Effects of age and viral determinants on chronicity as an outcome of experimental woodchuck hepatitis virus infection

Increased virulence due to multiple infection in Daphnia leads to limited growth in 1 of 2 co-infecting microsporidian parasites

Recent outbreaks of various infectious diseases have highlighted the ever-present need to understand the drivers of the outbreak and spread of disease. Although much of the research investigating diseases focuses on single infections, natural systems are dominated by multiple infections. These infections may occur simultaneously, but are often acquired sequentially, which may alter the outcome of infection. Using waterfleas (Daphnia magna) as a model organism, we examined the outcome of sequential and simultaneous multiple infections with 2 microsporidian parasites (Ordospora colligata and Hamiltosporidium tvaerminnensis) in a fully factorial design with 9 treatments and 30 replicates. We found no differences between simultaneous and sequential infections. However, H. tvaerminnensis fitness was impeded by multiple infection due to increased host mortality, which gave H. tvaerminnensis less time to grow. Host fecundity was also reduced across all treatments, but animals infected with O. colligata at a younger age produced the fewest offspring. As H. tvaerminnensis is both horizontally and vertically transmitted, this reduction in offspring may have further reduced H. tvaerminnensis fitness in co-infected treatments. Our findings suggest that in natural populations where both species co-occur, H. tvaerminnensis may evolve to higher levels of virulence following frequent co-infection by O. colligata.

Recent Drug Development in the Woodchuck Model of Chronic Hepatitis B

Infection with hepatitis B virus (HBV) is responsible for the increasing global hepatitis burden, with an estimated 296 million people being carriers and living with the risk of developing chronic liver disease and cancer. While the current treatment options for chronic hepatitis B (CHB), including oral nucleos(t)ide analogs and systemic interferon-alpha, are deemed suboptimal, the path to finding an ultimate cure for this viral disease is rather challenging. The lack of suitable laboratory animal models that support HBV infection and associated liver disease progression is one of the major hurdles in antiviral drug development. For more than four decades, experimental infection of the Eastern woodchuck with woodchuck hepatitis virus has been applied for studying the immunopathogenesis of HBV and developing new antiviral therapeutics against CHB. There are several advantages to this animal model that are beneficial for performing both basic and translational HBV research. Previous review articles have focused on the value of this animal model in regard to HBV replication, pathogenesis, and immune response. In this article, we review studies of drug development and preclinical evaluation of direct-acting antivirals, immunomodulators, therapeutic vaccines, and inhibitors of viral entry, gene expression, and antigen release in the woodchuck model of CHB since 2014 until today and discuss their significance for clinical trials in patients.

Constrained evolution of overlapping genes in viral host adaptation: Acquisition of glycosylation motifs in hepadnaviral precore/core genes

Hepadnaviruses use extensively overlapping genes to expand their coding capacity, especially the precore/core genes encode the precore and core proteins with mostly identical sequences but distinct functions. The precore protein of the woodchuck hepatitis virus (WHV) is N-glycosylated, in contrast to the precore of the human hepatitis B virus (HBV) that lacks N-glycosylation. To explore the roles of the N-linked glycosylation sites in precore and core functions, we substituted T77 and T92 in the WHV precore/core N-glycosylation motifs (⁷⁵NIT⁷⁷ and ⁹⁰NDT⁹²) with the corresponding HBV residues (E77 and N92) to eliminate the sequons. Conversely, these N-glycosylation sequons were introduced into the HBV precore/core gene by E77T and N92T substitutions. We found that N-glycosylation increased the levels of secreted precore gene products from both HBV and WHV. However, the HBV core (HBc) protein carrying the E77T substitution was defective in supporting virion secretion, and during infection, the HBc E77T and N92T substitutions impaired the formation of the covalently closed circular DNA (cccDNA), the critical viral DNA molecule responsible for establishing and maintaining infection. In cross-species complementation assays, both HBc and WHV core (WHc) proteins supported all steps of intracellular replication of the heterologous virus while WHc, with or without the N-glycosylation sequons, failed to interact with HBV envelope proteins for virion secretion. Interestingly, WHc supported more efficiently intracellular cccDNA amplification than HBc in the context of either HBV or WHV. These findings reveal novel determinants of precore secretion and core functions and illustrate strong constraints during viral host adaptation resulting from their compact genome and extensive use of overlapping genes.

Hepadnaviruses infect a wide range of hosts. The human hepatitis B virus (HBV) and woodchuck hepatitis virus (WHV) are two closely related hepadnaviruses. In contrast to the WHV precore protein, which is N-glycosylated, the HBV precore protein lacks N-glycosylation. As precore and core proteins expressed from the overlapping precore/core genes share most of their sequences but have distinct functions, we investigated the roles of the N-linked glycosylation sequons in HBV and WHV precore/core genes. Our results revealed an important role of the N-linked glycosylation sequons in enhancing precore secretion levels and regulating core protein functions in virion secretion and infection. Furthermore, cross-species complementation assays using HBV and WHV core proteins and HBV or WHV genomes defective in core protein expression indicated that both HBV and WHV core proteins could support intracellular viral replication but not virion secretion of the heterologous virus. These results provide novel insights into the evolution of overlapping genes during host adaptation of hepadnaviruses.

Agonistic Activation of Cytosolic DNA Sensing Receptors in Woodchuck Hepatocyte Cultures and Liver for Inducing Antiviral Effects

Immune modulation for the treatment of chronic hepatitis B (CHB) has gained more traction in recent years, with an increasing number of compounds designed for targeting different host pattern recognition receptors (PRRs). These agonistic molecules activate the receptor signaling pathway and trigger an innate immune response that will eventually shape the adaptive immunity for control of chronic infection with hepatitis B virus (HBV). While definitive recognition of HBV nucleic acids by PRRs during viral infection still needs to be elucidated, several viral RNA sensing receptors, including toll-like receptors 7/8/9 and retinoic acid inducible gene-I-like receptors, are explored preclinically and clinically as possible anti-HBV targets. The antiviral potential of viral DNA sensing receptors is less investigated. In the present study, treatment of primary woodchuck hepatocytes generated from animals with CHB with HSV-60 or poly(dA:dT) agonists resulted in increased expression of interferon-gamma inducible protein 16 (IFI16) or Z-DNA-binding protein 1 (ZBP1/DAI) and absent in melanoma 2 (AIM2) receptors and their respective adaptor molecules and effector cytokines. Cytosolic DNA sensing receptor pathway activation correlated with a decline in woodchuck hepatitis virus (WHV) replication and secretion in these cells. Combination treatment with HSV-60 and poly(dA:dT) achieved a superior antiviral effect over monotreatment with either agonist that was associated with an increased expression of effector cytokines. The antiviral effect, however, could not be enhanced further by providing additional type-I interferons (IFNs) exogenously, indicating a saturated level of effector cytokines produced by these receptors following agonism. In WHV-uninfected woodchucks, a single poly(dA:dT) dose administered via liver-targeted delivery was well-tolerated and induced the intrahepatic expression of ZBP1/DAI and AIM2 receptors and their effector cytokines, IFN-β and interleukins 1β and 18. Receptor agonism also resulted in increased IFN-γ secretion of peripheral blood cells. Altogether, the effect on WHV replication and secretion following in vitro activation of IFI16, ZBP1/DAI, and AIM2 receptor pathways suggested an antiviral benefit of targeting more than one cytosolic DNA receptor. In addition, the in vivo activation of ZBP1/DAI and AIM2 receptor pathways in liver indicated the feasibility of the agonist delivery approach for future evaluation of therapeutic efficacy against HBV in woodchucks with CHB.

Combination Treatment with the Vimentin-Targeting Antibody hzVSF and Tenofovir Suppresses Woodchuck Hepatitis Virus Infection in Woodchucks

Current treatment options for patients infected with hepatitis B virus (HBV) are suboptimal, because the approved drugs rarely induce cure due to the persistence of the viral DNA genome in the nucleus of infected hepatocytes, and are associated with either severe side effects (pegylated interferon-alpha) or require life-long administration (nucleos(t)ide analogs). We report here the evaluation of the safety and therapeutic efficacy of a novel, humanized antibody (hzVSF) in the woodchuck model of HBV infection. hzVSF has been shown to act as a viral entry inhibitor, most likely by suppressing vimentin-mediated endocytosis of virions. Targeting the increased vimentin expression on liver cells by hzVSF after infection with HBV or woodchuck hepatitis virus (WHV) was demonstrated initially. Thereafter, hzVSF safety was assessed in eight woodchucks naïve for WHV infection. Antiviral efficacy of hzVSF was evaluated subsequently in 24 chronic WHV carrier woodchucks by monotreatment with three ascending doses and in combination with tenofovir alafenamide fumarate (TAF). Consistent with the proposed blocking of WHV reinfection, intravenous hzVSF administration for 12 weeks resulted in a modest but transient reduction of viral replication and associated liver inflammation. In combination with oral TAF dosing, the antiviral effect of hzVSF was enhanced and sustained in half of the woodchucks with an antibody response to viral proteins. Thus, hzVSF safely but modestly alters chronic WHV infection in woodchucks; however, as a combination partner to TAF, its antiviral efficacy is markedly increased. The results of this preclinical study support future evaluation of this novel anti-HBV drug in patients.

