The Concept of Immune Tolerance in Chronic Hepatitis B Virus Infection Is Alive and Well

"Treat-all" Strategy for Patients with Chronic Hepatitis B Virus Infection in China: Are We There Yet?

Chronic hepatitis B remains the primary cause of liver-related events in China. The World Health Organization set a goal to eliminate viral hepatitis as a public health threat by 2030. However, achieving this goal appears challenging due to the current low rates of diagnosis and treatment. The "Treat-all" strategy, which proposes treating all patients with detectable hepatitis B virus (HBV) DNA or even all patients with positive HBsAg, has been suggested to simplify anti-HBV treatment. In 2022, the Chinese Society of Hepatology and the Chinese Society of Infectious Diseases updated the guidelines for the prevention and treatment of chronic hepatitis B in China, expanding antiviral indications and simplifying the treatment algorithm. According to this latest guideline, nearly 95% of patients with detectable HBV DNA are eligible for antiviral treatment. This review aimed to provide a detailed interpretation of the treatment indications outlined in the Chinese Guidelines for the Prevention and Treatment of Chronic Hepatitis B (version 2022) and to identify gaps in achieving the "Treat-all" strategy in China.

Latest insights into the epidemiology, characteristics, and therapeutic strategies of chronic hepatitis B patients in indeterminate phase

As a hepatotropic virus, hepatitis B virus (HBV) can establish a persistent chronic infection in the liver, termed, chronic hepatitis B (CHB), which causes a series of liver-related complications, including fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). HCC with HBV infection has a significantly increased morbidity and mortality, whereas it could be preventable. The current goal of antiviral therapy for HBV infection is to decrease CHB-related morbidity and mortality, and achieve sustained suppression of virus replication, which is known as a functional or immunological cure. The natural history of chronic HBV infection includes four immune phases: the immune-tolerant phase, immune-active phase, inactive phase, and reactivation phase. However, many CHB patients do not fit into any of these defined phases and are regarded as indeterminate. A large proportion of indeterminate patients are only treated with dynamic monitoring rather than recommended antiviral therapy, mainly due to the lack of definite guidelines. However, many of these patients may gradually have significant liver histopathological changes during disease progression. Recent studies have focused on the prevalence, progression, and carcinogenicity of indeterminate CHB, and more attention has been given to the prevention, detection, and treatment for these patients. Herein, we discuss the latest understanding of the epidemiology, clinical characteristics, and therapeutic strategies of indeterminate CHB, to provide avenues for the management of these patients.

Current Challenges and Future Perspectives of Diagnosis of Hepatitis B Virus

It is estimated that approximately 260 million people worldwide are infected with the hepatitis B virus (HBV), which is one of the leading causes of liver disease and liver cancer throughout the world. Compared with developed countries, low-income and middle-income countries have limited access to resources and advanced technologies that require highly specialized staff for HBV diagnosis. In spite of the heavy burden caused by hepatitis B virus, 90% of people are still undiagnosed. The World Health Organization (WHO) goal of eliminating hepatitis B by 2030 seems very difficult to achieve due to the existing diagnostic infrastructure in low-resource regions. The majority of diagnostic laboratories still use hepatitis B surface antigen (HBsAg)-based tests. WHO's elimination plan is at risk of derailment due to phases like the window period, immune control, and occult HBV infection (OBI) not being detected by standard tests. Here, in this article, we are focusing on various diagnostic platforms for the better diagnosis of HBV. The aim of the elimination of HBV can only be achieved by detecting all phases of HBV infection, which can be executed by a combined approach of using new marker assays along with advanced pretesting and testing methods.

Histologic changes in immune-tolerant patients with chronic hepatitis B: a systematic review and meta-analysis

