Effect of the G1896A precore mutation on drug sensitivity and replication yield of lamivudine-resistant HBV in vitro

CRISPR-Cas13b-mediated suppression of HBV replication and protein expression

BACKGROUND & AIMS

New antiviral approaches that target multiple aspects of the HBV replication cycle to improve rates of functional cure are urgently required. HBV RNA represents a novel therapeutic target. Here, we programmed CRISPR-Cas13b endonuclease to specifically target the HBV pregenomic RNA and viral mRNAs in a novel approach to reduce HBV replication and protein expression.

METHODS

Cas13b CRISPR RNAs (crRNAs) were designed to target multiple regions of HBV pregenomic RNA. Mammalian cells transfected with replication competent wild-type HBV DNA of different genotypes, a HBV-expressing stable cell line, a HBV infection model and a hepatitis B surface antigen (HBsAg)-expressing stable cell line were transfected with PspCas13b-BFP (blue fluorescent protein) and crRNA plasmids, and the impact on HBV replication and protein expression was measured. Wild-type HBV DNA, PspCas13b-BFP and crRNA plasmids were simultaneously hydrodynamically injected into mice, and serum HBsAg was measured. PspCas13b mRNA and crRNA were also delivered to a HBsAg-expressing stable cell line via lipid nanoparticles and the impact on secreted HBsAg determined.

RESULTS

Our HBV-targeting crRNAs strongly suppressed HBV replication and protein expression in mammalian cells by up to 96% (p <0.0001). HBV protein expression was also reduced in a HBV-expressing stable cell line and in the HBV infection model. CRISPR-Cas13b crRNAs reduced HBsAg expression by 50% (p <0.0001) in vivo. Lipid nanoparticle-encapsulated PspCas13b mRNA reduced secreted HBsAg by 87% (p = 0.0168) in a HBsAg-expressing stable cell line.

CONCLUSIONS

Together, these results show that CRISPR-Cas13b can be programmed to specifically target and degrade HBV RNAs to reduce HBV replication and protein expression, demonstrating its potential as a novel therapeutic option for chronic HBV infection.

IMPACT AND IMPLICATIONS

Owing to the limitations of current antiviral therapies for hepatitis B, there is an urgent need for new treatments that target multiple aspects of the HBV replication cycle to improve rates of functional cure. Here, we present CRISPR-Cas13b as a novel strategy to target HBV replication and protein expression, paving the way for its development as a potential new treatment option for patients living with chronic hepatitis B.

HBV PreC interacts with SUV39H1 to induce viral replication by blocking the proteasomal degradation of viral polymerase

Hepatitis B e antigen (HBeAg) seropositivity during the natural history of chronic hepatitis B (CHB) is known to coincide with significant increases in serum and intrahepatic HBV DNA levels. However, the precise underlying mechanism remains unclear. In this study, we found that PreC (HBeAg precursor) genetic ablation leads to reduced viral replication both in vitro and in vivo. Furthermore, PreC impedes the proteasomal degradation of HBV polymerase, promoting viral replication. We discovered that PreC interacts with SUV39H1, a histone methyltransferase, resulting in a reduction in the expression of Cdt2, an adaptor protein of CRL4 E3 ligase targeting HBV polymerase. SUV39H1 induces H3K9 trimethylation of the Cdt2 promoter in a PreC-induced manner. CRISPR-mediated knockout of endogenous SUV39H1 or pharmaceutical inhibition of SUV39H1 decreases HBV loads in the mouse liver. Additionally, genetic depletion of Cdt2 in the mouse liver abrogates PreC-related HBV replication. Interestingly, a negative correlation of intrahepatic Cdt2 with serum HBeAg and HBV DNA load was observed in CHB patient samples. Our study thus sheds light on the mechanistic role of PreC in inducing HBV replication and identifies potential therapeutic targets for HBV treatment.

Hepatitis B doubly spliced protein (HBDSP) promotes hepatocellular carcinoma cell apoptosis via ETS1/GATA2/YY1-mediated p53 transcription

IMPORTANCE

Hepatitis B virus (HBV) spliced variants are associated with viral persistence or pathogenicity. Hepatitis B doubly spliced protein (HBDSP), which has been previously reported as a pleiotropic transactivator protein, can potentially serve as an HBV virulence factor. However, the underlying mechanisms of HBDSP in HBV-associated liver diseases remain to be elucidated. In this study, we revealed that HBDSP promotes cellular apoptosis and induces wt-p53-dependent apoptotic signaling pathway in wt-p53 hepatocellular cells by transactivating p53 transcription, and increases the release of HBV progeny. Therefore, HBDSP may promote the HBV particles release through wt-p53-dependent hepatocellular apoptosis. Our findings suggest that blocking HBDSP-induced wt-p53-dependent apoptosis might have therapeutic values for chronic hepatitis B.

In Vitro Systems for Studying Different Genotypes/Sub-Genotypes of Hepatitis B Virus: Strengths and Limitations

Hepatitis B virus (HBV) infects the liver resulting in end stage liver disease, cirrhosis, and hepatocellular carcinoma. Despite an effective vaccine, HBV poses a serious health problem globally, accounting for 257 million chronic carriers. Unique features of HBV, including its narrow virus-host range and its hepatocyte tropism, have led to major challenges in the development of suitable in vivo and in vitro model systems to recapitulate the HBV replication cycle and to test various antiviral strategies. Moreover, HBV is classified into at least nine genotypes and 35 sub-genotypes with distinct geographical distributions and prevalence, which have different natural histories of infection, clinical manifestation, and response to current antiviral agents. Here, we review various in vitro systems used to study the molecular biology of the different (sub)genotypes of HBV and their response to antiviral agents, and we discuss their strengths and limitations. Despite the advances made, no system is ideal for pan-genotypic HBV research or drug development and therefore further improvement is required. It is necessary to establish a centralized repository of HBV-related generated materials, which are readily accessible to HBV researchers, with international collaboration toward advancement and development of in vitro model systems for testing new HBV antivirals to ensure their pan-genotypic and/or customized activity.

Hepatitis B e Antigen Inhibits NF-κB Activity by Interrupting K63-Linked Ubiquitination of NEMO

Viruses have adopted diverse strategies to suppress antiviral responses. Hepatitis B virus (HBV), a virus that is prevalent worldwide, manipulates the host's innate immune system to evade scavenging. It is reported that the hepatitis B e antigen (HBeAg) can interfere with NF-κB activity, which then leads to high viral loads, while HBV with the G1896A mutation remains infectious without the production of HBeAg but can induce more severe proinflammatory response and liver damage. The aim of current work was to study the molecular mechanism by which HBeAg suppresses interleukin-1β (IL-1β)-stimulated NF-κB activity, which leads to the suppression of the innate immune responses to HBV infection. Our study revealed that HBeAg could interact with NEMO, a regulatory subunit associated with IκB kinase, which regulates the activation of NF-κB. HBeAg suppressed the IL-1β-induced tumor necrosis factor (TNF)-associated factor 6 (TRAF6)-dependent K63-linked ubiquitination of NEMO, thereby downregulating NF-κB activity and promoting virus replication. We further demonstrated the inhibitory effect of HBeAg on the NF-κB signaling pathway using primary human hepatocytes, HBV-infected HepG2-NTCP cells, and clinical liver samples. Our study reveals a molecular mechanism whereby HBeAg suppresses IL-1β-induced NF-κB activation by decreasing the TRAF6-dependent K63-linked ubiquitination of NEMO, which may thereby enhance HBV replication and promote a persistent infection.IMPORTANCE The role of HBeAg in inflammatory responses during the infection of hepatitis B virus (HBV) is not fully understood, and several previous reports with regard to the NF-κB pathway are controversial. In this study, we showed that HBeAg could suppress both Toll-like receptor 2 (TLR2)- and IL-1β-induced activation of NF-κB in cells and clinical samples, and we further revealed novel molecular mechanisms. We found that HBeAg can associate with NEMO, the regulatory subunit for IκB kinase (IKK) that controls the NF-κB signaling pathway, and thereby inhibits TRAF6-mediated K63-linked ubiquitination of NEMO, resulting in downregulation of NF-κB activity and promotion of virus replication. In contrast, the HBeAg-negative HBV mutant can induce higher levels of NF-κB activity. These results are important for understanding the HBV-induced pathogenesis of chronic hepatitis and indicate that different clinical measures should be considered to treat HBeAg-positive and HBeAg-negative infections. Our findings represent a conceptual advance in HBV-related suppression of NF-κB signaling.

