Effect of retreatment with interferon alone or interferon plus ribavirin on hepatitis C virus quasispecies diversification in nonresponder patients with chronic hepatitis C

Alpha interferon (IFN-alpha) treatment is effective on a long-term basis in only 15 to 25% of patients with chronic hepatitis C, The results of recent trials indicate that response rates can be significantly increased when IF N-alpha is given in combination with ribavirin, However, a large number of patients do not respond even to combination therapy. Nonresponsiveness to I FN is characterized by evolution of the hepatitis C virus (HCV) quasispecie s. Little is known about the changes occurring within the HCV genomes when nonresponder patients are retreated with IFN or with IFN plus ribavirin. In the present study we have examined the genetic divergence of HCV quasispec ies during unsuccessful retreatment with IFN or IFN plus ribavirin, Fifteen nonresponder patients with HCV-1 (4 patients with HCV-1a and 11 patients w ith HCV-lb) infection were studied while being retreated for 2 months (phas e 1) with IFN-alpha (6 MU given three times a week), followed by IFN plus r ibavirin or IFN alone for an additional 6 months (phase 2). HCV quasispecie s diversification in the E2 hypervariable region-1 (HVR1) and in the putati ve NS5A IFN sensitivity determining region (ISDR) were analyzed for phase 1 and phase 2 by using the heteroduplex tracking assay and clonal frequency analysis techniques. A major finding of this study was the relatively rapid evolution of the HCV quasispecies observed in both treatment groups during the early phase 1 compared to the late phase 2 of treatment. The rate of q uasispecies diversification in HVR1 was significantly higher during phase 1 versus phase 2 both in patients who received IFN plus ribavirin (P = 0.017 ) and in patients who received IFN alone (P = 0.05). A trend toward higher rates of quasispecies evolution in the ISDR was also observed during phase 1 in both groups, although the results did not reach statistical significan ce. However, the NS5A quasispecies appeared tea be rather homogeneous and s table in most nonresponder patients, suggesting the presence of a single we ll-fit major variant, resistant to antiviral treatment, in agreement with p ublished data which have identified an IFN sensitivity determinant region w ithin the NS5A, During the entire 8 months of retreatment, there was no dif ference in the rate of fixation of mutation between patients who received c ombination therapy and patients who were treated with IFN alone, suggesting that ribavirin had no major effects on the evolution of the HCV quasispeci es after the initial 2 months of IFN therapy.