RNA processing and protein expression of HLA ‐B*07: 44N

Background The assignment of human leukocyte antigen ( HLA ) null alleles is clinically relevant in the setting of stem cell transplantation. Cell surface expression profiling and mRNA processing analysis of the HLA ‐B allele previously designated as B*07:44 , have been performed. Materials and Methods Cell surface expression of HLA ‐B*07:44 was determined using flow cytometry. Genomic full‐length and HLA ‐B*07 ‐specific cDNA sequencing were carried out by Sanger procedure. Results Flow cytometric analysis confirmed previous serologic results and demonstrated a lack of cell membrane expression of the HLA ‐B protein. The mRNA processing, studied using direct HLA ‐B*07 ‐specific cDNA sequencing, revealed the presence of a unique, aberrantly spliced mRNA , with a deletion of the last 43 bp on the 5’‐end of exon 4. The substitution from T to G at genomic position 1799 compared to B*07:02:01 introduced a new and stronger splice donor site at exon 4. This alternative splicing produced an mRNA containing a premature stop codon at position 280, explaining the absence of mature HLA‐B7 protein on the cell surface. Conclusion These findings led us to consider this HLA ‐B variant as a HLA null allele. The World Health Organization ( WHO ) Nomenclature Committee has since renamed this variant B*07: 44N .