Precore G1896A mutation is associated with reduced rates of HBsAg seroclearance in treated HIV hepatitis B virus co-infected patients from Western Africa

The nucleotide substitution G1896A on the precore (pc) region has been implicated in virological and serological responses during treatment in hepatitis B virus (HBV)-infected patients. Whether this mutation affects the therapeutic course of HIV-HBV co-infected patients, especially from Western Africa, is unknown. In this prospective cohort study, 86 antiretroviral (ARV)-naïve HIV-HBV co-infected patients from Côte d'Ivoire, initiating ARV-treatment containing lamivudine (n = 53) or tenofovir (n = 33), had available baseline pc sequences. Association of the pcG1896A mutation with time to undetectable HBV-DNA, hepatitis B "e" antigen (HBeAg) seroclearance (in HBeAg-positive patients), and hepatitis B surface antigen (HBsAg) seroclearance was evaluated using Cox proportional hazards regression. At ARV-initiation, median HBV-DNA was 6.04 log₁₀ copies/mL (IQR = 3.70-7.93) with 97.7% harbouring HBV genotype E. Baseline pcG1896A mutation was identified in 51 (59.3%) patients, who were more commonly HBeAg-negative (P < .001) and had basal core promotor A1762T/G1764A mutations (P < .001). Patients were followed for a median 36 months (IQR = 24-36). Cumulative proportion of undetectable HBV-DNA was significantly higher in patients with baseline mutation (pcG1896A = 86.6% vs no pcG1896A = 66.9%, P = .04), but not after adjusting for baseline HBV-DNA levels and anti-HBV agent (P = .2). No difference in cumulative proportion of HBeAg seroclearance was observed between mutation groups (pcG1896A = 57.1% vs no pcG1896A = 54.3%, P = .7). Significantly higher cumulative proportion of HBsAg seroclearance was observed in patients without this mutation (pcG1896A = 0% vs no pcG1896A = 36.9%, P < .001), even after adjusting for baseline HBsAg quantification and anti-HBV agent (P < .001). In conclusion, lacking the pcG1896A mutation before ARV initiation appeared to increase HBsAg seroclearance rates during treatment. The therapeutic implications of this mutation need further exploration in this setting.

In vitro studies identify a low replication phenotype for hepatitis B virus genotype H generally associated with occult HBV and less severe liver disease

Hepatitis B virus (HBV) exists as 9 major genotypes and multiple subtypes, many of which exhibit differences in pathogenicity and treatment response. Genotype H identified in Central America is associated with low incidence of liver disease and HCC, but higher incidence of occult HBV (low level HBV DNA positivity, HBsAg negative). The replication phenotype of genotype H associated with less severe forms of liver disease is unknown. We hypothesized that the reduced pathogenesis associated with this genotype may be due to by lower rates of viral replication and/or secretion compared to other characterised strains. We used transient transfection and infection cell culture models to characterise the replication phenotype, compared to our D3 reference strain. Genotype H exhibited reduced viral replication and altered envelope protein expression compared to genotype D, with functional studies showing that low replication was in part likely due to sequence differences in the major transcriptional regulatory region.

RFX1 participates in doxorubicin-induced hepatitis B virus reactivation

Cytotoxic chemotherapy drugs, including doxorubicin, can directly promote hepatitis B virus (HBV) replication, but the mechanism has not been fully clarified. This study investigated the potential mechanism underlying the cytotoxic chemotherapy‐mediated direct promotion of HBV replication. We found that HBV replication and regulatory factor X box 1 gene (RFX1) expression were simultaneously promoted by doxorubicin treatment. The amount of RFX1 bound to the HBV enhancer I was significantly increased under doxorubicin treatment. Furthermore, the activity of doxorubicin in promoting HBV replication was significantly attenuated when the expression of endogenous RFX1 was knocked down, and the EP element of HBV enhancer I, an element that mediated the binding of RFX1 and HBV enhancer I, was mutated. In addition, two different sequences of the conserved EP element were found among HBV genotypes A‐D, and doxorubicin could promote the replication of HBV harboring either of the conserved EP elements. Here, a novel pathway in which doxorubicin promoted HBV replication via RFX1 was identified, and it might participate in doxorubicin‐induced HBV reactivation. These findings would be helpful in preventing HBV reactivation during anticancer chemotherapy.

Clinical and virological implications of A1846T and C1913A/G mutations of hepatitis B virus genome in severe liver diseases

OBJECTIVE

Mutations occurring within different genes of hepatitis B virus (HBV) genome may have different clinical implications. This study aimed to observe the clinical and virological implications of the A1846T and C1913A/G mutations of HBV genome in the development and treatment outcome of severe liver diseases, which has not been previously determined.

MATERIALS AND METHODS

A total of 438 cases of patients with liver diseases were retrospectively reviewed, including 146 with mild chronic hepatitis B infection (CHB-M), 146 with severe chronic hepatitis B infection (CHB-S), and 146 with acute-on-chronic liver failure (ACLF). Partial or full-length HBV genome was directly sequenced. Replicons containing A1846T, C1913A or other mutant sequences, or the wild-type counterparts were constructed respectively, and then transfected into HepG2 cells for phenotype analysis.

RESULTS

There was significant difference in the detection rates of A1846T (30.82%, 40.41% and 55.48%, respectively) and C1913A/G (15.52%, 28.77%, and 35.62%, respectively) among patients with CHB-M, those with CHB-S, and those with ACLF (p < .01). A1846T was significantly associated with the mortality of ACLF patients within six months after the disease onset (OR 1.704, p = .041). In vitro experiment revealed that A1846T mutant resulted in 3.20-fold and 1.85-fold increase of replication capacity and promoter activity, respectively compared with wild type counterpart (p < .001), while C1913A led to a significant decrease of core protein expression (p < .05).

CONCLUSION

Occurrence of A1846T and C1913A is positively associated with clinical presentations of severe liver disease. A1846T mutation is significantly associated with poor prognosis of ACLF.

Analysis of HBV basal core promoter/precore gene variability in patients with HBV drug resistance and HIV co-infection in Northwest Ethiopia

Background

We recently reported complex hepatitis B virus (HBV) drug resistant and concomitant vaccine escape hepatitis B surface antigen (HBsAg) variants during human immunodeficiency virus (HIV) co-infection and antiretroviral therapy (ART) exposure in Ethiopia. As a continuation of this report using the HBV positive sera from the same study participants, the current study further analyzed the HBV basal core promoter (BCP)/precore (PC) genes variability in patients with HBV drug resistance (at tyrosine-methionine-aspartate-aspartate (YMDD) reverse transcriptase (RT) motifs) and HIV co-infection in comparison with HBV mono-infected counterparts with no HBV drug resistant gene variants.

Materials and methods

A total of 143 participants of HBV-HIV co-infected (n = 48), HBV mono-infected blood donors (n = 43) and chronic liver disease (CLD) patients (n = 52) were included in the study. The BCP/PC genome regions responsible for HBeAg expression from the EcoRI site (nucleotides 1653–1959) were sequenced and analyzed for the BCP/PC mutant variants.