The serological diagnostic criteria for the immune-tolerant (IT) phase have not been strictly defined and it is hard to determine an accurate rate for significant histologic changes among IT patients. The aim of this study was to establish a baseline rate of significant histologic changes and to determine the main characteristics of IT patients. We systematically searched PubMed, Embase, and Web of Science. Studies reporting liver biopsy results (inflammation grade or fibrosis stage) for adults with chronic hepatitis B virus (HBV) infection in the IT phase diagnosed by serological criterion were included to pool the rate of significant histologic changes. Studies that enrolled subjects with confirmed chronic HBV infection in the IT phase diagnosed by serological and liver biopsy criteria (dual criteria) were included to pool the mean values of main characteristics among IT patients. Of 319 studies screened, 15 were eventually included in the meta-analysis. The pooled rates of significant liver fibrosis and inflammatory activity for 10 studies were 10% (95% confidence interval [CI] 0.06-0.18) and 16% (95% CI 0.07-0.31), respectively. The pooled mean values of age, alanine aminotransferase level, HBV DNA level, and HBsAg level for another 5 studies with IT patients diagnosed by dual criteria were 30.7 years (95% CI 27.31-34.09), 26.64 IU/mL (95% CI 24.45-28.83), 8.41 log₁₀ cp/mL (95% CI 7.59-9.23), and 4.24 log₁₀ IU/mL (95% CI 3.67-4.82), respectively. Significant histologic changes were not rare events among IT patients. Strictly defined serological diagnostic criteria for the IT phase are warranted.

Perspectives on current controversial issues in the management of chronic HBV infection

Clinical and basic research in the past decades has achieved consensus in the understanding of chronic hepatitis B virus (HBV) infection and the management of chronic hepatitis B and HBV-cirrhosis. However, debatable challenges to the existing consensus in the concept and/or definitions have emerged. These include (1). alanine aminotransferase upper limit of normal: traditional laboratory-defined vs fixed; (2). nomenclature for phases of chronic HBV infection: classical vs EASL proposal; (3). indication of antiviral therapy: to treat patients vs to treat HBV; (4). finite vs indefinite long-term antiviral therapy: A. finite therapy in HBV-cirrhosis; B. retreatment decision: biochemical markers vs HBsAg/ALT kinetics. The pros and cons of these controversial issues were reviewed, assessed, and discussed in depth based on relevant lines of scientific evidence, intended to clarify or solve these controversial issues.

Changes in serum hepatitis B surface and e antigen, interferon-inducible protein 10, and aminotransferase levels during combination therapy of immune-tolerant chronic hepatitis B

BACKGROUND AND AIMS

Treatment of immune-tolerant (IT) children and adults with combined peginterferon alfa-2a and entecavir results in a decline in serum HBeAg and HBsAg concentrations but rarely results in loss of HBeAg or sustained off-treatment response. Factors associated with declines in these viral antigens during treatment remain unexplored.

APPROACH AND RESULTS

We investigated the pattern of virologic and biochemical response in 86 participants (59 children, 27 adults) by serial quantitative measurement of HBsAg (qHBsAg), quantitative HBeAg (qHBeAg), HBV RNA, interferon-inducible protein (IP-10), IL-18, and alanine aminotransferase (ALT). Each individual had previously been treated with 8 weeks of entecavir followed by 40 weeks of combined peginteferon and entecavir. We defined the interrelationships between these parameters and virologic response measured as nadir declines from baseline for HBeAg and HBsAg. The patterns of HBsAg and HBeAg decline were similar in pediatric and adult participants. Higher levels of IP-10 were observed during treatment in participants with greater ALT elevations and greater reductions of qHBsAg and qHBeAg. Individuals with peak ALT values exceeding three times the upper limit of normal were significantly more likely to have >1 log10 decline in both viral antigens. HBV DNA became undetectable in 21 of 86 (24%) and HBV RNA in 4 of 77 (5%) during therapy, but both markers remained negative only in those who became HBsAg negative, all of whom also had ALT elevations.

CONCLUSIONS

Induction of IP-10 during peginterferon treatment in adults and children in the IT phase of chronic HBV infection is associated with ALT elevations and decline in viral antigens, suggesting a degree of interferon-inducible viral control.

Long-term hepatitis B virus infection of rhesus macaques requires suppression of host immunity

Hepatitis B virus has infected a third of the world's population, and 296 million people are living with chronic infection. Chronic infection leads to progressive liver disease, including hepatocellular carcinoma and liver failure, and there remains no reliable curative therapy. These gaps in our understanding are due, in large part, to a paucity of animal models of HBV infection. Here, we show that rhesus macaques regularly clear acute HBV infection, similar to adult humans, but can develop long-term infection if immunosuppressed. Similar to patients, we longitudinally detected HBV DNA, HBV surface antigen, and HBV e antigen in the serum of experimentally infected animals. In addition, we discovered hallmarks of HBV infection in the liver, including RNA transcription, HBV core and HBV surface antigen translation, and covalently closed circular DNA biogenesis. This pre-clinical animal model will serve to accelerate emerging HBV curative therapies into the clinic.

