Revisiting Hepatitis B Virus: Challenges of Curative Therapies

Augmented epigenetic repression of hepatitis B virus covalently closed circular DNA by interferon-α and small-interfering RNA synergy

The persistence of hepatitis B virus (HBV) covalently closed circular DNA (cccDNA) is a key obstacle for HBV cure. This study aims to comprehensively assess the effect of interferon (IFN) and small-interfering RNA (siRNA) combination on the cccDNA minichromosome. Utilizing both cell and mouse cccDNA models, we compared the inhibitory effects of IFNα, siRNA, and their combination on cccDNA activity and assessed its epigenetic state. IFNα2 treatment alone reduced HBV RNAs, HBeAg, and HBsAg levels by approximately 50%, accompanied by a low-level reconstitution of SMC5/6-a chromatin modulator that restricts cccDNA transcription. HBx-targeting siRNA (siHBx) achieved significant suppression of viral antigens and reconstitution of SMC5/6, but this effect could be reversed by the deacetylase inhibitor Belinostat. The combination of IFN with siHBx resulted in over 95% suppression of virological markers, reduction in epigenetic activation modifications (H3Ac and H4Ac) on cccDNA, and further reduced cccDNA accessibility, with the effect not reversible by Belinostat. In an extracellular humanized IFNAR C57BL/6 mouse model harboring recombinant cccDNA, the effect of combination of clinically used pegylated IFNα2 and GalNac-siHBx was further clarified, indicating a higher and more durable suppression of cccDNA activity compared to either therapy alone. In conclusion, the combination of IFNα and siRNA achieves a more potent and durable epigenetic inhibition of cccDNA activity in cell and mouse models, compared to monotherapy. These findings deepen the understanding of cccDNA modulation and strengthen the scientific basis for the potential of combination therapy.

IMPORTANCE

Since there are currently no approved drugs targeting and silencing covalently closed circular DNA (cccDNA), achieving a "functional cure" remains difficult. This study aims to comprehensively compare the effects of IFNα, small-interfering RNA targeting hepatitis B virus (HBV), and their combination on the activity, accessibility, and epigenetic modifications of cccDNA minichromosomes in cell models. A more durable and stable inhibition of HBV RNAs and antigens expression by IFNα and HBx-targeting siRNA (siHBx) synergy was observed, associated with augmented epigenetic repression of the cccDNA minichromosome. Besides, in an extracellular humanized IFNAR mouse model harboring recombinant cccDNA with an intact response to human IFNα, the synergistic effect of clinically used pegylated IFNα2 and in-house-developed GalNac-siHBx was further clarified.

METTL14 Induced N6-Methyladenosine Modification of FOXP4 mRNA in HBV-HCC

Chronic hepatitis B virus infections are a significant cause of liver cirrhosis and cancer. Our research reveals that HBV infection leads to a marked increase in m6A modification of Foxp4 mRNA, resulting in enhanced stability of the mRNA and a subsequent increase in Foxp4 mRNA levels. Analysis of biopsy samples from chronic HBV patients demonstrated consistent upregulation of m6A-modified Foxp4 mRNA levels alongside increased Foxp4 mRNA levels. Functionally, Foxp4 was found to promote proliferation, migration, and invasion of hepatocellular carcinoma (HCC) cells in laboratory settings. Additionally, HBV gene expression was shown to activate the PI3K/AKT pathway by modulating Foxp4 mRNA stability in HCC cells. This study provides valuable insights into the underlying mechanisms of HBV infection and its potential implications for cancer development.

Hepatitis B: Model Systems and Therapeutic Approaches

Hepatitis B virus (HBV) infection is a major global health issue and ranks among the top causes of liver cirrhosis and hepatocellular carcinoma. Although current antiviral medications, including nucleot(s)ide analogs and interferons, could inhibit the replication of HBV and alleviate the disease, HBV cannot be fully eradicated. The development of cellular and animal models for HBV infection plays an important role in exploring effective anti-HBV medicine. During the past decades, advancements in several cell culture systems, such as HepG2.2.15, HepAD38, HepaRG, hepatocyte-like cells, and primary human hepatocytes, have propelled the research in inhibiting HBV replication and expression and thus enriched our comprehension of the viral life cycle and enhancing antiviral drug evaluation efficacy. Mouse models, in particular, have emerged as the most extensively studied HBV animal models. Additionally, the present landscape of HBV therapeutics research now encompasses a comprehensive assessment of the virus's life cycle, targeting numerous facets and employing a variety of immunomodulatory approaches, including entry inhibitors, strategies aimed at cccDNA, RNA interference technologies, toll-like receptor agonists, and, notably, traditional Chinese medicine (TCM). This review describes the attributes and limitations of existing HBV model systems and surveys novel advancements in HBV treatment modalities, which will offer deeper insights toward discovering potentially efficacious pharmaceutical interventions.

Recent advances in different interactions between toll-like receptors and hepatitis B infection: a review

Hepatitis B virus (HBV) B infections remain a primary global health concern. The immunopathology of the infection, specifically the interactions between HBV and the host immune system, remains somewhat unknown. It has been discovered that innate immune reactions are vital in eliminating HBV. Toll-like receptors (TLRs) are an essential category of proteins that detect pathogen-associated molecular patterns (PAMPs). They begin pathways of intracellular signals to stimulate pro-inflammatory and anti-inflammatory cytokines, thus forming adaptive immune reactions. HBV TLRs include TLR2, TLR3, TLR4, TLR7 and TLR9. Each TLR has its particular molecule to recognize; various TLRs impact HBV and play distinct roles in the pathogenesis of the disease. TLR gene polymorphisms may have an advantageous or disadvantageous efficacy on HBV infection, and some single nucleotide polymorphisms (SNPs) can influence the progression or prognosis of infection. Additionally, it has been discovered that similar SNPs in TLR genes might have varied effects on distinct populations due to stress, diet, and external physical variables. In addition, activation of TLR-interceded signaling pathways could suppress HBV replication and increase HBV-particular T-cell and B-cell reactions. By identifying these associated polymorphisms, we can efficiently advance the immune efficacy of vaccines. Additionally, this will enhance our capability to forecast the danger of HBV infection or the threat of dependent liver disease development via several TLR SNPs, thus playing a role in the inhibition, monitoring, and even treatment guidance for HBV infection. This review will show TLR polymorphisms, their influence on TLR signaling, and their associations with HBV diseases.

The Significance of N6-Methyladenosine RNA Methylation in Regulating the Hepatitis B Virus Life Cycle

N6-methyladenosine (m6A) RNA methylation has recently emerged as a significant co-transcriptional modification involved in regulating various RNA functions. It plays a vital function in numerous biological processes. Enzymes referred to as m6A methyltransferases, such as the methyltransferaselike (METTL) 3-METTL14-Wilms tumor 1 (WT1)-associated protein (WTAP) complex, are responsible for adding m6A modifications, while m6A demethylases, including fat mass and obesity-associated protein (FTO) and alkB homolog 5 (ALKBH5), can remove m6A methylation. The functions of m6A-methylated RNA are regulated through the recognition and interaction of m6A reader proteins. Recent research has shown that m6A methylation takes place at multiple sites within hepatitis B virus (HBV) RNAs, and the location of these modifications can differentially impact the HBV infection. The addition of m6A modifications to HBV RNA can influence its stability and translation, thereby affecting viral replication and pathogenesis. Furthermore, HBV infection can also alter the m6A modification pattern of host RNA, indicating the virus's ability to manipulate host cellular processes, including m6A modification. This manipulation aids in establishing chronic infection, promoting liver disease, and contributing to pathogenesis. A comprehensive understanding of the functional roles of m6A modification during HBV infection is crucial for developing innovative approaches to combat HBV-mediated liver disease. In this review, we explore the functions of m6A modification in HBV replication and its impact on the development of liver disease.

Interconnection of cellular autophagy and endosomal vesicle trafficking and its role in hepatitis B virus replication and release

Hepatitis B virus (HBV) produces and releases various particle types, including complete virions, subviral particles with envelope proteins, and naked capsids. Recent studies demonstrate that HBV exploits distinct intracellular membrane trafficking pathways, including the endosomal vesicle trafficking and autophagy pathway, to assemble and release viral and subviral particles. Herein, we summarize the findings about the distinct roles of autophagy and endosomal membrane trafficking and the interaction of both pathways in HBV replication, assembly, and release.

