RNA and protein expression of HLA-A(∗)23:19Q

The assignment of null alleles is clinically relevant in stem cell transplantation, in particular for donor selection. It is unclear how questionable (Q) alleles, having an unknown expression profile, should be considered in matching criteria. In this study we analyzed the RNA and protein expression profile of a questionable allele encountered in a sample of the Guadeloupe population: GD23Q, HLA-A(∗)23:19Q, 29:02:01. Full-length DNA sequencing of HLA-A(∗)23:19Q revealed a single polymorphism at position 619 (G>A) compared to HLA-A(∗)23:01:01. Serological typing showed only the presence of HLA-A29; HLA-A(∗)23:19Q was not detected on the cell surface. The absence of HLA-A(∗)23:19Q surface expression was shown by flow cytometry using a directly labeled monoclonal antibody and a panel of five indirectly labeled polyclonal antibodies all directed against HLA-A23 (HLA-A9) molecules. Allele specific amplification revealed the absence of intact full-length mRNA, but the presence of two major alternatively spliced mRNAs: sequencing identified that in one variant exon 3 is missing and in the other variant introns 2 and 3 are retained. Based upon the lack of HLA-A(∗)23:19Q surface expression and the presence of aberrant mRNA transcripts only, this study shows that HLA-A(∗)23:19Q is non-expressed.