Quantitative HBsAg versus HBV DNA in Predicting Significant Hepatitis Activity of HBeAg-Positive Chronic HBV Infection

(1) Background: As specialparameters in predicting significant hepatitis activity of hepatitis B e antigen (HBeAg)-positive chronic hepatitis B virus (HBV) infection, the quantitative standard of HBV DNA has not been agreed and that of hepatitis B surface antigen(HBsAg) has not been formed. Our objective is to evaluate the validity of HBsAg and HBV DNA in predicting the significant hepatitis activity of HBeAg-positive patients. (2) Methods: A population of 516 patients with HBeAg-positive chronic HBV infection was enrolled. Serum ALT was measured using an Abbott Architect c16000 autoanalyzer; diagnoses of liver pathological grade and stage referred to the Scheuer standard. Three levels of significant hepatitis activity were preset, which were successively “ALT ≥ 20 IU/L or Grade > G1 or Stage > S1”, “ALT ≥ 30 IU/L or Grade > G1 or Stage > S1” and “ALT ≥ 40 IU/L or Grade > G1 or Stage > S1”. (3) Results: A subpopulation of 288 patients with possible high HBV replication was selected based on locally weighted scatterplot smoothing regression curves between ALT and HBsAg, HBeAg and HBV DNA. In the subpopulation with possible high HBV replication, areas under receiver operating characteristic curves of HBsAg for predicting the three levels of significant hepatitis activity were successively 0.868, 0.839 and 0.789, which were all significantly greater than those of HBV DNA, as those were successively 0.553, 0.550 and 0.574 (p = 0.0002, p < 0.0001 and p < 0.0001). With the standard of HBsAg ≤ 4.699 log₁₀ IU/mL, the sensitivity and specificity of HBsAg for predicting the three levels of significant hepatitis activity were successively 75.81% and 81.82%, 79.23% and 78.57% and 80.82% and 67.44%. (4) Conclusion: Quantitative HBsAg instead of HBV DNA is valuable in predicting significant hepatitis activity of HBeAg-positive chronic HBV infection.

An Overview of the Current Hepatitis B Treatment Strategies after Liver Transplantation

Currently, liver transplantation (LT) is considered as the only option for the treatment of patients with various causes of liver failure, including patients with chronic hepatitis B virus (HBV) infections. Overall, patients with HBV who undergo LT are at increased risk of hepatitis B infection recurrence. Although the current knowledge regarding the pathophysiology of this infection has been dramatically increased over the past few decades, it is still considered a complex disease process with varying degrees of clinical characteristics and changing patterns over time. There are various treatment strategies for preventing HBV recurrence in the LT setting. Generally, these regimens include oral nucleoside/ nucleotide analogues (NAs), hepatitis B immune globulin (HBIG), and vaccines or the combination of these drugs. The treatment strategy of choice should be based on cost-effectiveness, along with other patients underlying conditions. In this case, studies indicate that potent NAs are more cost-effective than HBIG in most case scenarios. In this article, we aimed to review the general medications used in the prophylaxis of the recurrence of HBV infection after LT.

Blocking Entry of Hepatitis B and D Viruses to Hepatocytes as a Novel Immunotherapy for Treating Chronic Infections

Background

Chronic hepatitis B and D virus (HBV/HDV) infections can cause cancer. Current HBV therapy using nucleoside analogues (NAs) is life-long and reduces but does not eliminate the risk of cancer. A hallmark of chronic hepatitis B is a dysfunctional HBV-specific T-cell response. We therefore designed an immunotherapy driven by naive healthy T cells specific for the HDV antigen (HDAg) to bypass the need for HBV-specific T cells in order to prime PreS1-specific T cells and PreS1 antibodies blocking HBV entry.

Methods

Ten combinations of PreS1 and/or HDAg sequences were evaluated for induction of PreS1 antibodies and HBV- and HDV-specific T cells in vitro and in vivo. Neutralization of HBV by PreS1-specific murine and rabbit antibodies was evaluated in cell culture, and rabbit anti-PreS1 were tested for neutralization of HBV in mice repopulated with human hepatocytes.

Results

The best vaccine candidate induced T cells to PreS1 and HDAg, and PreS1 antibodies blocking HBV entry in vitro. Importantly, adoptive transfer of PreS1 antibodies prevented, or modulated, HBV infection after a subsequent challenge in humanized mice.

Conclusions

We here describe a novel immunotherapy for chronic HBV/HDV that targets viral entry to complement NAs and coming therapies inhibiting viral maturation.

