•NAs will be an important component of the first new combinations to be tested in clinical trials.•Add on in NA-suppressed patients, pretreatment with NAs (sequential combination) or combination with ...other DAAs and/or immuno-modulatory therapies are all possible in theory but there is only limited knowledge or experience to make informed choices.•NA pre-treatment or combination with NA would: a) cooperate to achieve complete suppression of HBV DNA polymerase, b) contribute to reduce the recycling of mature capsides to the nucleus and reduce of cccDNA pool, c) limit viral spread to uninfected hepatocytes, d) partially restore HBV specific CD4 and CD8 T cell function, e) reduce the risk of hepatic flares and limit liver damage in case of efficient immune restoration, f) decrease the risk of resistance to new drugs.
The latest generation of nucleo(t)side analogs (NAs) provide robust virus suppression with high barrier to resistance. Long term NAs treatment is associated with a partial restoration in HBV-specific T-cell functions, regression of fibrosis, no disease progression and a reduction of HCC risk but rarely lead to cure and life-long treatments is often required. New insights into the hepatitis B viral life cycle and the host immune response have expanded the potential targets for drug therapies with interesting antiviral candidates and novel immunotherapeutic approaches in early stage development. Here we review the mode of action of current drugs (NAs and PEG IFN) and new classes of anti-HBV compounds, focusing on the possible role of nucleo(t)side analogs in future combination therapies.
Chronic hepatitis B (CHB) virus infection is a major public health burden and the leading cause of hepatocellular carcinoma. Despite the efficacy of current treatments, hepatitis B virus (HBV) cannot ...be fully eradicated due to the persistence of its minichromosome, or covalently closed circular DNA (cccDNA). The HBV community is investing large human and financial resources to develop new therapeutic strategies that either silence or ideally degrade cccDNA, to cure HBV completely or functionally. cccDNA transcription is considered to be the key step for HBV replication. Transcription not only influences the levels of viral RNA produced, but also directly impacts their quality, generating multiple variants. Growing evidence advocates for the role of the co-transcriptional regulation of HBV RNAs during CHB and viral replication, paving the way for the development of novel therapies targeting these processes. This review focuses on the mechanisms controlling the different co-transcriptional processes that HBV RNAs undergo, and their contribution to both viral replication and HBV-induced liver pathogenesis.
Summary Antiviral drug resistance is a crucial factor that frequently determines the success of long-term therapy for chronic hepatitis B. The development of resistance to nucleos(t)ide analogues has ...been associated with exacerbations in liver disease and increased risk of emergence of multidrug resistance. The selection of a potent nucleos(t)ide analogue with a high barrier to resistance as a first-line therapy, such as entecavir or tenofovir, provides the best chance of achieving long-term treatment goals and should be used wherever possible. The barrier to resistance of a given nucleos(t)ide analogue is influenced by genetic barrier, drug potency, patient adherence, pharmacological barrier, viral fitness, mechanism of action, and cross-resistance. In countries with limited health-care resources, the selection of a therapy with a high barrier to resistance is not always possible and alternative strategies for preventing resistance might be needed, although limited data are available to support these strategies.
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•GS-9620 has no direct antiviral activity against HBV.•Type I IFN induced by GS-9620 durably suppresses HBV without reducing cccDNA levels.•GS-9620-induced cytokines enhance HBV ...antigen presentation.•Established HBV infection does not modulate innate immune sensing or signaling.
GS-9620, an oral agonist of toll-like receptor 7 (TLR7), is in clinical development for the treatment of chronic hepatitis B (CHB). GS-9620 was previously shown to induce prolonged suppression of serum viral DNA and antigens in the woodchuck and chimpanzee models of CHB. Herein, we investigated the molecular mechanisms that contribute to the antiviral response to GS-9620 using in vitro models of hepatitis B virus (HBV) infection.
