Alloimmune hemolytic anemia resulting from graft-versus-host reaction induced by group O graft in renal transplant recipients with ABO incompatibility

Acute hemolytic anemia is one of the side effects associated with cyclospor in and tacrolimus therapy, and three mechanisms have been described to acco unt for hemolytic anemia in patients receiving these drugs: drug induced he molysis, autoimmune hemolysis and alloimmune hemolysis resulting from donor lymphocytes derived from the allograft (passenger lymphocyte syndrome). We report four cases of renal transplant recipients who developed alloimmune hemolytic anemia due to minor ABO incompability while under treatment with cyclosporin (two) and tacrolimus (two). The anti-erythrocyte antibodies res ponsible for hemolysis were of the IgG isotype and showed anti-A or anti-B specificity. These findings suggest that the hemolysis could be related to alloantibodies derived from the clonal development of donor B lymphocytes i n the recipients (microchimerism). In summary, hemolytic anemia due to ABO- minor incompatibility occurs infrequently after renal transplantation. Risk s are higher for patients A, B or AB blood group receiving an O blood group graft under treatment with cyclosporin or tacrolimus. Follow-up of these p atients is warranted for the early detection and optimal management may be achieved by reduction of immunosuppression and change to mycophenolate mofe til.