Reduced-intensity conditioning followed by allogeneic hematopoietic cell transplantation in myeloid diseases

Within the past years, reduced or modified doses of chemotherapy or radiotherapy have been widely studied for conditioning before allogeneic hematopoietic cell transplantation in patients with myeloid leukemia not eligible for conventional transplantation. The main goal was to reduce the substantial treatment-related mortality in this patient population while preserving the potential curative graft-versus-leukemia effect. This review summarizes results of published trials using reduced-intensity conditioning (RIC) in patients with acute myeloid leukemia (AML), myelodysplastic syndrome (MDS), chronic myeloid leukemia (CML), and myelofibrosis. In most of the published trials conditioning contained fludarabine (90–180 mg/m²) in combination with busulfan (4×10 mg/kg), melphalan (90–140 mg/m²), or 2–5 Gy total body irradiation (TBI). Peripheral blood hematopoietic stem cells from related or unrelated donors were used as graft source in most of the studies. Post-transplantation immunosuppression consisted of cyclosporine combined with methotrexate or mycophenolate mofetil. Although the majority of the patients were above the age of 50 years, early treatment-related mortality was rather low. Nevertheless, the rate of clinically significant graft-versus-host disease (GVHD) seemed to be comparable to conventional transplants in most of the protocols. The outcome differed between trials, but diagnosis and disease status pre-transplant significantly influenced outcome. In summary, this approach is feasible and provides access to the curative potential of allogeneic stem cell transplantation for patients with higher age or comorbidities. Since the majority of the reports included heterogeneous patient populations, mostly with a short follow-up, more and specifically randomized studies are needed to define the role of RIC before allogeneic hematopoietic cell transplantation.