Inactivated genotype 1a, 2a and 3a HCV vaccine candidates induced broadly neutralising antibodies in mice

Objective: A prophylactic vaccine is needed to control the HCV epidemic, with genotypes 1-3 causing >80% of worldwide infections. Vaccine development is hampered by HCV heterogeneity, viral escape including protection of conserved neutralising epitopes and suboptimal efficacy of HCV cell culture systems. We developed cell culture-based inactivated genotype 1-3 HCV vaccine candidates to present natively folded envelope proteins to elicit neutralising antibodies. Design: High-yield genotype 1a, 2a and 3a HCV were developed by serial passage of TNcc, J6cc and DBN3acc in Huh7.5 cells and engineering of acquired mutations detected by next-generation sequencing. Neutralising epitope exposure was determined in cell-based neutralisation assays using human monoclonal antibodies AR3A and AR4A, and polyclonal antibody C211. BALB/c mice were immunised with processed and inactivated genotype 1a, 2a or 3a viruses using AddaVax, a homologue of the licenced adjuvant MF-59. Purified mouse and patient serum IgG were assayed for neutralisation capacity; mouse IgG and immune-sera were assayed for E1/E2 binding. Results: Compared with the original viruses, high-yield viruses had up to ∼1000 fold increased infectivity titres (peak titres: 6-7 log10 focus-forming units (FFU)/mL) and up to ∼2470 fold increased exposure of conserved neutralising epitopes. Vaccine-induced IgG broadly neutralised genotype 1-6 HCV (EC50: 30-193 μg/mL; mean 71 μg/mL), compared favourably with IgG from chronically infected patients, and bound genotype 1-3 E1/E2; immune-sera endpoint titres reached up to 32 000. Conclusion: High-yield genotype 1-3 HCV could be developed as basis for inactivated vaccine candidates inducing broadly neutralising antibodies in mice supporting further preclinical development.