Identification of immunodominant T cell epitopes of the hepatitis B virus nucleocapsid antigen

T cell epitope: friend or foe? Immunogenicity of biologics in context

Like vaccines, biologic proteins can be very immunogenic for reasons including route of administration, dose frequency and the underlying antigenicity of the therapeutic protein. Because the impact of immunogenicity can be quite severe, regulatory agencies are developing risk-based guidelines for immunogenicity screening. T cell epitopes are at the root of the immunogenicity issue. Through their presentation to T cells, they activate the process of anti-drug antibody development. Preclinical screening for T cell epitopes can be performed in silico, followed by in vitro and in vivo validation. Importantly, screening for immunogenicity is complicated by the discovery of regulatory T cell epitopes, which suggests that immunogenicity testing must now take regulatory T cells into consideration. In this review, we address the application of computational tools for preclinical immunogenicity assessment, the implication of the discovery of regulatory T cell epitopes, and experimental validation of those assessments.

Molecular characterization and functional analysis of occult hepatitis B virus infection in Chinese patients infected with genotype C

Occult HBV infection is defined as the persistence of HBV DNA in individuals negative for HBV surface antigen (HBsAg), and many different mechanisms have been reported in different countries. However, in China, one of the endemic areas for HBV infection, no reports have been published on occult HBV infection. The present study investigated the virological features and the mechanism of occult HBV infection in China. Full-length HBV DNA from eight patients with occult HBV infection (S1-S8) and three HBsAg-positive cases (SWT1-SWT3) was cloned and sequenced. Additionally, four entire linear HBV genomes from occult cases were transfected transiently into HepG2 cells. The sequencing results showed two major mutations in patients with occult HBV infection as follows: deletions in the pre-S1 (S3, S4, and S7) and X (S1, S2, and S5) regions. Such deletions covered the S promoter and the basal core promoter (BCP), and function analysis of these variants also showed a decrease in DNA replication and antigen expression. Two patients with occult infection (S6 and S8) had no mutations capable of interfering with viral replication and gene expression in the major viral population. Thus, the deletions in the S promoter and the BCP regions that disable the regulatory elements may be the reason for the absence of HBsAg, and multiple mechanisms may be responsible for occult HBV infection.

Primary occult hepadnavirus infection induces virus-specific T-cell and aberrant cytokine responses in the absence of antiviral antibody reactivity in the Woodchuck model of hepatitis B virus infection

Although the virological features of serologically silent hepadnaviral primary occult infection (POI) have been relatively well recognized in the woodchuck model of hepatitis B virus infection, the characteristics of accompanying immune responses remain unknown. In this study, the kinetics of woodchuck hepatitis virus (WHV)-specific and generalized (mitogen-induced) T-cell proliferative responses and cytokine expression profiles in circulating lymphoid cells and the liver, along with WHV-specific antibody responses, were investigated during experimentally induced POI and subsequent challenge with a liver-pathogenic dose (>10(3) virions) or liver-nonpathogenic dose (50 virions) of the same virus. The data revealed that POI, which does not prompt WHV surface antigenemia, antiviral antibody response, and hepatitis or protect from challenge with a liver-pathogenic virus dose, was accompanied by the appearance of a strong WHV-specific T-cell response directed against multiple viral epitopes that intermittently persisted at low levels for up to 10-months during follow-up. Furthermore, immediately after exposure to a liver-nonpathogenic dose of WHV, lymphocytes acquired a heightened capacity to proliferate in response to mitogenic stimuli and displayed augmented expression of alpha interferon, interleukin-12 (IL-12), and IL-2, but not tumor necrosis factor alpha. Overall, the kinetics of WHV-specific and mitogen-induced T-cell proliferative and cytokine responses in POI were closely comparable to those seen in infection induced by liver-pathogenic viral doses. The data demonstrated that virus-specific T-cell proliferative reactivity is a very sensitive indicator of exposure to hepadnavirus, even to small amounts inducing serologically mute infection. They also showed that hepadnaviral POI is not only a molecularly but also an immunologically identifiable and distinctive entity.

[Hepatitis B core antigen expression pattern predicts response to lamivudine therapy in patients with chronic hepatitis B]

BACKGROUNDS/AIMS

Negative hepatitis B core antigen (HBcAg) staining in hepatocytes is indicative of viral replication by an active immune response. HBcAg is expressed mainly in the cytoplasm in patients with active hepatitis and hepatocyte regeneration, and mainly in the nuclei of hepatocytes in patients with minimal liver injury in the absence of hepatocyte regeneration. The aim of this study was to elucidate whether the existence and expression pattern of HBcAg predicts the response to antiviral treatment.

METHODS

The study involved 58 patients with biopsy-proven chronic hepatitis B who were treated with lamivudine. Hepatitis B e antigen (HBeAg), antibody to HBeAg, hepatitis B virus DNA, and alanine aminotransferase in serum were recorded every 3 months. The inflammation grade and the fibrosis stage of chronic hepatitis were scored from 0 to 4 according to lobular inflammation, portal inflammation, periportal inflammation, and fibrosis.

RESULTS

The 58 patients included 49(84%) HBcAg-positive patients, with HBcAg staining confined to the cytoplasm in 15(31%) and in both cytoplasm and nuclei in 34(69%). The grade of lobular inflammation and the total histology score were significantly higher in patients with cytoplasmic expression of HBcAg than in HBcAg-negative patients (lobular inflammation: 2.9 vs 2.1, P=0.02; total histology score: 12.2 vs 10.3, P=0.04). The virologic responses at 3, 6, 9, and 12 months differed significantly between the cytoplasmic and mixed expression groups (P<0.01).

CONCLUSIONS

The expression pattern of HBcAg (including its possible absence) before initial therapy appears to predict the response to antiviral treatment.

Core mutations in patients with acute episodes of chronic HBV infection are associated with the emergence of new immune recognition sites and the development of high IgM anti-HBc index values

Acute exacerbations in HBeAg negative patients with chronic hepatitis B virus (HBV) infection are invariably associated with concurrent increases in the index of IgM class antibodies against the core protein (anti-HBc) of the virus. This study aimed to investigate whether this was related to the clearance of variants from the quasispecies pool and the appearance of new ones, with aminoacid substitutions in well recognized B-cell epitopes. In this study, 5 HBeAg negative patients (A to E) with 13 sequential serum samples (A1-A2, B1-B2-B3, C1-C2, D1-D2-D3, E1-E2-E3) were investigated after amplification of the entire core encoding region followed by cloning/sequencing studies. The sequences at different time points were compared with those from a single HBeAg positive patient with no apparent acute exacerbations. The results from sequence comparison showed that virus variants emerged in all (A2, B3, C2, D3, E2, and E3) but two (B2 and D2) subsequent sera with amino-acid substitutions affecting B-cell epitopes. It is concluded that the rise in the values of IgM anti-HBc may be attributed to the alteration of the antigenic epitopes leading to new antibody production in the majority of the cases. However, it appears that increases in IgM anti-HBc indexes in a few cases may relate to other possible mechanisms which are discussed.