Involvement of Innate Immune Receptors in the Resolution of Acute Hepatitis B in Woodchucks

The antiviral property of small agonist compounds activating pattern recognition receptors (PRRs), including toll-like and RIG-I receptors, have been preclinically evaluated and are currently tested in clinical trials against chronic hepatitis B (CHB). The involvement of other PRRs in modulating hepatitis B virus infection is less known. Thus, woodchucks with resolving acute hepatitis B (AHB) after infection with woodchuck hepatitis virus (WHV) were characterized as animals with normal or delayed resolution based on their kinetics of viremia and antigenemia, and the presence and expression of various PRRs were determined in both outcomes. While PRR expression was unchanged immediately after infection, most receptors were strongly upregulated during resolution in liver but not in blood. Besides well-known PRRs, including TLR7/8/9 and RIG-I, other less-characterized receptors, such as IFI16, ZBP1/DAI, AIM2, and NLRP3, displayed comparable or even higher expression. Compared to normal resolution, a 3-4-week lag in peak receptor expression and WHV-specific B- and T-cell responses were noted during delayed resolution. This suggested that PRR upregulation in woodchuck liver occurs when the mounting WHV replication reaches a certain level, and that multiple receptors are involved in the subsequent induction of antiviral immune responses. Liver enzyme elevations occurred early during normal resolution, indicating a faster induction of cytolytic mechanisms than in delayed resolution, and correlated with an increased expression of NK-cell and CD8 markers and cytolytic effector molecules. The peak liver enzyme level, however, was lower during delayed resolution, but hepatic inflammation was more pronounced and associated with a higher expression of cytolytic markers. Further comparison of PRR expression revealed that most receptors were significantly reduced in woodchucks with established and progressing CHB, and several RNA sensors more so than DNA sensors. This correlated with a lower expression of receptor adaptor and effector molecules, suggesting that persistent, high-level WHV replication interferes with PRR activation and is associated with a diminished antiviral immunity based on the reduced expression of immune cell markers, and absent WHV-specific B- and T-cell responses. Overall, the differential expression of PRRs during resolution and persistence of WHV infection emphasizes their importance in the ultimate viral control during AHB that is impaired during CHB.

Application of the woodchuck animal model for the treatment of hepatitis B virus-induced liver cancer

This review describes woodchucks chronically infected with the woodchuck hepatitis virus (WHV) as an animal model for hepatocarcinogenesis and treatment of primary liver cancer or hepatocellular carcinoma (HCC) induced by the hepatitis B virus (HBV). Since laboratory animal models susceptible to HBV infection are limited, woodchucks experimentally infected with WHV, a hepatitis virus closely related to HBV, are increasingly used to enhance our understanding of virus-host interactions, immune response, and liver disease progression. A correlation of severe liver pathogenesis with high-level viral replication and deficient antiviral immunity has been established, which are present during chronic infection after WHV inoculation of neonatal woodchucks for modeling vertical HBV transmission in humans. HCC in chronic carrier woodchucks develops 17 to 36 mo after neonatal WHV infection and involves liver tumors that are comparable in size, morphology, and molecular gene signature to those of HBV-infected patients. Accordingly, woodchucks with WHV-induced liver tumors have been used for the improvement of imaging and ablation techniques of human HCC. In addition, drug efficacy studies in woodchucks with chronic WHV infection have revealed that prolonged treatment with nucleos(t)ide analogs, alone or in combination with other compounds, minimizes the risk of liver disease progression to HCC. More recently, woodchucks have been utilized in the delineation of mechanisms involved in innate and adaptive immune responses against WHV during acute, self-limited and chronic infections. Therapeutic interventions based on modulating the deficient host antiviral immunity have been explored in woodchucks for inducing functional cure in HBV-infected patients and for reducing or even delaying associated liver disease sequelae, including the onset of HCC. Therefore, woodchucks with chronic WHV infection constitute a well-characterized, fully immunocompetent animal model for HBV-induced liver cancer and for preclinical evaluation of the safety and efficacy of new modalities, which are based on chemo, gene, and immune therapy, for the prevention and treatment of HCC in patients for which current treatment options are dismal.

Treatment with the Immunomodulator AIC649 in Combination with Entecavir Produces Antiviral Efficacy in the Woodchuck Model of Chronic Hepatitis B

As current interventions for chronic hepatitis B (CHB) rarely induce cure, more effective drugs are needed. Short-term treatment of woodchucks with the novel immunomodulator AIC649, a parapoxvirus-based stimulator of toll-like receptor 9 dependent and independent pathways, has been shown to reduce viral DNA and surface antigen via a unique, biphasic response pattern. The present study evaluated long-term AIC649 treatment in combination with Entecavir for potency and safety in woodchucks. AIC649 monotreatment induced modest reductions in serum viral DNA and surface and e antigens that were associated with the same biphasic response pattern previously observed. Entecavir monotreatment reduced transiently viremia but not antigenemia, while AIC649/Entecavir combination treatment mediated superior viral control. Undetectability of viral antigens and elicitation of antibodies in AIC649/Entecavir-treated woodchucks correlated with the expression of interferons and suppression of viral replication in liver. Combination treatment was well tolerated, and liver enzyme elevations were minor and transient. It was concluded that the AIC649-mediated effects were most likely based on an improvement and/or reconstitution of antiviral immune responses that are typically deficient in CHB. As a combination partner to Entecavir, the antiviral efficacy of AIC649 was markedly enhanced. This preclinical study supports future evaluation of AIC649 for treatment of human CHB.

Designing a therapeutic hepatitis B vaccine to circumvent immune tolerance

An effective prophylactic hepatitis B virus (HBV) vaccine has long been available but is ineffective for chronic infection. The primary cause of chronic hepatitis B (CHB) and greatest impediment for a therapeutic vaccine is the direct and indirect effects of immune tolerance to HBV antigens. The resulting defective CD4⁺/CD8⁺ T cell response, poor cytokine production, insufficient neutralizing antibody (nAb) and poor response to HBsAg vaccination characterize CHB infection. The objective of this study was to develop virus-like-particles (VLPs) that elicit nAb to prevent viral spread and prime CD4⁺/CD8⁺ T cells to eradicate intracellular HBV. Eight neutralizing B cell epitopes from the envelope PreS1 region were consolidated onto a species-variant of the HBV core protein, the woodchuck hepatitis core antigen (WHcAg). PreS1-specific B cell epitopes were chosen because of preferential expression on HBV virions. Because WHcAg and HBcAg are not crossreactive at the B cell level and only partially cross-reactive at the CD4⁺/CD8⁺ T cell level, CD4⁺ T cells specific for WHcAg-unique T cell sites can provide cognate T-B cell help for anti-PreS1 Ab production that is not curtailed by immune tolerance. Immunization of immune tolerant HBV transgenic (Tg) mice with PreS1-WHc VLPs elicited levels of high titer anti-PreS1 nAbs equivalent to wildtype mice. Passive transfer of PreS1 nAbs into human-liver chimeric mice prevented acute infection and cleared serum HBV from mice previously infected with HBV in a model of CHB. At the T cell level, PreS1-WHc VLPs and hybrid WHcAg/HBcAg DNA immunogens elicited HBcAg-specific CD4⁺ Th and CD8⁺ CTL responses.

Innate and adaptive immunity associated with resolution of acute woodchuck hepatitis virus infection in adult woodchucks

Viral and/or host factors that are directly responsible for the acute versus chronic outcome of hepatitis B virus (HBV) infection have not been identified yet. Information on immune response during the early stages of HBV infection in humans is mainly derived from blood samples of patients with acute hepatitis B (AHB), which are usually obtained after the onset of clinical symptoms. Features of intrahepatic immune response in these patients are less studied due to the difficulty of obtaining multiple liver biopsies. Woodchuck hepatitis virus (WHV) infection in woodchucks is a model for HBV infection in humans. In the present study, five adult woodchucks were experimentally infected with WHV and then followed for 18 weeks. Blood and liver tissues were frequently collected for assaying markers of WHV replication and innate and adaptive immune responses. Liver tissues were further analyzed for pathological changes and stained for important immune cell subsets and cytokines. The increase and subsequent decline of viral replication markers in serum and liver, the elicitation of antibodies against viral proteins, and the induction of virus-specific T-cell responses indicated eventual resolution of acute WHV infection in all animals. Intrahepatic innate immune makers stayed unchanged immediately after the infection, but increased markedly during resolution, as determined by changes in transcript levels. The presence of interferon-gamma and expression of natural killer (NK) cell markers suggested that a non-cytolytic response mechanism is involved in the initial viral control in liver. This was followed by the expression of T-cell markers and cytolytic effector molecules, indicating the induction of a cytolytic response mechanism. Parallel increases in regulatory T-cell markers suggested that this cell subset participates in the overall immune cell infiltration in liver and/or has a role in regulating AHB induced by the cytolytic response mechanism. Since the transcript levels of immune cell markers in blood, when detectable, were lower than in liver, and the kinetics, except for NK-cells and interferon-gamma, did not correlate well with their intrahepatic expression, this further indicated enrichment of immune cells within liver. Conclusion: The coordinated interplay of innate and adaptive immunity mediates viral clearance in the woodchuck animal model of HBV infection. The initial presence of NK-cell associated interferon-gamma response points to an important role of this cytokine in HBV resolution.

