Neutralization resistance of hepatitis C virus can be overcome by recombinant human monoclonal antibodies.

Immunotherapy and vaccine development for hepatitis C virus (HCV) will depend on broadly reactive neutralizing antibodies (NAbs). However, studies in infectious strain JFH1-based culture systems expressing patient-derived Core-NS2 proteins have suggested neutralization resistance for specific HCV strains, in particular, of genotype 2. To further examine this phenomenon, we developed a panel of HCV genotype 2 recombinants for testing of sensitivity to neutralization by chronic-phase patient sera and lead human monoclonal antibodies (HMAbs). The novel Core-NS2 recombinants, with patient-derived genotype 2a (strain T9), 2b (strains DH8 and DH10), and 2c (strain S83) consensus sequences, were viable in Huh7.5 hepatoma cells without requirement for adaptive mutations, reaching HCV infectivity titers of 3.9-4.5 log(10) focus-forming units per milliliter. In in vitro neutralization assays, we demonstrated that the novel genotype 2 viruses as well as prototype strains J6/JFH1(2a) and J8/JFH1(2b), all with authentic envelope proteins, were resistant to neutralization by genotype 2a, 2b, 2c, 2j, 2i, and 2q patient sera. However, these patient sera had high titers of HCV-specific NAbs, because they efficiently reduced the infectivity of J6(2a) and J8(2b) with deleted hypervariable region 1. The genotype 2a, 2b, and 2c viruses, found resistant to polyclonal patient sera neutralization, were efficiently neutralized by two lead HMAbs (AR4A and HC84.26). Conclusion: Using novel 2a, 2b, and 2c cell-culture systems, expressing authentic envelope proteins, we demonstrated resistance of HCV to patient-derived polyclonal high-titer NAbs. However, the same genotype 2 culture viruses were all sensitive to HMAbs recognizing conformational epitopes, indicating that neutralization resistance of HCV can be overcome by applying recombinant antibodies. These findings have important implications for HCV immunotherapy and vaccine development. (Hepatology 2013;58:1587-1597)