A novel recombinant cccDNA-based mouse model with long term maintenance of rcccDNA and antigenemia

Potential role of liver-resident CD3+ macrophages in HBV clearance in a mouse hepatitis B model

Background & Aims

Chronic HBV infection usually causes cirrhosis and hepatocellular carcinoma. Comparative investigations of acute and chronic HBV cases would help determine the immune responses crucial for viral clearance.

Methods

A fast-cleared HBV mouse model was established in Alb-Cre mice via hydrodynamic injection of HBV plasmid, while persistent HBV model mice were generated via recombinant covalently closed circular DNA-adeno-associated virus 8 infection. The single-cell transcriptomes of CD45+ intrahepatic non-parenchymal cells from these mice were conducted. Multiplexed immunohistochemistry and flow cytometry were used to confirm the findings from single-cell transcriptomes. Transwell, coculture, and adoptive transfer experiments were performed to study the generation and functions of macrophages.

Results

Twenty-four clusters of immune cells were identified. Myeloid cells, including granulocytes, monocytes, and dendritic cells, are activated early in HBV fast-cleared mice. Significantly, a cluster of CD3+ macrophages was found in the viral clearance phase, which was confirmed in liver tissue from five acute patients with HBV. These cells highly expressed CXCL1, tumor necrosis factor alpha, and HBsAg-specific T cell receptors. The transwell assay revealed that CD3+ macrophages originate from macrophages (n = 6). T cells and anti-HBsAg antibodies are indispensable for their differentiation, which was further confirmed in T- and/or B-cell-deficient mice. Interestingly, these CD3+ macrophages capable of killing peptide-loaded hepatocytes and engulfing IgG-coated beads were persistently detectable in the mouse liver for 10 weeks after HBV clearance. The expression levels of CD5L and Bcl2, two classical antiapoptotic proteins, increased (p <0.001), suggesting that the CD3+ macrophages are long-term resident populations. Finally, adoptive transfer of CD3+ macrophages accelerated HBV clearance in mice (n = 5, p <0.01).

Conclusions

We identified long-term polyfunctional CD3+ macrophages residing in HBV fast-cleared livers that could help elucidate the immune responses involved in eliminating HBV.

Impact and implications

The liver is a special organ with unique immune characteristics and tolerance to foodborne antigens. Chronic infections can develop in newborns after exposure to HBV; however, acute infections usually occur in adults, indicating that immune cells in the liver tissue microenvironment can also effectively fight against the virus. Nevertheless, the mechanisms involved in acute HBV infection have rarely been studied. In this study, we identified a macrophage population with both T cell and macrophage characteristics in the livers of acute HBV model mice and revealed that these macrophages play important roles in HBV clearance. Moreover, we confirmed that this population is derived from macrophages in the presence of virus-specific T cells and antibodies. This finding highlights the complexity of antiviral immune responses in liver microenvironments.

Augmented epigenetic repression of hepatitis B virus covalently closed circular DNA by interferon-α and small-interfering RNA synergy

The persistence of hepatitis B virus (HBV) covalently closed circular DNA (cccDNA) is a key obstacle for HBV cure. This study aims to comprehensively assess the effect of interferon (IFN) and small-interfering RNA (siRNA) combination on the cccDNA minichromosome. Utilizing both cell and mouse cccDNA models, we compared the inhibitory effects of IFNα, siRNA, and their combination on cccDNA activity and assessed its epigenetic state. IFNα2 treatment alone reduced HBV RNAs, HBeAg, and HBsAg levels by approximately 50%, accompanied by a low-level reconstitution of SMC5/6-a chromatin modulator that restricts cccDNA transcription. HBx-targeting siRNA (siHBx) achieved significant suppression of viral antigens and reconstitution of SMC5/6, but this effect could be reversed by the deacetylase inhibitor Belinostat. The combination of IFN with siHBx resulted in over 95% suppression of virological markers, reduction in epigenetic activation modifications (H3Ac and H4Ac) on cccDNA, and further reduced cccDNA accessibility, with the effect not reversible by Belinostat. In an extracellular humanized IFNAR C57BL/6 mouse model harboring recombinant cccDNA, the effect of combination of clinically used pegylated IFNα2 and GalNac-siHBx was further clarified, indicating a higher and more durable suppression of cccDNA activity compared to either therapy alone. In conclusion, the combination of IFNα and siRNA achieves a more potent and durable epigenetic inhibition of cccDNA activity in cell and mouse models, compared to monotherapy. These findings deepen the understanding of cccDNA modulation and strengthen the scientific basis for the potential of combination therapy.

