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1991;88:7978C7982. active intracellular processing of Nazartinib mesylate the antigen as well as on the surface of tumor cells. Moreover, by genetic fusion we armed the TCR-like antibody with a potent toxin and exhibited that it can serve as a targeting moiety killing tumor cells in a peptide-specific, MHC-restricted manner similar to cytotoxic T-cell Lymphocytes. 1. Introduction Most patients with metastatic prostate and breast cancers are provided with the limited benefits from standard chemo and hormone-based therapies. During the recent years, much effort has been invested in developing new approaches, such as immunotherapy, to improve therapeutic abilities, by combining the tumor-specificity of cell-mediated immunity with the freedom from toxic chemotherapies. Recent immunotherapy approaches employ the theory that CD8+ CTL’s recognize and kill tumor cells which display peptides from tumor-associated antigens presented by MHC class I molecules. Several tumor antigens and HLA allele-specific peptides from prostate cancer-associated antigens have been identified as CD8+ T cell epitopes, including HLA-A2-binding peptides derived from prostate specific antigen (PSA)[1-2], prostate-specific membrane antigen (PSMA)[3], prostate stem cell antigen (PSCA)[4-5], and prostate acid phosphatase6, that are all now components of current vaccine trials [5-11]. Identification of new tumor specific antigens is an essential step for successful development of immunotherapy approaches. As a result of this understanding, new genes specifically expressed in human breast and prostate cancer have been identified recently by utilizing new gene discovery tools [12-14]. One of these, TARP(T-cell receptor gamma alternate reading frame protein), is expressed on breast and prostate cancer cells [15,16]. It was shown that TARP was expressed on >90% of cancer specimens examined [9,15]. In order to define new breast and prostate CD8+ T cell tumor antigens, two wild-type HLA-A2 epitopes from TARP were identified [17]. The wild-type sequences were also improved by sequence modifications to produce epitope-enhanced peptides. Both wild-type and enhanced epitopes induced peptide-specific Mouse monoclonal to APOA4 CD8+ T cell responses in A2Kb transgenic mice. restimulation of human CD8+ T cells from a prostate cancer patient resulted in CD8+ T cells reactive to the peptide epitopes that could lyse HLA-A2+ human breast malignancy cells (MCF-7) expressing TARP. Epitope-specific human CD8+ T cells were also enumerated in patients’ peripheral blood by tetramer staining. These data suggest that HLA-A2-binding TARP epitopes could be incorporated into a potential vaccine for both breast and prostate cancer. One of the major problems with class I MHC-peptide complexes is the lack of molecular tools to directly study, quantitate, Nazartinib mesylate and visualize their expression on tumor cells, antigen-presenting cells, and other lymphoid tissues. Soluble T cell receptors have been proven difficult to engineer [18] and their inherent low affinity for their target limit their use as a molecular tool to study the ligand [19,20]. An alternative approach is usually to mimic the unique specificity of the TCR by generating high-affinity soluble antibody molecules that bind the T cell epitope with a peptide-specific, MHC-restricted manner. Using antibody phage display approaches, we have recently generated such unique molecules, coined TCR-like antibodies, against a variety of tumor Nazartinib mesylate and viral epitopes restricted to human HLA-A2, the most frequent MHC allele in humans. These antibodies were utilized to detect, visualize, and quantitate the number of specific tumor and viral associated HLA-A2/peptide complexes on tumor cells, APCs, and virus-infected cells [21-26]. Another possible application of TCR-like antibodies is usually their use as targeting molecules to efficiently eliminate tumor cells due to the fact that they can mimic the unique fine specificity of T-cells. This can achieved by using the antibodies or their fragments as targeting moieties and arming them with effector modalities such as potent toxins, chemotherapeutic drugs, isotopes, or Nazartinib mesylate biological entities such as cytokines [27-33]. In this study, we isolated human recombinant TCR-like antibodies directed against the novel TARP T cell epitopes expressed in complex with MHC class I HLA-A2 molecules. These molecules have been used to directly detect, by flow cytometry, the specific HLA-A2/TARP epitopes on antigen presenting cells as well as on breast and prostate cancer cells. Moreover, the TARP/HLA-A2-specific TCR-like antibody gene was fused to a truncated form of Pseudomonas exotoxin A to form a recombinant antibody-toxin fusion molecule [34]. The fusion molecule.