritic cells are highly potent APCs, and are the only APC that can prime naive CTL. While dendritic cell precursors present in human blood can take up antigen, they do not function as potent APCs. On the other hand, the mature dendritic cell is the most potent APC, but it does not take up antigen spontaneously in vitro. In the past, it was necessary to treat mature dendritic cells with physical force (liposomes, osmotic shock) or to coat them with exogenous small (8-11 amino acids in length; generally 9-mer) peptide antigens to enable them to act as APC. The present invention enables introduction of an exogenously added protein into the class I pathway of a mature dendritic cell. Such induction can be effected in vitro, by isolating APCs such as dendritic cells, "pulsing" or contacting them with the polypeptide complex for an extended period of time, then using the pulsed APCs to stimulate autologous T-cells in vitro or in vivo. In the latter case, the pulsed APCs are administered (approximately 10 7 cells/ injection) to the subject. The response of the subject is measured by monitoring the induction of a cytolytic T-cell response, a helper T-cell response and antibody response towards the antigen in peripheral blood mononuclear cells by methods well known in the art. Multiple doses may be administered to produce an adequate response. The use of GM-CSF fusion antigen-stimulated dendritic cells yields superior results to other approaches, such as the peptide pulsed dendritic cell preparations. That is, while dendritic cells pulsed with 8-11-mer peptides are able to induce immunity, such immunity is directed to a single T-cell epitope. Proteins incoφorated into liposomes or delivered to the dendritic cells by osmotic shock induce reactivity towards multiple T-cell epitopes; however, this process is relatively ineffective due to the inherent toxicity of these treatments to dendritic cells. In contrast, GM-CSF fusion antigens of the present invention induce immunity towards multiple epitopes and preserve and enhance at the same time viability and function of the dendritic cell. In practice, the compositions of the present invention are found to induce a cellular (T-cell) activation that is multivalent and substantially higher than that produced by a selected antigen alone. In experiments carried out in support ofthe present invention, the fusion protein consisting of PAP and GM-CSF described in the previous section was used for in vitro introduction to dendritic cells and subsequent activation of cytolytic T cells, as detailed in Example 4. Briefly, HLA-A2.1 positive PBMNC were isolated by standard methods and primed with the fusion protein for 2-5 days. The cell mixture was depleted of CD4 + T-cells, separated into high and low density fractions, and the separate cultures were re-stimulated weekly with autologous PAP GM-CSF pulsed APCs. Lytic potential of the T-cells present in the fractions was assessed using a standard chromium release assay using an HLA-A2.1 -transgenic prostate carcinoma cell line as target. This novel cell line was constructed according to the methods detailed in Example 3 herein and is useful in screening and analysis of HLA class I restricted cytotoxic T-lymphocytes. Results ofthe lysis assays are presented in FIG. 6. As shown, of the four different T-cell cultures tested, three displayed substantial dose-dependent cytotoxicity towards the prostate carcinoma target. The highest degree of cytotoxicity was effected by cells that fractionated into the high density pellet fraction on day 5 (open circles, 5-day P). High (open squares, 2-day P) and low (closed squares, 2-day IF) density cells primed for two days showed roughly equal potency. Cell cultures derived from day 5 low density interface fraction (closed circles, 5-day IF) displayed little or no cytotoxicity. FIG. 7 shows that the tumor-specific cytolysis was substantially reduced in the presence of the HLA class I-specific blocking antibody W6/32 at an Effector:Target (E T) ratio of 10:1 and is completely eliminated by the antibody at an E T ration of 3.3/1. Control antibody CA 141 did not reduce T-cell mediated killing. These experiments demonstrate that the interaction with the target cell is mediated by via classical T-cell receptor/HLA-class I restricted antigen-specific pathway. The foregoing results demonstrate the efficacy of fusion polypeptide complexes formed in accordance with the present invention in stimulating T-cell responses in vitro. These responses can be compared to those stimulated by the antigen alone (in the absence of the dendritic cell binding protein). In addition, their multivalent character can be tested by standard methods. IV. Therapeutic applications A. In vitro/ex vivo Therapy The present invention provides for induction by isolated or soluble proteins of cellular immunity in vitro by presenting a specific antigen to an antigen presenting cell (APC), such as a dendritic cell, as part of an immunogenic fusion protein. As