IMPORTANCE

Since there are currently no approved drugs targeting and silencing covalently closed circular DNA (cccDNA), achieving a "functional cure" remains difficult. This study aims to comprehensively compare the effects of IFNα, small-interfering RNA targeting hepatitis B virus (HBV), and their combination on the activity, accessibility, and epigenetic modifications of cccDNA minichromosomes in cell models. A more durable and stable inhibition of HBV RNAs and antigens expression by IFNα and HBx-targeting siRNA (siHBx) synergy was observed, associated with augmented epigenetic repression of the cccDNA minichromosome. Besides, in an extracellular humanized IFNAR mouse model harboring recombinant cccDNA with an intact response to human IFNα, the synergistic effect of clinically used pegylated IFNα2 and in-house-developed GalNac-siHBx was further clarified.

Optimized RNA interference therapeutics combined with interleukin-2 mRNA for treating hepatitis B virus infection

This study aimed to develop a pan-genotypic and multifunctional small interfering RNA (siRNA) against hepatitis B virus (HBV) with an efficient delivery system for treating chronic hepatitis B (CHB), and explore combined RNA interference (RNAi) and immune modulatory modalities for better viral control. Twenty synthetic siRNAs targeting consensus motifs distributed across the whole HBV genome were designed and evaluated. The lipid nanoparticle (LNP) formulation was optimized by adopting HO-PEG2000-DMG lipid and modifying the molar ratio of traditional polyethylene glycol (PEG) lipid in LNP prescriptions. The efficacy and safety of this formulation in delivering siHBV (tLNP/siHBV) along with the mouse IL-2 (mIL-2) mRNA (tLNP/siHBVIL2) were evaluated in the rAAV-HBV1.3 mouse model. A siRNA combination (terms "siHBV") with a genotypic coverage of 98.55% was selected, chemically modified, and encapsulated within an optimized LNP (tLNP) of high efficacy and security to fabricate a therapeutic formulation for CHB. The results revealed that tLNP/siHBV significantly reduced the expression of viral antigens and DNA (up to 3log10 reduction; vs PBS) in dose- and time-dependent manners at single-dose or multi-dose frequencies, with satisfactory safety profiles. Further studies showed that tLNP/siHBVIL2 enables additive antigenic and immune control of the virus, via introducing potent HBsAg clearance through RNAi and triggering strong HBV-specific CD4+ and CD8+ T cell responses by expressed mIL-2 protein. By adopting tLNP as nucleic acid nanocarriers, the co-delivery of siHBV and mIL-2 mRNA enables synergistic antigenic and immune control of HBV, thus offering a promising translational therapeutic strategy for treating CHB.

Progress of Infection and Replication Systems of Hepatitis B Virus

Despite the long-standing availability of effective prophylaxis, chronic hepatitis B virus (HBV) infection remains a formidable public health threat. Antiviral treatments can limit viral propagation, but prolonged therapy is necessary to control HBV replication. Robust in vitro models of HBV infection are indispensable prerequisites for elucidating viral pathogenesis, delineating virus-host interplay and developing novel therapeutic, preventative countermeasures. Buoyed by advances in molecular techniques and tissue culture systems, investigators have engineered numerous in vitro models of the HBV life cycle. However, all current platforms harbor limitations in the recapitulation of natural infection. In this article, we comprehensively review the HBV life cycle, provide an overview of existing in vitro HBV infection and replication systems, and succinctly present the benefits and caveats in each model with the primary objective of constructing refined experimental models that closely mimic native viral infection and offering robust support for the ambitious "elimination of hepatitis by 2030" initiative.

