Strategies to eliminate HBV infection

Novel Approaches to Inhibition of HBsAg Expression from cccDNA and Chromosomal Integrants: A Review

Hepatitis B virus (HBV) is a widely prevalent liver infection that can cause acute or chronic hepatitis. Although current treatment modalities are highly effective in the suppression of viral levels, they cannot eliminate the virus or achieve definitive cure. This is a consequence of the complex nature of HBV-host interactions. Major challenges to achieving sustained viral suppression include the presence of a high viral burden from the HBV DNA and hepatitis B surface antigen (HBsAg), the presence of reservoirs for HBV replication and antigen production, and the HBV-impaired innate and adaptive immune response of the host. Those therapeutic methods include cell entry inhibitors, HBsAg inhibitors, gene editing approaches, immune-targeting therapies and direct inhibitors of covalently closed circular DNA (cccDNA). Novel approaches that target these key mechanisms are now being studied in preclinical and clinical phases. In this review article, we provide a comprehensive review on mechanisms by which HBV escapes elimination from current treatments, and highlight new agents to achieve a definitive HBV cure.

A computational study of a stochastic fractal-fractional hepatitis B virus infection incorporating delayed immune reactions via the exponential decay

Recently, researchers have become interested in modelling, monitoring, and treatment of hepatitis B virus infection. Understanding the various connections between pathogens, immune systems, and general liver function is crucial. In this study, we propose a higher-order stochastically modified delay differential model for the evolution of hepatitis B virus transmission involving defensive cells. Taking into account environmental stimuli and ambiguities, we presented numerical solutions of the fractal-fractional hepatitis B virus model based on the exponential decay kernel that reviewed the hepatitis B virus immune system involving cytotoxic T lymphocyte immunological mechanisms. Furthermore, qualitative aspects of the system are analyzed such as the existence-uniqueness of the non-negative solution, where the infection endures stochastically as a result of the solution evolving within the predetermined system's equilibrium state. In certain settings, infection-free can be determined, where the illness settles down tremendously with unit probability. To predict the viability of the fractal-fractional derivative outcomes, a novel numerical approach is used, resulting in several remarkable modelling results, including a change in fractional-order δ with constant fractal-dimension ϖ, δ with changing ϖ, and δ with changing both δ and ϖ. White noise concentration has a significant impact on how bacterial infections are treated.

The Progress and Promise of RNA Medicine─An Arsenal of Targeted Treatments

In the past decade, there has been a shift in research, clinical development, and commercial activity to exploit the many physiological roles of RNA for use in medicine. With the rapid success in the development of lipid-RNA nanoparticles for mRNA vaccines against COVID-19 and with several approved RNA-based drugs, RNA has catapulted to the forefront of drug research. With diverse functions beyond the role of mRNA in producing antigens or therapeutic proteins, many classes of RNA serve regulatory roles in cells and tissues. These RNAs have potential as new therapeutics, with RNA itself serving as either a drug or a target. Here, based on the CAS Content Collection, we provide a landscape view of the current state and outline trends in RNA research in medicine across time, geography, therapeutic pipelines, chemical modifications, and delivery mechanisms.

Use of a Deep Learning Approach for the Sensitive Prediction of Hepatitis B Surface Antigen Levels in Inactive Carrier Patients

Deep learning is a subset of machine learning that can be employed to accurately predict biological transitions. Eliminating hepatitis B surface antigens (HBsAgs) is the final therapeutic endpoint for chronic hepatitis B. Reliable predictors of the disappearance or reduction in HBsAg levels have not been established. Accurate predictions are vital to successful treatment, and corresponding efforts are ongoing worldwide. Therefore, this study aimed to identify an optimal deep learning model to predict the changes in HBsAg levels in daily clinical practice for inactive carrier patients. We identified patients whose HBsAg levels were evaluated over 10 years. The results of routine liver biochemical function tests, including serum HBsAg levels for 1, 2, 5, and 10 years, and biometric information were obtained. Data of 90 patients were included for adaptive training. The predictive models were built based on algorithms set up by SONY Neural Network Console, and their accuracy was compared using statistical analysis. Multiple regression analysis revealed a mean absolute percentage error of 58%, and deep learning revealed a mean absolute percentage error of 15%; thus, deep learning is an accurate predictive discriminant tool. This study demonstrated the potential of deep learning algorithms to predict clinical outcomes.

Cytokines and Chemokines in HBV Infection

Chronic hepatitis B virus (HBV) infection remains a leading cause of hepatic inflammation and damage. The pathogenesis of chronic hepatitis B (CHB) infection is predominantly mediated by persistent intrahepatic immunopathology. With the characterization of unique anatomical and immunological structure, the liver is also deemed an immunological organ, which gives rise to massive cytokines and chemokines under pathogenesis conditions, having significant implications for the progression of HBV infection. The intrahepatic innate immune system is responsible for the formidable source of cytokines and chemokines, with the latter also derived from hepatic parenchymal cells. In addition, systemic cytokines and chemokines are disturbed along with the disease course. Since HBV is a stealth virus, persistent exposure to HBV-related antigens confers to immune exhaustion, whereby regulatory cells are recruited by intrahepatic chemokines and cytokines, including interleukin-10 and transforming growth factor β, are involved in such series of causal events. Although the considerable value of two types of available approved treatment, interferons and nucleos(t)ide analogues, effectively suppress HBV replication, neither of them is sufficient for optimal restoration of the immunological attrition state to win the battle of the functional or virological cure of CHB infection. Notably, cytokines and chemokines play a crucial role in regulating the immune response. They exert effects by directly acting on HBV or indirectly manipulating target immune cells. As such, specific cytokines and chemokines, with a potential possibility to serve as novel immunological interventions, combined with those that target the virus itself, seem to be promising prospects in curative CHB infection. Here, we systematically review the recent literature that elucidates cytokine and chemokine-mediated pathogenesis and immune exhaustion of HBV infection and their dynamics triggered by current mainstream anti-HBV therapy. The predictive value of disease progression or control and the immunotherapies target of specific major cytokines and chemokines in CHB infection will also be delineated.

