Expression of the SART1 tumor-rejection antigen in human osteosarcomas. We recently reported a tumor-rejection antigen, SART1259, possessing tumor epitopes capable of inducing cytotoxic T lymphocytes (CTLs). This study investigated the expression of SART1259 antigen in osteosarcoma and other skeletal malignant tumors to explore for a potential molecule for use in specific immunotherapy. The SART1259 antigen was detected in the cytosol fraction of 13 of 21 (62%) osteosarcoma cell lines and 3 of 8 (38%) osteosarcoma tissues, and 3 of 10 (30%) malignant fibrous histiocytoma (MFH) tissues. The HLA-A24+ and SART1259+ osteosarcoma cells were recognized by the HLA-A24 restricted and SART1 specific CTLs. These results raise a possibility that the SART1259 would be an appropriate molecule for use in specific immunotherapy of approximately one-third of HLA-A24+ patients with osteosarcoma and MFH.