Un-manipulated donor lymphocyte infusion (DLI) is used after stem cell transplantation to treat and prevent relapse, to prevent infections and to establish full donor chimerism. The addition of mature T cells which exhibit a broad repertoire of T cell immunity against viral antigens, as well as against cancer antigens, might provide a clinical benefit. However, an expected side effect of the presence of mature T cells is the potential occurrence of acute graft-versus-host disease (aGvHD). The use of a suicide gene switch which would trigger the initiation of the apoptosis of the alloreactive T cells by the infusion of a drug would represent the potential optimal strategy for restoring early immunity with a built in "safety switch" against GvHD side effects. Evidence has emerged that low-dose DLI followed by dose escalation can achieve higher clinical response rate with lower GvHD occurrence. Optimization of DLI dose and schedule as well as strategies of donor T-cell manipulation may lead to the consistent ability to separate GvHD from graft-versus-tumor (GvT) activity and improve the safety of DLI treatment. Our strategy is to infuse escalating doses of manipulated T cells (from the same donor who provided the original hematopoietic stem cell graft) in adults and children with recurrent or minimal residual disease (MRD) hematologic malignancies post-allogeneic transplant to accelerate immune reconstitution thus improving graft versus leukemic effect while reducing the severity of GvHD.