Molecular features of the hepatitis B virus nucleocapsid T-cell epitope 18-27: interaction with HLA and T-cell receptor

Immune escape pathways from the HBV core18-27 CD8 T cell response are driven by individual HLA class I alleles

Background and aims

There is growing interest in T cell-based immune therapies for a functional cure of chronic HBV infection including check-point inhibition, T cell-targeted vaccines or TCR-grafted effector cells. All these approaches depend on recognition of HLA class I-presented viral peptides. The HBV core region 18-27 is an immunodominant target of CD8+ T cells and represents the prime target for T cell-based therapies. Here, a high-resolution analysis of the core18-27 specific CD8+ T cell and the selected escape pathways was performed.

Methods

HLA class I typing and viral sequence analyses were performed for 464 patients with chronic HBV infection. HBV-specific CD8+ T-cell responses against the prototype and epitope variants were characterized by flow cytometry.

Results

Consistent with promiscuous presentation of the core18-27 epitope, antigen-specific T cells were detected in patients carrying HLA-A*02:01, HLA-B*35:01, HLA-B*35:03 or HLA-B*51:01. Sequence analysis confirmed reproducible selection pressure on the core18-27 epitope in the context of these alleles. Interestingly, the selected immune escape pathways depend on the presenting HLA-class I-molecule. Although cross-reactive T cells were observed, some epitope variants achieved functional escape by impaired TCR-interaction or disturbed antigen processing. Of note, selection of epitope variants was exclusively observed in HBeAg negative HBV infection and here, detection of variants associated with significantly greater magnitude of the CD8 T cell response compared to absence of variants.

Conclusion

The core18-27 epitope is highly variable and under heavy selection pressure in the context of different HLA class I-molecules. Some epitope variants showed evidence for impaired antigen processing and reduced presentation. Viruses carrying such escape substitutions will be less susceptible to CD8+ T cell responses and should be considered for T cell-based therapy strategies.

Next Generation Sequencing-Based Identification of T-Cell Receptors for Immunotherapy Against Hepatocellular Carcinoma

Hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC) remains a global health concern, and HBV proteins may be ideal targets for T cell-based immunotherapy for HCC. There is a need for fast and efficient identification of HBV-specific T cell receptors (TCRs) for the development of TCR-transduced T (TCR-T) cell-based immunotherapy. Two widely employed TCR identification approaches, T cell clonal expansion and single-cell sequencing, involve a TCR singularization process for the direct identification of Vα and Vβ pairs of TCR chains. Clonal expansion of T cells is well known to have tedious time and effort requirements due to the use of T cell cultures, whereas single-cell sequencing is limited by the requirements of cell sorting and the preparation of a single-cell immune-transcriptome library as well as the massive cost of the whole procedure. Here, we present a next-generation sequencing (NGS)-based HBV-specific TCR identification that does not require the TCR singularization process. Conclusion: Two pairing strategies, ranking-based strategy and α-β chain mixture-based strategy, have proved to be useful for NGS-based TCR identification, particularly for polyclonal T cells purified by a peptide-major histocompatibility complex (pMHC) multimer-based approach. Functional evaluation confirmed the specificity and avidity of two identified HBV-specific TCRs, which may potentially be used to produce TCR-T cells to treat patients with HBV-related HCC.

Acetaldehyde suppresses HBV-MHC class I complex presentation on hepatocytes via induction of ER stress and Golgi fragmentation

