Hepatitis B virus replication in human HepG2 cells mediated by hepatitis B virus recombinant baculovirus

Stem Cell-Derived Hepatocyte-Like Cells for Hepatitis B Virus Infection

Hepatitis B, the leading cause of liver diseases worldwide, is a result of infection with hepatitis B virus (HBV). Due to its obligate intracellular life cycle, culture systems for efficient HBV replication are vital. Although basic and translational research on HBV has been performed for many years, conventional hepatocellular culture systems are not optimal. These studies have greatly benefited from recent improvements in cell culture models based on stem cell technology for HBV replication and infection studies. Here we describe a protocol for the differentiation of human stem cell-derived hepatocyte-like cells (HLCs) and subsequent HBV infection. HLCs are capable of expressing hepatocyte markers and host factors important for hepatic function maintenance. These cells fully support HBV infection and virus-host interactions. Stem cell-derived HLCs provide a new tool for antiviral drug screening and development.

Recovery Infectious Enterovirus 71 by Bac-to-Bac Expression System in vitro and in vivo

Enterovirus 71 (EV71) is one of the most important etiological agents for hand-foot-mouth disease. Compared with coxsackievirus A16 infection, EV71 infection is often associated with severe central nervous system complications, such as encephalitis, encephalomyelitis, and acute flaccid paralysis in infants and young children. In this study, we constructed a recombinant baculovirus with T7 ribonucleic acid polymerase under the control of a cytomegalovirus promoter and simultaneously engineered the T7 promoter upstream of a full-length EV71 complementary deoxyribonucleic acid. After transduction into mammalian cells, typical cytopathic effects (CPEs) and VP1 signals were detected in cells transfected with recombinant baculovirus. Additionally, viral particles located in the cytoplasm of human rhabdomyosarcoma cells (Rd) and Vero cells were observed by electron microscope, indicating that EV71 was recovered using a Bac-to-Bac expression system in vitro. After four passages, the rescued virus had a growth curve and plaque morphology similar to those of the parental virus. Furthermore, the Vp1 gene and the protein from the mouse brain were detected by reverse transcription polymerase chain reaction and immunohistochemistry after intracerebral injection of purified recombinant baculovirus. Typical CPEs were observed after inoculation of the supernatant from mouse brain to Rd cells, revealing a reconstruction of EV71 in vivo. Thus, we established a new approach to rescue EV71 based on a baculovirus expression system in vitro and in vivo, which may provide a safe and convenient platform for fundamental research and a strategy to rescue viruses that currently lack suitable cell culture and animal models.

SMYD3 promotes hepatocellular carcinoma progression by methylating S1PR1 promoters

Hepatocellular carcinoma (HCC) is one of the most common malignancies worldwide. SET and MYND domain-containing protein 3 (SMYD3) has been shown to promote the progression of various types of human cancers, including liver cancer; however, the detailed molecular mechanism is still largely unknown. Here, we report that SMYD3 expression in HCC is an independent prognostic factor for survival and promotes the proliferation and migration of HCC cells. We observed that SMYD3 upregulated sphingosine-1-phosphate receptor 1 (S1PR1) promoter activity by methylating histone 3 (H3K4me3). S1PR1 was expressed at high levels in HCC samples, and high S1PR1 expression was associated with shorter survival. S1PR1 expression was also positively correlated with SMYD3 expression in HCC samples. We confirmed that SMYD3 promotes HCC cell growth and migration in vitro and in vivo by upregulating S1PR1 expression. Further investigations revealed that SMYD3 affects critical signaling pathways associated with the progression of HCC through S1PR1. These findings strongly suggest that SMYD3 has a crucial function in HCC progression that is partially mediated by histone methylation at the downstream gene S1PR1, which affects key signaling pathways associated with carcinogenesis and the progression of HCC.

A novel piperazine derivative that targets hepatitis B surface antigen effectively inhibits tenofovir resistant hepatitis B virus

Chronic hepatitis B virus (HBV) infection is a global problem. The loss of hepatitis B surface antigen (HBsAg) in serum is a therapeutic end point. Prolonged therapy with nucleoside/nucleotide analogues targeting the HBV-polymerase may lead to resistance and rarely results in the loss of HBsAg. Therefore, inhibitors targeting HBsAg may have potential therapeutic applications. Here, we used computational virtual screening, docking, and molecular dynamics simulations to identify potential small molecule inhibitors against HBsAg. After screening a million molecules from ZINC database, we identified small molecules with potential anti-HBV activity. Subsequently, cytotoxicity profiles and anti-HBV activities of these small molecules were tested using a widely used cell culture model for HBV. We identified a small molecule (ZINC20451377) which binds to HBsAg with high affinity, with a KD of 65.3 nM, as determined by Surface Plasmon Resonance spectroscopy. Notably, the small molecule inhibited HBsAg production and hepatitis B virion secretion (10 μM) at low micromolar concentrations and was also efficacious against a HBV quadruple mutant (CYEI mutant) resistant to tenofovir. We conclude that this small molecule exhibits strong anti-HBV properties and merits further testing.

Advances in HBV infection and replication systems in vitro

Background

Hepatitis B virus (HBV) is a DNA virus belonging to the Hepadnaviridae family that has limited tissue and species specificity. Due to the persistence of HBV covalently closed circular DNA (cccDNA) in host cells after HBV infection, current antiviral drugs cannot eradicate HBV. Therefore, the development of an active cell culture system supporting HBV infection has become the key to studying HBV and developing effective therapeutic drugs.

Main body

This review summarizes the significant research achievements in HBV cell culture systems in vitro, including embryonic hepatocytes and primary hepatocytes, which support the virus infection process most similar to that in the body and various liver tumor cells. The discovery of the bile-acid pump sodium-taurocholate co-transporting polypeptide (NTCP) as the receptor of HBV has advanced our understanding of HBV biology. Subsequently, various liver cancer cells overexpressing NTCP that support HBV infection have been established, opening a new door for studying HBV infection. The fact that induced pluripotent stem cells that differentiate into hepatocyte-like cells support HBV infection provides a novel idea for the establishment of an HBV cell culture system.

Conclusion

Because of the host and tissue specificity of HBV, a suitable in vitro HBV infection system is critical for the study of HBV pathogenesis. Nevertheless, recent advances regarding HBV infection in vitro offer hope for better studying the biological characteristics of HBV, the pathogenesis of hepatitis B, the screening of anti-HBV drugs and the mechanism of carcinogenesis.

