Present and future DNA vaccines for chronic hepatitis B treatment

Elimination of the hepatitis B virus: A goal, a challenge

The hepatitis B elimination is a goal proposed by the WHO to be achieved by 2030 through the adoption of synergistic measures for the prevention and chronic HBV infection treatment. Complete cure is characterized by the HBV elimination from the body and is the goal of the chronic hepatitis B treatment, which once achieved, will enable the hepatitis B elimination. This, today, has been a scientific challenge. The difficulty in achieving a complete cure is due to the indefinite maintenance of a covalently closed episomal circular DNA (cccDNA) reservoir and the maintenance and persistence of an insufficient and dysfunctional immune response in chronically infected patients. Among the measures adopted to eliminate hepatitis B, two have the potential to directly interfere with the virus cycle, but with limited effect on HBV control. These are conventional vaccines-blocking transmission and antiviral therapy-inhibiting replication. Vaccines, despite their effectiveness in protecting against horizontal transmission and preventing mother-to-child vertical transmission, have no effect on chronic infection or potential to eliminate the virus. Treatment with antivirals suppresses viral replication, but has no curative effect, as it has no action against cccDNA. Therapeutic vaccines comprise an additional approach in the chronic infection treatment, however, they have only a modest effect on the immune system, enhancing it temporarily. This manuscript aims to address (1) the cccDNA persistence in the hepatocyte nucleus and the immune response dysfunction in chronically infected individuals as two primary factors that have hampered the treatment and HBV elimination from the human body; (2) the limitations of antiviral therapy and therapeutic vaccines, as strategies to control hepatitis B; and (3) the possibly promising therapeutic approaches for the complete cure and elimination of hepatitis B.

Novel therapeutic approaches for the management of hepatitis infections

Hepatitis B virus (HBV) & hepatitis C virus (HCV) infection is a substantial reason for morbidity and mortality around the world. Chronic hepatitis B (CHB) infection is connected with an enhanced risk of liver cirrhosis, liver decompensation and hepatocellular carcinoma (HCC). Conventional therapy do face certain challenges, for example, poor tolerability and the growth of active resistance. Thus, novel treatment procedures are essential to accomplish the initiation of strong and stable antiviral immune reactions of the individuals. This review explores the current nanotechnology-based carriers for drug and vaccine delivery to treat HBV and HCV.

Recent advances in understanding T cell activation and exhaustion during HBV infection

Chronic hepatitis B virus (HBV) infection remains a major public health concern globally, and T cell responses are widely believed to play a pivotal role in mediating HBV clearance. Accordingly, research on the characteristics of HBV-specific T cell responses, from activation to exhaustion, has advanced rapidly. Here, we summarize recent developments in characterizing T cell immunity in HBV infection by reviewing basic and clinical research published in the last five years. We provide a comprehensive summary of the mechanisms that induce effective anti-HBV T cell immunity, as well as the latest developments in understanding T cell dysfunction in chronic HBV infection. Furthermore, we briefly discuss current novel treatment strategies aimed at restoring anti-HBV T cell responses.

Development of Therapy Based on the Exploration of Biological Events Underlying the Pathogenetic Mechanisms of Chronic Hepatitis B Infection

According to the World Health Organization (WHO), an estimated 296 million people are chronically infected with hepatitis B virus (HBV). Approximately 15-25% of these people develop complications such as advanced chronic liver diseases (ACLDs). Mortality due to HBV-related complications accounted for an estimated 882,000 deaths in 2019. Potent preventive vaccines have already restricted new HBV infections, and several drugs are available to treat chronic HBV infections. However, the positive impacts of these drugs have been recorded in only a few patients with chronic HBV infection. These drugs do not show long-term efficacy and cannot halt the progression to complications. Thus, more effective and evidence-based therapeutic strategies need to be urgently developed for patients with chronic HBV infection. CHB is a pathological entity induced by HBV that progresses due to impaired host immunity. This indicates the inherent limitations of antiviral-drug-based monotherapy for treating patients with chronic HBV infection. Additionally, commercially available antiviral drugs are not available to patients in developing and resource-constrained countries, posing a challenge to achieving the following WHO goal: "Elimination of Hepatitis by 2030". As such, this review aimed to provide insights regarding evidence-based and effective management strategies for chronic HBV infection.

