LAUSR

BACKGROUND & AIMS A prophylactic vaccine targeting multiple HCV genotypes (gt) is urgently required to meet World Health Organization (WHO) elimination targets. Neutralizing antibodies (nAb), CD4+ and CD8+ T-cells are associated with spontaneous clearance of HCV, and each may contribute to protective immunity. However, current vaccine candidates generate either nAbs or T-cells targeting genetically variable epitopes and have failed to show efficacy in human trials. We have previously shown that a simian adenovirus vector (ChAdOx1) encoding conserved sequences across gt1-6 (ChAd-Gt1-6), and separately gt-1a E2 protein with variable regions deleted (E2Δ123HMW ), generates pan-genotypic T-cells and nAbs respectively. We now aim to develop a vaccine to generate both viral-specific B and T-cell responses concurrently. APPROACH & RESULTS We show that vaccinating with ChAd-Gt1-6 and E2Δ123HMW sequentially in mice generates T-cell and antibody (Ab) responses comparable to either vaccine given alone. We encoded E2Δ123 in ChAdOx1 (ChAd-E2Δ123) and show that this given with E2Δ123HMW protein boost induces greater CD81-E2 inhibitory and HCV-pseudoparticle nAb titers compared to E2Δ123HMW prime-boost. We developed 'bivalent' viral vector vaccines (ChAdOx1 and modified vaccinia Ankara (MVA)) encoding both Gt1-6 and E2Δ123 immunogens ('Gt1-6-E2Δ123') generating polyfunctional CD4+ and CD8+ T-cells and nAb titers in prime/boost strategies. This approach generated nAb responses comparable to monovalent E2Δ123 ChAd/MVA vaccines and superior to three doses of recombinant E2Δ123HMW protein, whilst also generating high magnitude T-cell responses. CONCLUSION These data are an important step forward for the development of a pan-genotype HCV vaccine to elicit T-cells and nAbs for future assessment in humans.