Assessment of HLA-B Genetic Variation with an HLA-B Leader Tool and Implications in Clinical Transplantation.

Sequence variation in the HLA-B gene is critically linked to differential immune responses. A dimorphism at -21 of HLA-B exon 1 gives rise to leader peptides that are markers for risk of acute graft-versus-host disease (GVHD), relapse, and mortality after unrelated donor and cord blood transplantation. To optimize the selection of stem cell transplant sources based on the HLA-B leader, an HLA-B Leader Assessment Tool ("BLEAT") was developed to automate the assignment of leader genotypes, define HLA-B leader match statuses, and rank order candidate stem cell sources according to clinical risk. The base cohort consisted of 9,417,614 registered donors from the Be The Match Registry® with HLA-B typing. Among these donors, the performance of BLEAT was assessed in 1,098,358 donors with sequence data for HLA-B exon 1 (2,196,716 haplotypes). The accuracy of leader assignment was then assessed in a second cohort of 1,259 patients and their unrelated transplant donors. We furthermore established the frequencies of HLA-B leader genotype (MM, MT, TT) representations in broad racial categories in the 9.42 million donors. BLEAT has direct applications for the selection of optimal stem cell sources for transplantation and broad utility in basic and clinical research in pharmacogenomics, vaccine development, and cancer and infectious disease studies of human populations.