A Highly Attenuated Vesicular Stomatitis Virus-Based Vaccine Platform Controls Hepatitis B Virus Replication in Mouse Models of Hepatitis B

CD4+ T cells reverse surface antigen persistence in a mouse model of HBV replication

IMPORTANCE

Hepatitis B virus (HBV) is a leading causative agent of viral hepatitis. A preventative vaccine has existed for decades, but only limited treatment options are available for people living with chronic HBV. Animal models for studying HBV are constrained due to narrow viral tropism, impeding understanding of the natural immune response to the virus. Here, using a vector to overcome the narrow host range and establish HBV replication in mice, we identified the role of helper T cells in controlling HBV. We show that helper T cells promote the B cell's ability to generate antibodies that remove HBV and its associated surface antigen from the blood and that transfer of purified helper T cells from HBV-immunized mice can reverse the accumulation of virus and antigen, furthering our understanding of the immune response to HBV.

Cellular Id1 inhibits hepatitis B virus transcription by interacting with the novel covalently closed circular DNA-binding protein E2F4

Hepatitis B virus (HBV) infection is a major risk factor for hepatocellular carcinoma (HCC), which required developing novel therapies targeting the inhibition of HBV transcription and replication due to current limited treatment options. We explored novel target for the development of novel therapies targeting the inhibition of HBV replication and transcription. The expression of Id1 and E2F4 in HCC cells and tissues was detected by qRT-PCR and western blot. We investigated the Id1 and E2F4-mediated transcription of HBV infection by using HepG2.2.15, HepAD38, HepG2-NTCP cell lines and AAV/HBV-infected mice. Interactions between the two host proteins and viral covalently closed circular DNA (cccDNA) were assessed using subcellular localization, protein-protein interaction, chromatin immunoprecipitation, and luciferase assays. Ectopic Id1 significantly reduced HBV transcription and replication in both HBV-expressing cells and AAV/HBV-infected mice. Id1 and E2F4 could form a heterodimer to prevent E2F4 from promoting HBV transcription and replication. E2F4 could directly bind to cccDNA and activate the HBV core promoter in cell lines. Furthermore, in vitro binding experiments confirmed that the sequence 1758'-TTAAAGGTC-1766', which is highly conserved among HBV genotypes, is the target site of the E2F4 homodimer. The findings suggest that E2F4 function as novel cccDNA-binding protein to directly activate HBV transcription by binding to Cp promoter region. Our results highlight the ability that E2F4 represent a pan-potential therapeutic target against HBV transcription and provide more clues to better understand the life cycle of HBV.

Virus-based vaccine vectors with distinct replication mechanisms differentially infect and activate dendritic cells

The precise mechanism by which many virus-based vectors activate immune responses remains unknown. Dendritic cells (DCs) play key roles in priming T cell responses and controlling virus replication, but their functions in generating protective immunity following vaccination with viral vectors are not always well understood. We hypothesized that highly immunogenic viral vectors with identical cell entry pathways but unique replication mechanisms differentially infect and activate DCs to promote antigen presentation and activation of distinctive antigen-specific T cell responses. To evaluate differences in replication mechanisms, we utilized a rhabdovirus vector (vesicular stomatitis virus; VSV) and an alphavirus-rhabdovirus hybrid vector (virus-like vesicles; VLV), which replicates like an alphavirus but enters the cell via the VSV glycoprotein. We found that while virus replication promotes CD8⁺ T cell activation by VLV, replication is absolutely required for VSV-induced responses. DC subtypes were differentially infected in vitro with VSV and VLV, and displayed differences in activation following infection that were dependent on vector replication but were independent of interferon receptor signaling. Additionally, the ability of the alphavirus-based vector to generate functional CD8⁺ T cells in the absence of replication relied on cDC1 cells. These results highlight the differential activation of DCs following infection with unique viral vectors and indicate potentially discrete roles of DC subtypes in activating the immune response following immunization with vectors that have distinct replication mechanisms.

In Vivo Mouse Models for Hepatitis B Virus Infection and Their Application

Despite the availability of effective vaccination, hepatitis B virus (HBV) infection continues to be a major challenge worldwide. Research efforts are ongoing to find an effective cure for the estimated 250 million people chronically infected by HBV in recent years. The exceptionally limited host spectrum of HBV has limited the research progress. Thus, different HBV mouse models have been developed and used for studies on infection, immune responses, pathogenesis, and antiviral therapies. However, these mouse models have great limitations as no spread of HBV infection occurs in the mouse liver and no or only very mild hepatitis is present. Thus, the suitability of these mouse models for a given issue and the interpretation of the results need to be critically assessed. This review summarizes the currently available mouse models for HBV research, including hydrodynamic injection, viral vector-mediated transfection, recombinant covalently closed circular DNA (rc-cccDNA), transgenic, and liver humanized mouse models. We systematically discuss the characteristics of each model, with the main focus on hydrodynamic injection mouse model. The usefulness and limitations of each mouse model are discussed based on the published studies. This review summarizes the facts for considerations of the use and suitability of mouse model in future HBV studies.