Cryopreserved primary human hepatocytes (PHH) and differentiated HepaRG (dHepaRG) cells were infected with HBV and treated with GS-9620, conditioned media from human peripheral blood mononuclear cells treated with GS-9620 (GS-9620 conditioned media GS-9620-CM), or other innate immune stimuli. The antiviral and transcriptional response to these agents was determined.
GS-9620 had no antiviral activity in HBV-infected PHH, consistent with low level TLR7 mRNA expression in human hepatocytes. In contrast, GS-9620-CM induced prolonged reduction of HBV DNA, RNA, and antigen levels in PHH and dHepaRG cells via a type I interferon (IFN)-dependent mechanism. GS-9620-CM did not reduce covalently closed circular DNA (cccDNA) levels in either cell type. Transcriptional profiling demonstrated that GS-9620-CM strongly induced various HBV restriction factors – although not APOBEC3A or the Smc5/6 complex – and indicated that established HBV infection does not modulate innate immune sensing or signaling in cryopreserved PHH. GS-9620-CM also induced expression of immunoproteasome subunits and enhanced presentation of an immunodominant viral peptide in HBV-infected PHH.
Type I IFN induced by GS-9620 durably suppressed HBV in human hepatocytes without reducing cccDNA levels. Moreover, HBV antigen presentation was enhanced, suggesting additional components of the TLR7-induced immune response played a role in the antiviral response to GS-9620 in animal models of CHB.
GS-9620 is a drug currently being tested in clinical trials for the treatment of chronic hepatitis B virus (HBV) infection. GS-9620 has previously been shown to suppress HBV in various animal models, but the underlying antiviral mechanisms were not completely understood. In this study, we determined that GS-9620 does not directly activate antiviral pathways in human liver cells, but can induce prolonged suppression of HBV via induction of an antiviral cytokine called interferon. However, interferon did not destroy the HBV genome, suggesting that other parts of the immune response (e.g. activation of immune cells that kill infected cells) also play an important role in the antiviral response to GS-9620.
Representatives from academia, industry, regulatory agencies, and patient groups convened in March 2019 with the primary goal of developing agreement on chronic hepatitis B virus (HBV) treatment ...endpoints to guide clinical trials aiming to “cure” HBV. Agreement among the conference participants was reached on some key points. “Functional” but not sterilising cure is achievable and should be defined as sustained HBsAg loss in addition to undetectable HBV DNA 6 months post‐treatment. The primary endpoint of phase III trials should be functional cure; HBsAg loss in ≥30% of patients was suggested as an acceptable rate of response in these trials. Sustained virologic suppression (undetectable serum HBV DNA) without HBsAg loss 6 months after discontinuation of treatment would be an intermediate goal. Demonstrated validity for the prediction of sustained HBsAg loss was considered the most appropriate criterion for the approval of new HBV assays to determine efficacy endpoints. Clinical trials aimed at HBV functional cure should initially focus on patients with HBeAg‐positive or negative chronic hepatitis, who are treatment‐naïve or virally suppressed on nucleos(t)ide analogues. A hepatitis flare associated with an increase in bilirubin or international normalised ratio should prompt temporary or permanent cessation of an investigational treatment. New treatments must be as safe as existing nucleos(t)ide analogues. The primary endpoint for phase III trials for HDV coinfection should be undetectable serum HDV RNA 6 months after stopping treatment. On treatment HDV RNA suppression associated with normalisation of alanine aminotransferase is considered an intermediate goal. In conclusion, regarding HBV “functional cure”, the primary goal is sustained HBsAg loss with undetectable HBV DNA after completion of treatment and the intermediate goal is sustained undetectable HBV DNA without HBsAg loss after stopping treatment.
