A newly identified MAGE-3-derived, HLA-A24-restricted peptide is naturally processed and presented as a CTL epitope on MAGE-3-expressing gastrointestinal cancer cells

PURPOSE: In order to broaden the possibility for anti-MAGE-3 immune targeting, it is important to identify HLA-A24-restricted epitopes derived from MAGE-3, since HLA-A24 is one of the most common alleles in Japanese and Asian people. In the present study, we defined a new MAGE-3 derived, HLA-A24-binding peptide presented as a CTL epitope on gastrointestinal cancer cells. MATERIALS AND METHODS: A panel of MAGE-3-derived peptides (9mer and 10mer) with the HLA-A24-binding motif was selected, and identification of MAGE-3-derived, HLA-A24-restricted CTL epitopes was performed by a reverse immunology approach. To induce MAGE-3-peptide specific CTLs, PBMCs were repeatedly stimulated with monocyte-derived, mature DCs pulsed with the peptides. Subsequent peptide-induced T cells were tested for their specificities by ELISPOT, tetramer and cytotoxic assay. CTL clones were then obtained from the CTL line by limiting dilution. RESULTS: The peptide-inducing CTLs revealed that MAGE-3(113)-peptide was reacted as a CTL epitope in a HLA-A24-restricted fashion, confirmed by ELISPOT and cytotoxic assays. In addition, the MAGE-3(113)-specific CTL clones, confirmed by tetramer assay, showed that the MAGE-3(113) epitope is naturally processed and presented as the CTL epitope on MAGE-3-expressing gastrointestinal cancer cells by evaluating the cold target inhibition assays. CONCLUSION: The newly identified MAGE-3(113)-peptide epitope is naturally processed and presented as the CTL epitope on MAGE-3-expressing gastrointestinal cancer cells, indicating that anti-MAGE-3 immune targeting with the MAGE-3(113) peptide is a promising approach for treatment.