Therapeutic vaccines in treating chronic hepatitis B: the end of the beginning or the beginning of the end?

Antiviral Response across Genotypes after Treatment of Chronic Hepatitis B Patients with the Therapeutic Vaccine NASVAC or Pegylated Interferon

An open-level, randomized and treatment-controlled clinical trial has shown that a therapeutic vaccine containing hepatitis B surface antigen (HBsAg) and hepatitis B core antigen (HBcAg) (NASVAC) is endowed with antiviral and liver protecting capacity and is safer than pegylated interferon (Peg-IFN) in patients with chronic hepatitis B (CHB). The present study provides information about the role of the hepatitis B virus (HBV) genotype in this phase III clinical trial. From a total of 160 patients enrolled in this trial, the HBV genotypes of 133 patients were characterized, and NASVAC induced a stronger antiviral effect (HBV DNA reduction below 250 copies per mL) than Peg-IFN. The antiviral effects and alanine aminotransferase levels were not significantly different among different HBV genotypes in NASVAC-treated patients. However, a significantly higher proportion of genotype-D patients receiving NASVAC showed better therapeutic effects, compared to genotype-D patients receiving Peg-IFN, with a marked difference of 44%. In conclusion, NASVAC seems to be a better alternative to Peg-IFN, especially in patients with HBV genotype-D patients. This reflects the attractiveness of NASVAC in countries where genotype D is highly prevalent. The mechanisms underlying the effect of HBV genotype are being studied in a new clinical trial.

Improving Therapeutic Vaccination against Hepatitis B-Insights from Preclinical Models of Immune Therapy against Persistent Hepatitis B Virus Infection

Chronic hepatitis B affects more than 250 million individuals worldwide, putting them at risk of developing liver cirrhosis and liver cancer. While antiviral immune responses are key to eliminating hepatitis B virus (HBV) infections, insufficient antiviral immunity characterized by failure to eliminate HBV-infected hepatocytes is associated with chronic hepatitis B. Prophylactic vaccination against hepatitis B successfully established protective immunity against infection with the hepatitis B virus and has been instrumental in controlling hepatitis B. However, prophylactic vaccination schemes have not been successful in mounting protective immunity to eliminate HBV infections in patients with chronic hepatitis B. Here, we discuss the current knowledge on the development and efficacy of therapeutic vaccination strategies against chronic hepatitis B with particular emphasis on the pathogenetic understanding of dysfunctional anti-viral immunity. We explore the development of additional immune stimulation measures within tissues, in particular activation of immunogenic myeloid cell populations, and their use for combination with therapeutic vaccination strategies to improve the efficacy of therapeutic vaccination against chronic hepatitis B.

Peptides to combat viral infectious diseases

Viral infectious diseases have resulted in millions of deaths throughout history and have created a significant public healthcare burden. Tremendous efforts have been placed by the scientific communities, health officials and government organizations to detect, treat, and prevent viral infection. However, the complicated life cycle and rapid genetic mutations of viruses demand continuous development of novel medicines with high efficacy and safety profiles. Peptides provide a promising outlook as a tool to combat the spread and re-emergence of viral infection. This article provides an overview of five viral infectious diseases with high global prevalence: influenza, chronic hepatitis B, acquired immunodeficiency syndrome, severe acute respiratory syndrome, and coronavirus disease 2019. The current and potential peptide-based therapies, vaccines, and diagnostics for each disease are discussed.

Knockdown of Virus Antigen Expression Increases Therapeutic Vaccine Efficacy in High-Titer Hepatitis B Virus Carrier Mice

BACKGROUND & AIMS

Hepatitis B virus (HBV) infection persists because the virus-specific immune response is dysfunctional. Therapeutic vaccines might be used to end immune tolerance to the virus in patients with chronic infection, but these have not been effective in patients so far. In patients with chronic HBV infection, high levels of virus antigens might prevent induction of HBV-specific immune responses. We investigated whether knocking down expression levels of HBV antigens in liver might increase the efficacy of HBV vaccines in mice.