Analysis of N6-Methyladenosine Modification of HBV RNA by Methylated RNA Immunoprecipitation

Of all the chemical modifications of RNAs, the N6-methyladenosine (m6A) modification is the most prevalent and well-characterized RNA modification that is functionally implicated in a wide range of biological processes. The m6A modification occurs in hepatitis B virus (HBV) RNAs and this modification regulates the HBV life cycle in several ways. Thus, understanding the mechanisms underlying m6A modification of HBV RNAs is crucial in understanding HBV infectious process and associated pathogenesis. Here, we describe the currently utilized method in the detection and characterization of m6A-methylated RNAs during viral infection.

Detection of Hepatitis B Virus Covalently Closed Circular DNA and Intermediates in Its Formation

Hepatitis B virus (HBV) infection remains a global public health issue, and approximately 294 million individuals worldwide are chronically infected with HBV. Approved antivirals rarely cure chronic HBV infection due to their inability to eliminate the HBV covalently closed circular DNA (cccDNA), the viral episome, in the nucleus of infected hepatocytes. The persistence of cccDNA underlies the chronic nature of HBV infection and the frequent relapse after the cessation of antiviral treatment. However, drug development targeting cccDNA formation and maintenance is hindered by the lack of sufficient biological knowledge on cccDNA, and of its reliable detection due to its low abundance and the presence of high levels of HBV DNA species similar to cccDNA. Here, we describe a Southern blot method for reliably detecting the HBV cccDNA even in the presence of high levels of plasmid DNA and other HBV DNA species, based on the efficient removal of plasmid DNA and all DNA species with free 3' ends. This approach also allows the detection of certain potential intermediates during cccDNA formation.

A computational spatial whole-Cell model for hepatitis B viral infection and drug interactions

Despite a vaccine, hepatitis B virus (HBV) remains a world-wide source of infections and deaths. We develop a whole-cell computational platform combining spatial and kinetic models describing the infection cycle of HBV in a hepatocyte host. We simulate key parts of the infection cycle with this whole-cell platform for 10 min of biological time, to predict infection progression, map out virus-host and virus-drug interactions. We find that starting from an established infection, decreasing the copy number of the viral envelope proteins shifts the dominant infection pathway from capsid secretion to re-importing the capsids into the nucleus, resulting in more nuclear-localized viral covalently closed circular DNA (cccDNA) and boosting transcription. This scenario can mimic the consequence of drugs designed to manipulate viral gene expression. Mutating capsid proteins facilitates capsid destabilization and disassembly at nuclear pore complexes, resulting in an increase in cccDNA copy number. However, excessive destabilization leads to premature cytoplasmic disassembly and does not increase the cccDNA counts. Finally, our simulations can predict the best drug dosage and its administration timing to reduce the cccDNA counts. Our adaptable computational platform can be parameterized to study other viruses and identify the most central viral pathways that can be targeted by drugs.

Opportunities and considerations for studying liver disease with microphysiological systems on a chip

Advances in microsystem engineering have enabled the development of highly controlled models of the liver that better recapitulate the unique in vivo biological conditions. In just a few short years, substantial progress has been made in creating complex mono- and multi-cellular models that mimic key metabolic, structural, and oxygen gradients crucial for liver function. Here we review: 1) the state-of-the-art in liver-centric microphysiological systems and 2) the array of liver diseases and pressing biological and therapeutic challenges which could be investigated with these systems. The engineering community has unique opportunities to innovate with new liver-on-a-chip devices and partner with biomedical researchers to usher in a new era of understanding of the molecular and cellular contributors to liver diseases and identify and test rational therapeutic modalities.

Acute Hepatitis A and Hepatitis B Coinfection in a Young Female: A Case Report and Literature Review

Background

Hepatitis is one of the common infectious diseases that can infect patients in various forms. Based on their characteristics and clinical features, they can cause irreparable complications in patients. Coinfections and superinfections between its variant have been reported, but the coinfection of acute HAV and HBV is rarely reported. Case Presentation. In this case report, we presented a case with severe malaise, nausea, vomiting, generalized jaundice, and a history of recent tattooing and travel to the HAV endemic area. In our evaluation, she had a positive HBsAg, HBeAg, anti-HBs IgM, anti-HAV IgM, and negative result in HCV antibody, HIV antibody, and anti-HAV IgG. The coinfection of HAV/HBV was confirmed for her.

Conclusion

Physicians should differentiate hepatitis A and hepatitis B superinfection or coinfection, based on history and laboratory testing, to prevent complications with appropriate treatment.

Quantification of the hepatitis B virus cccDNA: evidence-based guidelines for monitoring the key obstacle of HBV cure

OBJECTIVES

A major goal of curative hepatitis B virus (HBV) treatments is the reduction or inactivation of intrahepatic viral covalently closed circular DNA (cccDNA). Hence, precise cccDNA quantification is essential in preclinical and clinical studies. Southern blot (SB) permits cccDNA visualisation but lacks sensitivity and is very laborious. Quantitative PCR (qPCR) has no such limitations but inaccurate quantification due to codetection of viral replicative intermediates (RI) can occur. The use of different samples, preservation conditions, DNA extraction, nuclease digestion methods and qPCR strategies has hindered standardisation. Within the ICE-HBV consortium, available and novel protocols for cccDNA isolation and qPCR quantification in liver tissues and cell cultures were compared in six laboratories to develop evidence-based guidance for best practices.

DESIGN

Reference material (HBV-infected humanised mouse livers and HepG2-NTCP cells) was exchanged for cross-validation. Each group compared different DNA extraction methods (Hirt extraction, total DNA extraction with or without proteinase K treatment (+PK/-PK)) and nuclease digestion protocols (plasmid-safe ATP-dependent DNase (PSD), T5 exonuclease, exonucleases I/III). Samples were analysed by qPCR and SB.

RESULTS

Hirt and -PK extraction reduced coexisting RI forms. However, both cccDNA and the protein-free relaxed circular HBV DNA (pf-rcDNA) form were detected by qPCR. T5 and Exo I/III nucleases efficiently removed all RI forms. In contrast, PSD did not digest pf-rcDNA, but was less prone to induce cccDNA overdigestion. In stabilised tissues (eg, Allprotect), nucleases had detrimental effects on cccDNA.

CONCLUSIONS

We present here a comprehensive evidence-based guidance for optimising, controlling and validating cccDNA measurements using available qPCR assays.

Forthcoming Developments in Models to Study the Hepatitis B Virus Replication Cycle, Pathogenesis, and Pharmacological Advancements

Hepatitis, liver cirrhosis, and hepatocellular carcinoma are all manifestations of chronic hepatitis B. Its pathogenesis and molecular mechanism remain mysterious. As medical science progresses, different models are being used to study the disease from the physiological and molecular levels. Animal models have played an unprecedented role in achieving in-depth knowledge of the disease while posing no risk of harming humans throughout the study. The scarcity of acceptable animal models has slowed progress in hepatitis B virus (HBV) research and preclinical testing of antiviral medicines since HBV has a narrow species tropism and exclusively infects humans and higher primates. The development of human chimeric mice was supported by a better understanding of the obstacles to interspecies transmission, which has substantially opened the way for HBV research in vivo and the evaluation of possible chronic hepatitis B therapeutics. Animal models are cumbersome to handle, not accessible, and expensive. Hence, it is herculean to investigate the HBV replication cycle in animal models. Therefore, it becomes essential to build a splendid in vitro cell culture system to demonstrate the mechanisms attained by the HBV for its multiplication and sustenance. We also addressed the advantages and caveats associated with different models in examining HBV.

Spermidine enhances the efficacy of adjuvant in HBV vaccination in mice

Background: Various vaccine adjuvants have been developed to eliminate HBV from patients with chronic HBV infection. In addition, spermidine (SPD), a type of polyamine, has been reported to enhance the activity of immune cells. In the present study, we investigated whether the combination of SPD and vaccine adjuvant enhances the HBV antigen-specific immune response to HBV vaccination. Methods: Wild-type and HBV-transgenic (HBV-Tg) mice were vaccinated 2 or 3 times. SPD was orally administered in drinking water. Cyclic guanosine monophosphate-AMP (cGAMP) and nanoparticulate CpG-ODN (K3-SPG) were used as the HBV vaccine adjuvants. The HBV antigen-specific immune response was evaluated by measuring the HBsAb titer in blood collected over time and the number of interferon-γ producing cells by enzyme-linked immunospot assay. Results: The administration of HBsAg + cGAMP + SPD or HBsAg + K3-SPG + SPD significantly enhanced HBsAg-specific interferon-γ production by CD8 T cells from wild-type and HBV-Tg mice. The administration of HBsAg, cGAMP, and SPD increased serum HBsAb levels in wild-type and HBV-Tg mice. In HBV-Tg mice, the administration of SPD + cGAMP or SPD + K3-SPG with HBV vaccination significantly reduced HBsAg levels in the liver and serum.

