Immunohematologic issues in ABO-incompatible allogeneic hematopoietic stem cell transplantation.

It is a conceptual paradox to perform allogeneic hematopoietic stem cell transplantations across the ABO blood group border, when we, on the other hand, put so much effort into preventing ABO-incompatible transfusions. In clinical practice though it is still controversial whether ABO-incompatible allogeneic hematopoietic stem cell transplant have detrimental effects on patient outcomes in view of overall survival, non-relapse mortality, and graft-versus-host disease. However, the number of ABO-incompatible transplantations will probably continue to increase, unless solid evidence about contraindications can be presented. In the meantime, all necessary measures to reduce the acute hemolysis risk have to be taken regarding graft manipulation and correct selection of ABO group blood components for transfusion. In addition the immunohematologic challenges dealing with gradual ABO group shift have to be handled. These puzzling but exciting issues are addressed briefly in this What's Happening manuscript.