Synthesis and evaluation of new phenyl acrylamide derivatives as potent non-nucleoside anti-HBV agents

As a continuation of our previous work, a series of new phenyl acrylamide derivatives (4Aa-g, 4Ba-t, 5 and 6a-c) were designed and synthesized as non-nucleoside anti-HBV agents. Among them, compound 4Bs could potently inhibit HBV DNA replication in wild-type and lamivudine (3TC)/entecavir resistant HBV mutant strains with IC₅₀ values of 0.19 and 0.18 μM, respectively. Notably, the selective index value of 4Bs was above 526, indicating the favorable safety profile. Interestingly, unlike nucleoside analogue 3TC, 4Bs could significantly inhibit 3.5 kb pgRNA expression. Molecular docking study revealed that 4Bs could fit well into the dimer-dimer interface of HBV core protein by hydrophobic, π-π and H-bond interactions. Considering the potent anti-HBV activity, low toxicity and diverse anti-HBV mechanism from that of nucleoside anti-HBV agent 3TC, compound 4Bs might be a promising lead to develop novel non-nucleoside anti-HBV therapeutic agents, and warranted further investigation.

In Vitro Systems for Studying Different Genotypes/Sub-Genotypes of Hepatitis B Virus: Strengths and Limitations

Hepatitis B virus (HBV) infects the liver resulting in end stage liver disease, cirrhosis, and hepatocellular carcinoma. Despite an effective vaccine, HBV poses a serious health problem globally, accounting for 257 million chronic carriers. Unique features of HBV, including its narrow virus-host range and its hepatocyte tropism, have led to major challenges in the development of suitable in vivo and in vitro model systems to recapitulate the HBV replication cycle and to test various antiviral strategies. Moreover, HBV is classified into at least nine genotypes and 35 sub-genotypes with distinct geographical distributions and prevalence, which have different natural histories of infection, clinical manifestation, and response to current antiviral agents. Here, we review various in vitro systems used to study the molecular biology of the different (sub)genotypes of HBV and their response to antiviral agents, and we discuss their strengths and limitations. Despite the advances made, no system is ideal for pan-genotypic HBV research or drug development and therefore further improvement is required. It is necessary to establish a centralized repository of HBV-related generated materials, which are readily accessible to HBV researchers, with international collaboration toward advancement and development of in vitro model systems for testing new HBV antivirals to ensure their pan-genotypic and/or customized activity.

Construction of a replication-competent hepatitis B virus vector carrying secreted luciferase transgene and establishment of new hepatitis B virus replication and expression cell lines

BACKGROUND

Previously, we have successfully constructed replication-competent hepatitis B virus (HBV) vectors by uncoupling the P open reading frame (ORF) from the preC/C ORF to carefully design the transgene insertion site to overcome the compact organization of the HBV genome and maintain HBV replication competence. Consequently, the replication-competent HBV vectors carrying foreign genes, including pCH-BsdR, carrying blasticidin resistance gene (399 bp), and pCH-hrGFP, carrying humanized renilla green fluorescent protein gene (720 bp), were successfully obtained. However, the replication efficiency of the former is higher but it is tedious to use, while that of the latter is poor and cannot be quantified. Hence, we need to search for a new reporter gene that is convenient and quantifiable for further research.

AIM

To establish a helpful tool for intracellular HBV replication and anti-viral drugs screening studies.

METHODS

We utilized the replication-competent HBV viral vectors constructed by our laboratory, combined with the secreted luciferase reporter gene, to construct replication-competent HBV vectors expressing the reporter gene secretory Nanoluc Luciferase (SecNluc). HepG2.TA2-7 cells were transfected with this vector to obtain cell lines with stably secreted HBV particles carrying secNluc reporter gene.

RESULTS

The replication-competent HBV vector carrying the SecNluc reporter gene pCH-sNLuc could produce all major viral RNAs and a full set of envelope proteins and achieve high-level secreted luciferase expression. HBV replication intermediates could be produced from this vector. Via transfection with pTRE-sNLuc and selection by hygromycin, we obtained isolated cell clones, named HBV-NLuc-35 cells, which could secrete secNLuc recombinant viruses, and were sensitive to existing anti-HBV drugs. Using differentiated HepaRG cells, it was verified that recombinant HBV possessed infectivity.

CONCLUSION

Our research demonstrated that a replication-competent HBV vector carrying a secreted luciferase transgene possesses replication and expression ability, and the established HBV replication and expression cell lines could stably secrete viral particles carrying secNluc reporter gene. More importantly, the cell line and the secreted recombinant viral particles could be used to trace HBV replication or infection.

Stem Cell-Derived Hepatocyte-Like Cells as Model for Viral Hepatitis Research

Viral hepatitis, the leading cause of liver diseases worldwide, is induced upon infection with hepatotropic viruses, including hepatitis A, B, C, D, and E virus. Due to their obligate intracellular lifestyles, culture systems for efficient viral replication are vital. Although basic and translational research on viral hepatitis has been performed for many years, conventional hepatocellular culture systems are not optimal. These studies have greatly benefited from recent efforts on improving cell culture models for virus replication and infection studies. Here we summarize the use of human stem cell-derived hepatocyte-like cells for hepatotropic virus infection studies, including the dissection of virus-host interactions and virus-induced pathogenesis as well as the identification and validation of novel antiviral agents.

Assessment of quinazolinone derivatives as novel non-nucleoside hepatitis B virus inhibitors

Hepatitis B virus (HBV) infection is a worldwide public health issue. Search for novel non-nucleoside anti-HBV agents is of great importance. In the present study, a series of quinazolinones derivatives (4a-t and 5a-f) were synthesized and evaluated as novel anti-HBV agents. Among them, compounds 5e and 5f could significantly inhibit HBV DNA replication with IC₅₀ values of 1.54 μM and 0.71 μM, respectively. Interestingly, the selective index values of 5f was higher than that of lead compound K284-1405, suggesting 5f possessed relatively safety profile than K284-1405. Notably, 5e and 5f exhibited remarkably anti-HBV activities against lamivudine and entecavir resistant HBV strain with IC₅₀ values of 1.90 and 0.84 μM, confirming their effectiveness against resistant HBV strain. In addition, molecular docking studies indicated that compounds 5e and 5f could well fit into the dimer-dimer interface of HBV core protein dominated by hydrophobic interactions. Notably, their binding modes were different from the lead compound K284-1405, which may be attributed to the additional substituent groups in the quinazolinone scaffold. Taken together, 5e and 5f possessed novel chemical structure and potent anti-HBV activity against both drug sensitive and resistant HBV strains, thus warranting further research as potential non-nucleoside anti-HBV candidates.

