Prostatic acid phosphatase as a target molecule in specific immunotherapy for patients with nonprostate adenocarcinoma

Prostatic acid phosphatase (PAP) is one of the prostate-related antigens that are applicable to specific immunotherapy for patients with prostate cancer. In this study, we determined whether or not PAP could be a target molecule in specific immunotherapy for patients with nonprostate cancer. A variety of adenocarcinoma cell lines were examined for their PAP expression at the mRNA and protein levels by reverse transcription polymerase chain reaction and western blot analysis, respectively. Considerable percentages of colon, gastric, and breast cancer cell lines were found to be positive for PAP at both the mRNA and the protein levels. The PAP expression in cancer tissues was also confirmed by immunohistochemical staining. In addition, we examined whether cancer-reactive cytotoxic T lymphocytes (CTLs) could be induced from peripheral blood mononuclear cells (PBMCs) of human leukocyte antigen (HLA) A24⁺ nonprostate cancer patients by in vitro stimulation with a PAP peptide. As a result, tumor-specific CTLs could be induced from the PBMCs of HLA-A24 ⁺ colon and gastric cancer patients. Their cytotoxicity against HLA-A24⁺ cancer cells was dependent on PAP peptide-specific and CD8⁺ T cells. These findings indicate that PAP could be a target molecule in specific immunotherapy for patients with nonprostate adenocarcinomas including colon and gastric cancers.