Chronic delta hepatitis, caused by hepatitis delta virus (HDV), is the most severe form of viral hepatitis, affecting at least 20 million hepatitis B virus (HBV)-infected patients worldwide. HDV/HBV co- or superinfections are major drivers for hepatocarcinogenesis. Antiviral treatments exist only for HBV and can only suppress but not cure infection. Development of more effective therapies has been impeded by the scarcity of suitable small-animal models. We created a transgenic (tg) mouse model for HDV expressing the functional receptor for HBV and HDV, the human sodium taurocholate cotransporting peptide NTCP. Both HBV and HDV entered hepatocytes in these mice in a glycoprotein-dependent manner, but one or more postentry blocks prevented HBV replication. In contrast, HDV persistently infected hNTCP tg mice coexpressing the HBV envelope, consistent with HDV dependency on the HBV surface antigen (HBsAg) for packaging and spread. In immunocompromised mice lacking functional B, T, and natural killer cells, viremia lasted at least 80 days but resolved within 14 days in immunocompetent animals, demonstrating that lymphocytes are critical for controlling HDV infection. Although acute HDV infection did not cause overt liver damage in this model, cell-intrinsic and cellular innate immune responses were induced. We further demonstrated that single and dual treatment with myrcludex B and lonafarnib efficiently suppressed viremia but failed to cure HDV infection at the doses tested. This small-animal model with inheritable susceptibility to HDV opens opportunities for studying viral pathogenesis and immune responses and for testing novel HDV therapeutics.

Background & Aims Patients chronically infected with the hepatitis B virus (HBV) that are on long-term treatment with nucleoside or nucleotide analogues are at risk of selecting HBV strains with complex mutational patterns. We herein report two cases of HBV-infected patients with insufficient viral suppression despite dual antiviral therapy with entecavir (ETV) and tenofovir (TDF), of which one patient died from aggressive hepatocellular carcinoma (HCC). Methods Serum samples of the patients from different time-points were analyzed by ultra-deep pyrosequencing analysis. Identified HBV mutations were functionally analyzed after transient transfection of replication-competent HBV vectors into hepatoma cells in vitro. We assessed replication efficacy, resistance to antivirals and potential impact on HBV secretion (viral particles, exosomes). Results Sequencing analyses revealed the selection of the rtS78T HBV polymerase mutation in both cases that simultaneously creates a premature stop codon at sC69 and thereby deletes almost the entire small HBV surface protein. One of the patients had an additional 261-bp deletion in the preS1/S2 region. Functional analyses of the mutations in vitro revealed that the rtS78T/sC69* mutation, but not the preS1/S2 deletion, significantly enhanced viral replication and conferred reduced susceptibility to ETV and TDF. The sC69* mutation caused truncation of HBs protein, leading to impaired detection by commercial HBsAg assay, without causing intracellular HBsAg retention or affecting HBV secretion. Conclusions The rtS78T/c69* HBV mutation associated with enhanced replication and insufficient response to antiviral treatment may favor long-term persistence of these isolates. Along with increased production of HBV transcripts and the sustained secretion of viral particles in the absence of antigenic domains of S protein, this HBV mutation may predispose to carcinogenic effects.

Globally, over half a billion people are persistently infected with hepatitis B (HBV) and/or hepatitis C viruses. Chronic HBV and HCV infection frequently lead to fibrosis, cirrhosis and hepatocellular carcinoma (HCC). Co-infections with hepatitis delta virus (HDV), a subviral satellite requiring HBV for its propagation, accelerates the progression of liver disease toward HCC. The mechanisms by which these viruses cause malignant transformation, culminating in HCC, remain incompletely understood, partially due to the lack of adequate experimental models for dissecting these complex disease processes in vivo.