Absence of viral interference and different susceptibility to interferon between hepatitis B virus and hepatitis C virus in human hepatocyte chimeric mice

Enhanced host immune responses in presence of HCV facilitate HBV clearance in coinfection

Hepatitis B virus (HBV)/Hepatitis C virus (HCV) coinfection is frequently observed because of the common infection routine. Despite the reciprocal inhibition exerted by HBV and HCV genomes, the coinfection of HBV and HCV is associated with more severe forms of liver diseases. However, the complexity of viral interference and underlying pathological mechanism is still unclarified. With the demonstration of absence of direct viral interplay, some in vitro studies suggest the indirect effects of viral-host interaction on viral dominance outcome. Here, we comprehensively investigated the viral replication and host immune responses which might mediate the interference between viruses in HBV/HCV coinfected Huh7-NTCP cells and immunocompetent HCV human receptors transgenic ICR mice. We found that presence of HCV significantly inhibited HBV replication in vitro and in vivo irrespective of the coinfection order, while HBV did not affect HCV replication. Pathological alteration was coincidently reproduced in coinfected mice. In addition to the participation of innate immune response, an involvement of HCV in up-regulating HBV-specific immune responses was described to facilitate HBV clearance. Our systems partially recapitulate HBV/HCV coinfection and unveil the uncharacterized adaptive anti-viral immune responses during coinfection, which renews the knowledge on the nature of indirect viral interaction during HBV/HCV coinfection.

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HCV inhibited HBV replication in Huh7-NTCP cells.

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HCV suppressed HBV in immunocompetent mice.

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Induced innate immune response by HCV limited HBV replication.

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Presence of HCV enhanced HBV specific immune response.

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Moderate and acute live injure was caused by HBV/HCV coinfection.

Diminished hepatic IFN response following HCV clearance triggers HBV reactivation in coinfection

In patients with HBV and HCV coinfection, HBV reactivation leading to severe hepatitis has been reported with the use of direct-acting antivirals (DAAs) to treat HCV infection. Here we studied the molecular mechanisms behind this viral interaction. In coinfected cell culture and humanized mice, HBV replication was suppressed by HCV coinfection. In vitro, HBV suppression was attenuated when interferon (IFN) signaling was blocked. In vivo, HBV viremia, after initial suppression by HCV superinfection, rebounded following HCV clearance by DAA treatment that was accompanied by a reduced hepatic IFN response. Using blood samples of coinfected patients, IFN-stimulated gene products including C-X-C motif chemokine 10 (CXCL10), C-C motif chemokine ligand 5 (CCL5), and alanine aminotransferase (ALT) were identified to have predictive value for HBV reactivation after HCV clearance. Taken together, our data suggest that HBV reactivation is a result of diminished hepatic IFN response following HCV clearance and identify serologic markers that can predict HBV reactivation in DAA-treated HBV-HCV-coinfected persons.

TM6SF2 Promotes Lipidation and Secretion of Hepatitis C Virus in Infected Hepatocytes

BACKGROUND & AIMS

Hepatitis C virus (HCV) co-opts the very-low-density lipoprotein pathway for morphogenesis, maturation, and secretion, and circulates as lipoviroparticles (LVPs). We investigated the functions and underlying mechanisms of the lipid-associated TM6SF2 protein in modulating LVP formation and the HCV life cycle.

METHODS

We knocked down or overexpressed TM6SF2 in hepatic cells and examined HCV infection, measuring viral RNA and protein levels and infectious LVP titers. The density of secreted LVPs was evaluated by iodixanol gradient assay. We measured levels and patterns of TM6SF2 in liver biopsies from 73 patients with chronic hepatitis C, livers of HCV-infected humanized Alb-uPA/SCID/beige mice, and HCV-infected Huh7.5.1 cells.

RESULTS

TM6SF2 knockdown in hepatocytes reduced viral RNA and infectious viral particle secretion without affecting HCV genome replication, translation, or assembly. Overexpression of TM6SF2 reduced intracellular levels of HCV RNA and infectious LVPs, and conversely increased their levels in the culture supernatants. In HCV-infected cells, TM6SF2 overexpression resulted in production of more infectious LVPs in the lower-density fractions of supernatant. HCV infection increased TM6SF2 expression in cultured cells, humanized livers of mice, and liver tissues of HCV patients. TM6SF2 messenger RNA levels correlated positively with HCV RNA levels in liver biopsies from patients. SREBF2 appears to mediate the ability of HCV to increase the expression of TM6SF2 in hepatic cells.