Results

Among the major mutant variants detected, double BCP mutations (A1762T/G1764A) (25.9%), Kozak sequences mutations (nt1809-1812) (51.7%) and the classical PC mutations such as A1814C/C1816T (15.4%), G1896A (25.2%) and G1862T (44.8%) were predominant mutant variants. The prevalence of the double BCP mutations was significantly lower in HIV co-infected patients (8.3%) compared with HBV mono-infected blood donors (32.6%) and CLD patients (36.5%). However, the Kozak sequences BCP mutations and the majority of PC mutations showed no significant differences among the study groups. Moreover, except for the overall BCP/PC mutant variants, co-prevalence rates of each major BCP/PC mutations and YMDDRT motif associated lamivudine (3TC)/entecavir (ETV) resistance mutations showed no significant differences when compared with the rates of BCP/PC mutations without YMDD RT motif drug resistance gene mutations. Unlike HIV co-infected group, no similar comparison made among HBV mono-infected blood donors and CLD patients since none of them developed the YMDD RT motif associated 3TC/ETV resistance mutations. However, HBV mono-infected blood donors and CLD patients who had no any drug resistance gene variants developed comparable G1862T (60.6% vs. 65.1%) and G1896A (24.2% vs. 11.6%) PC gene mutations.

Conclusion

No correlation observed between the BCP/PC genome variability and the YMDD RT motif associated HBV drug resistance gene variants during HIV co-infection. Nevertheless, irrespective of HIV co-infection status, the higher records of the BCP/PC gene variability in this study setting indicate a high risk of potential HBeAg negative chronic HBV infection in Northwest Ethiopia.

The gRNA-miRNA-gRNA Ternary Cassette Combining CRISPR/Cas9 with RNAi Approach Strongly Inhibits Hepatitis B Virus Replication

The CRISPR/Cas9 system is a novel genome editing technology which has been successfully used to inhibit HBV replication. Here, we described a novel gRNA-microRNA (miRNA)-gRNA ternary cassette driven by a single U6 promoter. With an anti-HBV pri-miR31 mimic integrated between two HBV-specific gRNAs, both gRNAs could be separated from the long transcript of gRNA-miR-HBV-gRNA ternary cassette through Drosha/DGCR8 processing. The results showed that the gRNA-miR-HBV-gRNA ternary cassette could efficiently express two gRNAs and miR-HBV. The optimal length of pri-miRNA flanking sequence in our ternary cassette was determined to be 38 base pairs (bp). Besides, HBV-specific gRNAs and miR-HBV in gRNA-miR-HBV-gRNA ternary cassette could exert a synergistic effect in inhibiting HBV replication and destroying HBV genome in vitro and in vivo. Most importantly, together with RNA interference (RNAi) approach, the HBV-specific gRNAs showed the potent activity on the destruction of HBV covalently closed circular DNA (cccDNA). Since HBV cccDNA is an obstacle for the elimination of chronic HBV infection, the gRNA-miR-HBV-gRNA ternary cassette may be a potential tool for the clearance of HBV cccDNA.

Hepatitis B immunopathogenesis and immunotherapy

Worldwide there are over 248 million chronic carriers of HBV of whom about a third eventually develop severe HBV-related complications. Due to the major limitations of current therapeutic approaches, the development of more effective strategies to improve therapeutic outcomes in chronic hepatitis B (CHB) patients seems crucial. Immune activation plays a critical role in spontaneous viral control; therefore, new modalities based on stimulation of the innate and adaptive immune responses could result in the resolution of infection and are promising approaches. Here, we summarize the HBV immunopathogenesis, and discuss the encouraging results obtained from the promising immune-based innovations, such as therapeutic vaccination, cytokine therapy, cell-based therapies and blocking inhibitory receptors, as current and future immunotherapeutic interventions.

In Vitro Studies Show that Sequence Variability Contributes to Marked Variation in Hepatitis B Virus Replication, Protein Expression, and Function Observed across Genotypes

The hepatitis B virus (HBV) exists as 9 major genotypes (A to I), one minor strain (designated J) and multiple subtypes. Marked differences in HBV natural history, disease progression and treatment response are exhibited by many of these genotypes and subtypes. For example, HBV genotype C is associated with later hepatitis B e antigen (HBeAg) seroconversion and high rates of liver cancer compared to other HBV genotypes, whereas genotype A2 is rarely associated with HBeAg-negative disease or liver cancer. The reasons for these and other differences in HBV natural history are yet to be determined but could in part be due to sequence differences in the HBV genome that alter replicative capacity and/or gene expression. Direct comparative studies on HBV replication and protein expression have been limited to date due largely to the absence of infectious HBV cDNA clones for each of the HBV genotypes present in the same genetic arrangement. We have produced replication-competent infectious cDNA clones of the most common subtypes of genotypes A to D, namely, A2, B2, C2, D3, and the minor strain J, and compared their HBV replication phenotype using transient-transfection models. We identified striking differences in HBV replicative capacity as well as HBeAg and surface (HBsAg) protein expression across genotypes, which may in part be due to sequence variability in regulatory regions of the HBV genome. Functional analysis showed that sequence differences in the major upstream regulatory region across genotypes impacted promoter activity.

IMPORTANCE

There have been very few studies directly comparing the replication phenotype of different HBV genotypes, for which there are marked differences in natural history and disease progression worldwide. We have generated replication-competent 1.3-mer cDNA clones of the major genotypes A2, B2, C2, and D3, as well as a recently identified strain J, and identified striking differences in replicative capacity and protein expression that may contribute to some of the observed differences in HBV natural history observed globally.

Serum hepatitis B virus RNA is encapsidated pregenome RNA that may be associated with persistence of viral infection and rebound

BACKGROUND & AIMS

Hepatitis B virus (HBV) RNA in serum has recently been linked to efficacy and prognosis of chronic hepatitis B (CHB) treatment. This study explored the nature, origin, underlying mechanisms, and potential clinical significance of serum HBV RNA.

METHODS

The levels of HBV DNA and RNA were determined in the supernatant of induced HepAD38, HBV-expressing HepG2.2.15 cells and primary human hepatocytes (PHH), and in the serum of transgenic mice and CHB patients. NP-40 and proteinase K treatment, sucrose density gradient centrifugation, electron microscopy, northern blot, multiple identification PCRs and 5' rapid-amplification of cDNA ends were performed to identify the nature of serum HBV RNA.

RESULTS

Although significantly lower than HBV DNA levels, abundant HBV RNA was present in the serum of CHB patients. A series of experiments demonstrated that serum HBV RNA was pregenome RNA (pgRNA) and present in virus-like particles. HBV pgRNA virion levels increased after blocking the reverse transcription activity of HBV DNA polymerase, and decreased after blocking the encapsidation of pgRNA. Furthermore, the presence of HBV pgRNA virion was associated with risk of viral rebound after discontinuation of nucleot(s)ide analogues (NAs) therapy in CHB patients.

CONCLUSIONS

Serum HBV RNA was confirmed to be pgRNA present in virus-like particles. HBV pgRNA virions were produced from encapsidated particles in which the pgRNA was non- or partially reverse transcribed. Clinically, HBV pgRNA virion might be a potential biomarker for monitoring safe discontinuation of NA-therapy.

LAY SUMMARY

HBV may have another virion form in which the nucleic acid is composed of RNA, not DNA. The level of HBV RNA virion in serum may be associated with risk of HBV viral rebound after withdrawal of treatment, and therefore, a potential predictive biomarker to monitor the safe discontinuation of nucleot(s)ide analogues-therapy.

Advances and Challenges in Studying Hepatitis B Virus In Vitro

Hepatitis B virus (HBV) is a small DNA virus that infects the liver. Current anti-HBV drugs efficiently suppress viral replication but do not eradicate the virus due to the persistence of its episomal DNA. Efforts to develop reliable in vitro systems to model HBV infection, an imperative tool for studying HBV biology and its interactions with the host, have been hampered by major limitations at the level of the virus, the host and infection readouts. This review summarizes major milestones in the development of in vitro systems to study HBV. Recent advances in our understanding of HBV biology, such as the discovery of the bile-acid pump sodium-taurocholate cotransporting polypeptide (NTCP) as a receptor for HBV, enabled the establishment of NTCP expressing hepatoma cell lines permissive for HBV infection. Furthermore, advanced tissue engineering techniques facilitate now the establishment of HBV infection systems based on primary human hepatocytes that maintain their phenotype and permissiveness for infection over time. The ability to differentiate inducible pluripotent stem cells into hepatocyte-like cells opens the door for studying HBV in a more isogenic background, as well. Thus, the recent advances in in vitro models for HBV infection holds promise for a better understanding of virus-host interactions and for future development of more definitive anti-viral drugs.