Hepatitis B Virus Deregulates the Cell Cycle To Promote Viral Replication and a Premalignant Phenotype

Hepatitis B virus (HBV) infection is a major health problem worldwide, and chronically infected individuals are at high risk of developing cirrhosis and hepatocellular carcinoma (HCC). The molecular mechanisms whereby HBV causes HCC are largely unknown. Using a biologically relevant system of HBV infection of primary human hepatocytes (PHHs), we studied how HBV perturbs gene expression and signaling pathways of infected hepatocytes and whether these effects are relevant to productive HBV infection and HBV-associated HCC. Using a human growth factor antibody array, we first showed that HBV infection induced a distinct profile of growth factor production by PHHs, marked particularly by significantly lower levels of the transforming growth factor β (TGF-β) family of proteins in the supernatant. Transcriptome profiling next revealed multiple changes in cell proliferation and cell cycle control pathways in response to HBV infection. A human cell cycle PCR array validated deregulation of more than 20 genes associated with the cell cycle in HBV-infected PHHs. Cell cycle analysis demonstrated that HBV-infected PHHs are enriched in the G₂/M phase compared to the predominantly G₀/G₁ phase of cultured PHHs. HBV proviral host factors, such as PPARA, RXRA, and CEBPB, were upregulated upon HBV infection and particularly enriched in cells in the G₂/M phase. Together, these results support the notion that HBV deregulates cell cycle control to render a cellular environment that is favorable for productive HBV infection. By perturbing cell cycle regulation of infected cells, HBV may coincidently induce a premalignant phenotype that predisposes infected hepatocytes to subsequent malignant transformation.IMPORTANCE Hepatitis B virus (HBV) infection is a major health problem with high risk of developing hepatocellular carcinoma (HCC). By using a biologically relevant system of HBV infection of primary human hepatocytes (PHHs), we studied how HBV perturbs gene expression and whether these effects are relevant to HBV-associated HCC. HBV induced a distinct profile of growth factor production, marked particularly by significantly lower levels of the transforming growth factor β (TGF-β) family of proteins. Transcriptome profiling revealed multiple changes in cell proliferation and cell cycle control pathways. Cell cycle analysis demonstrated that HBV-infected PHHs are enriched in the G₂/M phase. HBV proviral host factors were upregulated upon infection and particularly enriched in cells in the G₂/M phase. Together, these results support the notion that HBV deregulates cell cycle control to render a cellular environment that is favorable for productive infection. This may coincidently induce a premalignant phenotype that predisposes infected hepatocytes to subsequent malignant transformation.

Hepatitis B Virus DNA Integration Occurs Early in the Viral Life Cycle in an In Vitro Infection Model via Sodium Taurocholate Cotransporting Polypeptide-Dependent Uptake of Enveloped Virus Particles

Chronic infection by hepatitis B virus (HBV) is the major contributor to liver disease worldwide. Though HBV replicates via a nuclear episomal DNA (covalently closed circular DNA [cccDNA]), integration of HBV DNA into the host cell genome is regularly observed in the liver in infected patients. While reported as a prooncogenic alteration, the mechanism(s) and timing of HBV DNA integration are not well understood, chiefly due to the lack of in vitro infection models that have detectable integration events. In this study, we have established an in vitro system in which integration can be reliably detected following HBV infection. We measured HBV DNA integration using inverse nested PCR in primary human hepatocytes, HepaRG-NTCP, HepG2-NTCP, and Huh7-NTCP cells after HBV infection. Integration was detected in all cell types at a rate of >1 per 10,000 cells, with the most consistent detection in Huh7-NTCP cells. The integration rate remained stable between 3 and 9 days postinfection. HBV DNA integration was efficiently blocked by treatment with a 200 nM concentration of the HBV entry inhibitor Myrcludex B, but not with 10 μM tenofovir, 100 U of interferon alpha, or a 1 μM concentration of the capsid assembly inhibitor GLS4. This suggests that integration of HBV DNA occurs immediately after infection of hepatocytes and is likely independent of de novo HBV genome replication in this model. Site analysis revealed that HBV DNA integrations were distributed over the entire human genome. Further, integrated HBV DNA sequences were consistent with double-stranded linear HBV DNA being the major precursor. Thus, we have established an in vitro system to interrogate the mechanisms of HBV DNA integration.IMPORTANCE Hepatitis B virus (HBV) is a common blood-borne pathogen and, following a chronic infection, can cause liver cancer and liver cirrhosis. Integration of HBV DNA into the host genome occurs in all known members of the Hepadnaviridae family, despite this form not being necessary for viral replication. HBV DNA integration has been reported to drive liver cancer formation and persistence of virus infection. However, when and the mechanism(s) by which HBV DNA integration occurs are not clear. In this study, we have developed and characterized an in vitro system to reliably detect HBV DNA integrations that result from a true HBV infection event and that closely resemble those found in patient tissues. Using this model, we showed that integration occurs when the infection is first established. Importantly, we provide here a system to analyze molecular factors involved in HBV integration, which can be used to develop strategies to halt its formation.

Human stem cell-derived hepatocytes as a model for hepatitis B virus infection, spreading and virus-host interactions

BACKGROUND & AIMS

One major obstacle of hepatitis B virus (HBV) research is the lack of efficient cell culture system permissive for viral infection and replication. The aim of our study was to establish a robust HBV infection model by using hepatocyte-like cells (HLCs) derived from human pluripotent stem cells.

METHODS

HLCs were differentiated from human embryonic stem cells and induced pluripotent stem cells. Maturation of hepatocyte functions was determined. After HBV infection, total viral DNA, cccDNA, total viral RNA, pgRNA, HBeAg and HBsAg were measured.

RESULTS

More than 90% of the HLCs expressed strong signals of human hepatocyte markers, like albumin, as well as known host factors required for HBV infection, suggesting that these cells possessed key features of mature hepatocytes. Notably, HLCs expressed the viral receptor sodium-taurocholate cotransporting polypeptide more stably than primary human hepatocytes (PHHs). HLCs supported robust infection and some spreading of HBV. Finally, by using this model, we identified two host-targeting agents, genistin and PA452, as novel antivirals.

CONCLUSIONS

Stem cell-derived HLCs fully support HBV infection. This novel HLC HBV infection model offers a unique opportunity to advance our understanding of the molecular details of the HBV life cycle; to further characterize virus-host interactions and to define new targets for HBV curative treatment.

LAY SUMMARY

Our study used human pluripotent stem cells to develop hepatocyte-like cells (HLCs) capable of expressing hepatocyte markers and host factors important for HBV infection. These cells fully support HBV infection and virus-host interactions, allowing for the identification of two novel antiviral agents. Thus, stem cell-derived HLCs provide a highly physiologically relevant system to advance our understanding of viral life cycle and provide a new tool for antiviral drug screening and development.

