SAT-407 - A novel chimpanzee adenoviral vectored HBV vaccine, encoding multiple HBV antigens with a shark invariant chain adjuvant, for use in HBV immunotherapy

Abstract

Background: Chronic hepatitis B virus (HBV) infects 257 million people globally. Current therapies suppress HBV but rebound occurs on cessation of therapy; novel therapeutic strategies are urgently required. Aim: To develop a potent therapeutic HBV vaccine that will induce T-cells to all major HBV antigens and generate anti-HBs antibodies, using Chimpanzee adenoviral vectors and shark class-II invariant (sIi) chain as a genetic adjuvant. Method: We designed two HBV immunogens SIi-HBV-CPmutS and HBV-CPmutS; encoding precore (PreC), core, non-functional polymerase (Pmut), PreS1, PreS2 and surface antigens (Figure 1a). The large envelope protein of HBV (composed of PreS1, PreS2 and surface proteins) was generated separately using furin 2A (F2A) peptide cleavage protein. A 26 amino-acid sequence, derived from shark invariant chain (sIi), was inserted at the 5’ end of the SIi-HBV-CPmutS immunogen. The immunogens were encoded in chimpanzee-adenoviral vector (ChAdOx2) and tested in naive mice given i.m. HBV-specific T-cell responses were assessed using IFN-ϒ ELISpot and intracellular cytokine (ICCS) assays. Results: Vaccination generated very high magnitude HBV specific T-cell responses to all HBV antigens (Figure 1b). The mean magnitude of total HBV-specific T-cell responses in inbred BALB/c and outbred CD1 mice were 3858 and 3821 spot forming units [SFU]/106 splenocytes (shown on the left side of figure 1b) and 4514 and 2979 SFU/106 intrahepatic lymphocytes (shown on the right side of figure 1b) respectively. ICCS showed that HBV specific CD8+ T cells were poly-functional producing both IFN-ϒ and TNF-α. The inclusion of shark invariant chain (data shown in blue coloured bars in figure 1b) significantly enhances the T-cell magnitude for both splenocytes (3821 mean total SFU/106 with sIi vs. 386 mean total SFU/106 without sIi, p<0.0001) and intrahepatic lymphocytes (2979 mean total SFU/106 with sIi vs. 461 mean total SFU/106 without SIi, p=0.0002). Importantly, T cells to the non-HBV SIi peptides were not generated. Conclusion: We have generated a highly potent HBV vaccine that induces T-cells against all major HBV proteins, using chimpanzee adenoviral vector and class-II invariant chain technologies. These pre-clinical studies pave the way for new studies of HBV immunotherapy in humans with chronic HBV infection.