Hematopoietic stem cell transplants from unrelated donors.

Transplantation of hematopoietic stem cells is now well established as life-saving therapy for patients with several different genetic and acquired diseases. This has been possible largely because of the identification of HLA as the human major histocompatibility system and the application of new technologies for improving the accuracy of HLA typing and matching. Clinical advances including the development of more effective immune suppression therapy and improvements in supportive care have also been critically important. The lack of HLA-identical sibling donors for most patients and the extensive polymorphism of HLA genes have necessitated establishing very large registries of HLA-typed volunteers. With more than 3 million donors now available worldwide, the number of patients identifying HLA matches has increased substantially. Despite a higher incidence of graft-versus-host disease (GVHD), the results of unrelated donor transplants are favorable when performed under optimal conditions with a well-matched donor. In order to provide transplants for all patients, improved methods for GVHD prophylaxis are needed that will make it possible to safely perform transplants even across limited degrees of HLA disparity.