In vivo infectivity of liver extracts after resolution of hepadnaviral infection following therapy associating DNA vaccine and cytokine genes.

DNA-based vaccination appears of promise for chronic hepatitis B immunotherapy, although there is an urgent need to increase its efficacy. In this preclinical study, we evaluated the therapeutic benefit of cytokine ( IL-2, IFN-γ) genes co-delivery with DNA vaccine targeting hepadnaviral proteins in the chronic duck hepatitis B virus ( DHBV) infection model. Then, we investigated the persistence of replication-competent virus in the livers of apparently resolved animals. DHBV carriers received four injections of plasmids encoding DHBV envelope and core alone or co-delivered with duck IL-2 ( Du IL-2) or duck IFN-γ ( Du IFN-γ) plasmids. After long-term (8 months) follow-up, viral covalently closed circular (ccc) DNA was analysed in duck necropsy liver samples. Liver homogenates were also tested for in vivo infectivity in neonatal ducklings. Co-delivery of Du IFN-γ resulted in significantly lower mean viremia starting from week 21. Viral ccc DNA was undetectable by conventional methods in the livers of 25% and 57% of animals co-immunized with Du IL-2 and Du IFN-γ, respectively. Interestingly, inoculation of liver homogenates from 7 such apparently resolved animals, exhibiting ccc DNA undetectable in Southern blotting and DHBV expression undetectable or restricted to few hepatocytes, revealed that three liver homogenates transmitted high-titre viremia (3-5×1010 vge/mL) to naïve animals. In conclusion, our results indicate that IFN-γ gene co-delivery considerably enhances immunotherapeutic efficacy of DNA vaccine targeting hepadnaviral proteins. Importantly, we also showed that livers exhibiting only minute amounts of hepadnaviral ccc DNA could induce extremely high-titre infection, highlighting the caution that should be taken in occult hepatitis B patients to prevent HBV transmission in liver transplantation context. [ABSTRACT FROM AUTHOR]