Transient hemolysis due to anti‐D and anti‐A 1 produced by engrafted donor's lymphocytes after allogeneic unmanipulated haploidentical hematopoietic stem cell transplantation

BACKGROUND Development of de novo alloantibodies against recipient's red blood cell (RBC) antigens by engrafted donor's lymphocytes is a known phenomenon in the setting of allogeneic hematopoietic stem cell transplantation (HSCT). This situation is usually clinically insignificant. We report a case of early clinically relevant hemolytic anemia in a blood group A 1 D+ patient, due to a limited production of anti‐D and anti‐A 1 produced by nonpreviously sensitized newly engrafted donor's immune system. CASE REPORT A 31‐year‐old Caucasian woman, blood group A 1 , D+, with Hodgkin's lymphoma, received an unmanipulated haploidentical allogeneic peripheral blood HSCT after a nonmyeloablative conditioning regimen. Donor blood group was A 2 B, D–. The patient had an uneventful course until Day +34, when she developed clinically significant hemolytic anemia with a positive direct antiglobulin test. Anti‐D and anti‐A 1 produced by the donor‐engrafted lymphocytes were detected both in serum and in eluate. The hemolysis produced an accelerated group change, turning the patient's ABO group into A 2 B 2 weeks after the detection of the alloantibodies. As the residual patient's RBCs progressively disappeared, anti‐D and anti‐A 1 production decreased and were not detected in serum by Day +41. CONCLUSION This case illustrates that de novo alloantibody production against ABO and D antigens by the newly engrafted donor's lymphocytes can occasionally cause clinically significant anemia. To our knowledge, this is the first case reported of clinically significant hemolytic anemia due to a transient anti‐D anti‐A 1 alloimmunization after T‐cell‐repleted haploidentical HSCT.