Alcohol consumption worsens hepatitis B virus (HBV) infection pathogenesis. We have recently reported that acetaldehyde suppressed HBV peptide-major histocompatibility complex I (MHC class I) complex display on hepatocytes, limiting recognition and subsequent removal of the infected hepatocytes by HBV-specific cytotoxic T lymphocytes (CTLs). This suppression was attributed to impaired processing of antigenic peptides by the proteasome. However, in addition to proteasome dysfunction, alcohol may induce endoplasmic reticulum (ER) stress and Golgi fragmentation in HBV-infected liver cells to reduce uploading of viral peptides to MHC class I and/or trafficking of this complex to the hepatocyte surface. Hence, the aim of this study was to elucidate whether alcohol-induced ER stress and Golgi fragmentation affect HBV peptide-MHC class I complex presentation on HBV+ hepatocytes. Here, we demonstrate that, while both acetaldehyde and HBV independently cause ER stress and Golgi fragmentation, the combined exposure provided an additive effect. Thus we observed an activation of the inositol-requiring enzyme 1α-X-box binding protein 1 and activation transcription factor (ATF)6α, but not the phospho PKR-like ER kinase-phospho eukaryotic initiation factor 2α-ATF4-C/EBP homologous protein arms of ER stress in HBV-transfected cells treated with acetaldehyde-generating system (AGS). In addition, Golgi proteins trans-Golgi network 46, GM130, and Giantin revealed punctate distribution, indicating Golgi fragmentation upon AGS exposure. Furthermore, the effects of acetaldehyde were reproduced by treatment with ER stress inducers, thapsigargin and tunicamycin, which also decreased the display of this complex and MHC class I turnover in HepG2.2.15 cells and HBV-infected primary human hepatocytes. Taken together, alcohol-induced ER stress and Golgi fragmentation contribute to the suppression of HBV peptide-MHC class I complex presentation on HBV+ hepatocytes, which may diminish their recognition by CTLs and promote persistence of HBV infection in hepatocytes.NEW & NOTEWORTHY Our current findings show that acetaldehyde accelerates endoplasmic reticulum (ER) stress by activating the unfolded protein response arms inositol-requiring enzyme 1α-X-box binding protein 1 and activation transcription factor (ATF)6α but not phospho PKR-like ER kinase-p eukaryotic initiation factor 2α-ATF4-C/EBP homologous protein in hepatitis B virus (HBV)-transfected HepG2.2.15 cells. It also potentiates Golgi fragmentation, as evident by punctate distribution of Golgi proteins, GM130, trans-Golgi network 46, and Giantin. While concomitantly increasing HBV DNA and HBV surface antigen titers, acetaldehyde-induced ER stress suppresses the presentation of HBV peptide-major histocompatibility complex I complexes on hepatocyte surfaces, thereby promoting the persistence of HBV infection in the liver.

Acetaldehyde suppresses the display of HBV-MHC class I complexes on HBV-expressing hepatocytes

Hepatitis B virus (HBV) infection and alcoholism are major public health problems worldwide, contributing to the development of end-stage liver disease. Alcohol intake affects HBV infection pathogenesis and treatment outcomes. HBV-specific cytotoxic T lymphocytes (CTLs) play an important role in HBV clearance. Many previous studies have focused on alcohol-induced impairments of the immune response. However, it is not clear whether alcohol alters the presentation of HBV peptide-major histocompatibility complex (MHC) class I complexes on infected hepatocytes resulting in escape of its recognition by CTLs. Hence, the focus of this study was to investigate the mechanisms by which ethanol metabolism affects the presentation of CTL epitope on HBV-infected hepatocytes. As demonstrated here, although continuous cell exposure to acetaldehyde-generating system (AGS) increased HBV load in HepG2.2.15 cells, it decreased the expression of HBV core peptide 18-27-human leukocyte antigen-A2complex (CTL epitope) on the cell surface. Moreover, we observed AGS-induced suppression of chymotrypsin- and trypsin-like proteasome activities necessary for peptide processing by proteasome as well as a decline in IFNγ-stimulated immunoproteasome (IPR) function and expression of PA28 activator and immunoproteasome subunits LMP7 and LMP2. Furthermore, IFNγ-induced activation of peptide-loading complex (PLC) components, such as transporter associated with antigen processing (TAP1) and tapasin, were suppressed by AGS. The attenuation of IPR and PLC activation was attributed to AGS-triggered impairment of IFNγ signaling in HepG2.2.15 cells. Collectively, all these downstream events reduced the display of HBV peptide-MHC class I complexes on the hepatocyte surface, which may suppress CTL activation and the recognition of CTL epitopes on HBV-expressing hepatocytes by immune cells, thereby leading to persistence of liver inflammation.NEW & NOTEWORTHY Our study shows that in HBV-expressing HepG2.2.15 cells, acetaldehyde alters HBV peptide processing by suppressing chymotrypsin- and trypsin-like proteasome activities and decreases IFNγ-stimulated immunoproteasome function and expression of PA28 activator and immunoproteasome subunits. It also suppresses IFNγ-induced activation of peptide-loading complex (PLC) components due to impairment of IFNγ signaling via the JAK-STAT1 pathway. These acetaldehyde-induced dysfunctions reduced the display of HBV peptide-MHC class I complexes on the hepatocyte surface, thereby leading to persistence of HBV infection.

