Allogeneic Hematopoietic Cell Transplantation After Nonmyeloablative Conditioning

High-dose chemoor chemoradiotherapy followed by allogeneic hematopoietic cell transplantation (HCT) has been recognized as an effective therapy for a number of hematologic malignancies with tumor cells resistant to conventional doses of chemotherapy (1). The aims of the high-dose conditioning are (i) to abolish host immune responsiveness prior to transplantation to avoid graft rejection and (ii) to deliver doses of cytotoxic anticancer agents beyond the range that is toxic to the bone marrow cells, thereby potentially increasing antitumor efficacy (1). The curative potential of allogeneic HCT is not only due to the high-dose chemoradiotherapy but also due to immune-mediated graft-versus-tumor (GVT) effects (2–4). The existence of a GVT effect was first suggested by Barnes et al. in 1956 (5). They observed that mice receiving syngeneic HCT and injection of congenic leukemic cells after total body irradiation (TBI) almost uniformly died from