Tracing the evolutionary history of hepadnaviruses in terms of e antigen and middle envelope protein expression or processing

Hepatitis B virus (HBV) is the prototype of hepadnaviruses, which can be subgrouped into orthohepadnaviruses infecting mammals, avihehepadnaviruses of birds, metahepadnaviruses of fish, and herpetohepadnaviruses of amphibians and reptiles. The middle (M) envelope protein and e antigen are new additions in the evolution of hepadnaviruses. They are alternative translation products of the transcripts for small (S) envelope and core proteins, respectively. For HBV, e antigen is converted from precore/core protein by removal of N-terminal signal peptide followed by furin-mediated cleavage of the basic C-terminus. This study compared old and newly discovered hepadnaviruses for their envelope protein and e antigen expression or processing. The S protein of bat hepatitis B virus (BHBV) and two metahepadnaviruses is probably myristoylated, in addition to two avihepadnaviruses. While most orthohepadnaviruses express a functional M protein with N-linked glycosylation near the amino-terminus, most metahepadnaviruses and herpetohepadnaviruses probably do not. These viruses and one orthohepadnavirus, the shrew hepatitis B virus, lack an open precore region required for e antigen expression. Potential furin cleavage sites (RXXR sequence) can be found in e antigen precursors of orthohepadnaviruses and avihepadnaviruses. Despite much larger precore/core proteins of avihepadnaviruses and their limited sequence homology with those of orthohepadnaviruses, their proximal RXXR motif can be aligned with a distal RXXR motif for orthohepadnaviruses. Thus, furin or another basic endopeptidase is probably the shared enzyme for hepadnaviral e antigen maturation. A precore-derived cysteine residue is involved in forming intramolecular disulfide bond of HBV e antigen to prevent particle formation, and such a cysteine residue is conserved for both orthohepadnaviruses and avihepadnaviruses. All orthohepadnaviruses have an X gene, while all avihepadnaviruses can express the e antigen. M protein expression appears to be the most recent event in the evolution of hepadnaviruses.

Therapeutic strategies for hepatitis B virus infection: towards a cure

Chronic hepatitis B virus (HBV) infection is a common cause of liver disease globally, with a disproportionately high burden in South-East Asia. Vaccines and nucleoside or nucleotide drugs are available and reduce both new infection rates and the development of liver disease in HBV-positive persons who adhere to long-term suppressive treatment. Although there is still considerable value in optimizing access to virus-suppressing regimens, the scientific and medical communities have embarked on a concerted journey to identify new antiviral drugs and immune interventions aimed at curing infection. The mechanisms and drug targets being explored are diverse; however, the field universally recognizes the importance of addressing the persistence of episomal covalently closed circular DNA, the existence of integrated HBV DNA in the host genome and the large antigen load, particularly of hepatitis B surface antigen. Another major challenge is to reinvigorate the exhausted immune response within the liver microenvironment. Ultimately, combinations of new drugs will be required to cure infection. Here we critically review the recent literature that describes the rationale for curative therapies and the resulting compounds that are being tested in clinical trials for hepatitis B.

Hepatitis B Virus Molecular Epidemiology, Host-Virus Interaction, Coinfection, and Laboratory Diagnosis in the MENA Region: An Update

Hepatitis B virus (HBV) is an enveloped partial double-stranded DNA virus that can cause acute and chronic hepatitis. According to the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC), 257 million people are living with HBV. Moreover, 20,900 acute hepatitis B cases were reported in 2016. Hepatitis B is highly prevalent in the African, Western Pacific, Eastern Mediterranean, South-East Asia, and European regions, respectively. Due to the high mutational rate of HBV and lack of reverse transcriptase proofreading activity, ten different genotypes with different geographical distributions have been identified. HBV pathogenesis and severity of infection depend on several host and viral factors, particularly, the genetic variability of both the host and virus. Although HBV infection is a global health concern, there is a lack of adequate studies and reports in the Middle East and North Africa (MENA) region. Here, we provide a review on HBV epidemiology, pathogenesis, host-pathogen interactions, coinfection with selected viruses, and laboratory diagnosis, focusing on studies conducted in the MENA region to determine the current situation of the HBV infection and outline the future study areas.

In Vivo Model Systems for Hepatitis B Virus Research

Hepatitis B virus (HBV) affects more than 257 million people globally, resulting in progressively worsening liver disease, manifesting as fibrosis, cirrhosis, and hepatocellular carcinoma. The exceptionally narrow species tropism of HBV restricts its natural hosts to humans and non-human primates, including chimpanzees, gorillas, gibbons, and orangutans. The unavailability of completely immunocompetent small-animal models has contributed to the lack of curative therapeutic interventions. Even though surrogates allow the study of closely related viruses, their host genetic backgrounds, immune responses, and molecular virology differ from those of HBV. Various different models, based on either pure murine or xenotransplantation systems, have been introduced over the past years, often making the choice of the optimal model for any given question challenging. Here, we offer a concise review of in vivo model systems employed to study HBV infection and steps in the HBV life cycle or pathogenesis.

Down-regulation of hepatitis delta virus super-infection in the woodchuck model

Mechanisms mediating clearance of hepatitis delta virus (HDV) are poorly understood. This study analyzed in detail profound down-regulation of HDV infection in the woodchuck model. Super-infection with HDV of woodchucks chronically infected with HBV-related woodchuck hepatitis virus produced two patterns. In the first, HDV viremia had a sharp peak followed by a considerable decline, and initial rise of HDV virions' infectivity followed by abrupt infectivity loss. In the second, HDV titer rose and later displayed plateau-like profile with high HDV levels; and HDV infectivity became persistently high when HDV titer reached the plateau. The infectivity loss was not due to defects in the virions' envelope, binding to anti-envelope antibodies, or mutations in HDV genome, but it correlated with profound reduction of the replication capacity of virion-associated HDV genomes. Subsequent finding that in virions with reduced infectivity most HDV RNAs were not full-length genomes suggests possible HDV clearance via RNA fragmentation.

Different responses in one-year-old and three-year-old grass carp reveal the mechanism of age restriction of GCRV infection

Grass carp is an important fish species in Chinese aquaculture, and can be afflicted by a hemorrhagic disease caused by the grass carp reovirus (GCRV). Interestingly, the affects of GCRV infection of grass carp are age-restricted, meaning that one-year-old grass carp can be infected and can suffer hemorrhagic disease, but three-year-old carp are not so afflicted. In this study, we investigated the mechanism responsible for this age-restricted pathology. We evaluated the relative copy number of GCRV RNA, the expression levels of proteins in blood, and changes in DNA methylation in carp from the two age groups after infection with GCRV. After GCRV infection, the relative copy number of GCRV RNA in three-year-old grass carp was significantly lower than in one-year-old carp. The differences in circulating protein levels mainly occurred in concentrated in complement and coagulation proteins, and the expression levels of these proteins were significantly higher in three-year-old grass carp than in one-year-old carp. Moreover, the expression levels of DNA methylation-related genes in the liver and spleen of one-year-old grass carp were significantly higher than those of three-year-old carp. These results suggested that as age of grass carp increases, faster and more efficient response of the immune system after viral infection, especially the complement system, and differences in DNA methylation may be important factors that affect the age restriction observed in GCRV infection. Our study provides new insights into the mechanisms underlying age restriction of GCRV infection.

Animal models for the study of hepatitis B virus infection

Even with an effective vaccine, an estimated 240 million people are chronically infected with hepatitis B virus (HBV) worldwide. Current antiviral therapies, including interferon and nucleot(s)ide analogues, rarely cure chronic hepatitis B. Animal models are very crucial for understanding the pathogenesis of chronic hepatitis B and developing new therapeutic drugs or strategies. HBV can only infect humans and chimpanzees, with the use of chimpanzees in HBV research strongly restricted. Thus, most advances in HBV research have been gained using mouse models with HBV replication or infection or models with HBV-related hepadnaviral infection. This review summarizes the animal models currently available for the study of HBV infection.

Mechanisms of Hepatitis B Virus Persistence

Hepatitis B virus (HBV) chronically infects 250 million people worldwide, resulting in nearly one million deaths annually. Studies in recent years have significantly improved our knowledge on the mechanisms of HBV persistence. HBV uses multiple pathways to harness host innate immunity to enhance its replication. It can also take advantage of the developing immune system and the not-yet-stabilized gut microbiota of young children to facilitate its persistence, and use maternal viral e antigen to educate immunity of the offspring to support its persistence after vertical transmission. The knowledge gained from these recent studies paves the way for the development of new therapies for the treatment of chronic HBV infection, which has so far been very challenging.