Is hepatitis B antigen in cord blood an immunotolerogen playing a critical role in the pathogenesis of chronic hepatitis B?

Recently, we showed that infants with or without fetal hepatitis B e antigen (HBeAg) exposure had comparable antibody response to hepatitis B vaccination and proposed that fetal HBeAg exposure appears to not induce immunotolerance to HBV. Here, we summarized the different results on the topic of fetal HBeAg exposure in inducing immunotolerance to HBV nucleocapsid protein, and the evidence to back up that the tendency of high infection rate in infants of HBeAg-positive mothers is more likely associated with higher maternal viral loads and is less likely associated with the fetal HBeAg exposure. We consider that whether fetal HBeAg exposure plays an important role in the pathogenesis of chronic HBV infection remains to be an open question.

Phenotypic and functional differences of HBV core-specific versus HBV polymerase-specific CD8+ T cells in chronically HBV-infected patients with low viral load

OBJECTIVE

A hallmark of chronic HBV (cHBV) infection is the presence of impaired HBV-specific CD8+ T cell responses. Functional T cell exhaustion induced by persistent antigen stimulation is considered a major mechanism underlying this impairment. However, due to their low frequencies in chronic infection, it is currently unknown whether HBV-specific CD8+ T cells targeting different epitopes are similarly impaired and share molecular profiles indicative of T cell exhaustion.

DESIGN

By applying peptide-loaded MHC I tetramer-based enrichment, we could detect HBV-specific CD8+ T cells targeting epitopes in the HBV core and the polymerase proteins in the majority of 85 tested cHBV patients with low viral loads. Lower detection rates were obtained for envelope-specific CD8+ T cells. Subsequently, we performed phenotypic and functional in-depth analyses.

RESULTS

HBV-specific CD8+ T cells are not terminally exhausted but rather exhibit a memory-like phenotype in patients with low viral load possibly reflecting weak ongoing cognate antigen recognition. Moreover, HBV-specific CD8+ T cells targeting core versus polymerase epitopes significantly differed in frequency, phenotype and function. In particular, in comparison with core-specific CD8+ T cells, a higher frequency of polymerase-specific CD8+ T cells expressed CD38, KLRG1 and Eomes accompanied by low T-bet expression and downregulated CD127 indicative of a more severe T cell exhaustion. In addition, polymerase-specific CD8+ T cells exhibited a reduced expansion capacity that was linked to a dysbalanced TCF1/BCL2 expression.

CONCLUSIONS

Overall, the molecular mechanisms underlying impaired T cell responses differ with respect to the targeted HBV antigens. These results have potential implications for immunotherapeutic approaches in HBV cure.

Deep sequencing identifies hepatitis B virus core protein signatures in chronic hepatitis B patients

BACKGROUND

We aimed to identify HBc amino acid differences between subgroups of chronic hepatitis B (CHB) patients.

METHODS

Deep sequencing of HBc was performed in samples of 89 CHB patients (42 HBeAg positive, 47 HBeAg negative). Amino acid types were compared using Sequence Harmony to identify subgroup specific sites between HBeAg-positive and -negative patients, and between patients with combined response and non-response to peginterferon/adefovir combination therapy.

RESULTS

We identified 54 positions in HBc where the frequency of appearing amino acids was significantly different between HBeAg-positive and -negative patients. In HBeAg negative patients, 22 positions in HBc were identified which differed between patients with treatment response and those with non-response. The fraction non-consensus sequence on selected positions was significantly higher in HBeAg-negative patients, and was negatively correlated with HBV DNA and HBsAg levels.