Influence of the basal core promoter and precore mutation on replication of hepatitis B virus and antiviral susceptibility of different genotypes

Mutations in the basal core promoter (BCP) and precore (PC) regions of the hepatitis B virus (HBV) are more common in genotypes B and C than in genotype A, suggesting that these mutations might affect replication competency depending on genotype. The purpose of the study was to investigate the influence of these mutations on the capacity of HBV for replication and antiviral drug susceptibility according to genotype. Genotypes A, B, and C of HBV strains with a BCP mutation, PC mutation, or BCP + PC mutation were made by site-directed mutagenesis. Replication competency of each construct and susceptibility to nucleos(t) ide analogues were tested in an Huh7 cell line. In genotype A, the BCP and BCP + PC mutations increased the viral replication around 6.5 times compared with the wild type, and the PC mutation alone similarly increased the viral replication around three times. In genotypes B and C, all three mutant types increased viral replication to a similar extent, regardless of mutation pattern. Interestingly, the BCP mutation appeared to have a greater effect on viral replication in genotype A than in genotypes B and C. This finding was unexpected because the BCP mutation is more common in HBV genotypes B and C. Moreover, the BCP, PC, and BCP + PC mutations decreased the sensitivity of HBV to antiviral agents to various degrees (2- to 10-fold) regardless of genotype. In conclusion, BCP and PC mutations increased viral replication regardless of HBV genotype and decreased in vitro antiviral susceptibility to the nucleos(t) ide analogues.

HBV clinical isolates expressing adefovir resistance mutations show similar tenofovir susceptibilities across genotypes B, C and D

BACKGROUND & AIMS

Hepatitis B virus (HBV) genotypes can influence clinical outcomes as well as response to antiviral therapy. This study evaluated the tenofovir (TFV) susceptibility of HBV genotype B, C and D clinical isolates with adefovir resistance-associated mutations (ADV-R).

METHODS

Full-length HBV isolates from patients infected with genotype B, C and D virus had rtA181T, rtA181V, rtN236T, rtA181T+rtN236T and rtA181V+rtN236T mutations introduced by site-directed mutagenesis. Phenotypic analyses were performed in HepG2 cells and susceptibility to TFV and ADV were assessed.

RESULTS

Clinical HBV isolates containing rtA181T, rtA181V or rtN236T as single mutants remained sensitive to TFV across genotypes B, C and D. Clinical isolates containing the rtA181T+rtN236T double mutant remained sensitive to TFV in genotype D but exhibited reduced susceptibility to TFV in genotypes B and C. Viruses containing the double mutant rtA181V+rtN236T in genotypes B and D exhibited reduced susceptibility to TFV with EC50 fold changes (FC) of 3.8 and 2.5, respectively, while genotype C viruses containing rtA181V+rtN236T either remained sensitive (FC=1.3) or exhibited reduced susceptibility to TFV (FC=2.9) depending on the isolate. All rtA181V+rtN236T isolates conferred reduced susceptibility to ADV (FC values 2.3-4.2).

CONCLUSIONS

Genotype B, C and D isolates with single ADV resistance mutations remained fully sensitive to TFV, while the double mutants rtA181T+rtN236T and rtA181V+rtN236T exhibited either no change or low-level reduced susceptibility to TFV across genotypes. These results are consistent with the clinical efficacy observed with tenofovir disoproxil fumarate (TDF) treatment across all genotypes in vivo and the limited impact of ADV-R mutations on TDF therapy.

Hepatitis B Virus-Related Hepatocellular Carcinoma: Pathogenic Mechanisms and Novel Therapeutic Interventions

BACKGROUND

Infection with the hepatitis B virus (HBV) is one of most important risk factors for hepatocellular carcinoma (HCC). Indeed, HBV is considered a group 1 human carcinogen and is a highly oncogenic agent. HBV cannot be effectively controlled or completely eliminated, so chronic HBV infection is a public health challenge worldwide.

SUMMARY

It is now believed that HBV-induced HCC involves a complex interaction between multiple viral and host factors. Many factors contribute to HBV-associated HCC, including products of HBV, viral integration and mutation, and host susceptibility. This review outlines the main pathogenic mechanisms with a focus on those that suggest novel targets for the prevention and treatment of HCC.

KEY MESSAGE

HBV infection is an important risk factor for HCC. Understanding the interaction between viral and host factors in HBV-induced HCC will reveal potential targets for future therapies.

PRACTICAL IMPLICATIONS

The two main therapeutic strategies consist of antiviral agents and immunotherapy-based approaches. Dendritic cell-based immunotherapy is promising for restoring the T cell-mediated antiviral immune response. Another approach is the specific expansion of the host's pool of HBV-specific T cells. Stimulation of the Toll-like receptors (TLRs), particularly TLR9, provides another means of boosting the antiviral response. Combination therapy with cytokines (interferon gamma and tumor necrosis factor alpha) plus lamivudine is more effective than these agents used alone. Therapeutic vaccines are being developed as an alternative to long-term antiviral treatment or as an adjunct.

Role of the line probe assay INNO-LiPA HBV DR and ultradeep pyrosequencing in detecting resistance mutations to nucleoside/nucleotide analogues in viral samples isolated from chronic hepatitis B patients

Despite the effectiveness of nucleoside/nucleotide analogues in the treatment of chronic hepatitis B (CHB), their long-term administration is associated with the emergence of resistant hepatitis B virus (HBV) mutants. In this study, mutations resulting in antiviral resistance in HBV DNA samples isolated from 23 CHB patients (nine treatment naïve and 14 treated previously) were studied using a line probe assay (INNO-LiPA HBV DR; Innogenetics) and ultradeep pyrosequencing (UDPS) methods. Whilst the INNO-LiPA HBV DR showed no resistance mutations in HBV DNA samples from treatment-naive patients, mutations mediating lamivudine resistance were detected in three samples by UDPS. Among patients who were treated previously, 19 mutations were detected in eight samples using the INNO-LiPA HBV DR and 29 mutations were detected in 12 samples using UDPS. All mutations detected by the INNO-LiPA HBV DR were also detected by UDPS. There were no mutations that could be detected by INNO-LiPA HBV DR but not by UDPS. A total of ten mutations were detected by UDPS but not by INNO-LiPA HBV DR, and the mean frequency of these mutations was 14.7 %. It was concluded that, although INNO-LiPA HBV DR is a sensitive and practical method commonly used for the detection of resistance mutations in HBV infection, UDPS may significantly increase the detection rate of genotypic resistance in HBV at an early stage.

Hepatitis B e antigen-suppressing mutations enhance the replication efficiency of adefovir-resistant hepatitis B virus strains

Hepatitis B e antigen (HBeAg) negative hepatitis B virus (HBV) infections caused by precore (PC) or basal core promoter (BCP) mutations are associated with disease progression and complications. PC or BCP mutations may enhance the replication capacity of distinct drug-resistance-associated polymerase mutations, but their effect on adefovir-resistant HBV mutants is unclear. Importantly, BCP mutations were an independent risk factor for virological breakthrough in lamivudine-resistant patients treated with adefovir. We aimed at addressing the functional consequences of PC and BCP mutations on the replication and drug susceptibility of adefovir-resistant HBV mutants. Therefore, HBV constructs with wild type (WT) or adefovir-resistant rtN236T, rtA181V and rtA181T mutations, with or without concomitant PC or BCP mutations, were analysed in vitro using molecular assays. The adefovir-resistant polymerase mutations rtN236T, rtA181V and rtA181T showed a drastically reduced viral replication compared with WT. Interestingly, additional PC or BCP mutations enhanced the reduced replication efficacy of adefovir-resistant constructs and restored HBV replication to WT level. HBV rtA181T mutants displayed abolished hepatitis B surface antigen (HBsAg) secretion, owing to a sW172* stop codon in the overlapping envelope gene. All rtN236T- or rtA181V/T-containing constructs, regardless of concomitant PC or BCP mutations, were resistant to adefovir, but remained susceptible to telbivudine, entecavir and tenofovir. In conclusion, adefovir drug resistance mutations reduced viral replication, which can be significantly increased by additional HBeAg-suppressing PC or BCP mutations. Because increased HBV replication in HBeAg-negative patients has been associated with an unfavourable clinical course, close monitoring appears indispensable during adefovir treatment in HBeAg-negative patients.