Mechanisms of Hepatitis B Virus cccDNA and Minichromosome Formation and HBV Gene Transcription

Hepatitis B virus (HBV) is the etiologic agent of chronic hepatitis B, which puts at least 300 million patients at risk of developing fibrosis, cirrhosis, and hepatocellular carcinoma. HBV is a partially double-stranded DNA virus of the Hepadnaviridae family. While HBV was discovered more than 50 years ago, many aspects of its replicative cycle remain incompletely understood. Central to HBV persistence is the formation of covalently closed circular DNA (cccDNA) from the incoming relaxed circular DNA (rcDNA) genome. cccDNA persists as a chromatinized minichromosome and is the major template for HBV gene transcription. Here, we review how cccDNA and the viral minichromosome are formed and how viral gene transcription is regulated and highlight open questions in this area of research.

The role of HBV cccDNA in occult hepatitis B virus infection

Occult hepatitis B virus (HBV) infection (OBI) refers to the presence of replication-competent HBV DNA in the liver, with or without HBV DNA in the blood, in individuals who tested negative for HBV surface antigen (HBsAg). In this peculiar phase of HBV infection, the covalently closed circular DNA (cccDNA) is in a low state of replication. Several advances have been made toward clarifying the mechanisms involved in such a suppression of viral activity, which seems to be mainly related to the host's immune control and epigenetic factors. Although the underlying mechanisms describing the genesis of OBI are not completely known, the presence of viral cccDNA, which remains in a low state of replication due to the host's strong immune suppression of HBV replication and gene expression, appears to be the causative factor. Through this review, we have provided an updated account on the role of HBV cccDNA in regulating OBI. We have comprehensively described the HBV cell cycle, cccDNA kinetics, current regulatory mechanisms, and the therapeutic methods of cccDNA in OBI-related diseases.

A spatiotemporally controlled recombinant cccDNA mouse model for studying HBV and developing drugs against the virus

Covalently closed circular (ccc) DNA is the template for hepatitis B virus (HBV) replication. The lack of small animal models for characterizing chronic HBV infection has hampered research progress in HBV pathogenesis and drug development. Here, we generated a spatiotemporally controlled recombinant cccDNA (rcccDNA) mouse model by combining Cre/loxP-mediated DNA recombination with the liver-specific "Tet-on/Cre" system. The mouse model harbors three transgenes: a single copy of the HBV genome (integrated at the Rosa26 locus, RHBV), H11-albumin-rtTA (spatiotemporal conditional module), and (tetO)₇-Cre (tetracycline response element), and is named as RHTC mouse. By supplying the RHTC mice with doxycycline (DOX)-containing drinking water for two days, the animals generate rcccDNA in hepatocytes, and the rcccDNA supports active HBV gene expression and can maintain HBV viremia persistence for over 60 weeks. Persistent HBV gene expression induces intrahepatic inflammation, fibrosis, and dysplastic pathology, which closely mirrors the disease progression in clinical patients. Bepirovirsen, an antisense oligonucleotide (ASO) targeting all HBV RNA species, showed dose-dependent antiviral effects in the RHTC mouse model. The spatiotemporally controlled rcccDNA mouse is convenient and reliable, providing versatile small animal model for studying cccDNA-centric HBV biology as well as evaluating antiviral therapeutics.

