Studies are ongoing involving the application of recombinant poxviruses and/or synthetic peptides as antitumor vaccines. These studies stress a basic understanding of the mechanisms of action and immunological impact of such vaccines in preclinical animal models and now in clinical trials. Much of this work has concentrated on the carcinoembryonic antigen (CEA) and products of the point-mutated ras p21 oncogene. The over-expression of tumor-associated antigen (Ag) (i.e., CEA) and/or the neo-expression of tumor-specific epitopes (i.e., point-mutated ras p21) may represent selective or unique targets for immune recognition, such as by T-lymphocytes which have been implicated as important elements for host defense against malignancy. We have conducted a collaborative Phase I trial in CEA- positive carcinoma patients receiving a vaccinia virus recombinant expressing the human CEA gene. We have examined dermal response as well as humoral and cell-mediated immunity. Overall, we found evidence in certain pools of patients for the enhancement of pre- existing anti-vaccinia responses, suggesting a successful """"""""clinical take"""""""". The extent of CEA-specific immunity is still under investigation. In a murine model, we explored and characterized distinct effector properties of host-derived T-lymphocytes reactive to mutated ras peptides, which was consistent with the induction of the CD4+ Th1 subset. BALB/c mice (H-2d) were immunized with a purified peptide, 13 amino acids in length, containing the substitution of Gly to Val at position 12, which is commonly found in human carcinomas. A CD4+ T-cell line was established, which expressed peptide-specific proliferation. Cytokine assays revealed the production of IL-2, IFN- g, TNF and GM-CSF. Moreover, MHC class II-restricted, Ag-specific cytotoxicity was demonstrable against syngeneic tumor cells expressing the epitope exogenously (via peptide-pulsing) or endogenously (via retrovirus transduction). Independent isolation of a second anti-ras CD4+ line revealed a very similar cytolytic and MHC class II-restricted profile. Furthermore, we are now exploring the possibility for the induction and expression of an anti-ras CD8+ cytotoxic T-lymphocyte response directed against this same point mutation. Based on these preclinical data in mice and in vitro studies with human cells, a collaborative Phase I clinical trial has been recently initiated employing point mutated ras peptides in adjuvant in carcinoma patients whose tumors harbor the point-mutated K-ras oncogene at codon 12.
