Modeling hepatitis B virus infection, immunopathology and therapy in mice

System Biology Investigation Revealed Lipopolysaccharide and Alcohol-Induced Hepatocellular Carcinoma Resembled Hepatitis B Virus Immunobiology and Pathogenesis

Hepatitis B infection caused by the hepatitis B virus is a life-threatening cause of liver fibrosis, cirrhosis, and hepatocellular carcinoma. Researchers have produced multiple in vivo models for hepatitis B virus (HBV) and, currently, there are no specific laboratory animal models available to study HBV pathogenesis or immune response; nonetheless, their limitations prevent them from being used to study HBV pathogenesis, immune response, or therapeutic methods because HBV can only infect humans and chimpanzees. The current study is the first of its kind to identify a suitable chemically induced liver cirrhosis/HCC model that parallels HBV pathophysiology. Initially, data from the peer-reviewed literature and the GeneCards database were compiled to identify the genes that HBV and seven drugs (acetaminophen, isoniazid, alcohol, D-galactosamine, lipopolysaccharide, thioacetamide, and rifampicin) regulate. Functional enrichment analysis was performed in the STRING server. The network HBV/Chemical, genes, and pathways were constructed by Cytoscape 3.6.1. About 1546 genes were modulated by HBV, of which 25.2% and 17.6% of the genes were common for alcohol and lipopolysaccharide-induced hepatitis. In accordance with the enrichment analysis, HBV activates the signaling pathways for apoptosis, cell cycle, PI3K-Akt, TNF, JAK-STAT, MAPK, chemokines, NF-kappa B, and TGF-beta. In addition, alcohol and lipopolysaccharide significantly activated these pathways more than other chemicals, with higher gene counts and lower FDR scores. In conclusion, alcohol-induced hepatitis could be a suitable model to study chronic HBV infection and lipopolysaccharide-induced hepatitis for an acute inflammatory response to HBV.

Human Immune System Mice With Autologous Tumor for Modeling Cancer Immunotherapies

Mouse models are the most commonly used in vivo system for biomedical research, in which immune-related diseases and therapies can be investigated in syngeneic and immunologically intact hosts. However, because there are significant differences between rodent and human, most findings from conventional mouse models cannot be applied to humans. The humanized mouse with a functional human immune system, also referred to as human immune system (HIS) mouse, is the only model available to date for in vivo studies in real-time of human immune function under physiological and pathological conditions. HIS mice with human tumor xenografts are considered an emerging and promising in vivo model for modeling human cancer immunotherapy. In this review, we briefly discuss the protocols to construct HIS mice and elaborate their pros and cons. Particular attention is given to HIS mouse models with human tumor that is autologous or genetically identical to the human immune system, which are discussed with examples of their usefulness in modeling human cancer immunotherapies.

Knockdown of Virus Antigen Expression Increases Therapeutic Vaccine Efficacy in High-Titer Hepatitis B Virus Carrier Mice

BACKGROUND & AIMS

Hepatitis B virus (HBV) infection persists because the virus-specific immune response is dysfunctional. Therapeutic vaccines might be used to end immune tolerance to the virus in patients with chronic infection, but these have not been effective in patients so far. In patients with chronic HBV infection, high levels of virus antigens might prevent induction of HBV-specific immune responses. We investigated whether knocking down expression levels of HBV antigens in liver might increase the efficacy of HBV vaccines in mice.

METHODS

We performed studies with male C57BL/6 mice that persistently replicate HBV (genotype D, serotype ayw)-either from a transgene or after infection with an adeno-associated virus that transferred an overlength HBV genome-and expressed HB surface antigen at levels relevant to patients. Small hairpin or small interfering (si)RNAs against the common 3'-end of all HBV transcripts were used to knock down antigen expression in mouse hepatocytes. siRNAs were chemically stabilized and conjugated to N-acetylgalactosamine to increase liver uptake. Control mice were given either entecavir or non-HBV-specific siRNAs and vaccine components. Eight to 12 weeks later, mice were immunized twice with a mixture of adjuvanted HBV S and core antigen, followed by a modified Vaccinia virus Ankara vector to induce HBV-specific B- and T-cell responses. Serum and liver samples were collected and analyzed for HBV-specific immune responses, liver damage, and viral parameters.