Novel Therapies of Hepatitis B and D

Hepatitis B virus (HBV) infection is a global public health issue and is a major cause of cirrhosis and hepatocellular carcinoma (HCC). Hepatitis D virus (HDV) requires the hepatitis B surface antigen (HBsAg) to replicate. The eradication of HBV, therefore, can also cure HDV. The current therapies for chronic hepatitis B and D are suboptimal and cannot definitely cure the viruses. In order to achieve functional or complete cure of these infections, novel therapeutic agents that target the various sites of the viral replicative cycle are necessary. Furthermore, novel immunomodulatory agents are also essential to achieve viral clearance. Many of these new promising compounds such as entry inhibitors, covalently closed circular DNA (cccDNA) inhibitors, small interfering RNAs (siRNAs), capsid assembly modulators and nucleic acid polymers are in various stages of clinical developments. In this review article, we provided a comprehensive overview of the structure and lifecycle of HBV, the limitations of the current therapies and a summary of the novel therapeutic agents for both HDV and HBV infection.

Low-level viremia in nucleoside analog-treated chronic hepatitis B patients

ABSTRACT

Low-level viremia (LLV) was defined as persistent or intermittent episodes of detectable hepatitis B virus (HBV) DNA (<2000 IU/mL, detection limit of 10 IU/mL) after 48 weeks of antiviral treatment. Effective antiviral therapies for chronic hepatitis B (CHB) patients, such as entecavir (ETV), tenofovir disoproxil fumarate (TDF), and tenofovir alafenamide (TAF), have been shown to inhibit the replication of HBV DNA and prevent liver-related complications. However, even with long-term antiviral therapy, there are still a number of patients with persistent or intermittent LLV. At present, the research on LLV to address whether adversely affect the clinical outcome is limited, and the follow-up treatment for these patients is open to question. At the same time, the mechanism of LLV is not clear. In this review, we summarize the incidence of LLV, the association between LLV and long-term outcomes, possible mechanisms, and management strategies in these patient populations.

Variable Proportions of Phylogenetic Clustering and Low Levels of Antiviral Drug Resistance among the Major HBV Sub-Genotypes in the Middle East and North Africa

Hepatitis B virus (HBV) infection remains a major public health threat in the Middle East and North Africa (MENA). Phylogenetic analysis of HBV can be helpful to study the putative transmission links and patterns of inter-country spread of the virus. The objectives of the current study were to analyze the HBV genotype/sub-genotype (SGT) distribution, reverse transcriptase (RT), and surface (S) gene mutations and to investigate the domestic transmission of HBV in the MENA. All HBV molecular sequences collected in the MENA were retrieved from GenBank as of 30 April 2021. Determination of genotypes/SGT, RT, and S mutations were based on the Geno2pheno (hbv) 2.0 online tool. For the most prevalent HBV SGTs, maximum likelihood phylogenetic analysis was conducted to identify the putative phylogenetic clusters, with approximate Shimodaira-Hasegawa-like likelihood ratio test values ≥ 0.90, and genetic distance cut-off values ≤ 0.025 substitutions/site as implemented in Cluster Picker. The total number of HBV sequences used for genotype/SGT determination was 4352 that represented a total of 20 MENA countries, with a majority from Iran (n = 2103, 48.3%), Saudi Arabia (n = 503, 11.6%), Tunisia (n = 395, 9.1%), and Turkey (n = 267, 6.1%). Genotype D dominated infections in the MENA (86.6%), followed by genotype A (4.1%), with SGT D1 as the most common in 14 MENA countries and SGT D7 dominance in the Maghreb. The highest prevalence of antiviral drug resistance was observed against lamivudine (4.5%) and telbivudine (4.3%). The proportion of domestic phylogenetic clustering was the highest for SGT D7 (61.9%), followed by SGT D2 (28.2%) and genotype E (25.7%). The largest fraction of domestic clusters with evidence of inter-country spread within the MENA was seen in SGT D7 (81.3%). Small networks (containing 3-14 sequences) dominated among domestic phylogenetic clusters. Specific patterns of HBV genetic diversity were seen in the MENA with SGT D1 dominance in the Levant, Iran, and Turkey; SGT D7 dominance in the Maghreb; and extensive diversity in Saudi Arabia and Egypt. A low prevalence of lamivudine, telbivudine, and entecavir drug resistance was observed in the region, with almost an absence of resistance to tenofovir and adefovir. Variable proportions of phylogenetic clustering indicated prominent domestic transmission of SGT D7 (particularly in the Maghreb) and relatively high levels of virus mobility in SGT D1.

