Bone Marrow transplantation (BMT) still remains the only curative treatment for a large number of patients with leukemia. It is now clear that even the most intensive treatment given to eradicate leukemia before the transplant leaves behind residual leukemia cells. It is now clear that donor immune cells given with the transplant exert a powerful immune against residual leukemia (called graft-versus-leukemia or GVL). At present the success of BMT in curing leukemia is offset by a treatment related mortality in the order of 20 percent for fully HLA matched BMT. Mortality related to the defective reconstitution of donor immunity following BMT leading to fatal cytomegalovirus pneumonia, and graft- versus-host disease (GVHD). We are investigating new ways of conferring GVL without causing GVHD. Our marrow transplant unit carries out applied clinical and laboratory research in allogeneic BMT for leukemia. The program aims to improve the outcome for patients undergoing BMT by developing new clinical treatment protocols and by laboratory work to understand the immune interactions between the donor and the recipient in order to favorably manipulate immune recovery following BMT.