Rational design of a multiepitope vaccine encoding T-lymphocyte epitopes for treatment of chronic hepatitis B virus infections

Protein sequences from multiple hepatitis B virus (HBV) isolates were analyzed for the presence of amino acid motifs characteristic of cytotoxic T-lymphocyte (CTL) and helper T-lymphocyte (HTL) epitopes with the goal of identifying conserved epitopes suitable for use in a therapeutic vaccine. Specifically, sequences bearing HLA-A1, -A2, -A3, -A24, -B7, and -DR supertype binding motifs were identified, synthesized as peptides, and tested for binding to soluble HLA. The immunogenicity of peptides that bound with moderate to high affinity subsequently was assessed using HLA transgenic mice (CTL) and HLA cross-reacting H-2(bxd) (BALB/c x C57BL/6J) mice (HTL). Through this process, 30 CTL and 16 HTL epitopes were selected as a set that would be the most useful for vaccine design, based on epitope conservation among HBV sequences and HLA-based predicted population coverage in diverse ethnic groups. A plasmid DNA-based vaccine encoding the epitopes as a single gene product, with each epitope separated by spacer residues to enhance appropriate epitope processing, was designed. Immunogenicity testing in mice demonstrated the induction of multiple CTL and HTL responses. Furthermore, as a complementary approach, mass spectrometry allowed the identification of correctly processed and major histocompatibility complex-presented epitopes from human cells transfected with the DNA plasmid. A heterologous prime-boost immunization with the plasmid DNA and a recombinant MVA gave further enhancement of the immune responses. Thus, a multiepitope therapeutic vaccine candidate capable of stimulating those cellular immune responses thought to be essential for controlling and clearing HBV infection was successfully designed and evaluated in vitro and in HLA transgenic mice.

T-regulatory lymphocytes and chronic viral hepatitis

Both hepatitis B virus (HBV) and hepatitis C virus (HCV) can cause persistent viral infection in humans. Chronic infection is associated with a risk of cirrhosis and hepatocellular carcinoma. The cause of chronic infection is unknown. A large body of evidence suggests that a failure of the adaptive immune response is critical in the establishment of chronic infection. Recently a new group of T cells (T-regulatory cells), that express CD4(+)CD25(+) and Foxp3, which can inhibit the cellular (CD4(+)/CD8(+)) immune response have been described. In this review the authors explore the thoughts regarding immune responses to HBV and HCV infections and the role of these T-regulatory cells in relation to the pathogenesis of chronic HBV and HCV infection and the potential for therapeutic intervention.

Five subgenotypes of hepatitis B virus genotype B with distinct geographic and virological characteristics

Several hepatitis B virus (HBV) subgenotypes, HBV/A1, A2, Bj and Ba, have been reported with respect to clinical differences among patients infected with these subgenotypes. The population genetics and phylogeography of HBV were investigated based on the complete genome sequences of 484 isolates with 108 from our chronic hepatitis B patients and the remaining from the GenBank database. Besides genotypes A-H (HBV/A-H), five subgenotypes were identified among 169 HBV/B isolates by phylogenetic analysis and nucleotide divergence. There were 27 isolates of subgenotype B(1) (HBV/B(1)) restricted to Japan, 104 isolates of HBV/B(2) with the widest distribution in most Asian countries, 4 isolates of HBV/B(3) restricted to Indonesia, 32 isolates of HBV/B(4) restricted to Vietnam, and 7 isolates of HBV/B(5) restricted to Philippines. HBV/B(2)-B(5) isolates carried a recombination with HBV/C over the precore and core genes. In addition to the characteristics of HBV/B(1)-B(5) at some cis-acting elements, the precore stop-codon mutant (G1896A) was significantly different among HBV/B(1), HBV/B(2), and HBV/B(4) (70.3%, 31.7%, 53.0%, P=0.001), while no such mutation was found in HBV/B(3) and B(5). Among characteristics of the HBV/B(1)-B(5) amino acid sequences, serotype adw (K(122)) was exclusive among HBV/B(1), HBV/B(2), and HB V/B(3) isolates, while serotype ayw (R(122)) was among the HBV/B(4) and HBV/B(5) isolates. Furthermore, distinct variations of T cell and B cell recognition epitopes within surface and core proteins were also found among these subgenotypes. In conclusion, subgenotypes HBV/B(1)-B(5) exhibited distinct geographical distributions, virologic characteristics, and probable clinical implications.

Vaccines and immunotherapies against hepatitis B and hepatitis C viruses

Both hepatitis B and hepatitis C viruses (HBV and HCV) cause chronic infections worldwide that are associated with development of liver diseases ranging from mild liver inflammation to hepatocellular carcinomas. While efficient preventive vaccines are available for HBV, efforts are ongoing to develop one in case of HCV. Yet, both infections share the fact that therapeutic agents available to treat already established infections are yet poorly efficient, toxic or associated with development of resistance. Thus, novel immune-based therapies are actively being developed to complement or replace standard antiviral treatments. Among those, development of therapeutic vaccines represents a major effort. Peptide-, recombinant protein- or viral vector-based vaccines have been engineered and tested at preclinical and clinical levels. Means to adjuvant these vaccines are being pursued, including approaches based on combining vaccines of different nature. This review will outline major advances in the field of both HBV and HCV therapeutic vaccine development with a particular focus on candidates presented at the 12th International Symposium on Viral Hepatitis and Liver Disease (July 2006, Paris, France).

Therapeutic vaccination of chronic hepatitis B patients with virus suppression by antiviral therapy: a randomized, controlled study of co-administration of HBsAg/AS02 candidate vaccine and lamivudine

Induction of curative immune responses by therapeutic vaccination in chronic viral infections such as chronic hepatitis B (CHB) is expected to be facilitated by reduction of viral load by antiviral treatment. In this open label, controlled, randomized study, 195 patients with HBeAg positive CHB were randomized to receive 12 doses of HBsAg with AS02B adjuvant candidate vaccine plus lamivudine daily for 52 weeks or lamivudine daily alone. The combined administration of vaccine and lamivudine was safe and well tolerated, but did not improve the HBe seroconversion rate (18.8%) when compared to treatment with lamivudine alone (16.1%) (p=0.6824). Despite induction of a vigorous HBsAg-specific lymphoproliferative response, cytokine production and anti-HBs antibodies, therapeutic vaccination with an adjuvanted HBsAg vaccine administered concomitantly with lamivudine did not demonstrate superior clinical efficacy in HBeAg positive CHB patients as compared to lamivudine therapy alone.

Identification of a novel hepatitis B virus precore/core deletion mutant in HIV/hepatitis B virus co-infected individuals

OBJECTIVES

Although HAART has resulted in improved health outcomes for most HIV-infected individuals, liver failure has emerged as a major cause of morbidity and mortality in people co-infected with hepatitis B virus (HBV). In HBV mono-infected individuals, core deletion mutants are associated with more aggressive liver disease. As HIV accelerates HBV liver disease progression, we hypothesized that HIV-HBV co-infected individuals have increased frequency of core mutations including deletions. To test this hypothesis, we have analysed genome-length sequences of HBV DNA from patients both prior to and during antiviral therapy.

