Non-myeloablative allogeneic stem cell transplantation is an option for the treatment of hematological malignancies as well as solid tumors. We recently proposed a cyclophosphamide-using non-myeloablative cell therapy in which donor lymphocytes infusion (DLI) was carried out after tolerance induction to donor cells. In this study, we tested the possibility that the cyclophosphamide-using cell therapy could be augmented by pre-immunization of donors before DLI. We initially assessed whether or not the cyclophosphamide-using cell therapy could also show antitumor effect against subcutaneously established colon 26 carcinoma. As a tumor antigen-derived peptide for colon 26, we used AH1, an immunodominant H-2Ld-binding peptide derived from the envelope protein (gp70) of an endogenous murine leukemia virus. The cyclophosphamide-using cell therapy with the DLI from donors which were pre-immunized with the AH1 peptide was compared with that from non-immunized mice. The cyclophosphamide-using cell therapy significantly suppressed subcutaneously established colon 26 carcinoma, and the tumor-rejected mice acquired the tumor-specific protective immunity. When combined with the DLI from donors that were immunized with AH1, antitumor effect of the cyclophosphamide-using cell therapy was significantly augmented. The DLI from tumor peptide-immunized donors showed no influence on donor chimerism and bodyweight of the treated mice, indicating no increased risk of graft-versus-host disease. Tumor-specific cytotoxic T lymphocytes could be generated from tumor-rejected mice. Our results indicate that the cyclophosphamide-using non-myeloablative cell therapy with the DLI from tumor peptide-immunized donors is a useful protocol to augment graft-versus-tumor effect without exacerbation of graft-versus-host disease.
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