Identification of squamous cell carcinoma antigen-derived peptides having the capacity of inducing cancer-reactive CTLs in HLA-A24+ cancer patients

Squamous cell carcinoma antigen (SCCA) is a useful marker for SCCs. In this study, we attempted to identify SCCA-derived peptides that could be applied in the development of specific immunotherapy for HLA-A24+ cancer patients with SCC or non-SCC. A variety of SCC and non-SCC lines were examined for their expression of SCCA mRNA using quantitative PCR. SCCA protein expression in cancer tissues was investigated by immunohistochemical staining. Thereafter, SCCA-derived peptide candidates were prepared based on their binding motifs to HLA-A24 molecules. Among these peptides, SCCA-derived peptides that were frequently recognized by humoral immunity were further tested for their ability to induce cancer-reactive cytotoxic T lymphocytes (CTLs) from the peripheral blood mononuclear cells of HLA-A24+ patients with SCC or non-SCC. As a result, the majority of SCC lines and tissues were positive for SCCA both at mRNA and protein levels. By contrast, non-SCC cancer tissues hardly expressed it at the protein level, although adenocarcinoma cell lines partly expressed it at the mRNA level. Four SCCA-derived peptides were frequently recognized by immunoglobulin G of both SCC and non-SCC cancer patients. Among these peptides, both the SCCA112-120 and SCCA215-224 peptides were found to effectively induce peptide-specific CTLs toward HLA-A24+ SCCA+ cancer cells from the peripheral blood mononuclear cells of both SCC and non-SCC cancer patients. Two newly identified SCCA-derived peptides with the ability to induce CTL activity in both SCC and non-SCC cancer patients may be applicable to specific immunotherapy for HLA-A24+ cancer patients with SCC, but not those with non-SCC.