Characterization of CD8+ cytotoxic T-lymphocyte responses after genetic immunization with retrovirus vectors expressing different forms of the hepatitis B virus core and e antigens

HBeAg Is Indispensable for Inducing Liver Sinusoidal Endothelial Cell Activation by Hepatitis B Virus

Background and Aims

Liver sinusoidal endothelial cells (LSECs) serve as sentinel cells to detect microbial infection and actively contribute to regulating immune responses for surveillance against intrahepatic pathogens. We recently reported that hepatitis B e antigen (HBeAg) stimulation could induce LSEC maturation and abrogate LSEC-mediated T cell suppression in a TNF-α and IL27 dependent manner. However, it remains unclear how HBeAg deficiency during HBV infection influences LSEC immunoregulation function and intrahepatic HBV-specific CD8 T cell responses.

Methods

The function of LSECs in regulating effector T cell response, intrahepatic HBV-specific CD8 T cell responses and HBV viremia were characterized in both HBeAg-deficient and -competent HBV hydrodynamic injection (HDI) mouse models.

Results

LSECs isolated from HBeAg-deficient HBV HDI mice showed a reduced capacity to promote T cell immunity in vitro compared with those isolated from wild-type HBV HDI mice. HBeAg expression replenishment in HBeAg-deficient HBV HDI mice restored the HBV-induced LSEC maturation, and resulted in potent intrahepatic anti-HBV CD8 T cell responses and efficient control of HBV replication. Moreover, in vivo TNF-α, but not IL27 blockade in HBV HDI mice impaired HBV-specific CD8 T cell immunity and delayed HBV clearance.

Conclusion

Our study underlines that HBeAg is indispensable for HBV-induced LSEC maturation to trigger intrahepatic HBV-specific T cell activation, and provides a new mechanism to elucidate the intrahepatic immune microenvironment regulation upon HBV exposure.

Immunomodulatory Function of HBeAg Related to Short-Sighted Evolution, Transmissibility, and Clinical Manifestation of Hepatitis B Virus

Hepatitis B virus (HBV) infection, a global public health problem can be asymptomatic, acute or chronic and can lead to serious consequences of infection, including cirrhosis, and hepatocellular carcinoma. HBV, a partially double stranded DNA virus, belongs to the family Hepadnaviridae, and replicates via reverse transcription of an RNA intermediate. This reverse transcription is catalyzed by a virus-encoded polymerase that lacks proof reading ability, which leads to sequence heterogeneity. HBV is classified into nine genotypes and at least 35 subgenotypes, which may be characterized by distinct geographical distributions. This HBV diversification and distinct geographical distribution has been proposed to be the result of the co-expansion of HBV with modern humans, after their out-of-Africa migration. HBeAg is a non-particulate protein of HBV that has immunomodulatory properties as a tolerogen that allows the virus to establish HBV infection in vivo. During the natural course of infection, there is seroconversion from a HBeAg-positive phase to a HBeAg-negative, anti-HBe-positive phase. During this seroconversion, there is loss of tolerance to infection and immune escape-HBeAg-negative mutants can be selected in response to the host immune response. The different genotypes and, in some cases, subgenotypes develop different mutations that can affect HBeAg expression at the transcriptional, translational and post-translational levels. The ability to develop mutations, affecting HBeAg expression, can influence the length of the HBeAg-positive phase, which is important in determining both the mode of transmission and the clinical course of HBV infection. Thus, the different genotypes/subgenotypes have evolved in such a way that they exhibit different modes of transmission and clinical manifestation of infection. Loss of HBeAg may be a sign of short-sighted evolution because there is loss of tolerogenic ability of HBeAg and HBeAg-negative virions are less transmissible. Depending on their ability to lead to HBeAg seroconversion, the genotype/subgenotypes exhibit varying degrees of short-sighted evolution. The “arms race” between HBV and the immune response to HBeAg is multifaceted and its elucidation intricate, with transmissibility and persistence being important for the survival of the virus. We attempt to shed some light on this complex interplay between host and virus.

Prospects and progress of DNA vaccines for treating hepatitis B

The hepatitis B virus (HBV) is a global cause of liver disease. The preventive HBV vaccine has effectively reduced the disease burden. However, an estimated 340 million chronic HBV cases are in need of treatment. Current standard therapy for chronic HBV blocks reverse transcription. As this therapy blocks viral maturation and not viral protein expression, any immune inhibition exerted by these proteins will remain throughout therapy. This may help to explain why these drugs rarely induce off-therapy responses. Albeit some restoration of immune function occurs during therapy, this is clearly insufficient to control replication. Central questions when considering therapeutic DNA vaccination as an addition to blocking virus production are as follows: what does one hope to achieve? What do we think is wrong and how can the vaccination correct this? We here discuss different scenarios with respect to the lack of success of tested DNA vaccines, and suggest strategies for improvement.

Identification of HLA-A*0201-restricted CD8+ T-cell epitope C₆₄₋₇₂ from hepatitis B virus core protein

The efficacy of a potential therapeutic vaccine against chronic hepatitis B virus (HBV) infection depends on the development of strong and multi-specific T cell responses. The potency of CD8+ cytotoxic T lymphocyte (CTL) responses toward HBV core antigen (HBcAg) has been shown to be critical for the outcomes of HBV chronic infection. In this study we have identified a previously undescribed HLA-A*0201-restricted HBcAg-specific CTL epitope (HBcAg₆₄₋₇₂, C₆₄₋₇₂, ELMTLATWV). T2 binding assay showed that C₆₄₋₇₂ had high affinity to HLA-A*0201 molecule. Functionally, the peptide C₆₄₋₇₂ could induce peptide-specific CTLs both in vivo (HLA-A2.1/K(b) transgenic mice) and in vitro (PBLs of healthy HLA-A2.1+ donors), as demonstrated by interferon-γ (IFN-γ) secretion upon stimulation with C₆₄₋₇₂-pulsed T2 cells or autologous human dendritic cells (DCs) respectively. HLA-A*0201-C₆₄₋₇₂ tetramer staining revealed the presence of a significant population of C₆₄₋₇₂-specific CTLs in C₆₄₋₇₂-stimulated CD8+ T cells. Furthermore, the peptide-specific cytotoxic reactivity and the production of perforin and granzyme B of CTLs also increased after stimulation with C₆₄₋₇₂-pulsed autologous DCs. These results indicate that the newly identified epitope C₆₄₋₇₂ has potential to be used in the development of immunotherapeutic approaches to HBV infection.