RESULTS

In both models of HBV infection, mice that express hepatocyte-specific small hairpin RNAs or that were given subcutaneous injections of siRNAs had reduced levels of HBV antigens, HBV replication, and viremia (1-3 log₁₀ reduction) compared to mice given control RNAs. Vaccination induced production of HBV-neutralizing antibodies and increased numbers and functionality of HBV-specific, CD8⁺ T cells in mice with low, but not in mice with high, levels of HBV antigen. Mice with initially high titers of HBV and knockdown of HBV antigen expression, but not mice with reduced viremia after administration of entecavir, developed polyfunctional, HBV-specific CD8⁺ T cells, and HBV was eliminated.

CONCLUSIONS

In mice with high levels of HBV replication, knockdown of HBV antigen expression along with a therapeutic vaccination strategy, but not knockdown alone, increased numbers of effector T cells and eliminated the virus. These findings indicate that high titers of virus antigens reduce the efficacy of therapeutic vaccination. Anti-HBV siRNAs and therapeutic vaccines are each being tested in clinical trials-their combination might cure chronic HBV infection.

Total saponins extracted from Abrus cantoniensis Hance suppress hepatitis B virus replication in vitro and in rAAV8-1.3HBV transfected mice

ETHNOPHARMACOLOGICAL RELEVANCE

Hepatitis B, an infectious disease caused by hepatitis B virus (HBV), is still a serious problem affecting global public health. Abrus cantoniensis Hance (AC), a traditional Chinese medicinal herb, has been used as a folk medicine for treating hepatitis in China from ancient times. However, its active ingredients are still unclear.

AIM OF STUDY

Our previous study indicated that saponins extracted from AC (ACS) were the active anti-HBV ingredients in AC. This study aimed to further investigate the anti-HBV effect of ACS in vitro and in vivo.

MATERIALS AND METHODS

HepG2.2.15 cells which consecutively produce HBV DNA and HBV antigens were used for in vitro test, and C57BL/6 mice infected by a recombinant adeno-associated virus 8 vector carrying 1.3 copies of HBV genome (rAAV8-HBV1.3) were used for in vivo test. The histopathological changes and the immune indices were evaluated in mice model. Genechip was conducted to identify genes and pathways regulated by ACS in HepG2.2.15 cells.

RESULTS

In this study, we confirmed that ACS treatment prominently inhibited production of HBV DNA, Hepatitis Be Antigen (HBeAg), and Hepatitis B surface antigen (HBsAg) in HepG2.2.15 cells. ACS treatment also decreased serum HBsAg, HBeAg, and HBV DNA level in rAAV8-1.3HBV transfected mice, which is in accordance with the in vitro results. Moreover, HBV infection-induced liver inflammation was significantly relieved by ACS, which could be observed in H&E staining and immunohistochemistry of HBcAg. ACS treatment elevated IFN-γ level in mice serum and increased CD4⁺ T cell percentage in splenocytes. KEGG pathway analysis showed that phenylalanine metabolism pathway and tyrosine metabolism pathway were greatly regulated by ACS treatment.

CONCLUSION

ACS exerted potent inhibitory effects on HBV replication both in vivo and in vitro, which may provide basis for its potential clinical usage.

Understanding Idiosyncratic Toxicity: Lessons Learned from Drug-Induced Liver Injury

Idiosyncratic adverse drug reactions (IADRs) encompass a diverse group of toxicities that can vary by drug and patient. The complex and unpredictable nature of IADRs combined with the fact that they are rare makes them particularly difficult to predict, diagnose, and treat. Common clinical characteristics, the identification of human leukocyte antigen risk alleles, and drug-induced proliferation of lymphocytes isolated from patients support a role for the adaptive immune system in the pathogenesis of IADRs. Significant evidence also suggests a requirement for direct, drug-induced stress, neoantigen formation, and stimulation of an innate response, which can be influenced by properties intrinsic to both the drug and the patient. This Perspective will provide an overview of the clinical profile, mechanisms, and risk factors underlying IADRs as well as new approaches to study these reactions, focusing on idiosyncratic drug-induced liver injury.