CONCLUSIONS

In studies of cells, mice and human liver tissues, we found TM6SF2 is required for maturation, lipidation, and secretion of infectious LVPs. HCV, in turn, up-regulates expression of TM6SF2 to facilitate productive infection.

Hepatitis B Virus Deregulates the Cell Cycle To Promote Viral Replication and a Premalignant Phenotype

Hepatitis B virus (HBV) infection is a major health problem worldwide, and chronically infected individuals are at high risk of developing cirrhosis and hepatocellular carcinoma (HCC). The molecular mechanisms whereby HBV causes HCC are largely unknown. Using a biologically relevant system of HBV infection of primary human hepatocytes (PHHs), we studied how HBV perturbs gene expression and signaling pathways of infected hepatocytes and whether these effects are relevant to productive HBV infection and HBV-associated HCC. Using a human growth factor antibody array, we first showed that HBV infection induced a distinct profile of growth factor production by PHHs, marked particularly by significantly lower levels of the transforming growth factor β (TGF-β) family of proteins in the supernatant. Transcriptome profiling next revealed multiple changes in cell proliferation and cell cycle control pathways in response to HBV infection. A human cell cycle PCR array validated deregulation of more than 20 genes associated with the cell cycle in HBV-infected PHHs. Cell cycle analysis demonstrated that HBV-infected PHHs are enriched in the G₂/M phase compared to the predominantly G₀/G₁ phase of cultured PHHs. HBV proviral host factors, such as PPARA, RXRA, and CEBPB, were upregulated upon HBV infection and particularly enriched in cells in the G₂/M phase. Together, these results support the notion that HBV deregulates cell cycle control to render a cellular environment that is favorable for productive HBV infection. By perturbing cell cycle regulation of infected cells, HBV may coincidently induce a premalignant phenotype that predisposes infected hepatocytes to subsequent malignant transformation.IMPORTANCE Hepatitis B virus (HBV) infection is a major health problem with high risk of developing hepatocellular carcinoma (HCC). By using a biologically relevant system of HBV infection of primary human hepatocytes (PHHs), we studied how HBV perturbs gene expression and whether these effects are relevant to HBV-associated HCC. HBV induced a distinct profile of growth factor production, marked particularly by significantly lower levels of the transforming growth factor β (TGF-β) family of proteins. Transcriptome profiling revealed multiple changes in cell proliferation and cell cycle control pathways. Cell cycle analysis demonstrated that HBV-infected PHHs are enriched in the G₂/M phase. HBV proviral host factors were upregulated upon infection and particularly enriched in cells in the G₂/M phase. Together, these results support the notion that HBV deregulates cell cycle control to render a cellular environment that is favorable for productive infection. This may coincidently induce a premalignant phenotype that predisposes infected hepatocytes to subsequent malignant transformation.

Hepatitis B virus sensitivity to interferon-α in hepatocytes is more associated with cellular interferon response than with viral genotype

Interferon-α (IFN-α) is used to treat chronic hepatitis B virus (HBV) infection, but only 20%-40% of patients respond well. Clinical observations have suggested that HBV genotype is associated with the response to IFN therapy; however, its role in viral responsiveness to IFN in HBV-infected hepatocytes remains unclear. Here, we produced infectious virions of HBV genotypes A to D to infect three well-recognized cell-culture-based HBV infection systems, including primary human hepatocytes (PHH), differentiated HepaRG (dHepaRG), and HepG2-NTCP cells to quantitatively compare the antiviral effect of IFN-α on HBV across genotypes and cell models. The efficacy of IFN-α against HBV in hepatocytes was generally similar across genotypes A2, B5, C2, and D3; however, it was significantly different among the infection models given that the half maximal inhibitory concentration value of IFN-α for inhibition of viral DNA replication in PHH (<20 U/mL) and dHepaRG cells were much lower than that in HepG2-NTCP cells (>500 U/mL). Notably, even in PHH, IFN-α did not reduce HBV covalently closed circular DNA at the concentrations for which viral antigens and DNA replication intermediates were strongly reduced. The three cell-culture models exhibited differential cellular response to IFN-α. The genes reported to be associated with responsiveness to IFN-α in patients were robustly induced in PHH while weakly induced in HepG2-NTCP cells upon IFN-α treatment. Reduction or promotion of IFN response in PHH or HepG2-NTCP cells significantly attenuated or improved the inhibitory capacity of IFN-α on HBV replication, respectively.

CONCLUSION

In the cell-culture-based HBV infection models, the sensitivity of HBV to IFN-α in hepatocytes is determined more by the cell-intrinsic IFN response than by viral genotype, and improvement of the IFN response in HepG2-NTCP cells promotes the efficacy of IFN-α against HBV. (Hepatology 2018;67:1237-1252).