CONCLUSIONS

Sequence Harmony identified a number of amino acid changes associated with HBeAg-status and response to peginterferon/adefovir combination therapy.

Immunogenicity of twenty peptides representing epitopes of the hepatitis B core and surface antigens by IFN-γ response in chronic and resolved HBV

Background

Patients with chronic hepatitis B virus infection (CHB) usually mount a modest T cell response against HBV epitopes. In order to determine immunogenic epitopes of HBV recognized by HBV-specific T cells, previous studies focused on previously confirmed HBV epitopes and assessed the T cell response by the number of HBV-specific T cells by IFN-γ ELISPOT.

Methods

We studied T cell functionality by combined in silico methods predicting HBV-specific epitopes and experimental investigations on the recognition of these epitopes. 30 chronic CHB patients and 10 patients with resolved HBV (RHB) were included in the study. We identified epitopes from the literature and by in silico analysis. These were evaluated for immunogenicity by use of synthetic peptides representing the epitopes through exposure to PBMCs from patients with CHB or RHB by IFN-γ ELISPOT. The number of IFN-γ producing cells (SFC), mean spot size (MSS) and stimulation index (SI) were recorded.

Results

The frequency of HBV-specific T cells producing IFN-γ after stimulation with HBV epitopes was similar in CHB and RHB patients. CHB patients had a higher MSS SI than RHB patients. Patients not carrying the HLA-A2 genotype had higher SFC SI and MSS SI. Patients with HLA-A11 had higher MSS SI compared to non- HLA-A11 allele patients. HBeAg-positive patients had a lower MSS SI, and none of the HBeAg positive patients had the HLA-A11 genotype. We found 3 immunogenic epitopes not described previously.

Conclusion

IFN-γ ELISPOT-determined MSS is an efficient marker for T cell recognition of epitopes. This experimental measure showed the in silico analysis for epitope prediction to be a valuable tool in future studies on HLA genotypes and HBV epitopes. This way our study now points to previously unappreciated consequences of carrying the HLA-A11 allele in terms of stronger immunity to HBV.

Genogeography and Immune Epitope Characteristics of Hepatitis B Virus Genotype C Reveals Two Distinct Types: Asian and Papua-Pacific

Distribution of hepatitis B virus (HBV) genotypes/subgenotypes is geographically and ethnologically specific. In the Indonesian archipelago, HBV genotype C (HBV/C) is prevalent with high genome variability, reflected by the presence of 13 of currently existing 16 subgenotypes. We investigated the association between HBV/C molecular characteristics with host ethnicity and geographical distribution by examining various subgenotypes of HBV/C isolates from the Asia and Pacific region, with further analysis on the immune epitope characteristics of the core and surface proteins. Phylogenetic tree was constructed based on complete HBV/C genome sequences from Asia and Pacific region, and genetic distance between isolates was also examined. HBV/C surface and core immune epitopes were analyzed and grouped by comparing the amino acid residue characteristics and geographical origins. Based on phylogenetic tree and geographical origins of isolates, two major groups of HBV/C isolates—East-Southeast Asia and Papua-Pacific—were identified. Analysis of core and surface immune epitopes supported these findings with several amino acid substitutions distinguishing the East-Southeast Asia isolates from the Papua-Pacific isolates. A west-to-east gradient of HBsAg subtype distribution was observed with adrq+ prominent in the East and Southeast Asia and adrq- in the Pacific, with several adrq-indeterminate subtypes observed in Papua and Papua New Guinea (PNG). This study indicates that HBV/C isolates can be classified into two types, the Asian and the Papua-Pacific, based on the virus genome diversity, immune epitope characteristics, and geographical distribution, with Papua and PNG as the molecular evolutionary admixture region in the switching from adrq+ to adrq-.

Intensity of HLA-A2 Expression Significantly Decreased in Occult Hepatitis B Infection

Background:

Occult hepatitis B infected (OBI) patients cannot eradicate hepatitis B virus (HBV)-DNA from their liver and peripheral blood, completely.