Small Animal Models for Human Immunodeficiency Virus (HIV), Hepatitis B, and Tuberculosis: Proceedings of an NIAID Workshop

The main advantage of animal models of infectious diseases over in vitro studies is the gain in the understanding of the complex dynamics between the immune system and the pathogen. While small animal models have practical advantages over large animal models, it is crucial to be aware of their limitations. Although the small animal model at least needs to be susceptible to the pathogen under study to obtain meaningful data, key elements of pathogenesis should also be reflected when compared to humans. Well-designed small animal models for HIV, hepatitis viruses and tuberculosis require, additionally, a thorough understanding of the similarities and differences in the immune responses between humans and small animals and should incorporate that knowledge into the goals of the study. To discuss these considerations, the NIAID hosted a workshop on 'Small Animal Models for HIV, Hepatitis B, and Tuberculosis' on May 30, 2019. Highlights of the workshop are outlined below.

Human macrophages and innate lymphoid cells: Tissue-resident innate immunity in humanized mice

Macrophages and innate lymphoid cells (ILCs) are tissue-resident cells that play important roles in organ homeostasis and tissue immunity. Their intricate relationship with the organs they reside in allows them to quickly respond to perturbations of organ homeostasis and environmental challenges, such as infection and tissue injury. Macrophages and ILCs have been extensively studied in mice, yet important species-specific differences exist regarding innate immunity between humans and mice. Complementary to ex-vivo studies with human cells, humanized mice (i.e. mice with a human immune system) offer the opportunity to study human macrophages and ILCs in vivo within their surrounding tissue microenvironments. In this review, we will discuss how humanized mice have helped gain new knowledge about the basic biology of these cells, as well as their function in infectious and malignant conditions. Furthermore, we will highlight active areas of investigation related to human macrophages and ILCs, such as their cellular heterogeneity, ontogeny, tissue residency, and plasticity. In the near future, we expect more fundamental discoveries in these areas through the combined use of improved humanized mouse models together with state-of-the-art technologies, such as single-cell RNA-sequencing and CRISPR/Cas9 genome editing.

Antiviral effects of a niobium-substituted heteropolytungstate on hepatitis B virus-transgenic mice

To study the efficacy of a polyoxometalate, Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O, as an antiviral treatment in HBV transgenic mice. HBV transgenic mice were treated with Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O by intragastric administration. Adefovir and distilled water were administered as controls. Serum HBV DNA, liver HBV RNA levels were measured by quantitative RT-PCR. Serum HBsAg levels were measured by ELISA. The hepatitis B virus surface antigen (HBsAg) in liver cells was detected by immunohistochemistry (IHC). Pathological changes in the liver tissues were also observed by light and electron microscopy. Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O significantly decreased serum HBsAg and HBV DNA levels. Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O resulted in a 98% decrease in serum HBV DNA at 28 days, from 4.3 log₁₀ copies/ml at baseline to 2.5 log₁₀ copies/ml after treatment, and the inhibition rate of HBV DNA was higher than ADV at the same dose. The HBV replication levels in each group slightly increased at 7 days after withdrawal, but rebounded slightly more in the Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O treatment group compared to the H₂ O control group (p < .05). There were no differences in HBV RNA levels. No significant differences were observed in the pathology, but there were decreased HBsAg levels in the Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O-treated group compared to the control group. The results demonstrated that Cs₂ K₄ Na[SiW₉ Nb₃ O₄₀ ]·H₂ O displayed potent anti-HBV activity in HBV transgenic mice and supported for future clinic study.

Studying HBV Infection and Therapy in Immune-Deficient NOD-Rag1-/-IL2RgammaC-null (NRG) Fumarylacetoacetate Hydrolase (Fah) Knockout Mice Transplanted with Human Hepatocytes

Chimeric mouse models with a humanized liver provide a unique tool to study hepatic virus diseases, including viral infection, viral pathogenesis, and antiviral therapy. Here we describe a detailed protocol for studying hepatitis B infection in NRG-derived fumarylacetoacetate hydrolase (Fah) knockout mice repopulated with human hepatocytes. The procedures include (1) maintenance and genotyping of the homozygous NRG-fah/fah mutant mice (NRG/F), (2) intrasplenic injection of human hepatocytes, (3) NTBC drug reduction cycling to improve human hepatocyte repopulation, (4) human albumin detection, and (5) HBV infection and detection. The method is simple and allows for highly reproducible generation of NRG/F-hu Hep mice for studying HBV infection and therapy.

