Chronic hepatitis B virus (HBV) infection remains a major health burden and the main risk factor for the development of hepatocellular carcinoma worldwide. However, HBV is not directly cytopathic and ...liver injury appears to be mostly caused by repeated attempts of the host's immune responses to control the infection. Recent studies have shown that the unique replication strategy adopted by HBV enables it to survive within the infected hepatocyte while complex virus-host interplays ensure the virus is able to fulfil its replication requirements yet is still able to evade important host antiviral innate immune responses. Clearer understanding of the host and viral mechanisms affecting HBV replication and persistence is necessary to design more effective therapeutic strategies aimed at improving the management of patients with chronic HBV infection to eventually achieve viral eradication. This article focuses on summarising the current knowledge of factors influencing the course of HBV infection, giving emphasis on the use of novel assays and quantitative serological and intrahepatic biomarkers as tools for predicting treatment response and disease progression.
Antiviral resistance is now the single most important factor in treatment failure using nucleos(t)ide analogues (NA). Primary drug resistance mutations refer to amino acid change(s) that result in ...reduced susceptibility to an antiviral agent. Secondary compensatory mutations restore replication defects associated with primary drug resistance and may be associated with low level reduced susceptibility. Several evolutionary pathways of drug resistant HBV have been observed in patients treated with NAs. It is possible that the drug resistance mutations selected with one agent may affect the efficacy of other NAs. Several major HBV-evolutionary NA-resistance pathways (rtM204I/V, rtN236T and rtA181T/V) have now been characterised. The rtM204V/I pathway is responsible for resistance to the
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-nucleosides, such as lamivudine (LMV), telbivudine (LdT) and clevudine (CLD), and also entecavir (ETV), whilst the rtN236T pathway is responsible for adefovir (ADV) and tenofovir (TFV) resistance. Both pathways are associated with clusters of secondary mutations that can affect subsequent treatment with NAs (rtT184G, rtS202I) such as ETV. The third pathway, rtA181T/V, is associated with resistance to LMV and ADV and is a potential multi-drug resistance pathway and will probably have an impact on TFV sensitivity, either alone or with the rtN236T. In naïve patients treated with ETV, atleast three mutations arising at the same time are required: rtL180M + rtM204V plus either one of rtT184, rtS202 or rtM250 codon changes. Finally, in highly drug-experienced patients, clusters of mutations such as rtA181T/I233V/N236T/M250L, all on the one dominant HBV genome, are being detected which are associated with multi-drug resistance. Sequential treatment with nucleos(t)ide analogue reverse transcriptase inhibitors (NRTI) promotes multidrug resistance. It is likely, therefore, that development of multi-drug resistance could be reduced by combination therapy optimised to individual viral phenotypes.
The hepatitis B virus (HBV) mutation that encodes rtA181T is selected in the viral polymerase during antiviral drug therapy and can also encode a stop codon in the overlapping surface gene at amino ...acid 172 (sW172*) resulting in truncation of the last 55 amino acids of the C‐terminal hydrophobic region of the surface proteins. This mutation is usually detected as a mixed population with wild‐type HBV. In vitro analysis revealed that the rtA181T/sW172* variant is not only defective in secretion of viral particles causing intracellular retention of surface proteins, it also has a dominant negative effect on virion but not subviral particle secretion when coexpressed with the wild type. This dominant negative effect was attributed to the truncated S protein alone. Furthermore, these truncated surface proteins were less glycosylated, and the truncated L protein was able to support virion secretion. Examination of sequential HBV DNA levels in patients failing lamivudine or adefovir therapy where only the rtA181T change was detected via polymerase chain reaction sequencing revealed that viral load rebound did not occur or was not as large as usually observed with drug‐resistant HBV. Conclusion: The rtA181T/sW172* variant has a secretory defect and exerts a dominant negative effect on wild‐type HBV virion secretion. The selection of rtA181T/sW172* reduced the typical extent of virological breakthrough, resulting in a missed diagnosis of drug resistance if viral load was used as the only criterion for drug failure, necessitating HBV polymerase chain reaction sequencing or other genotypic methods to diagnose antiviral drug resistance in these cases. (HEPATOLOGY 2008.)
