Immuno-Hematologic Complexity of ABO-Incompatible Allogeneic HSC Transplantation

ABO incompatibility is not considered a contraindication for hematopoietic stem cell transplantation (HSCT). Approximately 30% of transplants from related donors and up to 50% of transplants from unrelated donors are ABO-incompatible. The immuno-hematologic investigationsmay evaluate donor/recipient ABO mismatch and anti-A/B isohemoagglutinins (IHAs) titration in pre-HSCT phase. Immediate hemolysis or delayed complications (passenger lymphocyte syndrome and pure red cell aplasia) can appear post-HSCT. Some preventive treatmentstake into consideration the manipulation of the product and decision-making algorithms based on the titration of IHAs in the recipient with clinical protocols for the removal/reduction of IHAs through plasma exchange or immunoadsorption procedures. Currently, the best approach in the managementof ABO-incompatibletransplant is not defined in expert consensus documents or with solid evidence. In addition, the methods for IHAs titration are not standardized. The transfusion strategy must consider both the blood group systems of the recipient and the donor until the RBC engraftment and the confirmed ABO conversion (forward and reverse typing) on two consecutive and independent samples. Therefore, ABO incompatibility in the HSCT is an important immuno-hematologic challenge and request all necessary preventive measures including the appropriate selection of ABO blood components for transfusion.