discussed above such induction is not generally observed in vitro using soluble, whole antigens as induction materials. In practice, dendritic cells are isolated from an individual, using known methods, or preferably, as described in Example 5. The dendritic cells (or other APCs) are mixed with 10 ng/ml equivalent of GM-CSF fusion antigen, as described in Example 4. The cell preparation may then be depleted of CD4 + T-cells by solid phase immunoadsoφtion and further fractionated to enrich for cells having cytolytic activity. Doses of about 10 7 cells are then administered to the subject by intravenous or central injection according to established procedures (e.g., infusion over 30 to 60 minutes). The responsiveness of the subject to tins treatment is measured by monitoring the induction of a cytolytic T-cell response, a helper T-cell response and antibody response towards the antigen in peripheral blood mononuclear cells by methods well known in the art. In addition to the direct in vivo administration regiment described above, the APC cells can be used, for example, in ex vivo somatic therapy, in vivo implantable devices and ex vivo extra-coφoreal devices. They can also be employed in the screening of antigenicity and immunogenicity of peptide epitopes from tumor- and virus-specific antigens. In certain cases, it may be advantageous to use cells obtained from one individual to treat a condition in a second individual. For example, HIV-infected individuals with AIDS are often not able to mount anti-viral T-cell responses. In such cases, CTL can be isolated from healthy HLA-matched individuals, such as siblings, be stimulated or primed with antigen-pulsed DC in vitro, expanded, and administered back to the HIV-infected individuals. B. In vivo Therapy The fusion protein compositions described herein can also be administered directly to an individual as a vaccine, in order to stimulate the individual's cellular immunity pathways in vivo. Here a dose of about 5 to 200 microgram/kg fusion protein, is administered, preferably at days 0, 14 and 28 with an optional boosting dose at 6 months. The response of the subject is measured by monitoring the induction of a cytolytic T-cell response, a helper T-cell response and antibody response towards the antigen in peripheral blood mononuclear cells by methods well known in the art. C. Results from Experimental Models of Immunostimulation Example 6A provides details of the construction of fusion antigens and injection protocols used in an experimental rat model of immunostimulation. A fusion protein made up of rat PAP and rat GM-CSF was injected directly into rats (in vivo stimulation) or to stimulate rat dendritic cells for later injection into rats (ex vivo induction). It is necessary to use rat molecules and cells, since human effector cells do not function normally in other species and are, in addition, antigenic in other species, such as rat. Moreover, the target antigen (PAP) is different between humans and other species, and human GM-CSF would not be expected to produce the same type of effect in other species. Nonetheless, it is understood that the use of rat cells in rats should provide a model system for the use of human cells and proteins in humans. As detailed in Example 6, rat prostatic acid phosphatase (ratPAP) was prepared recombinantly and was fused to rat GM-CSF. Dendritic cells from rat splenic tissue were pulsed with ratPAP-ratGM-CSF and were injected into normal rats. In addition, alternate delivery systems were tested, since autologous PAP-directed immunization has not previously been carried out, to the best of our knowledge. In studies carried out in support of the present invention and detailed in Example 6B, rats were immunized with either (i) ratPAP-ratGM-CSF pulsed dendritic cells, (ii) ratPAP-ratGM- CSF alone, or (iii) rat PAP in conventional CFA adjuvant. Rat organs (prostate plus six major organ systems) were later examined for immunopathology evoked by autologous PAP-directed immunization. According to the rat model system, it was expected that a successful immune response would result in immune targeting of PAP-expressing organs, and in particular, the prostate. As shown in Table 1 , the histopathology studies show that immunizations with rat PAP-rat GM-CSF pulsed dendritic cells or with rat PAP rat GM-CSF fusion protein induce organ- specific autoimmunity that is limited to the prostate. In contrast, immunization with ratPAP/CFA protein did not produce this result. This result demonstrates that PAP-GM-CSF itself and PAP-GM-CSF pulsed dendritic cells produce antigen-specific autoimmunity that is significantly better than, and in fact, cannot be produced by, the antigen alone in association wim a conventional adjuvants. Table 1 Organ Histopathology* of immune and non-immune rats 1 PAP ND ND ND ND ND ND 1 Mild multifocal lymphocytic GM inflammation in the interstitium 2 PAP ND ND ND ND ND ND 1 Mild multifocal lymphocytic GM inflammation in uie interstitium ' Pathology grading: ND = Not evaluated; N = No significant lesions; 1 = trace/mild; 2 = mild; 3 = moderate; 4 = severe. b Immunization groups: animals IC, 2C, 3C, 4C were non-immunized controls; animals 5T, 6T, 7T, 8T were immunized with rat PAP rat GM-CSF pulsed dendritic cells; animals ICFA, 2CFA were immunized with rat PAP immersed in CFA; animals 1 PAP GM, 2 PAP GM were immunized with recombinant rat PAP rat GM-CSF. The following examples illustrate, but in no way are intended to limit the invention. Example 1 Construction of PAP/GM-CSF Fusion Proteins If not described otherwise, general cloning procedures were performed according to standard techniques as described in Sambrook, et al. , Molecular Cloning: A Laboratory Manual (1989). Human PAP was cloned from the prostate carcinoma cell line LnCaP.FGC (American Type Culture Collection, Rockland Maryland; "ATCC"). Synthetic oligonucleotide primers containing the sequence CGGCTCTCCTCAACATGAGAGC were custom synthesized according to standard methods by Keystone Labs (Menlo Park, CA). These primers are homologous to the 5 ' end of the known PAP cDNA sequence which is published in the GenBank database. Hind III, Mun I or Xho I restriction sites were attached, according to the requirements of the particular expression vector used. On the 3 ' end an oligonucleotide of the sequence CACAGGATCCATCTGTACTGTCCTCAGTACC was constructed that mutated away the stop codon 387 of the PAP sequence and substituted for it a Bam HI site that codes for amino acids glycine and serine. This Bam HI site was used to fuse the PAP cDNA to the GM-CSF cDNA, which was cloned from peripheral blood mononuclear cells (PBMNC), based on the sequence which is published in GenBank. At the GM-CSF 5 ' end a Bam HI site was attached to an oligonucleotide GACTGGATCCGCACCCGCCCGCTCGCCC that is homologous to the nucleotides that code for amino acids 18-23 in the GM-CSF sequence. The 3 ' end of GM-CSF was generated with a an oligonucleotide GATCTCTAGAGCTTGGCCAGCCTCATCTGG that ends after the in frame stop of GM-CSF and creates an Xba I cloning site. Poly A+ RNA was isolated from cell line LnCaP.FGC and from PBMNC with the Micro Fast track kit (Invitrogen) according to the manual supplied by the manufacturer. The Poly A+ RNA was then reverse transcribed with the cDNA cycle kit (Invitrogen) according to procedures described in the accompanying manual. First strand cDNA was then subjected to 25 cycles of polymerase chain reaction (PCR) wim the above described primers. The conditions on a Perkin-Elmer thermal cycler 9600 were as follows. 25 cycles of amplification were performed at: Denaturation: 94°C, 15 seconds; annealing 55°C, 15 seconds; extension 72°C, 60 seconds. The 25 cycles were followed by a final extension period of 420 seconds at 72°C. The PCR products were analyzed on agarose gels. They were digested with the appropriate restriction enzymes and cloned into the vectors pCR3 (Invitrogen) to create pCR3-PAP-GM (not shown), pCEP 4 (Invitrogen) to create pCEP4-PAP GM (FIG. 3A) and into pBacPac 8 (Clontech) to create PAPHGMBAC (FIG. 3B). The DNA sequences ofthe cloned constructs were confirmed using standard methods on a fluorescent sequencer Model ABI 373A (Applied Biosystems, Foster City, CA). The nucleotide sequence and the deduced amino acid sequences are presented as SEQ ID NO.: 1 and SEQ ID NO: 2, in FIG. 1, respectively. pCR3 PAP-GM was electroporated into COS -7 cells (ATCC) for transient expression experiments. After it was confirmed that a protein of the predicted size, immunological identity and function could be expressed transiently in COS-7 and 293-EBNA (Invitrogen) cells stable transfectants were generated in tiie human embryonic kidney cell line 293-EBNA, using an episomal expression vector pCEP4 (Invitrogen, San Diego, CA). After electroporation and selection in hygromycin, recombinant clones were generated by plating the cells under limiting dilution conditions and screening for PAP bioactivity in the cellular tissue culture supernatants. The highest producing clones were adapted to protein-free media and grown in CellMax hollow fiber bioreactors (Gibco, Gaithersberg, MD). Spent media from the cultures were collected, pooled and clarified by centrifugation. They were then passaged over an immunoaffinity column tiiat was made by coupling the human PAP-specific monoclonal antibody ATCC HB8526 (ATCC) to a Sepharose resin. After washing, the bound material was eluted at low pH, neutralized and dialyzed against physiological buffer. The eluted fraction was analyzed by denaturing SDS-PAGE electrophoresis under reducing conditions. The resulting gel showed a single protein band at 75 kD which corresponds to the predicted size of fully glycosylated PAP-GM-CSF. PAPHGM-BAC was also used to generate a recombinant Autographa californica nuclear polyhedrosis virus (AcNPV, baculovirus) by homologous recombination of PAPHGM-BAC with BacPAKό viral DNA (Clontech, Palo Alto, CA). Reagents were used from the