ABSTRACT
Traditionally, human leukocyte antigen (HLA)-mismatched hematopoietic cell transplantation (HCT) has been considered ill-advised in a routine clinical practice due to excessive serious post-transplant complications, such as graft failure, graft-versus-host disease, and prolonged immunosuppression resulting in increased fatal infections. Recent introduction of new HCT techniques, especially in the area of conditioning therapy, has improved outcomes of HLAmismatched HCT considerably. Using several regimens of reduced-intensity conditioning (RIC), it is now possible to perform allogeneic HCT in patients without HLA-matched donors in the family or in the registry from HLA-mismatched family donors. Furthermore, due to less rigorous nature of RIC therapy, elderly patients (up to 70 years of age) and patients who have been treated heavily especially with a previous HCT can also be treated. In this review, we gave a brief historical background for the development of allogeneic HCT, discussed rationale for the use RIC for HLA-mismatched HCT, and summarized trial results of HLA-mismatched HCT after RIC. Lastly, future areas of research regarding HLA-mismatched HCT were discussed.