Suppression of interferon-mediated anti-HBV response by single CpG methylation in the 5'-UTR of TRIM22

OBJECTIVE

Interferons (IFNs) mediate direct antiviral activity. They play a crucial role in the early host immune response against viral infections. However, IFN therapy for HBV infection is less effective than for other viral infections.

DESIGN

We explored the cellular targets of HBV in response to IFNs using proteome-wide screening.

RESULTS

Using LC-MS/MS, we identified proteins downregulated and upregulated by IFN treatment in HBV X protein (HBx)-stable and control cells. We found several IFN-stimulated genes downregulated by HBx, including TRIM22, which is known as an antiretroviral protein. We demonstrated that HBx suppresses the transcription of TRIM22 through a single CpG methylation in its 5'-UTR, which further reduces the IFN regulatory factor-1 binding affinity, thereby suppressing the IFN-stimulated induction of TRIM22.

CONCLUSIONS

We verified our findings using a mouse model, primary human hepatocytes and human liver tissues. Our data elucidate a mechanism by which HBV evades the host innate immune system.

Hepatitis B virus evades innate immunity of hepatocytes but activates cytokine production by macrophages

Hepatitis B virus (HBV) infects hepatocytes specifically and causes immune-mediated liver damage. How HBV interacts with the innate immunity at the early phase of infection, either with hepatocytes or other cells in the liver, remains controversial. To address this question, we utilized various human cell-culture models and humanized Alb-uPA/SCID mice. All these models were unable to mount an interferon (IFN) response despite robust HBV replication. To elucidate the mechanisms involved in the lack of IFN response, we examined whether HBV actively inhibits innate immune functions of hepatocytes. By treating HBV-infected cells with known inducers of the IFN signaling pathway, we observed no alteration of either sensing or downstream IFN response by HBV. We showed that the DNA innate sensing pathways are poorly active in hepatocytes, consistent with muted innate immune recognition of HBV. Upon exposure to high-level HBV, human macrophages could be activated with increased inflammatory cytokine expressions.

CONCLUSION

HBV behaves like a "stealth" virus and is not sensed by, nor actively interferes with, the intrinsic innate immunity of infected hepatocytes. Macrophages are capable of sensing HBV, but require exposure to high HBV titers, potentially explaining the long "window period" during acute infection and HBV's propensity to chronic infection. (Hepatology 2017;66:1779-1793).

Association of hepatitis status with surgical outcomes in patients with dual hepatitis B and C related hepatocellular carcinoma

Background

The conception that serological hepatitis markers determined surgical prognosis of hepatocellular carcinoma (HCC) associated with hepatitis B (HBV) or hepatitis C (HCV) has been well defined. However, little is known about the relationship between surgical outcomes and serological hepatitis markers in patients with dual HBV and HCV related HCC.

Methods

A retrospective analysis of the clinical data of 39 HCC patients with HBV-HCV coinfection who underwent curative hepatectomy between 2001 and 2011 was performed. HBV DNA quantification, expression of HBV antigens, anti-HCV signal-to-cutoff ratio (S/CO) and some clinicopathological characteristics were investigated to show the potential relationship among them and the surgical prognosis.

Results

The Cox proportional hazards model identified that HBV DNA quantification of 1,000 IU/mL or higher, HBeAg seropositivity, tumor size of greater than 5 cm, multiple tumors, and vascular invasion were risk factors for HCC prognosis. Thus, HBV DNA quantification, HBsAg level, HBeAg status and HCV-Ab level which may reveal the hepatitis status were further analyzed. The overall survival time in the group with high (≥1,000 IU/mL) HBV DNA quantification was significantly lower than the group with low (<1,000 IU/mL) HBV DNA quantification. Similarly, the high HBsAg level (≥1,000 IU/mL) was associated with poor survival compared with the low HBsAg level. Moreover, HBeAg seropositivity determined a higher cumulative risk for death. However, no significant difference was observed in overall survival time between the groups with low (<10.9 S/CO) and high (≥10.9 S/CO) HCV-Ab level. Compared to HCV-Ab high-level group, the serological HBsAg level was observed significantly higher in HCV-Ab low-level group. Furthermore, the data we analyzed showed these 4 serological hepatitis markers were not correlated with cumulative recurrence rate. On multivariate analysis, none of serological hepatitis markers was an independent prognostic factor for HCC patients with dual hepatitis B and C.

