Identification of an interferon-γ-inducible carcinoembryonic antigen (CEA) CD8+ T-cell epitope, which mediates tumor killing in CEA transgenic mice

This study describes a CD8⁺ T-cell line specific for a MHC class I-restricted carcinoembryonic antigen (CEA) epitope, residues 526-533, isolated from CEA transgenic (CEA.Tg) mice immunized with a recombinant vaccinia-CEA vaccine. Incubation of splenocytes from the immune CEA.Tg mice with the CEA_526-533 peptide resulted in the outgrowth of low-avidity CD8⁺ T cells, which produced IFN-γ and mediated perforin-dependent tumor cell lysis. However, the CEA peptide-specific T cells killed CEA-expressing murine colorectal tumor cells only after pretreatment of the targets with murine IFN-γ (muIFN-γ), and lysis was H-2D^b- restricted and involved the Fas-FasL-mediated cytotoxic pathway. When the CEA peptide-specific T cells were used as in vivo effectors in adoptive T-cell transfer studies, muIFN-γ treatment of the CEA.Tg mice was again required for T-cell-dependent growth suppression of CEA-expressing metastatic tumors. The results indicate that (a) vaccination of mice carrying the human CEA gene with recombinant vaccinia-CEA generates a CEA epitope-specific, CD8-dependent CTL response, (b) CEA, a normal, tissue-specific antigen, can also serve as a target for antitumor immunity after the adoptive transfer of CEA peptide-specific T cells, and (c) muIFN-γ might be an effective cancer vaccine adjuvant by virtue of its ability to augment the susceptibility of tumor targets to cell-mediated lysis.