Deficiencies in the acute-phase cell-mediated immune response to viral antigens are associated with development of chronic woodchuck hepatitis virus infection following neonatal inoculation

Longterm Outcome of Therapeutic Vaccination with a Third Generation Pre-S/S HBV Vaccine (PreHevbrioR) of Chronically HBV Infected Patients

Several antiviral treatment regimens for chronic hepatitis B (CHB) virus infection have been shown to be effective in suppressing viral load and reducing the risk of hepatocellular injury and its complications. It has been hypothesized that high levels of circulating HBV surface antigen(s) may lead to immune tolerance against HBV and contribute to chronic carriership. Conversely, low-level HBsAg may create a window for the reconstitution of an HBV-specific immune response through vaccination and control of infection. Previous studies in non-responders to yeast-derived HBV vaccines, using a third-generation pre-S/S vaccine, have led to up to 95% anti-HBs seroconversion. This report evaluates the long-term outcome after experimental vaccination with a pre-S/S HBV vaccine intended as a therapeutic intervention in chronic HBV carriers. Four low-level HBsAg carriers (<500 IU/mL) were vaccinated three to seven times with 20 μg PreHevbrioR. Three out of four carriers eliminated HBsAg completely and seroconverted to anti-HBs. One patient seroconverted to anti-HBs but remained with a borderline HBsAg titer (10 IU/mL). Serum anti-HBs levels following repeated vaccination varied between 27 and >1000 IU/L, respectively. Long-term observation (>6 years) showed that after discontinuing NUC treatment for at least two years, HBsAg and HBV DNA remained negative with anti-HBs positive titers ranging between 80 and >1000 IU/L. Based on our preliminary observations, there is a rationale to further evaluate the role of this vaccine as a therapeutic agent.

Identification of antibodies cross-reactive with woodchuck immune cells and activation of virus-specific and global cytotoxic T cell responses by anti-PD-1 and anti-PD-L1 in experimental chronic hepatitis B and persistent occult hepadnaviral infection

Woodchuck (Marmota monax) infected with woodchuck hepatitis virus (WHV) is the most pathogenically compatible naturally occurring model of human hepatitis B virus (HBV) infection, chronic hepatitis B, and HBV-induced hepatocellular carcinoma. This system plays a crucial role in discovery and preclinical evaluation of anti-HBV therapies. Its utilization remains tempered by the relatively narrow range of validated immunologic and molecular tools. We evaluated commercial antibodies against immune cell phenotypic markers and T cell molecules for cross-reactivity with woodchuck antigenic equivalents. The confirmed antibodies against programed cell death protein-1 (PD-1) and its ligand (PD-L1) were examined for ex vivo ability to activate WHV-specific, global and bystander cytotoxic T cells (CTLs) in chronic hepatitis and asymptomatic infection persisting after self-resolved acute hepatitis. Examination of 65 antibodies led to identification or confirmation of 23 recognizing woodchuck T, regulatory T, B and natural killer cells, T cell-associated PD-1, PD-L1, CTLA-4 and TIM-3 molecules, CD25 and CD69 markers of T cell activation, and interferon gamma (IFNγ). Antibodies against woodchuck PD-1 and PD-L1 triggered in vitro highly individualized WHV-specific and global activation of CTLs in both chronic hepatitis and persistent occult infection. WHV-specific CTLs were more robustly augmented by anti-PD-1 than by anti-PD-L1 in chronic hepatitis, while global IFNγ-positive CTL response was significantly suppressed in chronic hepatitis compared to persistent occult infection. Anti-PD-1 and anti-PD-L1 also occasionally activated CTLs to specificities other than those tested suggesting their potency to trigger side effects. This was particularly apparent when T cells from chronic hepatitis were treated with anti-PD-L1. The current findings indicate that inhibition of the PD-1/PD-L1 pathway could reactivate virus-specific and global T cell responses in both chronic hepatitis and asymptomatic persistent infection. They suggest a mechanism of potential reactivation of clinically silent infection during anti-PD-1/PD-L1 treatment and indicate that this therapy may also subdue occult HBV infection.

Needle-free, spirulina-produced Plasmodium falciparum circumsporozoite vaccination provides sterile protection against pre-erythrocytic malaria in mice

Antibodies against the Plasmodium falciparum circumsporozoite protein (PfCSP) can block hepatocyte infection by sporozoites and protect against malaria. Needle-free vaccination strategies are desirable, yet most PfCSP-targeted vaccines like RTS,S require needle-based administration. Here, we evaluated the edible algae, Arthrospira platensis (commonly called 'spirulina') as a malaria vaccine platform. Spirulina were genetically engineered to express virus-like particles (VLPs) consisting of the woodchuck hepatitis B core capsid protein (WHcAg) displaying a (NANP)₁₅ PfCSP antigen on its surface. PfCSP-spirulina administered to mice intranasally followed by oral PfCSP-spirulina boosters resulted in a strong, systemic anti-PfCSP immune response that was protective against subcutaneous challenge with PfCSP-expressing P. yoelii. Unlike male mice, female mice did not require Montanide adjuvant to reach high antibody titers or protection. The successful use of spirulina as a vaccine delivery system warrants further development of spirulina-based vaccines as a useful tool in addressing malaria and other diseases of global health importance.

Recent Drug Development in the Woodchuck Model of Chronic Hepatitis B

Infection with hepatitis B virus (HBV) is responsible for the increasing global hepatitis burden, with an estimated 296 million people being carriers and living with the risk of developing chronic liver disease and cancer. While the current treatment options for chronic hepatitis B (CHB), including oral nucleos(t)ide analogs and systemic interferon-alpha, are deemed suboptimal, the path to finding an ultimate cure for this viral disease is rather challenging. The lack of suitable laboratory animal models that support HBV infection and associated liver disease progression is one of the major hurdles in antiviral drug development. For more than four decades, experimental infection of the Eastern woodchuck with woodchuck hepatitis virus has been applied for studying the immunopathogenesis of HBV and developing new antiviral therapeutics against CHB. There are several advantages to this animal model that are beneficial for performing both basic and translational HBV research. Previous review articles have focused on the value of this animal model in regard to HBV replication, pathogenesis, and immune response. In this article, we review studies of drug development and preclinical evaluation of direct-acting antivirals, immunomodulators, therapeutic vaccines, and inhibitors of viral entry, gene expression, and antigen release in the woodchuck model of CHB since 2014 until today and discuss their significance for clinical trials in patients.

Diverse Virus and Host-Dependent Mechanisms Influence the Systemic and Intrahepatic Immune Responses in the Woodchuck Model of Hepatitis B

Woodchuck infected with woodchuck hepatitis virus (WHV) represents the pathogenically nearest model of hepatitis B and associated hepatocellular carcinoma (HCC). This naturally occurring animal model also is highly valuable for development and preclinical evaluation of new anti-HBV agents and immunotherapies against chronic hepatitis (CH) B and HCC. Studies in this system uncovered a number of molecular and immunological processes which contribute or likely contribute to the immunopathogenesis of liver disease and modulation of the systemic and intrahepatic innate and adaptive immune responses during hepadnaviral infection. Among them, inhibition of presentation of the class I major histocompatibility complex on chronically infected hepatocytes and a role of WHV envelope proteins in this process, as well as augmented hepatocyte cytotoxicity mediated by constitutively expressed components of CD95 (Fas) ligand- and perforin-dependent pathways, capable of eliminating cells brought to contact with hepatocyte surface, including activated T lymphocytes, were uncovered. Other findings pointed to a role of autoimmune response against hepatocyte asialoglycoprotein receptor in augmenting severity of liver damage in hepadnaviral CH. It was also documented that WHV in the first few hours activates intrahepatic innate immunity that transiently decreases hepatic virus load. However, this activation is not translated in a timely manner to induction of virus-specific T cell response which appears to be hindered by defective activation of antigen presenting cells and presentation of viral epitopes to T cells. The early WHV infection also induces generalized polyclonal activation of T cells that precedes emergence of virus-specific T lymphocyte reactivity. The combination of these mechanisms hinder recognition of virus allowing its dissemination in the initial, asymptomatic stages of infection before adaptive cellular response became apparent. This review will highlight a range of diverse mechanisms uncovered in the woodchuck model which affect effectiveness of the anti-viral systemic and intrahepatic immune responses, and modify liver disease outcomes. Further exploration of these and other mechanisms, either already discovered or yet unknown, and their interactions should bring more comprehensive understanding of HBV pathogenesis and help to identify novel targets for therapeutic and preventive interventions. The woodchuck model is uniquely positioned to further contribute to these advances.