Objectives:

The main aim of this study was to investigate the rate of HLA-A2 expression on peripheral blood mononuclear cells (PBMCs) of patients with OBI.

Materials and Methods:

In this experimental study, intensity of HLA-A2 was measured on the PBMCs of 57 OBI patients and 100 HBsAg-/anti-HBc+/HBV-DNA samples were enrolled as controls; measurements were performed using the flow cytometry technique.

Results:

Flow cytometric analysis indicated that 19 (33.3%) OBI patients and 28 (28%) controls expressed HLA-A2 antigen on their PBMCs. There was no significant difference between the two groups regarding the rate of individuals expressing HLA-A2 antigen. Statistical analyses showed that the intensity of HLA-A2 expression significantly decreased in OBI patients (3.58 ± 0.1) in comparison to healthy controls (4.21 ± 0.25; P < 0.001).

Conclusions:

According to these results it can be concluded that decreased intensity of HLA-A2 on the PBMCs of OBI patients may lead to resistance of HBV in the patients.

Tapasin modification on the intracellular epitope HBcAg18-27 enhances HBV-specific CTL immune response and inhibits hepatitis B virus replication in vivo

HBV-specific cytotoxic T-lymphocyte (CTL) activity has a very important role in hepatitis B virus clearance. Present studies suggest that Tapasin, a endoplasmic reticulum (ER) chaperone, stabilizes the peptide-receptive MHC I conformation, allowing peptide exchange and increasing more peptides to be translocated into the ER. We have previously testified that cytoplasmic transduction peptide (CTP)-HBcAg(18-27)-Tapasin fusion protein could enter cytoplasm of dendritic cells, and enhance T cells' response to generate specific CTLs efficiently in vitro. In the present study, we evaluated specific immune responses of CTP-HBcAg(18-27)-Tapasin fusion protein in HLA-A2 transgenic mice (H-2K(b)) and anti-viral ability in HBV transgenic mice, and explored the mechanisms probably involved in. The studies showed that CTP-HBcAg(18-27)-Tapasin not only increased production of cytokine IFN-γ and interleukin-2 (IL-2), compared with CTP-HBcAg(18-27), HBcAg(18-27)-Tapasin, and PBS, but also significantly induced the higher percentages of IFN-γ+CD8(+) T cells and specific CTL responses in HLA-A2 transgenic mice. Moreover, enhancement of specific CTL activity induced by the fusion protein reduced HBV DNA and hepatitis B surface antigen (HBsAg) levels and decreased the expression of HBsAg and hepatitis B core antigen (HBcAg) in liver tissue of HBV transgenic mice. In addition, CTP-HBcAg(18-27)-Tapasin could upregulate the expression of JAK2, Tyk2, STAT1, and STAT4 in T lymphocytes in HLA-A2 transgenic mice splenocytes. However, there was no significant difference on the expressions of JAK1, JAK3, and STAT6 between each group. In conclusion, CTP-HBcAg(18-27)-Tapasin fusion protein could enhance not only the percentages of CTLs but also induce robust specific CTL activity and inhibits hepatitis B virus replication in vivo, which was associated with activation of the JAK/STAT signaling pathway.

Multipeptide immune response to cancer vaccine IMA901 after single-dose cyclophosphamide associates with longer patient survival

IMA901 is the first therapeutic vaccine for renal cell cancer (RCC) consisting of multiple tumor-associated peptides (TUMAPs) confirmed to be naturally presented in human cancer tissue. We treated a total of 96 human leukocyte antigen A (HLA-A)*02(+) subjects with advanced RCC with IMA901 in two consecutive studies. In the phase 1 study, the T cell responses of the patients to multiple TUMAPs were associated with better disease control and lower numbers of prevaccine forkhead box P3 (FOXP3)(+) regulatory T (T(reg)) cells. The randomized phase 2 trial showed that a single dose of cyclophosphamide reduced the number of T(reg) cells and confirmed that immune responses to multiple TUMAPs were associated with longer overall survival. Furthermore, among six predefined populations of myeloid-derived suppressor cells, two were prognostic for overall survival, and among over 300 serum biomarkers, we identified apolipoprotein A-I (APOA1) and chemokine (C-C motif) ligand 17 (CCL17) as being predictive for both immune response to IMA901 and overall survival. A randomized phase 3 study to determine the clinical benefit of treatment with IMA901 is ongoing.