BacPAK baculovirus expression system (Clontech) and procedures were carried out essentially as described in the product manual. PAPHGM-BAC and BacPAKό were co-transfected into SF21 cells (Clontech) by lipofection. The spent tissue culture supernatant was collected on day 5. It was titered onto fresh SF21 cells which were then grown in semisolid media for another 4 days. After the monolayers were stained with neutral red, viral plaques were identified and picked widi a Pasteur pipet. Recombinant plaque-purified virus was eluted into fresh media and was then used to screen for production of PAP-GM-CSF in fresh SF21 cells. Positive plaques were identified and used to generate viral stocks and recombinant protein in subsequent rounds of infecting fresh SF21 cells. The media of production cultures were collected three days after infection. They were then processed as described for PAP-GM-CSF that was derived from 293-EBNA cells. Analysis of the immunoaffinity-purified protein revealed a single protein band at 64 kD after silver staining of an SDS-PAGE gel. Example 2 Bioactivity of PAP-GM-CSF fusion proteins PAP-GM-CSF fusion proteins from all expression systems described in Example 1 were analyzed for their ability to support the growth of GM-CSF dependent cell lines. They were also analyzed for enzymatic activity in acid phosphatase assays. Standard bioassays were used to determine the GM-CSF bioactivity. GM-CSF Activity. The GM-CSF dependent human erythroleukemia cell line TF-1 (ATCC, Rockville, MD) and the acute monocytic leukemia cell line AML-193 (ATCC) were used to analyze whether GM-CSF retains its bioactivity after fusion to PAP. The cell lines which are routinely cultured in GM-CSF-containing media were starved in regular media for 24 hours before the assay. They were plated at 1500 cells per well in triplicates in tissue culture medium. Test supernatants or recombinant GM-CSF as a positive control were added to the cells. Cells were cultured for 72 hours and were then pulsed for 4 hours with 1 microcurie tritiated thymidine per well to determine rate of DNA synthesis. FIG. 4 shows that both mammalian derived and insect cell-derived PAP-GM-CSF support the growth of GM-CSF dependent cell lines. The calculated relative bioactivity of PAP-GM-CSF is 20% of the activity of control recombinant GM-CSF dependent cell lines on a molar basis. Acid Phosphatase Activity. The bioactivity of the second component of the fusion protein was determined in an enzymatic assay for acid phosphatase activity. Acid phosphatase was measured as the ability of the protein to hydrolyze para-nitrophenyl phosphate (pNPP) at acid pH. Briefly, the test liquid was diluted in 50mM sodium citrate pH 4.8. pNPP is added to a final concentration of 2 mg/ml. After 30 minutes incubation at 37°C, an equal volume of 1M NaOH was added to the reaction. Hydrolyzed pNPP under these conditions has a yellow color which can be quantified with a spectrophotometer at 405 nm. FIG. 5 shows that both mammalian derived and insect cell derived PAP-GM-CSF hydrolyzed pNPP under acid conditions. Thus, it is clear that the original biological activity of both PAP and of GM-CSF is conserved in PAP-GM-CSF fusion proteins. Example 3 Generation of a target cell line for HLA class I-restricted cytotoxic T-lymphocytes If not otherwise described, all tissue culture techniques, cell manipulations and assays were performed according to standard techniques. In order to generate a prostate cancer cell line that could be used as a target cell on a defined genetic background an HLA A2.1 -transgenic prostate cancer cell line was generated. HLA A2.1 is the best studied restriction element in human HLA class I restricted immune responses and is the most frequent allele in Caucasians. A cDNA that codes for the published sequence (GenBank) of HLA A2.1 was isolated and cloned from the lymphoblastoid cell line JY. HLA A2.1 heavy chain cDNA was amplified with the sense primer 5-AgACgCCgAggAT- ggCC-3 ' and the anti-sense primer 5-CCTCTCTggAACAggAAAgATg-3 '. Methods and conditions were as described for PAP and GM-CSF except that the cell line JY (obtained from Dr. Ed Engleman, Stanford University Blood Bank, Stanford, CA) was used as starting material. The resulting gene fragment was cloned into the pCR3 vector wim the TA-cloning kit (Invitrogen). The prostate carcinoma cell line LnCaP.FGC (ATCC) was transfected with this expression plasmid which confers the expression of HLA A2.1. The parent cell line does not express the A2.1 allele. After drug selection in G418 (Gibco) the resulting transfectants were selected for HLA A2.1 expression by solid phase immunoadsorption ("panning") with a HLA A2.1-specific monoclonal antibody (BB7.1, ATCC). The resulting cell line homoge¬ neously expressed HLA-A2.1 whilst its parent remained negative. This novel transgenic cell line is uniquely useful in the screening and analysis of HLA class I restricted cytotoxic T-lymphocytes. Example 4 Induction of prostate