Our laboratory is investigating several well-characterized human carcinoma antigens (Ag), including carcinoembyronic antigen (CEA) and point-mutated ras p21. The over-expression of tumor-associated Ag and/or the neo- expression of tumor-specific epitopes may represent selective or unique targets for immune recognition, particularly by T lymphocytes which have been implicated as integral effector elements for host antitumor activity. Thus, we have begun to evaluate the repertoire of host cellular immune responses induced by active immunization to CEA and point-mutated ras p21. In a murine C57BL/6 (H-2b) model, we have examined whether active immunization with a recombinant vaccinia virus expressing human CEA (rV- CEA) could induce T cell responses, which might correlate with and/or participate in the tumor rejection mechanism. Overall, we have shown that: (1) T cells from rV-CEA mice elicited Ag-specific proliferation to soluble CEA protein; (2) T cells from rV-CEA mice mediated specific lysis of CEA+ bearing tumor target cells; and (3) splenocytes from rV-CEA mice expressed antitumor activity through adoptive immunotherapy. Similarly, we have shown that lymphocytes from rV-CEA immunized rhesus monkeys displayed Ag- specific proliferation responses. More recently, we have examined whether active immunization with short synthetic peptides, which mimic point- mutated epitopes of ras p21 proteins, could induce T cell responses in a murine BALB/c (H-2d) model. Overall, we have shown that: (1) mice immunized with a 13-mer ras peptide, containing the substitution of glycine at position 12 for valine, demonstrated specific T cell proliferation to the immunizing peptide. No autoimmune response was detectable to the normal ras p21 sequence; (2) CD4+ T cells (line and clones) were established in vitro, which retained peptide specificity; and (3) CD4+ T cells secreted a spectrum of cytokines (e.g., IL2, IFN-gamma, TNF or GM-CSF) and some effectors expressed cytotoxicity against tumor target cells incubated with the specific peptide. Taken collectively, we demonstrate that a rV-CEA construct and point-mutated ras p21 peptides are immunogenic in animal models, which may have important implications for active specific immunotherapy of human carcinoma.