Significance of T-Cell Subsets for Clinical Response to Peginterferon Alfa-2a Therapy in HBeAg-Positive Chronic Hepatitis B Patients

Introduction

The adaptive immune response may reflect the immunomodulatory efficacy during peginterferon alfa-2a (PEG-IFN α-2a) treatment in chronic hepatitis B (CHB) patients. We evaluated the predictive efficiency of T-cell subsets on patient's response to PEG-IFN α-2a treatment.

Methods

The proportions of CD8+PD-1+, CD8+Tim-3+ and CD4+CD25high T-cells were measured at baseline and week 52 in CHB patients who underwent PEG-IFN α-2a treatment. The proportions of T-cell subsets were compared among different responders and non-responders (determined by biochemical, serological, and virological responses).

Results

The baseline proportions of the three T-cell subsets were significantly higher in CHB patients (65 cases) than in healthy controls (28 cases), while the proportions declined significantly after 52 weeks of PEG-IFN treatment. Responders (ALT < 40 IU/L, 89.2% [58/65]; HBV DNA < 2.7 log10 IU/ml, 66.2% [43/65]; and HBeAg seroconversion [SR], 53.9% [35/65]) experienced more pronounced declines in the proportion of T-cell subsets compared to non-responders. In particular, the baseline proportions of CD4+CD25high T-cells displayed significant difference between SR and non-SR groups. The stepwise logistic regression analysis identified that CD4+CD25high T-cells combined with baseline HBV DNA and ALT can predict SR and CR (ALT < 40 IU/L, HBV DNA < 2.7 log10 IU/mL and HBeAg seroconversion) after 52 weeks of PEG-IFN treatment with high accuracy.

Conclusion

PEG-IFN therapy induces significant declines in the proportion of some key T-cell subsets in HBeAg-positive patients. The model constructed with CD4+CD25high T-cells combined with ATL and HBV DNA may help to predict the efficacy of PEG-IFN α-2a therapy.

STING signaling activation inhibits HBV replication and attenuates the severity of liver injury and HBV-induced fibrosis

The covalently closed circular DNA (cccDNA) of HBV plays a crucial role in viral persistence and is also a risk factor for developing HBV-induced diseases, including liver fibrosis. Stimulator of interferon genes (STING), a master regulator of DNA-mediated innate immune activation, is a potential therapeutic target for viral infection and virus-related diseases. In this study, agonist-induced STING signaling activation in macrophages was revealed to inhibit cccDNA-mediated transcription and HBV replication via epigenetic modification in hepatocytes. Notably, STING activation could efficiently attenuate the severity of liver injury and fibrosis in a chronic recombinant cccDNA (rcccDNA) mouse model, which is a proven suitable research platform for HBV-induced fibrosis. Mechanistically, STING-activated autophagic flux could suppress macrophage inflammasome activation, leading to the amelioration of liver injury and HBV-induced fibrosis. Overall, the activation of STING signaling could inhibit HBV replication through epigenetic suppression of cccDNA and alleviate HBV-induced liver fibrosis through the suppression of macrophage inflammasome activation by activating autophagic flux in a chronic HBV mouse model. This study suggests that targeting the STING signaling pathway may be an important therapeutic strategy to protect against persistent HBV replication and HBV-induced fibrosis.

A Novel Mouse Model Harboring Hepatitis B Virus Covalently Closed Circular DNA

BACKGROUND AND AIMS

The persistence of viral covalently closed circular DNA (cccDNA) is the major obstacle for antiviral treatment against hepatitis B virus (HBV). Basic and translational studies are largely hampered due to the lack of feasible small animal models to support HBV cccDNA formation. The aim of this study is to establish a novel mouse model harboring cccDNA.

METHODS

An adeno-associated virus (AAV) vector carrying a replication-deficient HBV1.04-fold genome (AAV-HBV1.04) was constructed. The linear HBV genome starts from nucleotide 403 and ends at 538, which results in the splitting of HBV surface and polymerase genes. Different HBV replication markers were evaluated for AAV-HBV1.04 plasmid-transfected cells, the AAV-HBV1.04 viral vector-transduced cells, and mice injected with the AAV-HBV1.04 viral vector.