SETTING

Prospective HIV/HBV co-infected cohort study.

METHODS

Genomic length HBV DNA was amplified by PCR from the serum samples of ten HIV/HBV co-infected individuals and five HBV mono-infected individuals prior to the commencement of lamivudine therapy and again after nine to 74 months of treatment. The complete genomes were sequenced and in order to further analyse some mutations, their frequency was determined in additional HIV/HBV co-infected and HBV mono-infected individuals.

RESULTS

A novel -1G mutation was identified in the HBV precore and overlapping core genes that truncated the deduced precore/core proteins. The mutant genome was the dominant species in some HIV/HBV co-infected individuals and was more prevalent in HIV/HBV co-infected individuals than HBV mono-infected individuals. The mutation was also associated with high HBV DNA concentrations in HIV/HBV co-infected individuals. Additional mutations were identified in the core/precore and polymerase genes and regulatory regions.

CONCLUSION

Mutations in the HBV core and precore genes may be contributing to disease pathogenesis in HIV/HBV co-infected individuals.

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.

Analysis of the core gene of hepatitis B virus in Korean patients

BACKGROUND/AIMS

As the core gene of hepatitis B virus (HBV) is a major immunological target, its mutation may evoke or evade immune clearance. We investigated the frequency and location of HBV core gene substitutions according to hepatitis B e antigen (HBeAg) status and viral replication status, and evaluated the association of these substitutions with the different stages of chronic HBV infection in Korean patients.

METHODS

The study population included 45 HBeAg-positive/DNA-positive patients (group I), 49 HBeAg-negative/DNA-positive patients (II) and 50 HBeAg-negative/DNA-negative patients (III). The HBV core gene was analysed by polymerase chain reaction (PCR) and sequencing.

RESULTS

The frequency of core gene substitutions increased from group I to group III. Substitutions were commonly detected at codons 87, 97, 112 and 130. The frequency of substitutions at codons 87 and 112 was higher in groups II/III than in group I. The frequency of the codon I97F substitutions was the highest in group III. However, the codon 130 substitution was more frequently found in groups I/II than in group III.

CONCLUSION

Core gene substitutions were more frequently detected in HBeAg-negative and/or HBV DNA-negative patients. The substitutional hot spots were codons 87, 97, 112 and 130; substitutions at these codons might play a role in immune-modulation during the course of chronic HBV infection.

Impact of hepatitis B virus basic core promoter mutations on T cell response to an immunodominant HBx-derived epitope

The hepatitis B X (HBx) protein is a crucial component in HBV infection in vivo and has been implicated in HCC. In this study, we aimed to detect and characterize peripheral HBx-specific T cells in chronically infected patients at the inactive carrier state of the disease. HBx-specific IFN-gamma-secreting T cells were found in 36 of 52 patients (69%), and 78% (28/36) of responding patients had T cells targeting epitopes in the carboxy-terminal part of HBx. IL-10 secretion after the stimulation of T cells with HBx-derived peptides was weak or undetectable. IFN-gamma-secreting T cells recognized a previously unknown immunodominant CD4+ T cell epitope, HBx 126-140 (EIRLKVFVLGGCRHK), in 86% (24 of 28) of patients. This peptide bound several HLA-DR molecules (HLA-DRB1*0101, HLA-DRB1*0401, HLA-DRB1*1301, and HLA-DRB5*0101). Its coding sequence overlaps a domain of the HBV genome encompassing the basic core promoter (BCP) region. Taking into account the selection of viral core promoter mutants during HBV infection, we found that HBV variants with BCP mutations were present in patient sera. We further demonstrated that these viral mutant sequences activated T cells specific for the immunodominant epitope only weakly, if at all. This is the first study linking BCP mutations and HBx-specific T cell responses.

CONCLUSION

Wild-type and variant peptides may represent potential tools for monitoring the HBV-specific T cell responses involved in sequence evolution during disease progression. Finally, the degenerate HLA-DR binding of this promiscuous, immunodominant peptide would make it a valuable component of vaccines for protecting large and ethnically diverse patient populations.

Molecular and functional analysis of occult hepatitis B virus isolates from patients with hepatocellular carcinoma

Occult HBV infection is characterized by the persistence of HBV DNA in the liver of individuals negative for HBV surface antigen (HBsAg). Occult HBV may exist in the hepatocytes as a free genome, although the factors responsible for the very low viral replication and gene expression usually observed in this peculiar kind of infection are mostly unknown. Aims of this study were to investigate whether the viral genomic variability might account for the HBsAg negativity and the inhibition of the viral replication in occult HBV carriers, and to verify in vitro the replication capability of occult HBV strains. We studied liver viral isolates from 17 HBV patients, 13 with occult infection and 4 HBsAg-positive. Full-length HBV genomes from each case were amplified and directly sequenced. Additionally, full-length HBV DNA from eight occult-HBV and two HBsAg-positive cases were cloned and sequenced. Finally, three entire, linear HBV genomes from occult cases were transiently transfected in HuH7 cells. Direct sequencing showed the absence of mutations capable of interfering with viral replication and gene expression in the major viral population of each case. Cloning experiments showed highly divergent HBV strains both in HBsAg-positive and HBsAg-negative individual cases (range of divergence 1.4%-7.1%). All of the 3 transfected full-length HBV isolates showed normal patterns of replication in vitro.

CONCLUSION

Multiple viral variants accumulate in the liver of occult HBV-infected patients. Occult HBV strains are replication-competent in vitro, suggesting that host, rather than viral factors are responsible for cryptic HBV infection.

Analysis of the complete hepatitis B virus genome in patients with genotype C chronic hepatitis in relation to HBeAg and anti-HBe

To investigate the relationship between viral factors and the development of chronic hepatitis B, the entire hepatitis B virus (HBV) genome of chronic carriers at different disease stages were analyzed. Eighty genotype C HBV carriers including 12 hepatitis B e antigen (HBeAg) positive asymptomatic carriers (Group A), 49 HBeAg positive patients with chronic liver diseases (Group B) and 19 anti-HBe positive patients with chronic liver diseases (Group C) were studied. HBV nucleic acid from serum samples was sequenced directly and compared with GenBank reference sequences HBV X01587 and M12906. On phylogenetic analysis, 76 cases were genotype C2. Of the 76 genotype C2 cases, the nucleotide and amino acid substitution rates in the precore/core region were significantly higher in Groups B and C than in Group A, also in Group C than in Group B. The nucleotide substitution rates in the full genome and the core promoter region were significantly higher in Group C than in Group A, also in group C than in Group B. The nucleotide and amino acid substitution rates in the X region were significantly higher in Group C than in Group A. The amino acid substitution rate in the pre-S2 region was significantly higher in Group C than in Group B. Deletion mutations were found mainly in Groups B and C. This whole genome analysis of HBV chronic carriers suggested that the nucleotide substitutions and deletions in HBV were closely associated with the pathogenesis of chronic HBV infection.