The clinical implications of hepatitis B virus genotypes and HBeAg in pediatrics

Although a successful vaccine against HBV has been implemented in 184 countries, eradication of hepatitis B virus (HBV) is still not on the horizon. There are over 240 million chronic carriers of HBV globally. The risk of developing chronic hepatitis ranges from >90% in newborns of hepatitis Be antigen (HBeAg)‐positive mothers, 25%–35% in children under 5 years of age and <5% in adults. HBeAg, a non‐particulate viral protein, is a marker of HBV replication. This is the only HBV antigen to cross the placenta, leading to specific unresponsiveness of helper T cells to the capsid protein and HBeAg in newborns. HBeAg is tolerated in utero and acts as a tolerogen after birth. Perinatal transmission is frequent when mothers are HBeAg‐positive, whereas it occurs less frequently when mothers are HBeAg‐negative. Sequence heterogeneity is a feature of HBV. Based on an intergroup divergence >7.5% across the complete genome, HBV is classified phylogenetically into at least nine genotypes. With between ~4% and 8% intergroup nucleotide divergence, genotypes A–D, F, H and I are classified further into subgenotypes. HBV genotypes/subgenotypes may have distinct geographical distribution and can develop different mutations in the regions of the HBV genome that code for HBeAg. These differences can be related to the role of HBV genotypes to the natural history of infection and mode of transmission. Thus genotypes/subgenotypes of HBV can be responsible for the different natural history of infection and modes of transmission in children, found in various regions of the world, where different genotypes/subgenotypes prevail. Copyright © 2016 John Wiley & Sons, Ltd.

AIC649 Induces a Bi-Phasic Treatment Response in the Woodchuck Model of Chronic Hepatitis B

AIC649 has been shown to directly address the antigen presenting cell arm of the host immune defense leading to a regulated cytokine release and activation of T cell responses. In the present study we analyzed the antiviral efficacy of AIC649 as well as its potential to induce functional cure in animal models for chronic hepatitis B. Hepatitis B virus transgenic mice and chronically woodchuck hepatitis virus (WHV) infected woodchucks were treated with AIC649, respectively. In the mouse system AIC649 decreased the hepatitis B virus titer as effective as the “gold standard”, Tenofovir. Interestingly, AIC649-treated chronically WHV infected woodchucks displayed a bi-phasic pattern of response: The marker for functional cure—hepatitis surface antigen—first increased but subsequently decreased even after cessation of treatment to significantly reduced levels. We hypothesize that the observed bi-phasic response pattern to AIC649 treatment reflects a physiologically “concerted”, reconstituted immune response against WHV and therefore may indicate a potential for inducing functional cure in HBV-infected patients.

Intrahepatic Transcriptional Signature Associated with Response to Interferon-α Treatment in the Woodchuck Model of Chronic Hepatitis B

Recombinant interferon-alpha (IFN-α) is an approved therapy for chronic hepatitis B (CHB), but the molecular basis of treatment response remains to be determined. The woodchuck model of chronic hepatitis B virus (HBV) infection displays many characteristics of human disease and has been extensively used to evaluate antiviral therapeutics. In this study, woodchucks with chronic woodchuck hepatitis virus (WHV) infection were treated with recombinant woodchuck IFN-α (wIFN-α) or placebo (n = 12/group) for 15 weeks. Treatment with wIFN-α strongly reduced viral markers in the serum and liver in a subset of animals, with viral rebound typically being observed following cessation of treatment. To define the intrahepatic cellular and molecular characteristics of the antiviral response to wIFN-α, we characterized the transcriptional profiles of liver biopsies taken from animals (n = 8-12/group) at various times during the study. Unexpectedly, this revealed that the antiviral response to treatment did not correlate with intrahepatic induction of the majority of IFN-stimulated genes (ISGs) by wIFN-α. Instead, treatment response was associated with the induction of an NK/T cell signature in the liver, as well as an intrahepatic IFN-γ transcriptional response and elevation of liver injury biomarkers. Collectively, these data suggest that NK/T cell cytolytic and non-cytolytic mechanisms mediate the antiviral response to wIFN-α treatment. In summary, by studying recombinant IFN-α in a fully immunocompetent animal model of CHB, we determined that the immunomodulatory effects, but not the direct antiviral activity, of this pleiotropic cytokine are most closely correlated with treatment response. This has important implications for the rational design of new therapeutics for the treatment of CHB.

Capacity of a natural strain of woodchuck hepatitis virus, WHVNY, to induce acute infection in naive adult woodchucks

Woodchuck hepatitis virus (WHV) is often used as surrogate to study mechanism of HBV infection. Currently, most infections are conducted using strains WHV7 or WHV8 that have very high sequence identity. This study focused on natural strain WHVNY that is more genetically distant from WHV7. Three naive adult woodchucks inoculated with WHVNY developed productive acute infection with long lasting viremia. However, only one of two woodchucks infected with WHV7 at the same multiplicity demonstrated productive liver infection. Quantification of intracellular WHV RNA and DNA replication intermediates; percentages of core antigen-positive hepatocytes; and serum relaxed circular DNA showed that strains WHVNY and WHV7 displayed comparable replication levels and capacities to induce acute infection in naive adult woodchucks. Strain WHVNY was therefore validated as valuable reagent to analyze the mechanism of hepadnavirus infection, especially in co- and super-infection settings, which required discrimination between two related virus genomes replicating in the same liver.

Infection Patterns Induced in Naive Adult Woodchucks by Virions of Woodchuck Hepatitis Virus Collected during either the Acute or Chronic Phase of Infection

The infectivity of hepadnavirus virions produced during either acute or chronic stages of infection was compared by testing the ability of the virions of woodchuck hepatitis virus (WHV) to induce productive acute infection in naive adult woodchucks. Serum WHV collected during acute infection was compared to virions harvested from WHV-infected woodchucks during either (i) early chronic infection, when WHV-induced hepatocellular carcinoma (HCC) was not yet developed, or (ii) late chronic infection, when established HCC was terminal. All tested types of WHV inoculum were related, because they were collected from woodchucks that originally were infected with standardized WHV7 inoculum. Despite the individual differences between animals, the kinetics of accumulation of serum relaxed circular DNA of WHV demonstrated that the virions produced during early or late chronic infection are fully capable of inducing productive acute infection with long-lasting high viremia. These findings were further supported by the analysis of such intrahepatic markers of WHV infection as replicative intermediate DNA, covalently closed circular DNA, pregenomic RNA, and the percentage of WHV core antigen-positive hepatocytes measured at several time points over the course of 17.5 weeks after the inoculation. In addition, the observed relationship between the production of antibodies against WHV surface antigens and parameters of WHV infection appears to be complex. Taken together, the generated data suggest that in vivo hepadnavirus virions produced during different phases of chronic infection did not demonstrate any considerable deficiencies in infectivity compared to that of virions generated during the acute phase of infection.

IMPORTANCE

The generated data suggest that infectivity of virions produced during the early or late stages of chronic hepadnavirus infection is not compromised. Our novel results provided several lines of further evidence supporting the idea that during the state of chronic infection in vivo, the limitations of hepadnavirus cell-to-cell spread/superinfection (observed recently in the woodchuck model) are not due to the diminished infectivity of the virions circulating in the blood and likely are (i) related to the properties of hepatocytes (i.e., their capacity to support hepadnavirus infection/replication) and (ii) influenced by the immune system. The obtained results further extend the understanding of the mechanisms regulating the persistence of hepadnavirus infection. Follow-up studies that will further investigate hepadnavirus cell-to-cell spread as a potential regulator of the chronic state of the infection are warranted.

Superinfection with woodchuck hepatitis virus strain WHVNY of livers chronically infected with strain WHV7

The determinants of the maintenance of chronic hepadnaviral infection are yet to be fully understood. A long-standing unresolved argument in the hepatitis B virus (HBV) research field suggests that during chronic hepadnaviral infection, cell-to-cell spread of hepadnavirus is at least very inefficient (if it occurs at all), virus superinfection is an unlikely event, and chronic hepadnavirus infection can be maintained exclusively via division of infected hepatocytes in the absence of virus spread. Superinfection exclusion was previously shown for duck HBV, but it was not demonstrated for HBV or HBV-related woodchuck hepatitis virus (WHV). Three woodchucks, which were chronically infected with the strain WHV7 and already developed WHV-induced hepatocellular carcinomas (HCCs), were superinfected with another WHV strain, WHVNY. Six weeks after the superinfection, the woodchucks were sacrificed and tissues of the livers and HCCs were examined. The WHVNY superinfection was demonstrated by using WHV strain-specific PCR assays and (i) finding WHVNY relaxed circular DNA in the serum samples collected from all superinfected animals during weeks one through six after the superinfection, (ii) detecting replication-derived WHVNY RNA in the tissue samples of the livers and HCCs collected from three superinfected woodchucks, and (iii) finding WHVNY DNA replication intermediates in tissues harvested after the superinfection. The results are consistent with the occurrence of continuous but inefficient hepadnavirus cell-to-cell spread and superinfection during chronic infection and suggest that the replication space occupied by the superinfecting hepadnavirus in chronically infected livers is limited. The findings are discussed in the context of the mechanism of chronic hepadnavirus infection.

IMPORTANCE

This study aimed to better understand the determinants of the maintenance of chronic hepadnavirus infection. The generated data suggest that in the livers chronically infected with woodchuck hepatitis virus, (i) hepadnavirus superinfection and cell-to-cell spread likely continue to occur and (ii) the virus spread is apparently inefficient, which is consistent with the interpretation that a limited number of cells in the livers facilitates the spread of hepadnavirus. The limitations of the cell-to-cell virus spread most likely are mediated at the level of the cells and do not reflect the properties of the virus. Our results further advance the understanding of the mechanism of chronic hepadnavirus infection. The significance of the continuous but limited hepadnavirus spread and superinfection for the maintenance of the chronic state of infection should be further evaluated in follow-up studies in order to determine whether blocking the virus spread would facilitate the suppression of chronic hepadnavirus infection.