Conclusion

Among HCC patients with HBV-HCV coinfection, those who with preoperatively high HBV DNA quantification or HBeAg seropositivity had a short survival time and served as poor survival indicators. Serological expression of HBV status rather than HCV status might potentially dominate the surgical outcomes of the Chinese HCC patients with HBV-HCV coinfection.

Electronic supplementary material

The online version of this article (doi:10.1186/s13027-017-0137-6) contains supplementary material, which is available to authorized users.

Molecular dissection of HBV evasion from restriction factor tetherin: A new perspective for antiviral cell therapy

Viruses have evolved various strategies to escape from the innate cellular mechanisms inhibiting viral replication and spread. Extensive evidence has highlighted the ineffectiveness of interferon (IFN) therapy against chronic hepatitis B virus (HBV) infection, implying the existence of mechanisms by which HBV evades IFN-induced antiviral responses. In our current study, we demonstrate that HBV surface protein (HBs) plays a crucial role in counteracting the IFN-induced antiviral response mediated by tetherin (also known as BST-2). The type I IFN treatment of HBV-producing cells marginally but significantly inhibited the release of HBsAg and viral DNA, but this release was recovered by the knockdown of tetherin. HBs can interact with tetherin via its fourth transmembrane domain thereby inhibiting its dimerization and antiviral activity. The expression of a tetherin mutant devoid of the HBs-binding domain promoted a prominent restriction of HBV particle production that eventually resulted in the alleviation of caspase-1-mediated cytotoxicity and interleukin-1β secretion in induced pluripotent stem cell (iPSC)-derived hepatocytes. Our current results thus reveal a previously undescribed molecular link between HBV and tetherin during the course of an IFN-induced antiviral response. In addition, strategies to augment the antiviral activity of tetherin by impeding tetherin-HBs interactions may be viable as a therapeutic intervention against HBV.

Hepatitis B Surface Antigen Loss and Hepatocellular Carcinoma Development in Patients With Dual Hepatitis B and C Infection

Hepatitis B virus (HBV) and hepatitis C virus (HCV) infections are 2 major causes of chronic viral hepatitis. It is still unclear how HCV coinfection affects HBV replication and clinical outcomes in HBV/HCV coinfected patients.We conducted a longitudinal study, which enrolled 111 patients with HBV/HCV coinfection and 111 propensity score-matched controls with HBV monoinfection. Both groups had comparable baseline age, sex, fibrosis stage, levels of HBV DNA, and HBV surface antigen (HBsAg). The HCV coinfection and other host/viral factors were correlated with various outcomes, including HBsAg loss and cirrhosis/hepatocellular carcinoma (HCC) development.After a 10-year follow-up, we found that HCV coinfection itself was not associated with HBsAg loss. However, coinfected patients with alanine aminotransferase (ALT) level >80 U/L had a higher chance of HBsAg loss than those with ALT level ≤80 U/L [hazard ratio (95% confidence interval): 4.41 (1.75-11.15)] or matched controls with HBV monoinfection [hazard ratio (95% confidence interval): 3.40 (1.54-7.50)]. Besides, both HCV coinfection and higher ALT levels were associated with higher HCC risks and the HCC risks remained even after HBsAg loss in HBV/HCV con-infected patient.HCV coinfection is not associated with HBsAg loss. A higher ALT level is a major determinant of HBsAg loss in patients with HBV/HCV coinfection. Both HCV coinfection and a higher ALT level were independent risk factors of HCC.

Clinical and virological features of occult hepatitis B in patients with HBsAg seroclearance post-treatment or spontaneously

BACKGROUND

Occult hepatitis B virus (HBV) infection (OHB) may exist in patients experiencing hepatitis B surface antigen (HBsAg) seroclearance.

AIMS

We examined the clinical and virological features of OHB in patients who lost HBsAg post-treatment or spontaneously.

METHODS

We collected 44 patients with HBsAg seroclearance: 15 patients with dual HBV/hepatitis C virus (HCV) infection who lost HBsAg after peginterferon alfa-2a (PEG-IFN) plus ribavirin therapy; 13 HBV mono-infected patients who lost HBsAg after various oral antiviral therapies; and 16 patients who lost HBsAg spontaneously. OHB was defined as detectable serum HBV DNA in the absence of HBsAg. Viral mutations associated with OHB were identified by comparison with matched controls that remained positive for HBsAg, and further characterized in vitro.

RESULTS

The prevalence of OHB was 34.1% (15/44) in all patients, which was not significantly different among three groups. One mutation in surface promoter/polymerase region, C3050T (preS1T68I), was identified to be associated with the seroclearance of HBsAg in six cases. This mutation does not change the amino acid sequence of the polymerase protein. The S promoter activity was significantly lower in the construct containing C3050T mutation as compared with the wild-type (P = 0.0008). However, this mutation did not affect HBV replication, transcription and translation in the context of the full-length HBV genome. OHB was not rare in patients with HBsAg seroclearance.