Emerging Therapies for Chronic Hepatitis B and the Potential for a Functional Cure

Worldwide, an estimated 296 million people are living with chronic hepatitis B virus (HBV) infection, with a significant risk of morbidity and mortality. Current therapy with pegylated interferon (Peg-IFN) and indefinite or finite therapy with nucleoside/nucleotide analogues (Nucs) are effective in HBV suppression, hepatitis resolution, and prevention of disease progression. However, few achieve hepatitis B surface antigen (HBsAg) loss (functional cure), and relapse often occurs after the end of therapy (EOT) because these agents have no direct effect on durable template: covalently closed circular DNA (cccDNA) and integrated HBV DNA. Hepatitis B surface antigen loss rate increases slightly by adding or switching to Peg-IFN in Nuc-treated patients and this loss rate greatly increases up to 39% in 5 years with finite Nuc therapy with currently available Nuc(s). For this, great effort has been made to develop novel direct-acting antivirals (DAAs) and immunomodulators. Among the DAAs, entry inhibitors and capsid assembly modulators have little effect on reducing HBsAg levels; small interfering RNA, antisense oligonucleotides, and nucleic acid polymers in combination with Peg-IFN and Nuc may reduce HBsAg levels significantly, even a rate of HBsAg loss sustained for > 24 weeks after EOT up to 40%. Novel immunomodulators, including T-cell receptor agonists, check-point inhibitors, therapeutic vaccines, and monoclonal antibodies may restore HBV-specific T-cell response but not sustained HBsAg loss. The safety issues and the durability of HBsAg loss warrant further investigation. Combining agents of different classes has the potential to enhance HBsAg loss. Compounds directly targeting cccDNA would be more effective but are still in the early stage of development. More effort is required to achieve this goal.

Development of Therapeutic Vaccine for Chronic Hepatitis B: Concept, Cellular and Molecular Events, Design, Limitation, and Future Projection

Four decades have passed since the first usage of the therapeutic vaccine in patients with chronic hepatitis B (CHB). However, there is no approved regimen of vaccine therapy for the treatment of CHB. This is mainly attributable to faulty conception, an improper understanding of the cellular and molecular mechanisms of CHB, and the impaired design of vaccine therapy for CHB. With the advent of new techniques and a better understanding of cellular and molecular mechanisms underlying the genesis of CHB, the limitations and failures of previous regimens of therapeutic vaccines have been primarily understood. Additionally, the importance of immune therapy for treating millions of CHB patients and achieving the target of "Elimination of Hepatitis by 2030" has been focused on in the international arena. This has been amplified by the apparent limitation of commercially available antiviral drugs that are infinite in duration, endowed with safety concerns, and unable to cure liver damage due to their minimal immune modulation capacities. The proposed review article comprehensively discusses each of these points and proposes evidence-based approaches for viable types of vaccine therapy for the treatment of CHB.

PD-L1 Silencing in Liver Using siRNAs Enhances Efficacy of Therapeutic Vaccination for Chronic Hepatitis B

In chronic hepatitis B virus (HBV) infection, virus-specific T cells are scarce and partially dysfunctional. Therapeutic vaccination is a promising strategy to induce and activate new virus-specific T cells. In long-term or high-level HBV carriers, however, therapeutic vaccination by itself may not suffice to cure HBV. One reason is the impairment of antiviral T cells by immune checkpoints. In this study, we used small-interfering RNA (siRNA) in combination with a heterologous prime-boost therapeutic vaccination scheme (TherVacB) to interfere with a major immune checkpoint, the interaction of programmed death protein-1 (PD-1) and its ligand (PDL-1). In mice persistently replicating HBV after infection with an adeno-associated virus harboring the HBV genome, siRNA targeting PD-L1 resulted in a higher functionality of HBV-specific CD8+ T cells after therapeutic vaccination, and allowed for a more sustained antiviral effect and control of HBV in peripheral blood and in the liver. The antiviral effect was more pronounced if PD-L1 was down-regulated during prime than during boost vaccination. Thus, targeting PD-L1 using siRNA is a promising approach to enhance the efficacy of therapeutic vaccination and finally cure HBV.