Innate and adaptive immunity associated with resolution of acute woodchuck hepatitis virus infection in adult woodchucks

Viral and/or host factors that are directly responsible for the acute versus chronic outcome of hepatitis B virus (HBV) infection have not been identified yet. Information on immune response during the early stages of HBV infection in humans is mainly derived from blood samples of patients with acute hepatitis B (AHB), which are usually obtained after the onset of clinical symptoms. Features of intrahepatic immune response in these patients are less studied due to the difficulty of obtaining multiple liver biopsies. Woodchuck hepatitis virus (WHV) infection in woodchucks is a model for HBV infection in humans. In the present study, five adult woodchucks were experimentally infected with WHV and then followed for 18 weeks. Blood and liver tissues were frequently collected for assaying markers of WHV replication and innate and adaptive immune responses. Liver tissues were further analyzed for pathological changes and stained for important immune cell subsets and cytokines. The increase and subsequent decline of viral replication markers in serum and liver, the elicitation of antibodies against viral proteins, and the induction of virus-specific T-cell responses indicated eventual resolution of acute WHV infection in all animals. Intrahepatic innate immune makers stayed unchanged immediately after the infection, but increased markedly during resolution, as determined by changes in transcript levels. The presence of interferon-gamma and expression of natural killer (NK) cell markers suggested that a non-cytolytic response mechanism is involved in the initial viral control in liver. This was followed by the expression of T-cell markers and cytolytic effector molecules, indicating the induction of a cytolytic response mechanism. Parallel increases in regulatory T-cell markers suggested that this cell subset participates in the overall immune cell infiltration in liver and/or has a role in regulating AHB induced by the cytolytic response mechanism. Since the transcript levels of immune cell markers in blood, when detectable, were lower than in liver, and the kinetics, except for NK-cells and interferon-gamma, did not correlate well with their intrahepatic expression, this further indicated enrichment of immune cells within liver. Conclusion: The coordinated interplay of innate and adaptive immunity mediates viral clearance in the woodchuck animal model of HBV infection. The initial presence of NK-cell associated interferon-gamma response points to an important role of this cytokine in HBV resolution.

Characterization Of The Interaction Between Subviral Particles Of Hepatitis B Virus And Dendritic Cells - In Vitro Study

Background

During an infection with hepatitis B virus (HBV), infectious particles (Dane particles) can be detected in addition to aggregates of the subviral particles (SVP) which is considered an immune escaping mechanism for the virus. Dendritic cells (DCs) are a specialized type of antigen-presenting cell (APC) that can activate native T-cells to prime an immune response controlling HBV infection. The aim of this study was to characterize the interaction between HBVsvp and DCs in vitro.

Methods

HBVsvp that comprises surface and core proteins were produced in vitro by HepG2.2.15 as a culturing system; DCs derived from the bone marrow of mice were pulsed by HBVsvp. A different pattern of cytokines secreted by bone-marrow-derived dendritic cells from C56BL/6 mice pulsed with HBVsvp were analyzed. The interactions between HBVsvp and DCs were characterized using FACS analysis, protein assay, Western blot, and immunofluorescence staining.

Results

Pulsation of DCs with HBVsvp resulted in strong activation and higher secretion of DC cytokines including INF-α, INF-γ, TNF-α, IL-1α, IL-10, and IL-12; but not for IL-1β, IL-2, IL-6, and IL-15. The production of CXCL-10/IP-10 was increased during the observation period and reached the maximal secretion after 24 hrs (p < 0.001). In total protein assay, we found significantly higher protein concentration in HBVsvp stimulated DC groups compared to not activated DCs (p < 0.001). Both 24 kDa small surface antigen (HBVs) and the 21 kDa core protein (HBVc) were detected in activated DCs. For DCs immunofluorescence staining, our data showed clear differences in the morphology of DCs between negative control and those pulsed with HBVsvp.

Conclusion

Result demonstrates a significant complex interaction between HBVsvp and DCs, in vitro.

An Assessment of Upper Limits of Normal for ALT and the Impact on Evaluating Natural Course of Chronic Hepatitis B Virus Infection in Chinese Children

BACKGROUND

The current upper limits of normal (ULN) for serum alanine aminotransferase (ALT) are increasingly challenged. We aimed to re-evaluate the ULN for ALT and assess the potential impact on the classification of natural course of chronic hepatitis B virus (HBV) infection in children.

METHODS

Laboratory data obtained from three hospitals in China were retrospectively analysed. In total, 2054 children with chronic HBV infection and 8149 healthy children at age ≤18 years were included in the study.

RESULTS

Age-specific and gender-specific ULNs for ALT, at averages of 30 U/L for boys and 24 U/L for girls, were calculated from the data of healthy children. Using the revised ULNs vs. the current ULNs (40-50 U/L), 31-60% vs. 9-17% of the 2054 HBV-infected children had an abnormal result as seen in their ALT baseline analysis, and the highest abnormality rate was seen in the infants. Data of 516 HBV-infected children were applied for the classification of clinical phase, 28.8% vs. 19.8% of the children were classified into the phases of hepatitis B e antigen (HBeAg-)positive/negative hepatitis. During a median follow-up of 62 months, 39 of 153 children underwent HBeAg seroconversion, whereas 3 of them had persistently "normal" ALT, according to the current ULN.

CONCLUSIONS

The revision of ULN for ALT in children substantially impacts the classification of the natural course of chronic HBV infection. Mild ALT fluctuation is common during the stage childhood, suggesting a need to rethink the current conceptions of immune tolerance and natural course of chronic HBV infection in the children.

Dynamics of the Immune Response in Acute Hepatitis B Infection

Background

Acute hepatitis B virus infection in adults is generally self-limiting but may lead to chronicity in a minority of patients.

Methods

We included 9 patients with acute hepatitis B virus (HBV) infection and collected longitudinal follow-up samples. Natural killer (NK) cell characteristics were analyzed by flowcytometry. HBV-specific T-cell function was analyzed by in vitro stimulation with HBV peptide pools and intracellular cytokine staining.

Results

Median baseline HBV DNA load was 5.12 log IU/mL, and median ALT was 2652 U/mL. Of 9 patients, 8 cleared HBsAg within 6 months whereas 1 patient became chronically infected. Early time points after infection showed increased CD56^bright NK cells and an increased proportion of cells expressing activation markers. Most of these had normalized at week 24, while the proportion of TRAIL-positive CD56^bright NK cells remained high in the chronically infected patient. In patients who cleared HBV, functional HBV-specific CD8+ and CD4+ responses could be observed, whereas in the patient who developed chronic infection, only low HBV-specific T-cell responses were observed.

Conclusions

NK cells are activated early in the course of acute HBV infection. Broad and multispecific T-cell responses are observed in patients who clear acute HBV infection, but not in a patient who became chronically infected.

Tolerance and immunity to pathogens in early life: insights from HBV infection

Immunity is not static but varies with age. The immune system of a newborn infant is not "defective" or "immature." Rather, there are distinct features of innate and adaptive immunity from fetal life to adulthood, which may alter the susceptibility of newborn infants to infections compared to adults. Increased protection to certain infectious diseases during early life may benefit from a dampened immune response as a result of decreased immune pathology. This concept may offer an alternative interpretation of the different pathological manifestations clinically observed in hepatitis B virus (HBV)-infected patients during the natural history of infection. Herein, we review the immune pathological features of HBV infection from early life to adulthood and challenge the concept of a generic immune tolerant state in young people. We then discuss how the different clinical and virological manifestations during HBV infection may be related to the differential antiviral immunity and pro-inflammatory capacity generated at different ages. Lastly, we address the potential to consider earlier therapeutic intervention in HBV-infected young patients to achieve effective immune control leading to better outcomes.