In Vitro Studies Show that Sequence Variability Contributes to Marked Variation in Hepatitis B Virus Replication, Protein Expression, and Function Observed across Genotypes

The hepatitis B virus (HBV) exists as 9 major genotypes (A to I), one minor strain (designated J) and multiple subtypes. Marked differences in HBV natural history, disease progression and treatment response are exhibited by many of these genotypes and subtypes. For example, HBV genotype C is associated with later hepatitis B e antigen (HBeAg) seroconversion and high rates of liver cancer compared to other HBV genotypes, whereas genotype A2 is rarely associated with HBeAg-negative disease or liver cancer. The reasons for these and other differences in HBV natural history are yet to be determined but could in part be due to sequence differences in the HBV genome that alter replicative capacity and/or gene expression. Direct comparative studies on HBV replication and protein expression have been limited to date due largely to the absence of infectious HBV cDNA clones for each of the HBV genotypes present in the same genetic arrangement. We have produced replication-competent infectious cDNA clones of the most common subtypes of genotypes A to D, namely, A2, B2, C2, D3, and the minor strain J, and compared their HBV replication phenotype using transient-transfection models. We identified striking differences in HBV replicative capacity as well as HBeAg and surface (HBsAg) protein expression across genotypes, which may in part be due to sequence variability in regulatory regions of the HBV genome. Functional analysis showed that sequence differences in the major upstream regulatory region across genotypes impacted promoter activity.

IMPORTANCE

There have been very few studies directly comparing the replication phenotype of different HBV genotypes, for which there are marked differences in natural history and disease progression worldwide. We have generated replication-competent 1.3-mer cDNA clones of the major genotypes A2, B2, C2, and D3, as well as a recently identified strain J, and identified striking differences in replicative capacity and protein expression that may contribute to some of the observed differences in HBV natural history observed globally.

α-Glucosidase Inhibitors Have a Prolonged Antiviral Effect against Hepatitis B Virus through the Sustained Inhibition of the Large and Middle Envelope Glycoproteins

Previous work has shown that the secretion of enveloped hepatitis B virus (HBV) DNA and the HBV middle envelope protein (MHBs) are sensitive to glucosidase inhibition. Here, it is shown that HBV DNA secretion remains depressed after the removal of the glucosidase inhibitor and long after glucosidase function returns to normal. For example, glycoprocessing and the secretion of α-1 anti-trypsin returned to normal within 3 h of the removal of the glucosidase inhibitor. In contrast, the secretion of HBV did not return to normal for more than 7 days after the removal of the inhibitor. Consistent with the inhibition of HBV virion secretion, the levels of HBV L and HBV M proteins were also reduced by treatment with the glucosidase inhibitor and remained reduced for 7 days after compound withdrawal. The implications of the prolonged antiviral effect against HBV and the use of glucosidase inhibitors as antiviral agents are discussed.

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.

The recombined cccDNA produced using minicircle technology mimicked HBV genome in structure and function closely

HBV covalently closed circular DNA (cccDNA) is drug-resistant and responsible for viral persistence. To facilitate the development of anti-cccDNA drugs, we developed a minicircle DNA vector (MC)-based technology to produce large quantity of recombined cccDNA (rcccDNA) resembling closely to its wild-type counterpart both in structure and function. The rcccDNA differed to the wild-type cccDNA (wtcccDNA) only in that it carried an extra 36-bp DNA recombinant product attR upstream of the preC/C gene. Using a procedure similar to standard plasmid production, milligrams of rcccDNA can be generated in common laboratories conveniently. The rcccDNA demonstrated many essential biological features of wtcccDNA, including: (1) undergoing nucleation upon nucleus entry; (2) serving as template for production of all HBV RNAs and proteins; (3) deriving virions capable of infecting tree shrew, and subsequently producing viral mRNAs, proteins, rcccDNA and infectious virions. As an example to develop anti-cccDNA drugs, we used the Crispr/Cas9 system to provide clear-cut evidence that rcccDNA was cleaved by this DNA editing tool in vitro. In summary, we have developed a convenient technology to produce large quantity of rcccDNA as a surrogate of wtcccDNA for investigating HBV biology and developing treatment to eradicate this most wide-spreading virus.

Advances and Challenges in Studying Hepatitis B Virus In Vitro

Hepatitis B virus (HBV) is a small DNA virus that infects the liver. Current anti-HBV drugs efficiently suppress viral replication but do not eradicate the virus due to the persistence of its episomal DNA. Efforts to develop reliable in vitro systems to model HBV infection, an imperative tool for studying HBV biology and its interactions with the host, have been hampered by major limitations at the level of the virus, the host and infection readouts. This review summarizes major milestones in the development of in vitro systems to study HBV. Recent advances in our understanding of HBV biology, such as the discovery of the bile-acid pump sodium-taurocholate cotransporting polypeptide (NTCP) as a receptor for HBV, enabled the establishment of NTCP expressing hepatoma cell lines permissive for HBV infection. Furthermore, advanced tissue engineering techniques facilitate now the establishment of HBV infection systems based on primary human hepatocytes that maintain their phenotype and permissiveness for infection over time. The ability to differentiate inducible pluripotent stem cells into hepatocyte-like cells opens the door for studying HBV in a more isogenic background, as well. Thus, the recent advances in in vitro models for HBV infection holds promise for a better understanding of virus-host interactions and for future development of more definitive anti-viral drugs.

Stable Human Hepatoma Cell Lines for Efficient Regulated Expression of Nucleoside/Nucleotide Analog Resistant and Vaccine Escape Hepatitis B Virus Variants and Woolly Monkey Hepatitis B Virus

Hepatitis B virus (HBV) causes acute and chronic hepatitis B (CHB). Due to its error-prone replication via reverse transcription, HBV can rapidly evolve variants that escape vaccination and/or become resistant to CHB treatment with nucleoside/nucleotide analogs (NAs). This is particularly problematic for the first generation NAs lamivudine and adefovir. Though now superseded by more potent NAs, both are still widely used. Furthermore, resistance against the older NAs can contribute to cross-resistance against more advanced NAs. For lack of feasible HBV infection systems, the biology of such variants is not well understood. From the recent discovery of Na⁺-taurocholate cotransporting polypeptide (NTCP) as an HBV receptor new in vitro infection systems are emerging, yet access to the required large amounts of virions, in particular variants, remains a limiting factor. Stably HBV producing cell lines address both issues by allowing to study intracellular viral replication and as a permanent source of defined virions. Accordingly, we generated a panel of new tetracycline regulated TetOFF HepG2 hepatoma cell lines which produce six lamivudine and adefovir resistance-associated and two vaccine escape variants of HBV as well as the model virus woolly monkey HBV (WMHBV). The cell line-borne viruses reproduced the expected NA resistance profiles and all were equally sensitive against a non-NA drug. The new cell lines should be valuable to investigate under standardized conditions HBV resistance and cross-resistance. With titers of secreted virions reaching >3x10⁷ viral genome equivalents per ml they should also facilitate exploitation of the new in vitro infection systems.