Nucleic acid vaccines: A taboo broken and prospect for a hepatitis B virus cure

Although a prophylactic vaccine is available, hepatitis B virus (HBV) remains a major cause of liver-related morbidity and mortality. Current treatment options are improving clinical outcomes in chronic hepatitis B; however, true functional cure is currently the exception rather than the rule. Nucleic acid vaccines are among the emerging immunotherapies that aim to restore weakened immune function in chronically infected hosts. DNA vaccines in particular have shown promising results in vivo by reducing viral replication, breaking immune tolerance in a sustained manner, or even decimating the intranuclear covalently closed circular DNA reservoir, the hallmark of HBV treatment. Although DNA vaccines encoding surface antigens administered by conventional injection elicit HBV-specific T cell responses in humans, initial clinical trials failed to demonstrate additional therapeutic benefit when administered with nucleos(t)ide analogs. In an attempt to improve vaccine immunogenicity, several techniques have been used, including codon/promoter optimization, coadministration of cytokine adjuvants, plasmids engineered to express multiple HBV epitopes, or combinations with other immunomodulators. DNA vaccine delivery by electroporation is among the most efficient strategies to enhance the production of plasmid-derived antigens to stimulate a potent cellular and humoral anti-HBV response. Preliminary results suggest that DNA vaccination via electroporation efficiently invigorates both arms of adaptive immunity and suppresses serum HBV DNA. In contrast, the study of mRNA-based vaccines is limited to a few in vitro experiments in this area. Further studies are needed to clarify the prospects of nucleic acid vaccines for HBV cure.

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.

MCPIP1 inhibits Hepatitis B virus replication by destabilizing viral RNA and negatively regulates the virus-induced innate inflammatory responses

Monocyte chemotactic protein-induced protein 1 (MCPIP1) is an inflammatory regulator in immune response. Recently, MCPIP1 has also been identified as a host antiviral factor against certain virus infection including human immunodeficiency virus, dengue virus and hepatitis C virus. However, whether MCPIP1 could restrict the replication of hepatitis B virus (HBV), a DNA pararetrovirus belonging to Hepadnaviridae family, has not been investigated. In this study, we found that MCPIP1 expression was up-regulated in mouse livers upon acute HBV replication and in HBV-replicated hepatoma cells or HBV-stimulated macrophages. Enforced MCPIP1 expression by hydrodynamic DNA injection in vivo significantly inhibited HBV replication in the mouse livers. Then in vitro studies by overexpression or knockdown assays in cell-lines identified the direct antiviral effect of MCPIP1 on HBV replication. RNA immunoprecipitation and decay assay further suggested that MCPIP1 potently restricted HBV replication through directly binding viral RNA and degrading RNA via its RNase activity, but not deubiquitinase activity. Moreover, we further verified that MCPIP1 negatively regulated HBV-induced proinflammatory cytokines, such as IL-1β, TNF-α and IL-6 in macrophages. Taken together, our data expand MCPIP1's range of viral targets to DNA virus and also demonstrate the negative regulatory role of MCPIP1 in suppressing virus-induced inflammatory response, suggesting MCPIP1 as a potential therapeutic target for treating HBV-related diseases via inducing a host defense against HBV and reducing inflammatory injury meanwhile.

A dendritic cell receptor-targeted chimeric immunotherapeutic protein (C-HBV) for the treatment of chronic hepatitis B

In chronic Hepatitis B Virus (HBV) infections HBV-specific T cells are functionally impaired. Immunotherapy may restore HBV-specific T cell responses essential for sustained disease remission off-treatment and induction of a functional cure. Chimigen® Molecules are fusion proteins of antigen(s) with the Fc fragment of a xenotypic antibody designed to target specific receptors on dendritic cells (DCs). Here we describe the production and pre-clinical evaluation of Chimigen® HBV (C-HBV), containing HBV PreS1 and PreS2 peptide fragments, HBV core and murine Fc, produced in insect cells. C-HBV binding to immature DCs and internalization by endocytosis was FcγRII (CD32) and mannose receptor (CD206) dependent and led to increased MHC I and MHC II surface expression. Upon exposure of human T cells isolated from HBV un-infected healthy and chronically HBV-infected donors to C-HBV-pulsed mature DCs ex vivo, C-HBV induced vigorous T cell proliferation and enhanced expression of IFN-γ, TNF-α, perforin and granzyme B in both CD4⁺ and CD8⁺ T cell subsets. Re-stimulation of C-HBV-activated T cells from chronically infected donors with HBV PreS1/PreS2 and core overlapping peptides induced IFN-γ production in both CD4⁺ and CD8⁺ populations. C-HBV-activation of peripheral blood mononuclear cells (PBMCs) from chronically HBV-infected patients stimulated granzyme B production by CD4⁺CD25^- T responder (Tresp) cells, accompanied by an increase in Annexin V staining on CD4⁺CD25⁺ T regulatory (Treg) cell phenotype, consistent with apoptosis. The observed HBV-specific cellular responses induced by C-HBV ex vivo suggest that C-HBV is a promising immunotherapeutic candidate for the treatment of chronic HBV infections.

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.