KIR : HLA association with clinical manifestations of HBV infection in Madurai, south India

The antiviral action of natural killer (NK) cells is regulated by a wide repertoire of germ-line encoded membrane receptors which recognize the expression of certain self-molecules on target cells. Among the receptors, killer cell immunoglobulinlike receptor (KIR) which recognizes the expression of human leukocyte antigen (HLA) class I has a predominant role in regulating the effector functions of NK cells, particularly in viral infections.We studied a total of 128 hepatitis B virus (HBV) patients (15 acute, 43 asymptomatic, 27 chronic and 43 with other liver diseases) while attending the Department of Medical Gastroenterology, Government Rajaji Hospital, Madurai, India, and 128 ethnic matched control to find the association between the KIR : HLA genes and differential manifestations of HBV. KIR and its ligand HLA polymorphism were identified by DNAPCR methods. The activatory receptor KIR-2DS1 was significantly elevated in various disease categories, namely asymptomatic, chronic and other HBV, except acute HBV infection. Whereas, KIR 2DS3 in acute and chronic patients and KIR 2DS5 and 3DS1 in asymptomatic individuals. Among various KIR-HLA combinations, homozygous 2DS2:C1 and individuals with 3DSI:BW4 (OR = 3.23, CI = 1.55-6.7, Pc = 0.02) are associated with HBV asymptomatism, while most of the two domain inhibitory receptors with their ligands showed significant risk in other liver diseases. Further, KIR3DL1 : HLA Bw4Iso80 (OR = 3.89, 95% CI = 1.58-9.55, Pc = 0.004) is related with higher risk for asymptomatic infection when compared with chronic HBV. Thus, the select KIR : HLA alleles and combinations seem to direct the NK cell activities and immune response in different directions resulting in varied symptoms and manifestations in the subgroups of HBV-infected patients studied.

The Woodchuck, a Nonprimate Model for Immunopathogenesis and Therapeutic Immunomodulation in Chronic Hepatitis B Virus Infection

The woodchuck hepatitis virus (WHV) and its host, the eastern woodchuck, is a very valuable model system for hepatitis B virus infection. Many aspects of WHV replication and pathogenesis resemble acute and chronic hepatitis B infection in patients. Since the establishment of immunological tools, woodchucks were used to develop new therapeutic vaccines and immunomodulatory approaches to treat chronic hepadnaviral infections. Combination therapy of nucleos(t)ide analogs, with prime-boost vaccination and triple therapy, including immunomodulatory strategies by blocking the interaction of the programmed death-1 (PD-1) receptor with its ligand inducing a potent T-cell response in chronic WHV carrier woodchucks, suppression of viral replication, and complete elimination of the virus in 30% of the animals. Both strategies may be used for future therapies in patients with chronic hepatitis B.

Woodchuck hepatitis virus core gene deletions and proliferative responses of peripheral blood mononuclear cells stimulated by an immunodominant epitope: a viral immune escape in the woodchuck model of chronic hepatitis B?

Marmota monax and its natural infection by woodchuck hepatitis virus (WHV) could be used as a predictive model for evaluating mechanisms of viral persistence during chronic hepatitis B virus (HBV) infection. The aim of this study was to investigate the presence of viral variants in the core gene of chronically WHV-infected woodchucks that showed two different patterns of peripheral blood mononuclear cells' (PBMCs') responses after stimulation with a specific WHV core peptide. Sequences' analysis of the WHV core region from eight WHV chronically infected woodchucks have been performed after in vitro stimulation with an immunodominant epitope of the WHV core protein (amino acids [aa] 96-110). Following this stimulation, positive PBMC responses at each point of follow-up were observed for four animals (group A), and weak immune responses at one or a few points of follow-up were observed for the remaining four animals (group B). The WHV core gene sequences contained amino acid deletions (aa 84-126, aa 84-113) in three of four group A animals and in none of group B animals. In the group A animals, the same deletions were observed in liver specimens and in two of four tumor specimens. Hepatocellular carcinoma (HCC) was diagnosed in all group A animals and in one group B animal. In conclusion, internal deletions in the core region correlated with a sustained PBMC response to the immunogenic peptide (96-110) of the core protein. A possible role of this relationship in hepatocarcinogenesis could be hypothesized; however, this needs to be investigated in patients with chronic HBV infection. The evaluation of virus-specific T-cell responses and T-cell epitopes that are possibly related to the mechanisms of viral evasion should be further investigated in order to design combined antiviral and immune approaches to control chronic HBV infection.

Therapeutic vaccination and immunomodulation in the treatment of chronic hepatitis B: preclinical studies in the woodchuck

Infection with hepatitis B virus (HBV) may lead to subclinical, acute or chronic hepatitis. In the prevaccination era, HBV infections were endemic due to frequent mother to child transmission in large regions of the world. However, there are still estimated 240 million chronic HBV carriers today and ca. 620,000 patients die per year due to HBV-related liver diseases. Recommended treatment of chronic hepatitis B with interferon-α and/or nucleos(t)ide analogues does not lead to satisfactory results. Induction of HBV-specific T cells by therapeutic vaccination or immunomodulation may be an innovative strategy to overcome virus persistence. Vaccination with commercially available HBV vaccines in patients with or without therapeutic reduction of viral load did not result in effective immune control of HBV infection, suggesting that combination of antiviral treatment with new formulations of therapeutic vaccines is needed. The woodchuck (Marmota monax) and its HBV-like woodchuck hepatitis virus are a useful preclinical animal model for developing new therapeutic approaches in chronic hepadnaviral infections. Several innovative approaches combining antiviral treatments using nucleos(t)ide analogues, with prime-boost vaccination using DNA vaccines, new hepadnaviral antigens or recombinant adenoviral vectors were tested in the woodchuck model. In this review, we summarize these encouraging results obtained with these therapeutic vaccines. In addition, we present potential innovations in immunostimulatory strategies by blocking the interaction of the inhibitory programmed death receptor 1 with its ligand in this animal model.

Virus-specific immune response in HBeAg-negative chronic hepatitis B: relationship with clinical profile and HBsAg serum levels

BACKGROUND AIMS

The immune impairment characterizing chronic hepatitis B (cHBV) infection is thought to be the consequence of persistent exposure to viral antigens. However, the immune correlates of different clinical stages of cHBV and their relation with different levels of HBsAg have not been investigated. The aim of the present study was to evaluate the relationship between HBV-specific T cells response and the degree of in vivo HBV control and HBsAg serum levels in HBeAg-HBeAb+ cHBV.

METHODS

Peripheral blood mononuclear cells from 42 patients with different clinical profiles (treatment-suppressed, inactive carriers and active hepatitis) of cHBV, 6 patients with resolved HBV infection and 10 HBV-uninfected individuals were tested with overlapping peptides spanning the entire HBV proteome. The frequency and magnitude of HBV-specific T cell responses was assessed by IFNγ ELISPOT assay. Serum HBsAg was quantified with a chemiluminescent immunoassay.

RESULTS

The total breadth and magnitude of HBV-specific T cell responses did not differ significantly between the four groups. However, inactive carriers targeted preferentially the core region. In untreated patients, the breadth of the anti-core specific T cell response was inversely correlated with serum HBsAg concentrations as well as HBV-DNA and ALT levels and was significantly different in patients with HBsAg levels either above or below 1000 IU/mL. The same inverse association between anti-core T cell response and HBsAg levels was found in treated patients.

CONCLUSIONS

Different clinical outcomes of cHBV infection are associated with the magnitude, breadth and specificity of the HBV-specific T cell response. Especially, robust anti-core T cell responses were found in the presence of reduced HBsAg serum levels, suggesting that core-specific T cell responses can mediate a protective effect on HBV control.

New insights into how HBV manipulates the innate immune response to establish acute and persistent infection

The mechanisms by which HBV establishes and maintains chronic infection are poorly understood. Although adult acquired HBV is generally cleared by a robust immune response, most individuals infected at childbirth or in very early childhood develop lifelong chronic infection. In addition, acute infections are unresolved in approximately 5% of individuals infected in adulthood. The host cell mechanisms that ensure establishment and resolution of acute infection and persistent infection remain unclear. Currently, two schools of thought suggest that either HBV is a 'stealth' virus, which initially establishes infection by avoiding host innate immune responses, or that HBV facilitates initial infection and progression to persistence by actively manipulating the host innate immune response to its advantage. There is increasing evidence that activation of innate host cell signalling pathways plays a major role in limiting adult acquired HBV infection and that, in turn, HBV has evolved numerous strategies to counteract these defence mechanisms. In this review, we summarize current knowledge regarding innate immune responses to HBV infection and discuss how HBV regulates cell signalling pathways to its advantage, particularly in the setting of chronic HBV infection. In turn, we show how an intimate knowledge of innate immune responses is driving development of novel therapeutic agents to treat chronic HBV infection.

Alteration in cellular immunity after chronic hepatitis B deteriorated into severe hepatitis and its significance

BACKGROUND

It is difficult to predict what type of chronic hepatitis B (CHB) progresses to chronic severe hepatitis B.

