Alternative donor transplantation for aplastic anemia.

Patients with severe aplastic anemia who do not have a human leukocyte antigen (HLA)-identical sibling generally receive immunosuppressive therapy as a first-line therapy, with allogeneic transplantation being reserved for those who do not have an adequate sustained response. Barriers to the use of unrelated-donor transplantation for aplastic anemia include identifying a suitable alternative donor, and risks of graft failure, regimen-related toxicity, and graft-versus-host disease (GVHD). Despite the more than 14 million adults registered with donor registries worldwide, only approximately 50% of patients of Caucasian descent will have an available and fully HLA-matched unrelated adult donor; the rate is substantially lower for non-Caucasians. While umbilical cord blood allows transplantation with greater donor-recipient HLA disparity (without excessive risk of GVHD), risks of graft failure and transplant-related mortality are higher than after transplantation of adult donor grafts. Among patients with a suitable donor, recent changes in pre-transplant conditioning regimens have lowered the risks of organ toxicity and graft failure. Although advances in donor HLA typing and selection practices and improved GVHD prophylaxis have lowered the risk, GVHD remains an important obstacle to long-term symptom-free survival. Despite these limitations, unrelated-donor transplantation offers the best chance of long-term survival for many patients in whom current immunosuppression strategies are not effective. Wider applicability of alternative-donor transplantation for aplastic anemia will require better approaches to prevent graft failure and GVHD and to expand the pool of unrelated-donor grafts. This includes exploring strategies to effectively use alternative grafts such as umbilical cord blood.