cancer-specific CTL by PAP-GM-CSF A T-cell in vitro priming and expansion system was used to establish the utility of PAP-GM-CSF in the generation of HLA class I restricted CTL. HLA- A2.1 -positive PBMNC were isolated by standard methods on density gradient (FICOLL-HYPAQUE, Pharmacia Fine Chemicals, Piscataway, NJ) having a density of 1.077 gr/ml. The cells were primed with 10 ng/ml equivalent of PAP-GM-CSF for two or five days. (GM-CSF potency equivalent was measured on a GM-CSF dependent cell line as detailed in Example 3; the actual weight used was twenty-fold higher because of the different size and specific activity of PAP-GM-CSF.) The cell preparation was then depleted of CD4+ T-cells by solid phase immunoadsoφtion and separated into low density and high density cells over a 1.068 gr/ml density gradient. The different fractions were then cultured separately in AIM V media (Gibco, Gaithersberg, MD) supplemented with rIL-2 (20 U/ml). Autologous PBMNC that were cultured in 20 ng/ml PAP-GM-CSF in Aim V media were used as antigen presenting cells for re-stimulation at weekly intervals. Lytic potential of the cells was assessed in a standard 4-hour chromium release assay with the HLA-A2-1 -transgenic prostate carcinoma cell line LnCaP.FGC as a target. FIG. 6 shows induction of Prostate-carcinoma LnCaP.FGC/A2.1 -specific cytotoxic T-lymphocytes by PAP-GM-CSF pulsed antigen presenting cells. HLA-A2.1 positive PBL were primed with 10 ng/ml GM-CSF equivalents of PAP-GM-CSF for two or five days. The cultures were depleted of CD4 + T-cells and separated into low (IF) and high (P) density fractions over a Nycodenz density gradient having a density of 1.068 gr/ml. To investigate whether the observed cytotoxicity was a HLA-class I-restricted CD8+ cytolytic T-cell mediated phenomenon a blocking assay with the monomoφhic HLA class I-specific monoclonal antibody W6/32 (ATCC) antibody was performed. W6/32 blocks HLA class I mediated killing in standard assays, whilst control antibody CA141 is specific for HLA class II (DR) and will not interfere with class I restricted killing. T-cell cultures which were derived from the 5 day pellet fraction (described above) which displayed the highest cytotoxicity were used for this experiment. The T-cell lines used in experiment contained 38% CD3/CD8 positive T-cells. Their lytic potential was assessed in a standard 4-hour chromium release assay with the HLA-A2-1 -transgenic Prostate carcinoma cell line LnCaP.FGC as a target. FIG. 7 shows that tumor-specific cytolysis was substantially reduced in the presence of the HLA class I blocking antibody W6/32 at an Effector :Target (E/T) ratio of 10:1 and is completely eliminated by the antibody at an E T ration of 3.3/1. Control antibody CA 141 did not reduce T-cell mediated killing. These experiments demonstrate that the interaction with the target cell is mediated by via classical T-cell receptor/HLA-class I restricted antigen-specific pathway. Example 5 Preparation of Dendritic cells Buffy coats prepared from one unit of blood from HLA-A0201 positive volunteer healthy donors are obtained from the Stanford University Blood Center (Stanford, CA). Cells are harvested from the leukopacs, diluted to 60 mL using Ca + + /Mg + + free phosphate buffered saline (D-PBS; Gibco Laboratories, Grand Island, NY) and layered over two 15 mL columns of organosilanized colloidal silica (OCS) separation medium (prepared as described by Dora in U.S. Patent 4,927,749, incoφorated herein by reference, at a density 1.0720 gr/ml, pH 7.4, 280 mOsm/kg H 2 O) in 50 mL centrifuge tubes, preferably cell-trap tubes. The OCS medium is preferably prepared by reacting and thus blocking the silanol groups of colloidal silica (approx. 10-20 nm diameter particles) with an alkyl trimethoxy silane reagent. Related colloidal silicas and methods for production thereof are disclosed in U.S. Patent 4,927,749 to Dorn. In a preferred embodiment, the OCS density gradient material is diluted to an appropriate specific density in a physiological salt solution supplemented with polyvinyl¬ pyrrolidone (PVP) such as PVP-10 available from Sigma Chemical Co. (St. Louis, MO). The tubes are centrifuged at 1000 x g for 35 minutes at room temperature. The centrifuge run is allowed to stop without braking and the peripheral blood mononuclear cells (PBMC), present at the interface, are harvested. PBMC are re-suspended in D-PBS, centrifuged once at 650 x g for 10 minutes and twice more at 200 x g for 5 minutes to remove platelets. Platelet-depleted PBMC are re-suspended in 60 mL of D-PBS, layered on top of two columns of 15 mL of OCS (density 1.0610 gr/ml, 280 mOsm/kg H 2 O) in a centrifuge tube and centrifuged at 650 x g for 25 minutes at 4°C without braking. The resulting interface (primarily monocytes) and pellet cells (primarily lymphocytes) are harvested and washed with D-PBS by centrifugation at room temperature (once at 650 x g for 10 minutes and twice thereafter at 200 x g for 5 minutes). In instances where