Hematopoietic stem cell transplantation (HSCT) from HLA-mismatched donor has come to be performed more frequently than before. The risks of graft failure and graft-versus-host disease (GVHD) are higher in HLA-mismatched HSCT than HLA-matched HSCT. HLA-specific antibody, HLA-specific T lymphocytes, and activated NK cells due to a lack of inhibitory signal, but not HLA molecule itself, cause graft failure and GVHD. This text starts with a quick review of the requirement for HSCT donor, followed by the review of the effect of HLA-specific antibody, HLA-specific T lymphocytes, and activated NK cells on graft failure, acute GVHD, and chronic GVHD, The effect of minor histocompatibility antigen-specific antibody and T lymphocytes on graft failure and GVHD will be also discussed.