HBcAg18-27 epitope fused to HIV-Tat 49-57 adjuvanted with CpG ODN induces immunotherapeutic effects in transgenic mice

Successful immunotherapy of chronic hepatitis B virus (HBV) infection is expected to be characterized by enhanced activation of immune responses. Combining the specificity of hepatitis B core antigen (HBcAg) cytotoxic T lymphocyte (CTL) epitope, the cell-penetrating property of human immunodeficiency virus-1 (HIV)-Tat peptide, and the adjuvanticity of CpG oligodeoxynucleotides (CpG ODNs) may elicit strong immune responses and therapeutic effects in HBV infection. We synthesized a fusion peptide containing HBcAg18-27 CTL epitope and HIV-Tat(49-57) peptide. The fusion peptide was intramuscularly injected to HBV transgenic mice with CpG ODN as adjuvant at 2-week intervals three times. The percentages of CD3(+), CD4(+) and CD8(+) cells in spleen lymphocytes and the levels of circulating interferon (IFN)-gamma and interleukin (IL)-2 were determined for the evaluation of immune responses and the levels of serum HBV DNA and the expression of hepatitis B surface antigen (HBsAg) and HBcAg in liver tissue were determined for the assessment of therapeutic effects. Our results showed that the synthesized fusion peptide adjuvanted with CpG ODN could induce significant increase of the percentages of CD3(+), CD4(+) and CD8(+) cells and the levels of IFN-gamma and IL-2, indicating the strong immune responses, and reduced HBV DNA levels and decreased expression of HBsAg and HBcAg in liver tissue, suggesting the therapeutic effects. Collectively, our study supports that HBcAg18-27 CTL epitope fused to HIV-Tat(49-57) peptide adjuvanted with CpG ODN may be a promising strategy for immunotherapy of chronic HBV infection.

Immunopathology of hepatitis B virus infection

The interaction between immune responses and hepatitis B virus (HBV) is coordinated between innate and adaptive immunity. Anti-HBs antibodies protect the host by blocking the binding ability of HBV. Anti-HBc antibodies are detected with persistent HBV infection. The presence of anti-HBe antibodies is often associated with recovery from active diseases and is clinically used as a benchmark to assess response to treatment. Our studies have revealed that the anti-HBV immunoglobulins secreted are different in subclass patterns in different HBV infection status populations. These revelations may help to understand HBV escape and persistent infection and to develop strategies for prevention and therapeutic management of HBV infection.

A mechanism to explain the selection of the hepatitis e antigen-negative mutant during chronic hepatitis B virus infection

Hepatitis B virus (HBV) expresses two structural forms of the nucleoprotein, the intracellular nucleocapsid (hepatitis core antigen [HBcAg]) and the secreted nonparticulate form (hepatitis e antigen [HBeAg]). The aim of this study was to evaluate the ability of HBcAg- and HBeAg-specific genetic immunogens to induce HBc/HBeAg-specific CD4(+)/CD8(+) T-cell immune responses and the potential to induce liver injury in HBV-transgenic (Tg) mice. Both the HBcAg- and HBeAg-specific plasmids primed comparable immune responses. Both CD4(+) and CD8(+) T cells were important for priming/effector functions of HBc/HBeAg-specific cytotoxic T-lymphocyte (CTL) responses. However, a unique two-step immunization protocol was necessary to elicit maximal CTL priming. Genetic vaccination did not prime CTLs in HBe- or HBc/HBeAg-dbl-Tg mice but elicited a weak CTL response in HBcAg-Tg mice. When HBc/HBeAg-specific CTLs were adoptively transferred into HBc-, HBe-, and HBc/HBeAg-dbl-Tg mice, the durations of the liver injury and inflammation were significantly greater in HBeAg-Tg recipient mice than in HBcAg-Tg mice. Importantly, liver injury in HBc/HBeAg-dbl-Tg mice was similar to the injury observed in HBeAg-Tg mice. Loss of HBeAg synthesis commonly occurs during chronic HBV infection; however, the mechanism of selection of HBeAg-negative variants is unknown. The finding that hepatocytes expressing wild-type HBV (containing both HBcAg and HBeAg) are more susceptible to CTL-mediated clearance than hepatocytes expressing only HBcAg suggest that the HBeAg-negative variant may have a selective advantage over wild-type HBV within the livers of patients with chronic infection during an immune response and may represent a CTL escape mutant.

Phase I clinical trial in healthy adults of a nasal vaccine candidate containing recombinant hepatitis B surface and core antigens

BACKGROUND

The nasal vaccine candidate (NASVAC), comprising hepatitis B virus (HBV) surface (HBsAg) and core antigens (HBcAg), has been shown to be highly immunogenic in animal models.

