Transfusion policy in ABO‐incompatible allogeneic stem cell transplantation

As a result of the fact that the human leucocyte antigen (HLA) system is inherited independently from the ABOblood group system, approximately 40–50% of all haematopoietic stem cell transplants (HSCT) are performed across the ABO-blood group barrier. There are three kinds of ABO incompatibility: minor incompatibility (in 20–25% of transplants) is characterized by the ability of donor B lymphocytes to produce antirecipient alloantibodies (e.g. group O donor to a group A recipient). In contrast, major incompatibility (in 20–25% of transplants) is characterized by the presence of antidonor alloantibodies (e.g. group A donor to a group O recipient). Bidirectional ABO-incompatibility (up to 5% of transplants) occurs when both donor and recipient produce alloantibodies against each other’s red cell (e.g. group A donor to a group B recipient). Several studies demonstrated that an ABO mismatch does not affect the incidence of graft rejection and does not cause slower engraftment of neutrophils and platelets. However, haemolytic transfusion reactions may occur [1]. A distinction can be made between immediate (during graft infusion) and delayed (during engraftment) immune haemolysis. Another phenomenon that may occur is pure red cell aplasia (PRCA) which is seen in 15–20% of cases after a major ABO-incompatible transplant. This phenomenon is explained as to be due to alloantibody-producing plasma cells which are relatively resistant to chemoand radiotherapy. Antibodies produced by such surviving plasma cells of the recipient are responsible for the inhibition of the growth of RBC precursors in the bone marrow [2]. Recommendations for transfusion policy in cases of ABO-incompatible stem cell transplantation and management of RBC transfusions in cases of PRCA or relapse of the underlying disease are not well defined in the literature. To obtain information on these aspects the following questions were sent to various transplant centres and departments of blood group serology and transfusion medicine. We received 10 contributions for this Forum. The participating centers are listed in Table 1. In Table 2, all answers are summarized.