Reduced-intensity conditioning and nonmyeloabla-tive regimens allowed engraftment of allogeneic hematopoietic cells and the development of GvT effects. Remarkably, a minimally toxic regimen of 2 Gy TBI with or without fludarabine followed by post-grafting immunosuppression with MMF and CSP assured engraftment rates similar to those following myeloablative conditioning. Antitumor responses occurred after the achievement of full donor T-cell chimerism, though complete remissions required extended periods of time, with some patients achieving complete remissions more than 1 year after transplant. In patients with slowly progressing diseases such as CLL, low-grade NHL, chronic-phase CML, or with more aggressive diseases in complete remission, nonmyeloablative conditioning may be sufficient to achieve engraftment and cure. In patients with aggressive diseases such as acute leukemias, multiple myeloma, high-grade lymphomas, and Hodgkin's disease not in complete remission, cytoreduction by preceding chemotherapy or autologous HCT may be required. Remaining challenges include prevention

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