METHODS

A phase I double-blinded, placebo-controlled randomized clinical trial was carried out in 19 healthy male adults with no serologic markers of immunity/infection to HBV. This study was aimed at exploring the safety and immunogenic profile of nasal co-administration of both HBV recombinant antigens. The trial was performed according to Good Clinical Practice guidelines. Participants ranged in age from 18 to 45 years and were randomly allocated to receive a mixture of 50 microg HBsAg and 50 microg HBcAg or 0.9% physiologic saline solution, as a placebo, via nasal spray in a five-dose schedule at 0, 7, 15, 30, and 60 days. A total volume of 0.5 ml was administered in two dosages of 125 microl per nostril. Adverse events were actively recorded 1 h, 6 h, 12 h, 24 h, 48 h, 72 h, 7 days and 30 days after each dose. Anti-HBs and anti-HBc titers were evaluated using corresponding ELISA kits at days 30 and 90.

RESULTS

The vaccine candidate was safe and well tolerated. Adverse reactions included sneezing (34.1%), rhinorrhea (12.2%), nasal stuffiness (9.8%), palate itching (9.8%), headache (9.8%), and general malaise (7.3%). These reactions were all self-limiting and mild in intensity. No severe or unexpected events were recorded during the trial. The vaccine elicited anti-HBc seroconversion in 100% of subjects as early as day 30 of the immunization schedule, while a seroprotective anti-HBs titer (>or=10 IU/l) was at a maximum at day 90 (75%). All subjects in the placebo group remained seronegative during the trial.

CONCLUSION

The HBsAg-HBcAg vaccine candidate was safe, well tolerated and immunogenic in this phase I study in healthy adults. To our knowledge, this is the first demonstration of safety and immunogenicity for a nasal vaccine candidate comprising HBV antigens.

Immune responses to recombinant Mycobacterium smegmatis expressing fused core protein and preS1 peptide of hepatitis B virus in mice

Attenuated strains of bacteria have been developed as potential live vectors to express homologous or heterologous antigens of many pathogens for inducing protective immune responses. The non-pathogenic and rapidly growing Mycobacterium smegmatis can be transformed effectively by genes for pathogenic antigens, and has been used as a valuable vector for the development of live vaccines. However, little is known on whether M. smegmatis could be transformed with the genes for HBV antigens and could express those genes, and whether vaccination with recombinant M. smegmatis could induce humoral and cellular immune responses in vivo. Both the core protein and preS1 peptide of the hepatitis B virus (HBV) are immunogenic and can induce cellular and humoral immune responses. This made them ideal platform for the development of new vaccines. In the present study, both recombinant M. smegmatis and DNA vaccines were generated to express the CS1 antigen, a fusion protein that comprises truncated core protein (amino acids 1-155) and preS1 peptide (amino acids 1-55) of HBV. Following vaccination of BALB/c mice with the live recombinant M. smegmatis, the CS1-based DNA vaccine, or controls, antigen-specific humoral and cellular immune responses were characterized. Vaccination with live recombinant M. smegmatis induced a stronger cellular immune response and a longer period of humoral immune response than with the DNA vaccination. These results indicate that the recombinant M. smegmatis can express efficiently immunogenic CS1 antigen of HBV in vivo, and may be used for the prevention of HBV infection.

Statistical evaluation for detection of peptide specific interferon-gamma secreting T-cells induced by HIV vaccine determined by ELISPOT assay

Interferon-gamma (IFN-gamma) secreting T-cells play an important role in immunodeficiency virus (HIV) disease pathogenesis. A common technique to determine the efficacy of the HIV vaccines in murine models is to compare the number of IFN-gamma secreting T-cells induced by HIV vaccine to a control group. The measurement of IFN-gamma secreting T-cells relies on an ELISPOT assay. This assay is carried out in triplicate wells from the same mouse on the same ELISPOT plate. The numbers of spot forming cells (SFC) from these wells are correlated counts. Traditionally, simple statistical methods, such as ANOVA or Kruskall-Wallis tests, are performed on means by mouse. These approaches ignore the fact that the data are correlated counts. Count data are usually assumed to follow the Poisson distribution. However, some count data exhibit overdispersion that can affect the test statistics. The negative binomial distribution is an alternative to the Poisson distribution in the presence of overdispersion. Hence, negative binomial regression is a more suitable approach for overdispersed count data. In this study, we used a negative binomial regression to determine that IL-12 was a good adjuvant. The results of the study using a negative binomial regression are discussed.

Immune Tolerance Split between Hepatitis B Virus Precore and Core Proteins

The function of the hepatitis B virus (HBV) precore or HBeAg is largely unknown because it is not required for viral assembly, infection, or replication. However, the HBeAg does appear to play a role in viral persistence. It has been suggested that the HBeAg may promote HBV chronicity by functioning as an immunoregulatory protein. As a model of chronic HBeAg exposure and to examine the tolerogenic potential of the HBV precore and core (HBcAg) proteins, HBc/HBeAg-transgenic (Tg) mice crossed with T cell receptor (TCR)-Tg mice expressing receptors for the HBc/HBeAgs (i.e., TCR-antigen double-Tg pairs) were produced. This study revealed three phenotypes of HBe/HBcAg-specific T-cell tolerance: (i) profound T-cell tolerance most likely mediated by clonal deletion, (ii) T-cell clonal ignorance, and (iii) nondeletional T-cell tolerance mediated by clonal anergy and dependent on the structure, location, and concentration of the tolerogen. The secreted HBeAg is significantly more efficient than the intracellular HBcAg at eliciting T-cell tolerance. The split T-cell tolerance between the HBeAg and the HBcAg and the clonal heterogeneity of HBc/HBeAg-specific T-cell tolerance may have significant implications for natural HBV infection and especially for precore-negative chronic hepatitis.

