Delayed donor red cell engraftment and pure red cell aplasia (PRCA) are wellrecognized complications of major ABOincompatible hematopoietic stem cell transplantation (SCT) performed by means of myeloablative conditioning. To evaluate these events following reducedintensity nonmyeloablative SCT (NST), consecutive series of patients with major ABO incompatibility undergoing either NST (fludarabine/cyclophosphamide conditioning) or myeloablative SCT (cyclophosphamide/high-dose total body irradiation) were compared. Donor red blood cell (RBC) chimerism (initial detection of donor RBCs in peripheral blood) was markedly delayed following NST versus myeloablative SCT (median, 114 versus 40 days; P < .0001) and strongly correlated with decreasing host antidonor isohemagglutinin levels. Antidonor isohemagglutinins declined to clinically insignificant levels more slowly following NST than myeloablative SCT (median, 83 versus 44 days; P ؍ .03). Donor RBC chimerism was delayed more than 100 days in 9 of 14 (64%) and PRCA occurred in 4 of 14 (29%) patients following NST, while neither event occurred in 12 patients following myeloablative SCT. Conversion to full donor myeloid chimerism following NST occurred significantly sooner in cases with, compared with cases without, PRCA (30 versus 98 days; P ؍ .008). Cyclosporine withdrawal appeared to induce graftmediated immune effects against recipient isohemagglutinin-producing cells, resulting in decreased antidonor isohemagglutinin levels and resolution of PRCA following NST. These data indicate that significantly delayed donor erythropoiesis is (1) common following major ABO-incompatible NST and (2)
IntroductionThe ABO blood group system is of critical importance in transfusion medicine, but has had less dramatic impact in hematopoietic transplantation. 1-4 ABO antigens are potently immunogenic and are expressed on multiple tissues in addition to red blood cells (RBCs). 5 Human beings begin to produce isohemagglutinins against non-self-ABO antigens shortly after birth and continue to do so throughout adult life. 1 Since ABO and human leukocyte antigens (HLAs) are inherited independently, ABO incompatibility may occur in up to 20% to 40% of HLA-matched allogeneic hematopoietic stem cell transplants (SCTs). 4 Graft failure does not occur with increased frequency, and most studies indicate that the incidence of graft-versus-host disease (GVHD) is also not increased following ABO-incompatible versus ABO-identical SCT. 2,4,6 Although increased transfusion requirements and immunohematologic events occur, the overall impact of ABO incompatibility in SCT is generally considered low, provided that appropriate transfusion practices are followed. 2,4,[7][8][9][10] Major ABO incompatibility in SCTs, defined as incompatibility of donor ABO antigens with the recipient's immune system, has been associated with pure red cell aplasia (PRCA) following conventional myeloablative conditioning. [11][12][13][14][15][16][17] Proposed risks for PRCA in this setting include the use of cyclosporine ...