The global burden of hepatitis B virus (HBV) is enormous, with 257 million persons chronically infected, resulting in more than 880,000 deaths per year worldwide. HBV exists as nine different ...genotypes, which differ in disease progression, natural history and response to therapy. HBV is an ancient virus, with the latest reports greatly expanding the host range of the Hepadnaviridae (to include fish and reptiles) and casting new light on the origins and evolution of this viral family. Although there is an effective preventive vaccine, there is no cure for chronic hepatitis B, largely owing to the persistence of a viral minichromosome that is not targeted by current therapies. HBV persistence is also facilitated through aberrant host immune responses, possibly due to the diverse intra-host viral populations that can respond to host-mounted and therapeutic selection pressures. This Review summarizes current knowledge on the influence of HBV diversity on disease progression and treatment response and the potential effect on new HBV therapies in the pipeline. The mechanisms by which HBV diversity can occur both within the individual host and at a population level are also discussed.
•Advances in understanding the natural history of hepatitis B have led to new definitions of the major phases of infection.•New phases are high replicative, low inflammatory (formerly immune ...tolerant) and non-replicative (formerly inactive carrier).•The new concept of trained immunity may alter future hepatitis B treatment strategies.•The current goal of treatment for chronic hepatitis B is a functional cure.•Experimental therapies now under development target viral and host factors and previously inaccessible pathways.
The host immune system plays an important role in chronic hepatitis B (CHB), both in viral clearance and hepatocellular damage. Advances in our understanding of the natural history of the disease have led to redefining the major phases of infection, with the “high replicative, low inflammatory” phase now replacing what was formerly termed the “immune tolerant” phase, and the “nonreplicative phase” replacing what was formerly termed the “inactive carrier” phase. As opposed to the earlier view that HBV establishes chronic infection by exploiting the immaturity of the neonate’s immune system, new findings on trained immunity show that the host is already somewhat “matured” following birth, and is actually very capable of responding immunologically, potentially altering future hepatitis B treatment strategies. While existing therapies are effective in reducing viral load and necroinflammation, often restoring the patient to near-normal health, they do not lead to a cure except in very rare cases and, in many patients, viremia rebounds after cessation of treatment. Researchers are now challenged to devise therapies that will eliminate infection, with a particular focus on eliminating the persistence of viral cccDNA in the nuclei of hepatocytes. In the context of chronic hepatitis B, new definitions of ‘cure’ are emerging, such as ‘functional’ and ‘virological’ cure, defined by stable off-therapy suppression of viremia and antigenemia, and the normalization of serum ALT and other liver-related laboratory tests. Continued advances in the understanding of the complex biology of chronic hepatitis B have resulted in the development of new, experimental therapies targeting viral and host factors and pathways previously not accessible to therapy, approaches which may lead to virological cures in the near term and functional cures upon long term follow-up. This article forms part of a symposium in Antiviral Research on “An unfinished story: from the discovery of the Australia antigen to the development of new curative therapies for hepatitis B.”
Summary In the past 10 years, there has been a lot of enthusiasm surrounding the use of serum hepatitis B surface antigen (HBsAg) quantification to predict disease activity and monitor treatment ...response in chronic hepatitis B. The measurement of HBsAg levels have been standardized in IU/ml, and nowadays it is almost a mandatory measurement due to the development of new antiviral treatments aiming at HBsAg seroclearance, i.e., functional cure of hepatitis B. Recently, there has been an improved understanding of the molecular virology of HBsAg, and particularly the relative roles of covalently closed circular DNA and integrated hepatitis B virus (HBV) DNA. This has shed new light on the interpretation of HBsAg levels in different phases of chronic hepatitis B. HBsAg level can assist the differentiation of immune tolerance and immune clearance in hepatitis B e antigen (HBeAg)-positive patients, and it can predict inactive disease and spontaneous HBsAg seroclearance in HBeAg-negative patients. The determination of HBsAg level is pivotal to individualize pegylated interferon (PegIFN) treatment; it is the key investigation to decide early termination of PegIFN among non-responders. Among patients treated by nucleos(t)ide analogues, responders tend to have dramatic reduction of HBsAg to low levels, which may be followed by HBsAg seroclearance. With newer data on combination treatment of PegIFN and nucleos(t)ide analogues as well as emerging new antiviral agents, HBsAg quantification is expected to become increasingly important to monitor and guide antiviral therapy for chronic hepatitis B.
