Structural analysis of HLA-A2.4 functional variant KNE. Implications for the mapping of HLA-A2-specific T-cell epitopes

HLA-A2 antigens are divided into four subtypes, designated A2.1 to A2.4, by the use of cytolytic T lymphocytes (CTL). The A2.4 subtype consists of a functionally heterogeneous group of variants that are not recognized by A2.1-, A2.2-, or A2.3-specific CTL lines while it is indistinguishable from A2.1 by isoelectric focusing. The structure of an A2.4 variant expressed on donor KNE has been established by comparative peptide mapping with A2.1 and radiochemical sequencing. It was found to differ from A2.1 by a single amino acid change of Cys to Tyr at position 99. This position is only moderately polymorphic and has not previously been found to vary in any other HLA or H-2 variants. The nature of the change is compatible with its generation by one-point mutation from A2.1. The only other previously characterized A2.4 variant, CLA, differs from A2.1 by a single amino acid replacement at position 9. Both residues 9 and 99 are located in homologous positions within the alpha 1 and alpha 2 domains, respectively. The results shown contribute to the molecular interpretation of the heterogeneity of CTL recognition within the HLA-A2.4 group of antigens.