Alternative splicing of hepatitis B virus: A novel virus/host interaction altering liver immunity

BACKGROUND & AIMS

Hepatitis B virus (HBV) RNA can undergo alternative splicing, but the relevance of this post-transcriptional regulation remains elusive. The mechanism of HBV alternative splicing regulation and its impact on liver pathogenesis were investigated.

METHODS

HBV RNA-interacting proteins were identified by RNA pull-down, combined with mass spectrometry analysis. HBV splicing regulation was investigated in chemically and surgically induced liver damage, in whole HBV genome transgenic mice and in hepatoma cells. Viral and endogenous gene expression were quantified by quantitative reverse transcription polymerase chain reaction, Western blot and enzyme-linked immunosorbent assay. Resident liver immune cells were studied by fluorescence-activated cell sorting.

RESULTS

HBV pregenomic RNA-interacting proteins were identified and 15% were directly related to the splicing machinery. Expression of these splicing factors was modulated in HBV transgenic mice with liver injuries and contributed to an increase of the HBV spliced RNA encoding for HBV splicing-generated protein (HBSP). HBSP transgenic mice with chemically induced liver fibrosis exhibited attenuated hepatic damage. The protective effect of HBSP resulted from a decrease of inflammatory monocyte/macrophage recruitment through downregulation of C-C motif chemokine ligand 2 (CCL2) expression in hepatocytes. In human hepatoma cells, the ability of HBSP to control CCL2 expression was confirmed and maintained in a whole HBV context. Finally, viral spliced RNA detection related to a decrease of CCL2 expression in the livers of HBV chronic carriers underscored this mechanism.

CONCLUSION

The microenvironment, modified by liver injury, increased HBSP RNA expression through splicing factor regulation, which in turn controlled hepatocyte chemokine synthesis. This feedback mechanism provides a novel insight into liver immunopathogenesis during HBV infection. Lay summary: Hepatitis B virus persists for decades in the liver of chronically infected patients. Immune escape is one of the main mechanisms developed by this virus to survive. Our study highlights how the crosstalk between virus and liver infected cells may contribute to this immune escape.

Markov modeling in hepatitis B screening and linkage to care

Background

With up to 240 million people chronically infected with hepatitis B worldwide, including an estimated 2 million in the United States, widespread screening is needed to link the infected to care and decrease the possible consequences of untreated infection, including liver cancer, cirrhosis and death. Screening is currently fraught with challenges in both the developed and developing world. New point-of-care tests may have advantages over standard-of-care tests in terms of cost-effectiveness and linkage to care. Stochastic modeling is applied here for relative utility assessment of point-of-care tests and standard-of-care tests for screening.

Methods

We analyzed effects of point-of-care versus standard-of-care testing using Markov models for disease progression in individual patients. Simulations of large cohorts with distinctly quantified models permitted the assessment of particular screening schemes. The validity of the trends observed is supported by sensitivity analyses for the simulation parameters.

Results

Increased utilization of point-of-care screening was shown to decrease hepatitis B-related mortalities and increase life expectancy at low projected expense.

Conclusions

The results suggest that standard-of-care screening should be substituted by point-of-care tests resulting in improved linkage to care and decrease in long-term complications.

A new model mimicking persistent HBV e antigen-negative infection using covalently closed circular DNA in immunocompetent mice

Despite the availability of an effective vaccine, hepatitis B virus (HBV) infection remains a major health problem. HBV e antigen (HBeAg)-negative strains have become prevalent. Previously, no animal model mimicked the clinical course of HBeAg-negative HBV infection. To establish an HBeAg-negative HBV infection model, the 3.2-kb full-length genome of HBeAg-negative HBV was cloned from a clinical sample and then circularized to form covalently closed circular (cccDNA). The resulting cccDNA was introduced into the liver of C57BL/6J mice through hydrodynamic injection. Persistence of the HBeAg-negative infection was monitored at predetermined time points using HBV-specific markers including HBV surface antigen (HBsAg), HBeAg, and HBV core antigen (HBcAg) as well as DNA copies. Throughout the study, pAAV-HBV1.2 was used as a control. In mice injected with HBeAg-negative cccDNA, the HBV infection rate was 100% at the initial stage. HBsAg levels increased up to 1 week, at which point levels peaked and dropped quickly thereafter. In 60% of injected mice, HBsAg and HBcAg persisted for more than 10 weeks. High numbers of HBV DNA copies were detected in the serum and liver. Moreover, cccDNA persisted in the liver tissue of HBeAg-negative mice. In contrast to the pAAV-HBV 1.2 injected mice, no HBeAg was found in mice injected with HBeAg-negative HBV throughout the study period. These results demonstrate the first successful establishment of a model of HBeAg-negative HBV-persistent infection in immunocompetent mice. Compared to pAAV-HBV1.2-injected mice, the infection persistence and levels of serum virological and biochemical markers were approximately equal in the model mice. This model will be useful for mechanistic studies on HBeAg-negative HBV infection and will facilitate the evaluation of new antiviral drugs.