OBJECTIVES

This study aimed to observe changes in the HBV-specific and -nonspecific cellmediated immune responses after CHB deteriorates into severe hepatic disease and explore the significance of such changes.

PATIENTS AND METHODS

This study aimed to observe changes in the HBV-specific and -nonspecific cell-mediated immune responses after CHB deteriorates into severe hepatic disease and explore the significance of such changes.

RESULTS

In 49 of 255 CHB patients (19.22%), the disease developed into chronic severe hepatitis (early stage) an average of 10.06 ± 1.73 days after admission. CD4+ and NK cells levels in Group A were lower after progression into severe hepatitis than on the second day of admission (baseline) (P < 0.01). CD8+ cells and nonspecific CTL levels in Group A were higher after progression than at baseline (P < 0.01), and latter was higher than in Group B at baseline (P < 0.01); the levels of CD8+ cells and nonspecific CTLs in Group A after progression were significantly higher than those of Group B 10 days after admission (P < 0.01). There were no significant differences in HBV-specific CTL levels in Group A before and after progression to severe hepatitis (P > 0.05).

CONCLUSIONS

Our results suggest that the immunological pathogenesis of chronic severe hepatitis B is related to significant rises in CD8+ and nonspecific CTL levels and that such increases predict that the disease will deteriorate into severe hepatitis.

Alteration in cellular immunity after chronic hepatitis B deteriorated into severe hepatitis and its significance

BACKGROUND

It is difficult to predict what type of chronic hepatitis B (CHB) progresses to chronic severe hepatitis B.

OBJECTIVES

This study aimed to observe changes in the HBV-specific and -nonspecific cellmediated immune responses after CHB deteriorates into severe hepatic disease and explore the significance of such changes.

PATIENTS AND METHODS

This study aimed to observe changes in the HBV-specific and -nonspecific cell-mediated immune responses after CHB deteriorates into severe hepatic disease and explore the significance of such changes.

RESULTS

In 49 of 255 CHB patients (19.22%), the disease developed into chronic severe hepatitis (early stage) an average of 10.06 ± 1.73 days after admission. CD4+ and NK cells levels in Group A were lower after progression into severe hepatitis than on the second day of admission (baseline) (P < 0.01). CD8+ cells and nonspecific CTL levels in Group A were higher after progression than at baseline (P < 0.01), and latter was higher than in Group B at baseline (P < 0.01); the levels of CD8+ cells and nonspecific CTLs in Group A after progression were significantly higher than those of Group B 10 days after admission (P < 0.01). There were no significant differences in HBV-specific CTL levels in Group A before and after progression to severe hepatitis (P > 0.05).

CONCLUSIONS

Our results suggest that the immunological pathogenesis of chronic severe hepatitis B is related to significant rises in CD8+ and nonspecific CTL levels and that such increases predict that the disease will deteriorate into severe hepatitis.

Kinetics of immune responses to hepatitis B virus infection

The pathogenesis of hepatitis B is mainly triggered by the host's cellular immune responses to hepatitis B virus (HBV) infection, and the immune responses against the virus depends on the interaction of various immune cells. Current research of immunity to hepatitis B infection mainly focuses on understanding the differences between patients who can control HBV infection and those with persistent infection. In this paper, we analyze how immunological events influence the development of innate and adaptive immunity needed to control HBV infection and explore the mechanisms by which high levels of viral antigens, CD4⁺ T cells, programmed death 1 (PD-1), the presence of regulatory T cells, and impaired dendritic cell functions maintain the HBV-specific immunological failure.

Electroporation enhances immunogenicity of a DNA vaccine expressing woodchuck hepatitis virus surface antigen in woodchucks

The development of therapeutic vaccines for chronic hepatitis B virus (HBV) infection has been hampered by host immune tolerance and the generally low magnitude and inconsistent immune responses to conventional vaccines and proposed new delivery methods. Electroporation (EP) for plasmid DNA (pDNA) vaccine delivery has demonstrated the enhanced immunogenicity of HBV antigens in various animal models. In the present study, the efficiency of the EP-based delivery of pDNA expressing various reporter genes first was evaluated in normal woodchucks, and then the immunogenicity of an analog woodchuck hepatitis virus (WHV) surface antigen (WHsAg) pDNA vaccine was studied in this model. The expression of reporter genes was greatly increased when the cellular uptake of pDNA was facilitated by EP. The EP of WHsAg-pDNA resulted in enhanced, dose-dependent antibody and T-cell responses to WHsAg compared to those of the conventional hypodermic needle injection of WHsAg-pDNA. Although subunit WHsAg protein vaccine elicited higher antibody titers than the DNA vaccine delivered with EP, T-cell response rates were comparable. However, in WHsAg-stimulated mononuclear cell cultures, the mRNA expression of CD4 and CD8 leukocyte surface markers and Th1 cytokines was more frequent and was skewed following DNA vaccination compared to that of protein immunization. Thus, the EP-based vaccination of normal woodchucks with pDNA-WHsAg induced a skew in the Th1/Th2 balance toward Th1 immune responses, which may be considered more appropriate for approaches involving therapeutic vaccines to treat chronic HBV infection.

Inhibitory KIR and specific HLA-C gene combinations confer susceptibility to or protection against chronic hepatitis B

Antiviral activity of natural killer (NK) cells is regulated partially through inhibitory and activating killer cell immunoglobulin-like receptors (KIR) interacting with human leukocyte antigen C (HLA-C) ligands. The highly polymorphic nature of HLA-C and KIR genes endows individuals with diverse HLA-C/KIR combinations, which may confer susceptibility to or protection against a certain challenge. We analyzed the genes encoding KIR receptors and HLA-C ligands and HLA-C/KIR combinations in patients with chronic hepatitis B and healthy subjects. We found that inhibitory receptor KIR2DL1 in combination with HLA-C2 ligand confers susceptibility to chronic hepatitis B (CHB), whereas inhibitory receptor KIR2DL3 or KIR2DL3 homozygote in the presence of HLA-C1C1 genotype shows protection against CHB. Our data reveal that inhibitory NK cell interactions are important in determining antiviral immunity and that distinct affinity inhibitory responses will exert different impact on the development of CHB.

Dendritic cells can effectively be pulsed by HBVsvp and induce specific immune reactions in mice

Eradication of chronic Hepatitis B virus (HBV) infection, marked by HBs seroconversion, is very rarely achieved by treatment with nucleoside and nucleotide analogs. Therapeutic cell based approaches, like interferon therapy, have a higher chance of seroconversion. Dendritic cells (DC) are key players in the cellular immune response and have been shown to play an important role in controlling HBV infection. In this study, the potential of ex vivo activated DC to induce specific immune responses against HBV was examined. DC derived from bone-marrow of BALB/c or C56BL/6 mice were pulsed with HBV subviral particles (HBVsvp), derived from the HepG2.2.15 cell line. HepG2.2.15 produces subviral particles consisting of the HBc and HBs proteins. Thus, the entire "viral surface" is presented to DC to induce an immune reaction. In vitro pulsation with HBVsvp successfully activated bone-marrow derived DC, demonstrated by FACS analysis showing increased MHCII, CD 86 and CCR-7. Immunization of mice, via subcutaneous injection of the activated DC, induced HBV specific immune reactions which were measured by ELISA, ELISPOT and T-cell proliferation analysis. Vaccination with ex vivo activated DC may be a promising tool for therapeutic or prophylactic approaches against the Hepatitis B virus.

Glucosidase inhibition enhances presentation of de-N-glycosylated hepatitis B virus epitopes by major histocompatibility complex class I in vitro and in woodchucks

In this report, the possibility of pharmacologically altering the hepatitis B virus (HBV) epitopes presented by major histocompatibility complex class I on infected cells is demonstrated. The HBV middle envelope glycoprotein (MHBs) maturation appears to require calnexin-mediated folding. This interaction is dependent on glucosidases in the endoplasmic reticulum. Prevention of HBV envelope protein maturation in cultured cells through use of glucosidase inhibitors, such as 6-O-butanoyl castanospermine and N-nonyl deoxynorjirimycin, resulted in MHBs degradation by proteasomes. The de-N-glycosylation associated with polypeptide degradation was predicted to result in conversion of asparagine residues into aspartic acid residues. This prediction was confirmed by showing that peptides corresponding to the N-glycosylation sequons of MHBs, but with aspartic acid replacing asparagine, (1) can prime human cytotoxic T lymphocytes that recognize HBV-producing cells and (2) that the presentation of these envelope motifs by major histocompatibility complex class I is enhanced by incubation with glucosidase inhibitors. Moreover, although peripheral blood mononuclear cells isolated from woodchucks chronically infected with woodchuck hepatitis virus and vaccinated with woodchuck hepatitis virus surface antigen could be induced to recognize the natural MHBs asparagine-containing peptides, only cells isolated from animals treated with glucosidase inhibitor recognized the aspartic acid-containing peptides.