MHC-E-Restricted CD8+ T Cells Target Hepatitis B Virus-Infected Human Hepatocytes

Currently 247 million people are living with chronic hepatitis B virus infection (CHB), and the development of novel curative treatments is urgently needed. Immunotherapy is an attractive approach to treat CHB, yet therapeutic approaches to augment the endogenous hepatitis B virus (HBV)-specific T cell response in CHB patients have demonstrated little success. In this study, we show that strain 68-1 rhesus macaque (RM) CMV vaccine vectors expressing HBV Ags engender HBV-specific CD8+ T cells unconventionally restricted by MHC class II and the nonclassical MHC-E molecule in RM. Surface staining of human donor and RM primary hepatocytes (PH) ex vivo revealed the majority of PH expressed MHC-E but not MHC class II. HBV-specific, MHC-E-restricted CD8+ T cells from RM vaccinated with RM CMV vaccine vectors expressing HBV Ags recognized HBV-infected PH from both human donor and RM. These results provide proof-of-concept that MHC-E-restricted CD8+ T cells could be harnessed for the treatment of CHB, either through therapeutic vaccination or adoptive immunotherapy.

Designing a therapeutic hepatitis B vaccine to circumvent immune tolerance

An effective prophylactic hepatitis B virus (HBV) vaccine has long been available but is ineffective for chronic infection. The primary cause of chronic hepatitis B (CHB) and greatest impediment for a therapeutic vaccine is the direct and indirect effects of immune tolerance to HBV antigens. The resulting defective CD4⁺/CD8⁺ T cell response, poor cytokine production, insufficient neutralizing antibody (nAb) and poor response to HBsAg vaccination characterize CHB infection. The objective of this study was to develop virus-like-particles (VLPs) that elicit nAb to prevent viral spread and prime CD4⁺/CD8⁺ T cells to eradicate intracellular HBV. Eight neutralizing B cell epitopes from the envelope PreS1 region were consolidated onto a species-variant of the HBV core protein, the woodchuck hepatitis core antigen (WHcAg). PreS1-specific B cell epitopes were chosen because of preferential expression on HBV virions. Because WHcAg and HBcAg are not crossreactive at the B cell level and only partially cross-reactive at the CD4⁺/CD8⁺ T cell level, CD4⁺ T cells specific for WHcAg-unique T cell sites can provide cognate T-B cell help for anti-PreS1 Ab production that is not curtailed by immune tolerance. Immunization of immune tolerant HBV transgenic (Tg) mice with PreS1-WHc VLPs elicited levels of high titer anti-PreS1 nAbs equivalent to wildtype mice. Passive transfer of PreS1 nAbs into human-liver chimeric mice prevented acute infection and cleared serum HBV from mice previously infected with HBV in a model of CHB. At the T cell level, PreS1-WHc VLPs and hybrid WHcAg/HBcAg DNA immunogens elicited HBcAg-specific CD4⁺ Th and CD8⁺ CTL responses.

Updates in the management of hepatitis B in children

Introduction: Universal infant hepatitis B virus (HBV) vaccination program has reduced HBV infection dramatically in vaccinated young generations. Management of chronically infected children is still challenging concerning high viral load with mostly mild diseases, yet with a nonnegligible proportion of advanced diseases, and long-term effect of antivirals. However, with more potent antivirals approved for pediatric patients, to start antivirals earlier in eligible patients may benefit their outcomes. This review aimed to update the current management of chronic hepatitis B in children.Areas covered: This review covered the natural history of chronic HBV infection, management of chronic hepatitis B in children from the past to the present, current consensus on the treatment of chronic hepatitis B in children, controversies in cessation of oral antivirals, and management of special populations such as pregnancy and co-infections.Expert opinions: Without contraindication, peginterferon is recommended for immune-active children ≥ 3 years old. For those intolerant, decompensating or preferring oral therapy, first-line Nucleos(t)ide analogs (NUC), Entecavir or Tenofovir, may be applied. For immune-tolerant or inactive carriers, close monitoring is crucial. When to stop NUCs and novel therapies for HBV cure await further research.

