Interferon-alpha therapy exerts selective pressure on hepatitis C virus quasispecies equilibrium

Two patients with chronic hepatitis C virus (HCV) genotype 2b infection wer e studied. They responded biochemically to interferon (IFN) but had early v irological and later biochemical relapse. The HCV quasispecies equilibrium in these patients was studied by a combination of cloning, sequencing and c onstruction of phylogenetic trees. Another patient with chronic HCV genotyp e 2b infection was followed every 6 months for 30 months (induding one epis ode of biochemical exacerbation) to serve as the control. Quasispecies equi librium drifted during IFN therapy but moved back in the direction of the o riginal equilibrium during biochemical relapse. In the control patient, the re was no significant drifting throughout the follow-up period. These data suggest that IFN therapy exerts selective pressure on HCV quasispecies equi librium.