Nonmyeloablative hematopoietic
cell transplantation can cure patients with
hematologic malignancies but has reported limited success against solid
tumors. This is possibly because of profound peripheral tolerance mechanisms and/or suboptimal
tumor recognition by effector T lymphocytes. We report that in mice developing spontaneous
prostate cancer, nonmyeloablative minor histocompatibility mismatched
hematopoietic stem cell transplantation, and donor lymphocyte infusion of unmanipulated lymphocytes combined with posttransplant
tumor-specific vaccination circumvents
tumor-specific tolerance, allowing acute
tumor rejection and the establishment of protective immunosurveillance. Although donor-derived
tumor-specific T cells readily differentiated into effector cells and infiltrated the
tumor soon after infusion, they were alone insufficient for
tumor eradication, which instead required the concomitance of minor histocompatibiltiy
antigen-specific CD8(+) T-cell responses. The establishment of protective immunosurveillance was best induced by posttransplant
tumor-specific vaccination. Hence, these results provide the proof of principle that
tumor-specific T-cell responses have to be harnessed together with minor histocompatibility responses and sustained by posttransplant
tumor-specific vaccination to improve the efficacy of allotransplantion for the cure of solid
tumors.