Hemagglutinating virus of Japan protein is efficient for induction of CD4+ T-cell response by a hepatitis B core particle-based HIV vaccine

By using the hepatitis B core (HBc) protein gene as a carrier, HIV-1 env V3 gene was inserted into the carrier gene, and the HIV gene was expressed inside a chimeric HIV-HBc particle (HIV-HBc), which was a unique candidate for induction of HIV-specific CTL activity. This was seen significantly in mice without the need of an adjuvant, because other responses specific for the HIV peptide such as T-cell proliferation and antibody production were not induced. However, when hemagglutinating virus of Japan (HVJ) protein was incorporated into an anionic liposome containing HIV peptide (HIV-HVJ-liposome) and was used as a booster immunization in HIV-HBc primed animals, the HIV-specific T-cell response and enhanced CTL activity were clearly induced in consecutively immunized animals. Furthermore, the HIV-specific humoral immune response was also induced and a neutralization activity was detected in the immune sera. Thus, when an HIV peptide antigen is expressed inside the virus like a particle of HBc, it can induce both cellular and humoral immunities when an HVJ-HIV-liposome, but not an HIV-liposome, is inoculated as the booster antigen. The HVJ-stimulated splenocytes secreted IL-18 and IL-12 to synergistically enhance the secretion of IFN-gamma in vitro. These findings suggest that the HVJ protein is effective at inducing the HIV-specific immunities, if used as part of a booster antigen in the consecutive immunization regimen.

Recombinant hepatitis B core antigen carrying preS1 epitopes induce immune response against chronic HBV infection

Many studies have provided evidence that core antigen of hepatitis B virus (HBcAg) is extremely immunogenic, HBcAg can be function as both a T-cell-dependent antigen and a T-cell-independent antigen, and thus may be a promising candidate for therapeutic vaccine for control of chronic HBV infection. HBcAg is also an effective carrier for heterologous peptide epitopes. The preS1 is a surface protein of HBV and is immunogenic at the T and B cell level. The amino acid sequence 21-47 of preS1 is crucial for HBV binding to human hepatocytes as well as to PBMC and haematopoietic cell lines of the B cell lineage. Here we expressed a chimeric protein named HBVCS1, created by fusing the preS1 sequence 3-55 to the carboxyl terminus of the truncated HBcAg sequence 1-155 in E. coli. Analysis of its antigenicity and immunogenicity revealed that both HBc and preS1 epitopes are surface accessible, and that fusion of preS1 did not affect the HBc antigenicity and immunogenicity of the truncated HBc sequence. HBVCS1 induced strong anti-HBc and moderate anti-preS1 immune responses as well specific T-cell response in Balb/c mice. HBVCS1 vaccination reduced of the titer of HBsAg and HBV DNA in sera of HBV-Tg mice. These results indicate that HBVCS1 may have potential as a therapeutic vaccine for treatment of HBV chronic infection.

Exploring the biological basis of hepatitis B e antigen in hepatitis B virus infection

The function of the hepatitis B e antigen (HBeAg) is largely unknown because it is not required for viral assembly, replication, or infection. In this report we chronicle clinical and experimental studies in an attempt to understand the role of HBeAg in natural infection. These studies largely have focused on clinical-pathologic features of HBeAg-negative variants in acute and chronic HBV infection, mutational analysis in animal models of hepadnavirus infection, and the use of transgenic murine models. The clinical and experimental data suggest that serum HBeAg may serve an immunoregulatory role in natural infection. To the contrary, cytosolic HBeAg serves as a target for the inflammatory immune response. These dual roles of the HBeAg and its ability to activate or tolerize T cells show the complexity of the interactions between the HBeAg and the host during HBV infection.

Decreased ratio of CD4/CD8 lymphocytes might be predictive for successful interferon alpha and lamivudine combined therapy in childhood chronic hepatitis B infection: A preliminary study

BACKGROUND

In the development of chronic hepatitis with hepatitis B virus infection and in response to therapy, the immune status of the infected host plays a critical role. In this study, immunological variables were assessed in patients before interferon alpha and lamivudine therapy to determine if any pretreatment immunological parameter could be an indicator of response to therapy in childhood chronic hepatitis B infection.

METHODS

Forty-four patients with chronic hepatitis B virus infection, aged 9.0 +/- 3.9 years, were enrolled in the study. The pretreatment clinical features, biochemical test results, histological activity indexes and immunological parameters were evaluated. All patients received interferon alpha for 6 months and lamivudine for 52 weeks. Four patients who could not be followed up were excluded from the study. The other 40 patients have been followed for a mean period of 27.5 +/- 9.7 months after therapy discontinuation.

RESULTS

Seventeen patients showed loss of hepatitis B early antigen (HBeAg) with appearance of anti-HBe (42.5%) and six of those who responded also showed loss of hepatitis B surface antigen (HBsAg) with the presence of anti-HBs (15%). Except elevated aspartate aminotransferase levels, there was no significantly correlation between response and sex, age, pretreatment duration of disease and histological activity indexes. Pretreatment immunoglobulins (Ig), IgG subclasses, complement C3, C4 and secretory IgA levels were also not found to be significantly related to response. The evaluation of lymphocyte subsets showed that therapy responders had significantly reduced pretreatment ratios of CD4/CD8+ lymphocytes due to prominent increased percentages of CD8+ cells. The other cellular immunity parameters and some cell surface adhesion molecules were similar in both groups.

CONCLUSION

This study emphasizes the importance of increased pretreatment CD8+ lymphocyte percentages leading to a significant decrease in CD4/CD8 ratio in chronic hepatitis B virus infection of childhood as an immunological factor predicting response to treatment.