CpG oligodeoxynucleotides discriminately enhance binding capacity of human naïve B cells to Hepatitis B virus epitopes

CpG oligodeoxynucleotides (CpG ODN) have the potential to enhance the antigen-presenting cells function of human naïve B cells. In this study, we aim to define the effect of CpG ODNs on the binding capacity of human naïve B cells for different Hepatitis B virus (HBV) epitopes. Three HLA-A2 restricted epitopes were selected to incubate with CpG ODN-primed human naïve B cells. Binding capacity for each epitope and expression of CD80, CD86, class I major histocompatibility complex (MHC), and class II MHC of naïve B cells was tested, respectively, by flow cytometry. CpG ODNs, especially ODN 2216, enhanced the binding capacity of human naïve B cells for HBV epitopes (p < 0.01), and induced markedly higher expression of CD80, CD86, class I MHC, and class II MHC. The binding capacity of CpG-treated naive B cells for each epitope was significantly different. In all the 3 subjects, CpG ODN 2216-primed naïve B cells showed the highest binding ability for Env172-180 compared with the other epitopes with a high expression of co-stimulatory and MHC molecules. CpG ODN showed the potential to selectively enhance the binding capacity of human naïve B cells for HBV epitopes. These results suggest new strategies for development of vaccine design.

Stability screening of arrays of major histocompatibility complexes on combinatorially encoded flow cytometry beads

The binding and stabilization capacity of potential T cell epitopes to class I MHC molecules form the basis for their immunogenicity and provide fundamental insight into factors that dictate cellular immune responses. We have developed a versatile high throughput cell-free method to measure MHC stability by capturing a variety of MHC products on the surface of streptavidin-coated particles followed by flow cytometry analysis. Arrays of peptide-MHC combinations, generated by exchanging conditional ligand-loaded MHC, could be probed in a single experiment, thus combining the molecular precision of biochemically purified MHCs with high content multiparametric flow cytometry-based assays. Semiquantitative determination of the peptide affinity for the restriction element could also be accomplished through competition experiments using this bead-based assay. Furthermore, the generated peptide-MHC reagents could directly be applied to antigen-specific CD8(+) T lymphocyte analysis. The combinatorial labeling of beads allowed straightforward identification by their unique fluorescent signatures and provided a convenient means for extended assay multiplexing.

Molecular and clinical characteristics of hepatitis B virus in Korea

Korea is an endemic area of hepatitis B virus (HBV) infection but very little is known about the molecular characteristics of HBV isolates from Korean patients or the association with disease progression. The complete HBV genome sequences from 53 Korean patients with chronic hepatitis B, advanced cirrhosis, or hepatocellular carcinoma (HCC) were analyzed to identify (i) subgenotype distribution and genetic diversity and (ii) signature mutations associated with liver disease progression. With the exception of 1 patient infected with HBV/B, all 52 patients (98.1%) were infected with HBV/C, subgenotype C2. These strains were 98.4% identical and the frequency of amino acid substitutions occurring within key immunological epitopes increased with disease severity. A number of amino acid/nucleotide substitutions were associated with HCC, namely sR24K (HBsAg), SI126T (HBsAg), and pcA1846T (precore gene) mutations (P = 0.029, 0.001, and 0.008, respectively). HBV harboring deletions in the pre-S region were also associated with increased liver disease severity (chronic hepatitis B vs. cirrhosis, P = 0.040; chronic hepatitis B vs. HCC, P = 0.040). Despite the high degree of sequence conservation, several key HBV mutations were associated with disease progression. Prospective studies with larger cohorts of patients are required to evaluate further the clinical manifestation of HBV/C2 in Korea.

