7–12 This complicated pathway may explain why escape from this immunodominant HIV epitope occurs only late in infection. In HCV we have previously shown that fitness constraints

limit the ability to mutate at the main HLA-B27 binding anchor of the immunodominant HLA-B27 epitope that is located within a conserved region of the RNA-dependent RNA polymerase (NS5B2841-2849). Instead, a mosaic of several mutations at the T-cell receptor contact residues within the epitope needs to evolve in order to allow significant escape from the HLA-B27-restricted CD8+ T-cell response.6, 13 Similar to HIV, these results suggest that viral escape cannot be achieved easily, giving the T-cell response sufficient time to clear the BGB324 cell line virus. These virological factors presumably contribute to the protective effect of HLA-B27. Although there is strong immunological and virological evidence that the protective effect of HLA-B27 in HIV and HCV infection,

respectively, is indeed linked to these particular immunodominant epitopes, this has not been conclusively demonstrated, as this would require a prospective analysis of a large number of B27-positive subjects with acute infection. In order to determine the contribution of the viral epitope on protection by HLA-B27, we took advantage of the fact that the immunodominant viral region targeted by HLA-B27-restricted CD8+ T cells is conserved in HCV BVD-523 supplier genotype 1 only, in which the protective effect of HLA-B27 has been described.6 In other HCV genotypes, e.g., genotype 3a (the most frequent genotype after genotype 1 in most countries) the epitope sequence differs by three out of nine amino acid residues from genotype 1. We therefore hypothesized that lack of recognition of the epitope in

patients infected with HCV genotypes other than 1 might lead to a loss DCLK1 of protection by HLA-B27. In order to test this hypothesis, in this study we analyzed the CD8+ T-cell response and autologous viral sequences in a new cohort of HLA-B27+ patients acutely or chronically infected with HCV genotype 3a and determined the frequency of HLA-B27 in a large cohort of patients chronically infected with HCV genotype 1 or 3a. Our results suggest that HLA-B27 is indeed protective in patients with HCV genotype 1 infection but not in patients infected with HCV genotype 3a. This lack of protection is most likely caused by intergenotypic sequence differences leading to the loss of the immunodominant HLA-B27 epitope in infection with HCV genotypes other than 1. Our results further support the important role of a single immunodominant NS5B epitope in mediating the protective and genotype-specific effect of HLA-B27 in HCV infection. CTL, cytotoxic T lymphocyte; HCV, hepatitis C virus; HIV, human immunodeficiency virus; HLA-B27, human leukocyte antigen B27; INF-γ interferon-γ NS5B, nonstructural protein 5B; PBMC, peripheral blood mononuclear cell.