Humanized chimeric mouse models of hepatitis B virus infection

Hepatitis B virus (HBV) infection is associated with an increased risk of hepatic cirrhosis, hepatocellular carcinoma, fulminant hepatitis and end-stage hepatic failure. Despite the availability of anti-HBV therapies, HBV infection remains a major global public health problem. Developing an ideal animal model of HBV infection to clarify the details of the HBV replication process, the viral life cycle, the resulting immunoresponse and the precise pathogenesis of HBV is difficult because HBV has an extremely narrow host range and almost exclusively infects humans. In this review, we summarize and evaluate animal models available for studying HBV infection, especially focusing on humanized chimeric mouse models, and we discuss future development trends regarding immunocompetent humanized mouse models that can delineate the natural history and immunopathophysiology of HBV infection.

Drug-induced liver injury: Advances in mechanistic understanding that will inform risk management

Drug-induced liver injury (DILI) is a major public health problem. Intrinsic (dose-dependent) DILI associated with acetaminophen overdose is the number one cause of acute liver failure in the US. However, the most problematic type of DILI impacting drug development is idiosyncratic, occurring only very rarely among treated patients and often only after several weeks or months of treatment with the offending drug. Recent advances in our understanding of the pathogenesis of DILI suggest that three mechanisms may underlie most hepatocyte effects in response to both intrinsic and idiosyncratic DILI drugs: mitochondrial dysfunction, oxidative stress, and alterations in bile acid homeostasis. However, in some cases hepatocyte stress promotes an immune response that results in clinically important idiosyncratic DILI. This review discusses recent advances in our understanding of the pathogenesis of both intrinsic and idiosyncratic DILI as well as emerging tools and techniques that will likely improve DILI risk identification and management.

An ELISPOT-Based Assay to Measure HBV-Specific CD8+ T Cell Responses in Immunocompetent Mice

Despite some important limitations, immunocompetent mouse models of HBV replication remain an essential tool for studying cellular and humoral immunity to the virus. CD8⁺ T cells are a critical component of the immune response to HBV due to their ability to both kill virus-infected hepatocytes and produce cytokines such as IFN-γ that non-cytopathically inhibit virus replication. A number of techniques can be used to measure the magnitude, specificity, and functionality of HBV-specific CD8⁺ T cells, each having its own unique advantages. We describe here the enzyme-linked immunospot (ELISPOT)-based assay, which, compared to other methods, is sensitive, cost-effective, and rapid and requires relatively little optimization, specialized training, or equipment.

Humanized Mouse Models of Clinical Disease

Immunodeficient mice engrafted with functional human cells and tissues, that is, humanized mice, have become increasingly important as small, preclinical animal models for the study of human diseases. Since the description of immunodeficient mice bearing mutations in the IL2 receptor common gamma chain (IL2rg^null) in the early 2000s, investigators have been able to engraft murine recipients with human hematopoietic stem cells that develop into functional human immune systems. These mice can also be engrafted with human tissues such as islets, liver, skin, and most solid and hematologic cancers. Humanized mice are permitting significant progress in studies of human infectious disease, cancer, regenerative medicine, graft-versus-host disease, allergies, and immunity. Ultimately, use of humanized mice may lead to the implementation of truly personalized medicine in the clinic. This review discusses recent progress in the development and use of humanized mice and highlights their utility for the study of human diseases.

