Identification and nucleotide sequence of a new null allele, HLA B*3540N

We report the definition of an HLA class I null allele that has been identified within the B35 group by a combination of serological and molecular typing. This allele, which has been named B*3540N, was detected in a French, potential unrelated hematopoietic stem cell donor of unknown ethnic origin, selected as a probable match for an Irish patient. The presence of the null allele was initially determined by the absence of B35 reactivity by serological typing, in contrast to positive reactions by PCR-SSP and PCR-SSO typing. Subsequent sequencing of clones containing the full genomic sequence of the B*35 allele identified a single nucleotide deletion within exon 4 which resulted in the introduction of a stop codon downstream within exon 4.