CONCLUSION

These data suggest that pharmacological intervention with glucosidase inhibitors can alter the MHBs epitopes presented. This editing of the amino acid sequence of the polypeptide results in a new epitope, or "editope", with possible medical significance.

Therapeutic vaccination in chronic hepatitis B: preclinical studies in the woodchuck

Recommended treatment of chronic hepatitis B with interferon-α and/or nucleos(t)ide analogues does not lead to a satisfactory result. Induction of HBV-specific T cells by therapeutic vaccination or immunotherapies may be an innovative strategy to overcome virus persistence. Vaccination with commercially available HBV vaccines in patients did not result in effective control of HBV infection, suggesting that new formulations of therapeutic vaccines are needed. The woodchuck (Marmota monax) is a useful preclinical model for developing the new therapeutic approaches in chronic hepadnaviral infections. Several innovative approaches combining antiviral treatments with nucleos(t)ide analogues, DNA vaccines, and protein vaccines were tested in the woodchuck model. In this paper we summarize the available data concerning therapeutic immunization and gene therapy using recombinant viral vectors approaches in woodchucks, which show encouraging results. In addition, we present potential innovations in immunomodulatory strategies to be evaluated in this animal model.

The woodchuck: a model for therapeutic vaccination against hepadnaviral infection

Interferon-alpha and nucleoside analogues are available for the treatment of chronic hepatitis B virus (HBV) infection but do not lead to a satisfactory result. New findings about the immunological control of HBV during acute infection suggest the pivotal role of T-cell mediated immune responses. Several preclinical and clinical trials were undertaken to explore the possibility of stimulating specific immune responses in chronically infected animals and patients by vaccination. However, vaccination with commercially available HBV vaccines in patients and immunization in woodchucks with core or surface proteins of woodchuck hepatitis virus (WHV) did not result in effective control of HBV and WHV infection, suggesting that new formulations of therapeutic vaccines are needed. Some new approaches combining antiviral treatments with nucleoside analogues, DNA vaccines and protein vaccines were tested in the woodchuck model. It could be shown that therapeutic vaccinations are able to stimulate specific B- and T-cell responses and to achieve transient suppression of viral replication. These results suggest the great potential of therapeutic vaccination in combination with antivirals to reach an effective and sustained control of HBV infection.

Identification of Acute Self-Limited Hepatitis B among Patients Presenting with Hepatitis B Virus-Related Acute Hepatitis: A Hospital-Based Epidemiological and Clinical Study

This study aimed to identify acute self-limited hepatitis B (ASL-HB) among patients presenting with hepatitis B virus (HBV)-related acute hepatitis. Data were available for 220 patients diagnosed with HBV-related acute hepatitis, of whom 164 had acute hepatitis B (AHB). Of these, 160 were confirmed as ASL-HB: three (1.9%) evolved to chronic hepatitis B and one (0.6%) developed fulminant hepatitis and died. Comparisons were also made between AHB and acute infections with hepatitis A (HA) and hepatitis E (HE) viruses. During the study period, the number of patients with AHB exceeded the sum of those with acute HA and acute HE infections. There was no distinct seasonal peak for AHB infection, whereas both acute HA and acute HE infections occurred more frequently in the spring. Clinical symptoms and physical signs were similar for all three types of hepatitis, but significant differences were seen in some biochemical parameters. In conclusion, this study suggests that symptomatic AHB is not rare in China but it seldom evolves to chronic hepatitis B.

Rapid immunity to vaccination with woodchuck hepatitis virus surface antigen using cationic liposome-DNA complexes as adjuvant

Complexes of cationic liposomes and non-coding DNA (CLDC) have shown promise as vaccine adjuvant. Using the woodchuck animal model of hepatitis B virus (HBV) infection, the immunogenic effects of CLDC were evaluated following vaccination with three doses of woodchuck hepatitis virus surface antigen (WHsAg) adjuvanted with either CLDC or conventional alum and administered intramuscularly (im) or subcutaneously (sc). IM vaccination with WHsAg and CLDC elicited antibodies earlier, in more woodchucks, and with higher titers than WHsAg and alum. After two vaccine doses, antibody titers were higher following im than sc administration. Woodchucks administered two vaccine doses sc received the third vaccine dose im, and antibody responses reached titers comparable to those elicited by im administration. Following the second vaccine dose, im vaccination with WHsAg and CLDC induced T cell responses to WHsAg and selected WHs peptides and expression of the leukocyte surface marker CD8 and of the Th1 cytokines interferon-gamma and tumor necrosis factor alpha in woodchucks. T cell responses and CD8/cytokine expression were diminished in woodchucks from the other groups suggesting that this vaccine regimen induced a skew toward Th1 immune responses. The present study in woodchucks demonstrates that CLDC-adjuvanted WHsAg vaccine administered im resulted in a more rapid induction of humoral and cellular immune responses compared to conventional, alum-adjuvanted WHsAg vaccine. While less rapid, the immune responses following sc administration can prime the im immune responses. This adjuvant activity of CLDC over alum may be beneficial for therapeutic vaccination in chronic HBV infection.

Semliki forest virus expressing interleukin-12 induces antiviral and antitumoral responses in woodchucks with chronic viral hepatitis and hepatocellular carcinoma

A vector based on Semliki Forest virus (SFV) expressing high levels of interleukin-12 (SFV-enhIL-12) has previously demonstrated potent antitumoral efficacy in small rodents with hepatocellular carcinoma (HCC) induced by transplantation of tumor cells. In the present study, the infectivity and antitumoral/antiviral effects of SFV vectors were evaluated in the clinically more relevant woodchuck model, in which primary HCC is induced by chronic infection with woodchuck hepatitis virus (WHV). Intratumoral injection of SFV vectors expressing luciferase or IL-12 resulted in high reporter gene activity within tumors and cytokine secretion into serum, respectively, demonstrating that SFV vectors infect woodchuck tumor cells. For evaluating antitumoral efficacy, woodchuck tumors were injected with increasing doses of SFV-enhIL-12, and tumor size was measured by ultrasonography following treatment. In five (83%) of six woodchucks, a dose-dependent, partial tumor remission was observed, with reductions in tumor volume of up to 80%, but tumor growth was restored thereafter. Intratumoral treatment further produced transient changes in WHV viremia and antigenemia, with >or=1.5-log(10) reductions in serum WHV DNA in half of the woodchucks. Antitumoral and antiviral effects were associated with T-cell responses to tumor and WHV antigens and with expression of CD4 and CD8 markers, gamma interferon, and tumor necrosis factor alpha in peripheral blood mononuclear cells, suggesting that immune responses against WHV and HCC had been induced. These experimental observations suggest that intratumoral administration of SFV-enhIL-12 may represent a strategy for treatment of chronic HBV infection and associated HCC in humans but indicate that this approach could benefit from further improvements.

HBV-Specific Adaptive Immunity

The successful control of HBV infection requires an efficient expansion of distinct elements of the adaptive immune system (B cells, helper and cytotoxic T cells) that, due to the hepatotropic nature of HBV, need to operate in the liver parenchyma. In this respect, we will discuss broad features of HBV immunity in patients with resolved or chronic HBV infection and analyze how the liver environment can directly modulate HBV-immunity.

Correlation of virus and host response markers with circulating immune complexes during acute and chronic woodchuck hepatitis virus infection

Woodchuck hepatitis virus (WHV) is an established model for human hepatitis B virus. The kinetics of virus and host responses in serum and liver during acute, self-limited WHV infection in adult woodchucks were studied. Serum WHV DNA and surface antigen (WHsAg) were detected as early as 1 to 3 weeks following experimental infection and peaked between 1 and 5 weeks postinfection. Thereafter, serum WHsAg levels declined rapidly and became undetectable, while WHV DNA levels became undetectable much later, between 4 and 20 weeks postinfection. Decreasing viremia correlated with transient liver injury marked by an increase in serum sorbitol dehydrogenase (SDH) levels. Clearance of WHV DNA from serum was associated with the normalization of serum SDH. Circulating immune complexes (CICs) of WHsAg and antibodies against WHsAg (anti-WHs) that correlated temporarily with the peaks in serum viremia and WHs antigenemia were detected. CICs were no longer detected in serum once free anti-WHs became detectable. The detection of CICs around the peak in serum viremia and WHs antigenemia in resolving woodchucks suggests a critical role for the humoral immune response against WHsAg in the early elimination of viral and subviral particles from the peripheral blood. Individual kinetic variation during WHV infections in resolving woodchucks infected with the same WHV inoculum and dose is likely due to the outbred nature of the animals, indicating that the onset and magnitude of the individual immune response determine the intensity of virus inhibition and the timing of virus elimination from serum.