Cytotoxic immune response after retroviral-mediated hepatic gene transfer in rat does not preclude expression from adeno-associated virus 1 transduced muscles

Intravenous delivery of nls-lacZ retroviral vectors to the regenerating liver triggers a cytotoxic immune response directed against transduced hepatocytes. We sought to determine whether prior immunization with retroviral vectors impacted on adeno-associated virus (AAV)-mediated muscular expression of the same transgene. The first group of rats first received nls-lacZ retroviral vectors intravenously after a partial hepatectomy. Thirty days later they received AAV vectors intramuscularly in both legs. In the second group, animals received the same vectors in the opposite sequence (i.e., AAV first and retroviruses 20 days later). In the first group, immune response occurred after retrovirus delivery with appearance of anti-beta-galactosidase antibodies and elimination of transduced hepatocytes. However, the immune response did not prevent sustained (9-month) beta-galactosidase expression in AAV-injected muscles. In the second group, AAV injections did not induce immune response and resulted in beta-galactosidase expression in myofibers. In this group, subsequent delivery of retroviral vectors triggered appearance of immune response and elimination of transduced hepatocytes. However, the immune response did not modify beta-galactosidase expression in AAV-transduced myofibers for up to 9 months. These results demonstrate a differential susceptibility between retrovirally transduced liver and AAV-transduced muscles to immune response against the transgene product.

DNA-based immunotherapy: potential for treatment of chronic viral hepatitis?

Persistent HBV and HCV infection represent major causes of chronic liver disease with a high risk of progression to liver cirrhosis and hepatocellular carcinoma (HCC). Conventional protein-based vaccines are highly efficacious in preventing HBV infection; whereas in therapeutic settings with chronically infected patients, results have been disappointing. Prophylactic vaccination against HCV infection has not yet been achieved due to many impediments including frequent spontaneous mutations of the virus with escape from immune system control. Using animal models it has been demonstrated that DNA-based immunisation strategies may overcome this problem because of their potential to induce immunity against multiple viral epitopes. DNA-based vaccines mimic the effect of live attenuated viral vaccines, eliciting cell mediated immunity in addition to inducing humoral responses. Efficacy may further be improved by addition of DNA encoding immunomodulatory cytokines and more recently, direct genetic modulation of antigen-presenting cells, such as dendritic cells (DC), has been shown to increase antigen-specific immune responses. This review focuses on immunological aspects of chronic HBV and HCV infection and on the potential of DNA- and DC-based vaccines for the treatment of chronic viral hepatitis.

Cytotoxic immune response blunts long-term transgene expression after efficient retroviral-mediated hepatic gene transfer in rat

Vectors derived from oncoretroviruses can transduce a small proportion of hepatocytes when injected in the regenerating liver. Transgene expression may be sustained for months without immune response. In striking contrast, we observed a rapid extinction when the intravenous injection of a high input of nuclear beta-galactosidase (beta-gal) expression vector, one day after partial hepatectomy, led to a significant proportion of transduced cells in the liver. Extinction was associated with liver inflammation on tissue sections and appearance of antibodies against the transgene product, while vector genomes became undetectable in liver tissue by PCR. These observations suggested the elimination of transduced cells by an immune response. Transgenic rats tolerant for cytoplasmic beta-gal, or normal rats depleted in CD8 T lymphocytes, steadily expressed the beta-gal vector. In the spleen of normal rats, we detected cytotoxic cells directed against cells expressing beta-gal after the injection of the beta-gal vector. In jaundiced Gunn rats deficient in bilirubin glucuronosyl transferase (BGT1) and treated with a human BGT1 cDNA expression vector, we observed the same kinetics of extinction as well as the appearance of anti-BGT1 antibodies. This study demonstrates that retrovirus-mediated gene transfer may induce cytotoxic T lymphocytes specifically directed against transgene-expressing cells.

Anti-HBc IgG subclasses in different populations by comparing a variety of ELISA plates

The number of IgG subclasses for hepatitis B virus (HBV) core antigen (anti-HBc), demonstrated for HBV-infected individuals, was measured by enzyme-linked immunosorbent assay (ELISA). Four commercially available hepatitis B core antigen (HBcAg) plates and one prepared plate were tested for ELISA sensitivity by the detection of 14 serum samples drawn from HBV chronic carriers, cured patients, vaccinees, and non-infected individuals. Differences in optical density (OD) values were obtained by comparing data gathered from the five plate types, suggesting that different plates may have different binding capabilities for each anti-HBc IgG subclass and, thus, contribute to the different ELISA sensitivities. Of these plates, the GB plate showed the most obvious absorbance changes for anti-HBc subclasses in different populations. These data also indicated different patterns for IgG-specific subclasses for various populations. For HBsAg+ carriers, the OD for IgG1 was greater than for IgG3. By contrast, the OD for IgG3 was higher than that for IgG1 in those subjects who were negative for HBsAg.

Molecular basis for the interaction of the hepatitis B virus core antigen with the surface immunoglobulin receptor on naive B cells

The nucleocapsid of the hepatitis B virus (HBV) is composed of 180 to 240 copies of the HBV core (HBc) protein. HBc antigen (HBcAg) capsids are extremely immunogenic and can activate naive B cells by cross-linking their surface receptors. The molecular basis for the interaction between HBcAg and naive B cells is not known. The functionality of this activation was evidenced in that low concentrations of HBcAg, but not the nonparticulate homologue HBV envelope antigen (HBeAg), could prime naive B cells to produce anti-HBc in vitro with splenocytes from HBcAg- and HBeAg-specific T-cell receptor transgenic mice. The frequency of these HBcAg-binding B cells was estimated by both hybridoma techniques and flow cytometry (B7-2 induction and direct HBcAg binding) to be approximately 4 to 8% of the B cells in a naive spleen. Cloning and sequence analysis of the immunoglobulin heavy- and light-chain variable (VH and VL) domains of seven primary HBcAg-binding hybridomas revealed that six (86%) were related to the murine and human VH1 germ line gene families and one was related to the murine VH3 family. By using synthetic peptides spanning three VH1 sequences, one VH3 sequence, and one VLkappaV sequence, a linear motif in the framework region 1 (FR1)complementarity-determining region 1 (CDR1) junction of the VH1 sequence was identified that bound HBcAg. Interestingly, the HBcAg-binding motif was present in the VL domain of the HBcAg-binding VH3-encoded antibody. Finally, two monoclonal antibodies containing linear HBcAg-binding motifs blocked HBcAg presentation by purified naive B cells to purified HBcAg-primed CD4(+) T cells. Thus, the ability of HBcAg to bind and activate a high frequency of naive B cells seems to be mediated through a linear motif present in the FR1-CDR1 junction of the heavy or light chain of the B-cell surface receptor.