Advances in Targeting the Innate and Adaptive Immune Systems to Cure Chronic Hepatitis B Virus Infection

“Functional cure” is being pursued as the ultimate endpoint of antiviral treatment in chronic hepatitis B (CHB), which is characterized by loss of HBsAg whether or not anti-HBs antibodies are present. “Functional cure” can be achieved in <10% of CHB patients with currently available therapeutic agents. The dysfunction of specific immune responses to hepatitis B virus (HBV) is considered the major cause of persistent HBV infection. Thus, modulating the host immune system to strengthen specific cellular immune reactions might help eliminate HBV. Strategies are needed to restore/enhance innate immunity and induce HBV-specific adaptive immune responses in a coordinated way. Immune and resident cells express pattern recognition receptors like TLRs and RIG I/MDA5, which play important roles in the induction of innate immunity through sensing of pathogen-associated molecular patterns (PAMPs) and bridging to adaptive immunity for pathogen-specific immune control. TLR/RIG I agonists activate innate immune responses and suppress HBV replication in vitro and in vivo, and are being investigated in clinical trials. On the other hand, HBV-specific immune responses could be induced by therapeutic vaccines, including protein (HBsAg/preS and HBcAg), DNA, and viral vector-based vaccines. More than 50 clinical trials have been performed to assess therapeutic vaccines in CHB treatment, some of which display potential effects. Most recently, using genetic editing technology to generate CAR-T or TCR-T, HBV-specific T cells have been produced to efficiently clear HBV. This review summarizes the progress in basic and clinical research investigating immunomodulatory strategies for curing chronic HBV infection, and critically discusses the rather disappointing results of current clinical trials and future strategies.

Virus-like Vesicles Expressing Multiple Antigens for Immunotherapy of Chronic Hepatitis B

Infections with hepatitis B virus (HBV) can initiate chronic hepatitis and liver injury, causing more than 600,000 deaths each year worldwide. Current treatments for chronic hepatitis B are inadequate and leave an unmet need for immunotherapeutic approaches. We designed virus-like vesicles (VLV) as self-amplifying RNA replicons expressing three HBV antigens (polymerase, core, and middle surface) from a single vector (HBV-VLV) to break immune exhaustion despite persistent HBV replication. The HBV-VLV induces HBV-specific T cells in naive mice and renders them resistant to acute challenge with HBV. Using a chronic model of HBV infection, we demonstrate efficacy of HBV-VLV priming in combination with DNA booster immunization, as 40% of treated mice showed a decline of serum HBV surface antigen below the detection limit and marked reduction in liver HBV RNA accompanied by induction of HBsAg-specific CD8 T cells. These results warrant further evaluation of HBV-VLV for immunotherapy of chronic hepatitis B.

Heterologous prime-boost immunization with vesiculovirus-based vectors expressing HBV Core antigen induces CD8+ T cell responses in naïve and persistently infected mice and protects from challenge

Chronic hepatitis B virus (HBV) infections cause more than 800,000 deaths per year and currently approved treatments do not cure the disease. Because a hallmark of acute infection resolution is the presence of functional CD8⁺ T cells to the virus, activation of the immune system with therapeutic vaccines represents a potential approach for treating chronic hepatitis B. In this study, we evaluated the immunogenicity and efficacy of two attenuated vesiculovirus-based platforms expressing HBV Core antigen, the highly attenuated vesicular stomatitis virus (VSV) N4CT1 and a unique vaccine platform [virus-like vesicles (VLV)] that is based on a Semliki Forest virus replicon expressing the VSV glycoprotein. We found that heterologous prime-boost immunization with VLV and N4CT1 induced Core-specific CD8⁺ T cell responses in naïve mice. When immunized mice were later challenged with AAV-HBV, functional Core-specific CD8⁺ T cells were present in the liver, and mice were protected from establishment of persistent infection. In contrast, when mice with pre-established persistent HBV replication received prime-boost immunization, functional Core-specific CD8⁺ T cells were found in the spleen but not in the liver. These results highlight the importance of investigating the therapeutic value of different HBV antigens alone and in combination using preclinical animal models, and understanding the correlation between anti-HBV efficacy in these models with human infection.