RNA processing and protein expression of HLA‐B07:44N

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 .