CONCLUSIONS

These results indicate that the combination of HBV vaccine adjuvant and SPD induces a stronger humoral and cellular immune response through T-cell activation. These treatments may support the development of a strategy to completely eliminate HBV.

Overview of the development of HBV small molecule inhibitors

Like tuberculosis and Acquired Immune Deficiency Syndrome (AIDS), hepatitis B is a globally recognized major public health threat. Although there are many small-molecule drugs for the treatment of hepatitis B, the approved drugs cannot eradicate the pathogenic culprit covalently closed circular DNA in patients, so the patients need long-term medication to control HBV amplification. Driven by a high unmet medical need, many pharmaceutical companies and research institutions have been engaged in the development of anti-HBV drugs to achieve a functional cure for chronic hepatitis B as soon as possible. This review summarizes the pathogenesis of hepatitis B virus and the research progress in the development of anti-HBV small molecule drugs, and introduces the cccDNA formation and transcription inhibitors and core inhibitors in detail, especially emphasizes the role of chinese herbal medicine in the treatment of chronic hepatitis B. Furthermore, this review proposes three potential strategies for cccDNA eradication in the future. We believe this review will provide meaningful guidance to achieve a functional cure for viral hepatitis B in the future.

Screening of an epigenetic compound library identifies BRD4 as a potential antiviral target for hepatitis B virus covalently closed circular DNA transcription

HBV cccDNA is the persistent form of viral genome, which exists in host cell nucleus as an episomal minichromosome decorated with histone and non-histone proteins. cccDNA is the authentic viral transcription template and resistant to current antivirals. Growing evidence shows that the transcriptional activity of cccDNA minichromosome undergoes epigenetic regulations, suggesting a new perspective for anti-cccDNA drug development through targeting histone modifications. In this study, we screened an epigenetic compound library in the cccDNA reporter cell line HepBHAe82, which produces the HA-tagged HBeAg in a cccDNA-dependent manner. Among the obtained hits, a bromodomain-containing protein 4 (BRD4) inhibitor MS436 exhibited marked inhibition of cccDNA transcription in both HBV stable cell line HepAD38 and HepG2-NTCP or primary human hepatocyte infection system under noncytotoxic concentrations. Chromatin immunoprecipitation (ChIP) assay demonstrated that MS436 dramatically reduced the enrichment of H3K27ac, an activating histone modification pattern, on cccDNA minichromosome. RNAseq differential analysis showed that MS436 does not drastically change host transcriptome or induce any known anti-HBV factors/pathways, indicating a direct antiviral effect of MS436 on cccDNA minichromosome. Interestingly, the MS436-mediated inhibition of cccDNA transcription is accompanied by cccDNA destabilization in HBV infection and a recombinant cccDNA system, indicating that BRD4 activity may also play a role in cccDNA maintenance. Furthermore, depletion of BRD4 by siRNA knockdown or PROTAC degrader resulted in cccDNA inhibition in HBV-infected HepG2-NTCP cells, further validating BRD4 as an antiviral target. Taken together, our study has demonstrated the practicability of HepBHAe82-based anti-HBV drug screening system and provided a proof-of-concept for targeting HBV cccDNA with epigenetic compounds.

Characterization of Intracellular Precore-Derived Proteins and Their Functions in Hepatitis B Virus-Infected Human Hepatocytes

Hepatitis B virus (HBV) precore protein is not essential for viral replication but is thought to facilitate chronic infection. In addition to the secreted precore products, including the hepatitis B e antigen (HBeAg) and PreC protein, intracellular precore-derived proteins in HBV-infected human hepatocytes remain poorly characterized, and their roles, if any, remain largely unknown. Here, we detected multiple precore derivatives, including the nonprocessed precursor p25 and the processing intermediate p22, in HBV-infected human hepatocytes as well as human hepatoma cells overexpressing the HBV precore protein. Both p25 and p22 showed phosphorylated and unphosphorylated forms, which were located in different intracellular compartments. Interestingly, precore expression was associated with decreases in intracellular HBV core protein (HBc) and secreted DNA-containing virions but was also associated with an increase in secreted empty virions. The decrease in HBc by precore could be attributed to cytosolic p22, which caused HBc degradation, at least in part by the proteasome, and consequently decreased HBV pregenomic RNA packaging and DNA synthesis. In addition, cytosolic p22 formed chimeric capsids with HBc in the cell, which were further secreted in virions. In contrast, the PreC antigen, like HBeAg, was secreted via the endoplasmic reticulum (ER)-Golgi secretory pathway and was thus unable to form capsids in the cell or be secreted in virions. Furthermore, p25, as well as p22, were secreted in virions from HBV-infected human hepatocytes and were detected in the sera of HBV-infected chimpanzees. In summary, we have detected multiple intracellular precore-derived proteins in HBV-infected human hepatocytes and revealed novel precore functions in the viral life cycle. IMPORTANCE Chronic hepatitis B remains a worldwide public health issue. The hepatitis B virus (HBV) precore protein is not essential for HBV replication but may facilitate viral persistence. In this study, we have detected multiple precore protein species in HBV-infected human hepatocytes and studied their functions in the HBV life cycle. We found that the HBV precore proteins decreased intracellular HBV core protein and reduced secretion of complete virions but enhanced secretion of empty virions. Interestingly, the cytosolic precore protein species formed chimeric capsids with the core protein and were secreted in virions. Our results shed new light on the functions of intracellular precore protein species in the HBV life cycle and have implications for the roles of precore proteins in HBV persistence and pathogenesis.

Release of hepatitis B virions is positively regulated by glucose-regulated protein 78 through direct interaction with preS1

In this study, we investigated the mechanism of hepatitis B virus (HBV)-enveloped particle release. Specifically, we used preS1 as a bait protein to screen host proteins using mass spectroscopy, with the results of immunofluorescence, western blot, co-immunoprecipitation, isothermal titration calorimetry, and pull-down assays identifying glucose-regulated protein (GRP)78 as a specific target for preS1 binding. We employed transcriptome sequencing, enzyme-linked immunosorbent assays, and particle gel assays to investigate the mechanism of GRP78-mediated positive regulation of HBV-enveloped particle release. Additionally, we performed phage-display, surface plasmon resonance, and molecular-docking assays to assess peptides inhibiting enveloped-particle release. We found that HBV upregulated GRP78 expression in liver cell lines and the serum of patients with chronic hepatitis B. Furthermore, GRP78 promoted the release of HBV-enveloped particles in vitro and in vivo within an HBV transgenic mouse model. Moreover, we identified interactions of preS1 peptides with GRP78 via hydrogen bonding and hydrophobic interactions, which effectively inhibited its interaction with HBV-enveloped particles and their subsequent release. These findings provide novel insights regarding HBV virion release, and demonstrated that GRP78 interacted with preS1 to positively regulate the release of HBV-enveloped particles, suggesting GRP78 as a potential therapeutic target for inhibiting HBV infection.

Hepatitis B functional cure and immune response

Hepatitis B virus (HBV) is a hepatotropic virus, which damage to hepatocytes is not direct, but through the immune system. HBV specific CD4+ T cells can induce HBV specific B cells and CD8+ T cells. HBV specific B cells produce antibodies to control HBV infection, while HBV specific CD8+ T cells destroy infected hepatocytes. One of the reasons for the chronicity of HBV infection is that it cannot effectively activate adoptive immunity and the function of virus specific immune cells is exhausted. Among them, virus antigens (including HBV surface antigen, e antigen, core antigen, etc.) can inhibit the function of immune cells and induce immune tolerance. Long term nucleos(t)ide analogues (NAs) treatment and inactive HBsAg carriers with low HBsAg level may "wake up" immune cells with abnormal function due to the decrease of viral antigen level in blood and liver, and the specific immune function of HBV will recover to a certain extent, thus becoming the "dominant population" for functional cure. In turn, the functional cure will further promote the recovery of HBV specific immune function, which is also the theoretical basis for complete cure of hepatitis B. In the future, the complete cure of chronic HBV infection must be the combination of three drugs: inhibiting virus replication, reducing surface antigen levels and specific immune regulation, among which specific immunotherapy is indispensable. Here we review the relationship, mechanism and clinical significance between the cure of hepatitis B and immune system.