the dendritic cells are used to generate peptide-specific cytotoxic T lymphocytes (CTL) for puφoses of elucidating their antigen presentation function, the interface fraction (mostly monocytes) is re-suspended in cold pooled human AB serum (Irvine Scientific, Santa Ana, CA) to which an equal volume of 80% AB serum 20% dimethyl sulfoxide (DMSO) (Sigma Chemical Company, St. Louis, MO) is added dropwise. The resulting cell suspension is aliquoted into cryovials and frozen in liquid nitrogen. The monocytes can be used for re- stimulation of CTL for expansion. The pellet fraction is re-suspended in 100 mL of AB Culture Medium, inoculated into two T-75 tissue culture flasks and cultured in a humidified 5% CO 2 incubator for 40 hours. Following the incubation, the non-adherent cells are harvested by moderate pipeting, washed and re-suspended at a concentration of 2 - 5 x 10 6 cells/mL in AB Culture Medium. The cell suspension is layered onto four columns of 4.0 mL OCS separation medium (density 1.0565 gr/ml, pH 7.4, 280 mOsm/kg H 2 O), in AB Culture Medium and centrifuged at 650 x g for 20 minutes at room temperature without braking. The interface and pellet cells are harvested and washed in AB Culture Medium (Basal RPMI-1640 medium, Gibco Laboratories, Grand Island, NY) by centrifugation once at 650 x g for 10 minutes and twice thereafter at 200 x g for 5 minutes each at room temperature. The yield and viability of both cell fractions is estimated by counting on a hemocytometer using trypan blue exclusion. The purity of dendritic cells in the interface fraction is quantified following analysis on a flow cytometer (FACS). Dendritic cells are characterized as negative for cell phenotype markers CD3 (T lymphocytes), CDU (monocytes), CD16 (NK cells) and CD20 (B-cells) and positive for HLA class II expression using dual staining with HLA-DR (on the FITC channel) and a cocktail of CD3, CD14, CD16, CD20 (on the PE channel). Dual staining with IgG2a on both the FITC and PE channels can be used as isotype control. The moφhology of the cells can also be evaluated using photomicroscopy. The DC enriched fraction contains large sized veiled cells with cytoplasmic processes extending from the cell surface, features characteristic of DC. Example 6 In vivo efficacy of PAP-GM-CSF-pulsed dendritic cells A. Construction, expression and bioactivity of recombinant ratPAP and GM-CSF fusion proteins Recombinant rat PAP-rat-GM-CSF was constructed as follows: rPAP cDNA was amplified from first strand cDNA made from mRNA isolated from rat prostrate (Harlan) using primers which delineate the fragment containing nucleotides 15-1177 (Genbank Acc. M32397) and which add an exogenous Xho I restriction site at the 5'-end and exogenous BamHI and Bin I sites at the 3'-end to facilitate insertion into the pBacPAK8 vector. In the absence of GM fusion, the Bin I site encodes an in-frame stop codon. Mature rat GM-CSF cDNA was amplified by PCR from first strand cDNA made from mRNA isolated from ConA-stimulated rat splenocytes using primers which delineate nucleotides 1-384 (GenBank Acc. U00620) and add an exogenous BamHI site at the 5'-end and an exogenous Xba I site at the 3'-end. The ratPAP and ratPAP-ratGM-CSF plasmids were each mixed with linearized BV viral genome plasmid and the mixtures were transfected into SF21 cells using Lipofectin as supplied in a recombinant BV transfection kit (Clontech). Six days after transfection, the culture supernatants were collected and titrated on Sf21 monolayers under agarose to form viral plaques. Four days later the cells were stained with neutral red and candidate viral plaques were picked and expanded on Sf21 cells to screen for recombinant BV using PAP enzymatic activity as a readout. PAP + BV clones were chosen and expanded in SF21 large-scale suspension cultures for viral stocks and subsequently for protein production using protein-free Sf900 II media (Gibco/BRL). All proteins exhibited PAP enzymatic activity as shown by hydrolysis of PNPP, the enzyme substrate used in a standard acid phosphatase assay and, in the case of GM-CSF fusion proteins, GM-CSF bioactivity as shown by bioassay on GM-NFS- O cells. GM-CSF bioacti¬ vity of a representative fusion protein example, ratPAP-ratGM-CSF (FIG. 9), was determined in a GM-CSF rat cell proliferation assay carried out using the GM-CSF-dependent cell line GM-NFS-60. Five thousand cells were plated per well in 200 μl of media with the designated amounts of cytokine. Proliferation was determined by pulsing with 1 μCi pHJthymidine per well during the final 4 hr of a 48 hr assay. Crude baculovirus culture supernatant or with lOng/ml commercially available recombinant mouse GM-CSF (rmGM) was diluted and added to the cultured cells as indicated, and proliferation was measured. RatPAP was expressed as a fusion protein with a tail of 6 histidine-residues (ratPAP(HiSa)) attached to its C-terminus. It was purified by means of metal -chelate affinity chromatography (Ni-NTA columns), according to standard methods. A typical purification resulted in >90% pure recombinant protein. Purification of ratPAP-ratGM-CSF was performed by a combination of ion-exchange/hydrophobic interaction chromatography. This procedure typically yields >50% pure rat PAP-GM-CSF. B. Immunization of Animals Male inbred rats were used in all studies that were designed to address the immunogenicity of ratPAP in vivo. The goal of such studies was to determine whether immunity towards the autoantigen rat PAP could be elicited. Normal 8-week old male rats (Wistar or COP) were immunized with PAP in CFA (approx. 