Humoral and CD4(+) T helper (Th) cell responses to the hepatitis C virus non-structural 3 (NS3) protein: NS3 primes Th1-like responses more effectively as a DNA-based immunogen than as a recombinant protein

The non-structural 3 (NS3) protein is one of the most conserved proteins of hepatitis C virus, and T helper 1 (Th1)-like responses to NS3 in humans correlate with clearance of infection. Several studies have proposed that DNA-based immunizations are highly immunogenic and prime Th1-like responses, although few head-to-head comparisons with exogenous protein immunizations have been described. A full-length NS3/NS4A gene was cloned in eukaryotic vectors with expression directed to different subcellular compartments. Inbred mice were immunized twice in regenerating tibialis anterior (TA) muscles with either plasmid DNA or recombinant NS3 (rNS3). After two 100 micrograms DNA immunizations, specific antibody titres of up to 12960 were detected at week 5, dominated by IgG2a and IgG2b. NS3-specific CD4(+) T cell responses in DNA-immunized mice peaked at day 13, as measured by proliferation and IL-2 and IFN-gamma production. Mice immunized with 1-10 micrograms rNS3 without adjuvant developed antibody titres comparable to those of the DNA-immunized mice, but dominated instead by IgG1. CD4(+) T cell responses in these mice showed peaks of IL-2 response at day 3 and IL-6 and IFN-gamma responses at day 6. With adjuvant, rNS3 was around 10-fold more immunogenic with respect to speed and magnitude of the immune responses. Thus, immunization with rNS3 in adjuvant is superior to DNA immunization with respect to kinetics and quantity in priming specific antibodies and CD4(+) T cells. However, as a DNA immunogen, NS3 elicits stronger Th1-like immune responses, whereas rNS3 primes a mixed Th1/Th2-like response regardless of the route, dose or adjuvant.

ELISPOT assay for detection of peptide specific interferon-gamma secreting cells in rhesus macaques

A reliable procedure to measure antigen specific T cell responses in rhesus macaques is required to determine the efficacy of vaccines and immunotherapies. The currently available T cell assays are poorly quantifiable or technically difficult to perform. Classical 51Cr-release cytotoxic T cell (CTL) assays are cumbersome and difficult to quantitate reproducibly. Detection of specific T-cell using MHC-peptide tetrameric complexes is highly sensitive, but requires knowledge of MHC type and prior identification of T cell epitopes. We therefore developed a rhesus interferon-gamma (IFN-gamma) ELISPOT assay capable of detecting IFN-gamma secretion in response to stimulation with pooled 20-mer peptides. Peripheral blood mononuclear cells (PBMCs) from rhesus monkeys immunized with a DNA vaccine and recombinant canary pox encoding the Plasmodium knowlesi circumsporozoite protein (PkCSP) were incubated with pools of peptides from PkCSP. Positive responses to peptide pools and individual peptides ranging from 100 to 450 spot forming cells (SFC)/10(6) PBMC were detected in four of four immunized monkeys and in zero of two control monkeys. In two monkeys studied in detail, the IFN-gamma response was focussed on a single 20-mer peptide, QGDGANAGQPQAQGDGANAG, and was dependent on CD4(+), but not CD8(+), T cells. Background responses in control monkeys and preimmunization PBMCs ranged from 10 to 50 SFC/10(6) PBMC. The average within assay and between assay coefficients of variation (CV) for this peptide ELISPOT were 21.9 and 24.7%, respectively. This peptide IFN-gamma assay will be a useful tool for evaluation of T cell responses in rhesus macaques.

Cytotoxic T cell responses against hepatitis B virus polymerase induced by genetic immunization

BACKGROUND/AIMS

Individuals with chronic hepatitis B may benefit from genetic (DNA-based) immunization through induction of viral clearance by enhancement of suboptimal cellular immune responses. While marked cellular immune responses to hepatitis B virus (HBV) nucleocapsid and envelope proteins occur after genetic immunization in mice, it is unknown whether genetic immunization is capable of eliciting such responses to HBV polymerase. We wished to develop assays for the determination of HBV polymerase specific immune responses in mice and investigate whether genetic immunization may elicit humoral and cellular immune responses to HBV polymerase.

METHODS

BALB/c (H-2d) mice were injected with a DNA expression construct for HBV polymerase. Humoral immune responses to HBV polymerase were analyzed with a newly established ELISA. Cellular immune responses were determined using recombinant vaccinia virus infected target cells expressing HBV polymerase at high levels.

RESULTS

Assays for the detection of HBV polymerase-specific immune responses were developed. Immunized animals exhibited substantial polymerase-specific cytotoxic T lymphocyte responses. However, no humoral immune responses to HBV polymerase were detectable.

CONCLUSIONS

Our study demonstrates that DNA-based immunization will generate substantial CTL responses to HBV polymerase and may be an important component of an immunotherapeutic strategy to combat chronic HBV infection.