CONCLUSIONS

One mutation, C3050T (preS1T68I), decreased S promoter activity; nevertheless, other factors may play more important role in the clearance of HBsAg in these OHB patients.

Mouse models of hepatitis B and delta virus infection

Liver disease associated to persistent infection with the hepatitis B virus (HBV) continues to be a major health problem of global impact. Therapeutic regimens currently available can efficiently suppress HBV replication; however, the unique replication strategies employed by HBV permit the virus to persist within the infected hepatocytes. As a consequence, relapse of viral activity is commonly observed after cessation of treatment with polymerase inhibitors. Among the HBV chronically infected patients, more than 15million patients are estimated to be co-infected with the hepatitis delta virus (HDV), a defective satellite virus that needs the HBV envelope for propagation. No specific drugs are currently available against HDV, while nucleos(t)ide analogs are not effective against HDV replication. Since chronic HBV/HDV co-infection leads to the most severe form of chronic viral hepatitis in men, a better understanding of the molecular mechanisms of HDV-mediated pathogenesis and the development of improved therapeutic approaches is urgently needed. The obvious limitations imposed by the use of great apes and the paucity of robust experimental models of HBV infection have hindered progresses in understanding the complex network of virus-host interactions that are established in the course of HBV and HDV infections. This review focuses on summarizing recent advances obtained with well-established and more innovative experimental mouse models, giving emphasis on the strength of infection systems based on the reconstitution of the murine liver with human hepatocytes, as tools for elucidating the whole life cycle of HBV and HDV, as well as for studies on interactions with the infected human hepatocytes and for preclinical drug evaluation.

Long-term elimination of hepatitis C virus from human hepatocyte chimeric mice after interferon-γ gene transfer

Chronic hepatitis C virus (HCV) infection is a leading cause of cirrhosis, liver failure, and hepatocellular carcinoma. Although the combination therapy employing pegylated interferon (IFN)-α and ribavirin is effective, this treatment is effective in only approximately 50% patients with genotype 1 HCV infection. IFN-γ is a potent anti-HCV agent that exhibits its antiviral action through a receptor distinct from that for IFN-α. Therefore, IFN-γ application might provide an alternative approach to IFN-α-based therapies. However, recombinant IFN-γ protein exhibits a poor pharmacokinetic property, that is, a very short half-life. It is our hypothesis that sustained IFN-γ serum concentrations produced by gene transfer could effectively eliminate HCV in vivo. We examined the in vivo antiviral activity in human hepatocyte chimeric mice infected with genotype 1b HCV at high HCV RNA titers (10(5)-10(7) copies/ml). The human IFN-γ-expressing plasmid vector pCpG-huIFNγ exhibited prolonged transgene expression in mice compared with the plasmid vector pCMV-huIFNγ. Moreover, the gene transfer of pCpG-huIFNγ eliminated HCV from the liver of the chimeric mice for a sustained period. On the contrary, administration of pCMV-huIFNγ could not eliminate HCV. In conclusion, we found that a single pCpG-huIFNγ injection resulted in long-term elimination of HCV RNA in chimeric mice, providing, for the first time, direct evidence that chronic infection with high titer HCV in vivo can be treated by sustained IFN-γ treatment.

HLA-DQB1*03 confers susceptibility to chronic hepatitis C in Japanese: a genome-wide association study

Hepatitis C virus (HCV) establishes a chronic infection in 70-80% of infected individuals. Many researchers have examined the effect of human leukocyte antigen (HLA) on viral persistence because of its critical role in the immune response against exposure to HCV, but almost all studies have proven to be inconclusive. To identify genetic risk factors for chronic HCV infection, we analyzed 458,207 single nucleotide polymorphisms (SNPs) in 481 chronic HCV patients and 2,963 controls in a Japanese cohort. Next, we performed a replication study with an independent panel of 4,358 cases and 1,114 controls. We further confirmed the association in 1,379 cases and 25,817 controls. In the GWAS phase, we found 17 SNPs that showed suggestive association (P < 1 × 10^-5). After the first replication study, we found one intronic SNP in the HLA-DQ locus associated with chronic HCV infection, and when we combined the two studies, the association reached the level of genome-wide significance. In the second replication study, we again confirmed the association (P_combined = 3.59 × 10⁻¹⁶, odds ratio [OR] = 0.79). Subsequent analysis revealed another SNP, rs1130380, with a stronger association (OR=0.72). This nucleotide substitution causes an amino acid substitution (R55P) in the HLA-DQB1 protein specific to the DQB1*03 allele, which is common worldwide. In addition, we confirmed an association with the previously reported IFNL3-IFNL4 locus and propose that the effect of DQB1*03 on HCV persistence might be affected by the IFNL4 polymorphism. Our findings suggest that a common amino acid substitution in HLA-DQB1 affects susceptibility to chronic infection with HCV in the Japanese population and may not be independent of the IFNL4 genotype.

