Prophylactic and therapeutic HBV vaccination by an HBs-expressing cytomegalovirus vector lacking an interferon antagonist

Cytomegalovirus (CMV)-based vaccines show promising effects against chronic infections in non-human primates. Therefore, we examined the potential of HBV vaccines based on mouse CMV (MCMV) vectors expressing the small HBsAg. Immunological consequences of vaccine virus attenuation were addressed by either replacing the dispensable gene m157 (‘MCMV-HBs’) or the gene M27 (‘ΔM27-HBs’), the latter encodes a potent interferon antagonist targeting the transcription factor STAT2. M27 was chosen, since human cytomegalovirus (HCMV) encodes an analogous gene product, which also induced proteasomal STAT2 degradation by exploiting Cullin RING ubiquitin ligases. Vaccinated mice were challenged with HBV through hydrodynamic injection. MCMV-HBs and ΔM27-HBs vaccination achieved accelerated HBV clearance in serum and liver as well as robust HBV-specific CD8+ T cell responses. When we explored the therapeutic potential of MCMV-based vaccines, especially the combination of ΔM27-HBs prime and DNA boost vaccination resulted in increased intrahepatic HBs-specific CD8+ T cell responses and HBV clearance in persistently infected mice. Our results demonstrated that vaccines based on a replication competent MCMV attenuated through the deletion of an interferon antagonist targeting STAT2 elicit robust anti-HBV immune responses and mediate HBV clearance in mice in prophylactic and therapeutic immunization regimes.