Prevention of Hepatitis B Virus Infection and Liver Cancer

Hepatocellular carcinoma (HCC) is one of the five leading causes of cancer death in human. Hepatitis B virus (HBV) is the most common etiologic agent of HCC in the world. Prevention is the best way to control cancer. There are three levels of liver cancer prevention, i.e., primary prevention by HBV vaccination targeting the general population starting from birth dose, secondary prevention by antiviral agent for high-risk subjects with chronic HBV infection, and tertiary prevention by antiviral agent to prevent recurrence for patients who have been successfully treated for liver cancer. Primary prevention by hepatitis B vaccination is most cost effective, the cancer preventive efficacy support it as the first successful example of cancer preventive vaccine in human. Addition of hepatitis B immunoglobulin immediately after birth and antiviral agent during the third trimester of pregnancy to block mother-to-infant transmission of HBV are existing or possible emerging strategies to enhance the prevention efficacy of HBV infection and its related liver cancer. Secondary prevention with current antiviral agents may reduce the risk or delay the onset of HCC development, but could not eradicate HBV infection and HCC. Better antiviral therapeutic agents are needed for better secondary prevention.

Intrahepatic Expression of C-C Motif ligand 5 in Patients with Chronic Hepatitis B

BACKGROUND

C-C motif ligand 5 (CCL5) is reported to play a key role in acute and chronic liver diseases. However, the association between CCL5 and chronic hepatitis B (CHB) remains to be explored. We aimed to investigate the CCL5 expression in the liver tissues of CHB patients and compared the CCL5 expression among CHB patients with different stages of liver inflammation and fibrosis.

METHODS

Liver tissue specimens from 51 CHB patients who underwent liver biopsy and twelve healthy liver donors were included in the present study. CCL5 expression in the liver tissues was analyzed using immunohistochemistry. The hepatic inflammation grades and fibrotic stages of CHB patients were assessed by the Scheuer classification system.

RESULTS

Livers of CHB patients exhibited significantly accumulated CCL5+ cells when compared to those of healthy controls (42.80 ± 4.37 vs. 7.25 ± 0.99/HPF, P < .001). CHB patients with higher hepatic inflammation grades had more CCL5+ cells in their livers than those with lower grades (P < .05). However, the numbers of CCL5+ cells were not correlated with the fibrotic stages in CHB patients (r = .073, P = .61). The number of CCL5+ cells in the liver tissues of CHB patients was positively correlated with alanine transaminase levels (r = .278, P = .041) and aspartate aminotransferase levels (r = .328, P = .009).

CONCLUSIONS

CHB patients have a significant accumulation of CCL5+ cells in the liver, and CCL5 may play a pathological role in hepatic inflammation of CHB.

Ciclopirox inhibits Hepatitis B Virus secretion by blocking capsid assembly

Chronic hepatitis B virus (HBV) infection can cause cirrhosis and hepatocellular carcinoma and is therefore a serious public health problem. Infected patients are currently treated with nucleoside/nucleotide analogs and interferon α, but this approach is not curative. Here, we screen 978 FDA-approved compounds for their ability to inhibit HBV replication in HBV-expressing HepG2.2.15 cells. We find that ciclopirox, a synthetic antifungal agent, strongly inhibits HBV replication in cells and in mice by blocking HBV capsid assembly. The crystal structure of the HBV core protein and ciclopirox complex reveals a unique binding mode at dimer-dimer interfaces. Ciclopirox synergizes with nucleoside/nucleotide analogs to prevent HBV replication in cells and in a humanized liver mouse model. Therefore, orally-administered ciclopirox may provide a novel opportunity to combat chronic HBV infection by blocking HBV capsid assembly.

Novel tumour antigens and the development of optimal vaccine design

The interplay between tumours and the immune system has long been known to involve complex interactions between tumour cells, immune cells and the tumour microenvironment. The progress of checkpoint inhibitors in the clinic in the last decade has highlighted again the role of the immune system in the fight against cancer. Numerous efforts have been undertaken to develop ways of stimulating the cellular immune response to eradicate tumours. These interventions include the identification of appropriate tumour antigens as targets for therapy. In this review, we summarize progress in selection of target tumour antigen. Targeting self antigens has the problem of thymic deletion of high-affinity T-cell responses leaving a diminished repertoire of low-affinity T cells that fail to kill tumour cells. Thymic regulation appears to be less stringent for differentiation of cancer-testis antigens, as many tumour rejection antigens fall into this category. More recently, targeting neo-epitopes or post-translational modifications such as a phosphorylation or stress-induced citrullination has shown great promise in preclinical studies. Of particular interest is that the responses can be mediated by both CD4 and CD8 T cells. Previous vaccines have targeted CD8 T-cell responses but more recently, the central role of CD4 T cells in orchestrating inflammation within tumours and also differentiating into potent killer cells has been recognized. The design of vaccines to induce such immune responses is discussed herein. Liposomally encoded ribonucleic acid (RNA), targeted deoxyribonucleic acid (DNA) or long peptides linked to toll-like receptor (TLR) adjuvants are the most promising new vaccine approaches. These exciting new approaches suggest that the 'Holy Grail' of a simple nontoxic cancer vaccine may be on the horizon. A major hurdle in tumour therapy is also to overcome the suppressive tumour environment. We address current progress in combination therapies and suggest that these are likely to show the most promise for the future.

Current and future directions of management of hepatitis B: steps toward a cure

Universal hepatitis B virus vaccination has been effective in reducing incident chronic hepatitis B but will not have the requisite effect on the prevalence of end-stage liver disease in chronically infected persons. The natural history and immunological stages of hepatitis B virus infection are still being defined. Over three decades, current therapies have reduced morbidity from chronic hepatitis B. The majority require nucleoside analog maintenance therapy. The preferential preservation of covalently closed circular DNA (cccDNA), and capsid reverse transcriptase–cccDNA interactions currently precludes cure in most. A functional cure in  the host may require several synergistic antiviral and immunological intercessions. The correct sequencing and combinations of treatment with either host or viral targeting agents have yet to be determined. Proven surrogates for cccDNA for clinical trials are required. Different strategies may become apparent for patients at different stages of the disease. Curative therapies will require affordability. This review focuses on steps toward a cure.