METHODS

We performed studies with male C57BL/6 mice that persistently replicate HBV (genotype D, serotype ayw)-either from a transgene or after infection with an adeno-associated virus that transferred an overlength HBV genome-and expressed HB surface antigen at levels relevant to patients. Small hairpin or small interfering (si)RNAs against the common 3'-end of all HBV transcripts were used to knock down antigen expression in mouse hepatocytes. siRNAs were chemically stabilized and conjugated to N-acetylgalactosamine to increase liver uptake. Control mice were given either entecavir or non-HBV-specific siRNAs and vaccine components. Eight to 12 weeks later, mice were immunized twice with a mixture of adjuvanted HBV S and core antigen, followed by a modified Vaccinia virus Ankara vector to induce HBV-specific B- and T-cell responses. Serum and liver samples were collected and analyzed for HBV-specific immune responses, liver damage, and viral parameters.

RESULTS

In both models of HBV infection, mice that express hepatocyte-specific small hairpin RNAs or that were given subcutaneous injections of siRNAs had reduced levels of HBV antigens, HBV replication, and viremia (1-3 log₁₀ reduction) compared to mice given control RNAs. Vaccination induced production of HBV-neutralizing antibodies and increased numbers and functionality of HBV-specific, CD8⁺ T cells in mice with low, but not in mice with high, levels of HBV antigen. Mice with initially high titers of HBV and knockdown of HBV antigen expression, but not mice with reduced viremia after administration of entecavir, developed polyfunctional, HBV-specific CD8⁺ T cells, and HBV was eliminated.

CONCLUSIONS

In mice with high levels of HBV replication, knockdown of HBV antigen expression along with a therapeutic vaccination strategy, but not knockdown alone, increased numbers of effector T cells and eliminated the virus. These findings indicate that high titers of virus antigens reduce the efficacy of therapeutic vaccination. Anti-HBV siRNAs and therapeutic vaccines are each being tested in clinical trials-their combination might cure chronic HBV infection.

A unique B cell epitope-based particulate vaccine shows effective suppression of hepatitis B surface antigen in mice

OBJECTIVE

This study aimed to develop a novel therapeutic vaccine based on a unique B cell epitope and investigate its therapeutic potential against chronic hepatitis B (CHB) in animal models.

METHODS

A series of peptides and carrier proteins were evaluated in HBV-tolerant mice to obtain an optimised therapeutic molecule. The immunogenicity, therapeutic efficacy and mechanism of the candidate were investigated systematically.

RESULTS

Among the HBsAg-aa119-125-containing peptides evaluated in this study, HBsAg-aa113-135 (SEQ13) exhibited the most striking therapeutic effects. A novel immunoenhanced virus-like particle carrier (CR-T3) derived from the roundleaf bat HBV core antigen (RBHBcAg) was created and used to display SEQ13, forming candidate molecule CR-T3-SEQ13. Multiple copies of SEQ13 displayed on the surface of this particulate antigen promote the induction of a potent anti-HBs antibody response in mice, rabbits and cynomolgus monkeys. Sera and purified polyclonal IgG from the immunised animals neutralised HBV infection in vitro and mediated efficient HBV/hepatitis B virus surface antigen (HBsAg) clearance in the mice. CR-T3-SEQ13-based vaccination induced long-term suppression of HBsAg and HBV DNA in HBV transgenic mice and eradicated the virus completely in hydrodynamic-based HBV carrier mice. The suppressive effects on HBsAg were strongly correlated with the anti-HBs level after vaccination, suggesting that the main mechanism of CR-T3-SEQ13 vaccination therapy was the induction of a SEQ13-specific antibody response that mediated HBV/HBsAg clearance.

CONCLUSIONS

The novel particulate protein CR-T3-SEQ13 suppressed HBsAg effectively through induction of a humoural immune response in HBV-tolerant mice. This B cell epitope-based therapeutic vaccine may provide a novel immunotherapeutic agent against chronic HBV infection in humans.

Overcoming immune tolerance in chronic hepatitis B by therapeutic vaccination

The currently used nucleoside analogs (i.e. entecavir and tenofovir) with high barrier-to-resistance efficiently suppress viral replication, limit inflammation and reduce the sequelae of chronic hepatitis B, but cannot cure the disease and thus have to be applied long-term. Therapeutic vaccination as an approach to cure chronic hepatitis B has shown promising pre-clinical results, nevertheless the proof of its efficacy in clinical trials is still missing. This may be partially due to suboptimal vaccine design. A main obstacle in chronic hepatitis B, however, is the high load of viral antigens expressed and secreted, which has been proposed to cause antigen-specific immune tolerance. Reduction of the viral antigen load is therefore considered a key factor for success of immune-based therapies. Although nucleoside analogs do not reduce viral antigen expression, new antiviral strategies are becoming available. Targeting viral translation by siRNA or targeting release of HBsAg from infected hepatocytes by nucleic acid polymers both reduce the antigen load. They may be considered as pre-treatment for therapeutic vaccination to increase the potential to elicit an HBV-specific immune response able to control and cure chronic HBV infection.

