Does donor–recipient ABO incompatibility protect against relapse after allogeneic bone marrow transplantation in first remission acute myeloid leukemia?

It is not known if donor–recipient ABO blood group incompatibility contributes to graft-versus-leukemia after allogeneic BMT. One hundred and nineteen patients with acute myeloid leukemia in first remission underwent non-T cell-depleted marrow allografts from HLA-identical siblings after TBI and cyclophosphamide (n = 72) or melphalan (n = 47). GVHD prophylaxis comprised cyclosporine alone or cyclosporine-methotrexate. Twenty-two patients relapsed at 3–46 months (median 7): 18 of 76 patients with ABO-matched donors and four of 43 patients with ABO-mismatched donors (actuarial 5-year probabilities 33 ± 6% vs 12 ± 6%; P = 0.028). The incidence of acute and chronic GVHD was not affected by ABO mismatch. The following factors were studied in Cox analysis for effect on outcome: gender, age, FAB subtype, ABO mismatch, CR–transplant interval, conditioning, TBI dose, nucleated cell dose, lymphocyte recovery, acute GVHD, and chronic GVHD. Donor–recipient ABO match was the only factor independently associated with a higher risk of relapse (RR = 3.7; 95% Cl, 1.1–12.6; P = 0.04). ABO mismatch was also associated with superior overall and disease-free survivals. We conclude that ABO incompatibility may influence relapse rates and survival favorably after allogeneic BMT. It is not known if this holds true for allogeneic blood stem cell transplants.