Interleukin-7 augments CD8+ T cells function and promotes viral clearance in chronic hepatitis C virus infection

Interleukin (IL)-7 is a potent proliferation, activation, and survival cytokine for CD8⁺ T cells to improve viral and tumor specific CD8⁺ T cell responses. However, the role of IL-7 in regulation of dysfunctional hepatitis C virus (HCV)-specific CD8⁺ T cells was not fully elucidated. Thus, a total of 53 patients with chronic hepatitis C and 24 healthy individuals were enrolled in the current study. Serum IL-7 and its receptor α chain CD127 expression was measured. The modulatory function of IL-7 to CD8⁺ T cells was investigated in both direct and indirect contact co-culture with HCVcc-infected Huh7.5 cells. Both serum IL-7 and CD127 expression on CD8⁺ T cells was significantly reduced in chronic HCV-infected patients, which was negatively correlated with HCV RNA. Stimulation of IL-7 promoted both cytotoxicity and cytokines (interferon-γ, tumor necrosis factor-α, and IL-2) production of CD8⁺ T cells from patients with chronic hepatitis C. Moreover, IL-7 increased proliferation of CD8⁺ T cells, while downregulated a critical repressor of cytokine signaling, suppressor of cytokine signaling 3 (SOCS3). The IL-7-mediated enhancement effects to CD8⁺ T cells were dependent on IL-6 production. The current data suggested that IL-7 induced both cytolytic and noncytolytic functions of CD8⁺ T cells probably via repression of SOCS3. IL-7 might be considered as one of the therapeutic candidates for treatment of chronic HCV infection.

Toward cure chronic hepatitis B infection and hepatocellular carcinoma prevention: Lessons learned from nucleos(t)ide analogues therapy

Nucleos(t)ide analogues (NAs) could successfully suppress hepatitis B virus (HBV) replication in patients with chronic hepatitis B (CHB). However, due to probable development of drug resistance or low/delayed response, these treatments may not be satisfactory. In addition to the HBV DNA polymerase inhibiting activity, these drugs could lead to changes in cytokines profiles. It is important to monitor these changes so that they could be used as target of treatment. Evaluating the previously reported immune responses due to NAs treatments, it was concluded that interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α), interleukin-4 (IL-4), and IL-12 increase after the treatment. This will be followed by the improved capacity of immune cells for eliminating HBV. In contrast, regulatory responses including IL-10 and transforming growth factor-beta (TGF-β) significantly decreased as the result of NAs therapy. Unexpectedly, T helper (Th) 17-associated cytokines also decreased significantly. These results could be used to employ the new strategies to suppress viral replication, minimize HBV DNA levels, inducing hepatitis B e antigen (HBeAg) seroconversion or even hepatitis B surface antigen (HBsAg) seroclearance. In order to accomplish these goals, extended treatment with high dose of both IL-12 and IFN in combination with high barrier to resistance NA might significantly improve the HBsAg seroclearance rate. Considering the danger of emerging aberrant immune responses, determining the optimum dosage as well as close monitoring of patients during the treatment is strongly advised. In order to make HBV immunotherapy practical, further studies are needed to confirm these results.

Treatment of hepatitis B virus: an update

Chronic hepatitis B virus infection is a global health concern as it affects over 240 million people worldwide and an estimated 686,000 people die annually as a result of complications of the disease. With the development of newer antiviral drugs, viral suppression of HBV is achievable, however elimination of HBV from infected individuals (functional cure) remains an issue. Due to persistence of HBV DNA (cccDNA) in infected cells, chronically infected patients who discontinue therapy prior to HBsAg loss or seroconversion are likely to relapse. Several novel therapeutic strategies are being researched and studied in clinical trials. Here we review these novel strategies to achieve sustained cure or elimination of HBV. These strategies include the targeting of the host or viral factors required for viral persistence as well as therapeutic vaccines.

Hepitopes: A live interactive database of HLA class I epitopes in hepatitis B virus

Increased clinical and scientific scrutiny is being applied to hepatitis B virus (HBV), with focus on the development of new therapeutic approaches, ultimately aiming for cure. Defining the optimum natural CD8+ T cell immune responses that arise in HBV, mediated by HLA class I epitope presentation, may help to inform novel immunotherapeutic strategies. Therefore, we have set out to develop a comprehensive database of these epitopes in HBV, coined ‘Hepitopes’. This undertaking has its foundations in a systematic literature review to identify the sites and sequences of all published class I epitopes in HBV. We also collected information regarding the methods used to define each epitope, and any reported associations between an immune response to this epitope and disease outcome. The results of this search have been collated into a new open-access interactive database that is available at http://www.expmedndm.ox.ac.uk/hepitopes. Over time, we will continue to refine and update this resource, as well as inviting contributions from others in the field to support its development. This unique new database is an important foundation for ongoing investigations into the nature and impact of the CD8+ T cell response to HBV.