Immunology of hepatitis B and hepatitis C virus infections

Hepatitis B (HBV) and hepatitis C (HCV) viruses are the two major causes of chronic liver inflammation worldwide. Despite distinct virologic features, both viruses are preferentially hepatotropic, not directly cytopathic, and elicit liver diseases that share several aspects of their natural history. HBV and HCV infections also share some important features of the adaptive antiviral immune response. We describe the innate immune response in the early phase following infection, and how these early events may influence the development of the adaptive immune response in these two important viral infections. The mechanisms by which high levels of viral antigens, liver immunological features, the presence of regulatory T cells and impaired dendritic cell functions may maintain the HBV- and HCV-specific immunological failure, characteristic of chronic hepatitis B and C patients, are also evaluated.

Intrahepatic expression of genes affiliated with innate and adaptive immune responses immediately after invasion and during acute infection with woodchuck hepadnavirus

The importance of effective immune responses in recovery from acute hepadnaviral hepatitis has been demonstrated. However, there is no conclusive delineation of virological and immunological events occurring in the liver immediately after hepadnavirus invasion and during the preacute phase of infection. These very early events might be of primary importance in determining the recovery or progression to chronic hepatitis and the intrinsic hepadnaviral propensity to persist. In this study, applying the woodchuck model of acute hepatitis B, the hepatic kinetics of hepadnavirus replication and activation of genes encoding cytokines, cytotoxicity effectors, and immune cell markers were quantified in sequential liver biopsies collected from 1 h postinoculation onward by sensitive real-time cDNA amplification assays. The results revealed that hepadnavirus replication is established in the liver as early as 1 hour after infection. In 3 to 6 h, significantly augmented intrahepatic transcription of gamma interferon and interleukin-12 were evident, suggesting activation of antigen-presenting cells. In 48 to 72 h, NK and NKT cells were activated and virus replication was transiently but significantly reduced, implying that this early innate response is at least partially successful in limiting virus propagation. Nonetheless, T cells were activated 4 to 5 weeks later when hepatitis became histologically evident. Collectively, our data demonstrate that virus replication is initiated and the innate response activated in the liver soon after exposure to a liver-pathogenic dose of hepadnavirus. Nevertheless, this response is unable to prompt a timely adaptive T-cell response, in contrast to infections caused by other viral pathogens.

Immunogenicity in mice and rabbits of DNA vaccines expressing woodchuck hepatitis virus antigens

The licensed vaccine against hepatitis B virus (HBV) is an effective means to prevent infection, but is not an effective therapeutic strategy to treat established chronic infections when used alone. In an animal model of chronic HBV infection (the woodchuck experimentally infected with woodchuck hepatitis virus (WHV)), the combination of conventional vaccine and potent antiviral drugs has shown promise as a potential therapeutic intervention. This approach might be improved further through the application of newer vaccine technologies. In the present study, we evaluated electroporation (EP)-based intramuscular (i.m.) delivery of a codon-optimized DNA vaccine for the WHV surface antigen (WHsAg) in mice and rabbits. In mice, this immunization procedure compared favorably to vaccination by i.m. injection of the DNA vaccine or i.m. administration of a recombinant WHsAg-alum vaccine, exhibiting characteristics expected to be beneficial for a therapeutic vaccine strategy. These included dose efficiency, consistency, vigorous induction of antibody responses to WHsAg, as well as a Th1 bias. Following scale-up to rabbits, a species that approximates the size of the woodchuck, the EP dosing regimen was markedly more effective than conventional i.m. injection of the DNA vaccine. Taken together, these results provide the foundation for studies of EP-based DNA immunization in the woodchuck in order to further assess its potential as an immunotherapeutic approach for treatment of chronic HBV infection in humans.

Understanding the immunopathogenesis of chronic hepatitis B virus: an Asian prospective

The study of hepatitis B virus (HBV) immunity has been mainly focused on understanding the differences between subjects who are able to control HBV infection and patients with persistent infection. These studies have been instrumental in increasing our knowledge on the pathogenesis of the disease caused by HBV. However, it is possible that heterogeneity of host and virus factors which segregate in ethnically distinct HBV infected populations might modify important aspects of the immune response against HBV. In this review, we reexamine the kinetics and the pattern of HBV-specific immunity associated with control or persistence of infection. We then discuss how the epidemiological, genetic and viral characteristics peculiar to Asian patients can impact the profile of HBV-specific immunity.

Aberrant lymphocyte activation precedes delayed virus-specific T-cell response after both primary infection and secondary exposure to hepadnavirus in the woodchuck model of hepatitis B virus infection

The contribution of virus-specific T lymphocytes to the outcome of acute hepadnaviral hepatitis is well recognized, but a reason behind the consistent postponement of this response remains unknown. Also, the characteristics of T-cell reactivity following reexposure to hepadnavirus are not thoroughly recognized. To investigate these issues, healthy woodchucks (Marmota monax) were infected with liver-pathogenic doses of woodchuck hepatitis virus (WHV) and investigated unchallenged or after challenge with the same virus. As expected, the WHV-specific T-cell response appeared late, 6 to 7 weeks postinfection, remained high during acute disease, and then declined but remained detectable long after the resolution of hepatitis. Interestingly, almost immediately after infection, lymphocytes acquired a heightened capacity to proliferate in response to mitogenic (nonspecific) stimuli. This reactivity subsided before the WHV-specific T-cell response appeared, and its decline coincided with the cells' augmented susceptibility to activation-induced death. The analysis of cytokine expression profiles confirmed early in vivo activation of immune cells and revealed their impairment of transcription of tumor necrosis factor alpha and gamma interferon. Strikingly, reexposure of the immune animals to WHV swiftly induced hyperresponsiveness to nonspecific stimuli, followed again by the delayed virus-specific response. Our data show that both primary and secondary exposures to hepadnavirus induce aberrant activation of lymphocytes preceding the virus-specific T-cell response. They suggest that this activation and the augmented death of the cells activated, accompanied by a defective expression of cytokines pivotal for effective T-cell priming, postpone the adaptive T-cell response. These impairments likely hamper the initial recognition and clearance of hepadnavirus, permitting its dissemination in the early phase of infection.

Infection of neonates with murine gammaherpesvirus 68 results in enhanced viral persistence in lungs and absence of infectious mononucleosis syndrome

We used the murine gammaherpesvirus 68 (γHV-68), which serves as a model for human gammaherpesvirus infection, to determine whether age at infection altered the pattern of gammaherpesvirus pathogenesis. We infected mice intranasally at 8 days old (pups) and 6 weeks old (adults) to investigate differences in γHV-68 pathogenesis. There was no difference between adults or pups in acute infection in the lungs at 6 days post-infection (p.i.). However, mice infected as pups exhibited a more disseminated viral infection with viral DNA detected in the spleen, liver and heart as measured by quantitative PCR (Q-PCR). In addition, viral DNA was detected in the lungs of mice infected as pups until 60 days p.i. Three viral transcripts (M2, M3 and M9) were expressed at both 30 and 60 days p.i. In contrast, no viral DNA or mRNA expression was detected in lungs of mice infected as adults at 30 or 60 days p.i. Mice infected as adults experienced a peak in latent infection in the spleen at 16 days p.i., corresponding with an increase in splenic weight and expansion of the Vβ4+ CD8+ T-cell population, similar to infectious mononucleosis observed following infection of young adults with Epstein–Barr virus. However, the increase in splenic weight of infected pups was not as pronounced and no significant increase in Vβ4+ CD8+ T-cell expansion was observed in infected pups. Together, these data suggest that the pathogenesis of murine gammaherpesvirus γHV-68 is age-dependent.