Hepatitis B virus molecular biology and pathogenesis

As obligate intracellular parasites, viruses need a host cell to provide a milieu favorable to viral replication. Consequently, viruses often adopt mechanisms to subvert host cellular signaling processes. While beneficial for the viral replication cycle, virus-induced deregulation of host cellular signaling processes can be detrimental to host cell physiology and can lead to virus-associated pathogenesis, including, for oncogenic viruses, cell transformation and cancer progression. Included among these oncogenic viruses is the hepatitis B virus (HBV). Despite the availability of an HBV vaccine, 350-500 million people worldwide are chronically infected with HBV, and a significant number of these chronically infected individuals will develop hepatocellular carcinoma (HCC). Epidemiological studies indicate that chronic infection with HBV is the leading risk factor for the development of HCC. Globally, HCC is the second highest cause of cancer-associated deaths, underscoring the need for understanding mechanisms that regulate HBV replication and the development of HBV-associated HCC. HBV is the prototype member of the Hepadnaviridae family; members of this family of viruses have a narrow host range and predominately infect hepatocytes in their respective hosts. The extremely small and compact hepadnaviral genome, the unique arrangement of open reading frames, and a replication strategy utilizing reverse transcription of an RNA intermediate to generate the DNA genome are distinguishing features of the Hepadnaviridae. In this review, we provide a comprehensive description of HBV biology, summarize the model systems used for studying HBV infections, and highlight potential mechanisms that link a chronic HBV-infection to the development of HCC. For example, the HBV X protein (HBx), a key regulatory HBV protein that is important for HBV replication, is thought to play a cofactor role in the development of HBV-induced HCC, and we highlight the functions of HBx that may contribute to the development of HBV-associated HCC.

Experimental models of hepatitis B and C - new insights and progress

Viral hepatitis is a major cause of morbidity and mortality, affecting hundreds of millions of people worldwide. Hepatitis-causing viruses initiate disease by establishing both acute and chronic infections, and several of these viruses are specifically associated with the development of hepatocellular carcinoma. Consequently, intense research efforts have been focusing on increasing our understanding of hepatitis virus biology and on improving antiviral therapy and vaccination strategies. Although valuable information on viral hepatitis emerged from careful epidemiological studies on sporadic outbreaks in humans, experimental models using cell culture, rodent and non-human primates were essential in advancing the field. Through the use of these experimental models, improvement in both the treatment and prevention of viral hepatitis has progressed rapidly; however, agents of viral hepatitis are still among the most common pathogens infecting humans. In this Review, we describe the important part that these experimental models have played in the study of viral hepatitis and led to monumental advances in our understanding and treatment of these pathogens. Ongoing developments in experimental models are also described.

A historical perspective on the discovery and elucidation of the hepatitis B virus

The discovery in 1965 of the "Australia antigen," subsequently identified as the hepatitis B virus surface antigen (HBsAg), was such a watershed event in virology that it is often thought to mark the beginning of hepatitis research, but it is more accurately seen as a critical breakthrough in a long effort to understand the pathogenesis of infectious hepatitis. A century earlier, Virchow provided an authoritative explanation of "catarrhal jaundice," which did not consider an infectious etiology, but the transmission of jaundice by human serum was clearly identified in two outbreaks in 1885, and the distinction between "infectious" and "serum" hepatitis was recognized by the early 1920s. The inability to culture a virus or reproduce either syndrome in laboratory animals led to numerous studies in human volunteers; by the end of World War II, it was known that the diseases were caused by different filterable agents, and the terms "hepatitis A" and "B" were introduced in 1947 (though some long-incubation cases then designated B must in retrospect have been hepatitis C). The development of a number of liver function tests during the 1950s led to the recognition of anicteric infections and the existence of chronic carriers, but little more could be done until an infectious agent had been identified. Once Blumberg and colleagues had found a specific viral marker, the vast amount of accumulated epidemiologic and clinical data, together with huge numbers of stored serum samples, enabled rapid progress in understanding hepatitis B, and revealed the existence of a vast population of chronically infected people in Asia, Oceania and Africa. In this article, we place the identification of the Australia antigen within the historical context of research on viral hepatitis. Following a chronological review from 1865 to 1965, we summarize how the discovery led to improved safety of blood transfusion, the development of a highly effective vaccine and the eventual identification of the hepatitis C, D and E viruses. This article forms part of a symposium in Antiviral Research on "An unfinished story: from the discovery of the Australia antigen to the development of new curative therapies for chronic hepatitis B."

