The extent of HLA class II allele level disparity in unrelated bone marrowtransplantation: analysis of 1259 National Marrow Donor Program donor-recipient pairs

A comprehensive analysis of the HLA-D region loci, DRB1, DRB3, DRB5, DQA1, DQB1, DPA1 and DPB1, was performed to determine allelic diversity and under lying HLA disparity in 1259 bone marrow recipients and their unrelated dono rs transplanted through the National Marrow Donor Program. Although 43.0% o f DRB1 alleles known to exist at the beginning of the study were found in t his predominantly Caucasian transplant population, a few alleles predominat ed at each locus. In recipients, 67.1% of DRB1 alleles identified were one or two of six common DRB1 alleles, Only 118 (9.4%) donor-recipient pairs we re matched for all alleles of DRB1, DQA1, DQB1, DPA1 and DPB1, While 79.4% of the pairs were matched for DRB1, only 13.2% were matched for DPB1 allele s, Almost 66% of pairs differed by more than one allele mismatch and 59.0% differed at more than one HLA-D locus. DQB1 was matched in 85.9% of DRB1-ma tched pairs. In contrast, only 13.9% of the pairs matched for DRB1, DQA1 an d DQB1 were also matched for DPA1 and DPB1, This database, highlighting the underlying HLA disparity within the pairs, forms the foundation of an ongo ing study to establish the relationship between HLA matching and successful outcome in unrelated allogeneic stem cell transplant.