Hepatitis B virus polymerase impairs interferon-α-induced STA T activation through inhibition of importin-α5 and protein kinase C-δ

Treatment with exogenous interferon (IFN)-α is not effective in the majority of patients with chronic hepatitis B virus (HBV) infection. Recent evidence suggests that HBV has evolved strategies to block the nuclear translocation of signal transducer and activator of transcription (STAT) 1 to limit IFN-α-induced cellular antiviral responses. However, it remains unclear whether STAT1 translocation is impaired in chronic hepatitis B patients and what mechanisms are involved. Here we report that the expression of HBV polymerase (Pol) in human hepatic cell lines inhibited induction of IFN-stimulated genes and resulted in a weakened antiviral activity of IFN-α. Ectopic expression of Pol suppressed IFN-α-induced STAT1 serine 727 phosphorylation and STAT1/2 nuclear accumulation, whereas STAT1 tyrosine 701 phosphorylation, and STAT1-STAT2 heterodimer formation were not affected. Further studies demonstrated that Pol interacted with the catalytic domain of protein kinase C-δ (PKC-δ) and perturbed PKC-δ phosphorylation and its association with STAT1, which resulted in the suppression of STAT1 Ser727 phosphorylation. Moreover, Pol was found to interfere with nuclear transportation of STAT1/2 by competitively binding to the region of importin-α5 required for STAT1/2 recruitment. Truncation analysis suggested that the terminal protein and RNase H domains of Pol were able to bind to PKC-δ and importin-α5, respectively, and were responsible for the inhibition of IFN-α signaling. More importantly, the inhibition of STAT1 and PKC-δ phosphorylation were confirmed in a hydrodynamic-based HBV mouse model, and the blockage of IFN-α-induced STAT1/2 nuclear translocation was observed in HBV-infected cells from liver biopsies of chronic HBV patients.

CONCLUSIONS

These results demonstrate a role for Pol in HBV-mediated antagonization of IFN-α signaling and provide a possible molecular mechanism by which HBV resists the IFN therapy and maintains its persistence.

Inhibition of the HCV core protein on the immune response to HBV surface antigen and on HBV gene expression and replication in vivo

The hepatitis C virus (HCV) core protein is a multifunctional protein that can interfere with the induction of an immune response. It has been reported that the HCV core protein inhibits HBV replication in vitro. In this study, we test the effect of the HCV core gene on the priming of the immune response to hepatitis B surface antigen (HBsAg) and on the replication of HBV in vivo. Our results showed that the full-length HCV core gene inhibits the induction of an immune response to the heterogeneous antigen, HBsAg, at the site of inoculation when HCV core (pC191) and HBsAg (pHBsAg) expression plasmids are co-administered as DNA vaccines into BALB/c mice. The observed interference effect of the HCV core occurs in the priming stage and is limited to the DNA form of the HBsAg antigen, but not to the protein form. The HCV core reduces the protective effect of the HBsAg when the HBsAg and the HCV core are co-administered as vaccines in an HBV hydrodynamic mouse model because the HCV core induces immune tolerance to the heterogeneous HBsAg DNA antigen. These results suggest that HCV core may play an important role in viral persistence by the attenuation of host immune responses to different antigens. We further tested whether the HCV core interfered with the priming of the immune response in hepatocytes via the hydrodynamic co-injection of an HBV replication-competent plasmid and an HCV core plasmid. The HCV core inhibited HBV replication and antigen expression in both BALB/c (H-2d) and C57BL/6 (H-2b) mice, the mouse models of acute and chronic hepatitis B virus infections. Thus, the HCV core inhibits the induction of a specific immune response to an HBsAg DNA vaccine. However, HCV C also interferes with HBV gene expression and replication in vivo, as observed in patients with coinfection.