Deep sequencing of the hepatitis B virus in hepatocellular carcinoma patients reveals enriched integration events, structural alterations and sequence variations

Chronic hepatitis B virus (HBV) infection is epidemiologically associated with hepatocellular carcinoma (HCC), but its role in HCC remains poorly understood due to technological limitations. In this study, we systematically characterize HBV in HCC patients. HBV sequences were enriched from 48 HCC patients using an oligo-bead-based strategy, pooled together and sequenced using the FLX-Genome-Sequencer. In the tumors, preferential integration of HBV into promoters of genes (P < 0.001) and significant enrichment of integration into chromosome 10 (P < 0.01) were observed. Integration into chromosome 10 was significantly associated with poorly differentiated tumors (P < 0.05). Notably, in the tumors, recurrent integration into the promoter of the human telomerase reverse transcriptase (TERT) gene was found to correlate with increased TERT expression. The preferred region within the HBV genome involved in integration and viral structural alteration is at the 3'-end of hepatitis B virus X protein (HBx), where viral replication/transcription initiates. Upon integration, the 3'-end of the HBx is often deleted. HBx-human chimeric transcripts, the most common type of chimeric transcripts, can be expressed as chimeric proteins. Sequence variation resulting in non-conservative amino acid substitutions are commonly observed in HBV genome. This study highlights HBV as highly mutable in HCC patients with preferential regions within the host and virus genome for HBV integration/structural alterations.

Hepatitis B virus genotype C encoding resistance mutations that emerge during adefovir dipivoxil therapy: in vitro replication phenotype

INTRODUCTION

Hepatitis B virus (HBV) can be classified into ten genotypes (A-J), with genotypes B and C being the most common in Asia. Recent data suggest that the HBV genotype can influence disease progression, and genotype C has been associated with more aggressive liver disease than that of other genotypes. Although there is a preventative vaccine, chronic infection remains a public health problem with oral nucleos(t)ide analog therapy being the most common treatment. The HBV genome is composed of four partially overlapping reading frames, meaning that substitutions in the HBV polymerase selected during NA therapy may also alter the overlapping HBV surface antigen (HBsAg). We have recently shown that for HBV genotype D, the rtA181T/sW172stop substitution conferring resistance to adefovir dipivoxil (ADV) alters secretion of HBsAg and exerts a dominant-negative effect on wild-type virion secretion. However, the effect of this and other ADV-resistance-associated mutations on HBV replication and HBsAg secretion for the HBV genotype C, the genotype with the most severe clinical prognosis, is unknown.

METHODS/RESULTS

We constructed 1.2-mer infectious cDNA clones of HBV genotype C encoding mutations associated with ADV resistance and established an in vitro replication assay in Huh7 cells. Decreased levels of HBV DNA and HBsAg were detected for all ADV variants relative to the 1.2-mer wild-type polymerase control plasmid. Importantly, less HBsAg was detected in the cells transfected with the rtA181T resistance mutants, and the overlapping sW172stop mutation ablated secretion of HBsAg into cell culture supernatants.

CONCLUSIONS

The identification of secretion-defective HBV in the setting of ADV therapy for HBV genotype C, and to a lesser extent HBV genotype B, has major implications for the diagnosis and treatment of HBV in the Asia-Pacific region, as it is likely that quantitative HBsAg and viral load testing of serum from patients infected with HBV encoding rtA181T and rtN236T substitutions may not accurately reflect the level of replication within hepatocytes.

Direct acting antivirals for the treatment of chronic viral hepatitis

The development and evaluation of antiviral agents through carefully designed clinical trials over the last 25 years have heralded a new dawn in the treatment of patients chronically infected with the hepatitis B and C viruses, but not so for the D virus (HBV, HCV, and HDV). The introduction of direct acting antivirals (DDAs) for the treatment of HBV carriers has permitted the long-term use of these compounds for the continuous suppression of viral replication, whilst in the case of HCV in combination with the standard of care [SOC, pegylated interferon (PegIFN), and ribavirin] sustained virological responses (SVRs) have been achieved with increasing frequency. Progress in the case of HDV has been slow and lacking in significant breakthroughs.This paper aims to summarise the current state of play in treatment approaches for chonic viral hepatitis patients and future perspectives.

In vitro replication phenotype of a novel (-1G) hepatitis B virus variant associated with HIV co-infection

The -1G mutant HBV is more prevalent in individuals co-infected with HIV/HBV than in individuals infected with HBV alone and in some cases is the dominant virus in circulation. This mutant is created by the deletion of a dGMP (-1G) from the guanine rich homopolymer sequence located at nts 2,085-2,090 (numbering from EcoRI site as position 1) in the HBV core gene. This deletion causes a frameshift generating a premature stop codon at (64) Asn in the HBV core gene (codon 93 in the precore gene), that truncates the precore protein, precursor of the secreted hepatitis B "e" antigen (HBeAg), and the core protein which forms the viral nucleocapsid. However, the replication phenotype of the -1G mutant HBV is unknown. An in vitro cell culture model in which hepatoma cells were transiently transfected with infectious cDNAs was used to show that the -1G mutant HBV is incapable of autonomous replication and, as expected, replication was restored to wild-type (wt) levels by supplying HBV core protein in trans. Although the -1G mutation had no deleterious effect on intracellular HBV-DNA levels, high levels of -1G mutant HBV relative to wt HBV reduced virus secretion and HBeAg secretion relative to empty vector controls. Importantly, the -1G mutant HBV also caused intracellular retention of truncated precore protein in the endoplasmic reticulum (ER) and Golgi apparatus. Together, these effects may be contributing to the increased pathology observed in the setting of HIV/HBV co-infection.

Hepatitis B precore protein: pathogenic potential and therapeutic promise

Hepatitis B virus (HBV), a small and economically packaged double-stranded DNA virus, represents an enormous global health care burden. In spite of an effective vaccine, HBV is endemic in many countries. Chronic hepatitis B (CHB) results in the development of significant clinical outcomes such as liver disease and hepatocellular carcinoma (HCC), which are associated with high mortality rates. HBV is a non-cytopathic virus, with the host's immune response responsible for the associated liver damage. Indeed, HBV appears to be a master of manipulating and modulating the immune response to achieve persistent and chronic infection. The HBV precore protein or hepatitis B e antigen (HBeAg) is a key viral protein involved in these processes, for instance though the down-regulation of the innate immune response. The development of new therapies that target viral proteins, such as HBeAg, which regulates of the immune system, may offer a new wave of potential therapeutics to circumvent progression to CHB and liver disease.