Induction of vigorous helper and cytotoxic T cell as well as B cell responses by dendritic cells expressing a modified antigen targeting receptor-mediated internalization pathway

Efficient Ag presentation is essential to induce effective cellular and humoral immune responses. Thus, one central goal of current immunotherapy and vaccine development is to enhance Ag presentation to induce potent and broad immune responses. Here, a novel Ag presentation strategy is developed by transducing dendritic cells (DCs) to produce an Ag for presentation as an exogenous Ag to efficiently induce both humoral and cellular immunity. The principle of this strategy is illustrated by genetically modifying DCs to secrete a model hepatitis B virus Ag fused with a cell-binding domain and to process the fusion Ag as an exogenous Ag after receptor-mediated internalization for MHC class I and II presentation. Vigorous Ag-specific CD4(+) helper and CD8(+) cytotoxic T cell, as well as B cell, responses were induced by the transduced DCs in mouse models. Thus, this novel strategy uses a receptor-mediated internalization process to efficiently induce all arms of the adaptive immunity and may provide a powerful means to develop potent vaccines and immunotherapies.

Emergence of the precore mutant late in chronic hepatitis B infection correlates with the severity of liver injury and mutations in the core region

OBJECTIVE

The reason that precore negative mutants (e-minus DNA) gradually become predominant in some patients during chronic hepatitis B virus infection is not clear. Theoretically, as long as both e-plus and e-minus DNA share the same epitopes in the core region, HBcAg-specific cytotoxic T lymphocytes (CTLs) cannot distinguish between the target peptides expressed by e-plus and e-minus DNA. Therefore, e-minus DNA may be accompanied by additional mutations in the core region, which may affect cytotoxic T lymphocyte recognition. To examine this possibility, the sequences of the precore and the entire core region of the hepatitis B virus genome were analyzed from paired serum samples in CH-B patients who experienced HBeAg to anti-HBe seroconversion (SC).

METHODS

Patients were divided into two groups. Group A patients (n = 17) genome-converted to e-minus DNA in the precore region, which abolished HBeAg secretion within 3-4 yr after SC. Group B patients (n = 16) retained precore wild-type DNA for more than 3-4 yr after SC. To investigate the impact of the emergence of precore mutant type DNA on liver injury, alanine aminotransferase (ALT) levels were also examined.

RESULTS

ALT flares were more severe among patients in group A than in group B. The average mean ALT level during the HBeAg negative phase of chronic infection was 54 +/- 38 in group A and 28 +/- 24 in group B. The average maximal ALT level during the HBeAg negative phase was 235 +/- 249 in group A and 83 +/- 106 in group B. Furthermore, all 17 patients in group A developed new core mutants during genome conversion. The average number of mutations in the core gene was 0.9 +/- 1.2 before genome conversion (e-plus DNA dominant phase) and increased to 2.8 +/- 1.3 for the 3-4 yr during genome conversion (e-minus DNA dominant phase). In contrast, only 56% (nine of 16) of patients in group B developed new core mutations after the loss of HBeAg. The average number of mutations in the core gene was 1.8 +/- 1.3 before SC (HBeAg-positive and e-plus DNA dominant phase), and decreased to 1.1 +/- 1.1 for 3-4 yr after seroconversion (anti-HBe-positive and e-plus DNA dominant phase).

CONCLUSIONS

These data indicate that the emergence of a predominant precore negative genotype late in chronic hepatitis B virus infection is associated with the selection of additional mutations in the core gene, as well as with liver injury.

H-2(d) mice born to and reared by HBeAg-transgenic mothers do not develop T cell tolerance toward the hepatitis B virus core gene products

The function of the secretory core gene product (HBeAg) of the human hepatitis B virus (HBV) is unknown. It has been proposed that this protein may be passed from the mother to her offspring at the perinatal stage where it might induce immune tolerance. In a previous study we have shown that the murine placenta presents an efficient barrier for the HBe protein and that H-2(b) mice born to HBeAg-positive transgenic mothers do not develop tolerance of specific cytotoxic T cells. In the present work we demonstrate that transgenic mice expressing high serum levels of HBeAg secrete only small amounts of this protein into their milk and excrete minute amounts of the viral gene product in their urine. Furthermore, it is shown that nontransgenic H-2(d) mice born to and reared by HBeAg-positive mothers exhibit a reactivity of HBc/eAg-specific CD4(+) Th cells and CD8(+) cytotoxic T cells comparable to that of normal isogenic control mice. In accordance with this observation the humoral immune responses directed against the HBeAg were comparable between these two groups of animals. This finding indicates that H-2(d) mice potentially exposed to small amounts of maternal HBeAg transferred by the transplacental, lactogenic, or renal route do not develop tolerance toward the HBV core gene products. These data challenge the hypothesis that a potential function of the HBeAg may be to operate as a tolerogen at the perinatal developmental stage.

In vivo retrovirus-mediated gene transfer to the liver of dogs results in transient expression and induction of a cytotoxic immune response

Gene transfer in regenerating dog liver using high-titer recombinant retroviral vectors carrying the E. coli beta-galactosidase gene was studied. Supernatants containing amphotropic or gibbon ape pseudotyped recombinant retroviruses were infused into a peripheral vein in beagle dogs after partial hepatectomy. The kinetics of liver regeneration were determined in the animals and daily infusions were carried out for 4 or 5 days during the regeneration period. Up to 2.8% of hepatocytes were beta-galactosidase positive at the end of the procedure. However, the number of positive cells declined rapidly and few positive hepatocytes were detected after 3 weeks. PCR demonstrated the disappearance of the provirus. Histologically, inflammatory lesions were observed in the transduced livers. Finally, we demonstrated the presence of a cytotoxic T lymphocyte immune response directed against beta-galactosidase-expressing cells, which could explain the disappearance of the transgene. This work suggests that the efficiency of in vivo gene delivery using high-titer retroviral vectors directly infused into the circulation may be hampered by a cytotoxic immune response against the infected cells.