Replication of a chronic hepatitis B virus genotype F1b construct

Genotype F is one of the less-studied genotypes of human hepatitis B virus, although it is widely distributed in regions of Central and South American. Our previous studies have shown that HBV genotype F is prevalent in Chile, and phylogenetic analysis of its full-length sequence amplified from the sera of chronically infected patients identified it as HBV subgenotype F1b. We have previously reported the full-length sequence of a HBV molecular clone obtained from a patient chronically infected with genotype F1b. In this report, we established a system to study HBV replication based on hepatoma cell lines transfected with full-length monomers of the HBV genome. Culture supernatants were analyzed after transfection and found to contain both HBsAg and HBeAg viral antigens. Consistently, fractionated cell extracts revealed the presence of viral replication, with both cytoplasmic and nuclear DNA intermediates. Analysis of HBV-transfected cells by indirect immunofluorescence or immunoelectron microscopy revealed the expression of viral antigens and cytoplasmic viral particles, respectively. To test the functionality of the ongoing viral replication further at the level of chromatinized cccDNA, transfected cells were treated with a histone deacetylase inhibitor, and this resulted in increased viral replication. This correlated with changes posttranslational modifications of histones at viral promoters. Thus, the development of this viral replication system for HBV genotype F will facilitate studies on the regulation of viral replication and the identification of new antiviral drugs.

Clonal expansion of hepatocytes with a selective advantage occurs during all stages of chronic hepatitis B virus infection

Hepatocyte clone size was measured in liver samples of 21 patients in various stages of chronic hepatitis B virus (HBV) infection and from 21 to 76 years of age. Hepatocyte clones containing unique virus-cell DNA junctions formed by the integration of HBV DNA were detected using inverse nested PCR. The maximum hepatocyte clone size tended to increase with age, although there was considerable patient-to-patient variation in each age group. There was an upward trend in maximum clone size with increasing fibrosis, inflammatory activity and with seroconversion from HBV e-antigen (HBeAg)-positive to HBeAg-negative, but these differences did not reach statistical significance. Maximum hepatocyte clone size did not differ between patients with and without a coexisting hepatocellular carcinoma. Thus, large hepatocyte clones containing integrated HBV DNA were detected during all stages of chronic HBV infection. Using laser microdissection, no significant difference in clone size was observed between foci of HBV surface antigen (HBsAg)-positive and HBsAg-negative hepatocytes, suggesting that expression of HBsAg is not a significant factor in clonal expansion. Laser microdissection also revealed that hepatocytes with normal-appearing histology make up a major fraction of the cells undergoing clonal expansion. Thus, preneoplasia does not appear to be a factor in the clonal expansion detected in our assays. Computer simulations suggest that the large hepatocyte clones are not produced by random hepatocyte turnover but have an as-yet-unknown selective advantage that drives increased clonal expansion in the HBV-infected liver.

New insights into hepatitis B virus biology and implications for novel antiviral strategies

Hepatitis B virus (HBV), a small DNA virus with a unique replication mode, can cause chronic hepatitis (CHB), which is characterized by the persistence of the viral covalently closed circular DNA that serves as the template for HBV replication and the production of large amounts of secreted HBV surface antigen (HBsAg) that is present in excess of the levels of infectious virus. Despite the success of currently approved antiviral treatments for CHB patients, including interferon and nucleotide analogs, which suppress HBV replication and reduce the risk of CHB-related liver diseases, these therapies fail to eradicate the virus in most of the patients. With the development of the cell and animal models for HBV study, a better understanding of the HBV life cycle has been achieved and a series of novel antiviral strategies that target different stages of HBV replication have been designed to overcome the viral factors that contribute to HBV persistence. Such basic HBV research advancements and therapeutic developments are the subject of this review.

Hepatitis B Virus X Protein (HBx) Is Responsible for Resistance to Targeted Therapies in Hepatocellular Carcinoma: Ex Vivo Culture Evidence

PURPOSE

Molecular targeted therapy is an important approach for advanced hepatocellular carcinoma (HCC). Hepatitis B virus-related HCC (HBV-HCC) accounts for approximately 50% of all HCC cases. Bortezomib, a proteasome inhibitor (PI), is used extensively for the treatment of hematologic malignancies, but its application in HCC, particularly in HBV-HCC, has not been fully explored.

EXPERIMENTAL DESIGN

The effects of bortezomib on HCC tissues were evaluated by TUNEL assays. The growth inhibitory activity was measured using cell viability assays, and apoptosis was measured using flow cytometry. The levels of HBx, P-Raf/Raf, and P-Erk/Erk expression were measured by Western blot analysis. The ability of the MEK inhibitor PD98059 to enhance the cell killing activity of bortezomib was evaluated using ex vivo and in vivo methods.

RESULTS

The potency of bortezomib varied among HCC samples and cell lines, and HBV/HBx expression was associated with resistance to bortezomib. Bortezomib increased the levels of P-Raf and P-Erk in HBV/HBx-positive cells but not in HBV/HBx-negative HCC cells or in breast cancer or glioblastoma multiform cells. HBx was also upregulated after exposure to bortezomib, which was associated with the inhibition of proteasome activity. P-Erk upregulation mediated by bortezomib was effectively suppressed by the addition of the MEK inhibitor PD98059. Moreover, bortezomib and PD98059 synergistically inhibited HCC cell proliferation, as measured using both ex vivo and in vivo models.

CONCLUSIONS

Our studies demonstrate for the first time that HBx causes resistance to bortezomib in HCC, and this resistance can be antagonized by a MEK signaling inhibitor, providing a novel therapeutic approach.