Hepatitis B virus basal core promoter mutations A1762T/G1764A are associated with genotype C and a low serum HBsAg level in chronically-infected HBeAg-positive Chinese patients

The present study was aimed to obtain baseline information of basal core promoter A1762T/G1764A and precore G1896A mutations of hepatitis B virus (HBV) in 192 HBeAg-positive chronically-infected Chinese patients, who were potential candidates for antiviral treatment. The detection of these mutations (including minor mutant subpopulations) was achieved by direct sequencing, whose sensitivity for minor mutant subpopulations identification was confirmed by clone sequencing. Patients enrolled were infected with either genotype B (46.35%) or C (53.65%) HBV identified by routine tests in our laboratory. The A1762T/G1764A or G1896A mutations were detected in 125specimens (125/192, 65.10%), in which 77 (77/125, 61.60%) existed as subpopulations. The A1762T/G1764A mutations were found to be more prevalent in genotype C than that in genotype B HBV [62.14% (64/103) vs. 20.22% (18/89), P<0.0001]. There is no statistically significant link between G1896A and genotypes. The emergence of A1762T/G1764A mutations was also found to be associated with an older age, an elevated ALT/AST level, and a lower HBsAg level in serum [wild-type vs. mutant: 4.57 (3.46-5.42) vs. 3.93 (2.51-5.36), P<0.0001]. In conclusion, HBV basal core promoter mutations A1762T/G1764A are associated with genotype C and a low serum HBsAg level in chronically-infected HBeAg-positive Chinese patients.

A type-specific nested PCR assay established and applied for investigation of HBV genotype and subgenotype in Chinese patients with chronic HBV infection

BACKGROUND

Many studies have suggested that hepatitis B virus (HBV) genotypes show not only geographical distribution and race specificity, but also are associated with disease progression and response to interferon treatment. The objective of this study was to develop a nested polymerase chain reaction (nPCR) assay for genotypes A-D and subgenotypes B1, B2, C1 and C2 of hepatitis B virus (HBV) and to investigate the distribution characteristics of HBV genotypes/subgenotype in China.

METHODS

After redesigning the primers and optimizing the reaction conditions using common Taq polymerase, the sensitivity, specificity and reproducibility of the method were evaluated using plasmids and serum samples. In total, 642 serum samples from patients with chronic HBV infection were applied to investigate the distribution of HBV genotype and subgenotype in China.

RESULTS

The genotype and subgenotype could be identified when the HBV DNA load of a sample was ≥10(2.3) IU/mL. For the 639 successfully genotyped samples, the sequencing results of 130 randomly selected samples (20.3%, 130/639) were consistent with those of the nPCR method. The present study showed that HBV genotype B (11.2%, 72/642), C (68.2%, 438/642) and D (7.2%, 46/642) were circulating in China, while genotype C was the dominant strain except for western region where genotype D was the prevalent strain. The main subgenotypes of genotypes B and C were B2 (87.5%, 63/72) and C2 (92.9%, 407/438), respectively.

CONCLUSIONS

The low-cost nPCR method would be a useful tool for clinical and epidemiological investigation in the regions where genotypes A-D are predominant.

Impact of hepatitis B e antigen-suppressing mutations on the replication efficiency of entecavir-resistant hepatitis B virus strains

Hepatitis B e antigen (HBeAg)-negative hepatitis B commonly requires long-term treatment with nucleos(t)ide analogues aiming at persistently suppressing hepatitis B virus (HBV) replication to halt progression of liver disease and prevent complications. Entecavir (ETV) is widely used in HBeAg-negative hepatitis B, but distinct HBV polymerase mutations can confer resistance against ETV, in conjunction with lamivudine resistance. Precore (PC) and basal core promoter (BCP) mutations that underlie HBeAg-negativity enhance replication of lamivudine-resistant mutants. To comprehensively analyse the impact of PC or BCP mutations on viral replication of ETV-resistant HBV mutants, replication-competent HBV constructs were generated harbouring lamivudine resistance (rtM204V/rtL180M, rtM204I) plus ETV resistance (rtS202G, rtS202I or rtT184G) on wild-type (WT)-, PC- and BCP-backgrounds. Functional consequences on viral fitness and susceptibility to antivirals were assessed in vitro. The presence of any ETV resistance drastically reduced viral replication when compared to WT HBV. In rtS202G mutants (plus lamivudine resistance), addition of either PC or BCP mutations moderately enhanced the reduced replication, without reaching WT HBV levels. In rtS202I or rtT184G mutants, PC and BCP mutations did not significantly improve viral fitness. All ETV-resistant constructs, independently of PC or BCP mutations, showed resistance towards ETV and lamivudine, but remained susceptible to tenofovir. Our data demonstrate that HBeAg-suppressing PC or BCP mutations cannot restore the strongly reduced replicative capacity of ETV-resistant HBV mutants to WT level, although they moderately increase replication of rtS202G combination mutants. ETV resistance thereby differs from lamivudine resistance alone, corroborating that ETV is in short term a safe option for HBeAg-negative patients.

The hepatitis B e antigen suppresses IL-1β-mediated NF-κB activation in hepatocytes

Previous clinical studies have demonstrated an association between the hepatitis B e antigen and Toll-like receptor (TLR) expression and signalling. Therefore, the aim of this study was to develop an in vitro assay to measure the effect of hepatitis B virus proteins, including the precore protein, on signalling mediated by members of the Toll-like/interleukin 1 (TIR) superfamily, by measuring NF-κB promoter activity. The basal level of NF-κB reporter activity was measured in three hepatocyte cell lines (Huh7, HepG2 and PH5CH8) and one kidney cell line (HEK293) using a luciferase assay. All cell lines were virtually refractory to stimulation with lipopolysaccharide; however, PH5CH8 cells had a robust activation of NF-κB in response to IL-1β stimulation, with ∼ 40-fold higher activation than the unstimulated control, a higher degree of activation than that observed in either Huh7 and HepG2, or HEK293 and HEK293-TLR2 cells. In PH5CH8 cells transfected with pCI expression constructs and stimulated with IL-1β, we showed that the precursor form of the precore protein, p25, inhibits NF-κB activation by up to 30% and the cytosolic form, p22, inhibits NF-κB activation by 70%. The core protein, p21, which shares significant homology with the precore protein except for a 10-amino acid extension at the N-terminus, had no effect on NF-κB activation. We hypothesize that the inhibition of IL-1β-mediated NF-κB activation by the precore protein may be a mechanism that allows the virus to persist, suggesting a role for the pool of precore protein that remains intracellular.

Ultra-deep pyrosequencing analysis of the hepatitis B virus preCore region and main catalytic motif of the viral polymerase in the same viral genome

Hepatitis B virus (HBV) pregenomic RNA contains a hairpin structure (ε) located in the preCore region, essential for viral replication. ε stability is enhanced by the presence of preCore variants and ε is recognized by the HBV polymerase (Pol). Mutations in the retrotranscriptase domain (YMDD) of Pol are associated with treatment resistance. The aim of this study was to analyze the preCore region and YMDD motif by ultra-deep pyrosequencing (UDPS). To evaluate the UDPS error rate, an internal control sequence was inserted in the amplicon. A newly developed technique enabled simultaneous analysis of the preCore region and Pol in the same viral genome, as well as the conserved sequence of the internal control. Nucleotide errors in HindIII yielded a UDPS error rate <0.05%. UDPS study confirmed the possibility of simultaneous detection of preCore and YMDD mutations, and demonstrated the complexity of the HBV quasispecies and cooperation between viruses. Thermodynamic stability of the ε signal was found to be the main constraint for selecting main preCore mutations. Analysis of ε-signal variability suggested the essential nature of the ε structural motif and that certain nucleotides may be involved in ε signal functions.

The YMDD and rtA194T mutations result in decreased replication capacity in wild-type HBV as well as in HBV with precore and basal core promoter mutations

BACKGROUND

A recent study indicated that addition of the hepatitis B e antigen (HBeAg) precore (PC) or basal core promoter (BCP) mutations to wild-type HBV offset the reduced replication of the HBV polymerase rtA194T±rtL180M+rtM204V mutations. rtA194T was reportedly associated with tenofovir resistance. We investigated these findings in genotype D HBV, where both PC and BCP naturally occur in vivo.