Experimental models and therapeutic approaches for HBV

Liver disease associated to persistent infection with the hepatitis B virus (HBV) continues to be a major health problem of global impact. In spite of the existence of an effective vaccine, approximately 360 million people are chronically infected worldwide, who are at high risk of developing liver cirrhosis and hepatocellular carcinoma. Although current therapeutic regimens can efficiently suppress viral replication, the unique replication strategies employed by HBV permit the virus to persist within the infected hepatocytes. As a consequence, relapse of viral activity is commonly observed after cessation of treatment with polymerase inhibitors. The narrow host range of HBV has hindered progresses in understanding specific steps of HBV replication and the development of more effective therapeutic strategies aiming at achieving sustained viral control and, eventually, virus eradication. This review will focus on summarizing recent advances obtained with well-established and more innovative experimental models, giving emphasis on the strength of the different systems as tools for elucidating distinct aspects of HBV persistence and for the development of new therapeutic approaches.

IFN-α inhibits HBV transcription and replication in cell culture and in humanized mice by targeting the epigenetic regulation of the nuclear cccDNA minichromosome

HBV infection remains a leading cause of death worldwide. IFN-α inhibits viral replication in vitro and in vivo, and pegylated IFN-α is a commonly administered treatment for individuals infected with HBV. The HBV genome contains a typical IFN-stimulated response element (ISRE), but the molecular mechanisms by which IFN-α suppresses HBV replication have not been established in relevant experimental systems. Here, we show that IFN-α inhibits HBV replication by decreasing the transcription of pregenomic RNA (pgRNA) and subgenomic RNA from the HBV covalently closed circular DNA (cccDNA) minichromosome, both in cultured cells in which HBV is replicating and in mice whose livers have been repopulated with human hepatocytes and infected with HBV. Administration of IFN-α resulted in cccDNA-bound histone hypoacetylation as well as active recruitment to the cccDNA of transcriptional corepressors. IFN-α treatment also reduced binding of the STAT1 and STAT2 transcription factors to active cccDNA. The inhibitory activity of IFN-α was linked to the IRSE, as IRSE-mutant HBV transcribed less pgRNA and could not be repressed by IFN-α treatment. Our results identify a molecular mechanism whereby IFN-α mediates epigenetic repression of HBV cccDNA transcriptional activity, which may assist in the development of novel effective therapeutics.

Hepatitis B virus limits response of human hepatocytes to interferon-α in chimeric mice

BACKGROUND & AIMS

Interferon (IFN)-α therapy is not effective for most patients with chronic hepatitis B virus (HBV) infection for reasons that are not clear. We investigated whether HBV infection reduced IFN-α-mediated induction of antiviral defense mechanisms in human hepatocytes.

METHODS

Human hepatocytes were injected into severe combined immune-deficient mice (SCID/beige) that expressed transgenic urokinase plasminogen activator under control of the albumin promoter. Some mice were infected with HBV; infected and uninfected mice were given injections of human IFN-α. Changes in viral DNA and expression of human interferon-stimulated genes (ISGs) were measured by real-time polymerase chain reaction, using human-specific primers, and by immunohistochemistry.

RESULTS

Median HBV viremia (0.8log) and intrahepatic loads of HBV RNA decreased 3-fold by 8 or 12 hours after each injection of IFN-α, but increased within 24 hours. IFN-α activated expression of human ISGs and nuclear translocation of signal transducers and activators of transcription-1 (STAT1) in human hepatocytes that repopulated the livers of uninfected mice. Although baseline levels of human ISGs were slightly increased in HBV-infected mice, compared with uninfected mice, IFN-α failed to increase expression of the ISGs OAS-1, MxA, MyD88, and TAP-1 (which regulates antigen presentation) in HBV-infected mice. IFN-α did not induce nuclear translocation of STAT1 in HBV-infected human hepatocytes. Administration of the nucleoside analogue entecavir (for 20 days) suppressed HBV replication but did not restore responsiveness to IFN-α.

CONCLUSIONS

HBV prevents induction of IFN-α signaling by inhibiting nuclear translocation of STAT1; this can interfere with transcription of ISGs in human hepatocytes. These effects of HBV might contribute to the limited effectiveness of endogenous and therapeutic IFN-α in patients and promote viral persistence.

EGFR and EphA2 are host factors for hepatitis C virus entry and possible targets for antiviral therapy

Hepatitis C virus (HCV) is a major cause of liver disease, but therapeutic options are limited and there are no prevention strategies. Viral entry is the first step of infection and requires the cooperative interaction of several host cell factors. Using a functional RNAi kinase screen, we identified epidermal growth factor receptor and ephrin receptor A2 as host cofactors for HCV entry. Blocking receptor kinase activity by approved inhibitors broadly impaired infection by all major HCV genotypes and viral escape variants in cell culture and in a human liver chimeric mouse model in vivo. The identified receptor tyrosine kinases (RTKs) mediate HCV entry by regulating CD81-claudin-1 co-receptor associations and viral glycoprotein-dependent membrane fusion. These results identify RTKs as previously unknown HCV entry cofactors and show that tyrosine kinase inhibitors have substantial antiviral activity. Inhibition of RTK function may constitute a new approach for prevention and treatment of HCV infection.