Therapeutic vaccination for chronic hepatitis B: A systematic review and meta-analysis

Therapeutic vaccines may be promising treatments for chronic hepatitis B (CHB), but their clinical efficacy and safety are unclear. We conducted a systematic review of the evidence for the efficacy and safety of therapeutic vaccines in CHB patients. We searched PubMed, EMBASE and Google Scholar from 1990 until present and abstracts from EASL, APASL and AASLD from 2012 to 2017 and selected randomized controlled trials of CHB patients, comparing therapeutic vaccines with no treatment or standard of care. The Cochrane Risk of Bias tool v2.0 and GRADE method were used. Analyses were stratified by hepatitis B e antigen (HBeAg) status and the comparator (therapeutic vaccines vs no treatment, or therapeutic vaccines + standard of care vs standard of care). Efficacy outcomes were HBeAg seroconversion, hepatitis B virus DNA reduction and hepatitis B virus surface antigen (HBsAg) loss, measured at the end of treatment or end of follow-up. Effects were reported as risk differences with 95% confidence intervals using a random effects model. Fifteen studies were included. A wide variety of therapeutic vaccines were tested. For HBeAg clearance at the end of follow-up, when comparing therapeutic vaccines vs no therapy, RD = 0.01, 95% CI -0.05 to 0.07, and when comparing therapeutic vaccines + standard of care vs standard of care, RD = 0.03, 95% CI -0.03 to 0.09. For HBVDNA reduction at the end of follow-up, when comparing therapeutic vaccines vs no therapy, RD = -0.03, 95% CI -0.08 to 0.02, and when comparing therapeutic vaccines + standard of care, RD = 0.15, 95% CI 0.02-0.28. There were only a few studies on HBsAg loss, and hence, the findings were inconclusive. The only efficacy finding was HBVDNA reduction at the end of follow-up for therapeutic vaccines + standard of care vs standard of care; otherwise, therapeutic vaccines do not appear to be efficacious for the treatment of CHB, but were limited by few RCTs, suboptimal therapeutic vaccines and patient selection.

Vaccination with a DNA vaccine encoding CD317-targeting HBs antigen elicits enhanced immunity in mice

BACKGROUND

Conventional hepatitis B virus (HBV) vaccines fail to induce protective antibody titers in 5-10% of immune-competent vaccines. Therefore, safe and effective HBV vaccines are still clinically needed.

METHODS

In this study, we developed a plasmid DNA vaccine encoding CD317 single-chain fragment variable (α317scFv) linked with the hepatitis B surface antigen (HBsAg) and detected the humoral and cellular immune responses elicited by this vaccine in BALB/c mice.

RESULTS

Vaccination with this fusion DNA vaccine in BALB/c mice induced more robust antiviral T cell and antibody immunity against HBsAg. Compared with mice vaccinated with control vaccine encoding HBsAg, the level of serum-circulating anti-HBsAg antibody (HBsAb) was nearly double in fusion DNA-vaccinated mice. More interesting, splenic lymphocytes isolated from fusion DNA-vaccinated mice showed more potent proliferation and IFN-γ production after being re-stimulated with recombinant HBsAg in vitro. And not only that, the cytotoxicity of fusion DNA vaccine-sensitized splenocytes was ∼3-fold higher than that of controls.

CONCLUSION

Taken together, our results reveal that the fusion DNA vaccine can induce more effective immunological protection against HBV, and is a promising candidate for preventing HBV infection.

Nucleic acid polymer REP 2139 and nucleos(T)ide analogues act synergistically against chronic hepadnaviral infection in vivo in Pekin ducks

Nucleic acid polymer (NAP) REP 2139 treatment was shown to block the release of viral surface antigen in duck HBV (DHBV)-infected ducks and in patients with chronic HBV or HBV/hepatitis D virus infection. In this preclinical study, a combination therapy consisting of REP 2139 with tenofovir disoproxil fumarate (TDF) and entecavir (ETV) was evaluated in vivo in the chronic DHBV infection model. DHBV-infected duck groups were treated as follows: normal saline (control); REP 2139 TDF; REP 2139 + TDF; and REP 2139 + TDF + ETV. After 4 weeks of treatment, all animals were followed for 8 weeks. Serum DHBsAg and anti-DHBsAg antibodies were monitored by enzyme-linked immunosorbent assay and viremia by qPCR. Total viral DNA and covalently closed circular DNA (cccDNA) were quantified in autopsy liver samples by qPCR. Intrahepatic DHBsAg was assessed at the end of follow-up by immunohistochemistry. On-treatment reduction of serum DHBsAg and viremia was more rapid when REP 2139 was combined with TDF or TDF and ETV, and, in contrast to TDF monotherapy, no viral rebound was observed after treatment cessation. Importantly, combination therapy resulted in a significant decrease in intrahepatic viral DNA (>3 log) and cccDNA (>2 log), which were tightly correlated with the clearance of DHBsAg in the liver.