METHODS

A plasmid containing a wild-type 1.3 genome length genotype D HBV laboratory strain was used as a parent for PC, BCP, rtA194T±rtL180M+rtM204V, rtL180M+rtM204V and rtM204I mutants. Viral replication was evaluated by Southern blot analysis of intracellular HBV core DNA following transient transfection of HepG2 cells. Drug susceptibility was evaluated by quantitative PCR of intracellular HBV DNA.

RESULTS

PC and BCP mutations each increased HBV DNA replication by approximately 200% over wild-type. rtA194T reduced replication by <40%, whereas rtL180M+rtM204V, rtL180M+rtA194T+rtM204V or rtM204I each reduced by >75% from their respective wild-type, PC or BCP genome backbone (P<0.05). The enhanced replication by PC or BCP offset the reduction by rtA194T; however, the other reverse transcriptase (RT) mutations in PC or BCP backbones remained significantly lower than wild-type (P<0.05). Regardless of the backbone, rtA194T±rtL180M+rtM204V remained susceptible to tenofovir in vitro. rtA194T alone remained susceptible to lamivudine, while rtL180M+rtM204V and rtL180M+rtA194T+rtM204V were resistant.

CONCLUSIONS

PC or BCP mutations increased HBV DNA replication, offset the decreased replication by rtA194T alone, but they did not fully rescue the impaired replication conferred by other RT mutations as compared with wild-type. rtA194T±rtL180M+rtM204V did not confer tenofovir resistance.

Molecular genetics of HBV infection

HBV has evolved a unique life cycle that results in the production of enormous viral loads during active replication without actually killing the infected cells directly. Two of the key events in the viral life cycle of HBV involve firstly the generation of a covalently closed circular (ccc)DNA transcriptional template, either from input genomic DNA or newly replicated capsid-associated DNA, and secondly, reverse transcription of the viral pregenomic (pg)RNA to form progeny HBV DNA genomes. New data are emerging regarding the epigenetic control of cccDNA, which might represent another key factor involved in the pathogenesis and natural history of the disease. Because HBV uses reverse transcription to copy its genome, mutant viral genomes emerge frequently. Particular selection pressures, both endogenous (host immune clearance) and exogenous (vaccines and antiviral drugs), readily select out these escape mutants. The particular viral mutations or combination of mutations that directly affect the clinical outcome of infection are not known; however, four major 'pathways' of antiviral drug resistance-associated substitutions have now been identified. Further studies are clearly needed to identify the pathogenetic basis and clinical sequelae arising from the selection of these particular mutants. In the clinical context of antiviral drug resistance, treating physicians need to adopt therapeutic strategies that effectively control viral replication. Finally, the role of host genetics in influencing the outcome of HBV disease in the context of natural history and therapy is beginning to aid understanding in pathogenesis and, when this knowledge is linked to pathogen-specific databases, this should translate into more individualized patient care.

Targeting the hepatitis B virus precore antigen with a novel IgNAR single variable domain intrabody

The Hepatitis B virus precore protein is processed in the endoplasmic reticulum (ER) into secreted hepatitis B e antigen (HBeAg), which acts as an immune tolerogen to establish chronic infection. Downregulation of secreted HBeAg should improve clinical outcome, as patients who effectively respond to current treatments (IFN-α) have significantly lower serum HBeAg levels. Here, we describe a novel reagent, a single variable domain (V(NAR)) of the shark immunoglobulin new antigen receptor (IgNAR) antibodies. V(NAR)s possess advantages in stability, size (~14 kDa) and cryptic epitope recognition compared to conventional antibodies. The V(NAR) domain displayed biologically useful affinity for recombinant and native HBeAg, and recognised a unique conformational epitope. To assess therapeutic potential in targeting intracellular precore protein to reduce secreted HBeAg, the V(NAR) was engineered for ER-targeted in vitro delivery to function as an intracellular antibody (intrabody). In vitro data from HBV/precore hepatocyte cell lines demonstrated effective intrabody regulation of precore/HBeAg.

Stimulation of the interleukin-1 receptor and Toll-like receptor 2 inhibits hepatitis B virus replication in hepatoma cell lines in vitro

BACKGROUND

Toll-like receptors (TLRs) are a key component of the innate immune system and TLR2 has been shown to be involved in the immunopathogenesis of hepatitis B virus (HBV) infection in vivo. We investigated the role of TLR2 stimulation of virus-infected hepatocyte cell lines as a potential antiviral mechanism in vitro.

METHODS

The hepatoblastoma cell line HepG2 was transduced with recombinant HBV baculoviruses and the hepatoma cell line Huh-7 was transiently transfected with complimentary DNA clones of HBV. HBV viral replication was quantified after stimulation with interleukin (IL)-1beta and Pam-2-Cys, a synthetic TLR2 ligand, by measuring intracellular core-associated single-stranded HBV DNA using Southern blot hybridization, as well as viral nucleocapsid formation using a non-denaturing immunoblot method.

RESULTS

Stimulation of both cell lines in vitro with IL-1beta and Pam-2-Cys, both known to induce expression of the pro inflammatory cytokines tumour necrosis factor-alpha and IL-8 via a nuclear factor-kappaB dependent pathway, resulted in the inhibition of HBV DNA replication in the transduced HepG2 cells by up to 90% and nucleocapsid formation in the transiently transfected Huh-7 cells by up to 30%, when compared with mock-treated cells.

CONCLUSIONS

Hepatoma cell lines expressed functional IL-1 receptor and TLR2 receptors, which when stimulated led to a signalling cascade that inhibited HBV replication. These data support an active role for hepatocytes in inhibiting HBV replication and provide a rationale for the development of TLR agonists as potentially novel antiviral agents.

Differential impact of immune escape mutations G145R and P120T on the replication of lamivudine-resistant hepatitis B virus e antigen-positive and -negative strains

Immune escape variants of the hepatitis B virus (HBV) represent an emerging clinical challenge, because they can be associated with vaccine escape, HBV reactivation, and failure of diagnostic tests. Recent data suggest a preferential selection of immune escape mutants in distinct peripheral blood leukocyte compartments of infected individuals. We therefore systematically analyzed the functional impact of the most prevalent immune escape variants, the sG145R and sP120T mutants, on the viral replication efficacy and antiviral drug susceptibility of common treatment-associated mutants with resistance to lamivudine (LAM) and/or HBeAg negativity. Replication-competent HBV strains with sG145R or sP120T and LAM resistance (rtM204I or rtL180M/rtM204V) were generated on an HBeAg-positive and an HBeAg-negative background with precore (PC) and basal core promoter (BCP) mutants. The sG145R mutation strongly reduced HBsAg levels and was able to fully restore the impaired replication of LAM-resistant HBV mutants to the levels of wild-type HBV, and PC or BCP mutations further enhanced viral replication. Although the sP120T substitution also impaired HBsAg secretion, it did not enhance the replication of LAM-resistant clones. However, the concomitant occurrence of HBeAg negativity (PC/BCP), sP120T, and LAM resistance resulted in the restoration of replication to levels of wild-type HBV. In all clones with combined immune escape and LAM resistance mutations, the nucleotide analogues adefovir and tenofovir remained effective in suppressing viral replication in vitro. These findings reveal the differential impact of immune escape variants on the replication and drug susceptibility of complex HBV mutants, supporting the need of close surveillance and treatment adjustment in response to the selection of distinct mutational patterns.

Hepatitis B virus variants

HBV replicates through reverse transcription of an RNA intermediate; the inherent lack of proofreading causes a high mutation frequency. Mutations in the precore and core promoter regions that abolish or reduce the production of hepatitis B e antigen occur most commonly. Patients with these HBV variants remain viremic and can develop progressive liver disease. Mutations in the core promoter region are associated with an increased risk of hepatocellular carcinoma. Exogenous selection pressure might favor certain mutations. Mutations in the HBV polymerase that confer resistance to nucleoside and nucleotide analog treatments are a major barrier to the success of therapy for hepatitis B. The development of antiviral drug resistance negates the initial treatment response and can lead to hepatitis flares and hepatic decompensation. Prompt addition of another drug to which the virus is not cross-resistant is required. Mutations in the HBV surface protein that facilitate escape from host immunity are responsible for the failure of immune prophylaxis in infants who received HBV vaccine and in liver transplant recipients who received hepatitis B immune globulin.

