Strain-specific T-cell suppression and protective immunity in patients with chronic hepatitis C virus infection

Hepatitis C virus (HCV) frequently persists with an apparently ineffective antiviral T-cell response. We hypothesized that some patients may be exposed to multiple HCV subtypes and that strain-specific T cells could contribute to the viral dynamics in this setting. To test this hypothesis, CD4 T-cell responses to three genotype 1a-derived HCV antigens and HCV antibody serotype were examined in chronically HCV infected (genotypes 1a, 1b, 2, 3, and 4) and spontaneously HCV recovered subjects. Consistent with multiple HCV exposure, 63% of patients infected with genotypes 2 to 4 (genotypes 2-4) and 36% of those infected with genotype 1b displayed CD4 T-cell responses to 1a-derived HCV antigens, while 29% of genotype 2-4-infected patients showed serotype responses to genotype 1. Detection of 1a-specific T cells in patients without active 1a infection suggested prior self-limited 1a infection with T-cell-mediated protection from 1a but not from non-1a viruses. Remarkably, CD4 T-cell responses to 1a-derived HCV antigens were weakest in patients with homologous 1a infection and greater in non-1a-infected patients: proportions of patients responding were 19% (1a), 36% (1b), and 63% (2-4) (P = 0.0006). Increased 1a-specific CD4 T-cell responsiveness in non-1a-infected patients was not due to increased immunogenicity or cross-reactivity of non-1a viruses but directly related to sequence divergence. We conclude that the T-cell response to the circulating virus is either suppressed or not induced in a strain-specific manner in chronically HCV infected patients and that, despite their ability to clear one HCV strain, patients may be reinfected with a heterologous strain that can then persist. These findings provide new insights into host-virus interactions in HCV infection that have implications for vaccine development.