Transfusion strategy and allo-immunization to red blood cell antigens after allogeneic hematopoietic stem cell transplantation with partial donor/recipient Rh matching.

Background: After allogeneic hematopoietic stem cell transplantation (alloHSCT), the HAS recommends transfusing red blood cells (RBCs) matched for Rh ("Rhesus") phenotypes, and the EFS recommends respecting both donor and recipient Rh phenotypes. We previously reported a 10.3% allo-immunization rate in 58 Rh-incompatible alloHSCT recipients transfused in the donor phenotype: none was directed against the mismatched donor Rh antigens.

Study design and methods: In this single-center retrospective study, we investigated the incidence of allo-immunization to RBC antigens during the first year after alloHSCT in 264 patients with partial donor/recipient Rh matching, and transfused from alloHSCT with RBCs expressing at least one donor Rh antigen absent from the recipient.

Results: Six patients had a positive RBC antibody screening test (allo-immunization rate: 2.3%). In five cases, the antibodies were unrelated to the transfusion strategy. One patient presented a temporary anti-C, possibly related to the transfusion strategy, occurring in a context of immune hemolytic anemia.

Discussion: Our findings indicate that the transfusion of RBC in the donor Rh phenotype is associated with a low rate of immunization to RBC antigens. These results question the current transfusion guidelines in alloHSCT recipients, aiming to limit the use of short-supply RBCs phenotypes.