Immune escape pathways from the HBV core18-27 CD8 T cell response are driven by individual HLA class I alleles

Background and aims

There is growing interest in T cell-based immune therapies for a functional cure of chronic HBV infection including check-point inhibition, T cell-targeted vaccines or TCR-grafted effector cells. All these approaches depend on recognition of HLA class I-presented viral peptides. The HBV core region 18-27 is an immunodominant target of CD8+ T cells and represents the prime target for T cell-based therapies. Here, a high-resolution analysis of the core18-27 specific CD8+ T cell and the selected escape pathways was performed.

Methods

HLA class I typing and viral sequence analyses were performed for 464 patients with chronic HBV infection. HBV-specific CD8+ T-cell responses against the prototype and epitope variants were characterized by flow cytometry.

Results

Consistent with promiscuous presentation of the core18-27 epitope, antigen-specific T cells were detected in patients carrying HLA-A*02:01, HLA-B*35:01, HLA-B*35:03 or HLA-B*51:01. Sequence analysis confirmed reproducible selection pressure on the core18-27 epitope in the context of these alleles. Interestingly, the selected immune escape pathways depend on the presenting HLA-class I-molecule. Although cross-reactive T cells were observed, some epitope variants achieved functional escape by impaired TCR-interaction or disturbed antigen processing. Of note, selection of epitope variants was exclusively observed in HBeAg negative HBV infection and here, detection of variants associated with significantly greater magnitude of the CD8 T cell response compared to absence of variants.

Conclusion

The core18-27 epitope is highly variable and under heavy selection pressure in the context of different HLA class I-molecules. Some epitope variants showed evidence for impaired antigen processing and reduced presentation. Viruses carrying such escape substitutions will be less susceptible to CD8+ T cell responses and should be considered for T cell-based therapy strategies.

Design, Synthesis, and Evaluation of a Set of Carboxylic Acid and Phosphate Prodrugs Derived from HBV Capsid Protein Allosteric Modulator NVR 3-778

Hepatitis B virus (HBV) capsid protein (Cp) is necessary for viral replication and the maintenance of viral persistence, having become an attractive target of anti-HBV drugs. To improve the water solubility of HBV capsid protein allosteric modulator (CpAM) NVR 3-778, a series of novel carboxylic acid and phosphate prodrugs were designed and synthesized using a prodrug strategy. In vitro HBV replication assay showed that these prodrugs maintained favorable antiviral potency (EC50 = 0.28−0.42 µM), which was comparable to that of NVR 3-778 (EC50 = 0.38 µM). More importantly, the cytotoxicity of prodrug N8 (CC50 > 256 µM) was significantly reduced compared to NVR 3-778 (CC50 = 13.65 ± 0.21 µM). In addition, the water solubility of prodrug N6 was hundreds of times better than that of NVR 3-778 in three phosphate buffers with various pH levels (2.0, 7.0, 7.4). In addition, N6 demonstrated excellent plasma and blood stability in vitro and good pharmacokinetic properties in rats. Finally, the hemisuccinate prodrug N6 significantly improved the candidate drug NVR 3-778’s water solubility and increased metabolic stability while maintaining its antiviral efficacy.

When does hepatitis B virus meet long-stranded noncoding RNAs?

Hepatitis B virus (HBV) infection in humans and its associated diseases are long-standing problems. HBV can produce a large number of non-self-molecules during its life cycle, which acts as targets for innate immune recognition and initiation. Among these, interferon and its large number of downstream interferon-stimulated gene molecules are important early antiviral factors. However, the development of an effective antiviral immune response is not simple and depends not only on the delicate regulation of the immune response but also on the various mechanisms of virus-related immune escape and immune tolerance. Therefore, despite there being a relatively well-established consensus on the major pathways of the antiviral response and their component molecules, the complete clearance of HBV remains a challenge in both basic and clinical research. Long-noncoding RNAs (lncRNAs) are generally >200 bp in length and perform different functions in the RNA strand encoding the protein. As an important part of the IFN-inducible genes, interferon-stimulated lncRNAs are involved in the regulation of several HBV infection-related pathways. This review traces the basic elements of such pathways and characterizes the various recent targets of lncRNAs, which not only complement the regulatory mechanisms of pathways related to chronic HBV infection, fibrosis, and cancer promotion but also present with new potential therapeutic targets for controlling HBV infection and the malignant transformation of hepatocytes.

Combination strategies to durably suppress HIV-1: Soluble T cell receptors

Immunotherapeutic interventions to enhance natural HIV-specific CD8+ T cell responses, such as vaccination or adoptive T cell transfer, have been a major focus of HIV cure efforts. However, these approaches have not been effective in overcoming viral immune evasion mechanisms. Soluble T cell receptor (TCR) bispecifics are a new class of 'off-the-shelf' therapeutic designed to address these limitations. These biologics are built on the Immune mobilising monoclonal TCRs against X disease (ImmTAX) platform, which was pioneered in oncology and recently validated by the FDA's approval of tebentafusp for treatment of metastatic uveal melanoma. ImmTAV® are an application of this technology undergoing clinical development for the elimination of chronic viral infections. ImmTAV molecules comprise an affinity-enhanced virus-specific TCR fused to an anti-CD3 effector domain. Engineering of the TCR confers extraordinary specificity and affinity for cognate viral antigen and the anti-CD3 enables retargeting of non-exhausted cytolytic T cells, irrespective of their specificity. These features enable ImmTAV molecules to detect and kill infected cells, even when expressing very low levels of antigen, bypassing ineffective host immune responses. Furthermore, the modularity of the platform allows for engineering of TCRs that effectively target viral variants. In this review, we discuss the progress made in the development of ImmTAV molecules as therapeutics for functional cure of chronic hepatitis B and HIV, from concept to the clinic.

Rapamycin inhibits hepatitis B virus covalently closed circular DNA transcription by enhancing the ubiquitination of HBx

Hepatitis B virus (HBV) infection is still a serious public health problem worldwide. Antiviral therapies such as interferon and nucleos(t)ide analogs efficiently control HBV replication, but they cannot eradicate chronic hepatitis B (CHB) because of their incapacity to eliminate endocellular covalently closed circular DNA (cccDNA). Thus, there is a necessity to develop new strategies for targeting cccDNA. As cccDNA is difficult to clear, transcriptional silencing of cccDNA is a possible effective strategy. HBx plays a vitally important role in maintaining the transcriptional activity of cccDNA and it could be a target for blocking the transcription of cccDNA. To screen new drugs that may contribute to antiviral therapy, the ability of 2,000 small-molecule compounds to inhibit HBx was examined by the HiBiT lytic detection system. We found that the macrolide compound rapamycin, which is clinically used to prevent acute rejection after organ transplantation, could significantly reduce HBx protein expression. Mechanistic studies demonstrated that rapamycin decreased the stability of the HBx protein by promoting its degradation via the ubiquitin-proteasome system. Moreover, rapamycin inhibited HBV RNA, HBV DNA, and cccDNA transcription levels in HBV-infected cells. In addition, HBx deficiency abrogated the inhibition of cccDNA transcription induced by rapamycin. Similar results were also confirmed in a recombinant cccDNA mouse model. In summary, we report a new small-molecule, rapamycin, which targets HBx to block HBV cccDNA transcription and inhibit HBV replication. This approach can identify new strategies to cure CHB.

Conserved Lysine Residues of Hepatitis B Virus Core Protein Are Not Required for Covalently Closed Circular DNA Formation

Hepatitis B virus (HBV) core protein (HBc), the building block of the viral capsid, plays a critical role throughout the HBV life cycle. There are two highly conserved lysine residues, namely, K7 and K96, on HBc, which have been proposed to function at various stages of viral replication, potentially through lysine-specific posttranslational modifications (PTMs). Here, we substituted K7 and K96 with alanine or arginine, which would also block potential PTMs on these two lysine residues, and tested the effects of these substitutions on HBV replication and infection. We found that the two lysine residues were dispensable for all intracellular steps of HBV replication. In particular, all mutants were competent to form the covalently closed circular DNA (cccDNA) via the intracellular amplification pathway, indicating that K7 and K96, or any PTMs of these residues, were not essential for nucleocapsid uncoating, a prerequisite for cccDNA formation. Furthermore, we found that K7A and K7R mutations did not affect de novo cccDNA formation and RNA transcription during infection, indicating that K7 or any PTMs of this residue were dispensable for HBV infection. In addition, we demonstrated that the HBc K7 coding sequence (AAA), as part of the HBV polyadenylation signal UAUAAA, was indispensable for viral RNA production, implicating this cis requirement at the RNA level, instead of any function of HBc-K7, likely constrains the identity of the 7th residue of HBc. In conclusion, our results provided novel insights regarding the roles of lysine residues on HBc, and their coding sequences, in the HBV life cycle. IMPORTANCE Hepatitis B virus (HBV) infection remains a public health burden that affects 296 million individuals worldwide. HBV core protein (HBc) is involved in almost all steps in the HBV life cycle. There are two conserved lysine residues on HBc. Here, we found that neither of them is essential for HBV intracellular replication, including the formation of covalently closed circular DNA (cccDNA), the molecular basis for establishing and sustaining the HBV infection. However, K96 is critical for virion morphogenesis, while the K7 coding sequence, but not HBc-K7 itself, is indispensable, as part of the RNA polyadenylation signal, for HBV RNA production from cccDNA. Our results provide novel insights regarding the role of the conserved lysine residues on HBc, and their coding sequences, in viral replication, and should facilitate the development of antiviral drugs against the HBV capsid protein.