Hepatitis B virus (HBV) remains a significant cause of mortality and morbidity worldwide, since chronic HBV infection is associated with elevated risk of cirrhosis and hepatocellular carcinoma. ...Current licensed therapies against HBV efficiently suppress viral replication; however, they do not have significant effects on the intrahepatic covalently closed circular DNA (cccDNA) of the viral minichromosome responsible for viral persistence. Thus, life-long treatment is required to avoid viral rebound. There is a significant need for novel therapies that can reduce, silence or eradicate cccDNA, thus preventing HBV reemergence after treatment withdrawal. In this review, we discuss the latest developments and applications of gene editing and related approaches for directly targeting HBV DNA and, more specifically, cccDNA in infected hepatocytes.
Over the past few decades there has been remarkable progress in viral hepatitis. Beginning with discovery of the viral agents, we now have reliable methods to diagnose and monitor all hepatitis virus ...infections, as well significant advances in treatment and prevention. Nonetheless, important challenges remain. This supplement to Gut looks forward to the next generation of challenges in the field of viral hepatitis, and this introductory article highlights several key issues.
Hepatitis B virus (HBV) is currently viewed as a stealth virus that does not elicit innate immunity in vivo. This assumption has not yet been challenged in vitro because of the lack of a relevant ...cell culture system. The HepaRG cell line, which is physiologically closer to differentiated hepatocytes and permissive to HBV infection, has opened new perspectives in this respect.HBV baculoviruses were used to initiate an HBV replication in both HepG2 and HepaRG cells. To monitor HBV replication, the synthesis of encapsidated DNA, and secretion of hepatitis B surface antigen (HBsAg), was respectively analyzed by southern blot and enzyme‐linked immunosorbent assay. The induction of a type I interferon (IFN) response was monitored by targeted quantitative reverse transcription polymerase chain reaction (qRT‐PCR), low‐density arrays, and functional assays. The invalidation of type I IFN response was obtained by either antibody neutralization or RNA interference. We demonstrate that HBV elicits a strong and specific innate antiviral response that results in a noncytopathic clearance of HBV DNA in HepaRG cells. Challenge experiment showed that transduction with Bac‐HBV‐WT, but not with control baculoviruses, leads to this antiviral response in HepaRG cells, whereas no antiviral response is observed in HepG2 cells. Cellular gene expression analyses showed that IFN‐β and other IFN‐stimulated genes were up‐regulated in HepG2 and HepaRG cells, but not in cells transduced by control baculoviruses. Interestingly, a rescue of viral replication was observed when IFN‐β action was neutralized by antibodies or RNA interference of type I IFN receptor. Conclusion: Our data suggest that a strong HBV replication is able to elicit a type I IFN response in HepaRG‐transduced cells. (HEPATOLOGY 2009.)
Patients with chronic hepatitis B (CHB) can be successfully treated using nucleos(t)ide analogs (NA), but drug-resistant hepatitis B virus (HBV) mutants frequently arise, leading to treatment failure ...and progression to liver disease. There has been much research into the mechanisms of resistance to NA and selection of these mutants. Five NA have been approved by the US Food and Drug Administration for treatment of CHB; it is unlikely that any more NA will be developed in the near future, so it is important to better understand mechanisms of cross-resistance (when a mutation that mediates resistance to one NA also confers resistance to another) and design more effective therapeutic strategies for these 5 agents. The genes that encode the polymerase and envelope proteins of HBV overlap, so resistance mutations in polymerase usually affect the hepatitis B surface antigen; these alterations affect infectivity, vaccine efficacy, pathogenesis of liver disease, and transmission throughout the population. Associations between HBV genotype and resistance phenotype have allowed cross-resistance profiles to be determined for many commonly detected mutants, so genotyping assays can be used to adapt therapy. Patients that experience virologic breakthrough or partial response to their primary therapy can often be successfully treated with a second NA, if this drug is given at early stages of these events. However, best strategies for preventing NA resistance include first-line use of the most potent antivirals with a high barrier to resistance. It is important to continue basic research into HBV replication and pathogenic mechanisms to identify new therapeutic targets, develop novel antiviral agents, design combination therapies that prevent drug resistance, and decrease the incidence of complications of CHB.