Therapeutic vaccination in chronic hepatitis B: preclinical studies in the woodchuck model

Interferon-alpha and nucleoside analogues are available for the treatment of chronic hepatitis B virus (HBV) infection but do not lead to a satisfactory result. New findings about the immunological control of HBV during acute infection suggest the pivotal role of T-cell mediated immune responses. Several preclinical and clinical trials were undertaken to explore the possibility of stimulating specific immune responses in chronically infected animals and patients by vaccination. However, vaccination with commercially available HBV vaccines in patients and immunization in woodchucks with core or surface proteins of woodchuck hepatitis virus (WHV) did not result in effective control of HBV and WHV infection, suggesting that new formulations of therapeutic vaccines are needed. Some new approaches combining antiviral treatments with nucleoside analogues, DNA vaccines and protein vaccines were tested in the woodchuck model. It could be shown that therapeutic vaccinations are able to stimulate specific B- and T-cell responses and to achieve transient suppression of viral replication. These results suggest the great potential of therapeutic vaccination in combination with antivirals to reach an effective and sustained control of HBV infection.

Immune response and tolerance during chronic hepatitis B virus infection

The hepatitis B virus (HBV) is a hepatotropic non-cytopathic DNA virus that despite the presence of an effective prophylactic vaccine is estimated to infect 300 million people, with a particularly high prevalence in Asia and Africa. It causes liver diseases that vary greatly in severity from person to person. Some subjects control infection efficiently and clear the virus from the bloodstream either without clinically evident liver disease or with an acute inflammation of the liver (acute hepatitis) that can resolve without long-term clinical sequelae. Other patients fail to clear the virus and develop chronic infection. Most chronically infected patients remain asymptomatic without life-threatening liver disease but 10-30% develop liver cirrhosis with possible progression to liver cancer. Outcome of infection and the pathogenesis of liver disease are determined by virus and host factors, which have been difficult tofully elucidate because the host range of HBV is limited to man and chimpanzees. However, the study of animal models of related Hepadnavirus infections and transgenic mouse able to express individual HBV genes or replicate the entire viral genome have clarified several aspects connected to HBV infection. Furthermore, the ability to analyze many immunological phenomena ex vivo through direct quantification of Ag-specific T cells in humans and chimps has considerably increased our knowledge of HBV pathogenesis. Here, we will discuss the distinctions of HBV adaptive immunity between resolved and persistently infected patients and the host/viral factors that can cause and maintain them.

Chemoimmunotherapy of chronic hepatitis B virus infection in the woodchuck model overcomes immunologic tolerance and restores T-cell responses to pre-S and S regions of the viral envelope protein

Treatment of chronic hepatitis B virus (HBV) infection could combine potent antiviral drugs and therapeutic vaccines to overcome immunological tolerance and induce the recovery phenotype to protect against disease progression. Conventional vaccination of woodchucks chronically infected with the woodchuck hepatitis virus (WHV) elicited differential T-cell response profiles depending on whether or not carriers were treated with the potent antiviral drug clevudine (CLV), which significantly reduces viral and antigen loads. The differential T-cell responses defined both CLV-dependent and CLV-independent epitopes of the pre-S and S regions of the WHV envelope protein. Only combined treatment involving CLV and conventional vaccine therapeutically restored the T-cell response profile of chronic WHV carrier woodchucks to that seen in prophylactic vaccination and in recovery from acute WHV infection. The results have implications for mechanisms of immunological tolerance operating in chronic HBV infection and suggest that such combined chemoimmunotherapy may be useful for treatment of humans with chronic HBV infection.

Immunomodulation as an option for the treatment of chronic hepatitis B virus infection: preclinical studies in the woodchuck model

New therapeutic approaches for chronic hepatitis B virus infection based on immunomodulation are now under investigation. The woodchuck model for hepatitis B virus infection has emerged as a useful animal model for the evaluation of such approaches, after developing necessary assays and reagents for immunologic studies in this model. Conventional and novel vaccines such as DNA vaccines were tested in woodchucks for their ability to induce protective immune responses against challenge infection with the woodchuck hepatitis virus (WHV). Furthermore, immunotherapeutic approaches for the control of chronic hepadnaviral infection were evaluated in woodchucks. Immunizations with WHV proteins and DNA vaccines led to the development of antibodies to the WHV surface antigen and to a significant decrease of viral load in chronically WHV-infected woodchucks. Viral vector-mediated gene transfer was explored for the delivery of antiviral cytokines IFN-alpha in woodchucks and resulted in the decrease of viral replication. It is now generally accepted that a combination of antiviral treatment and immunization will be necessary to achieve successful immunomodulation with a long-term control of chronic hepatitis B virus infection.

Acute resolving woodchuck hepatitis virus (WHV) infection is associated with a strong cytotoxic T-lymphocyte response to a single WHV core peptide

Woodchucks infected with woodchuck hepatitis virus (WHV) are an excellent model for studying acute, self-limited and chronic hepadnaviral infections. Defects in the immunological response leading to chronicity are still unknown. Specific T-helper cell responses to WHV core and surface antigens (WHcAg and WHsAg, respectively) are associated with acute resolving infection; however, they are undetectable in chronic infection. Up to now, cytotoxic T-lymphocyte (CTL) responses could not be determined in the woodchuck. In the present study, we detected virus-specific CTL responses by a CD107a degranulation assay. The splenocytes of woodchucks in the postacute phase of WHV infection (18 months postinfection) were isolated and stimulated with overlapping peptides covering the whole WHcAg. After 6 days, the cells were restimulated and stained for CD3 and CD107a. One peptide (c96-110) turned out to be accountable for T-cell expansion and CD107a staining. Later, we applied the optimized degranulation assay to study the kinetics of the T-cell response in acute WHV infection. We found a vigorous T-cell response against peptide c96-110 with peripheral blood cells beginning at the peak of viral load (week 5) and lasting up to 15 weeks postinfection. In contrast, there was no T-cell response against peptide c96-110 detectable in chronically WHV-infected animals. Thus, with this newly established flow cytometric degranulation assay, we detected for the first time virus-specific CTLs and determined one immunodominant epitope of WHcAg in the woodchuck.

Immunosuppression reactivates viral replication long after resolution of woodchuck hepatitis virus infection

Resolution of hepatitis B virus (HBV) infection is characterized by coordinated humoral and cellular immune responses. Immunity is durable over decades, protecting the host from reinfection and potential activation of residual HBV. Woodchucks infected at birth with woodchuck hepatitis virus (WHV) cleared viremia and developed antibodies to surface antigen (anti-WHs). Woodchucks became seronegative for anti-WHs 3-6 years later, but in some, WHV DNA was detected in serum, liver, and/or peripheral blood mononuclear cells (PBMCs). Those with WHV DNA had increased in vitro cellular immune responses to viral antigens, CD4 and CD8 markers, and Th1-type cytokines, suggesting active WHV-specific T lymphocytes. Immunosuppression for 12 weeks using cyclosporine A in such woodchucks resulted in transient reactivation of WHV replication. Serum of 1 woodchuck that became positive for WHV DNA during immunosuppression was inoculated into WHV-susceptible woodchucks, and a productive infection was demonstrated. The results indicate that after infection durable cellular immunity to WHV is essential for the long-term control of viral replication and is probably maintained by continuous priming from residual virus.

CONCLUSION

These experimental observations demonstrate the potential of immunosuppression to reactivate HBV after resolution of infection.

The effect of surgical immunomodulation on liver inflammation and clearance of DHBV infection

The key to developing a therapeutic vaccine for chronic hepadnavirus infection lies in the characteristics of the host-immune response which leads to clearance of acute infection. Groups of 28-day-old ducks which had been surgically bursectomized (n = 10) or thymectomized (n = 13) on the day of hatch or were untreated (n = 21) were inoculated with 10(9) viral genome equivalents (vge) DHBV, then bled twice a week, and euthanased 40 days later. Serum and liver were tested for DHBV DNA and total leukocytes and peripheral blood mononuclear cells (PBMCs) counted. Liver and spleen sections were either stained with hematoxylin and eosin, and graded for inflammation or stained with peroxidase-labeled anti-human CD3 antibody and examined for T lymphocyte distribution. PBMC counts were similar in all groups. DHBV infection combined with bursectomy increased significantly, while thymectomy decreased significantly the total leukocyte count. The spleen and liver bursectomy increased T lymphocyte number while B cells were decreased. Converse changes were observed in thymectomized ducks. Histological evidence of hepatitis was present in infected control and bursectomized ducks but not in the uninfected control or infected thymectomized ducks. In control animals, DHBV challenge caused viremia in 17 and persistent infection in 11 (56%). Fewer thymectomized ducks (3/13, 23%) and significantly more (100%) bursectomized ducks remained persistently infected (P < 0.001). Unexpectedly, bursectomy led to persistence of infection while clearance of infection occurred normally in thymectomized ducks despite decreased T lymphocyte numbers. This suggests that clearance requires T and B lymphocyte collaboration.