Recent Drug Development in the Woodchuck Model of Chronic Hepatitis B

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

Expression of Functional Molecule on Plasmacytoid Dendritic Cells Is Associated With HBsAg Loss in HBeAg-Positive Patients During PEG-IFN α-2a Treatment

Objective

The ideal endpoint of antiviral therapy in chronic hepatitis B (CHB) patients is to clear hepatitis B surface antigen (HBsAg). This study aimed to evaluate whether the expression of functional molecules on plasmacytoid dendritic cells (pDCs) is associated with HBsAg loss in HBeAg-positive patients during peginterferon alpha-2a (PEG IFN α-2a) therapy.

Methods

A single-center prospective cohort study was performed in HBeAg-positive CHB patients who were treated with PEG-IFN α-2a and followed up for 4 years. HBsAg clearance, HBeAg loss and undetectable HBV DNA achieved by PEG-IFN α-2a therapy was considered as functional cure. The frequencies of pDC and CD86⁺ pDC in peripheral blood, and the mean fluorescence intensity of CD86 (CD86MFI) on the surface of pDC were measured at starting therapy, after 12 and 24 weeks of therapy.

Results

Of 63 patients enrolled, 17 patients achieved HBsAg loss. The baseline HBV DNA load in Non-functional-cure group was significantly higher than that in Functional cure group, and the CD86⁺ pDC% was significantly lower in patients without functional cure. HBV DNA load (OR=0.146, P = 0.002) and CD86⁺ pDC% (OR=1.183, P = 0.025) were independent factors associated with functional cure confirmed by binary logistic regression analysis. In the Functional cure group, HBsAg, HBeAg, and HBV DNA loads decreased remarkably after 12 weeks and 24 weeks of treatment compared to baseline. In Non-functional-cure group, CD86⁺ pDC% and CD86MFI increased significantly from baseline after 12 weeks of treatment. In the Functional cure group, compared with baseline, pDC% increased significantly at 24 weeks, while CD86MFI increased significantly after 24 weeks of treatment.

Conclusion

The lower the baseline HBV DNA load and the more the baseline CD86⁺ pDC%, the easier it is for patients to obtain functional cure.

Host cell-dependent late entry step as determinant of hepatitis B virus infection

Hepatitis B virus (HBV) has a highly restricted host range and cell tropism. Other than the human sodium taurocholate cotransporting polypeptide (huNTCP), the HBV entry receptor, host determinants of HBV susceptibility are poorly understood. Woodchucks are naturally infected with woodchuck hepatitis virus (WHV), closely related to HBV, but not with HBV. Here, we investigated the capabilities of woodchuck hepatic and human non-hepatic cell lines to support HBV infection. DNA transfection assays indicated that all cells tested supported both HBV and WHV replication steps post entry, including the viral covalently closed circular DNA (cccDNA) formation, which is essential for establishing and sustaining infection. Ectopic expression of huNTCP rendered one, but not the other, woodchuck hepatic cell line and the non-hepatic human cell line competent to support productive HBV entry, defined here by cccDNA formation during de novo infection. All huNTCP-expressing cell lines tested became susceptible to infection with hepatitis D virus (HDV) that shares the same entry receptor and initial steps of entry with HBV, suggesting that a late entry/trafficking step(s) of HBV infection was defective in one of the two woodchuck cell lines. In addition, the non-susceptible woodchuck hepatic cell line became susceptible to HBV after fusion with human hepatic cells, suggesting the lack of a host cell-dependent factor(s) in these cells. Comparative transcriptomic analysis of the two woodchuck cell lines revealed widespread differences in gene expression in multiple biological processes that may contribute to HBV infection. In conclusion, other than huNTCP, neither human- nor hepatocyte-specific factors are essential for productive HBV entry. Furthermore, a late trafficking step(s) during HBV infection, following the shared entry steps with HDV and before cccDNA formation, is subject to host cell regulation and thus, a host determinant of HBV infection.

Fundamental studies on, and development of therapies against, chronic hepatitis B virus (HBV) infection, which inflicts hundreds of millions worldwide, are impeded by deficiencies in HBV-susceptible animal models. HBV displays a strict species and cell tropism that are not clearly understood. Here, by studying replication of HBV, and the related woodchuck hepatitis virus, in human and woodchuck hepatic or non-hepatic cells, we found that non-hepatic human cells and some woodchuck hepatic cells could support productive HBV entry after expression of the human cell receptor for HBV. Moreover, by studying the infection of hepatitis D virus, which shares the same entry receptor and initial steps of entry with HBV, we could narrow down a host determinant of HBV infection operating at a late entry/trafficking step(s). Our study thus provides new insights into determinants of HBV host tropism and facilitates the development of HBV-susceptible animal models.

Prospects of viral vector-mediated delivery of sequences encoding anti-HBV designer endonucleases

Available treatment for chronic hepatitis B virus (HBV) infection offers modest functional curative efficacy. The viral replicative intermediate comprising covalently closed circular DNA (cccDNA) is responsible for persistent chronic HBV infection. Hence, current efforts have focused on developing therapies that disable cccDNA. Employing gene editing tools has emerged as an attractive strategy, with the end goal of establishing permanently inactivated cccDNA. Although anti-HBV designer nucleases are effective in vivo, none has yet progressed to clinical trial. Lack of safe and efficient delivery systems remains the limiting factor. Several vectors may be used to deliver anti-HBV gene editor-encoding sequences, with viral vectors being at the forefront. Despite the challenges associated with packaging large gene editor-encoding sequences into viral vectors, advancement in the field is overcoming such limitations. Translation of viral vector-mediated gene editing against HBV to clinical application is within reach. This review discusses the prospects of delivering HBV targeted designer nucleases using viral vectors.

Region-Specific Hepatitis B Virus Genome Exposure from Nucleocapsid Modulated by Capsid Linker Sequence and Inhibitor: Implications for Uncoating

Hepatitis B virus (HBV) contains a partially double-stranded, relaxed circular (RC) DNA genome synthesized within a nucleocapsid (NC) in the host cell cytoplasm. The release of RC DNA from the NC, in an ill-defined process called uncoating, to the nucleus is required for its conversion to the covalently closed circular (CCC) DNA, the viral episome serving as the transcriptional template for all viral RNAs necessary for replication and, thus, essential for establishing and sustaining viral infection. In efforts to better understand uncoating, we analyzed HBV core (HBc) mutants that show various levels of nuclear CCC DNA but little to no cytoplasmic RC DNA. We found that RC DNA could be synthesized by these mutants outside the cell, but in contrast to the wild type (wt), the mutant NCs were unable to protect RC DNA from digestion by the endogenous nuclease(s) in cellular lysates or exogenous DNase. Subcellular fractionation suggested that the major RC DNA-degrading activity was membrane associated. Digestion with sequence-specific and nonspecific DNases revealed the exposure of specific regions of RC DNA from the mutant NC. Similarly, treatment of wt NCs with a core inhibitor known to increase CCC DNA by affecting uncoating also led to region-specific exposure of RC DNA. Furthermore, a subpopulation of untreated wild type (wt) mature NCs showed site-specific exposure of RC DNA as well. Competition between RC DNA degradation and its conversion to CCC DNA during NC uncoating thus likely plays an important role in the establishment and persistence of HBV infection and has implications for the development of capsid-targeted antivirals. IMPORTANCE Disassembly of the hepatitis B virus (HBV) nucleocapsid (NC) to release its genomic DNA, in an ill-understood process called uncoating, is required to form the viral nuclear episome in the host cell nucleus, a viral DNA essential for establishing and sustaining HBV infection. The elimination of the HBV nuclear episome remains the holy grail for the development of an HBV cure. We report here that the HBV genomic DNA is exposed in a region-specific manner during uncoating, which is enhanced by mutations of the capsid protein and a capsid-targeted antiviral compound. The exposure of the viral genome can result in its rapid degradation or, alternatively, can enhance the formation of the nuclear episome, thus having a major impact on HBV infection and persistence. These results are thus important for understanding fundamental mechanisms of HBV replication and persistence and for the ongoing pursuit of an HBV cure.