Genotypes and genetic variability of hepatitis B virus

Sequence heterogeneity is a feature of hepatitis B virus (HBV), the prototype member of the family Hepadnaviridae. Based on an intergroup divergence of greater than 7.5% across the complete genome, HBV has been classified phylogenetically into 9 genotypes, A-I, with a putative 10th genotype 'J', isolated from a single individual. With between approximately 4 and 8% intergroup nucleotide divergence across the complete genome and good bootstrap support, genotypes A-D, F, H, and I are classified further into subgenotypes. There is a broad and highly statistically significant correlation between serological subtypes and genotypes, and in some cases, serological subtypes can be used to differentiate subgenotypes. The genotypes, and certain subgenotypes, have distinct geographical distributions and are important in both the clinical manifestation of infection and response to antiviral therapy. HBV genotypes/subgenotypes and genetic variability of HBV are useful in epidemiological and transmission studies, tracing human migrations, and in predicting the risk for the development of severe liver disease and response to antiviral therapy. Moreover, knowledge of the genotype/subgenotype is important in implementing preventative strategies. Thus, it is crucial that new strains are correctly assigned to their respective genotype/subgenotype and consistent, unambiguous, and generally accepted nomenclature is utilized.

The natural course of chronic hepatitis B virus infection and its management

Chronic infection with the hepatitis B virus (HBV) runs a long natural course during which underlying changes in liver histology can progress to cirrhosis and hepatic decompensation, as well as to hepatocellular carcinoma. Therapeutic intervention is currently aiming at suppression of HBV replication by applying a number of pharmacological agents. For an optimum use of available therapies, good knowledge of the natural course of chronic infection, as well as of the role played by several viral, host, and environmental factors, is mandatory. The larger part of this chapter deals with how to treat the various subsets of patients with chronic hepatitis B (CHB), using mainly three first-line drugs: pegylated interferon-α2a, entecavir, and tenofovir, administered either in finite courses or indefinitely. The frequency of virological, serological, biochemical, and histological responses in the various subsets of patients, both during and after stopping treatment, is reviewed. It is stressed that the application of the highly potent antivirals entecavir and tenofovir, with acceptable safety records and with a high barrier to HBV resistance, represents major progress in the treatment of CHB. Despite the hitherto important developments in the treatment of viral hepatitis B, clinical cure of chronic HBV infection with HBsAg loss is achievable only in a few treated patients while eradication of HBV infection appears unrealistic. Development of new pharmacological agents acting at multiple targets of the replicative cycle of HBV may achieve higher efficacy and even cure of CHB.

Nucleoside analogues alone or combined with vaccination prevent hepadnavirus viremia and induce protective immunity: alternative strategy for hepatitis B virus post-exposure prophylaxis

OBJECTIVES

The current strategies for hepatitis B virus (HBV) post-exposure prophylaxis (PEP) are not generally available in remote and rural areas of developing countries and/or carry potential risks for infection with blood-borne transmitted pathogens. Nucleotide analogues (NAs) are successfully used for human immunodeficiency virus PEP, and maybe effective for HBV PEP. In this study, we tested the NA-based strategies for HBV PEP using the Chinese woodchuck model.

METHODS

Chinese woodchucks were inoculated intravenously with different doses of woodchuck hepatitis virus (WHV). A deoxyguanosine analogue entacavir (ETV), a DNA vaccine pWHcIm, or ETV plus pWHcIm were applied to the infected animals 24h later. Twenty weeks later, the animals were re-challenged with WHV to test for the presence of immunity against WHV.

RESULTS

Inoculation with different WHV doses had a strong influence on the course of WHV infection; NA alone or in combination with a DNA vaccine completely prevented viremia after a high dose of WHV inoculation in Chinese woodchucks and induced partial or complete protective immunity, respectively.

CONCLUSIONS

NA-based PEP strategies (NA alone or in combination with vaccine) may be an alternative of HBV PEP, especially in those living in the remote and rural areas of the developing countries and the non-responders to the current vaccine, and may be valuable in the PEP of HBV and HIV co-infection after occupational and non-occupational exposure. Further clinical studies are warranted to confirm the valuable of NA-based strategies in HBV PEP.

Expression of matrix metalloproteinases and their inhibitors in the woodchuck model of hepatocellular carcinoma

Matrix metalloproteinases (MMPs) play a central role in tumor invasion and metastasis. Increased expression of MMPs occurs during development of hepatocellular carcinoma (HCC) in humans following infection with hepatitis B virus (HBV). Woodchucks are used as an animal model for hepadnavirus-induced HCC. All woodchucks infected chronically with woodchuck hepatitis virus (WHV), a virus that is closely related to HBV, develop HCC. In the present study MMPs and related molecules were investigated in woodchucks to better understand the mechanisms of extracellular matrix remodeling in HCC. Three groups of samples were studied: liver and HCC tissues from animals infected with WHV and age- and gender-matched normal liver from animals not infected with WHV. New partial gene sequences for woodchuck MMP-2, MMP-7, and MMP-9 as well as their inhibitors NGAL, TIMP-1, and TIMP-2 were identified and used for determination of expression levels in liver and HCC by qRT-PCR. Compared to liver of WHV-naïve woodchucks, high levels of MMP-1, MMP-2, MMP-7, NGAL, and TIMP-1 were detected in liver of animals infected with WHV. However, no differences were found for TIMP-2. MMP-9 expression was higher in HCC than in liver of animals not infected with WHV. Immunohistochemical staining demonstrated that MMP-9 immunoreactivity was most intense in HCC, correlating with the progression of liver disease. Upregulation of MMP-9 in HCC was confirmed by Western blotting and zymography analysis. Furthermore, the activity of woodchuck MMPs was suppressed by BiPS, a common inhibitor of mammalian MMPs. These results suggest the use of MMP inhibitors as a potential HCC treatment strategy that could be explored in woodchucks.

Hepatitis B virus genetic variants: biological properties and clinical implications

Hepatitis B virus (HBV) causes a chronic infection in 350 million people worldwide and greatly increases the risk of liver cirrhosis and hepatocellular carcinoma. The majority of chronic HBV carriers live in Asia. HBV can be divided into eight genotypes with unique geographic distributions. Mutations accumulate during chronic infection or in response to external pressure. Because HBV is an RNA-DNA virus the emergence of drug resistance and vaccine escape mutants has become an important clinical and public health concern. Here, we provide an overview of the molecular biology of the HBV life cycle and an evaluation of the changing role of hepatitis B e antigen (HBeAg) at different stages of infection. The impact of viral genotypes and mutations/deletions in the precore, core promoter, preS, and S gene on the establishment of chronic infection, development of fulminant hepatitis and liver cancer is discussed. Because HBV is prone to mutations, the biological properties of drug-resistant and vaccine escape mutants are also explored.

Animal Models of Human Viral Diseases

As the threat of exposure to emerging and reemerging viruses within a naive population increases, it is vital that the basic mechanisms of pathogenesis and immune response be thoroughly investigated. By using animal models in this endeavor, the response to viruses can be studied in a more natural context to identify novel drug targets, and assess the efficacy and safety of new products. This is especially true in the advent of the Food and Drug Administration's animal rule. Although no one animal model is able to recapitulate all the aspects of human disease, understanding the current limitations allows for a more targeted experimental design. Important facets to be considered before an animal study are the route of challenge, species of animals, biomarkers of disease, and a humane endpoint. This chapter covers the current animal models for medically important human viruses, and demonstrates where the gaps in knowledge exist.

Subset of Suz12/PRC2 target genes is activated during hepatitis B virus replication and liver carcinogenesis associated with HBV X protein

Chronic hepatitis B virus (HBV) infection is a major risk factor for developing liver cancer, and the HBV X protein (pX) has been implicated as a cofactor in hepatocyte transformation. We have shown that HBV replication as well as in vitro transformation by pX are associated with induction of the mitotic polo-like kinase 1 (Plk1) and down-regulation of the chromatin remodeling components Suz12 and Znf198. Herein, we demonstrate the same inverse relationship between Plk1 and Suz12/Znf198 in liver tumors from X/c-myc bitransgenic mice and woodchuck hepatitis virus (WHV)-infected woodchucks. Employing these animal models and the HBV replicating HepAD38 cells we examined the effect of Suz12/Znf198 down-regulation on gene expression. Genes analyzed include hepatic cancer stem cell markers BAMBI, DKK1,2, DLK1, EpCAM, MYC, and proliferation genes CCNA1, CCND2, IGFII, MCM4-6, PLK1, RPA2, and TYMS. Suz12 occupancy at the promoters of BAMBI, CCND2, DKK2, DLK1, EpCAM, and IGFII was demonstrated by chromatin immunoprecipitation in untransformed hepatocytes, but was markedly reduced in pX-transformed and Suz12 knockdown cells. Accordingly, we refer to these genes as "Suz12 repressed" genes in untransformed hepatocytes. The Suz12 repressed genes and proliferation genes were induced in HBV-replicating HepAD38 cells and, interestingly, they exhibited distinct expression profiles during hepatocellular carcinoma (HCC) progression in X/c-myc bitransgenics. Specifically, CCND2, EpCAM, and IGFII expression was elevated at the proliferative and preneoplastic stages in X/c-myc bitransgenic livers, whereas BAMBI and PLK1 were overexpressed in hepatic tumors from X/c-myc bitransgenics and WHV-infected woodchucks. Importantly, most of these genes were selectively up-regulated in HBV-induced HCCs.

