High-risk HLA alleles for severe acute graft-versus-host disease and mortality in unrelated donor bone marrow transplantation.

HLA molecules play an important role for immunoreactivity in allogeneic hematopoietic stem cell transplantation. To elucidate the effect of specific HLA alleles on acute graft-versus-host disease, we conducted a retrospective analysis using 6967 Japanese patients transplanted with T-cell-replete marrow from an unrelated donor. Using unbiased searches of patient and donor HLA alleles, patient and/or donor HLA-B51:01 (patient: HR, 1.37,P<0.001; donor: HR, 1.35,P<0.001) and patient HLA-C14:02 (HR, 1.35,P<0.001) were significantly associated with an increased risk of severe acute graft-versus-host disease. The finding that donor HLA-C14:02 was not associated with severe acute graft-versus-host disease prompted us to elucidate the relation of these high-risk HLA alleles with patient and donor HLA-C allele mismatches. In comparison to HLA-C allele match, patient mismatched HLA-C14:02 showed the highest risk of severe acute graft-versus-host disease (HR, 3.61,P<0.001) and transplant-related mortality (HR, 2.53,P<0.001) among all patient mismatched HLA-C alleles. Although patient HLA-C14:02 and donor HLA-C15:02 mismatch was usually KIR2DL-ligand mismatch in the graft-versus-host direction, the risk of patient mismatched HLA-C14:02 for severe acute graft-versus-host disease was obvious regardless of KIR2DL-ligand matching. The effect of patient and/or donor HLA-B51:01 on acute graft-versus-host disease was attributed not only to strong linkage disequilibrium of HLA-C14:02 and -B51:01, but also to the effect of HLA-B51:01 itself. With regard to clinical implications, patient mismatched HLA-C14:02 proved to be a potent risk factor for severe acute graft-versus-host disease and mortality, and should be considered a non-permissive HLA-C mismatch in donor selection for unrelated donor hematopoietic stem cell transplantation.