200μg) or with PAP-GM-CSF fusion protein (200 μg). After conclusion of the immunization, the rats were euthanized and their prostates were examined histologically. An additional group of rats was treated with ratPAP-ratGM-CSF pulsed dendritic cells. Dendritic cells from rat spleens were isolated as outlined in FIG. 10, pulsed overnight with ratPAP-ratGM-CSF that had been purified from baculovirus culture supernatant by a combination of cation-exchange chromatography, hydrophobic interaction chromatography and anion-exchange chromatography. Cells (5-10 x 10 6 cells/rat) were injected back into syngeneic hosts. Two weeks after the third immunization, animals were sacrificed and prostate, brain, lungs, heart, liver, kidney and colon were analyzed by a veterinarian histopathologist and compared to tissues from control animals which were not immunized. Phenotype of rat dendritic cells was determined using flow cytometry. To determine their antigen-presenting capacity, cells were used as stimulators in an allogeneic mixed lymphocyte reaction and their allostimulatory capacity to total splenocytes and to adherent splenocytes was compared. The typical range for dendritic cell purities obtained by this method is generally between 30% and 80%. The antigen-presenting capacity of dendritic cells from the rats was analyzed by using them as stimulators in an allogeneic mixed lymphocyte reaction with SD rat splenocytes as responders. Their allostimulatory capacity was compared to total splenocytes and to adherent splenocytes from both COP and SD strains. SD-splenocytes were not stimulated by syngeneic SD-splenocytes, adherent splenocytes or dendritic cells. When allogeneic COP stimulators are used, the dendritic cell fraction stimulates several orders of magnitude stronger than spleen cell or adherent spleen cells from COP rats. Histopathology of immunized rats. Histopathology was performed by a consulting veterinary histopathologist according to standard procedures. Animals were surveyed for histopathological changes to prostate, brain, lungs, heart, liver, kidney and colon, as summarized in Table 1. All organs in all control animals (IC, 2C, 3C, 4C) showed no significant change. All organs except the prostates in the treated animals showed no significant change. All animals treated with rat PAP rat GM-CSF pulsed dendritic cells suffered from interstitial prostatitis. The intensity varied: one animal (7T) had grade 1 (= trace) lesions, two animals (6T, 8T) had grade two lesions (= mild) and one animal (5T) had grade 3 (= moderate) lesions. Animals which were immunized with rat PAP in CFA (1CFA.2CFA) did not show any histopathology of the prostate. Animals that were immunized with rat PAP rat GM-CSF protein (1 PAP GM, 2 PAP GM) had a grade 1 interstitial lymphocytic prostatitis. Example 7 Construction and expression of p53-GM CSF fusion proteins The cellular tumor suppressor gene p53 was cloned according to publicly known sequences (Genbank database release 91, entry HSP53) by means of polymerase chain reaction with the sense primer CgCggATCCTCACTgCCATgg AggAgC and the antisense primer CTAgTCTAgA- CTCTgAgTCAggCCCTTCTgTC which includes anXBA I site that codes for a serine-arginine linker. GM-CSF was cloned as described in Example 1 except that primers CTAgTCTAgATC- TgCACCCgCCCgCTCgCCC (sense) andCCggAATTCTCAgTgATggTgATggTgATgCgATC- CTCTCATCTCCTggACTggCTCCCAgC (anti-sense) were used. The antisense primer codes for the sequences MetArgGlySerHisHisHisHisHisHis which is attached to the C-terminus of GM-CSF and can be used for detection and metal-chelate affinity chromatography purification of the fusion protein. The resulting sequences are shown in FIGS. 11 and 12. Recombinant baculovirus transfer vector and recombinant baculovirus was generated as described in Example 1. When expressed in SF21 insect cells as detailed in Example 1 this baculovirus produces p53-GM-CSF fusion protein which is used to generate anti-p53 immunity as described for the induction of anti-PAP immunity by PAP-GM-CSF in Examples 3, 4 and 6. The sequence of the recombinant fusion gene is shown in FIG. 11. The sequence of the produced polypeptide p53-GM-CSF is shown in FIG. 12. While the invention has been described with reference to specific methods and embodiments, it will be appreciated that various modifications and changes may be made without departing from the invention.

