[Optimal selection of alternative donors for allogeneic hematopoietic stem cell transplantation]

A human leukocyte antigen (HLA)-matched related donor is considered as the first donor candidate in case of allogenic hematopoietic stem cell transplantation (allo-HSCT). Given the declining birthrate and aging population in Japan, the number of sibling donors is also decreasing. Hence, candidates other than HLA-matched siblings, named "alternative donors," have attracted increasing attention. Improved graft-versus-host disease (GvHD) prophylaxis with posttransplant cyclophosphamide or pretransplant antithymocyte globulin represented a major breakthrough in allo-HSCT with alternative donors by overcoming the barriers of HLA mismatch. In addition, there have been improved outcomes of unrelated cord blood transplantation, owing to better unit selection along with improved GvHD prophylaxis and supporting strategies. These changes have expanded the range of donor options and consequently, increased donor availability at the critical moment for allo-HSCT. The next challenge that warrants further investigation is the development of personalized strategies to select the best donor from the available multiple options according to the status of each patient.