Influence of donor/recipient sex matching on outcome of allogeneic hematopoietic stem cell transplantation for aplastic anemia

Background. Increased risk of transplant related mortality in male recipients of female hematopoietic stem cell grafts and in vitro reactivity of lymphocytes against H-Y encoded gene products in females with rejected male grafts have been documented. An increased rejection of male grafts in female recipients is not reported for solid organ or stem cell transplants and the role of H-Y as transplantation antigen has been controversial. Methods. Data from 1481 patients with a hematopoietic stem cell transplant for aplastic anemia reported from 154 centers in 28 countries were analyzed. Outcome was compared between patients with donors of the same or opposite Sex. Results. Survival at 5 years was significantly better in patients with donors from the same sex: 68% vs. 60% (P=0.001). Male patients with female donors had a decreased survival (relative risk of death 1.52, P < 0.001) and an increased risk of severe graft-versus-host disease (relative risk 1.33, P=0.03) compared to recipients of sex-matched grafts. Female patients with male donors had a decreased survival (relative risk of death 1.44, P=0.01) and an increased risk of rejection (relative risk 2.20, P=0.01) compared to recipients of sex-matched grafts. In a subgroup analysis, the negative effects of donor/recipient sex-mismatching appeared confined to patients receiving conditioning regimens not containing antithymocyte globulin. Conclusions. These data confirm H-Y as a clinically relevant transplantation antigen, in both the graft-versus-host and the host-versus-graft direction. Wherever possible, donor-recipient sex-matching should be integrated into donor selection algorithms.