Prevention and treatment of relapse by bone marrow transplantation.

High, myeloablative doses of chemoradiotherapy represent the treatment of choice for a large number of malignant hematological diseases that cannot be successfully treated with conventional chemotherapy. Residual tumor cells following high dose chemotherapy represent the most common treatment failure, resulting in frequent relapse following autologous bone marrow transplantation (ABMT) and even allogeneic bone marrow transplantation (BMT). Graft vs leukemia (GVL) effects mediated by immunocompetent donor lymphocytes represent a major therapeutic potential of allogeneic BMT which results in reduced rate of relapse, especially when immune interactions between immunocompetent donor's T lymphocytes and host allogantigens is apparent, a reaction which might result in graft vs host disease (GVHD). Recent experiments in animal models of murine leukemias suggest that post-transplant immunotherapy may be successfully accomplished by lymphokine-mediated immunotherapy (LMI) and cell-mediated immunotherapy (CMI). Following allogeneic BMT, provided GVHD can be prevented by T-cell depletion, CMI may be amplified by repeated administration of immunocompetent donor's lymphocytes in graded increments following successful induction of chimerism and sustained hematopoiesis. GVL effects induced by CMI may be further potentiated by in-vivo administration of a short course of recombinant human interleukin-2 (rhIL2). Taken together, our data suggest that post-transplant immunotherapy by cytokines and adoptive cell therapy may successfully prevent relapse in patients at high-risk and even result in complete elimination of tumor cells following overt relapse. Thus, immunotherapy may represent an optimal approach for prevention and treatment of minimal residual disease.