Selection of HCV NS5A quasispecies during IFN therapy in patients with chronic HCV.

Interferon treatment of chronic hepatitis C virus infection is successful in a minority of patients. The sequence of the interferon sensitivity determining region (ISDR) of the NS5A protein may determine the outcome of therapy in patients infected with HCV genotype 1. To determine whether IFN treatment caused selection of ISDR quasispecies and whether sequences bearing the putative IFN-resistance motif (HCV-J sequence) were selected, we examined amino acid changes in the ISDR in patients with HCV of different genotypes with and without therapy. We found that the ISDR sequence was highly variable and variability was greatest in patients with HCV of genotype 1. IFN treatment was found to exert a selection pressure on ISDR quasispecies, but the putative interferon-resistant variant was not enriched in patients of any genotype. Hence factors other than the sequence of the ISDR region played a role in the IFN resistance of these patients.