Future Therapy for Hepatitis B Virus: Role of Immunomodulators

Although currently available therapies for chronic hepatitis B virus infection can suppress viremia and provide long-term benefits for patients, they do not lead to a functional cure for most patients. Advances in our understanding of the virus-host interaction and the recent remarkable success of immunotherapy in cancer offer new and promising strategies for developing immune modulators that may become important components of a total therapeutic approach to hepatitis B, some of which are now in clinical development. Among the immunomodulatory agents currently being investigated to combat chronic HBV are toll-like receptor agonists, immune checkpoint inhibitors, therapeutic vaccines, and engineered T cells. The efficacy of some immune modulatory therapies is compromised by high viral antigen levels. Cutting edge strategies, including RNA interference and CRISPR/Cas9, are now being studied that may ultimately be shown to have the capacity to lower viral antigen levels sufficiently to substantially increase the efficacy of these agents. The current advances in therapies for chronic hepatitis B are leading us toward the possibility of a functional cure.

Review article: novel therapies for hepatitis B virus cure - advances and perspectives

BACKGROUND

Current anti-viral therapies, interferon and nucleos(t)ide analogues, have been proven to reduce the progression of chronic hepatitis B (CHB). However, covalently closed circular DNA (cccDNA) of hepatitis B virus (HBV) persists, resulting in viral relapse after the discontinuation of treatment.

AIM

To discuss and review novel therapies for chronic hepatitis B infection.

METHODS

Recent published studies which searched from PubMed were comprehensive reviewed. The key words include chronic hepatitis B, hepatitis B virus cure, covalently closed circular DNA, direct acting anti-virals and host targeting agents.

RESULTS

Several novel agents through viral and host targets approaches are under investigations towards functional cure of HBV. On the one hand, direct acting anti-virals targeting virus itself, such as HBV new polymerase inhibitor, entry inhibitor, engineered site-specific nucleases and RNA interference, could inhibit amplification of cccDNA as well as intrahepatic HBV infection and eliminate or silence cccDNA transcription. Inhibitors of HBV nucleocapsid assembly suppress capsid formation and prevent synthesis of HBV DNA. On the other hand, host targeting agents (HTA) include lymphotoxin-β receptor agonist, toll-like receptor agonist, immune checkpoint inhibitors and adenovirus-based therapeutic vaccine. Through enhancing innate and adaptive immune responses, these agents could induce noncytolytic destruction of cccDNA or attack HBV-infected hepatocytes.

CONCLUSION

With these promising approaches, we hope to reach global hepatitis B virus control in the middle of this century.

Hepatotoxicity of targeted therapy for cancer

INTRODUCTION

Understanding the mechanism of DILI with MTA, and how to avoid and manage these toxicities is essential for minimising inferior cancer treatment outcomes. An organised and comprehensive overview of MTA-associated hepatotoxicity is lacking; this review aims to fill the gap.

AREAS COVERED

A literature review was performed based on published case reports and relevant studies or articles pertaining to the topics on PubMed. Food and Drug Administration drug information documents and search on the US National Library of Medicine LiverTox database was performed for all relevant MTA.

EXPERT OPINION

MTA-associated hepatotoxicity is common but rarely fatal. The pattern of hepatotoxicity is predominantly idiosyncratic. Pharmacogenomics show potential in predicting patients at risk of poorly metabolising or developing immunoallergic responses to MTA, but prospective data is scant. Preventing reactivation of viral hepatitis using anti-viral drugs, and avoidance of drug combinations at high risk of negative interactions are the most readily preventable measures for DILI.

Hepatitis B virus: new therapeutic perspectives

Current antiviral therapies have dramatically improved the long-term outcomes of patients with chronic hepatitis B virus (HBV) infection. Both interferon (IFN) and nucleos(t)ide analogue (NA) treatments have been shown to reduce the progression of liver disease in chronic hepatitis B (CHB) patients. However, persistent covalently closed circular DNA (cccDNA) can result in a viral relapse after discontinuation of antiviral treatment. On the basis of extensive research on the HBV lifecycle and virus-host interactions, several new agents focusing on viral and host targets are under development to cure HBV. New polymerase inhibitors, tenofovir alafenamide and besifovir provide effective and safer treatment for CHB patients. Agents targeting cccDNA, such as engineered site-specific nucleases and RNA interference therapeutics could eliminate cccDNA or silence cccDNA transcription. Inhibitors of HBV nucleocapsid assembly suppress capsid formation and prevent synthesis of HBV DNA. The HBV entry inhibitor, Myrcludex-B, has been shown to effectively inhibit amplification of cccDNA as well as the spread of intrahepatic infection. Agents targeting host factors that enhance innate and adaptive immune responses, including the lymphotoxin-β receptor agonist, toll-like receptor agonist, immune checkpoint inhibitors and adenovirus-based therapeutic vaccine, could play a critical role in the elimination of HBV-infected cells. With all of these promising approaches, we hope to reach the ultimate goal of a cure to HBV in the near future.

The current treatment situation and definitions of a cure for chronic HBV infection

HBV vaccination, while effective in reducing incident chronic disease in endemic regions, will not have the desired impact on the rates of end-stage liver disease in chronically infected persons. Over three decades, IFN-α and nucleoside analogs have reduced the morbidity from the disease. A large reservoir of chronic infection remains. The natural history of HBV infection is still being defined. Understanding the interactions between HBV and the host will be fundamental to achieving higher rates of cure. Curing hepatitis B will require several steps for either eradication, or a functional cure in the host. It is unclear whether covently closed circular DNA chromatin would need to be cleared to cure hepatitis B, or whether low threshold levels would slow the disease.

