Human carcinoembryonic antigen (CEA), which is extensively expressed in the majority of human cancers, is a potential target for specific immunotherapy using recombinant vaccines. A CEA-specific cytotoxic T- lymphocyte (CTL) line was established from a patient with metastatic colorectal carcinoma and cultured long-term in vitro. The cell line (designated V8T) was shown to be CD8+, CD2+/CD54+, CD45RO+/CD49d+, and CD11a+/CD58+. The V8T cell line lysed CAP-1 pulsed C1R-A2 cells. The cytotoxicity of the V8T cell line was shown to be MHC class I restricted. V8T long-term cultures were analyzed, and the results on the cytokine production, expression of homing-associated molecules (CD11a, CD49d), and cytotoxicity demonstrate stability of these phenotypes through long-term passage. A collaborative Phase I clinical trial has recently been completed in which a replication defective avian poxvirus (ALVAC) expressing the CEA gene (ALVAC-CEA) could elicit CEA-specific CTL responses in patients with metastatic carcinoma. Peripheral blood mononuclear cells (PBMCs) obtained from patients both before and after immunization with ALVAC-CEA were analyzed for T-cell responses. Cytotoxic CTL activities against C1R-A2 cells pulsed with the CEA peptide CAP-1 were observed only from T-cell cultures established from post-vaccination PBMCs. These T-cell lines also lysed allogeneic human carcinoma cell lines positive for HLA-A2 and CEA. A comparison of patient PBMC samples before and after vaccination revealed increases in CTL precursor frequencies in seven of nine post- vaccination samples. Phenotypic analysis of T-cell cultures indicated that between 70% and 98% of cells in the population were CD4-/CD8+ and CD4+/CD8+. A T-cell line was chosen for detailed analysis and shown to lyse autologous tumor cells. The addition of CEA peptide to these T- cell lines could induce the secretion of TNF-alpha and IFN-gamma. These studies indicated that ALVAC-CEA can elicit specific anti-CEA responses, forming a rational basis for using ALVAC-CEA in anti-cancer vaccine immunotherapy protocols for patients with CEA-positive carcinomas. We also investigated the ability of prostate specific antigen (PSA) epitopes to activate human cytotoxic T lymphocytes in vitro and in vivo. Previous studies have shown that two 10-mer PSA peptides (PSA-1 and PSA-3) selected to conform to human HLA-A2 motifs can elicit CTL responses in vitro. A longer PSA oligopeptide (39 mer) designated PSA-OP, which contains both the PSA-1 and PSA-3 HLA-A2 epitopes, and an additional CTL epitope (designated PSA-9) for the HLA- class I A3 allele, was investigated for the ability to induce cytotoxic T-cell activity. T-cell lines from different HLA-A2 and HLA-A3 donors were established by in vitro stimulation with PSA-OP. The CTL lines lysed PSA-OP as well as PSA-1 or PSA-3-pulsed C1R-A2 cells and PSA-OP and PSA-9-pulsed C1R-A3 cells, respectively. The CTL lines derived from the PSA-OP peptide also lysed PSA-positive prostate cancer cells. PSA- OP-derived T-cell lines also lysed recombinant vaccinia PSA-infected targets, but not targets infected with wild-type vaccinia. PSA-OP did not bind HLA-A2 and HLA-A3 molecules. The decrease in cytotoxicity in the presence of protease inhibitors suggests that PSA-OP is cleaved into shorter peptides that, in turn, can interact with HLA-class I molecules and, as a consequence, induce CTL-mediated lysis. We have also demonstrated that it is possible to induce CTL responses in HLA- A2.1/Kb transgenic mice by immunization with PSA-OP with adjuvant. These studies thus provide evidence that oligopeptides such as PSA-OP may be useful candidates for peptide-based cancer vaccines. - Carcinoembryonic antigen, Prostate specific antigen, T-cells, Tumor antigens, Vaccines, - Human Tissues, Fluids, Cells, etc.
