 There is no curative therapy once acute leukemia patients relapse after transplant. Patients who develop clinically significant graft versus host disease GVHD have a lower rate of relapse than those who do not develop GVHD. We are initiating this study of post-transplant fast withdrawal of immunosuppression and donor lymphocyte infusions, with a goal of achieving full donor chimerism in children with hematologic malignancies. If our hypothesis that full donor chimerism results in leukemia-free survival is correct, using immune modulation to achieve full donor chimerism should decrease relapse rate and thus increase survival. The goal of this Phase II study is to identify if achieving full donor chimerism in whole blood CD3 and leukemia-specific CD1415, CD19, CD33 and CD34 subset may decrease the risk of relapse of patients undergoing allogeneic transplant for hematologic malignancy. 