Specific delivery of microRNA93 into HBV-replicating hepatocytes downregulates protein expression of liver cancer susceptible gene MICA

Chronic hepatitis B virus (HBV) infection is a major cause of hepatocellular carcinoma (HCC). To date, the lack of efficient in vitro systems supporting HBV infection and replication has been a major limitation of HBV research. Although primary human hepatocytes support the complete HBV life cycle, their limited availability and difficulties with gene transduction remain problematic. Here, we used human primary hepatocytes isolated from humanized chimeric uPA/SCID mice as efficient sources. These hepatocytes supported HBV replication in vitro. Based on analyses of mRNA and microRNA (miRNA) expression levels in HBV-infected hepatocytes, miRNA93 was significantly downregulated during HBV infection. MiRNA93 is critical for regulating the expression levels of MICA protein, which is a determinant for HBV-induced HCC susceptibility. Exogenous addition of miRNA93 in HBV-infected hepatocytes using bionanocapsules consisted of HBV envelope L proteins restored MICA protein expression levels in the supernatant. These results suggest that the rescued suppression of soluble MICA protein levels by miRNA93 targeted to HBV-infected hepatocytes using bionanocapsules may be useful for the prevention of HBV-induced HCC by altering deregulated miRNA93 expression.

Endogenous antiviral microRNAs determine permissiveness for hepatitis B virus replication in cultured human fetal and adult hepatocytes

Superior cell culture models for hepatitis B virus (HBV) will help advance insights into host-virus interactions. To identify mechanisms regulating HBV replication, this study used cultured human HepG2 cells and adult or fetal hepatocytes transduced with adenoviral vector to express HBV upstream of green fluorescent protein. The vector efficiently transduced all cell types. In HepG2 cells, replicative viral intermediates, nucleocapsid-associated HBcAg, and HBsAg were expressed. However, in fetal or adult hepatocytes, pregenomic HBV RNA and viral RNAs were expressed, but nucleocapsid-associated HBcAg in cells or HBsAg in culture medium were absent, indicating interruptions in viral replication due to possible microRNA-related interference. MicroRNA profiling demonstrated that a large number of microRNAs with antiviral potential were differentially expressed in hepatocytes after culture. In transfection assays using HepG2 cells, candidate antiviral microRNAs, e.g., hsa-miR-24 or hsa-miR-638 decreased the levels of HBV transcripts or HBV gene products. Since candidate microRNAs could have targeted interferon response genes as an alternative explanation interferon signaling was examined. However, HBV replication in cultured hepatocytes was not restored despite successful inhibition of JAK1/2-STAT signaling by the inhibitor, ruxolitinib. Therefore, HBV was unable to complete replication in cultured hepatocytes due to expression of multiple antiviral microRNAs. This mechanism should help understand restrictions in HBV replication for developing HBV models in cultured cells while providing frameworks for pathophysiological studies of HBV replication in subsets of hepatocytes or stem/progenitor cells during hepatitis.

Selected phenotypic assays used to evaluate antiviral resistance and viral fitness of hepatitis B virus and its variants

Currently available antiviral therapies specifically target viral replication by blocking reverse transcription with orally given nucleos(t)ide analogues and are able to specifically suppress viral replication. The unique replication strategy of hepatitis B virus (HBV), however, allows long-term persistence of the viral genome within infected hepatocytes in spite of successful therapy. Thus, antiviral therapy needs to be continued for years. Therapy can result either in the emergence and selection of antiviral-resistant variants or the relapse of viral replication after the termination of antiviral therapy. Resistance is a major problem for 4 of the 5 approved HBV nucleos(t)ide analogues, but it is not the only reason for therapy failure. An accurate phenotypic in vitro assay for resistance allows the identification of a viral variant selected in vivo during antiviral therapy and helps to find therapeutic alternatives. Furthermore, these assays can be used to measure viral fitness and pathogenicity in vitro. With the help of these assays, the prediction of emerging viral variants with drug resistance or increased pathogenic potential can be realized. Phenotypic resistance tests for HBV are not trivial because the virus cannot be readily grown in cell culture. This review focuses on currently available phenotypic assays to evaluate antiviral resistance of HBV and fitness of viral variants in general.

TGF-β-miR-34a-CCL22 signaling-induced Treg cell recruitment promotes venous metastases of HBV-positive hepatocellular carcinoma

Portal vein tumor thrombus (PVTT) is strongly correlated to a poor prognosis for patients with hepatocellular carcinoma (HCC). In this study, we uncovered a causative link between hepatitis B virus (HBV) infection and development of PVTT. Mechanistically, elevated TGF-β activity, associated with the persistent presence of HBV in the liver tissue, suppresses the expression of microRNA-34a, leading to enhanced production of chemokine CCL22, which recruits regulatory T (Treg) cells to facilitate immune escape. These findings strongly suggest that HBV infection and activity of the TGF-β-miR-34a-CCL22 axis serve as potent etiological factors to predispose HCC patients for the development of PVTT, possibly through the creation of an immune-subversive microenvironment to favor colonization of disseminated HCC cells in the portal venous system.

Inhibition on hepatitis B virus in vitro of lectin from Musca domestica pupa via the activation of NF-κB

The present study reported that the secretions of HBsAg and HBeAg in HepG2.2.15 cells were significantly decreased under the treatment of lectin from Musca domestica pupa (MPL). Both the replication of hepatitis B virus (HBV) DNA and HBV cccDNA in cells, and the copies of extracellular HBV DNA were inhibited by MPL. The mRNA expressions of interleukin-2 (IL-2), gamma interferon (INF-γ) and MxA were up-regulated by MPL treatments, but down-regulated when nuclear factor-κB (NF-κB) signal pathway was blocked by pyrrolidine dithiocarbamate (PDTC). Subsequent investigation revealed that nuclear factor-κB inhibitory κB (IκB) in endochylema was inhibited and NF-κB was translocated into the nucleus. These findings indicate that MPL could inhibit HBV replication via the induction of the expression of IL-2, INF-γ and MxA through the activation of NF-κB.

Experimental models and therapeutic approaches for HBV

Liver disease associated to persistent infection with the hepatitis B virus (HBV) continues to be a major health problem of global impact. In spite of the existence of an effective vaccine, approximately 360 million people are chronically infected worldwide, who are at high risk of developing liver cirrhosis and hepatocellular carcinoma. Although current therapeutic regimens can efficiently suppress viral replication, the unique replication strategies employed by HBV permit the virus to persist within the infected hepatocytes. As a consequence, relapse of viral activity is commonly observed after cessation of treatment with polymerase inhibitors. The narrow host range of HBV has hindered progresses in understanding specific steps of HBV replication and the development of more effective therapeutic strategies aiming at achieving sustained viral control and, eventually, virus eradication. This review will focus on summarizing recent advances obtained with well-established and more innovative experimental models, giving emphasis on the strength of the different systems as tools for elucidating distinct aspects of HBV persistence and for the development of new therapeutic approaches.