Background & Aims Perinatal transmission of hepatitis B virus still occurs despite immunoprophylaxis in approximately 9% of children from highly viraemic mothers. Antiviral therapy in this setting ...has been suggested, however with limited evidence to direct agent choice. Methods We conducted a multi-centre, prospective, opt-in observational study of antiviral safety and efficacy in pregnant women with high viral load (>7 log IU/ml); lamivudine was used from 2007 to 2010 and tenofovir disoproxil fumarate (TDF) from late 2010. Outcomes of treated and untreated cohorts were compared. Results 120 women with 130 pregnancies used TDF (58), lamivudine (52 including four who switched due to TDF intolerance) and no therapy (20). 96% were HBeAg positive, with baseline viral load mean 7.8 log IU/ml (±0.72) and ALT median 25 U/L (18.75–33). Duration of antiviral theraphy before birth was mean 58 days (±19) TDF and 53 (±14) lamivudine. Viral load declined by 3.64 log IU/ml (±0.9) TDF and 2.81 log IU/ml (±1.33) lamivudine. Virologic failure (birth viral load >7 IU/ml) occurred in 3% and 18% respectively. Congenital abnormality rate and neonatal growth centiles were similar across cohorts. Perinatal transmission reduced significantly to 2% and 0% in TDF and lamivudine cohorts, compared with 20% in untreated. Conclusions TDF in this setting is safe, effective and more potent than lamivudine. Antiviral therapy did not adversely impact obstetric or infant parameters. More TDF intolerance occurred than expected. Perinatal transmission was significantly reduced in antiviral therapy cohorts.
In October 2018 a large number of international experts with complementary expertise came together in Taormina to participate in a workshop on occult hepatitis B virus infection (OBI). The objectives ...of the workshop were to review the existing knowledge on OBI, to identify issues that require further investigation, to highlight both existing controversies and newly emerging perspectives, and ultimately to update the statements previously agreed in 2008. This paper represents the output from the workshop.
Chronic hepatitis B virus (HBV) infection is a major health concern worldwide, frequently leading to liver cirrhosis, liver failure, and hepatocellular carcinoma. Evidence suggests that high viral ...antigen load may play a role in chronicity. Production of viral proteins is thought to depend on transcription of viral covalently closed circular DNA (cccDNA). In a human clinical trial with an RNA interference (RNAi)-based therapeutic targeting HBV transcripts, ARC-520, HBV S antigen (HBsAg) was strongly reduced in treatment-naïve patients positive for HBV e antigen (HBeAg) but was reduced significantly less in patients who were HBeAg-negative or had received long-term therapy with nucleos(t)ide viral replication inhibitors (NUCs). HBeAg positivity is associated with greater disease risk that may be moderately reduced upon HBeAg loss. The molecular basis for this unexpected differential response was investigated in chimpanzees chronically infected with HBV. Several lines of evidence demonstrated that HBsAg was expressed not only from the episomal cccDNA minichromosome but also from transcripts arising from HBV DNA integrated into the host genome, which was the dominant source in HBeAg-negative chimpanzees. Many of the integrants detected in chimpanzees lacked target sites for the small interfering RNAs in ARC-520, explaining the reduced response in HBeAg-negative chimpanzees and, by extension, in HBeAg-negative patients. Our results uncover a heretofore underrecognized source of HBsAg that may represent a strategy adopted by HBV to maintain chronicity in the presence of host immunosurveillance. These results could alter trial design and endpoint expectations of new therapies for chronic HBV.
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.(Hepatology 2015;62:1893–1908)
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