Identification of antigenic epitopes recognized by Mac-2 binding protein-specific cytotoxic T lymphocytes in an HLA-A24 restricted manner.

We previously reported that 90K/Mac-2 binding protein (M2BP) is highly expressed in lung cancer and that M2BP-specific immunity was observed in many patients with lung cancer. These findings suggested the possibility of using M2BP as a target antigen in cancer immunotherapy. In this study, we selected 11 peptides derived from M2BP with an HLA-A24 binding motif and analyzed their ability to induce M2BP-specific cytotoxic T lymphocytes (CTL). CTLs were generated with the M2BP-derived peptides from peripheral blood CD8-positive T lymphocytes of HLA-A24-positive healthy donors in multiple in vitro stimulations. Two CTLs, one induced with M2BP(241-250) (GYCASLFAIL) and the other with M2BP(568-576) (GFRTVIRPF), produced interferon-gamma in response to HLA-A24-positive TISI cells pulsed with the same peptide used for the in vitro stimulation. Although the CTLs induced with M2BP(241-250) reacted with both peptide-pulsed TISI cells and BT20 cells expressing both M2BP and HLA-A24, the CTLs induced with M2BP(568-576) did not react with BT20 cells. The cytokine production was blocked by antibodies against HLA class I in CTLs induced using M2BP(241-250), but not in CTLs induced using M2BP(568-576). These findings suggest that M2BP(241-250) is naturally processed from the native M2BP molecule in cancer cells and recognized by M2BP-specific CTLs in an HLA-A24 restriction. An M2BP-derived CTL epitope with an HLA-A24 binding motif was identified for the first time in this study, and it is expected to be useful as a target antigenic epitope in clinical immunotherapy for lung cancer.