Present and future therapies of hepatitis B: From discovery to cure

Hepatitis B virus (HBV) is a significant global pathogen, infecting more than 240 million people worldwide. While treatment for HBV has improved, HBV patients often require lifelong therapies and cure is still a challenging goal. Recent advances in technologies and pharmaceutical sciences have heralded a new horizon of innovative therapeutic approaches that are bringing us closer to the possibility of a functional cure of chronic HBV infection. In this article, we review the current state of science in HBV therapy and highlight new and exciting therapeutic strategies spurred by recent scientific advances. Some of these therapies have already entered into clinical phase, and we will likely see more of them moving along the development pipeline.

CONCLUSION

With growing interest in developing and efforts to develop more effective therapies for HBV, the challenging goal of a cure may be well within reach in the near future.

Hepatitis B vaccination and prevention of hepatocellular carcinoma

Hepatitis B virus (HBV) infection is a global health threat; with 240 million people are chronic carriers of the virus. The infection can cause acute and chronic liver disease including liver cirrhosis and hepatocellular carcinoma (HCC). On the basis of disease burden and the availability of safe and effective vaccines, World Health Organization has recommended that hepatitis B vaccine be incorporated into routine infant and childhood immunization programs for all countries. The efficacy of universal immunization has been proven in many countries, with substantial reductions of the prevalence of HBV carriage in children, adolescents and young adults. Most important, hepatitis B vaccination can protect them from HCC, as has been demonstrated in Taiwan and other countries. Nevertheless, the implementation of worldwide vaccination against HBV indeed requires more effort to overcome the social and economic challenges. To have a global control of HBV infection, we have to continue the universal HBV vaccination, interrupt the possible transmission routes and treat eligible patients with antiviral agents. However, current treatments are still far from ideal as they cannot eradicate intrahepatic HBV cccDNA, and lifelong administration of these agents will pose a major economic burden, especially in the endemic Asia-Pacific region. Thus we need innovative treatment strategies and novel agents with difference modes of action to overcome the unmet medical need for an efficient HBV cure with subsequent global eradication of HBV infection, hopefully by the first half of 21st century.

Delivery of cell-penetrating peptide-peptide nucleic acid conjugates by assembly on an oligonucleotide scaffold

Delivery to intracellular target sites is still one of the main obstacles in the development of peptide nucleic acids (PNAs) as antisense-antigene therapeutics. Here, we designed a self-assembled oligonucleotide scaffold that included a central complementary region for self-assembly and lateral regions complementing the PNAs. Assembly of cell-penetrating peptide (CPP)-PNAs on the scaffold significantly promoted endocytosis of PNAs by at least 10-fold in cell cultures, particularly for scaffolds in which the central complementary region was assembled by poly(guanine) and poly(cytosine). The antisense activity of CPP-PNAs increased by assembly on the scaffold and was further enhanced after co-assembly with endosomolytic peptide (EP)-PNA. This synergistic effect was also observed following the assembly of antigene CPP-PNAs\EP-PNAs on the scaffold. However, antigene activity was only observed by targeting episomal viral DNA or transfected plasmids, but not the chromosome in the cell cultures. In conclusion, assembly on oligonucleotide scaffolds significantly enhanced the antisense-antigene activity of PNAs by promoting endocytosis and endosomal escape. This oligonucleotide scaffold provided a simple strategy for assembly of multiple functional peptide-PNA conjugates, expanding the applications of PNAs and demonstrating the potential of PNAs as antiviral therapeutics.

New paradigms in hepatitis B management: only diamonds are forever

INTRODUCTION

The hepatitis B virus (HBV) causes chronic hepatitis B (CHB) in ∼350 million people worldwide who have an increased risk of end-stage liver disease and/or hepatocellular carcinoma.

SOURCES OF DATA

Several peer-reviewed papers featuring new approaches to anti-HBV management. Additionally, we also reviewed recent abstract presentations at international congresses.

AREAS OF AGREEMENT

There has been great progress in CHB therapy with the development of standard and pegylated interferon (i.e. PEG-IFN) as well as nucleos/tide analogs (NAs). IFN has both antiviral and immunomodulatory effects and through immune-mediated destruction of infected hepatocytes offers the possibility of finite therapy. However, this 'killing for a cure' antiviral strategy may not be tolerated in many, especially in cirrhotic patients. NAs inhibit viral reverse transcriptase, have few side effects and prevent liver disease progression, but cannot offer a cure as they have little effect on the resilient HBV covalently closed circular DNA (cccDNA) intermediate. Moreover, NAs such as tenofovir and entecavir offer a high genetic barrier to resistance, but are expensive and not readily available in many global regions.

GROWING POINTS

Despite significant treatment advances, there is increased recognition of the need for improved anti-HBV treatments, and new virologic tests for monitoring treatment response.

AREAS OF CONTROVERSY

The role of quantitative hepatitis B surface antigen, intrahepatic cccDNA levels and viral genotype in selecting treatment candidates and refining NA stopping rules.

AREAS TIMELY FOR DEVELOPING NEW RESEARCH

Potential new therapies include viral entry inhibitors, RNA interference technologies (i.e. RNAi) and small molecules that modulate cccDNA transcription, as well as novel immunomodulatory therapies to boost HBV-specific T cell responses. The ultimate goal of new tests and anti-HBV therapies is to reduce the burden and expense of life-long CHB treatment, as 'only diamonds are forever'.

Anti-HBV Drugs: Progress, Unmet Needs, and New Hope

Approximately 240 million people worldwide are chronically infected with hepatitis B virus (HBV), which represents a significant challenge to public health. The current goal in treating chronic HBV infection is to block progression of HBV-related liver injury and inflammation to end-stage liver diseases, including cirrhosis and hepatocellular carcinoma, because we are unable to eliminate chronic HBV infection. Available therapies for chronic HBV infection mainly include nucleos/tide analogues (NAs), non-NAs, and immunomodulatory agents. However, none of them is able to clear chronic HBV infection. Thus, a new generation of anti-HBV drugs is urgently needed. Progress has been made in the development and testing of new therapeutics against chronic HBV infection. This review aims to summarize the state of the art in new HBV drug research and development and to forecast research and development trends and directions in the near future.