The woodchuck as an animal model for pathogenesis and therapy of chronic hepatitis B virus infection

This review describes the woodchuck and the woodchuck hepatitis virus (WHV) as an animal model for pathogenesis and therapy of chronic hepatitis B virus (HBV) infection and disease in humans. The establishment of woodchuck breeding colonies, and use of laboratory-reared woodchucks infected with defined WHV inocula, have enhanced our understanding of the virology and immunology of HBV infection and disease pathogenesis, including major sequelae like chronic hepatitis and hepatocellular carcinoma. The role of persistent WHV infection and of viral load on the natural history of infection and disease progression has been firmly established along the way. More recently, the model has shed new light on the role of host immune responses in these natural processes, and on how the immune system of the chronic carrier can be manipulated therapeutically to reduce or delay serious disease sequelae through induction of the recovery phenotype. The woodchuck is an outbred species and is not well defined immunologically due to a limitation of available host markers. However, the recent development of several key host response assays for woodchucks provides experimental opportunities for further mechanistic studies of outcome predictors in neonatal- and adult-acquired infections. Understanding the virological and immunological mechanisms responsible for resolution of self-limited infection, and for the onset and maintenance of chronic infection, will greatly facilitate the development of successful strategies for the therapeutic eradication of established chronic HBV infection. Likewise, the results of drug efficacy and toxicity studies in the chronic carrier woodchucks are predictive for responses of patients chronically infected with HBV. Therefore, chronic WHV carrier woodchucks provide a well-characterized mammalian model for preclinical evaluation of the safety and efficacy of drug candidates, experimental therapeutic vaccines, and immunomodulators for the treatment and prevention of HBV disease sequelae.

Advantages to the use of rodent hepadnavirus core proteins as vaccine platforms

The hepatitis B core antigen (HBcAg) has been proposed as a useful particulate carrier platform for poorly immunogenic peptidic and carbohydrate B cell epitopes. However, biochemical and immunologic impediments have plagued this technology. Specifically, the "assembly" problem characterized by the low yield of unstable hybrid particles resulting from the insertion of foreign sequences and the "pre-existing immunity" problem due to the fact that the HBcAg is derived from a human pathogen have limited the development of this carrier technology. As a means of addressing the "pre-existing immunity" problem we have used the core proteins from the rodent hepdnaviruses. A number of advantages to the use of the rodent hepadnaviral core proteins as opposed to the HBcAg for vaccine design were defined including: equal or superior immunogenicity at the T and B cell levels; the use of the rodent core proteins does not compromise the anti-HBc diagnostic assay; the efficacy of the rodent core proteins as vaccine carriers will not be limited by pre-existing anti-HBc antibodies that are present in previously and currently HBV-infected persons; and the HBcAg-specific tolerance present in HBV chronic carriers can be circumvented by the use of the rodent core proteins.

Bicistronic woodchuck hepatitis virus core and gamma interferon DNA vaccine can protect from hepatitis but does not elicit sterilizing antiviral immunity

The immunity elicited against nucleocapsid of hepatitis B virus (HBV) and closely related woodchuck hepatitis virus (WHV) has been shown to be important in resolution of hepatitis and protection from infection. Further, activity of gamma interferon (IFN-gamma), which may directly inhibit hepadnavirus replication, promotes antiviral defense and favors T helper cell type 1 (Th1) response, which is seemingly a prerequisite of HBV clearance. In this study, to enhance induction of protective immunity against hepadnavirus, healthy woodchucks were immunized with a bicistronic DNA vaccine carrying WHV core (WHc) and woodchuck IFN-gamma (wIFN-gamma) gene sequences. Three groups, each group containing three animals, were injected once or twice with 0.5 mg, 0.9 mg, or 1.5 mg per dose of this vaccine. In addition, four animals received two injections of 0.6 mg or 1 mg WHc DNA alone. All animals were challenged with WHV. The results showed that four of nine animals injected with the bicistronic vaccine and one of four immunized with WHc DNA became protected from serologically evident infection and hepatitis. This protection was not linked to induction of WHc antigen-specific antibodies or T-cell proliferative response and was not associated with enhanced transcription of Th1 cytokines or 2',5'-oligoadenylate synthetase. Strikingly, all animals protected from hepatitis became reactive for WHV DNA and carried low levels of replicating virus in hepatic and lymphoid tissues after challenge with WHV. This study shows that the bicistronic DNA vaccine encoding both hepadnavirus core antigen and IFN-gamma was more effective in preventing hepatitis than that encoding virus core alone, but neither of them could mount sterile immunity against the virus or prevent establishment of occult infection.

Characterization of bioactive recombinant woodchuck interleukin-2 amplified by RLM-RACE and produced in eukaryotic expression system

Woodchucks (Marmota monax) infected with woodchuck hepatitis virus (WHV) represent a highly valuable laboratory model of hepatitis B virus (HBV) infection, in which molecular, immunological and pathological events occurring in infected humans are adequately reflected. To advance studies on T cell immune responses and propagation of hepadnavirus in T lymphocytes in this animal model, we determined the complete sequence of woodchuck interleukin-2 (wIL-2) cDNA by utilizing RNA ligase-mediated rapid amplification of cDNA ends (RLM-RACE) reaction. The wIL-2 sequence revealed a single open reading frame encoding for the predicted precursor protein comprised of a signal peptide and a 134 amino acid-long mature protein. The mature wIL-2 protein produced in the Escherichia coli expression system, designated as ec-rwIL-2, was found to be immunogenic but not biologically active. In contrast, precursor wIL-2 protein cloned into baculovirus transfer vector and expressed in Sf9 cells, designated as bac-rwIL-2, demonstrated functional competence. Further, bac-rwIL-2 was able to stimulate proliferation and to induce multiple daughter cell generations in woodchuck T cells, as well as facilitated the survival of standard IL-2-dependent mouse CTLL-2 cells in culture. Western blot analysis of bac-rwIL-2 using antibodies generated against ec-rwIL-2 revealed a single protein band of 15.5kDa. The availability of biologically active recombinant wIL-2 should facilitate ex vivo studies on functional competence of woodchuck T lymphocytes derived from different stages of hepadnaviral hepatitis and assist in recognizing their contribution to the pathogenesis of liver injury in the woodchuck model of hepatitis B.

Analysis of intrahepatic HBV-specific cytotoxic T-cells during and after acute HBV infection in humans

BACKGROUND/AIMS

Characteristics of the intrahepatic virus-specific T-cell response in patients with acute hepatitis B virus (HBV) infection have not been studied due to the risk of complications associated with standard liver biopsies. In this study we aimed to characterize the virus-specific CD8 + T-cell response in the liver of patients with acute HBV infection using fine-needle aspiration-biopsy (FNAB).

METHODS

In HLA-A2 positive patients with acute HBV infection a FNAB was performed at first presentation, at the time of HBsAg-seroconversion and 3 months after HBsAg-seroconversion. HLA-A2 tetramers were used to identify HBV-specific CD8 + T-cells in FNAB-cytology and peripheral blood (PB).

RESULTS

At first presentation there was a correlation between the frequency of intrahepatic CD8 + T-cells and the degree of liver damage. At all time points there was sequestering of HBV-specific CD8 + T-cells in the liver, and the percentage of intrahepatic HLA-DR expressing HBV-specific CD8 + T-cells was higher than in PB. Three months after HBsAg-seroconversion the frequency of intrahepatic HBV-specific CD8 + T-cells remained high.

CONCLUSIONS

HBV-specific CD8 + T-cells are compartmentalized in the liver during acute HBV infection. Their presence in the liver may suggest a role in the resolution of the infection. Intrahepatic HBV-specific CD8 + T cells remain detectable at high frequencies after HBsAg-seroconversion.

The immune response during hepatitis B virus infection

Hepatitis B virus (HBV) is a major cause of chronic liver inflammation worldwide. Recent knowledge of the virological and immunological events secondary to HBV infection has increased our understanding of the mechanisms involved in viral clearance and persistence. In this review, how the early virological and immunological events might influence the development of a coordinate activation of adaptive immunity necessary to control HBV infection is analysed. The mechanism(s) by which high levels of viral antigens, liver immunological features, regulatory cells and dendritic cell defects might maintain the HBV-specific immunological collapse, typical of chronic hepatitis B patients, is also examined.