Characterization of sequence variations in immunodominant regions of the HBV-nucleocapsid protein as a prerequisite for the development of an epitope-based vaccine

BACKGROUND/AIMS

In hepatitis B virus infection, viral elimination is dependent on an efficient antiviral T cell response which is not detectable in chronic hepatitis B. Therefore, new therapeutic concepts focus on T cell activation, such as epitope-based T cell-targeted vaccines. However, with the development of peptide-based vaccines in mind, viral mutations frequently described in hepatitis B within known immunodominant helper epitopes may have an influence on peptide selection.

METHODS

Mutant peptides within immunodominant epitopes (aa 1-20, aa 91-105, and aa 143-157) at position 12, 14, 93, 97, 147, 151, 153, and 155 were tested with peripheral blood mononuclear and specific clone cells for their ability to induce proliferation, produce cytokines, induce T cell receptor down-regulation or antagonize wild-type activity of the hepatitis B core antigen-specific CD4+ T cell clones.

RESULTS

Five variants could not induce T cell proliferation or cytokine production when the variants were presented alone. Coincubation with wild-type epitopes leads to T cell activation showing that the variants do not act as T cell receptor antagonists for hepatitis B virus-specific CD4+ T cells. In contrast, five other variants and wild-type peptides stimulated CD4+ T cell proliferation and production of Th1 cytokines.

CONCLUSIONS

Our data demonstrate that frequently occurring mutations within immunodominant epitopes have rather a nonstimulatory than a strengthening effect and thus should not included in a vaccine.

Immunopathogenesis of hepatitis B virus infection

Hepatitis B virus (HBV) infection is a non-cytopathic hepatotropic virus that can lead to severe liver disease including acute hepatitis, cirrhosis and hepatocellular carcinoma. Successful clearance of the virus as well as the establishment of liver disease is largely driven by a complex interaction between the virus and the host immune response. In this review, the immunological events, including both the innate and adaptive immune response are discussed in the setting of both acute and chronic HBV infection and liver disease.

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.

Spontaneous CD4+ T cell responses against TRAG-3 in patients with melanoma and breast cancers

The taxol resistance gene TRAG-3 was initially isolated from cancer cell lines that became resistant to taxol in vitro. TRAG-3 is a cancer germline Ag expressed by tumors of different histological types including the majority of melanoma, breast, and lung cancers. In the present study, we report that patients with stage IV melanoma and breast cancers developed spontaneous IFN-gamma-producing CD4+ T cell responses against a single immunodominant and promiscuous peptide epitope from TRAG-3 presented in the context of multiple HLA-DR molecules. The TRAG-3-specific CD4+ T cells and clones were expanded in vitro and recognized not only peptide pulsed APCs but also autologous dendritic cells (DCs) loaded with the TRAG-3 protein. All stage IV melanoma patients with TRAG-3-expressing tumors developed spontaneous CD4+ T cell responses against TRAG-3, demonstrating its strong immunogenicity. None of these patients had detectable IgG Ab responses against TRAG-3. TCRbeta gene usage studies of TRAG-3-specific CD4+ T cell clones from a melanoma patient and a normal donor suggested a restricted TCR repertoire in patients with TRAG-3-expressing tumors. Altogether, our data define a novel profile of spontaneous immune responses to cancer germline Ag-expressing tumors, showing that spontaneous TRAG-3-specific CD4+ T cells are directed against a single immunodominant epitope and exist independently of Ab responses. Because of its immunodominance, peptide TRAG-3(34-48) is of particular interest for the monitoring of spontaneous immune responses in patients with TRAG-3-expressing tumors and for the development of cancer vaccines.

Identification of novel HLA-DR1-restricted epitopes from the hepatitis B virus envelope protein in mice expressing HLA-DR1 and vaccinated human subjects

Helper T lymphocytes that control CD8(+) T-cell and antibody responses are key elements for the resolution of infection by the hepatitis B virus and for the development of effective immunological memory after hepatitis B vaccination. We have used H-2 class II-deficient mice that express the human MHC class II molecule, HLA-DR1, to identify novel hepatitis B virus envelope-derived T helper epitopes. We confirmed the immunogenicity of a previously described HLA-DR1-restricted epitope, and identified three novel epitopes. CD4(+) T-cell immune responses against these epitopes were detected in peripheral blood mononuclear cells from HLA-DR1(+) individuals vaccinated against hepatitis B. We showed that subjects receiving the currently available hepatitis B vaccines do not develop cross-reactive T helper responses against one of the novel epitopes which are structurally variable between different hepatitis B virus subtypes. These findings highlight the need for developing vaccines against a wider range of viral subtypes, and establish humanized mice as a convenient tool for identifying new immunogenic epitopes from pathogens.

Genome-wide characterisation of hepatitis B mutations involved in clinical outcome

Infection with the hepatitis B virus (HBV) leads to different disease outcomes, which can be broadly divided into three categories: acute mild infection, 'fulminant' and chronic hepatitis (long-term persistent form of the infection). The factors that influence the development of these different disease states are poorly understood and may include viral polymorphisms. To investigate this possibility, we analysed 116 published complete HBV genomes for which we knew disease outcome and had access to associated information on patients (age, sex and geographic origin). Our best statistical model correctly classified 72% of the cases and retained age and sex of the patient, as well as 29 candidate mutations. With the exception of one mutation in the X gene, all were located in the viral polymerase, suggesting this gene plays a critical role in clinical outcome. Our results highlight the importance of the genetics of HBV strains in the evolution of the disease and demonstrate that disease outcome can be predicted to a surprisingly large extent with a limited number of host and viral factors.

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.

Immune system and hepatitis B virus infection

The immune system plays an important role in determining the outcome of hepatitis B virus (HBV) infection. This is because recovery from of acute HBV infection is associated with a clear division in the profile of adaptive immune response. Multispecific antiviral CD4 and CD8 responses with a type 1 cytokine production can be observed in patients who recover from acute HBV infection. On the other hand, those who develop chronic infection tend to have a weak virus specific T cell response. Therapeutic strategies aimed at correcting this defective T cell reactivity could represent a complementary approach to the cure of chronic HBV infection.

Dynamics of hepatitis B virus clearance in chimpanzees

Mathematical modeling was performed to test the extent to which cytopathic and noncytopathic T cell effector functions contribute to resolution of hepatitis B virus (HBV) infection in three acutely infected chimpanzees. Simulations based exclusively on cytopathic functions show a poor fit to the data and would require the destruction and regeneration of approximately 11 livers for clearance to occur. In contrast, a simulation based on a combination of cytopathic and noncytopathic functions provided a significantly better fit to the data (P < 0.001) and required as much as 5-fold less destruction to clear the virus from the liver. The best fit simulation supports the notion that during the early phase of HBV clearance, noncytopathic T cell effector mechanisms inhibit viral replication and greatly shorten the half-life of the long lived covalently closed circular viral DNA transcriptional template, thereby limiting the extent to which cytopathic T cell effector functions and tissue destruction are required to terminate acute HBV infection.