Hepatitis B virus as a gene delivery vector activating foreign antigenic T cell response that abrogates viral expression in mouse models

Chronic hepatitis B virus (HBV) infection is characterized by functionally impaired T cell responses. To ensure active immunotherapy, the immune response must be switched from exhausted T cells to functional effectors that can attain the liver and cure the viral infection. We thus designed a recombinant HBV (rHBV) containing a modified viral core gene that specifically delivers a foreign antigenic polyepitope to the liver. This recombinant virus could only be self-maintained in hepatocytes already infected by HBV through capsid complementation. A strong foreign epitope-specific T cell response was first primed in the periphery by way of DNA immunization in human leukocyte antigen (HLA)-A2/DR1 transgenic mice. After the hydrodynamic (hyd.) injection of rHBV, expression of the foreign antigenic polyepitope in hepatocytes attracted/reactivated a vigorous T cell response in situ. Most liver-infiltrating CD8(+) T cells proved to be functional effectors. Following DNA priming and hyd. injection, the rHBV-based expression of hepatitis B surface antigen (HBsAg) in mouse liver was almost completely inhibited without causing major liver injury. Studies in HBsAg/HLA-A2/DR1 transgenic mice further validated our approach.

CONCLUSION

For the first time, HBV was used as a gene delivery vector, which strongly triggered functional T cell response and subsequently controlled the viral expression in the liver of surrogate mouse models for HBV infection. It might represent an innovative and promising strategy of active immunotherapy during HBV persistent infection. This concept could even be more generally extended to other chronic viral diseases.

HBcAg-pulsed dendritic cell vaccine induces Th1 polarization and production of hepatitis B virus-specific cytotoxic T lymphocytes

AIM

Dendritic cells (DCs) pulsed with HBsAg efficiently reverse the immune tolerance to hepatitis B virus (HBV) and induce HBV-specific cytotoxic T lymphocyte (CTL) responses in transgenic mice and healthy volunteers. However, it is not clear whether HBV core antigen (HBcAg)-pulsed DCs can effectively induce CD4(+) helper T cells polarization into Th1, which contribute to the induction and maintenance of HBV-specific CD8(+) T cells in chronic hepatitis B (CHB) patients. To address this issue, we conducted this study and investigated whether HBcAg-pulsed DCs could polarize Th1 cells and induce an HBcAg-specific CTL response.

METHODS

HBcAg-pulsed DCs were generated from 21 CHB patients. The capacity of the HBcAg-pulsed DC vaccine to stimulate CD4(+) and CD8(+) T cells to produce IFN-gamma and IL-4 was estimated by intercellular cytokine staining, and the HBcAg-pulsed DCs derived from 10 humam leucocyte antigen (HLA)-A2(+) CHB patients were tested for the induction of HBV-specific CTLs from autologous T cells by pentamer staining. The cytotoxicity of these CTLs was evaluated in vitro by flow cytometry.

RESULTS

The HBcAg-pulsed DCs derived from CHB patients exhibited a stronger capacity to stimulate autologous CD4(+) and CD8(+) T cells to release IFN-gamma rather than IL-4, which could induce HBV core 18-27 specific CTLs, suggesting a specific cytotoxicity against T2 cells that had been loaded with the HBV core 18-27 peptide in vitro.

CONCLUSION

HBcAg-pulsed DC vaccine derived from CHB patients efficiently induced autologous T cell polarization to Th1 and generation of HBV core 18-27 specific CTLs.

A mutant HBs antigen (HBsAg)183-191 epitope elicits specific cytotoxic T lymphocytes in acute hepatitis B patients

HBs antigen (HBsAg)183-191 (FLLTRILTI, R187 peptide) is a dominant human leucocyte antigen-A2 (HLA-A2)-restricted epitope associated with hepatitis B virus (HBV) infection in Caucasian populations. However, its prevalence is poorly understood in China, where there is a high incidence of HBV infection. In this report, we sequenced the region of HBsAg derived from 103 Chinese patients. Approximately 16.5% of the patients bore a mutant HBsAg183-191 epitope in which the original arginine (R187) was substituted with a lysine (K187 mutant peptide). Importantly, K187 still bound to HLA-A2 with high affinity, and elicited specific cytotoxic T lymphocyte (CTL) responses in HLA-A2/K(b) transgenic mice. K187-specific CTLs were also generated successfully in acute hepatitis B (AHB) patients, indicating that this mutant epitope is processed and presented effectively. Our findings show that R187-specific CTLs can cross-react with the K187 peptide. These findings reveal that K187 still has the property of an HLA-A2 restricted epitope, and elicits a protective anti-HBV CTL response in humans.