Hepatitis B virus e antigen downregulates cytokine production in human hepatoma cell lines

Disease activities of hepatitis B are affected by the status of hepatitis B e antigen (HBeAg). The function of the hepatitis B virus (HBV) precore or HBeAg is unknown. We assumed that HBeAg blocks aberrant immune responses, although HBeAg is not required for viral assembly, infection, or replication. We examined the interaction of HBeAg and the immune system, including cytokine production. The inflammatory cytokine TNF, IL-6, IL-8, IL-12A, IFN-α1, and IFN-ß mRNA were downregulated in HBeAg-positive HepG2, which stably expresses HBeAg, compared to HBeAg-negative HepG2 cells. The results of real-time RT-PCR-based cytokine-related gene arrays showed the downregulation of cytokine and IFN production. We also observed inhibition of the activation of NF-κB- and IFN-ß-promoter in HBeAg-positive HepG2, as well as inhibition of IFN and IL-6 production in HBeAg-positive HepG2 cell culture fluids. HBeAg might modify disease progression by inhibiting inflammatory cytokine and IFN gene expression, while simultaneously suppressing NF-κB-signaling- and IFNß-promoter activation.

Animal model for study of human hepatitis viruses

Human hepatitis B virus (HBV) and hepatitis C virus (HCV) infect only chimpanzees and humans. Analysis of both viruses has long been hampered by the absence of a small animal model. The recent development of human hepatocyte chimeric mice has enabled us to carry out studies on viral replication and cellular changes induced by replication of human hepatitis viruses. Various therapeutic agents have also been tested using this model. In the present review, we summarize published studies using chimeric mice and discuss the merits and shortcomings of this model.

Factors determining successful engraftment of hepatocytes and susceptibility to hepatitis B and C virus infection in uPA-SCID mice

BACKGROUND & AIMS

The human liver-uPA(+/+)-SCID mouse is currently the best small animal model available for viral hepatitis infection studies.

METHODS

We identify critical factors affecting animal survival, engraftment efficacy, kinetics of liver repopulation and virological outcome by analysing the data from 400 human hepatocyte transplantations and 115 subsequent HBV and/or HCV inoculations in this mouse model.

RESULTS

Almost one third of animals succumbed during the first week after hepatocyte transplantation. Only during this critical period, liver necrosis due to embolization of donor cells in the portal vein was observed. This may have caused a fatal acute liver failure that complicated the pre-existing chronic liver disease. From the second week onwards, confluent hepatocyte clusters repopulated the liver and restored its synthetic functions as evidenced by increasing human albumin levels in plasma. Xenogenic repopulation by human cells proceeded approximately 4-times slower compared to allogenic mouse hepatocytes. All HBV inoculations were successful, even in animals with low graft take. HCV infection rate varied substantially, although every donor cell type yielded infectable animals. A reproducible 100% HCV infectivity was reached with high quality inocula in animals with human albumin plasma levels >1 mg/ml. Superior animal survival, adequate liver engraftment and a high viral infection rate were observed after transplanting cryopreserved commercial human hepatocytes.

CONCLUSIONS

Our findings favour the use of commercially available, cryopreserved human hepatocytes for the humanization of the uPA(+/+)-SCID liver. While HBV infectivity criteria are less stringent, human albumin plasma levels exceeding 1 mg/ml are required for a consistent HCV infection in chimeric mice.

Interferons accelerate decay of replication-competent nucleocapsids of hepatitis B virus

Alpha interferon (IFN-alpha) is an approved medication for chronic hepatitis B. Gamma interferon (IFN-gamma) is a key mediator of host antiviral immunity against hepatitis B virus (HBV) infection in vivo. However, the molecular mechanism by which these antiviral cytokines suppress HBV replication remains elusive. Using an immortalized murine hepatocyte (AML12)-derived cell line supporting tetracycline-inducible HBV replication, we show in this report that both IFN-alpha and IFN-gamma efficiently reduce the amount of intracellular HBV nucleocapsids. Furthermore, we provide evidence suggesting that the IFN-induced cellular antiviral response is able to distinguish and selectively accelerate the decay of HBV replication-competent nucleocapsids but not empty capsids in a proteasome-dependent manner. Our findings thus reveal a novel antiviral mechanism of IFNs and provide a basis for a better understanding of HBV pathobiology.