RESULTS

Compared with the previously reported AAV-HBV1.2 construct, direct transfection of AAV-HBV1.04 plasmid failed to produce hepatitis B surface antigen and progeny virus. Interestingly, AAV-HBV1.04 viral vector transduction could result in the formation of cccDNA and the production of all HBV replication markers in vitro and in vivo. The formation of cccDNA could be blocked by ATR (ataxia-telangiectasia and Rad3-related protein) inhibitors but not HBV reverse transcription inhibitor or capsid inhibitors. The AAV-HBV1.04 mouse supported long-term HBV replication and responded to antiviral treatments.

CONCLUSIONS

This AAV-HBV1.04 mouse model can support HBV cccDNA formation through ATR-mediated DNA damage response. The de novo formed cccDNA but not the parental AAV vector can lead to the production of hepatitis B surface antigen and HBV progeny. This model will provide a unique platform for studying HBV cccDNA and developing novel antivirals against HBV infection.

Intramolecular recombination enables the formation of hepatitis B virus (HBV) cccDNA in mice after HBV genome transfer using recombinant AAV vectors

The mouse is not a natural host of hepatitis B virus (HBV) infection and - despite engraftment of hepatocytes with the HBV receptor - does not support formation of HBV covalently closed circular (ccc) DNA serving as a template for viral transcription and permitting persistent infection. In a recent study, cccDNA formation in mouse hepatocytes has been described following an HBV genome delivery by a recombinant, adeno-associated virus vector (rAAV) (Lucifora et al., 2017). The integrity of HBV cccDNA, its origin and functionality, however, remained open. In this study, we investigated the identity, origin, and functionality of cccDNA established in mice infected with rAAV carrying 1.3-fold overlength HBV genomes. We show that replication of HBV genotypes A, B, C and D can be initiated in mouse livers, and that cccDNA derived from all genotypes is detected. Restriction enzyme and exonuclease digestion as well as sequencing analysis of cccDNA amplicons revealed authentic HBV cccDNA without any detectable alteration compared to cccDNA established after HBV infection of human liver cells. Mouse livers transduced with a core protein-deficient HBV using rAAV still supported cccDNA formation demonstrating that the genesis of cccDNA was independent of HBV replication. When mice were infected with an rAAV-HBV1.3 carrying premature stop codons in the 5' but not in the 3' core protein open reading frame, the stop codon was partially replaced by the wild-type sequence. This strongly indicated that intramolecular recombination, based on >900 identical base pairs residing at the both ends of the HBV1.3 transgene was the origin of cccDNA formation. Accordingly, we observed a constant loss of cccDNA molecules from mouse livers over time, while HBeAg levels increased over the first two weeks after rAAV-HBV1.3 infection and remained constant thereafter, suggesting a minor contribution of the cccDNA molecules formed to viral transcription and protein expression. In summary, our results provide strong evidence that intramolecular recombination of an overlength, linear HBV genome, but not HBV genome recycling, enables cccDNA formation in rAAV-HBV mouse models.

Animal Models for the Study of Hepatitis B Virus Pathobiology and Immunity: Past, Present, and Future

Hepatitis B virus (HBV) infection is a global public health problem that plagues approximately 240 million people. Chronic hepatitis B (CHB) often leads to liver inflammation and aberrant repair which results in diseases ranging from liver fibrosis, cirrhosis, to hepatocellular carcinoma. Despite its narrow species tropism, researchers have established various in vivo models for HBV or its related viruses which have provided a wealth of knowledge on viral lifecycle, pathogenesis, and immunity. Here we briefly revisit over five decades of endeavor in animal model development for HBV and summarize their advantages and limitations. We also suggest directions for further improvements that are crucial for elucidation of the viral immune-evasion strategies and for development of novel therapeutics for a functional cure.