Despite recent characterization of hepatitis C virus-specific neutralizing antibodies, it is not clear to what extent immune pressure from neutralizing antibodies drives viral sequence evolution in vivo. This lack of understanding is particularly evident in acute infection, the phase when elimination or persistence of viral replication is determined and during which the importance of the humoral immune response has been largely discounted.

We analyzed envelope glycoprotein sequence evolution and neutralization of sequential autologous hepatitis C virus pseudoparticles in 8 individuals throughout acute infection.

Amino acid substitutions occurred throughout the envelope genes, primarily within the hypervariable region 1 of E2. When individualized pseudoparticles expressing sequential envelope sequences were used to measure neutralization by autologous sera, antibodies neutralizing earlier sequence variants were detected at earlier time points than antibodies neutralizing later variants, indicating clearance and evolution of viral variants in response to pressure from neutralizing antibodies. To demonstrate the effects of amino acid substitution on neutralization, site-directed mutagenesis of a pseudoparticle envelope sequence revealed amino acid substitutions in hypervariable region 1 that were responsible for a dramatic decrease in neutralization sensitivity over time. In addition, high-titer neutralizing antibodies peaked at the time of viral clearance in all spontaneous resolvers, whereas chronically evolving subjects displayed low-titer or absent neutralizing antibodies throughout early acute infection.

These findings indicate that, during acute hepatitis C virus infection in vivo, virus-specific neutralizing antibodies drive sequence evolution and, in some individuals, play a role in determining the outcome of infection.