Research Progress on the Mechanism of Persistent Low-Level HBsAg Expression in the Serum of Patients with Chronic HBV Infection

Among HBV-infected persons, there is a group of people with hepatitis B surface antigen (HBsAg) showing persistently low levels of expression. The production of low-level HBsAg does not mean a good outcome of chronic HBV infection. Patients still have virus replication and sustained liver damage, and they have the potential to transmit the infection. This risk poses a challenge to clinical diagnosis and blood transfusion safety and is a major concern of experts. However, the mechanism behind persistent low-level HBsAg expression in serum is not completely clear, and complete virus clearance by the host is vital. In this review, we summarize the research progress on the mechanism behind low-level expression of HBsAg in patients with chronic HBV infection in recent years.

N6-methyladenosine modification of the 5' epsilon structure of the HBV pregenome RNA regulates its encapsidation by the viral core protein

HBV infections are the leading cause of chronic hepatitis and carry the risk of liver cirrhosis and cancer. The HBV life cycle is perpetuated by an RNA intermediate termed pregenomic RNA (pgRNA), which is encapsidated by the viral core protein. The pgRNA packaging process is an essential step in viral replication. Here, we investigated the role of N6-methyladenosine (m⁶A) modification in the recognition of pgRNA by the core protein during encapsidation. m⁶A modification of 5′ epsilon structural motifs serves as the recognition signal for the core protein interaction, as evidenced by the failure of 5′ epsilon m⁶A mutant to encapsidate pgRNA. This study identifies the structural role of m⁶A modification in pgRNA encapsidation and provides an avenue in RNA–protein complex interactions.

Hepatitis B virus (HBV) contains a partially double-stranded DNA genome. During infection, its replication is mediated by reverse transcription (RT) of an RNA intermediate termed pregenomic RNA (pgRNA) within core particles in the cytoplasm. An epsilon structural element located in the 5′ end of the pgRNA primes the RT activity. We have previously identified the N6-methyladenosine (m⁶A)–modified DRACH motif at 1905 to 1909 nucleotides in the epsilon structure that affects myriad functions of the viral life cycle. In this study, we investigated the functional role of m⁶A modification of the 5′ ε (epsilon) structural element of the HBV pgRNA in the nucleocapsid assembly. Using the m⁶A site mutant in the HBV 5′ epsilon, we present evidence that m⁶A methylation of 5′ epsilon is necessary for its encapsidation. The m⁶A modification of 5′ epsilon increased the efficiency of viral RNA packaging, whereas the m⁶A of 3′ epsilon is dispensable for encapsidation. Similarly, depletion of methyltransferases (METTL3/14) decreased pgRNA and viral DNA levels within the core particles. Furthermore, the m⁶A modification at 5′ epsilon of HBV pgRNA promoted the interaction with core proteins, whereas the 5′ epsilon m⁶A site–mutated pgRNA failed to interact. HBV polymerase interaction with 5′ epsilon was independent of m⁶A modification of 5′ epsilon. This study highlights yet another pivotal role of m⁶A modification in dictating the key events of the HBV life cycle and provides avenues for investigating RNA–protein interactions in various biological processes, including viral RNA genome encapsidation in the context of m⁶A modification.

Untying relaxed circular DNA of hepatitis B virus by polymerase reaction provides a new option for accurate quantification and visualization of covalently closed circular DNA

Hepatitis B virus (HBV) is a small hepatotropic DNA virus that replicates via an RNA intermediate. After entry, the virus capsid carries relaxed circular DNA (rcDNA) into the nucleus where the viral genome is converted into covalently closed circular DNA (cccDNA), which serves as the template for all viral transcripts. To monitor cccDNA levels, preprocessing methods to eliminate rcDNA have emerged for quantitative PCR, although Southern blotting is still the only method to discriminate cccDNA from other DNA intermediates. In this study, we have established a robust method for untying mature rcDNA into double stranded linear DNA using specific polymerases. Untying rcDNA provides not only an alternative method for cccDNA quantification but also a sensitive method for visualizing cccDNA. We combined this method with plasmid-safe DNase and T5 exonuclease preprocessing and revealed that accurate quantification requires cccDNA digestion by a restriction enzyme because heat stability of cccDNA increases after T5 exonuclease treatment. In digital PCR using duplex TaqMan probes, fewer than 1000 copies of cccDNA were successfully visualized as double positive spots that were distinct from single positives derived from untied rcDNA. This method was further applied to the infection model of primary hepatocytes treated with nucleoside analogues and a core protein allosteric modulator to monitor cccDNA levels. Relative quantification of cccDNA by human genome copy demonstrated the possibility of precise evaluation of cccDNA level per nucleus. These results clearly indicate that the sequential reaction from untying rcDNA is useful to investigate cccDNA fates in a small fraction of nuclei.

Regulatory function of interferon-inducible 44-like for hepatitis B virus covalently closed circular DNA in primary human hepatocytes

AIM

Curing hepatitis B virus (HBV) infection requires elimination of covalently closed circular DNA (cccDNA). Interferon (IFN)-γ has noncytolytic antiviral potential; however, elimination of cccDNA could not be achieved. To enhance the regulatory effect, we comprehensively analyzed the host factors associated with cccDNA amplification and IFN-γ and IFN-α effects using an in vitro HBV infection system showing various transcription levels.

METHODS

Primary human hepatocytes were infected with HBV using genomic plasmids carrying the basic core promoter mutation A1762T/G1764A and/or the precore mutation G1896A and treated with IFN-γ and IFN-α. Comprehensive and functional studies involving microarray and small interfering RNA analysis revealed the host factors related to cccDNA regulation.

RESULTS

The HBV infection system reproduced the HBV life cycle and showed various propagation levels. Microarray analysis revealed 53 genes correlated with the cccDNA levels. Of the 53 genes, expression of IFN-induced protein 44-like (IFI44L) was significantly upregulated by IFN-γ and IFN-α. The anti-HBV effect of IFI44L is exerted regardless of IFN-γ or IFN-α by inhibiting the activation of nuclear factor-κB and signal transducer and activator of transcription 1 pathways.

CONCLUSIONS

Using the in vitro HBV infection system, an IFN-inducible molecule, IFI44L, associated with cccDNA amplification, was identified. These results suggest an innovative molecular strategy for the regulation of HBV cccDNA by controlling a novel host factor, IFI44L.

The role of gut microbiota in hepatitis B disease progression and treatment

Current therapeutic interventions can only suppress hepatitis B virus (HBV) replication or reduce complications without a cure. Therefore, further development of new treatment methods is critical for the global eradication of HBV. Accumulating evidence suggests that the liver and gut share an interconnected relationship referred to as the 'Gut-Liver Axis', where exchanges happen bi-directionally. The gut itself is the host to a unique microbiota profile which has metabolic, immunological, neurological and nutritional functions. Gut microbiota is not only constantly intersecting with the liver but also associated with hepatic injury when dysbiosis occurs. In recent years, there has been increased interest in gut microbiota and its implications on liver disease treatment. Progress has been made in understanding the complex relationship between chronic hepatitis B (CHB) and gut microbiota. New investigative techniques such as colony-free sequencing enabled new perspectives into this field. Mouse models and human studies revealed that HBV infection is associated with significant alteration of gut microbiota, which differ depending on the stage of CHB disease progression. Different mechanisms of the hepatic injury from gut microbiota dysbiosis have also been proposed based on findings of increased intestinal permeability to toxins, disruption of normal bacterial metabolism, and colonization of the gut by oral microbiota. New treatment methods targeting gut microbiota in CHB, such as probiotics and faecal microbiota transplant, have also gained promising results in recent years. The current review recapitulated the most recent investigations into the relationship between gut microbiota and CHB to provide research directions towards the new therapeutic target of CHB.