The rtA194T polymerase mutation impacts viral replication and susceptibility to tenofovir in hepatitis B e antigen-positive and hepatitis B e antigen-negative hepatitis B virus strains

Tenofovir is a new effective treatment option for patients with chronic hepatitis B, but could be potentially hampered by mutations in the hepatitis B virus (HBV) polymerase conferring drug resistance. Drug resistance may occur preferentially if long-term administration is required, for example, in patients with hepatitis B e antigen (HBeAg)-negative HBV infection bearing precore (PC) and basal core promoter (BCP) mutations. The rtA194T polymerase mutation has been found in HBV/HIV coinfected patients during tenofovir treatment and may be associated with tenofovir resistance. We generated replication-competent HBV constructs harboring rtA194T alone or in addition to lamivudine (LAM) resistance (rt180M + rtM204V), PC mutations, and BCP mutations and assessed their replicative capacity after transient transfection in human hepatoma cells. The rtA194T polymerase mutation alone or in conjunction with LAM resistance reduced the replication efficiency as compared with wild-type (WT) HBV. In contrast, combination of rtA194T (+/- LAM resistance) with HBeAg-negative PC or BCP mutants increased the replication capacity of the drug-resistant polymerase mutants, thereby restoring the viral replication to similar levels as WT clones. Clones harboring rtA194T showed partial resistance to tenofovir in vitro and also to LAM but remained susceptible to telbivudine and entecavir.

CONCLUSION

The rtA194T polymerase mutation is associated with partial tenofovir drug resistance and negatively impacts replication competence of HBV constructs. Viral replication, however, can be restored to WT levels, if these polymerase mutations occur together with precore or basic core promoter substitutions as found in HBeAg-negative hepatitis B. Patients with HBeAg-negative chronic HBV infection may therefore be at particular risk when developing drug resistance to tenofovir. Telbivudine or entecavir should be considered as effective alternative treatment options for these patients.

Molecular analysis of an HBsAg-negative hepatitis B virus mutant selected in a tenofovir-treated HIV-hepatitis B virus co-infected patient

The molecular analysis performed in an HIV-hepatitis B virus (HBV) coinfected patient revealed selection of an unusual HBV polymerase mutation (rtV191I) during tenofovir-containing therapy, conferring simultaneously immune escape by HBsAg negativity and resistance to lamivudine but not tenofovir. Phenotypic analysis revealed impaired replicative capacity of mutants, which could be restored by concomitant precore or basal core promoter mutations (HBe-antigen-negativity). HBV mutants carrying drug and vaccine resistance may represent a considerable individual risk and public health concern.

Association of baseline viral factors with response to lamivudine therapy in chronic hepatitis B patients with high serum alanine aminotransferase levels

BACKGROUND

With the exception of alanine aminotransferase (ALT) level, baseline factors predictive of therapeutic response to lamivudine in patients with hepatitis B e antigen (HBeAg)-positive chronic hepatitis B (CHB) remain unknown. We thus studied the influence of pre-therapy viral factors on end-of-treatment responses to lamivudine.

METHODS

A total of 116 treatment-naive HBeAg-positive CHB patients who had pre-therapy ALT level >5x the upper limit of normal (ULN) and received lamivudine for 12-18 months were enrolled. HBeAg seroclearance and combined HBeAg seroclearance, ALT normalization and undetectable hepatitis B virus DNA at the end of therapy were defined as primary and secondary endpoints, respectively. Pre-therapy viral factors including viral load, genotype, precore (PC) stop codon status, basal core promoter status and pre-S deletion were determined to correlate with therapeutic endpoints.

RESULTS

The frequency of patients with detectable PC stop codon mutation (G1896A), basal core promoter mutation (A1762T/G1764A) and pre-S deletion at baseline was 22.4%, 21.6% and 12.1%, respectively. After the end of 12-18 months of lamivudine therapy, the overall HBeAg seroclearance rate was 56.0%. Patients with HBeAg seroclearance had a higher prevalence of baseline PC stop codon mutation than those without (30.8% versus 11.8%; P=0.015). By using multivariate analyses, the odds ratio of patients with the PC stop codon mutation to develop HBeAg seroclearance was 3.33 (P=0.024). The presence of the PC stop codon mutation also correlated with the combined response.

CONCLUSIONS

For lamivudine-treated HBeAg-positive CHB patients with pre-therapy ALT levels >5xULN, the PC stop codon mutation could predict a higher HBeAg seroclearance rate at the end of 12-18 months of therapy.

Supportive role played by precore and preS2 genomic changes in the establishment of lamivudine-resistant hepatitis B virus

BACKGROUND

Hepatitis B virus (HBV) establishes lamivudine resistance via the resistance-causative rtM204V/I mutation and the replication-compensatory rtL180M mutation. However, both lamivudine-resistant viruses with and those without rtL180M can exist in clinical settings. To elucidate the differences between viruses with and those without rtL180M, we conducted full-length sequencing analysis of HBV derived from patients with type B chronic hepatitis showing lamivudine resistance.

METHODS

The full-length HBV DNA sequences derived from 44 patients showing lamivudine resistance were determined by polymerase chain reaction direct sequencing. Viral replicative competence was examined by in vitro transfection analysis using various HBV-expressing plasmids.

RESULTS

Throughout the HBV genome, a precore-defective A1896 mutation and a short deletion in the preS2 gene were detected more frequently in viruses without rtL180M than in those with it (64% vs. 17% [P < .005] and 50% vs. 10% [P < .01], respectively). In vitro transfection analysis revealed that the level of reduction in intracellular viral replication caused by the introduction of lamivudine resistance-associated mutations was lower in precore-defective and preS2-deleted viruses than in wild-type virus.

CONCLUSIONS

Both the precore-defective mutation and the preS2 deletion may play a supportive role in the replication of lamivudine-resistant HBV, which may be a reason for there being no need for the compensatory rtL180M mutation in lamivudine-resistant HBV possessing the precore and preS2 genomic changes.

Defective hepatitis B virus DNA is not associated with disease status but is reduced by polymerase mutations associated with drug resistance

Defective hepatitis B virus DNA (dDNA) is reverse-transcribed from spliced hepatitis B virus (HBV) pregenomic messenger RNA (pgRNA) and has been identified in patients with chronic HBV (CH-B). The major 2.2-kb spliced pgRNA encodes a novel HBV gene product, the hepatitis B splice protein (HBSP) via a deletion and frame shift within the polymerase. Although spliced RNA and HBSP expression have been associated with increased HBV DNA levels and liver fibrosis, the role of dDNA in HBV-associated disease is largely undefined. Our aims were to (1) compare the relative proportions of dDNA (% dDNA) in a range of HBV-infected serum samples, including patients with human immunodeficiency virus (HIV)/HBV coinfection and HBV-monoinfected persons with differing severities of liver disease, and (2) determine the effect of mutations associated with drug resistance on defective DNA production. Defective DNA was detected in 90% of persons with CH-B. There was no significant difference in the relative abundance of dDNA between the monoinfected and HIV/HBV-coinfected groups. We also found no association between the % dDNA and alanine aminotransferase, hepatitis B e antigen status, HBV DNA levels, fibrosis levels, compensated or decompensated liver cirrhosis, genotype, or drug treatment. However, the % dDNA was significantly lower in individuals infected with lamivudine-resistant (LMV-R) HBV compared with wild-type HBV (P < 0.0001), indicating that antiviral drug resistance alters the balance between defective and genomic length DNA in circulation. Experiments in vitro using HBV encoding LMV-R mutations confirmed these results.

CONCLUSION

Our results identified no association between dDNA and parameters associated with disease status and suggested that the relative abundance of dDNA is largely dependent on the integrity of the HBV polymerase and is unrelated to the severity of liver disease.