Identification of an HLA-B7 serological variant and its characterization by sequencing based typing

We have identified an HLA-B*07 variant allele, B*0716, in a Caucasoid cadav er kidney donor. The HLA class I type by polymerase chain reaction using se quence-specific primers (PCR-SSP) was A*01, 32; B*07, 08; Cw*07. Serologica l typing, using monoclonal and polyclonal anti-HLA antisera, gave disparate results for the B antigens. Monoclonal antibodies identified B7 and B8 ant igens but polyclonal antisera recognised only the B8 antigen. PCR using seq uencing based typing (PCR-SBT) confirmed the presence of both B*0703 and B* 0801 alleles but with a mutation in one of the alleles. The HLA-B*07 allele was isolated by allele-specific PCR and was shown to have a mutation, G--> T, at 292 in exon 2. This mutation changes codon 74, which encodes aspartic acid (GAC) present in all previously identified B*07 alleles, to tyrosine (TAC) in the variant. The serological results suggest that codon 74 is a cr ucial part of a B7 antigen-specific epitope recognised by tissue typing pol yclonal antisera.