Baculovirus as delivery system for gene transfer during hypothermic organ preservation

Concerns over the safety of conventional viral vectors have limited the translation of gene transfer from an exciting experimental procedure to a successful clinical therapy in transplantation. Baculoviruses are insect viruses, but have the ability to enter mammalian cells and deliver potential therapeutic molecules with no evidence of viral replication. This study provides evidence of the ability of recombinant baculovirus to enter mammalian kidneys and livers during cold preservation. Six kidneys and six liver lobules retrieved from large pigs were perfused with University of Wisconsin (UW) solution containing a baculovirus tagged with green fluorescent protein and preserved for 8 h. In addition, six kidneys were perfused with UW containing a baculovirus expressing red fluorescent protein and preserved for 24 h. Green fluorescent virus particles were detected within transduced kidneys and livers after 8 h standard cold storage and red fluorescent protein mRNA was detected in kidneys after 24 h of cold preservation. There were no significant differences in tissue architecture, cell morphology or ATP content between experimental organs and their controls. Ex vivo transduction of organs with recombinant baculovirus during conventional cold preservation was demonstrated with no evidence of additional injury or reduction in cell viability.

Targeting the hepatitis B virus precore antigen with a novel IgNAR single variable domain intrabody

The Hepatitis B virus precore protein is processed in the endoplasmic reticulum (ER) into secreted hepatitis B e antigen (HBeAg), which acts as an immune tolerogen to establish chronic infection. Downregulation of secreted HBeAg should improve clinical outcome, as patients who effectively respond to current treatments (IFN-α) have significantly lower serum HBeAg levels. Here, we describe a novel reagent, a single variable domain (V(NAR)) of the shark immunoglobulin new antigen receptor (IgNAR) antibodies. V(NAR)s possess advantages in stability, size (~14 kDa) and cryptic epitope recognition compared to conventional antibodies. The V(NAR) domain displayed biologically useful affinity for recombinant and native HBeAg, and recognised a unique conformational epitope. To assess therapeutic potential in targeting intracellular precore protein to reduce secreted HBeAg, the V(NAR) was engineered for ER-targeted in vitro delivery to function as an intracellular antibody (intrabody). In vitro data from HBV/precore hepatocyte cell lines demonstrated effective intrabody regulation of precore/HBeAg.

Fitness and infectivity of drug-resistant and cross-resistant hepatitis B virus mutants: why and how is it studied?

The emergence of hepatitis B virus (HBV) drug-resistant (and multidrug-resistant) strains during long-term therapy with nucleoside/nucleotide analogues is associated with treatment failure and, therefore, represents a clinical challenge. For clinicians, the close monitoring and management of resistance has become a key issue in clinical practice. For HBV virologists, the understanding of the mechanism of emergence of specific mutant strains in the viral quasispecies during treatment is also an important issue. If a particular viral strain can emerge in the quasispecies within a particular environment, it is probably because its fitness is superior to other strains. The present review focuses on viral fitness as well as viral infectivity, and in particular on technical means that are available to study this viral fitness in vitro and in animal models.

Hepatitis B virus replication in primary macaque hepatocytes: crossing the species barrier toward a new small primate model

The development of new anti-hepatitis B virus (HBV) therapies, especially immunotherapeutic approaches, has been limited by the lack of a primate model more accessible than chimpanzees. We have previously demonstrated that sylvanus and cynomolgus macaques are susceptible to in vivo HBV infection after intrahepatic HBV DNA inoculation. In this study, we evaluated the susceptibility of primary macaque hepatocytes (PMHs) to HBV infection with a highly efficient HBV genome-mediated transfer system via a recombinant baculovirus (Bac-HBV). Freshly prepared PMHs, isolated from macaque liver tissue by collagenase perfusion, were transduced with Bac-HBV, and intermediates of replication were followed for 9 days post-transduction. Evidence of HBV replication (hepatitis B surface antigen secretion, viral DNA, RNA, and covalently closed circular DNA) was detected from day 1 to day 9 post-transduction. HBV markers were dose-dependent and still detectable at a multiplicity of infection of 10. Importantly, transduced PMHs secreted all typical forms of HBV particles, as evidenced by a cesium chloride gradient as well as transmission electron microscopy. Furthermore, the Toll-like receptor 9 (TLR9) ligand was used to stimulate freshly prepared macaque peripheral blood mononuclear cells to generate TLR9-induced cytokines. We then demonstrated the antiviral effects of both TLR9-induced cytokines and nucleoside analogue (lamivudine) on HBV replication in transduced PMHs.

CONCLUSION

Baculovirus-mediated genome transfer initiated a full HBV replication cycle in PMHs; thus highlighted both the baculovirus efficiency in crossing the species barrier and macaque susceptibility to HBV infection. Moreover, our results demonstrate the relevance of thus system for antiviral compound evaluations with either nucleoside analogues or inhibitory cytokines. Cynomolgus macaques are readily available, are immunologically closely related to humans, and may therefore represent a promising model for the development of new immunotherapeutic strategies.

Heat stress cognate 70 host protein as a potential drug target against drug resistance in hepatitis B virus

Heat stress cognate 70 (Hsc70) is a host protein associated with hepatitis B virus (HBV) replication. The goal of this study was to investigate whether Hsc70 could be an anti-HBV drug target. Our results showed that introducing Hsc70 increased HBV replication in HBV(+) human hepatocytes (HepG2.2.15 cells). The coiled-coil region on Hsc70 (nucleotides 1533 to 1608; amino acids 511 to 536) was the key sequence for HBV replication. Knockdown of Hsc70 expression by RNA interference (RNAi) largely inhibited HBV replication with no cytotoxicity to the host. Using an Hsc70 mRNA screening assay, the natural compound oxymatrine (OMTR) was found to be a selective inhibitor for Hsc70 expression. Then, OMTR was used to investigate the potential of Hsc70 as an anti-HBV drug target. OMTR inhibited Hsc70 mRNA expression by 80% and HBV DNA replication by over 60% without causing cytotoxicity. The anti-HBV effect of OMTR appeared to be mediated by destabilizing Hsc70 mRNA. The half-life (T(1/2)) of Hsc70 mRNA decreased by 50% in OMTR-treated hepatocytes. The Hsc70 mRNA 3'-untranslated-region (UTR) sequence was the element responsible for OMTR's destabilization activity. OMTR suppressed HBV de novo synthesis at the reverse transcription stage from pregenomic RNA (pgRNA) to DNA and was active against either wild-type HBV or strains resistant to lamivudine, adefovir, and entecavir. Therefore, host Hsc70 could be a novel drug target against HBV, and OMTR appears to inhibit HBV replication by destabilizing Hsc70 mRNA. As the target is not a viral protein, OMTR is active for either wild-type HBV or strains resistant to reverse transcriptase (RT) inhibitors.