Inhibitory Activities of Ranunculus japonicus Thunb. Ethanol Extract against Hepatitis B Virus

The chronic hepatitis B virus (HBV) infection is a worldwide public health problem, which cannot be cured by current therapeutics due to the persistence of viral CCC DNA in the infected hepatocytes. Screening from medicinal herbs for anti-HBV activities showed that the ethanol extract from Ranunculus japonicus Thunb. could decrease the production of HBV e antigen (HBeAg). Further study showed that the extract had no effect on core protein expression but significantly reduced the efficiency of viral capsid assembly. The levels of viral pgRNA and total core DNA were not affected significantly. However, the ratio of RC DNA/SS DNA decreased, indicating that the conversion of RC DNA from SS DNA was delayed by the extract. More interestingly, though similar levels of RC DNA were accumulated, the CCC DNA level and its formation efficiency were reduced significantly, which was also consistent with the decreased level of HBeAg, indicating that Ranunculus japonicus Thunb. extract could inhibit the CCC DNA formation. Together, this study found that Ranunculus japonicus Thunb. extract could inhibit HBV replication at multiple steps, especially showed significant inhibitory effects on capsid assembly and CCC DNA formation. This article is protected by copyright. All rights reserved.

Cellular Id1 inhibits hepatitis B virus transcription by interacting with the novel covalently closed circular DNA-binding protein E2F4

Hepatitis B virus (HBV) infection is a major risk factor for hepatocellular carcinoma (HCC), which required developing novel therapies targeting the inhibition of HBV transcription and replication due to current limited treatment options. We explored novel target for the development of novel therapies targeting the inhibition of HBV replication and transcription. The expression of Id1 and E2F4 in HCC cells and tissues was detected by qRT-PCR and western blot. We investigated the Id1 and E2F4-mediated transcription of HBV infection by using HepG2.2.15, HepAD38, HepG2-NTCP cell lines and AAV/HBV-infected mice. Interactions between the two host proteins and viral covalently closed circular DNA (cccDNA) were assessed using subcellular localization, protein-protein interaction, chromatin immunoprecipitation, and luciferase assays. Ectopic Id1 significantly reduced HBV transcription and replication in both HBV-expressing cells and AAV/HBV-infected mice. Id1 and E2F4 could form a heterodimer to prevent E2F4 from promoting HBV transcription and replication. E2F4 could directly bind to cccDNA and activate the HBV core promoter in cell lines. Furthermore, in vitro binding experiments confirmed that the sequence 1758'-TTAAAGGTC-1766', which is highly conserved among HBV genotypes, is the target site of the E2F4 homodimer. The findings suggest that E2F4 function as novel cccDNA-binding protein to directly activate HBV transcription by binding to Cp promoter region. Our results highlight the ability that E2F4 represent a pan-potential therapeutic target against HBV transcription and provide more clues to better understand the life cycle of HBV.

The cytoplasmic LSm1-7 and nuclear LSm2-8 complexes exert opposite effects on Hepatitis B virus biosynthesis and interferon responses

Despite many studies on host or viral gene expression, how the cellular proteome responds to internal or external cues during the infection process remains unclear. In this study, we used a Hepatitis B Virus (HBV) replication model and performed proteomic analyses to understand how HBV evades innate immunity as a function of cell cycle progression. Specifically, we performed proteomic analyses of HBV-replicating cells in G1/S and G2/M phases, as a function of IFN-α treatment. We identified that the conserved LSm (Like-Sm1-8) proteins were differentially regulated in HBV replicating cells treated with IFN-α. Specifically, in G2/M phase, IFN-α increased protein level of LSm1, the unique subunit of cytoplasmic LSm1-7 complex involved in mRNA decay. By contrast, IFN-α decreased LSm8, the unique subunit of nuclear LSm2-8 complex, a chaperone of U6 spliceosomal RNA, suggesting the cytoplasmic LSm1-7 complex is antiviral, whereas the nuclear LSm2-8 complex is pro-viral. In HBV replication and infection models, siRNA-mediated knockdown of LSm1 increased all viral RNAs. Conversely, LSm8 knockdown reduced viral RNA levels, dependent on N6-adenosine methylation (m⁶A) of the epsilon stem-loop at the 5' end of pre-Core/pregenomic (preC/pg) RNA. Methylated RNA immunoprecipitation (MeRIP) assays demonstrated reduced viral RNA methylation by LSm8 knockdown, dependent on the 5' m6A modification, suggesting the LSm2-8 complex has a role in mediating this modification. Interestingly, splicing inhibitor Cp028 acting upstream of the LSm2-8 complex suppressed viral RNA levels without reducing the 5' m6A modification. This observation suggests Cp028 has novel antiviral effects, likely potentiating IFN-α-mediated suppression of HBV biosynthesis.

Bay41-4109-induced aberrant polymers of hepatitis b capsid proteins are removed via STUB1-promoted p62-mediated macroautophagy

The hepatitis B virus (HBV) core protein (HBc) functions in multiple steps of the viral life cycle. Heteroaryldihydropyrimidine compounds (HAPs) such as Bay41-4109 are capsid protein allosteric modulators that accelerate HBc degradation and inhibit the virion secretion of HBV, specifically by misleading HBc assembly into aberrant non-capsid polymers. However, the subsequent cellular fates of these HAP-induced aberrant non-capsid polymers are not well understood. Here, we discovered that that the chaperone-binding E3 ubiquitin ligase protein STUB1 is required for the removal of Bay41-4109-induced aberrant non-capsid polymers from HepAD38 cells. Specifically, STUB1 recruits BAG3 to transport Bay41-4109-induced aberrant non-capsid polymers to the perinuclear region of cells, thereby initiating p62-mediated macroautophagy and lysosomal degradation. We also demonstrate that elevating the STUB1 level enhances the inhibitory effect of Bay41-4109 on the production of HBeAg and HBV virions in HepAD38 cells, in HBV-infected HepG2-NTCP cells, and in HBV transgenic mice. STUB1 overexpression also facilitates the inhibition of Bay41-4109 on the cccDNA formation in de novo infection of HBV. Understanding these molecular details paves the way for applying HAPs as a potentially curative regimen (or a component of a combination treatment) for eradicating HBV from hepatocytes of chronic infection patients.

Hepatitis B virus (HBV) infects more than 250 million people worldwide chronically. It is a major pathogen causing liver cirrhosis and hepatocellular carcinoma now. The HBV capsid protein (HBc) plays multiple roles in the viral life cycle, and many antivirals targeting HBc such as Heteroaryldihydropyrimidine compounds (HAPs) are under clinical trial recently. This study aimed to investigate how a HAP compound Bay41-4109 induces the degradation of HBc protein. Bay41-4109 induces aberrant non-capsid polymers, which form in complex with the chaperone-binding E3 ubiquitin ligase protein STUB1 and co-chaperone BAG3 and are transported to the perinuclear compartment. Subsequently, Bay41-4109-induced aberrant non-capsid polymers are removed by p62-mediated macroautophagy and lysosomal degradation. STUB1 overexpression accelerates Bay41-4109-induced degradation of HBc protein, and thus enhances the effect of Bay41-4109 on inhibiting secretion of HBeAg and HBV virions. When Bay41-4109 are enforced during HBV infection, de novo cccDNA formation were also negatively regulated by STUB1 overexpression. Altogether, this study provides novel mechanistic insights into developing more potent and safe HAP-based antiviral treatment.

Research progress in hepatitis B virus covalently closed circular DNA

Hepatitis B virus (HBV) infections are a global public health issue. HBV covalently closed circular DNA (cccDNA), the template for the transcription of viral RNAs, is a key factor in the HBV replication cycle. Notably, many host factors involved in HBV cccDNA epigenetic modulation promote the development of hepatocellular carcinoma (HCC). The HBV cccDNA minichromosome is a clinical obstacle that cannot be efficiently eliminated. In this review, we provide an update on the advances in research on HBV cccDNA and further discuss factors affecting the modulation of HBV cccDNA. Hepatitis B virus X protein (HBx) contributes to HBV cccDNA transcription and the development of hepatocarcinogenesis through modulating host epigenetic regulatory factors, thus linking the cccDNA to hepatocarcinogenesis. The measurable serological biomarkers of continued transcription of cccDNA, the effects of anti-HBV drugs on cccDNA, and potential therapeutic strategies targeting cccDNA are discussed in detail. Thus, this review describes new insights into HBV cccDNA mechanisms and therapeutic strategies for cleaning cccDNA, which will benefit patients with liver diseases.