Institutional Animal Care and Use Committee Considerations Regarding the Use of Virus-Induced Carcinogenesis and Oncolytic Viral Models

The use of virus-induced carcinogenesis and oncologic experimental animal models is essential in understanding the mechanisms of cancer development to advance prevention, diagnosis, and treatment methods. The Institutional Animal Care and Use Committee (IACUC) is responsible for both the complex philosophical and practical considerations associated with animal models of cancer. Animal models of cancer carry their own unique issues that require special consideration from the IACUC. Many of the considerations to be discussed apply to cancer models in general; specific issues related to viral carcinogenesis or oncolytic viruses will be specifically discussed as they arise. Responsible animal use integrates good science, humane care, and regulatory compliance. To meet those standards, the IACUC, in conjunction with the research investigator and attending veterinarian, must address a wide range of issues, including animal model selection, cancer model selection, humane end point considerations, experimental considerations, postapproval monitoring, reporting requirements, and animal management and personnel safety considerations.

Targeting hepatitis B virus cccDNA using CRISPR/Cas9

Despite the existence of an excellent prophylactic vaccine and the development of highly effective inhibitors of the viral polymerase, chronic hepatitis B virus (HBV) infection remains a major source of morbidity and mortality, especially in Africa and Asia. A significant problem is that, while polymerase inhibitors can effectively prevent the production of viral genomic DNA from pre-genomic RNA transcripts, they do not prevent the transcription and translation of viral mRNAs from the covalently closed circular DNA (cccDNA) templates present in the nuclei of infected cells. Moreover, because these cccDNAs are highly stable, chronic HBV infections are only very rarely cured by the use of polymerase inhibitors and these drugs clearly cannot entirely prevent the subsequent development of HBV-related morbidities such as cirrhosis and hepatocellular carcinoma. As a result, there has been considerable interest in the possibility of developing treatment approaches that directly target cccDNA for elimination. Here, we discuss recent publications that analyze the ability of the bacterial CRISPR/Cas DNA editing machinery to be repurposed as a tool for the specific cleavage and destruction of HBV cccDNAs in the nuclei of infected cells and consider which steps will be necessary to make CRISPR/Cas targeting of HBV DNA a clinically feasible approach to the treatment of chronic infections in humans. This article forms part of a symposium in Antiviral Research on "An unfinished story: from the discovery of the Australia antigen to the development of new curative therapies for hepatitis B."

Hepatitis B virus reverse transcriptase - Target of current antiviral therapy and future drug development

Hepatitis B virus (HBV) infections rely on the proper functioning of the viral polymerase enzyme, a specialized reverse transcriptase (RT) with multiple activities. All currently approved antiviral drugs for the treatment of chronic HBV infection, except for interferon, target the RT and belong to the same chemical class - they are all nucleoside analogs. Viral DNA synthesis is carried out by the RT enzyme in several different steps, each with distinct RT conformational requirements. In principle, each stage may be targeted by distinct antiviral drugs. In particular, the HBV RT has the unique ability to initiate viral DNA synthesis using itself as a protein primer in a novel protein priming reaction. In order to help identify RT inhibitors and study their mechanisms of action, a number of experimental systems have been developed, each varying in its ability to dissect the protein priming stage and subsequent stages of viral DNA synthesis at the molecular level. Two of the most effective drugs to date, entecavir and tenofovir, can inhibit both the protein priming and the subsequent DNA elongation stages of HBV DNA synthesis. Interestingly, clevudine, a thymidine analog, can inhibit both protein priming and DNA elongation in a non-competitive manner and without being incorporated into the viral DNA. Thus, a nucleoside RT inhibitor (NRTI) can functionally mimic a non-NRTI (NNRTI) in its inhibition of the HBV RT. Therefore, novel NRTIs as well as NNRTIs may be developed to inhibit the DNA synthesis activity of the HBV RT. Furthermore, additional activities of the RT that are also essential to HBV replication, including specific recognition of the viral RNA and its packaging into viral nucleocapsids, may be exploited for antiviral development. To achieve a more potent inhibition of viral replication and ultimately cure chronic HBV infection, the next generation of anti-HBV therapies will likely need to include NRTIs, NNRTIs, and other agents that target the viral RT as well as other viral and host factors in various combinations. This article forms part of a symposium in Antiviral Research on "An unfinished story: from the discovery of the Australia antigen to the development of new curative therapies for hepatitis B."