Comparative antigenicity and immunogenicity of hepadnavirus core proteins

The hepatitis B virus core protein (HBcAg) is a uniquely immunogenic particulate antigen and as such has been used as a vaccine carrier platform. The use of other hepadnavirus core proteins as vaccine carriers has not been explored. To determine whether the rodent hepadnavirus core proteins derived from the woodchuck (WHcAg), ground squirrel (GScAg), and arctic squirrel (AScAg) viruses possess immunogen characteristics similar to those of HBcAg, comparative antigenicity and immunogenicity studies were performed. The results indicate that (i) the rodent core proteins are equal in immunogenicity to or more immunogenic than HBcAg at the B-cell and T-cell levels; (ii) major histocompatibility complex (MHC) genes influence the immune response to the rodent core proteins (however, nonresponder haplotypes were not identified); (iii) WHcAg can behave as a T-cell-independent antigen in athymic mice; (iv) the rodent core proteins are not significantly cross-reactive with the HBcAg at the antibody level (however, the nonparticulate "eAgs" do appear to be cross-reactive); (v) the rodent core proteins are only partially cross-reactive with HBcAg at the CD4+ T-cell level, depending on MHC haplotype; and (vi) the rodent core proteins are competent to function as vaccine carrier platforms for heterologous, B-cell epitopes. These results have implications for the selection of an optimal hepadnavirus core protein for vaccine design, especially in view of the "preexisting" immunity problem that is inherent in the use of HBcAg for human vaccine development.

Immunogenicity of a hepatitis B DNA vaccine administered to chronic HBV carriers

Hepatitis B virus (HBV) is the major pathogen of chronic hepatitis and liver disease worldwide. Despite the availability of effective vaccines against hepatitis B for many years, over 370 million people remain persistently infected with HBV. Viral persistence is thought to be related to poor HBV-specific T-cell responses. Based on clinical data, the development of efficient methods capable of inducing strong T-cell responses is an important and primary step toward the development of immunotherapeutics against chronic HBV infection. We designed a phase I clinical trial in chronic HBV carriers to assess safety, tolerability and immunogenicity of a DNA vaccine expressing HBV small (S) and middle (preS2 +S) envelope proteins. After occurrence of lamivudine breakthrough, 10 HBeAg positive patients with chronic hepatitis B were followed longitudinally before, during and after DNA vaccine therapy. Immunizations were well tolerated and adverse physical events were mild and considered unrelated to the vaccine. Proliferative responses to hepatitis B surface antigen (HBsAg) were detected in two patients after DNA injections. Following three injections of vaccine, interferon (IFN)-gamma-producing T-cells specific for the preS2 or the S antigen were detectable in 50 and 100% of the patients, respectively. Each patient recognized at least one peptide within the envelope domain encoded by the vaccine. Anti-preS2 antibodies and seroconversion to anti-HBe were detected in two patients. This study shows evidences for the safety and immunological efficacy of HBV-DNA vaccination and demonstrates that DNA vaccination can restore or activate T-cell responses in chronic HBV carriers.

Mutations in hepatitis B virus core regions correlate with hepatocellular injury in Chinese patients with chronic hepatitis B

AIM: To elucidate the relationship between the frequency of core mutations and the clinical activity of hepatitis B virus (HBV)-related liver disease and to characterize the amino acid changes in the core region of HBV.

METHODS: We studied 17 Chinese patients with chronic hepatitis B according to their clinical courses and patterns of the entire core region of HBV.

RESULTS: Amino acid changes often appeared in the HBV core region of the HBV gene in patients with high values of alanine aminotransferase (ALT) or with the seroconversion from HbeAg to anti-HBe. The HBV core region with amino acid changes had high frequency sites that corresponded to HLA I/II restricted recognition epitopes reported by some investigators.

CONCLUSION: The core amino acid changes of this study occur due to influence of host immune system. The presence of mutations in the HBV core region seems to be important for predicting the clinical activity of hepatitis B in Chinese patients.

Interferon prevents formation of replication-competent hepatitis B virus RNA-containing nucleocapsids

We have previously shown that IFN-beta inhibits hepatitis B virus (HBV) replication by noncytolytic mechanisms that either destabilize pregenomic (pg)RNA-containing capsids or prevent their assembly. Using immortalized murine hepatocyte cell lines stably transfected with a doxycycline (dox)-inducible HBV replication system, we now show that replication-competent pgRNA-containing capsids are not produced when the cells are pretreated with IFN-beta before HBV expression is induced with dox. Furthermore, the turnover rate of preformed HBV RNA-containing capsids is not changed in the presence of IFN-beta or IFN-gamma under conditions in which further pgRNA synthesis is inhibited by dox removal. In summary, these results demonstrate that types 1 and 2 IFN activate hepatocellular mechanism(s) that prevent the formation of replication-competent HBV capsids and, thereby, inhibit HBV replication.

Molecular analysis of HLA class II associations with hepatitis B virus clearance and vaccine nonresponsiveness

Clearance of acute hepatitis B virus (HBV) infection is associated with a vigorous CD4+ T-cell response focusing on the core protein. HLA class II glycoproteins present viral peptides to CD4+ T cells and influence the immune responses. HLA-DRB1*1301/2 have been associated with viral clearance, and HLA-DRB1*0301 is associated with nonresponse to vaccination with envelope proteins. Binding affinities of overlapping peptides covering the core and envelope proteins of HBV were measured to HLA glycoproteins encoded by HLA-DRA1*0101,-DRB1*0101 (HLA-DR1), HLA-DRA1*0101,-DRB1*0301 (HLA-DR3), HLA-DRA1*0101,-DRB1*0701 (HLA-DR7) and HLA-DRA1*0101,-DRB1*1301 (HLA-DR13) molecules and compared with published peptide-specific CD4+ T-cell responses. There are more high-affinity ligands (IC50 < 1 micromol/L) derived from the core protein than the surface antigen (P < .04 for HLA-DR1/7/13), but there was no increase in the number or the affinity of ligands for HLA-DR13. Clusters of particular core peptides bound to multiple HLA types, explaining the immunodominance of these regions for T-cell responses. Within the envelope protein, the low-affinity ligands (IC50 < 10 micromol/L) are found mainly in the surface antigen, with a marked paucity of ligands for HLA-DR3 (HLA-DR3 vs. non-DR3; P < .05) consistent with the lower vaccination responses for this HLA type. Of all peptides tested, 8 to 10 bound mainly to one HLA type, allowing a substantially greater breadth of response in heterozygotes. In conclusion, these data offer a mechanistic explanation for the dominant response to the HBV core protein during infection and support the direct involvement of the HLA-DRB1 gene in vaccine nonresponsiveness but not altered susceptibility to viral persistence.