A mouse model with age-dependent immune response and immune-tolerance for HBV infection

BACKGROUND

Viral clearance of human HBV infection largely depends on the age of exposure. Thus, a mouse model with age-dependent immune response and immune-tolerance for HBV infection was established.

METHODS

HBVRag1 mice were generated by crossing Rag1^-/- mice with HBV-Tg mice. Following adoptive transfer of splenocytes adult (8-9 weeks old) and young (3 weeks old) HBVRag1 mice were named as HBVRag-ReA and HBVRag-ReY mice respectively. The biochemical parameters that were associated with viral load and immune function, as well as the histological evaluation of the liver tissues between the two mouse models were detected. The immune tolerance of HBVRag-ReY mice that were reconstituted at the early stages of life was evaluated by quantitative hepatitis B core antibody assay, adoptive transfer, and modulation of gut microbiota with the addition of antibiotics.

RESULTS

HBVRag-ReA mice indicated apparent hepatocytes damage, clearance of HBsAg and production of HBsAb and HBcAb. HBVRag-ReY mice did not develop ALT elevation, and produced HBcAb and HBsAg. A higher number of hepatic CD8⁺ T and B cells promoted clearance of HBsAg in HBVRag-ReA mice following 30 days of lymphocyte transfer. In contrast to HBVRag-ReA mice, HBVRag-ReY mice exhibited higher levels of Th1/Th2 cytokines. HBVRag-ReY mice exhibited significantly higher (P < .01, approximately 10-fold) serum quantitative anti-HBc levels than HBV-Tg mice, which might be similar to the phase of immune clearance and immune tolerance in human HBV infection. Furthermore, the age-related tolerance in HBVRag-ReY mice that were sensitive to antibiotic treatment was different from that noted in HBV-Tg mice. GS-9620 could inhibit the production of HBsAg, whereas HBV vaccination could induce sustained seroconversion in HBVRag-ReY mice with low levels of HBsAg.

CONCLUSIONS

The present study described a mouse model with age-dependent immunity and immune-tolerance for HBV infection in vivo, which may mimic chronic HBV infection in humans.

Luteolin-7-O-Glucoside Present in Lettuce Extracts Inhibits Hepatitis B Surface Antigen Production and Viral Replication by Human Hepatoma Cells in Vitro

Hepatitis B virus (HBV) infection is endemic in Asia and chronic hepatitis B (CHB) is a major public health issue worldwide. Current treatment strategies for CHB are not satisfactory as they induce a low rate of hepatitis B surface antigen (HBsAg) loss. Extracts were prepared from lettuce hydroponically cultivated in solutions containing glycine or nitrate as nitrogen sources. The lettuce extracts exerted potent anti-HBV effects in HepG2 cell lines in vitro, including significant HBsAg inhibition, HBV replication and transcription inhibition, without exerting cytotoxic effects. When used in combination interferon-alpha 2b (IFNα-2b) or lamivudine (3TC), the lettuce extracts synergistically inhibited HBsAg expression and HBV replication. By using differential metabolomics analysis, Luteolin-7-O-glucoside was identified and confirmed as a functional component of the lettuce extracts and exhibited similar anti-HBV activity as the lettuce extracts in vitro. The inhibition rate on HBsAg was up to 77.4%. Moreover, both the lettuce extracts and luteolin-7-O-glucoside functioned as organic antioxidants and, significantly attenuated HBV-induced intracellular reactive oxygen species (ROS) accumulation. Luteolin-7-O-glucoside also normalized ROS-induced mitochondrial membrane potential damage, which suggests luteolin-7-O-glucoside inhibits HBsAg and HBV replication via a mechanism involving the mitochondria. Our findings suggest luteolin-7-O-glucoside may have potential value for clinical application in CHB and may enhance HBsAg and HBV clearance when used as a combination therapy.