The hepatitis B virus polymerase

Hepatitis B virus (HBV) is a hepatotropic, partially double-stranded DNA virus that replicates by reverse transcription and is a major cause of chronic liver disease and hepatocellular carcinoma. Reverse transcription is catalyzed by the four-domain multifunctional HBV polymerase (P) protein that has protein-priming, RNA- and DNA-dependent DNA synthesis (i.e., reverse transcriptase), and ribonuclease H activities. P also likely promotes the three strand transfers that occur during reverse transcription, and it may participate in immune evasion by HBV. Reverse transcription is primed by a tyrosine residue in the amino-terminal domain of P, and P remains covalently attached to the product DNA throughout reverse transcription. The reverse transcriptase activity of P is the target for the nucleos(t)ide analog drugs that dominate HBV treatment, and P is the target of ongoing efforts to develop new drugs against both the reverse transcriptase and ribonuclease H activities. Despite the unusual reverse transcription pathway catalyzed by P and the importance of P to HBV therapy, understanding the enzymology and structure of HBV P severely lags that of the retroviral reverse transcriptases due to substantial technical challenges to studying the enzyme. Obtaining a better understanding of P will broaden our appreciation of the diversity among reverse transcribing elements in nature, and will help improve treatment for people chronically infected with HBV.

Hepatitis B virus X (HBx) Protein Expression is Tightly Regulated by N6-methyladenosine Modification of its mRNA

Hepatitis B virus (HBV) encodes a regulatory protein termed HBx, that has been intensely studied in the past and shown to play a key role(s) in viral transcription and replication. In addition, a huge body of work exists in the literature related to signal transduction and possible mechanism(s) leading to hepatocarcinogenesis associated with infection. We have previously reported that HBV transcripts are modified by N6-methyladenosine (m6A) at the single consensus DRACH motif at 1905-1909 nucleotide (nt) in the epsilon structural element and this m6A modification affects the HBV life cycle. In this study, we present evidence that additional variants of m6A (DRACH) motifs are located within 1606 to 1809 nt correspond on the coding region of HBx mRNA and 3' untranslated region (UTR) of other viral mRNAs. Using the mutants of additional m6A site in 1606 to 1809 nt and a depletion strategy of m6A methyltransferases (METTL3/14) and reader proteins (YTHDFs), we show that m6A modification at 1616 nt, located in HBx coding region, regulates HBx protein expression. The HBx RNA and protein expressions were notably increased by the silencing of m6A reader YTHDF2 and methyltransferases as well as the mutation of m6A sites in the HBx coding region. However, other viral protein expressions were not affected by the m6A modification at 1616 nt. Thus, m6A modifications in the HBx open reading frame (ORF), downregulate HBx protein expression, commonly seen during HBV transfections, transgenic mice, and natural infections of human hepatocytes. These studies identify the functional role of m6A modification in the subtle regulation of HBx protein expression consistent with its possible role in establishing chronic hepatitis. Importance N6-methyladenosien (m6A) modifications have been recently implicated in the HBV life cycle. Previously, we observed that m6A modification occurs in the adenosine at 1907 nt of HBV genome and this modification regulates the viral life cycle. Here, we identified an additional m6A site located in 1616 nt of the HBV genome. This modification negatively affects HBx RNA and protein expression. In the absence of m6A methyltransferases (METTL3/14) and reader protein (YTHDF2), the HBx RNA and protein expression were increased. Using HBV mutants that lack m6A in the HBx coding region, we present the unique positional effects of m⁶A in the regulation of HBx protein expression.

Hepatitis B Virus Infection in Patients Receiving Allogeneic Hematopoietic Stem Cell Transplantation

Considering a steady increase in the number of allogeneic hematopoietic stem cell transplantations (allo-HSCT) worldwide and the significant proportion of the world’s population that has been exposed to hepatitis B virus (HBV) infection, HBV reactivation following allo-HSCT remains an important issue for post-transplant morbidity and mortality. Antiviral prophylaxis can reduce HBV replication, severity of HBV-related hepatitis, and mortality; therefore, identification of patients at risk is crucial. It is recommended that all recipients and donors should be screened for active or prior HBV infection, including HBsAg, antiHBc, and antiHBs. Adoptive immunity transfer from the donor seems to have protective effects against HBV reactivation. Antiviral prophylaxis should be initiated in all HBsAg-positive patients. HBsAg-negative, antiHBc-positive patients remain at risk; therefore, antiviral prophylaxis should be considered if baseline serum HBV DNA is detectable. In HBsAg-negative, antiHBc-positive patients without detectable HBV DNA, close monitoring of viral load with an on-demand therapy is necessary. Entecavir or tenofovir rather than lamivudine are more appropriate for the emergence of lamivudine resistance. The treatment duration remains unclear, with 6- to 12-month therapy after cessation of immunosuppressive therapy commonly recommended. Here we review the updated evidence and recent recommendations regarding HBV reactivation in patients undergoing allo-HSCT for individualized therapy.

Regulation of Hepatitis B Virus Virion Release and Envelopment Timing by Nucleocapsid and Envelope Interactions

Interactions between the N-terminal (assembly) domain (NTD) and the linker region of the hepatitis B virus (HBV) capsid protein and the large (L) envelope protein are required for virion formation, which occurs via budding of cytoplasmic mature nucleocapsids (NCs) containing the relaxed circular (RC) DNA genome into an intracellular membrane compartment containing viral envelope proteins. L-capsid interactions also negatively regulates covalently closed circular (CCC) DNA formation, which occurs after RC DNA release from mature NCs and nuclear import. We have now found that L could increase RC DNA in cytoplasmic mature NCs that are destabilized due to mutations in the NTD or the linker, even in those that apparently fail to support secretion of complete virions extracellularly. Other mutations in the capsid linker could block the effects of L on both cytoplasmic NC DNA and nuclear CCC DNA. Furthermore, the maturity of RC DNA in cytoplasmic NCs that was enhanced by L or found in secreted virions was modulated by the capsid linker sequence. The level and maturity of the cytoplasmic RC DNA was further influenced by the efficiency of extracellular virion secretion dependent on viral genotype-specific envelope proteins. These results suggest that interactions between the capsid and envelope proteins regulate one or more steps during virion secretion beyond initial capsid envelopment, and highlights the critical role of the capsid linker in regulating capsid-envelope interaction, including the timing of envelopment during NC maturation. Importance Hepatitis B virus (HBV) is a major human pathogen causing serious liver diseases including cancer. The interactions between the HBV capsid and the large (L) envelope protein is required for formation of infectious viral particles and also negatively regulate formation of an HBV DNA episome in the host cell nucleus, which serves as the sole transcriptional template capable of supporting all viral gene expression to sustain HBV replication and therefore, is the molecular basis of HBV persistence. Here, we report evidence indicating that L-capsid interactions modulate the timing of formation of infectious HBV particles during replication and facilitate extracellular release following their formation. Furthermore, a short linker sequence in the capsid protein plays a critical role in these processes as well as controls the amplification of the nuclear episome. These findings inform fundamental mechanisms of HBV replication as well as antiviral development targeting the HBV capsid and DNA episome.

Concentration of Na+-taurocholate-cotransporting polypeptide expressed after in vitro-transcribed mRNA transfection determines susceptibility of hepatoma cells for hepatitis B virus

Infection of hepatocytes by hepatitis B virus (HBV) depends on surface expression of its receptor Na+-taurocholate-cotransporting polypeptide (NTCP), but sufficient NTCP expression is lacking in most cell lines. NTCP can be introduced by plasmid transfection or transduction by viral vectors to render cells permissive for HBV. However, transient transfection of hepatocyte-derived cell lines is inefficient, resulting in inhomogeneous protein expression and does not allow to adapt the level of NTCP expression. We therefore utilized in vitro transcribed mRNA to introduce NTCP into cells. Optimization using alternative cap structures and nucleotide modifications rendered mRNA transfection into different non-hepatic and hepatic cell lines very efficient. After transfection of mRNA, surface expression and functionality of NTCP was demonstrated by staining with an N-terminal HBV-preS peptide and bile acid uptake. Introduction of NTCP by mRNA transfection increased susceptibility of hepatoma cells to HBV in a dose-dependent manner. Transfection of NTCP mRNA into non-liver cells, in contrast, supported bile acid uptake but did still not render the cells permissive for HBV, demonstrating the requirement for additional host factors. Introduction of candidate host factors by mRNA transfection will allow for fast and convenient analysis of the viral life cycle using a transient, but reliable expression system.

Treatments for HBV: A Glimpse into the Future

The hepatitis B virus is responsible for most of the chronic liver disease and liver cancer worldwide. As actual therapeutic strategies have had little success in eradicating the virus from hepatocytes, and as lifelong treatment is often required, new drugs targeting the various phases of the hepatitis B virus (HBV) lifecycle are currently under investigation. In this review, we provide an overview of potential future treatments for HBV.