Control of hepatitis B virus replication by innate response of HepaRG cells

Hepatitis B virus (HBV) is currently viewed as a stealth virus that does not elicit innate immunity in vivo. This assumption has not yet been challenged in vitro because of the lack of a relevant cell culture system. The HepaRG cell line, which is physiologically closer to differentiated hepatocytes and permissive to HBV infection, has opened new perspectives in this respect.HBV baculoviruses were used to initiate an HBV replication in both HepG2 and HepaRG cells. To monitor HBV replication, the synthesis of encapsidated DNA, and secretion of hepatitis B surface antigen (HBsAg), was respectively analyzed by southern blot and enzyme-linked immunosorbent assay. The induction of a type I interferon (IFN) response was monitored by targeted quantitative reverse transcription polymerase chain reaction (qRT-PCR), low-density arrays, and functional assays. The invalidation of type I IFN response was obtained by either antibody neutralization or RNA interference. We demonstrate that HBV elicits a strong and specific innate antiviral response that results in a noncytopathic clearance of HBV DNA in HepaRG cells. Challenge experiment showed that transduction with Bac-HBV-WT, but not with control baculoviruses, leads to this antiviral response in HepaRG cells, whereas no antiviral response is observed in HepG2 cells. Cellular gene expression analyses showed that IFN-beta and other IFN-stimulated genes were up-regulated in HepG2 and HepaRG cells, but not in cells transduced by control baculoviruses. Interestingly, a rescue of viral replication was observed when IFN-beta action was neutralized by antibodies or RNA interference of type I IFN receptor.

CONCLUSION

Our data suggest that a strong HBV replication is able to elicit a type I IFN response in HepaRG-transduced cells.

Stimulation of the interleukin-1 receptor and Toll-like receptor 2 inhibits hepatitis B virus replication in hepatoma cell lines in vitro

BACKGROUND

Toll-like receptors (TLRs) are a key component of the innate immune system and TLR2 has been shown to be involved in the immunopathogenesis of hepatitis B virus (HBV) infection in vivo. We investigated the role of TLR2 stimulation of virus-infected hepatocyte cell lines as a potential antiviral mechanism in vitro.

METHODS

The hepatoblastoma cell line HepG2 was transduced with recombinant HBV baculoviruses and the hepatoma cell line Huh-7 was transiently transfected with complimentary DNA clones of HBV. HBV viral replication was quantified after stimulation with interleukin (IL)-1beta and Pam-2-Cys, a synthetic TLR2 ligand, by measuring intracellular core-associated single-stranded HBV DNA using Southern blot hybridization, as well as viral nucleocapsid formation using a non-denaturing immunoblot method.

RESULTS

Stimulation of both cell lines in vitro with IL-1beta and Pam-2-Cys, both known to induce expression of the pro inflammatory cytokines tumour necrosis factor-alpha and IL-8 via a nuclear factor-kappaB dependent pathway, resulted in the inhibition of HBV DNA replication in the transduced HepG2 cells by up to 90% and nucleocapsid formation in the transiently transfected Huh-7 cells by up to 30%, when compared with mock-treated cells.

CONCLUSIONS

Hepatoma cell lines expressed functional IL-1 receptor and TLR2 receptors, which when stimulated led to a signalling cascade that inhibited HBV replication. These data support an active role for hepatocytes in inhibiting HBV replication and provide a rationale for the development of TLR agonists as potentially novel antiviral agents.

Hepatitis B virus and hepatitis C virus interaction in Huh-7 cells

BACKGROUND/AIMS

Co-infection with hepatitis B virus (HBV) and hepatitis C virus (HCV) increases the risk of development and the severity of chronic liver disease. Although dominant and suppressive effects of each virus over the other have been reported in vivo, in vitro studies of HBV/HCV co-infection have been limited to analysis of the effects of over-expression of HCV proteins on HBV replication.

METHODS

We have re-examined HBV/HCV interactions in Huh-7 cells following co-infection with cell culture-propagated HCV (HCVcc; genotype 2a) and a recombinant adenovirus vector capable of delivering a replication-competent HBV genome (AdHBV; genotype A).

RESULTS

While intracellular HCV RNA levels were significantly increased when cells were pre-infected with AdHBV, HCV replication and virion secretion were not altered by simultaneous infection with AdHBV or AdHBV superinfection of HCV-infected cells. Likewise intracellular and secreted HBV DNA levels and HBV promoter activities were either unchanged or modestly increased by HCVcc infection. Despite this, HCV E2 and HBsAg proteins colocalized extensively in co-infected cells suggesting shared stages in viral egress.

CONCLUSIONS

These studies indicate that there is little direct interaction of HBV and HCV in co-infected hepatocytes and imply that indirect effects of host-viral interactions dictate viral dominance in HBV/HCV co-infected individuals.

Detection of clonally expanded hepatocytes in chimpanzees with chronic hepatitis B virus infection

During a hepadnavirus infection, viral DNA integrates at a low rate into random sites in the host DNA, producing unique virus-cell junctions detectable by inverse nested PCR (invPCR). These junctions serve as genetic markers of individual hepatocytes, providing a means to detect their subsequent proliferation into clones of two or more hepatocytes. A previous study suggested that the livers of 2.4-year-old woodchucks (Marmota monax) chronically infected with woodchuck hepatitis virus contained at least 100,000 clones of >1,000 hepatocytes (W. S. Mason, A. R. Jilbert, and J. Summers, Proc. Natl. Acad. Sci. USA 102:1139-1144, 2005). However, possible correlations between sites of viral-DNA integration and clonal expansion could not be explored because the woodchuck genome has not yet been sequenced. In order to further investigate this issue, we looked for similar clonal expansion of hepatocytes in the livers of chimpanzees chronically infected with hepatitis B virus (HBV). Liver samples for invPCR were collected from eight chimpanzees chronically infected with HBV for at least 20 years. Fifty clones ranging in size from approximately 35 to 10,000 hepatocytes were detected using invPCR in 32 liver biopsy fragments (approximately 1 mg) containing, in total, approximately 3 x 10(7) liver cells. Based on searching the analogous human genome, integration sites were found on all chromosomes except Y, approximately 30% in known or predicted genes. However, no obvious association between the extent of clonal expansion and the integration site was apparent. This suggests that the integration site per se is not responsible for the outgrowth of large clones of hepatocytes.