Claims: IT IS CLAIMED: 1. A therapeutic composition, comprising an isolated potent antigen presenting cell effective to activate T-cells to produce a multivalent cellular immune response against a selected antigen, at a T-cell activation level substantially higher than that produced by such a potent antigen presenting cells stimulated by the selected antigen alone. 2. The therapeutic composition of claim 1 , wherein the potent antigen presenting cell is stimu¬ lated by exposing the cell in vitro to a polypeptide complex consisting essentially of a dendritic cell-binding protein and a polypeptide antigen selected from the group consisting of a tissue- specific tumor antigen and an oncogene gene product. 3. The therapeutic composition of claim 2, wherein the dendritic cell-binding protein is GM¬ CSF. 4. The therapeutic composition of claim 2, wherein the polypeptide antigen is the tumor- specific antigen prostatic acid phosphatase. 5. The therapeutic composition of claim 2, wherein the polypeptide antigen is an oncogene product peptide antigen selected from the group consisting of Her2, p21RAS, and p53. 6. The therapeutic composition of claim 2, wherein the polypeptide complex further comprises, between said dendritic cell-binding protein and said polypeptide antigen, a linker peptide. 7. The therapeutic composition of claim 2, wherein the potent antigen presenting cell is an activated dendritic cell. 8. A method of activating an isolated antigen presenting cell in vitro, comprising contacting said isolated antigen presenting cell with a polypeptide complex consisting essentially of a dendritic cell-binding protein covalently linked to a polypeptide antigen selected from the group consisting of a tissue-specific tumor antigen, and an oncogene product peptide antigen, wherein said activated antigen presenting cell is effective to activate a T-cell to produce a multivalent cellular immune response that is substantially higher than that produced by antigen presenting cells contacted with the selected polypeptide antigen alone. 9. The method of claim 8, wherein said dendritic cell-binding protein is GM-CSF. 10. The method of claim 8, wherein said polypeptide antigen is the tissue-specific tumor antigen prostatic acid phosphatase. 11. The method of claim 8, wherein the polypeptide complex is a fusion protein. 12. The method of claim 8, wherein said isolated antigen presenting cell is a dendritic cell. 13. A method of inducing a cytotoxic T-cell response in a vertebrate subject, comprising contacting an isolated antigen presenting cell with a polypeptide complex comprising a dendritic cell-binding protein covalently linked to a polypeptide antigen selected from the group consisting of a tissue-specific tumor antigen and an oncogene product peptide antigen for a period of time effective to activate said antigen presenting cell, and injecting said antigen presenting cell into the mammalian subject. 14. The method of claim 13, wherein said antigen presenting cell is a dendritic cell. 15. A polypeptide complex, comprising an isolated tissue-specific tumor antigen covalently linked to a dendritic cell-binding protein. 16. The polypeptide complex of claim 15, wherein said dendritic cell-binding protein is GM¬ CSF. 17. The polypeptide complex of claim 15, wherein said tissue-specific tumor antigen is prostatic acid phosphatase. 18. The polypeptide complex of claim 15, wherein the complex is a fusion protein. 19. The polypeptide fusion protein complex of claim 15, which further includes, between said dendritic cell binding protein and said tissue-specific tumor antigen, a linker peptide. 20. A polypeptide complex, comprising an isolated oncogene product peptide antigen covalently linked to a dendritic cell-binding protein. 21. The polypeptide complex of claim 20, wherein said dendritic cell-binding protein is GM¬ CSF. 22. The polypeptide complex of claim 20, wherein said oncogene product peptide antigen is selected from the group consisting of Her2, p21RAS, and p53. 23. The polypeptide complex of claim 20, wherein the complex is a fusion protein. 24. The polypeptide fusion protein of claim 20, which further includes, between said dendritic cell binding protein and said oncogene product antigen, a linker peptide. 25. An expression vector for producing an immunostimulatory fusion protein, comprising a nucleic acid molecule encoding a polypeptide complex consisting essentially of a dendritic cell- binding protein and a polypeptide antigen selected from the group consisting of a tissue-specific tumor antigen, and an oncogene product peptide antigen, said nucleic acid molecule inserted into an expression vector, wherein said nucleic acid molecule is operably linked to a selected promoter able to initiate transcription in a selected host cell. 26. The expression vector of claim 25, wherein said dendritic cell-binding protein is GM-CSF and said polypeptide antigen is the tissue-specific tumor antigen prostatic acid phosphatase. 27. The expression vector of claim 25, wherein said dendritic cell-binding protein is GM-CSF and said polypeptide antigen is the oncogene product peptide antigen Her2. 28. A substantially purified nucleic acid molecule encoding a fusion protein consisting essen¬ tially of GM-CSF and prostatic acid phosphatase. 29. A substantially purified nucleic acid molecule encoding a fusion protein consisting essen¬ tially of GM-CSF and Her2. 30. An expression system for producing a fusion protein consisting essentially of a dendritic cell-binding protein covalently linked to a polypeptide antigen selected from the group consisting of a tissue-specific tumor antigen and an oncogene product peptide antigen, comprising a nucleic acid sequence encoding a dendritic cell-binding protein, a nucleic acid sequence encoding the polypeptide antigen, each of said nucleic acid sequences inserted into an expression vector, wherein said nucleic acid sequences are operably linked to a promoter able to initiate transcription in a selected host cell, and said expression vector is carried within the host cell.

Inventors: LAUS REINER, RUEGG CURTIS LANDON, WU HONGYU, LAUS, REINER, RUEGG, CURTIS, LANDON, WU, HONGYU
Applicants: ACTIVATED CELL THERAPY INC, LAUS REINER, RUEGG CURTIS L, WU HONGYU, ACTIVATED CELL THERAPY, INC., LAUS, REINER, RUEGG, CURTIS, LANDON, WU, HONGYU
Application year: 1996
Main classification: C12N15
IPC codes: A61K31, A61K35, A61K39, A61P37, C07K14, C12N5, C12N9, C12N15, C12P21