Rationally engineered therapeutic proteins with reduced immunogenicity

Chronic administration of protein therapeutics may elicit unacceptable immune responses to the specific protein. Our hypothesis is that the immunogenicity of protein drugs can be ascribed to a few immunodominant helper T lymphocyte (HTL) epitopes, and that reducing the MHC binding affinity of these HTL epitopes contained within these proteins can generate drugs with lower immunogenicity. To test this hypothesis, we studied the protein therapeutic erythropoietin (Epo). Two regions within Epo, designated Epo 91-120 and Epo 126-155, contained HTL epitopes that were recognized by individuals with numerous HLA-DR types, a property common to immunodominant HTL epitopes. We then engineered analog epitopes with reduced HLA binding affinity. These analog epitopes were associated with reduced in vitro immunogenicity. Two modified forms of Epo containing these substitutions were shown to be bioactive and nonimmunogenic in vitro. These findings support our hypothesis and demonstrate that immunogenicity of protein drugs can be reduced in a systematic and predictable manner.

Reduced hepatitis B virus (HBV)-specific CD4+ T-cell responses in human immunodeficiency virus type 1-HBV-coinfected individuals receiving HBV-active antiretroviral therapy

Functional hepatitis B virus (HBV)-specific T cells are significantly diminished in individuals chronically infected with HBV compared to individuals with self-limiting HBV infection or those on anti-HBV therapy. In individuals infected with human immunodeficiency virus type 1 (HIV-1), coinfection with HBV is associated with an increased risk of worsening liver function following antiviral therapy and of more rapid HBV disease progression. Total HBV-specific T-cell responses in subjects with diverse genetic backgrounds were characterized by using a library of 15-mer peptides overlapping by 11 amino acids and spanning all HBV proteins. The magnitude and breadth of CD4(+) and CD8(+) T-cell responses to HBV in peripheral blood were examined by flow cytometry to detect gamma interferon production following stimulation with HBV peptide pools. Chronic HBV carriers (n = 34) were studied, including individuals never treated for HBV infection (n = 7), HBV-infected individuals receiving anti-HBV therapy (n = 13), and HIV-1-HBV-coinfected individuals receiving anti-HBV therapy (n = 14). CD4(+) and CD8(+) HBV-specific T-cell responses were more frequently detected and the CD8(+) T-cell responses were of greater magnitude and breadth in subjects on anti-HBV treatment than in untreated chronic HBV carriers. There was a significant inverse correlation between detection of a HBV-specific T-cell response and HBV viral load. HBV-specific CD4(+) and CD8(+) T-cell responses were significantly (fivefold) reduced compared with HIV-specific responses. Although, the frequency and breadth of HBV-specific CD8(+) T-cell responses were comparable in the monoinfected and HIV-1-HBV-coinfected groups, HBV-specific CD4(+) T-cell responses were significantly reduced in HIV-1-HBV-coinfected individuals. Therefore, HIV-1 infection has a significant and specific effect on HBV-specific T-cell immunity.

HBV core sequence: definition of genotype-specific variability and correlation with geographical origin

There are eight genotypes and nine subtypes of HBV. Small differences in geographical origin are associated with sequence changes in the surface gene. Here, we compared core gene sequences from different genotypes and geographical regions. Specific combinations of 24 amino acid substitutions at nine residues allowed allocation of a sequence to a subtype. Six of these nine residues were located in different T cell epitopes depending on HBV geographical area and/or genotype. Thirty-seven nucleotide changes were associated uniquely with specific genotypes and subtypes. Unique amino acid and nucleotide variants were found in a majority of sequences from specific countries as well as within subtype ayw2 and adr. Specific nucleotide motifs were defined for Korean, Indian, Chinese, Italian and Pacific region isolates. Finally, we observed amino acid motifs that were common to either South-east Asian or Western populations, irrespective of subtype. We believe that HBV strains spread within constrained ethnic groups, result in selection pressures that define sequence variability within each subtype. It suggests that particular T cell epitopes are specific for geographical regions, and thus ethnic groups; this may affect the design of immunomodulatory therapies.

Evolution of hepatitis B virus during primary infection in humans: transient generation of cytotoxic T-cell mutants

BACKGROUND & AIMS

Acute hepatitis B is a highly dynamic human viral infection during which the hepatitis B virus can generate many genetic variants.

METHODS

We analyzed the evolution of the hepatitis B virus genome in sequential serum samples from a unique cohort of patients with acute infection acquired from a single source.

RESULTS

We showed that most mutations were nonsynonymous, that genetic diversity was greatest at the peak of viremia, and that patients who resolved their infection ("resolvers") showed a significantly higher level of diversity in the core, surface, and polymerase genes compared with those who progressed to chronic infection. Overall, the core gene showed the greatest genetic diversity. In resolvers who possessed an HLA-A*0201 haplotype, the emergence of mutants in the immunodominant HLA-A*0201-restricted core 18-27 epitope was observed. Functional studies showed that these mutants were less able to stimulate interferon-gamma release from core 18-27 specific CD8 + T-cell lines. However, they appeared only as a transient low-abundance species and were rapidly displaced by wild-type sequences before resolution of infection, and their overall significance is uncertain.

CONCLUSIONS

Overall, genetic evolution of the hepatitis B virus differs at early time points between patients who experience acute resolving hepatitis B and those who progress to chronicity. These observations suggest that the rapid development of broadly reactive host immune responses leads to clearance of hepatitis B virus, even in the presence of possible CD8+ T-cell immune escape variants.

Induction or expansion of T-cell responses by a hepatitis B DNA vaccine administered to chronic HBV carriers

Despite the availability of effective hepatitis B vaccines for many years, over 370 million people remain persistently infected with hepatitis B virus (HBV). Viral persistence is thought to be related to poor HBV-specific T-cell responses. A phase I clinical trial was performed in chronic HBV carriers to investigate whether HBV DNA vaccination could restore T-cell responsiveness. Ten patients with chronic active hepatitis B nonresponder to approved treatments for HBV infection were given 4 intramuscular injections of 1 mg of a DNA vaccine encoding HBV envelope proteins. HBV-specific T-cell responses were assessed by proliferation, ELISpot assays, and tetramer staining. Secondary end points included safety and the monitoring of HBV viraemia and serological markers. Proliferative responses to hepatitis B surface antigen were detected in two patients after DNA injections. Few HBV-specific interferon gamma-secreting T cells were detectable before immunization, but the frequency of such responses was significantly increased by 3 DNA injections. Immunization was well tolerated. Serum HBV DNA levels decreased in 5 patients after 3 vaccine injections, and complete clearance was observed in 1 patient. In conclusion, this study provides evidence that HBV DNA vaccination is safe and immunologically effective. We demonstrate that DNA vaccination can specifically but transiently activate T-cell responses in some chronic HBV carriers who do not respond to current antiviral therapies.

Review of cytokine profiles in patients with hepatitis

The development of T helper 1 versus T helper 2 cells is a major branch point in the immune response and is an important determinant of the body’s response to an infectious pathogen, leading to protection of the host or dissemination of the disease. Resent studies have shown that there exist macrophage activation states in parallel to the T helper cell type 1/2 paradigm, and the T helper 1 development process is governed to a great degree by cytokine IL-12 provided mainly by antigen presenting cells such as macrophages and dendritic cells. A model in patients with hepatitis is proposed that links the pathogen, macrophage activation and T helper cell polarization.

