Effective graft-versus-leukemia effects independent of graft-versus-host disease after T cell-depleted allogeneic bone marrow transplantation in a murine model of B cell leukemia/lymphoma. Role of cell therapy and recombinant IL-2.

After allogeneic bone marrow transplantation (BMT) for leukemia, beneficial graft-vs-leukemia (GVL) effects are usually accompanied by potentially serious graft-vs-host disease (GVHD). Because T cell depletion is the only effective way to prevent GVHD it seems important to understand whether effective GVL can develop after BMT with T cell depletion in GVHD-free recipients. Well-established C57BL/6-->BALB/c chimeras that were free of GVHD, reconstituted with T cell-depleted allogeneic bone marrow cells, and inoculated 3 mo after BMT with a high inoculation of murine B cell leukemia (BCL1) showed no evidence of disease, whereas all control mice developed leukemia and died within 58 days. Results from adoptive transfer experiments in secondary naive BALB/c recipients indicated that all BCL1 cells were eliminated in the chimeras within 14 days. Hence, complete resistance to BCL1 developed in the chimeras despite complete tolerance to host alloantigens. The GVL effects observed in tolerant chimeras were further amplified by administration of immunocompetent allogeneic C57BL/6 spleen cells, low dose rIL-2, or both for 5 days. Our data suggest that GVL effects can develop even after T cell depletion in the absence of clinically overt GVHD and that GVL can be further amplified by rIL-2, either with or without use of additional immunocompetent donor T cells. Our data may provide the basis for new approaches to induce effective GVL after allogeneic BMT with cell therapy and rIL-2 at the stage of minimal residual disease, while avoiding early GVHD induced by the BMT procedure.