ABO-incompatible allogeneic hematopoietic stem cell transplantation

ABO blood group incompatibility is not a contraindication for allogeneic hematopoietic stem cell transplantation (allo-HSCT). An increasing number of ABO-incompatible HSCT (ABOi-HSCT) procedures have been performed along with advances in donor selection over the years. Currently, whether the recipient-donor ABO incompatibility has detrimental effects on post-HSCT outcomes is a matter of debate. Discrepancies across studies referring to various graft sources, donor types, conditioning regimens, and the use of immunomodulators complicate interpretations of the clinical outcomes of ABOi-HSCT, such as transfusion requirements, graft-versus-host disease (GVHD), disease relapse, overall survival (OS), and non-relapse mortality (NRM). Isohemagglutinins (ISO) targeting red blood cell (RBC) antigens are associated with post-HSCT immunohematological complications, including hemolysis, passenger lymphocyte syndrome (PLS), and pure red cell aplasia (PRCA). Immunohematological events occur frequently and are sometimes difficult to handle in clinical practice. Therefore, it is necessary to form a deeper understanding on the mechanism and a comprehensive management scheme for recipients of ABOi-HSCT. In this review, we summarized literature of the impact of ABO incompatibility on post-HSCT outcomes and outlined important immune-mediated hematological events.