Comparison of antibody response to hepatitis B vaccination in infants with positive or negative maternal hepatitis B e antigen (HBeAg) in cord blood: implication for the role of HBeAg as an immunotolerogen

Hepatitis B e antigen (HBeAg) has been considered to cause immunotolerance to hepatitis B virus (HBV) in newborn infants after fetal HBeAg exposure. This study compared anti-HBs responses to hepatitis B vaccination in infants who were born to HBeAg-positive and -negative mothers respectively, to investigate whether fetal HBeAg exposure may induce immunotolerance to HBV. Totally 265 infants who received recommended neonatal immunoprophylaxis against hepatitis B and had no HBV infection were included. Anti-HBs levels were compared between 124 infants with cord blood positive HBeAg and 141 infants with cord blood negative HBeAg at 7-12 months of age. The infants in two groups had similar age at the follow-up (10.0 ± 2.3 vs 10.1 ± 2.3 months, P = 0.590). Overall, 259 (97.7%) of 265 infants achieved anti-HBs levels (mIU/ml) ≥10 and 6 (2.3%) others had anti-HBs <10. Of 124 HBeAg-positive infants at birth, 46.0%, 39.5%, 12.1%, and 2.4% had anti-HBs levels (mIU/ml) ≥1000, 100-999.9, 10-99.9, and <10, respectively. Of 141 HBeAg-negative infants at birth, 35.5%, 48.9%, 13.5%, and 2.1% showed ≥1000, 100-999.9, 10-99.9, and <10, respectively. The proportions of each anti-HBs level between the two groups were comparable (all P > 0.05). Additionally, the distribution of anti-HBs response levels were also comparable in infants with high and low HBeAg levels (P = 0.818). In conclusions, the fetal HBeAg exposure does not inhibit the antibody response to neonatal hepatitis B vaccination. The data suggest that HBeAg appears not inducing immunotolerance to HBV.

Insights From Antiviral Therapy Into Immune Responses to Hepatitis B and C Virus Infection

There are 257 million persons worldwide with chronic hepatitis B virus (HBV) infection, a leading causes of liver cancer. Almost all adults with acute HBV infection have a rapid immune response to the virus, resulting in life-long immunity, but there is no cure for individuals with chronic HBV infection, which they acquire during early life. The mechanisms that drive the progression of HBV through distinct clinical phases to end-stage liver disease are poorly understood. Likewise, it is not clear whether and how immune responses can be modulated to allow control and/or clearance of intrahepatic HBV DNA. We review the innate and adaptive immune responses to acute and chronic HBV infections and responses to antiviral therapy. Comparisons with hepatitis C virus infection provide insights into the reversibility of innate inflammatory responses and the potential for successful therapy to recover virus-specific memory immune responses.

Type I Interferon Signaling Prevents Hepatitis B Virus-Specific T Cell Responses by Reducing Antigen Expression

Robust virus-specific CD8+ T cell responses are required for the clearance of hepatitis B virus (HBV). However, the factors that determine the magnitude of HBV-specific CD8+ T cell responses are poorly understood. To examine the impact of genetic variations of HBV on HBV-specific CD8+ T cell responses, we introduced three HBV clones (Aa_IND [Aa], C_JPN22 [C22], and D_IND60 [D60]) that express various amounts of HBV antigens into the livers of C57BL/6 (B6) (H-2b) mice and B10.D2 (H-2d) mice. In B6 mice, clone C22 barely induced HBV-specific CD8+ T cell responses and persisted the longest, while clone D60 elicited strong HBV-specific CD8+ T cell responses and was rapidly cleared. These differences between HBV clones largely diminished in H-2d mice. Interestingly, the magnitude of HBV-specific CD8+ T cell responses in B6 mice was associated with the HB core antigen expression level during the early phase of HBV transduction. Surprisingly, robust HBV-specific CD8+ T cell responses to clone C22 were induced in interferon-α/β receptor-deficient (IFN-αβR-/-) (H-2b) mice. The induction of HBV-specific CD8+ T cell responses to C22 in IFN-αβR-/- mice reflects enhanced HBV antigen expression because the suppression of antigen expression by HBV-specific small interfering RNA (siRNA) attenuated HBV-specific T cell responses in IFN-αβR-/- mice and prolonged HBV expression. Collectively, these results suggest that HBV genetic variation and type I interferon signaling determine the magnitude of HBV-specific CD8+ T cell responses by regulating the initial antigen expression levels.IMPORTANCE Hepatitis B virus (HBV) causes acute and chronic infection, and approximately 240 million people are chronically infected with HBV worldwide. It is generally believed that virus-specific CD8+ T cell responses are required for the clearance of HBV. However, the relative contributions of genetic variation and innate immune responses to the induction of HBV-specific CD8+ T cell responses are not fully understood. In this study, we discovered that different clearance rates between HBV clones after hydrodynamic transduction were associated with the magnitude of HBV-specific CD8+ T cell responses and initial HB core antigen expression. Surprisingly, type I interferon signaling negatively regulated HBV-specific CD8+ T cell responses by reducing early HBV antigen expression. These results show that the magnitude of the HBV-specific CD8+ T cell response is regulated primarily by the initial antigen expression level.