CONCLUSION

The distinct expression profile of the identified Suz12 repressed genes in combination with the proliferation genes hold promise as biomarkers for progression of chronic HBV infection to HCC.

Experimental chronic hepatitis B infection of neonatal tree shrews (Tupaia belangeri chinensis): a model to study molecular causes for susceptibility and disease progression to chronic hepatitis in humans

BACKGROUND

Hepatitis B virus (HBV) infection continues to be an escalating global health problem. Feasible and effective animal models for HBV infection are the prerequisite for developing novel therapies for this disease. The tree shrew (Tupaia) is a small animal species evolutionary closely related to humans, and thus is permissive to certain human viral pathogens. Whether tree shrews could be chronically infected with HBV in vivo has been controversial for decades. Most published research has been reported on adult tree shrews, and only small numbers of HBV infected newborn tree shrews had been observed over short time periods. We investigated susceptibility of newborn tree shrews to experimental HBV infection as well as viral clearance over a protracted time period.

RESULTS

Forty-six newborn tree shrews were inoculated with the sera from HBV-infected patients or tree shrews. Serum and liver samples of the inoculated animals were periodically collected and analyzed using fluorescence quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, Southern blot, and immunohistochemistry. Six tree shrews were confirmed and four were suspected as chronically HBV-infected for more than 48 (up to 228) weeks after inoculation, including three that had been inoculated with serum from a confirmed HBV-infected tree shrew.

CONCLUSIONS

Outbred neonatal tree shrews can be long-term chronically infected with HBV at a frequency comparable to humans. The model resembles human disease where also a smaller proportion of infected individuals develop chronic HBV related disease. This model might enable genetic and immunologic investigations which would allow determination of underlying molecular causes favoring susceptibility for chronic HBV infection and disease establishment vs. viral clearance.

Early age at time of primary Epstein-Barr virus infection results in poorly controlled viral infection in infants from Western Kenya: clues to the etiology of endemic Burkitt lymphoma

BACKGROUND

Infection with Epstein-Barr virus (EBV) early in life and repeated malaria exposure have been proposed as risk factors for endemic Burkitt lymphoma (eBL).

METHODS

Infants were enrolled from 2 rural sites in Kenya: the Kisumu District, where malaria transmission is holoendemic and risk for eBL is high, and the Nandi District, where malaria transmission is limited and the risk for eBL is low. Blood samples were taken from infants through 2 years of age to measure EBV viral load, EBV antibodies, and malaria parasitemia.

RESULTS

We observed a significantly younger age at time of primary EBV infection in children from Kisumu compared with children from Nandi (mean age, 7.28 months [±0.33 SEM] in Kisumu vs 8.39 months [±0.26 SEM] in Nandi), with 35.3% of children in Kisumu infected before 6 months of age. To analyze how different predictors affected EBV viral load over time, we performed multilevel mixed modeling. This modeling revealed that residence in Kisumu and younger age at first EBV infection were significant predictors for having a higher EBV viral load throughout the period of observation.

CONCLUSIONS

Children from a region at high risk for eBL were infected very early in life with EBV, resulting in higher viral loads throughout infancy.

Natural history of chronic hepatitis B in Euro-Mediterranean and African countries

Data derived from population, case-control, and cohort studies conducted in several Euro-Mediterranean and African countries disclose impressive similarities in the age and modes of hepatitis B virus (HBV) transmission and in the prevalence, duration, and outcome of the four phases of the natural history of chronic infection. Perinatal HBV infection is rare while the vast majority of chronic infections originate from horizontal HBV transmission to infants and children. HBeAg loss and seroconversion to anti-HBe occur in a few years time, usually during the second decade of life. HBeAg-negative/anti-HBe-positive chronic hepatitis B (CHB), predominates in these countries being 7-9 times more frequent than HBeAg-positive CHB. The predominance of HBeAg-negative CHB is largely linked to the molecular characteristics of HBV genotype D prevailing in European and African countries of the Mediterranean basin and of genotype E and subgenotype A1 that prevail in the other parts of Africa. The molecular characteristics of the African subgenotype A1 differ from those of European subgenotype A2 explaining the fact that patients infected subgenotype A1 demonstrate an earlier loss of HBeAg and seroconversion to anti-HBe during the natural course of HBV infection compared to those infected with subgenotype A2. It is proposed that the molecular characteristics of HBV genotypes and subgenotypes prevailing in Euro-Mediterranean and African countries acting in concert with host and environmental factors largely determine the natural history of chronic HBV infection and its significant differences from countries of HBV genotype C and B and of subgenotype Ae predominance. The knowledge of the natural history of chronic HBV infection in Euro-Mediterranean and African countries combined with wide screening programs for prompt recognition and treatment of chronic HBV infection both in its HBeAg-positive and -negative immune reactive phases can be expected to increase the efficacy of current and future therapeutic strategies.

Electroporation enhances immunogenicity of a DNA vaccine expressing woodchuck hepatitis virus surface antigen in woodchucks

The development of therapeutic vaccines for chronic hepatitis B virus (HBV) infection has been hampered by host immune tolerance and the generally low magnitude and inconsistent immune responses to conventional vaccines and proposed new delivery methods. Electroporation (EP) for plasmid DNA (pDNA) vaccine delivery has demonstrated the enhanced immunogenicity of HBV antigens in various animal models. In the present study, the efficiency of the EP-based delivery of pDNA expressing various reporter genes first was evaluated in normal woodchucks, and then the immunogenicity of an analog woodchuck hepatitis virus (WHV) surface antigen (WHsAg) pDNA vaccine was studied in this model. The expression of reporter genes was greatly increased when the cellular uptake of pDNA was facilitated by EP. The EP of WHsAg-pDNA resulted in enhanced, dose-dependent antibody and T-cell responses to WHsAg compared to those of the conventional hypodermic needle injection of WHsAg-pDNA. Although subunit WHsAg protein vaccine elicited higher antibody titers than the DNA vaccine delivered with EP, T-cell response rates were comparable. However, in WHsAg-stimulated mononuclear cell cultures, the mRNA expression of CD4 and CD8 leukocyte surface markers and Th1 cytokines was more frequent and was skewed following DNA vaccination compared to that of protein immunization. Thus, the EP-based vaccination of normal woodchucks with pDNA-WHsAg induced a skew in the Th1/Th2 balance toward Th1 immune responses, which may be considered more appropriate for approaches involving therapeutic vaccines to treat chronic HBV infection.

Establishing a new animal model for hepadnaviral infection: susceptibility of Chinese Marmota-species to woodchuck hepatitis virus infection

Hepatitis B virus infection (HBV) is a major medical problem in China. The lack of a suitable infection model in China is recognized as an obstacle for research on HBV in China. Chinese Marmota-species is phylogenetically closely related to Marmota monax, thus, it might be suitable to serve as an animal model for HBV infection. Therefore, we attempted to prove the claim about the existence of woodchuck hepatitis virus (WHV)-like viruses in Chinese Marmota-species and to determine the susceptibility of these species to experimental WHV infection. In the present study, 653 sera from three Chinese Marmota-species, Marmota himalayana, Marmota baibacina and Marmota bobak, were screened for WHV-like viruses by serological and molecular assays. The susceptibility to WHV of three species was investigated by experimental infection and monitored by testing of anti-WHc and WHsAg by ELISA, detection of WHV DNA by PCR, and detection of WHV replication intermediates and antigens in liver samples. No evidence for the existence of a genetically closely related virus to WHV in three Chinese Marmota-species was found by serological assays and PCR. M. himalayana was susceptible to WHV infection as inoculated animals became positive for anti-WHc, WHsAg and WHV DNA. Further, WHV replication intermediates and proteins were detected in liver samples. In contrast, M. baibacina remained negative for tested virological parameters. M. bobak species showed a limited susceptibility to WHV. Our data do not support early reports about WHV-like viruses in China. M. himalayana is suitable for the establishment of a model for hepadnaviral infection.

Glucosidase inhibition enhances presentation of de-N-glycosylated hepatitis B virus epitopes by major histocompatibility complex class I in vitro and in woodchucks

In this report, the possibility of pharmacologically altering the hepatitis B virus (HBV) epitopes presented by major histocompatibility complex class I on infected cells is demonstrated. The HBV middle envelope glycoprotein (MHBs) maturation appears to require calnexin-mediated folding. This interaction is dependent on glucosidases in the endoplasmic reticulum. Prevention of HBV envelope protein maturation in cultured cells through use of glucosidase inhibitors, such as 6-O-butanoyl castanospermine and N-nonyl deoxynorjirimycin, resulted in MHBs degradation by proteasomes. The de-N-glycosylation associated with polypeptide degradation was predicted to result in conversion of asparagine residues into aspartic acid residues. This prediction was confirmed by showing that peptides corresponding to the N-glycosylation sequons of MHBs, but with aspartic acid replacing asparagine, (1) can prime human cytotoxic T lymphocytes that recognize HBV-producing cells and (2) that the presentation of these envelope motifs by major histocompatibility complex class I is enhanced by incubation with glucosidase inhibitors. Moreover, although peripheral blood mononuclear cells isolated from woodchucks chronically infected with woodchuck hepatitis virus and vaccinated with woodchuck hepatitis virus surface antigen could be induced to recognize the natural MHBs asparagine-containing peptides, only cells isolated from animals treated with glucosidase inhibitor recognized the aspartic acid-containing peptides.

