Unfortunately, in many of the published studies conducted in patients receiving transplants from HLA-matched siblings, T cell-depletion used to prevent or treat GvHD increased the chances of other complications, namely graft failure and leukemia relapse. This is not surprising in light of studies of patients with both early and advanced leukemias that demonstrated a decreased risk of relapse associated with acute and/or chronic GvHD. Because the net effect of these opposing consequences of T cell-depletion on leukemia-free survival in related donor transplants is generally unfavorable, T cell-depletion for related donor marrow transplantation is controversial. The utility of T-cell depletion in unrelated-donor transplants needs to be determined.