Nonmyeloablative preparative regimens for allogeneic hematopoietic transplantation. Biology and current indications.

High-dose myeloablative therapy with allogeneic hematopoietic transplantation is an effective treatment for hematologic malignancies, but this approach is associated with a high risk of complications. The use of relatively nontoxic, nonmyeloablative, or reduced-intensity preparative regimens still allows engraftment and the generation of graft-vs-malignancy effects, is potentially curative for susceptible malignancies, and reduces the risk of treatment-related morbidity. Two general strategies along these lines have emerged, based on the use of (1) immunosuppressive chemotherapeutic drugs, usually a purine analog in combination with an alkylating agent, and (2) low-dose total body irradiation, alone or in combination with fludarabine (Fludara).