Contribution of HLA class I allele expression to CD8+ T-cell responses against Epstein-Barr virus.

Most immune responses to viral infections involve CD8+ T cells recognizing viral peptides of typically 9-10 amino acids in the groove of major histocompatibility complex (MHC) class I. Importantly, CD8+ T-cell responses appear to focus on few viral epitopes, a phenomenon termed immunodominance. While the understanding of this phenomenon has been based largely on experimental mice models, it is imperative to evaluate its contribution in humans, as the design of peptide-based vaccines may be influenced by immunodomination. Here, we present evidence that immunodominance can be detected among Epstein-Barr virus (EBV) epitopes associated with two of the most frequent class I alleles in Western Europe, human leucocyte antigen (HLA)-A2 and HLA-B7. CD8+ T-cell responses to HLA-A2-associated EBV epitopes were significantly reduced in individuals coexpressing HLA-B7. The impairment of HLA-A2-associated responses correlated with a dominant response to an HLA-B7 epitope. The data demonstrate a hierarchy in the human cellular immune response to immunodominant EBV epitopes presented by separate HLA class I alleles. This may have implications for EBV vaccine development as well as for the interpretation of isolated analysis of immunodominant responses to EBV.