CONCLUSION

These data suggest that pharmacological intervention with glucosidase inhibitors can alter the MHBs epitopes presented. This editing of the amino acid sequence of the polypeptide results in a new epitope, or "editope", with possible medical significance.

Therapeutic vaccination in chronic hepatitis B: preclinical studies in the woodchuck

Recommended treatment of chronic hepatitis B with interferon-α and/or nucleos(t)ide analogues does not lead to a satisfactory result. Induction of HBV-specific T cells by therapeutic vaccination or immunotherapies may be an innovative strategy to overcome virus persistence. Vaccination with commercially available HBV vaccines in patients did not result in effective control of HBV infection, suggesting that new formulations of therapeutic vaccines are needed. The woodchuck (Marmota monax) is a useful preclinical model for developing the new therapeutic approaches in chronic hepadnaviral infections. Several innovative approaches combining antiviral treatments with nucleos(t)ide analogues, DNA vaccines, and protein vaccines were tested in the woodchuck model. In this paper we summarize the available data concerning therapeutic immunization and gene therapy using recombinant viral vectors approaches in woodchucks, which show encouraging results. In addition, we present potential innovations in immunomodulatory strategies to be evaluated in this animal model.

Rapid immunity to vaccination with woodchuck hepatitis virus surface antigen using cationic liposome-DNA complexes as adjuvant

Complexes of cationic liposomes and non-coding DNA (CLDC) have shown promise as vaccine adjuvant. Using the woodchuck animal model of hepatitis B virus (HBV) infection, the immunogenic effects of CLDC were evaluated following vaccination with three doses of woodchuck hepatitis virus surface antigen (WHsAg) adjuvanted with either CLDC or conventional alum and administered intramuscularly (im) or subcutaneously (sc). IM vaccination with WHsAg and CLDC elicited antibodies earlier, in more woodchucks, and with higher titers than WHsAg and alum. After two vaccine doses, antibody titers were higher following im than sc administration. Woodchucks administered two vaccine doses sc received the third vaccine dose im, and antibody responses reached titers comparable to those elicited by im administration. Following the second vaccine dose, im vaccination with WHsAg and CLDC induced T cell responses to WHsAg and selected WHs peptides and expression of the leukocyte surface marker CD8 and of the Th1 cytokines interferon-gamma and tumor necrosis factor alpha in woodchucks. T cell responses and CD8/cytokine expression were diminished in woodchucks from the other groups suggesting that this vaccine regimen induced a skew toward Th1 immune responses. The present study in woodchucks demonstrates that CLDC-adjuvanted WHsAg vaccine administered im resulted in a more rapid induction of humoral and cellular immune responses compared to conventional, alum-adjuvanted WHsAg vaccine. While less rapid, the immune responses following sc administration can prime the im immune responses. This adjuvant activity of CLDC over alum may be beneficial for therapeutic vaccination in chronic HBV infection.

Semliki forest virus expressing interleukin-12 induces antiviral and antitumoral responses in woodchucks with chronic viral hepatitis and hepatocellular carcinoma

A vector based on Semliki Forest virus (SFV) expressing high levels of interleukin-12 (SFV-enhIL-12) has previously demonstrated potent antitumoral efficacy in small rodents with hepatocellular carcinoma (HCC) induced by transplantation of tumor cells. In the present study, the infectivity and antitumoral/antiviral effects of SFV vectors were evaluated in the clinically more relevant woodchuck model, in which primary HCC is induced by chronic infection with woodchuck hepatitis virus (WHV). Intratumoral injection of SFV vectors expressing luciferase or IL-12 resulted in high reporter gene activity within tumors and cytokine secretion into serum, respectively, demonstrating that SFV vectors infect woodchuck tumor cells. For evaluating antitumoral efficacy, woodchuck tumors were injected with increasing doses of SFV-enhIL-12, and tumor size was measured by ultrasonography following treatment. In five (83%) of six woodchucks, a dose-dependent, partial tumor remission was observed, with reductions in tumor volume of up to 80%, but tumor growth was restored thereafter. Intratumoral treatment further produced transient changes in WHV viremia and antigenemia, with >or=1.5-log(10) reductions in serum WHV DNA in half of the woodchucks. Antitumoral and antiviral effects were associated with T-cell responses to tumor and WHV antigens and with expression of CD4 and CD8 markers, gamma interferon, and tumor necrosis factor alpha in peripheral blood mononuclear cells, suggesting that immune responses against WHV and HCC had been induced. These experimental observations suggest that intratumoral administration of SFV-enhIL-12 may represent a strategy for treatment of chronic HBV infection and associated HCC in humans but indicate that this approach could benefit from further improvements.

Characterization of genotype-specific carboxyl-terminal cleavage sites of hepatitis B virus e antigen precursor and identification of furin as the candidate enzyme

Hepatitis B e antigen (HBeAg) is a secreted version of hepatitis B virus (HBV) core protein that promotes immune tolerance and persistent infection. It is derived from a translation product of the precore/core gene by two proteolytic cleavage events: removal of the amino-terminal signal peptide and removal of the carboxyl-terminal arginine-rich sequence. Four RXXR motifs are present at the carboxyl terminus of the HBeAg precursor, with the first two fused as (151)RRGRSPR(157). Genotype A possesses two extra amino acids at the first motif ((151)RRDRGRSPR(159)), which weakens the first motif and separates it from the second one. Western blot analysis of patient sera revealed a single HBeAg form for genotypes B to D but two additional forms of larger sizes for genotype A. Site-directed mutagenesis and transfection experiments with human hepatoma cell lines indicated that HBeAg of genotype B is derived from cleavage at the first ((151)RRGR(154)) motif. The major HBeAg form of genotype A corresponds to cleavage at the second ((156)RSPR(159)) motif, and the other two forms are cleavage products of the first ((151)RRDR(154)) and third ((166)RRRR(169)) motifs, respectively. Only the cleavage product of the third motif of genotype A was observed in furin-deficient LoVo cells, and an inhibitor of furin-like proprotein convertases blocked cleavage of the first and second motifs in human hepatoma cells. In conclusion, our study reveals genotypic differences in HBeAg processing and implicates furin as the major enzyme involved in the cleavage of the first and second RXXR motifs.

Correlation of virus and host response markers with circulating immune complexes during acute and chronic woodchuck hepatitis virus infection

Woodchuck hepatitis virus (WHV) is an established model for human hepatitis B virus. The kinetics of virus and host responses in serum and liver during acute, self-limited WHV infection in adult woodchucks were studied. Serum WHV DNA and surface antigen (WHsAg) were detected as early as 1 to 3 weeks following experimental infection and peaked between 1 and 5 weeks postinfection. Thereafter, serum WHsAg levels declined rapidly and became undetectable, while WHV DNA levels became undetectable much later, between 4 and 20 weeks postinfection. Decreasing viremia correlated with transient liver injury marked by an increase in serum sorbitol dehydrogenase (SDH) levels. Clearance of WHV DNA from serum was associated with the normalization of serum SDH. Circulating immune complexes (CICs) of WHsAg and antibodies against WHsAg (anti-WHs) that correlated temporarily with the peaks in serum viremia and WHs antigenemia were detected. CICs were no longer detected in serum once free anti-WHs became detectable. The detection of CICs around the peak in serum viremia and WHs antigenemia in resolving woodchucks suggests a critical role for the humoral immune response against WHsAg in the early elimination of viral and subviral particles from the peripheral blood. Individual kinetic variation during WHV infections in resolving woodchucks infected with the same WHV inoculum and dose is likely due to the outbred nature of the animals, indicating that the onset and magnitude of the individual immune response determine the intensity of virus inhibition and the timing of virus elimination from serum.

Intrahepatic expression of genes affiliated with innate and adaptive immune responses immediately after invasion and during acute infection with woodchuck hepadnavirus

The importance of effective immune responses in recovery from acute hepadnaviral hepatitis has been demonstrated. However, there is no conclusive delineation of virological and immunological events occurring in the liver immediately after hepadnavirus invasion and during the preacute phase of infection. These very early events might be of primary importance in determining the recovery or progression to chronic hepatitis and the intrinsic hepadnaviral propensity to persist. In this study, applying the woodchuck model of acute hepatitis B, the hepatic kinetics of hepadnavirus replication and activation of genes encoding cytokines, cytotoxicity effectors, and immune cell markers were quantified in sequential liver biopsies collected from 1 h postinoculation onward by sensitive real-time cDNA amplification assays. The results revealed that hepadnavirus replication is established in the liver as early as 1 hour after infection. In 3 to 6 h, significantly augmented intrahepatic transcription of gamma interferon and interleukin-12 were evident, suggesting activation of antigen-presenting cells. In 48 to 72 h, NK and NKT cells were activated and virus replication was transiently but significantly reduced, implying that this early innate response is at least partially successful in limiting virus propagation. Nonetheless, T cells were activated 4 to 5 weeks later when hepatitis became histologically evident. Collectively, our data demonstrate that virus replication is initiated and the innate response activated in the liver soon after exposure to a liver-pathogenic dose of hepadnavirus. Nevertheless, this response is unable to prompt a timely adaptive T-cell response, in contrast to infections caused by other viral pathogens.

