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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.

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.

Acute hepadnavirus infections either resolve or progress to chronicity. Factors that influence chronicity as an outcome of hepatitis B virus (HBV) infection in humans can be studied experimentally in the woodchuck model. Accordingly, several woodchuck hepatitis virus (WHV) inocula were characterized. Representative inocula had high titers of infectious virus (approximately 10 7.7 -10 9.5 woodchuck 50% infectious doses per milliliter [WID 50% /mL] by subcutaneous inoculation), with 1 WID 50% ranging between 21 and 357 physical virion particles. WHV7P1 (standard high dose, 5 ؋ 10 6 WID 50% ) produced a 72% chronicity rate (i.e., percent chronic of total infected) in neonatal woodchucks (1-3 days old). Comparable doses of WHV8P1 resulted in a lower chronicity rate in neonates (34% chronic) indicating that it represented a strain different from WHV7P1. Neonatal woodchucks were more susceptible to chronic infection by high doses of WHV7P1 (range, 65%-75% chronic) compared with 8-week-old weanlings (33% chronic) and adult woodchucks (0% chronic; i.e., all resolved). High doses of cloned wild-type viruses also induced high rates of chronicity in neonates (70%-80% chronic). Chronicity rates in neonates were decreased for low doses of WHV7P1 (500 WID 50% , 9% chronic) and for high doses of a precore WHeAg-minus mutant WHV8 clone (17% chronic). Thus, both age and viral determinants can influence chronicity as an outcome of experimental WHV infection. Standardized inocula will enable the study of mechanisms that initiate and maintain chronic hepadnavirus infection and also provide a means for developing WHV carriers for therapeutic studies. (HEPATOLOGY 2000;31:190-200.)The eastern woodchuck is naturally infected by a virus closely related to hepatitis B virus (HBV). Experimental infection of woodchucks with woodchuck hepatitis virus (WHV) has been of value in modeling virtually all aspects of HBV infection, pathogenesis, and therapy. 1,2 Development of the model has evolved to use woodchucks bred and reared under controlled environmental conditions, virus-and hostspecific assays for viral infection and disease, and standardized WHV inocula. Because titered HBV inocula have proven invaluable for developing the chimpanzee as a predictive model of HBV infection, disease, and vaccine protection, 3 titered WHV inocula were considered essential for further defining host and viral determinants that promote chronicity and disease progression to hepatocellular carcinoma (HCC) in hepadnavirus infection. In this study, we measured the infectivity of several WHV inocula and, using controlled doses of virus, showed that both animal age and viral determinants can affect chronicity as an outcome of WHV infection. These standardized inocula represent a useful resource for developing serum and tissue banks from selflimited and chronic WHV infections for studies of WHV pathogenesis, and for producing chronic carrier woodchucks at predictable frequencies. MATERIALS AND METHODSAnimals. Woodchucks were bred, maintained, and handled under contr...

A unique series of simple "unnatural" nucleosides has been discovered to inhibit hepatitis B virus (HBV) replication. Through structure-activity analysis it was found that the 3-OH group of the ␤-L-2-deoxyribose of the ␤-L-2-deoxynucleoside confers specific antihepadnavirus activity. The unsubstituted nucleosides ␤-L-2-deoxycytidine, ␤-L-thymidine, and ␤-L-2-deoxyadenosine had the most potent, selective, and specific antiviral activity against HBV replication. Human DNA polymerases (␣, ␤, and ␥) and mitochondrial function were not affected. In the woodchuck model of chronic HBV infection, viral load was reduced by as much as 10 8 genome equivalents/ml of serum and there was no drug-related toxicity. In addition, the decline in woodchuck hepatitis virus surface antigen paralleled the decrease in viral load. These investigational drugs, used alone or in combination, are expected to offer new therapeutic options for patients with chronic HBV infection.Infection with hepatitis B virus (HBV) is a major world health problem, affecting 5% of the population. More than 2 billion people have been infected with the virus, and 350 million of them are chronic carriers at risk of death from cirrhosis and liver cancer (49).Several strategies have been evaluated for the treatment of chronic HBV infection with the goal of eliminating persistent viral replication and preventing progression to chronic active hepatitis and liver failure. Currently, the only approved treatment options are alpha interferon (IFN) and lamivudine (␤-L-2Ј,3Ј-dideoxy-3Ј-thiacytidine [3TC]). Unfortunately, the rate of response to IFN is low, and drug-associated side effects are significant (24,55). Individuals who are immunosuppressed (e.g., transplant recipients or those coinfected with the human immunodeficiency virus [HIV]) rarely respond to IFN therapy (13). Lamivudine is a well-known example of the class of ␤-Lnucleoside analogs that has recently drawn attention as antiviral and anticancer agents (52). As with IFN, however, a complete antiviral response, as assessed by HBe seroconversion, is seen in only a minority of patients after 1 year of treatment (27). In addition, cessation of lamivudine therapy or development of viral resistance may lead to a marked rebound in viral replication which can be life threatening (hepatitis flare) in HIV-HBV-coinfected patients (2, 30). Lamivudine resistance is now recognized in 16 to 32% of HBV-infected patients after 1 year of treatment and in as many as 58% after 2 to 3 years (14,27,30).Since the Food and Drug Administration approved lamivudine for the treatment of HIV infection in the United States in 1996 and for HBV in 1998, intensive studies on "unnatural" L-nucleosides as agents against HIV, HBV, and herpesviruses (including Epstein-Barr virus [EBV]) and as anticancer agents have been conducted (23). Now, through an extensive structure-activity analysis, we have found that the 3Ј-OH group of the ␤-L-2Ј-deoxyribose of the ␤-L-2Ј-deoxynucleoside series confers unique specificity for anti-HBV activity. In this ...