Background & Aims New therapies for chronic hepatitis B (CHB) are urgently needed since current treatments rarely lead to cure. We evaluated whether the oral small molecule toll-like receptor (TLR7) agonist GS-9620 could induce durable anti-viral efficacy in woodchucks chronically infected with woodchuck hepatitis virus (WHV), a hepadnavirus closely related to human hepatitis B virus (HBV). Methods After evaluating the pharmacokinetics, pharmacodynamics and tolerability of oral GS-9620 in uninfected woodchucks, adult woodchucks chronically infected with WHV (n=7 per group) were dosed with GS-9620 or placebo for 4 or 8 weeks with different treatment schedules. Results GS-9620 treatment induced rapid, marked and sustained reduction in serum viral DNA (mean maximal 6.2 log10 reduction), and hepatic WHV DNA replicative intermediates, WHV cccDNA and WHV RNA, as well as loss of detectable serum WHV surface antigen (WHsAg). GS-9620 treatment also induced a sustained antibody response against WHsAg in a subset of animals. Strikingly, treatment reduced the incidence of hepatocellular carcinoma (HCC) from 71% in the placebo group to 8% in GS-9620-treated woodchucks with sustained viral load reduction. GS-9620 treatment was associated with reversible increases in serum liver enzymes and thrombocytopenia, and induced intrahepatic CD8+ T cell, NK cell, B cell and interferon (IFN) response transcriptional signatures. Conclusions The data demonstrate that short duration, finite treatment with the oral TLR7 agonist GS-9620 can induce a sustained antiviral response in the woodchuck model of CHB, and support investigation of this compound as a therapeutic approach to attain a functional cure in CHB patients.

This review describes the woodchuck and the woodchuck hepatitis virus (WHV) as an animal model for pathogenesis and therapy of chronic hepatitis B virus (HBV) infection and disease in humans. The establishment of woodchuck breeding colonies, and use of laboratory-reared woodchucks infected with defined WHV inocula, have enhanced our understanding of the virology and immunology of HBV infection and disease pathogenesis, including major sequelae like chronic hepatitis and hepatocellular carcinoma. The role of persistent WHV infection and of viral load on the natural history of infection and disease progression has been firmly established along the way. More recently, the model has shed new light on the role of host immune responses in these natural processes, and on how the immune system of the chronic carrier can be manipulated therapeutically to reduce or delay serious disease sequelae through induction of the recovery phenotype. The woodchuck is an outbred species and is not well defined immunologically due to a limitation of available host markers. However, the recent development of several key host response assays for woodchucks provides experimental opportunities for further mechanistic studies of outcome predictors in neonatal- and adult-acquired infections. Understanding the virological and immunological mechanisms responsible for resolution of self-limited infection, and for the onset and maintenance of chronic infection, will greatly facilitate the development of successful strategies for the therapeutic eradication of established chronic HBV infection. Likewise, the results of drug efficacy and toxicity studies in the chronic carrier woodchucks are predictive for responses of patients chronically infected with HBV. Therefore, chronic WHV carrier woodchucks provide a well-characterized mammalian model for preclinical evaluation of the safety and efficacy of drug candidates, experimental therapeutic vaccines, and immunomodulators for the treatment and prevention of HBV disease sequelae.

The Eastern woodchuck ( Marmota monax ) harbors a DNA virus (Woodchuck hepatitis virus [WHV]) that is similar in structure and replicative life cycle to the human hepatitis B virus (HBV). Like HBV, WHV infects the liver and can cause acute and chronic hepatitis. Furthermore, chronic WHV infection in woodchucks usually leads to development of hepatocellular carcinoma (HCC) within the first 2-4 years of life. The woodchuck model has been important in the preclinical evaluation of safety and efficacy of the antiviral drugs now in use for treatment of HBV infection and continues to serve as an important, predictive model for innovative forms of therapy of hepatitis B using antiviral nucleosides and immune response modifiers alone or in combination. Almost all woodchucks that become chronic WHV carriers after experimental neonatal inoculation develop HCC with a median HCC-free survival of 24 months and a median life expectancy of 30-32 months. The woodchuck model of viral-induced HCC has been used effectively for the development of new imaging agents for enhancement of detection of hepatic neoplasms by ultrasound and magnetic resonance imaging. The chemoprevention of HCC using long-term antiviral nucleoside therapy has been shown in the woodchuck, and "proof of principal" has been established for some of the innovative, molecular methods for treatment of HCC. The model is available for fundamental investigations of the viral and molecular mechanisms responsible for hepatocarcinogenesis and should have substantial value for future development of innovative methods for chemoprevention and gene therapy of human HCC.

The Eastern woodchuck (Marmota monax) is naturally infected with woodchuck hepatitis virus (WHV), a hepadnavirus closely related to the human hepatitis B virus (HBV). The woodchuck is used as an animal model for studying chronic hepatitis B (CHB) and HBV-associated hepatocellular carcinoma (HCC) in humans, but the lack of sequence information has hitherto precluded functional genomics analysis. To address this major limitation of the model, we report here the sequencing, assembly and annotation of the woodchuck transcriptome, together with the generation of custom woodchuck microarrays. Using this new platform, we characterized the transcriptional response to persistent WHV infection and WHV-induced HCC. This revealed that chronic WHV infection, like HBV, is associated with (i) a limited intrahepatic type I interferon response, (ii) intrahepatic induction of markers associated with T cell exhaustion, (iii) elevated levels of suppressor of cytokine signaling 3 (SOCS3) in the liver, and (iv) intrahepatic accumulation of neutrophils. Underscoring the translational value of the woodchuck model, this study also determined that WHV-induced HCC shares molecular characteristics with a subtype of human HCC with poor prognosis. Conclusion Our data establish the translational value of the woodchuck model and provide new insights into immune pathways which may play a role either in the persistence of HBV infection or the sequelae of CHB.