Different antiviral effects induced by interferon or entecavir in HDV infected human-chimeric uPA/SCID mice determined by new intrahepatic qRT-PCR assay

Chronic co-infection with hepatitis B and Delta viruses (HBV, HDV) is associated with more severe liver damage compared to HBV mono-infection. Knowledge of the virological changes induced by the different antiviral treatments available is scant. Aim of our study was to investigate the antiviral effects induced by pegylated interferon alpha (peg-IFN-α) and HBV polymerase inhibitors on HDV productivity in human-chimeric uPA/SCID mice and by using a novel strand-specific qRT-PCR strategy enabling detection of all HDV RNA replicative intermediates in patient liver biopsies. Methods: Chronic HBV/HDV infected humanized mice were treated with peg-IFN-α (n = 3), entecavir (ETV) (n = 4) or remained untreated (n = 3). Viremia was monitored by qRT-PCR. Genomic and antigenomic HDV RNA species were determined in liver samples obtained from humanized mice and patients using a new qRT-PCR assay based on a magnetic bead separation strategy. HDAg expression levels were analysed by immunohistochemistry and immunoblotting. Results: Ratios of genomic to antigenomic HDV RNA detected in humanized mice were comparable to those detected in HDV replicative patients (3.9 – 73.0). 4 weeks of peg-IFN-α administration led to 2.0-log reduction of both HBV and HDV viremia and to 1.2-log reduction of circulating HBsAg. In contrast, 4-week ETV treatment did not alter HDV titres and HBsAg levels substantially (< 0.5 log reduction), while it provoked a clear HBV viremia decrease of 3.3-log. Consistent with the serological data, IFN induced a strong decline of both genomic and antigenomic intrahepatic HDV RNA loads, whereas HDV RNA levels remained unchanged in ETV treated mice. Peg-IFN-α strongly reduced the amount of HDAg-positive human hepatocytes. Immunoblotting indicated that both small and large HDAg decreased upon IFN administration, while intrahepatic HDAg contents remained unchanged in ETV treated mice compared to untreated control mice. Conclusions: ETV mediated suppression of HBV replication did not significantly affect HBsAg levels, HDV productivity and release, as documented by the maintenance of HDV viremia and intrahepatic loads. In contrast, 4-week peg-IFN-α treatment efficiently suppressed HDV productivity by lowering both intrahepatic levels of genomic and antigenomic HDV RNA and amounts of HDAg-positive cells. The antiviral effects induced by IFN on HDV infected hepatocytes in a system lacking adaptive immune responses suggest that by targeting HDV replication intrahepatic clearance could be achievable.