The Hepatitis C Virus (HCV) E2 glycoprotein is a major target of the neutralizing antibody response with multiple type-specific and broadly neutralizing antibody epitopes identified. The 412-423 region can generate broadly neutralizing antibodies (bnNAbs) that block interaction with the cell surface receptor CD81, with activity towards multiple HCV genotypes. In this study we reveal the structure of the rodent MAb24 with an extensive contact area towards a peptide spanning the 412-423 region. The crystal structure of the MAb24-peptide 412-423 complex reveals the paratope bound to a peptide hairpin, highly similar to that observed with human MAb HCV1, but with a different angle of approach. In viral outgrowth experiments, we demonstrated 3 distinct genotype 2a viral populations that acquired resistance to MAb24 via N415D, N417S and N415D/H386R mutations. Importantly, the MAb24-resistant viruses exhibited significant increases in sensitivity to the majority of bnNAbs directed to epitopes within the 412-423 and in additional antigenic determinants located within E2 and the E1E2 complex. This study suggests that modification of N415 causes a global change in glycoprotein structure that increases its vulnerability to neutralization by other antibodies. This finding suggests that in the context of an antibody response to viral infection, acquisition of escape mutations to the 412-423 region renders the virus more susceptible to neutralization by other specificities of NAbs, effectively reducing the immunological fitness of the virus. A vaccine for HCV that generates polyspecific humoral immunity with specificity for the 412-423 region and at least one other region of E2 is desirable.IMPORTANCE Understanding how antibodies neutralize Hepatitis C Virus is essential for vaccine development. This study reveals for the first time that when HCV develops resistance to a major class of broadly neutralizing antibodies targeting the 412-423 region of E2, this results in a concomitant increase in sensitivity to neutralization by a majority of other broadly neutralizing antibody specificities. Vaccines for the prevention of HCV infection should therefore generate NAbs directed towards the 412-423 region of E2 and additional NAb epitopes within the viral glycoproteins.
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We gratefully acknowledge funding support from the Australian National Health and Medical Research Council through project grants 1020175,1080045 and 1106581 and fellowship to HED 1041897. FC was supported by future fellowship FT120100893 of the Australian Research Council. Data were collected on the MX1 beamline of the Australian Synchrotron. The authors gratefully acknowledge the contribution to this work of the Victorian Operational Infrastructure Support Program received by the Burnet Institute.