Hepatitis B virus infection

Hepatitis B virus (HBV) is a hepatotropic virus that can establish a persistent and chronic infection in humans through immune anergy. Currently, 3.5% of the global population is chronically infected with HBV, although the incidence of HBV infections is decreasing owing to vaccination and, to a lesser extent, the use of antiviral therapy to reduce the viral load of chronically infected individuals. The course of chronic HBV infection typically comprises different clinical phases, each of which potentially lasts for decades. Well-defined and verified serum and liver biopsy diagnostic markers enable the assessment of disease severity, viral replication status, patient risk stratification and treatment decisions. Current therapy includes antiviral agents that directly act on viral replication and immunomodulators, such as interferon therapy. Antiviral agents for HBV include reverse transcriptase inhibitors, which are nucleoside or nucleotide analogues that can profoundly suppress HBV replication but require long-term maintenance therapy. Novel compounds are being actively investigated to achieve the goal of HBV surface antigen seroclearance (functional cure), a serological state that is associated with a higher remission rate (thus, no viral rebound) after treatment cessation and a lower rate of cirrhosis and hepatocellular carcinoma. This Primer addresses several aspects of HBV infection, including epidemiology, immune pathophysiology, diagnosis, prevention and management.

Tolerance and immunity to pathogens in early life: insights from HBV infection

Immunity is not static but varies with age. The immune system of a newborn infant is not "defective" or "immature." Rather, there are distinct features of innate and adaptive immunity from fetal life to adulthood, which may alter the susceptibility of newborn infants to infections compared to adults. Increased protection to certain infectious diseases during early life may benefit from a dampened immune response as a result of decreased immune pathology. This concept may offer an alternative interpretation of the different pathological manifestations clinically observed in hepatitis B virus (HBV)-infected patients during the natural history of infection. Herein, we review the immune pathological features of HBV infection from early life to adulthood and challenge the concept of a generic immune tolerant state in young people. We then discuss how the different clinical and virological manifestations during HBV infection may be related to the differential antiviral immunity and pro-inflammatory capacity generated at different ages. Lastly, we address the potential to consider earlier therapeutic intervention in HBV-infected young patients to achieve effective immune control leading to better outcomes.

Immune Tolerant Chronic Hepatitis B: The Unrecognized Risks

Chronic infection with hepatitis B virus (HBV) progresses through multiple phases, including immune tolerant, immune active, immune control, and, in a subset of patients who achieve immune control, reactivation. The first, the immune tolerant phase, is considered to be prolonged in duration but essentially benign in nature, lacking long-term consequences, and thus not recommended for antiviral therapy. This review challenges the notion that the immune tolerant phase is truly benign and considers the possibility that events during this phase may contribute significantly to cirrhosis, hepatocellular carcinoma (HCC), and the premature death of 25% of HBV carriers worldwide. Thus, earlier treatment than recommended by current guidelines should be considered. Low therapeutic coverage exacerbated by restrictive treatment guidelines may facilitate disease progression in many patients but also increase the risk of neonatal and horizontal transmission from untreated mothers to their children. While a prophylactic vaccine exists, there are many areas worldwide where the treatment of adults and the delivery of an effective vaccination course to newborns present difficult challenges.

HBV DNA Integration: Molecular Mechanisms and Clinical Implications

Chronic infection with the Hepatitis B Virus (HBV) is a major cause of liver-related morbidity and mortality. One peculiar observation in cells infected with HBV (or with closely‑related animal hepadnaviruses) is the presence of viral DNA integration in the host cell genome, despite this form being a replicative dead-end for the virus. The frequent finding of somatic integration of viral DNA suggests an evolutionary benefit for the virus; however, the mechanism of integration, its functions, and the clinical implications remain unknown. Here we review the current body of knowledge of HBV DNA integration, with particular focus on the molecular mechanisms and its clinical implications (including the possible consequences of replication-independent antigen expression and its possible role in hepatocellular carcinoma). HBV DNA integration is likely to influence HBV replication, persistence, and pathogenesis, and so deserves greater attention in future studies.