CONCLUSION

Synergistic antiviral effects were observed when REP 2139 was combined with TDF or TDF + ETV leading to control of infection in blood and liver, associated with intrahepatic viral surface antigen elimination that persisted after treatment withdrawal. Our findings suggest the potential of developing such combination therapy for treatment of chronically infected patients in the absence of pegylated interferon. (Hepatology 2018;67:2127-2140).

The immune response of rhesus macaques to novel vaccines comprising hepatitis B virus S, PreS1, and Core antigens

Therapeutic vaccines represent a unique approach to hepatitis B virus (HBV) treatment and have the potential to induce long-term control of infection. This study explored the immune responses of rhesus macaques to novel vaccines comprising the S, PreS1, and Core antigens of the HBV that showed promise as prophylactic and therapeutic approaches in a mouse model. The tested vaccines included two DNA vaccines (pVRC-SS1, pVRC-CS1), an HBV particle subunit (HBSS1) vaccine and the recombinant vaccinia virus- (RVJ-) based vaccines (RVJSS1 and RVJCS1) in which SS1 containing S (1-223 aa) and PreS1 (21-47 aa), CS1 containing Core (1-144 aa) and PreS1 (1-42 aa). The humoral immunity and cell-mediated immunity (CMI) induced by vaccines comprising the S, PreS1, and Core antigens of HBV were investigated in a longitudinal study that continued up to 98 weeks after the firstvaccination. In rhesus macaques, anti-PreS1 antibody was induced more rapidly than anti-S or anti-Core antibody after DNA vaccination. The antibody and cell-mediated immune responses against S, PreS1, and C were significantly enhanced in macaques boosted with RVJSS1 and RVJCS1, whereas the cell-mediated response to C was most robust and durable. The immune response to S, PreS1, and C was restored by HBSS1 boosting and detected in macaques until weeks 74 and 98 after the first vaccination. Additionally, robust neutralizing activity was detected at week 52. In conclusion, novel HBV vaccine candidates, especially those used for therapeutic applications should incorporate the PreS1 and Core antigens.

New directions in hepatitis B therapy research

Chronic hepatitis B treatment is available for a long period, allowing disease control and infection suppression, but it is rarely responsible for HBsAg clearance. None of the drugs available aim at cccDNA, the obstacle in HBV infection eradication. Complications related to CHB, such as liver insufficiency, cirrhosis, and hepatocellular carcinoma are reduced in conditions of good viremia suppression, but still exist even after HBsAg seroclearance, what makes a need for urgent forthcoming of new therapeutics. Recent years brought promising and interesting results of experimental approaches, which are directed against different phases of HBV life cycle, target ccc DNA, or boost, and restore host immune response. Unfortunately, encouraging results in vitro and on animal models are not always reflected in human. Nevertheless, the multiplicity of novel antivirals allows to expect that at least some of them will enter clinical practice and relieve patients from chronic hepatitis B, fatal and devastating disease.

Nucleic Acid Polymers with Accelerated Plasma and Tissue Clearance for Chronic Hepatitis B Therapy

REP 2139 is a nucleic acid polymer (NAP) currently under clinical development for chronic hepatitis B (HBV) therapy. This preclinical study investigated different REP 2139 analogs that would display reduced accumulation in the serum and tissues, while retaining an antiviral effect against HBV infection. REP 2139 analogs were evaluated in human plasma, CD-1 mice, cynomolgus monkeys, and Pekin ducks. Discrete ribose transformation to 2'OH in selected riboadenosines resulted in a slow degradation in acidified human plasma that plateaued after 48 hr. REP 2165, a REP 2139 analog containing three unmodified riboadenosines equally spaced throughout the polymer, showed similar plasma clearance and tissue distribution as REP 2139 in mice and cynomolgus monkeys after a single dose. Interestingly, after repeated administration, accumulation of REP 2165 in plasma and organs was reduced, indicating a dramatically faster rate of clearance from organs after therapy was ended in both species. Both REP 2139 and REP 2165 were well tolerated at clinically relevant doses, with no alterations in liver, kidney, or hematological function. In chronic duck HBV (DHBV) infection, REP 2165 displayed significantly reduced liver accumulation after repeated dosing but retained antiviral activity similar to REP 2139. These results indicate the therapeutic potential of REP 2165 against chronic HBV infection in patients is similar to REP 2139, but with significantly reduced drug accumulation and improved tissue clearance.