Identification of antigenic escape variants in an immunodominant epitope of hepatitis C virus

Numerous investigators have postulated that one mechanism by which hepatiti s C virus (HCV) may evade the immune system is through the formation of esc ape mutants. This hypothesis is based largely on the observed mutability of the viral genome resulting in evolution of diverse quasispecies over the c ourse of infection. That such diversification is a product of viral RNA pol ymerase infidelity, immune-driven selection or a combination of the two pro cesses has not been addressed. We have examined sequence variability in a s pecific segment of HCV RNA encoding a known immunodominant region of the vi ral helicase, amino acids 358-375 of the non-structural 3 protein. Using se quence-specific oligonucleotide probe hybridization and automated DNA seque ncing, we report a high frequency of mutations, essentially all of which re sult in amino acid replacements, To assess the biological impact of such mu tations, corresponding chemically synthesized peptides were compared to wil d-type peptide in T cell proliferation assays. We observed that a sizeable fraction of such peptides stimulated attenuated or negligible levels of pro liferation by peripheral T cells from a chronically infected patient. This observation is consistent with expectations for immune-mediated selection o f escape variants at the epitope level. We postulate that such a mechanism may be important in the immunopathogenesis of HCV infections.