Impact of HLA allele mismatch at HLA-A, -B, -C, -DRB1, and -DQB1 on outcomes in haploidentical stem cell transplantation

The impact of human leukocyte antigen (HLA) allele mismatch on transplant outcomes in haploidentical stem cell transplantation (haplo-SCT) has not been established. We retrospectively studied 595 patients with hematologic malignancy who received haplo-SCT. The impact of multiple HLA allele mismatches (HLA-A, -B, -C, -DRB1, and -DQB1) and each HLA allele mismatch on transplant outcomes was analyzed. Greater number of HLA allele disparity does not appear worsen outcome. As for each HLA locus, HLA-A mismatch correlated with decreased rate of platelet engraftment (HR 0.740, P = .003); HLA-B mismatch independently correlated with decreased relapse rate (HR 0.494, P = .032) and improved disease-free survival and overall survival (HR 0.514, P = .003; HR 0.494, P = .002, respectively); HLA-C mismatch appeared to be protective for transplant-related mortality (TRM) (HR 0.567, P = .039); HLA-DRB1 mismatch was associated with increased cumulative incidence of grade II–IV acute graft-vs.-host disease (GVHD) (HR 1.942, P = .002). No associations of any HLA mismatch with delayed neutrophil engraftment or increased cumulative incidence of chronic GVHD were observed. Our data indicated that high degree of HLA allele mismatches did not adversely affect transplant outcomes in haplo-SCT and each HLA allele mismatch had different effect.