Recognition of Core- and Polymerase-derived immunogenic peptides included in novel therapeutic vaccine by T cells from Chinese chronic hepatitis B patients

Chronic hepatitis B (CHB) is one of the major public health challenges in the world. Due to a strong interplay between specific T-cell immunity and elimination of hepatitis B virus (HBV), efforts to develop novel immunotherapeutics are gaining attention. TG1050, a novel immunotherapy, has shown efficacy in an animal study. To support the clinical development of TG1050 in China, specific immunity to the fusion antigens of TG1050 was assessed in Chinese patients. One hundred and thirty subjects were divided into three groups as CHB patients, HBV spontaneous resolvers, and CHB patients with HBsAg loss after antiviral treatment. HBV-specific T-cell responses to pools of HBV Core or Polymerase genotype D peptides included in TG1050 were evaluated. HBV Core- or Polymerase-specific cells were detected in peripheral blood mononuclear cells (PBMCs) from the different cohorts. The frequencies and intensities of HBV Core-specific immune responses were significantly lower in CHB patients than in HBsAg loss subjects. In CHB patients, a dominant pool derived from Polymerase (Pol1) was the most immunogenic. CHB patients with low viral loads (<10⁶ IU/mL) were more likely to have a positive response specific to the Core peptide pool. Overall, genotype D-derived peptides included in TG1050 could raise broad and functional T-cell responses in PBMCs from Chinese CHB patients infected with genotype B/C isolates. Core-specific immunogenic domains appeared as "hot spots" with the capacity to differentiate between CHB vs HBsAg loss subjects. These observations support the extended application and associated immune monitoring of TG1050 in China.

An update on the strategies used for the treatment of chronic hepatitis B in children

Chronic hepatitis B (CHB) in children shows a variety of clinical presentations, which influence its natural course and treatment options. This report provides an overview of the ongoing strategies in pediatric CHB management. Interferon-α represents the first choice of treatment in children showing HBV replication and hepatic inflammation (immune active CHB), while the recommendation is to monitor inactive/immune-tolerant children (normal transaminases and low/absent viral replication). When circumstances preclude the use of Interferon-α and in cases of compensated/decompensated cirrhosis, entecavir for children above 2 years of age or tenofovir for children above 12 years of age are the nucleos(t)ide analogues recommended by the most recent guidelines.

Novel targets for hepatitis B virus therapy

Treatment with either pegylated interferon-alpha (pegIFN-α) or last generation nucleos(t)ide analogues (NAs) successfully leads to serum viral load suppression in most chronically infected hepatitis B (CHB) patients, but HBsAg loss is only achieved in 10% of the cases after a 5-year follow-up. Thus, therapy must be administered long-term and it will not completely eliminate infection because of the persistent hepatitis B virus (HBV) minichromosome in infected cells, and cannot completely abolish the risk of developing severe sequelae such as cirrhosis and hepatocellular carcinoma. Recent progress in the development of in vitro and in vivo models of HBV infection have helped renew interest in the investigation of the viral life cycle, as well as specific virus-host cell interactions to identify new targets for the development of new antiviral drugs. This includes either direct inhibition of viral replication by targeting fundamental steps such as entry, cccDNA formation/stability, viral transcripts, capsid assembly and secretion or the manipulation of the host immune system for better defence against infection. Multiple strategies are currently under investigation, including boosting endogenous innate responses and/or restoring adaptive immunity via engineering of HBV-specific T cells or via the use of inhibitors of negative regulators, as well as therapeutic vaccines. It is increasingly clear that multiple therapeutic strategies must be combined to reach a cure of HBV and that the definition of clinical, virological and immunological correlates for the management of treatment are urgently needed.