Antiviral effects of lamivudine, emtricitabine, adefovir dipivoxil, and tenofovir disoproxil fumarate administered orally alone and in combination to woodchucks with chronic woodchuck hepatitis virus infection

Adefovir dipivoxil (ADV) and tenofovir disoproxil fumarate (TDF) are nucleotide analogs that inhibit the replication of wild-type hepatitis B virus (HBV) and lamivudine (3TC)-resistant virus in HBV-infected patients, including those who are coinfected with human immunodeficiency virus. The combination of ADV or TDF with other nucleoside analogs is a proposed strategy for managing antiviral drug resistance during the treatment of chronic HBV infection. The antiviral effect of oral ADV or TDF, alone or in combination with 3TC or emtricitabine (FTC), against chronic woodchuck hepatitis virus (WHV) infection was evaluated in a placebo-controlled study in the woodchuck, an established and predictive model for antiviral therapy. Once-daily treatment for 48 weeks with ADV plus 3TC or TDF plus FTC significantly reduced serum WHV viremia levels from the pretreatment level by 6.2 log(10) and 6.1 log(10) genome equivalents/ml serum, respectively, followed by TDF plus 3TC (5.6 log(10) genome equivalents/ml), ADV alone (4.8 log(10) genome equivalents/ml), ADV plus FTC (one survivor) (4.4 log(10) genome equivalents/ml), TDF alone (2.9 log(10) genome equivalents/ml), 3TC alone (2.7 log(10) genome equivalents/ml), and FTC alone (2.0 log(10) genome equivalents/ml). Individual woodchucks across all treatment groups also demonstrated pronounced declines in serum WHV surface antigen, characteristically accompanied by declines in hepatic WHV replication and the hepatic expression of WHV antigens. Most woodchucks had prompt recrudescence of WHV replication after drug withdrawal, but individual woodchucks across treatment groups had sustained effects. No signs of toxicity were observed for any of the drugs or drug combinations administered. In conclusion, the oral administration of 3TC, FTC, ADV, and TDF alone and in combination was safe and effective in the woodchuck model of HBV infection.

Immunogenicity in mice and rabbits of DNA vaccines expressing woodchuck hepatitis virus antigens

The licensed vaccine against hepatitis B virus (HBV) is an effective means to prevent infection, but is not an effective therapeutic strategy to treat established chronic infections when used alone. In an animal model of chronic HBV infection (the woodchuck experimentally infected with woodchuck hepatitis virus (WHV)), the combination of conventional vaccine and potent antiviral drugs has shown promise as a potential therapeutic intervention. This approach might be improved further through the application of newer vaccine technologies. In the present study, we evaluated electroporation (EP)-based intramuscular (i.m.) delivery of a codon-optimized DNA vaccine for the WHV surface antigen (WHsAg) in mice and rabbits. In mice, this immunization procedure compared favorably to vaccination by i.m. injection of the DNA vaccine or i.m. administration of a recombinant WHsAg-alum vaccine, exhibiting characteristics expected to be beneficial for a therapeutic vaccine strategy. These included dose efficiency, consistency, vigorous induction of antibody responses to WHsAg, as well as a Th1 bias. Following scale-up to rabbits, a species that approximates the size of the woodchuck, the EP dosing regimen was markedly more effective than conventional i.m. injection of the DNA vaccine. Taken together, these results provide the foundation for studies of EP-based DNA immunization in the woodchuck in order to further assess its potential as an immunotherapeutic approach for treatment of chronic HBV infection in humans.

Infection of neonates with murine gammaherpesvirus 68 results in enhanced viral persistence in lungs and absence of infectious mononucleosis syndrome

We used the murine gammaherpesvirus 68 (γHV-68), which serves as a model for human gammaherpesvirus infection, to determine whether age at infection altered the pattern of gammaherpesvirus pathogenesis. We infected mice intranasally at 8 days old (pups) and 6 weeks old (adults) to investigate differences in γHV-68 pathogenesis. There was no difference between adults or pups in acute infection in the lungs at 6 days post-infection (p.i.). However, mice infected as pups exhibited a more disseminated viral infection with viral DNA detected in the spleen, liver and heart as measured by quantitative PCR (Q-PCR). In addition, viral DNA was detected in the lungs of mice infected as pups until 60 days p.i. Three viral transcripts (M2, M3 and M9) were expressed at both 30 and 60 days p.i. In contrast, no viral DNA or mRNA expression was detected in lungs of mice infected as adults at 30 or 60 days p.i. Mice infected as adults experienced a peak in latent infection in the spleen at 16 days p.i., corresponding with an increase in splenic weight and expansion of the Vβ4+ CD8+ T-cell population, similar to infectious mononucleosis observed following infection of young adults with Epstein–Barr virus. However, the increase in splenic weight of infected pups was not as pronounced and no significant increase in Vβ4+ CD8+ T-cell expansion was observed in infected pups. Together, these data suggest that the pathogenesis of murine gammaherpesvirus γHV-68 is age-dependent.

Chemoimmunotherapy of chronic hepatitis B virus infection in the woodchuck model overcomes immunologic tolerance and restores T-cell responses to pre-S and S regions of the viral envelope protein

Treatment of chronic hepatitis B virus (HBV) infection could combine potent antiviral drugs and therapeutic vaccines to overcome immunological tolerance and induce the recovery phenotype to protect against disease progression. Conventional vaccination of woodchucks chronically infected with the woodchuck hepatitis virus (WHV) elicited differential T-cell response profiles depending on whether or not carriers were treated with the potent antiviral drug clevudine (CLV), which significantly reduces viral and antigen loads. The differential T-cell responses defined both CLV-dependent and CLV-independent epitopes of the pre-S and S regions of the WHV envelope protein. Only combined treatment involving CLV and conventional vaccine therapeutically restored the T-cell response profile of chronic WHV carrier woodchucks to that seen in prophylactic vaccination and in recovery from acute WHV infection. The results have implications for mechanisms of immunological tolerance operating in chronic HBV infection and suggest that such combined chemoimmunotherapy may be useful for treatment of humans with chronic HBV infection.

Antiviral effect of orally administered (-)-beta-D-2-aminopurine dioxolane in woodchucks with chronic woodchuck hepatitis virus infection

(-)-beta-D-2-Aminopurine dioxolane (APD) is a nucleoside prodrug that is efficiently converted to 9-(beta-D-1,3-dioxolan-4-yl)guanine (DXG). DXG has antiviral activity in vitro against hepatitis B virus (HBV) but limited aqueous solubility, making it difficult to administer orally to HBV-infected individuals. APD is more water soluble than DXG and represents a promising prodrug for the delivery of DXG. A placebo-controlled, dose-ranging efficacy and pharmacokinetic study was conducted with woodchucks that were chronically infected with woodchuck hepatitis virus (WHV). APD was efficiently converted to DXG after oral and intravenous administrations of APD, with serum concentrations of DXG being higher following oral administration than following intravenous administration, suggestive of a considerable first-pass intestinal and/or hepatic metabolism. APD administered orally at 1, 3, 10, and 30 mg/kg of body weight per day for 4 weeks produced a dose-dependent antiviral response. Doses of 3 and 10 mg/kg/day reduced serum WHV viremia by 0.4 and 0.7 log(10) copies/ml, respectively. The 30-mg/kg/day dose resulted in a more pronounced, statistically significant decline in serum WHV viremia of 1.9 log(10) copies/ml and was associated with a 1.5-fold reduction in hepatic WHV DNA. Individual woodchucks within the highest APD dose group that had declines in serum WHV surface antigen levels, WHV viremia, and hepatic WHV DNA also had reductions in hepatic WHV RNA. There was a prompt recrudescence of WHV viremia following drug withdrawal. Therefore, oral administration of APD for 4 weeks was safe in the woodchuck model of chronic HBV infection, and the effect on serum WHV viremia was dose dependent.

Immunomodulation as an option for the treatment of chronic hepatitis B virus infection: preclinical studies in the woodchuck model

New therapeutic approaches for chronic hepatitis B virus infection based on immunomodulation are now under investigation. The woodchuck model for hepatitis B virus infection has emerged as a useful animal model for the evaluation of such approaches, after developing necessary assays and reagents for immunologic studies in this model. Conventional and novel vaccines such as DNA vaccines were tested in woodchucks for their ability to induce protective immune responses against challenge infection with the woodchuck hepatitis virus (WHV). Furthermore, immunotherapeutic approaches for the control of chronic hepadnaviral infection were evaluated in woodchucks. Immunizations with WHV proteins and DNA vaccines led to the development of antibodies to the WHV surface antigen and to a significant decrease of viral load in chronically WHV-infected woodchucks. Viral vector-mediated gene transfer was explored for the delivery of antiviral cytokines IFN-alpha in woodchucks and resulted in the decrease of viral replication. It is now generally accepted that a combination of antiviral treatment and immunization will be necessary to achieve successful immunomodulation with a long-term control of chronic hepatitis B virus infection.