Human leucocyte antigen alloimmunization after bone marrow transplantation: an association with chronic myelogenous leukaemia

Platelet refractoriness due to human leucocyte antigen (HLA) alloimmunization is a significant risk to allogeneic bone marrow transplant recipients. To identify factors contributing to this risk, we reviewed the records of 317 consecutive, paediatric, allogeneic bone marrow transplant recipients at a single institution. The 6-year estimated cumulative incidence of platelet refractoriness due to HLA alloimmunization was 2.6%+/-0.9%. The incidence among patients with chronic myelogenous leukaemia (CML) 12.5%+/-5.3% was significantly greater than that of other patients (1.1%+/-0.6%, P<0.001). Graft rejection (P=0.003) and the number of platelet transfusions during the first 90 d after bone marrow transplantation (BMT) (P=0.0025) were also significantly associated with alloimmunization. The association with CML and with graft rejection was not seen among patients alloimmunized before transplantation. Eight patients developed alloimmunization, of whom three had mismatched grafts and four had unrelated grafts. Alloantibody specificities, identified in seven patients, were unrelated to host or graft major histocompatibility complex (MHC). Host recognition of alloantigens in transfused blood products, not graft-host recognition, therefore seems predominantly responsible for the alloimmunization. These results show that paediatric CML patients have a significantly increased risk of platelet refractoriness due to HLA alloimmunization after BMT. Identifying the mechanism for the increased alloimmunization risk may assist in the development of therapies to prevent platelet refractoriness.