CRISPR/Cas9 nickase-mediated disruption of hepatitis B virus open reading frame S and X

Current antiviral therapies cannot cure hepatitis B virus (HBV) infection; successful HBV eradication would require inactivation of the viral genome, which primarily persists in host cells as episomal covalently closed circular DNA (cccDNA) and, to a lesser extent, as chromosomally integrated sequences. However, novel designer enzymes, such as the CRISPR/Cas9 RNA-guided nuclease system, provide technologies for developing advanced therapy strategies that could directly attack the HBV genome. For therapeutic application in humans, such designer nucleases should recognize various HBV genotypes and cause minimal off-target effects. Here, we identified cross-genotype conserved HBV sequences in the S and X region of the HBV genome that were targeted for specific and effective cleavage by a Cas9 nickase. This approach disrupted not only episomal cccDNA and chromosomally integrated HBV target sites in reporter cell lines, but also HBV replication in chronically and de novo infected hepatoma cell lines. Our data demonstrate the feasibility of using the CRISPR/Cas9 nickase system for novel therapy strategies aiming to cure HBV infection.

Therapeutic cancer vaccines

The clinical benefit of therapeutic cancer vaccines has been established. Whereas regression of lesions was shown for premalignant lesions caused by HPV, clinical benefit in cancer patients was mostly noted as prolonged survival. Suboptimal vaccine design and an immunosuppressive cancer microenvironment are the root causes of the lack of cancer eradication. Effective cancer vaccines deliver concentrated antigen to both HLA class I and II molecules of DCs, promoting both CD4 and CD8 T cell responses. Optimal vaccine platforms include DNA and RNA vaccines and synthetic long peptides. Antigens of choice include mutant sequences, selected cancer testis antigens, and viral antigens. Drugs or physical treatments can mitigate the immunosuppressive cancer microenvironment and include chemotherapeutics, radiation, indoleamine 2,3-dioxygenase (IDO) inhibitors, inhibitors of T cell checkpoints, agonists of selected TNF receptor family members, and inhibitors of undesirable cytokines. The specificity of therapeutic vaccination combined with such immunomodulation offers an attractive avenue for the development of future cancer therapies.

The epidemiological changes of HCV and HBV infections in the era of new antiviral therapies and the anti-HBV vaccine

The World Health Organization (WHO) resolution adopted in 2010 recognized viral hepatitis as a global health problem. In April 2014, for the first time, the WHO produced guidelines for the screening, care and treatment of persons with hepatitis C infections. In May 2014, a follow-up resolution urged WHO Member States to develop and implement a national strategy for the prevention, diagnosis and treatment of viral hepatitis based on the local epidemiological context. Although blood donor screening, which began in the early 1990s, has reduced the spread of the virus in the population, the WHO estimates that 150 million people are chronically infected with hepatitis C virus (HCV) and are at an increased risk of developing liver cirrhosis and hepatocellular carcinoma. In addition, 3-4 million people are infected each year. HCV treatment is currently evolving rapidly, and several drugs are in various stages of development. With regard to the hepatitis B virus (HBV), in March 2015, the WHO published the first guidelines for the prevention, care and treatment of persons with chronic hepatitis B infection, which were designed to complement the recent guidelines on HCV. Although the introduction of an effective vaccine against the hepatitis B virus has reduced the prevalence and health and economic impact of hepatitis in industrialized countries, the WHO estimates that more than 2 billion people are HBV-infected and 350 million people are chronic carriers.

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.

Synthetic RNAi triggers and their use in chronic hepatitis B therapies with curative intent

Current therapies for chronic hepatitis B virus infection (CHB) - nucleos(t)ide analogue reverse transcriptase inhibitors and interferons - result in low rates of functional cure defined as sustained off-therapy seroclearance of hepatitis B surface antigen (HBsAg). One likely reason is the inability of these therapies to consistently and substantially reduce the levels of viral antigen production. Accumulated evidence suggests that high serum levels of HBsAg result in exhaustion of the host immune system, rendering it unable to mount the effective antiviral response required for HBsAg clearance. New mechanistic approaches are required to produce high rates of HBsAg seroclearance in order to greatly reduce off-treatment disease progression. Already shown to be a clinically viable means of reducing gene expression in a number of other diseases, therapies based on RNA interference (RNAi) can directly target hepatitis B virus transcripts with high specificity, profoundly reducing the production of viral proteins. The fact that the viral RNA transcripts contain overlapping sequences means that a single RNAi trigger can result in the degradation of all viral transcripts, including all messenger RNAs and pregenomic RNA. Advances in the design of RNAi triggers have increased resistance to degradation and reduced nonspecific innate immune stimulation. Additionally, new methods to effectively deliver the trigger to liver hepatocytes, and specifically to the cytoplasmic compartment, have resulted in increased efficacy and tolerability. An RNAi-based drug currently in clinical trials is ARC-520, a dynamic polyconjugate in which the RNAi trigger is conjugated to cholesterol, which is coinjected with a hepatocyte-targeted, membrane-active peptide. Phase 2a clinical trial results indicate that ARC-520 was well tolerated and resulted in significant, dose-dependent reduction in HBsAg for up to 57days in CHB patients. RNAi-based therapies may play an important role in future therapeutic regimes aimed at improving HBsAg seroclearance and eliminating the need for lifelong therapy. This paper forms part of a symposium in Antiviral Research on "An unfinished story: from the discovery of the Australia antigen to the development of new curative therapies for hepatitis B."