Direct evidence that naturally occurring mutations within hepatitis B core epitope alter CD4+ T-cell reactivity

Exacerbations of chronic hepatitis B have been associated with accumulation of mutations in the HBV core gene, with amino acid (aa) substitutions clustering between aa 50 and 69. This region of the nucleocapsid protein is known as an immunodominant epitope for CD4+ T-lymphocytes, however the impact of these mutations on T-cell reactivity has not been investigated. For this purpose, we undertook fine mapping of the reactivity of peripheral blood lymphocytes, isolated from patients with acute (n = 8) or chronic hepatitis B (n = 10), against a panel of branched synthetic peptides. The peptide aa sequences corresponded to the wild type HBV (aa 50-69), or contained 1-3 aa changes derived on the basis of naturally occurring mutations. In four of eight patients with acute hepatitis B the wild type peptide 50-69, which corresponded to the core gene sequence of HBV present in these patients, induced a strong T-cell proliferative response. In the same cases, the T-cell response to the mutant peptides was altered at various degrees, depending on the number and the position of aa changes. The most pronounced inhibition of CD4+ T-cell response (between 44 and 92%) was caused by a peptide ligand with two aa substitutions at positions 64 and 67. These results demonstrate that mutations within immunodominant epitopes of the HBV nucleocapsid can affect the CD4+ T-lymphocyte reactivity, which may have a role for the accumulation of certain HBV strains after hepatitis flares during the course of chronic HBV infection.

Different hepatitis B virus core gene mutations in children with chronic infection and hepatocellular carcinoma

BACKGROUND

The significance of mutations of hepatitis B virus (HBV) precore/core antigen in causing persistent infection and subsequent liver diseases is debatable.

AIM

To investigate HBV core gene sequence changes in children with chronic HBV infection and their implications in hepatocellular carcinoma (HCC).

METHODS

Thirty one chronic HBV infected children with documented hepatitis B e antigen seroconversion selected from 415 long term carrier children and 12 HBV related HCC children were studied. Four serial serum samples before and after hepatitis B e antigen seroconversion from each of the 31 children, and one serum sample taken from the 12 HCC children were subjected to HBV core gene sequence analysis.

RESULTS

Mutations accumulated as chronic infection persisted and most frequently occurred at core gene codon 21 (29%), codon 147 (29%), codon 65 (16%), and precore stop codon 28 (74%) in the 31 chronic HBV infected children. Core gene mutation sites in HCC children were identified at core codons 74, 87, and 159. HCC children had more mutations in the core gene than those with chronic HBV infection (p=0.013).

CONCLUSION

Accumulation of mutations of HBV core region in HCC children differ from those in chronic HBV infected children. This may be a clue to the pathogenesis of paediatric HCC.

Characterization of HLA DR13-restricted CD4(+) T cell epitopes of hepatitis B core antigen associated with self-limited, acute hepatitis B

The HLA DR13 allele has been associated with a self-limited course of hepatitis B virus infection, possibly through the induction of a more vigorous hepatitis B core antigen (HBcAg) and/or hepatitis B e antigen-specific CD4(+) T cell response. HBcAg-specific CD4(+) T cell responses were investigated in three HLA DR13-positive subjects with self-limited, acute hepatitis B. HBcAg-specific, short-term T cell lines derived from these three subjects showed a dominant recognition of HBcAg peptides spanning aa 1-20 (P1), 11-30 (P2), 41-60 (P5), 111-131 (P12) and 141-160 (P15). In order to characterize these epitopes in more detail, CD4(+) T cell clones and cell lines were generated using HBcAg. Surprisingly, 11 of 12 T cell clones examined recognized P15; one recognized P10 (aa 91-111). Of four T cell lines, two recognized P15 and two recognized P5. By peptide mapping, the minimal epitope of P15 was located to residues (147)TVVRRRGRSP(156).

Immunological monitoring during therapeutic vaccination as a prerequisite for the design of new effective therapies: induction of a vaccine-specific CD4+ T-cell proliferative response in chronic hepatitis B carriers

We characterized the anti-viral T-cell response in 22 chronically infected patients, who participated in a European multi-center randomized placebo-controlled, double-blind study therapeutic vaccination trial with pre-S1, pre-S2 and S antigenic components of the hepatitis B virus (HBV). It induced a significant HBsAg-specific T-cell proliferation and the production of Th2-cytokines (i.e. IL-5). A specific induction of Th1-lymphokines was not detectable although this has been demonstrated in this study in response to the nucleocapsid protein (HBcAg). Further analysis indicated that this approach does not activate HBV-specific CD8+ T-lymphocytes as detected by ELISPOT-assay. Our results might explain why a specific therapeutic vaccine, although safe and well-tolerated is not always able to break tolerance leading to the clearance of the hepatitis B virus.

Approach to establishing a liver targeting gene therapeutic vector using naturally occurring defective hepatitis B viruses devoid of immunogenic T cell epitope

The development of liver-directed virus vector may play a crucial role in hepatic gene therapy. Hepatitis B virus (HBV) is the only known DNA virus that has hepatocyte specificity. In order to construct an efficient HBV-based vector for targeting the liver, we studied the potential use of naturally occurring defective HBVs obtained from hepatitis patients. The enhanced green fluorescent protein (EGFP) gene or small tag sequences (Flag) were introduced in frame into the deleted sites of the defective HBVs. One HBV defective in site for putative T cell epitope and a part of the polymerase gene tolerated EGFP insertion and was successfully packaged. This defective recombinant HBV harboring 48 bp Flag tag sequence instead of EGFP (rHBV-7-Flag) replicated well. Human primary hepatocytes could uptake rHBV-7-Flag virions, though in a low frequency, when exposed to the virions at a high density in the culture medium, and also express Flag tag sequences. This defective HBV-based vector may have a potential application in liver targeting gene therapy.

Control or persistence of hepatitis B virus: the critical role of initial host-virus interactions

Following infection with hepatitis B virus (HBV), the period before symptomatic disease is now recognized as a time of dynamic interaction between virus and host. Recent work has shown that this period is the phase of infection during which maximal changes in virus replication and the activation of critical components of the immune system occurs. This suggests that the different outcomes following exposure might be determined during the early phase of infection, before the onset of clinical disease. The hypothesis that small differences in the dynamic relationship between host and virus, such as in the kinetics of HBV replication, may influence the final outcome of infection, will be discussed.

