Clinical guide to ABO-incompatible allogeneic stem cell transplantation.

The independent genomic inheritance of the human leukocyte antigen (HLA) and the ABO-blood group system allows for HLA-matched hematopoietic progenitor cell transplantation (HCT) to occur in donors who are not matched for ABO blood groups. In fact, nearly one-half of all HCT will involve recipient-donor ABO incompatibility. This places the recipient at increased risk for acute and delayed hemolytic reactions, delayed RBC engraftment, and pure red blood cell aplasia. Additionally, clinical and laboratory evaluation for potential non-ABO, minor RBC antigen-antibody discrepancies may be beneficial to facilitate safe transfusions before, during, and after transplantation. In addition to posing potential clinical risks, analyses of outcomes in ABO-incompatible HCT have yielded inconsistent results with respect to overall survival, relapse risk, incidence of acute or chronic graft-versus-host disease, and engraftment of platelets and granulocytes. As such, pretransplantation donor-recipient evaluation and management for ABO-incompatible HCT requires adopting unique strategies when major, minor, and bidirectional differences exist. These strategies have the potential to improve patient outcomes and allow for effective management of the blood bank inventory. The purpose of this article is to describe practical approaches to screening for and managing ABO-incompatible HCT, with the goal of reducing preventable morbidity and mortality after transplantation.