Sequence, genetics and serology of a new HLA-B allele: B*4903

A new HLA-B allele - B*4903 - was detected by the polymerase chain reaction using sequence-specific priming (PCR-SSP), in a Caucasoid bone marrow panel donor, that differs from B*4901 by 8 nucleotides at positions 141, 142, 144, 165, 167, 193, 206 and 213 in exon 2. These substitutions all occur in HLA-B*51 and B*52 alleles and encode 4 amino acid substitutions at positions 24 (Thr to Ala), 32 (Leu to Gln), 41 (Thr to Ala) and 45 (Lys to Thr). This suggests that B*4903 occurred following a gene conversion-like event involving B*4901 and probably a B*51 allele. HLA-B*4903 was identified on a haplotype with: HLA-A*0201; Cw*07; DRB1*1302/34; DRB3*0301; DQA1*0102; DQB1*0604; BfS; C4A3; C4BQ0 and encodes a unique serological specificity which was characterised by the reactivity of 55 antisera directed towards at least four predicted epitopes. No further examples of B*4903 were found in 15,796 consecutive HLA PCR-SSP typed donors from the Welsh Bone Marrow Donor Registry, indicating that this allele has a phenotype frequency of <0.01% and a gene frequency of <0.00004.