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

In vitro proliferation of peripheral blood mononuclear cells was used to measure virus-specific cell-mediated immunity (vCMI) following neonatal woodchuck hepatitis virus (WHV) infection. Fifteen neonates were inoculated with the W8 strain of WHV. In 11, infection was resolved, and 4 became chronic carriers. Nineteen neonates were inoculated with the W7 strain and all became chronic carriers. Seven age-matched uninfected woodchucks served as controls. Virologic and vCMI profiles among the W8 and W7 infections were compared and related to the outcome of infection. Resolving woodchucks had robust, acute-phase vCMI to WHV antigens (core, surface, and x) and to several nonoverlapping core peptides. The acute-phase vCMI was associated temporally with the clearance of viral DNA and of surface antigen from serum at 14 to 22 weeks postinfection. In contrast, in approximately half of the W8 and W7 infections that progressed to chronicity, no significant acute-phase vCMI was detected. In the remaining carriers, acute-phase vCMI was observed, but it was less frequent and incomplete compared to that of resolved woodchucks. Serum viral load developed less rapidly in those carriers that had evidence of acute-phase vCMI, but it was still increased compared to that of resolving woodchucks. Thus, vigorous and multispecific acute-phase vCMI was associated with resolution of neonatal WHV infection. Absent or incomplete acute-phase vCMI was associated with the progression to chronic infection. By analogy, these results suggest that the onset of chronic hepatitis B virus (HBV) infection in humans may be associated with deficiencies in the primary T-cell response to acute HBV infection.

Structural and functional heterogeneity of naturally occurring hepatitis B virus variants

Most organisms have developed sophisticated machineries to preserve their genomic integrity. On the contrary hepatitis B virus (HBV), like a lot of other viruses can undergo rapid and drastic sequence changes, especially if the virus has to cope with natural or therapy induced antiviral mechanisms in the host. Here, we try to summarize possible implications for the molecular pathogenesis of HBV based on the extensive research on the genetic variants of HBV.

Modeling the T-helper cell response in acute and chronic hepatitis B virus infection using T-cell receptor transgenic mice

Chronicity following hepatitis B virus (HBV) infection may be maintained by high levels of viral proteins circulating in the serum. To examine the characteristics of T cells capable of co-existing with the secreted hepatitis B e-antigen (HBeAg), T-cell receptor (TCR) transgenic (Tg) mice were produced. To insure that HBeAg-specific T cells would not be deleted in the presence of serum HBeAg, the TCR alpha and beta-chain genes used to produce the TCR-Tg mice were derived from T-cell hybridomas from HBeAg-Tg mice. A TCR-Tg lineage (11/4-12) was produced that possessed a high frequency (approximately 67%) of CD4(+) T cells that expressed a TCR-Tg specific for the HBeAg. As predicted, when 11/4-12 TCR-Tg mice were bred with HBeAg-Tg mice no deletion of the HBeAg-specific CD4(+) T cells occurred in the thymus or the spleen. Functional analysis of the TCR-Tg T cells revealed that the HBeAg-specific CD4(+) T cells escaped deletion in the thymus and periphery by virtue of low avidity. Regardless of their low avidity, HBeAg-specific TCR-Tg T cells could be activated by exogenous HBeAg as measured by cytokine production in vitro and T-helper cell function for anti-HBe antibody production in vitro and in vivo. Furthermore, activated TCR-Tg HBeAg-specific T cells polarized to the Th(1) subset were able to elicit liver injury when transferred into HBeAg or HBcAg-Tg recipients. Therefore, HBeAg-specific CD4(+) T cells that can survive deletion or anergy in the presence of circulating HBeAg nonetheless are capable of being activated and of mediating liver injury in vivo.

Immune response induced by immunization with Hepatitis B virus core DNA isolated from chronic active hepatitis patients

There are many mutations in the gene encoding Hepatitis B virus (HBV) core antigen of chronic active hepatitis patients, and such mutations are most likely to be related to the severity of disease. Here, we constructed plasmids containing wild-type and deletion type of HBV core gene (HBc) to develop an experimental DNA vaccine and to compare immunogenicity of two types of HBc vaccine. Twenty-nine wild-types and seven deletion types of HBc were detected in sera of 32 Korean patients with chronic active hepatitis. Four wild-types (W1, W2, W4, W6) and two deletion types (D3, D4) of HBc were cloned into the pcDNA3 vector. Intramuscular immunization with wild-type HBc efficiently increased serum anti-HBc antibody response in a dose-dependent manner. Anti-HBc antibody response in mice injected with W6 increased 14 days after immunization, and peaked after 30 days and was maintained at least up to 50 days. W6 immunization induced a specific cytotoxic T lymphocyte response to W6-transfected 3LL (3LL-W6), and reduced the sizes of tumor mass of mice challenged with 3LL-W6 or 3LL transfected with D4. However, intramuscular immunization with D3 and D4 did not show antibody response at all. D3 and D4 have 157 bp (from 331 to 491 bp) and 122 bp (from 327 to 448 bp) gene deletion, respectively, and these encode class II MHC-restricted T-cell epitope. Altogether, these results suggest that mutant virus that has deleted HBc gene may evade immune systems due to loss of T-cell epitope.

Selection of hepatitis B virus variants with aminoacid substitutions inside the core antigen during interferon-alpha therapy

The hepatitis B virus (HBV) core antigen carries many epitopes relevant for B and T cell response that show aminoacid variation during viral infection. In a longitudinal analysis, sequential serum samples of 15 patients that suffered from chronic HBV infection were collected before, during, and after high-dose IFN-alpha treatment. The HBV preCore/Core (preC/C) sequence of the selected samples in each patient was determined and analysed for sequence variations compared to the pretreatment sample. The positions of HBV core aminoacid substitutions were assigned to immunodominant B, CD4(+) and CD8(+) cell epitopes. Seventy-five percent of all aminoacid substitutions were found within immunodominant T and B cell epitopes (12.5% were inside known HBV core mutation cluster regions) that show an increased number of clustered aminoacid substitutions during chronic HBV infection and overlap partially with the immunodominant epitopes. Only 12.5% of the detected core antigen aminoacid substitutions could not be assigned to any epitope or mutation cluster region. Stable HBV core antigen aminoacid substitutions, which were found between pretreatment sequence and the last sequence analysed during therapy, were found most frequently inside T helper cell epitopes. This longitudinal analysis of aminoacid substitutions inside the HBV core antigen in patients with chronic HBV infection shows that core aminoacid variations occur most frequently inside immunodominant HBV core epitopes, possibly due to an immuneselective pressure of the host against the virus. The data also suggest that stable HBV variants with aminoacid substitutions in immunodominant core epitopes can be selected during high-dose IFN-alpha therapy and persist after the end of treatment.

Targeting of HIV-1 Nef to the centrosome: implications for antigen processing

To gain a better understanding of the intracellular sites of antigen processing we have looked at the localization of human immunodeficiency virus (HIV)-1 Nef protein by confocal microscopic and biochemical means. We found that ubiquitin (Ub)-Nef fusion proteins were localized to the centrosome in transfected COS-7 cells, and that the colocalization was inhibited by the microtubule-disrupting agent, nocodazole. Interestingly, we found that Ub-Nef trafficking to the centrosome was not dependent upon the metabolic stability of Ub-Nef nor on the inhibition of proteasome activity. We also analyzed the MHC class I antigen processing of a reporter epitope linked to the Ub-Nef fusion proteins and found that Ub-Nef was processed in COS-7 cells. In addition, we show that this processing was inhibited by nocodazole. We suggest that the centrosome may serve as a site of antigen processing in vivo.