Long-term response to interferon alpha is unrelated to "interferon sensitivity determining region" variability in patients with chronic hepatitis C virus-1b infection

Background/Aims: Contradictory data have been reported about the predictive value of the variability in interferon sensitivity determining region (ISDR) of hepatitis C virus (HCV) genotype-lb on response to interferon-alpha (IFN-a) therapy. The aim of this study was to examine this issue in a series of patients with long-term response to IFN treatment. Methods: We retrospectively analyzed 24 patients with chronic HCV genotype-lb infection treated with IFN-a (total dose median 677, range 216-1350 MU) selected in 6 Italian Liver Units. These patients were defined as true long-term responders (LTR) since they showed persisting biochemical and virological responses to IFN treatment (mean follow-up 38 months). HCV genomes from pretreatment serum samples were amplified and directly sequenced. The ISDR amino-acid sequences obtained were aligned and compared with the published sequence of HCV-J. Results: Amino-acid substitutions were found in 23 of the 24 patients, and 22 of them showed an H to R amino-acid change at codon 2218. Fourteen patients showed only one mutation (at codon 2218), two had 2, five had 3, one had 4 and one had 5 mutations. When we compared the ISDR sequences from the 24 LTR with those of non-responders (NR), we found no significant correlation between the number of mutations and the response to therapy. Conclusions: Our results demonstrate that the persisting efficacy of IFN treatment in patients with chronic HCV is not related to the number of ISDR amino acid susbstitutions of the infecting viruses. Further studies are needed to verify whether other NSSA sequences outside the ISDR might be involved in the mechanisms of IFN resistance.