Impact of AB0-blood group incompatibility on the outcome of recipients of bone marrow transplants from unrelated donors in the Japan Marrow Donor Program.

BACKGROUND Although the AB0 blood group is one of two major antigen systems of relevance for transplantation in humans, there are still conflicting data concerning the influence of AB0 incompatibility on transplant outcome. This study investigated the effect of AB0 incompatibility in recipients of bone marrow transplants from unrelated donors. DESIGN AND METHODS We retrospectively analyzed data from 5,549 patients who underwent bone marrow transplantation from unrelated donors in the Japan Marrow Donor Program. RESULTS Overall survival rates in the group with major and minor mismatches were significantly lower than the rate in the AB0-identical group (AB0-identical 63.0%; major mismatch, 56.9%; minor mismatch, 57.1% at 1 year). Treatment-related mortality was higher in the major and minor mismatch groups, but there was no significant difference in the rate of relapse. Cox proportional hazards modeling showed that both major and minor AB0 incompatibility were significant risk factors for transplant-related mortality, independently of disease, patients' age, and HLA incompatibility. Delayed engraftment of neutrophils, platelets, and erythrocytes was observed in transplants with major incompatibility. There was a high incidence of grade 3 and 4 acute graft-versus-host disease in the groups with major and minor mismatches, which was caused by a high incidence of stage 2 to 4 liver graft-versus-host disease. Interestingly, the risk of grade 2 to 4 graft-versus-host disease in the major mismatch group was higher in patients with early engraftment of erythrocytes. Among the patients receiving reduced-intensity conditioning, the transplant-related mortality was also increased in AB0-incompatible transplants. CONCLUSIONS Major and minor AB0 incompatibility have specific effects on transplant-related mortality and acute graft-versus-host disease in recipients of bone marrow transplants from unrelated donors.