5′ triphosphorylated small interfering RNAs control replication of hepatitis B virus and induce an interferon response in human liver cells and mice

Background & Aims: Approved therapies for chronic hepatitis B include systemic administration of interferon (IFN)-alfa and inhibitors of hepatitis B virus (HBV) reverse-transcription. Systemic application of IFN-alfa is limited by side effects. Reverse-transcriptase inhibitors effectively control HBV replication, but rarely eliminate the virus and can select drug-resistant variants. We aimed to develop an alternative therapeutic approach that combines gene silencing with induction of IFN in the liver. Methods: To stimulate an immune response while inhibiting HBV activity, we designed 3 small interfering (si)RNAs that target highly conserved sequences and multiple HBV transcripts of all genotypes. A 5′-triphosphate (3p) was added to the siRNAs, turning them into a ligand for the cytosolic helicase retinoic acidinducible protein I, which becomes activated and induces expression of type-I IFNs. Antiviral activity was investigated in cell lines that replicate HBV, in HBV-infected primary human hepatocytes, and in HBV transgenic mice. Results: 3p-double-stranded RNA (3p-RNA) activated retinoic acidinducible protein I, induced a strong type I IFN response (expression of IFN-β) in liver cells and showed transient but strong antiviral activity. Bifunctional, HBV-specific, 3p-siRNAs controlled replication of HBV more efficiently and for longer periods of time than 3p-RNAs without silencing capacity or siRNAs that targeted identical sequences but did not contain 3p. Conclusions: HBV-specific 3p-siRNAs are bifunctional antiviral molecules that induce production of type I IFNs in the liver and target HBV RNAs to inhibit viral replication.