Identification of HLA-A*0201/-A*2402-restricted CTL epitope-peptides derived from a novel cancer/testis antigen, MCAK, and induction of a specific antitumor immune response.

Cancer immunotherapy is a potential therapeutic strategy, in addition to surgical treatment, radiotherapy, and chemotherapy. Cancer-specific immunotherapy, such as the MAGE peptide vaccine, has been utilized clinically. How-ever, there are inherent limits to the effectiveness of vaccinotherapy using a single antigen because of the expression frequency of cancer-specific antigens on tumor cells. Thus, identification of a new cancer-specific antigen is needed. In this study, we examined the possibility of using cancer-specific immunotherapy based upon mitotic centromere-associated kinesin (MCAK) which was previously identified as a novel cancer/testis antigen. To evaluate the feasibility of developing cancer immunotherapy using MCAK peptides, we studied HLA-A0201 and 2402 as targets for CTLs in the context of HLA class I molecules. By using a peptide with a sequence of AINPELLQL (amino acid positions 63-71 in MCAK, HLA-A0201) and FFEIYNGKL (amino acid positions 401-409 in MCAK, HLA-A2402), CTL responses could be induced from unseparated PBMCs by stimulation of freshly isolated, peptide-pulsed PBMCs as antigen-presenting cells (APCs) and also by using interleukin-7 and keyhole limpet hemocyanin in primary culture. The induced CTLs could lyse HLA-A-*0201/2402 colon and gastric cancer cells expressing MCAK, as well as the peptide-pulsed target cells, in an HLA class l, and CD8 restricted manner. The identification of the MCAK/HLA-A0201 and *2402 peptides suggests the possibility of designing peptide-based immunotherapeutic approaches that might prove effective in treating patients with MCAK-positive cancer.