Evolution of viral quasispecies in interferon-treated patients with chronic hepatitis C virus infection

Background/Aims: To evaluate whether interferon treatment failure/relapse i s related to changes in hepatitis C virus quasispecies complexity (number o f variants) or diversity (genetic relatedness of variants), Methods: We analyzed hypervariable region heterogeneity in hepatitis C viru s-infected patients by heteroduplex mobility assay and by phylogenetic anal ysis of sequenced clones. Sera from 11 patients were tested, Response was d efined biochemically and virologically, Patients were treated with 3 or 6 M IU interferon for 6 months and followed up for 6 months. Four patients were non-responders, four were transient responders and three untreated patient s served as controls, Three time points were studied for the non-responders (pre-interferon, end of interferon, end of 6 months of followup), two for the transient responders (pre-interferon and post follow-up) and two for th e controls (1 year apart), A total of 260 clones were examined by heterodup lex mobility assay and 144 clones were sequenced, Results: A linear correlation between heteroduplex mobility and nucleotide substitutions was observed, validating this method for assessment of quasis pecies diversity, Although complexity at each time point was similar in all groups, diversity increased significantly with interferon treatment, The p ercentage of new variants in follow up was significantly higher in non-resp onders than in controls, These new variants exhibited a greater change in h eteroduplex mobility, a higher percentage of changes in amino acids in nonr esponders compared to controls and were found to cluster separately from pr etreatment variants when analyzed phylogenetically, These changes were less marked in transient responders. Conclusions: These mutations may allow hepatitis C virus to escape antivira l effects of interferon therapy.