A HLA-Cw*03 allele, Cw*0322Q with limited or no expression

The formation of a somatic mutation in the HLA-B gene throughout the development of the disease from severe aplastic anaemia to acute myeloid leukaemia

We detected a somatic mutation in the HLA-B gene in a Czech hematooncological patient. We followed the development of this somatic mutation during the transition from severe aplastic anaemia through to myelodysplastic syndrome to acute myeloid leukaemia until haploidentical related transplantation. The somatic mutation differs from HLA-B*14:02 in exon 3 resulting in an exchange from cysteine to serine at position 101 of the mature protein. Homology modelling of mutated S101 in HLA-B*14 indicated possible conformational changes, which might also result in an aberrant expression. The assumption is that somatic mutation arose as a possible result of a selection mediated by a protective immune response against leukaemia.

Closing the gap: discrimination of the expression profile of HLA questionable alleles by a cytokine-induced secretion approach using HLA-A*32:11Q

Matching of human leukocyte antigen (HLA) alleles between donors and recipients plays a major role in hematopoietic stem cell transplantation (HSCT). Null or questionably expressed HLA allelic variants are a major issue in HLA matching, because the aberrant expression of such alleles can have a major impact on the outcome of HSCT and/or its complications such as graft-versus-host disease. The goal of this study was to investigate the potential of a recently developed cytokine-induced secretion assay to differentiate the expression levels of HLA-A*32:11Q (questionable) into a null (N) or low (L) expression variant. An amino acid mutation at position 164 of HLA-A*32:11Q disrupts the disulfide bridge in the α2 domain. HLA-A*32:11Q is not detectable by standard microlymphocytotoxicity assay. To this end, we cloned soluble HLA-A*32:11Q and a reference allele (HLA-A*32:01) into expression vectors and transfected/transduced HEK293 and K562 cells. Allele-expressing K562 cells were simultaneously transfected/transduced with a β2-microglobulin (B2M)-encoding vector to ensure the intact HLA structure with B2M. After treatment with proinflammatory cytokines, secreted soluble HLA molecules were determined by enzyme-linked immunosorbent assay in the supernatant and intracellular accumulation of the recombinant proteins by flow cytometry. HLA-A*32:11Q was nearly undetectable in untreated transfectants. Cytokine treatment increased the secretion of HLA-A*32:11Q to detectable levels and resulted in intracellular accumulation of the allele. There was no difference in mRNA transcription between the A*32 alleles. On the basis of these results, we recommend reclassification of HLA-A*32:11Q as a low expression (L) variant.