Hepatitis B immunopathogenesis and immunotherapy

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

New antiviral targets for innovative treatment concepts for hepatitis B virus and hepatitis delta virus

Current therapies of chronic hepatitis B (CHB) remain limited to pegylated-interferon-alpha (PegIFN-α) or any of the five approved nucleos(t)ide analogues (NUC) treatments. While viral suppression can be achieved in the majority of patients with the high-barrier-to-resistance new-generation of NUC, i.e. entecavir and tenofovir, HBsAg loss is achieved by PegIFN-α and/or NUC in only 10% of patients, after a 5-year follow-up. Attempts to improve the response by administering two different NUC or a combination of NUC and PegIFN-α have not provided a dramatic increase in the rate of functional cure. Because of this and the need of long-term NUC administration, there is a renewed interest regarding the understanding of various steps of the HBV replication cycle, as well as specific virus-host cell interactions, in order to define new targets and develop new antiviral drugs. This includes a direct inhibition of viral replication with entry inhibitors, drugs targeting cccDNA, siRNA targeting viral transcripts, capsid assembly modulators, and approaches targeting the secretion of viral envelope proteins. Restoration of immune responses is a complementary approach. The restoration of innate immunity against HBV can be achieved, with TLR agonists or specific antiviral cytokine delivery. Restoration of adaptive immunity may be achieved with inhibitors of negative checkpoint regulators, therapeutic vaccines, or autologous transfer of engineered HBV-specific T cells. Novel targets and compounds will readily be evaluated using both relevant and novel in vitro and in vivo models of HBV infection. The addition of one or several new drugs to current therapies should offer the prospect of a markedly improved response to treatments and an increased rate of functional cure. This should lead to a reduced risk of antiviral drug resistance, and to a decreased incidence of cirrhosis and hepatocellular carcinoma (HCC).

Combination therapy including CpG oligodeoxynucleotides and entecavir induces early viral response and enhanced inhibition of viral replication in a woodchuck model of chronic hepadnaviral infection

CpG oligodeoxynucleotides (ODNs) stimulate immune cells via TLR9 and are potentially useful immunomodulators for the treatment of chronic viral infections. In the present study, different classes of CpGs were tested for their capacities for innate immune activation and antiviral activities in the woodchuck model. A class P CpG ODN was found to stimulate interferon (IFN) production in woodchuck peripheral blood mononuclear cells (PBMCs) in vitro, and following subcutaneous administration in vivo, it was observed to induce IFN and MxA expression in woodchuck PBMCs. Combination treatment with CpG ODN and entecavir (ETV) led to effective suppression of the woodchuck hepatitis virus (WHV) load in the woodchucks, with early viral responses and inhibition of replication. The woodchuck hepatitis surface antigen (WHsAg) serum concentrations were strongly decreased by CpG and ETV together but not by either agent alone, indicating synergistic effects. However, viral control post-treatment was still transient, similar to that observed with ETV alone. Significantly elevated levels of serum aspartate aminotransferase (AST) but not of alanine aminotransferase (ALT) in some of the woodchucks receiving CpG ODN were noted, but these increases were resolved before the completion of treatment and were not associated with an elevated serum bilirubin level or coagulation disorders, suggesting the absence of a significant safety concern.

Advances in therapeutics for chronic hepatitis B

Chronic hepatitis B infection remains a major disease burden globally, and leads to high risk of hepatocellular carcinoma development. Current therapies of nucleot(s)ide analogues and interferon alpha treatment remain limited in their efficacy. Several key findings in the hepatitis B virus (HBV) life cycle have led to the development of novel antiviral drugs to inhibit viral replication and persistence. In addition, recent studies on HBV-specific innate and adaptive immune responses have advanced development of immunotherapy to restore immune mediated virus control in chronic hepatitis B patients. In this review, we discuss potential new therapeutic strategies targeting HBV or the host immune system that might lead to a sustained cure for chronic hepatitis B.

Chronic hepatitis B: A wave of new therapies on the horizon

This year marks the 50th anniversary of the discovery of the Australia antigen (Blumberg et al., 1965), which in 1967 was identified to be the hepatitis B virus (HBV) surface antigen. Even though several antiviral medications have been in use for the management of chronic HBV infection for more than 20years, sustained clearance of HBsAg, similar to the sustained viral response (SVR) or cure in chronic hepatitis C, occurs in only a minority of treated patients. Moreover, even after 10years of effective suppression of HBV viremia with current therapy, there is only a 40-70% reduction in deaths from liver cancer. Recent success in developing antivirals for hepatitis C that are effective across all genotypes has renewed interest in a similar cure for chronic HBV infection. In this article, we review a wave of newly identified drug targets, investigational compounds and experimental strategies that are now under clinical evaluation or in preclinical development. The paper forms part of a symposium in Antiviral Research on "An unfinished story: From the discovery of the Australia antigen to the development of new curative therapies for hepatitis B."