Stable alphavirus packaging cell lines for Sindbis virus and Semliki Forest virus-derived vectors

Alphavirus vectors are being developed for possible human vaccine and gene therapy applications. We have sought to advance this field by devising DNA-based vectors and approaches for the production of recombinant vector particles. In this work, we generated a panel of alphavirus vector packaging cell lines (PCLs). These cell lines were stably transformed with expression cassettes that constitutively produced RNA transcripts encoding the Sindbis virus structural proteins under the regulation of their native subgenomic RNA promoter. As such, translation of the structural proteins was highly inducible and was detected only after synthesis of an authentic subgenomic mRNA by the vector-encoded replicase proteins. Efficient production of biologically active vector particles occurred after introduction of Sindbis virus vectors into the PCLs. In one configuration, the capsid and envelope glycoproteins were separated into distinct cassettes, resulting in vector packaging levels of 10(7) infectious units/ml, but reducing the generation of contaminating replication-competent virus below the limit of detection. Vector particle seed stocks could be amplified after low multiplicity of infection of PCLs, again without generating replication-competent virus, suggesting utility for production of large-scale vector preparations. Furthermore, both Sindbis virus-based and Semliki Forest virus-based vectors could be packaged with similar efficiency, indicating the possibility of developing a single PCL for use with multiple alphavirus-derived vectors.

Behavior of a short preS1 epitope on the surface of hepatitis B core particles

The major immunodominant region of hepatitis B core particles is widely recognized as the most prospective target for the insertion of foreign epitopes, ensuring their maximal antigenicity and immunogenicity. This region was mapped around amino acid residues 79-81, which were shown by electron cryo-microscopy to be located on the tips of the spikes protruding from the surface of hepatitis B core shells. Here we tried to expose a model sequence, the short immunodominant hepatitis B preS1 epitope 31-DPAFR-35, onto the tip of the spike, with simultaneous deletion of varying stretches from the major immunodominant region of the HBc molecule. Accessibility to the monoclonal anti-preS1 antibody MA18/7 and specific immunogenicity of the preS1 epitope depended on the location and length of the deletion. While chimeras with deletions within the stretch 79-88 presented the preS1 epitope on their surface and demonstrated remarkable preS1 immunogenicity, the corresponding chimeras without any deletion or with a more prolonged deletion (79-93) were unable to provide such presentation and possessed a lower specific preS1 immunogenicity. Deletion of the stretch 79-81 was sufficient to avoid the intrinsic HBc immunogenicity of the core particles, although chimeras with deleted major immunodominant region retained their property to be recognized by human polyclonal or hyperimmune anti-HBc antibodies.

Hepatitis B core particles as a universal display model: a structure-function basis for development

Because it exhibits a remarkable capability to accept mutational intervention and undergo correct folding and self-assembly in all viable prokaryotic and eukaryotic expression systems, hepatitis B core (HBc) protein has been favored over other proposed particulate carriers. Structurally, the unusual alpha-helical organization of HBc dimeric units allows introduction of foreign peptide sequences into several areas of HBc shells, including their most protruding spikes. Progress toward full resolution of the spatial structure as well as accumulation of chimeric HBc-based structures has brought closer the knowledge-based design of future vaccines, gene therapy tools and other artificial particulate objects.

The hepatitis B virus e antigen cannot pass the murine placenta efficiently and does not induce CTL immune tolerance in H-2b mice in utero

The function of the secretory core gene product (HBeAg) of the human hepatitis B virus is unclear. It has been discussed that this protein may be passed from the mother to the fetus, where it might induce immunologic tolerance. Here we have examined this possibility with transgenic mice expressing high levels of HBeAg. Analysis of serum samples obtained from nontransgenic fetuses which developed in HBeAg-positive mothers showed no evidence that the HBeAg can pass the placenta. Moreover, direct examination of the HBeAg- and HBcAg-specific cytotoxic T-cell immune response of H-2b mice which developed in either transgenic or nontransgenic mothers revealed no indication that mice which could have been exposed to the HBeAg in utero become tolerant to HBV core gene products. From these data we conclude that the placenta represents an efficient barrier for HBeAg transfer and that the HBeAg does not tolerize cytotoxic T cells, at least in mice of the H-2b haplotype.

Characterization of humoral and CD4+ cellular responses after genetic immunization with retroviral vectors expressing different forms of the hepatitis B virus core and e antigens

The humoral and CD4+ cellular immune responses in mice following genetic immunization with three retroviral vectors encoding different forms of hepatitis B virus core antigen (HBcAg) and e antigen (HBeAg) were analyzed. The retroviral vectors induced expression of intracellular HBcAg (HBc[3A4]), secreted HBeAg (HBe[5A2]), or an intracellular HBcAg-neomycin phosphoryltransferase fusion protein (HBc-NEO[6A3]). Specific antibody levels and immunoglobulin G isotype restriction were highly dependent on both the host major histocompatibility complex and the transferred gene. Humoral and CD4+ cellular HBcAg and/or HBeAg (HBc/eAg)-specific immune responses following retroviral vector immunization were of a lower magnitude but followed the same characteristics compared with those after immunization with HBc/eAg in adjuvant. Two factors influenced the humoral responses. First, in vivo depletion of CD8+ cells in HBc-NEO[6A3]-immunized H-2k mice abrogated both HBcAg-specific antibodies and in vitro-detectable cytotoxic T lymphocytes. Second, priming of H-2b mice with an HBc/eAg-derived T-helper (Th) peptide in adjuvant prior to retroviral vector immunization greatly enhanced the HBc/eAg-specific humoral responses to all three vectors, suggesting that insufficient HBc/eAg-specific CD4+ Th-cell priming limits the humoral responses. In conclusion, direct injection of retroviral vectors seems to be effective in priming HBc/eAg-specific CD8+ but comparatively inefficient in priming CD4+ Th cells and subsequently specific antibodies. However, the limited HBc/eAg-specific CD4+ cell priming can effectively be circumvented by prior administration of a recombinant or synthetic form of HBc/eAg in adjuvant.