Polyionic vaccine adjuvants: another look at aluminum salts and polyelectrolytes

Adjuvants improve the adaptive immune response to a vaccine antigen by modulating innate immunity or facilitating transport and presentation. The selection of an appropriate adjuvant has become vital as new vaccines trend toward narrower composition, expanded application, and improved safety. Functionally, adjuvants act directly or indirectly on antigen presenting cells (APCs) including dendritic cells (DCs) and are perceived as having molecular patterns associated either with pathogen invasion or endogenous cell damage (known as pathogen associated molecular patterns [PAMPs] and damage associated molecular patterns [DAMPs]), thereby initiating sensing and response pathways. PAMP-type adjuvants are ligands for toll-like receptors (TLRs) and can directly affect DCs to alter the strength, potency, speed, duration, bias, breadth, and scope of adaptive immunity. DAMP-type adjuvants signal via proinflammatory pathways and promote immune cell infiltration, antigen presentation, and effector cell maturation. This class of adjuvants includes mineral salts, oil emulsions, nanoparticles, and polyelectrolytes and comprises colloids and molecular assemblies exhibiting complex, heterogeneous structures. Today innovation in adjuvant technology is driven by rapidly expanding knowledge in immunology, cross-fertilization from other areas including systems biology and materials sciences, and regulatory requirements for quality, safety, efficacy and understanding as part of the vaccine product. Standardizations will aid efforts to better define and compare the structure, function and safety of adjuvants. This article briefly surveys the genesis of adjuvant technology and then re-examines polyionic macromolecules and polyelectrolyte materials, adjuvants currently not known to employ TLR. Specific updates are provided for aluminum-based formulations and polyelectrolytes as examples of improvements to the oldest and emerging classes of vaccine adjuvants in use.

Towards the elimination and eradication of hepatitis B

Despite the introduction of vaccination, chronic hepatitis B remains a major cause of liver-related morbidity and mortality including cirrhosis, decompensated cirrhosis and hepatocellular carcinoma. Maintenance antiviral therapy is required for most people, as low rates of cure occur. The stated aim of therapy presently is HBV DNA suppression; effective suppression of viral replication is associated with significant reductions in morbidity from end-stage liver failure and to an extent, hepatocellular carcinoma. Unfortunately, major barriers to cure, such as a reservoir of episomal covalently closed circular DNA (cccDNA) (the HBV minichromosome), and a dysfunctional immune response, pose challenges. These barriers will need to be overcome to ensure higher rates of cure than can be achieved presently. Quantitative and diagnostic testing for HBV DNA is not generally available, hampering effective monitoring and treatment in low-income countries. The majority of patients in resource-constrained countries are not identified before the onset of cirrhosis. Without coordinated action, and transfer of new diagnostic technologies and treatments to low-income countries, recent therapeutic advances will have little effect on the global burden of disease. A shift to curative treatment for the majority would be a major advance in the elimination of hepatitis B. New and improved molecular therapeutics and immunological strategies for the treatment of chronic hepatitis are emerging, however. A number of promising lines of development are in progress. A curative regimen may require a combination of viral suppression via nucleoside analogue therapy to prevent cccDNA amplification and viral propagation, safe selective cccDNA inhibitors to deplete, silence or degrade cccDNA, agents to block the entry of HBV into the hepatocyte plus compounds to prevent capsid assembly and cccDNA interactions. Targeted immune activation could restore the exhausted immune cell repertoire.

Natural Killer p46 Controls Hepatitis B Virus Replication and Modulates Liver Inflammation

Natural killer (NK) cells play an important role in hepatitis B virus (HBV) infection control, and are regulated by a complex network of activating and inhibitory receptors. However, NK cell activity in HBV patients remains poorly understood. The objective of this study was to investigate the phenotypic and functional characteristics of circulating NK cells in patients during different chronic hepatitis B (CHB) infection stages. We investigated NK cell phenotypes, receptor expression and function in 86 CHB patients and 20 healthy controls. NK cells were purified and NK cell subsets were characterized by flow cytometry. Cytotoxic activity (CD107a) and interferon-gamma (IFN-γ) secretion were examined, and Natural Killer p46 (NKP46) blockade and spontaneous NK cell cytolytic activity against K562, HepG2 and HepG2.215 cell lines was studied. Activating NKp46 receptor expression was higher in inactive HBsAg carriers when compared with other groups (p = 0.008). NKp46 expression negatively correlated with HBV DNA (R = -0.253, p = 0.049) and ALT (R = -0.256, p = 0.045) levels. CD107a was higher in immune-activated groups when compared with immune-tolerant groups (p = 0.039). CD107a expression was related to viral load (p = 0.02) and HBeAg status (p = 0.024). In vitro NKp46 blockade reduced NK cell cytolytic activity against HepG2 and HepG2.215 cell lines (p = 0.02; p = 0.039). Furthermore, NK cells from high viral load CHB patients displayed significantly lower specific cytolytic activity against anti-NKp46-loaded K562 targets (p = 0.0321). No significant differences were observed in IFN-γ secretion (p > 0.05). In conclusion, NKp46 expression regulates NK cell cytolytic function. NKp46 may moderate NK cell activity during HBV replication suppression and HBV-associated liver damage and may be critical for NK cell activity during CHB infection.