A Systematic Review of T-cell Epitopes in Hepatitis B Virus: Identification, Genotypic Variation and Relevance to Antiviral Therapeutics

Background

The immune response to hepatitis B virus (HBV) is important for both viral control and disease pathogenesis. A detailed understanding of the HBV-specific T-cell responses may potentially lead to novel therapeutic strategies for HBV.

Methods

All English language journal articles (including articles in press) up to October 2007 were retrieved using searches of MEDLINE, EMBASE and the Cochrane Controlled Trial Registry. An extensive database of HBV sequences (SeqHepB) and GenBank were used to assess the degree of sequence variation in each epitope. The new standardized nomenclature for HBV amino acid position number was applied to all previously defined epitopes.

Results

Forty-four HBV-specific human leukocyte antigen (HLA) class I restricted and 32 HBV-specific HLA class II restricted epitopes have been defined and have been identified in all HBV genes. The majority of HLA class I restricted epitopes have been defined in HLA-A2-positive individuals in the setting of acute HBV infection. There is significant sequence variation of these epitopes within and between HBV genotypes. Newer HBV immunotherapeutics appear promising but are still in early phases of development.

Conclusions

Identification of HBV-specific epitopes in non-HLA-A2-positive individuals and recognition of genotypic variation across epitopes are important for the future development of novel immunotherapeutic strategies for the management of chronic HBV infection.

Peripheral blood dendritic cells are phenotypically and functionally intact in chronic hepatitis B virus (HBV) infection

Persistence of hepatitis B virus (HBV) infection is associated with reduced anti-viral T cell responses. Impaired dendritic cell (DC) function was suggested as the cause of reduced T cell stimulation in chronic HBV carriers. Thus, we compared myeloid (mDC) and plasmacytoid DC (pDC) from chronic HBV carriers and controls. Frequency and phenotype of isolated DC were analysed by fluorescence activated cell sorter staining, DC function by mixed lymphocyte reaction, cytokine bead array, intracellular cytokine staining, enzyme-linked immunosorbent assay and enzyme-linked immunospot. Expression of HBV DNA and mRNA was studied by polymerase chain reaction (PCR). Circulating total DC, mDC or pDC were not reduced in chronic HBV carriers. Isolated mDC and pDC from chronic HBV carriers exhibited similar expression of co-stimulatory molecules and alloreactive T helper cell stimulation as control DC, whether tested directly ex vivo or after in vitro maturation. Secretion of pro- and anti-inflammatory cytokines by CD40 or Toll-like receptor ligand-stimulated patient DC was intact, as was human leucocyte antigen A2-restricted HBV-specific cytotoxic lymphocyte stimulation. Although both DC populations contained viral DNA, viral mRNA was undetectable by reverse transcription-PCR, arguing against viral replication in DC. We found no quantitative, phenotypic or functional impairment of mDC or pDC in chronic hepatitis B, whether studied ex vivo or after in vitro maturation.

The high prevalence of the I27 mutant HBcAg18-27 epitope in Chinese HBV-infected patients and its cross-reactivity with the V27 prototype epitope

HBcAg18-27 (FLPSDFFPSV, V27 epitope) is a dominant HLA-A2-restricted epitope in hepatitis B virus (HBV)-infected patients. So far, the occurrence of the epitope has not been assessed in China, where the prevalence of chronic HBV infection is high. In this report, we sequenced the HBV core gene in 105 Chinese patients with chronic HBV infection. Approximately 93.3% (98/105) of the core genes that were sequenced contained mutations with amino acid substitution at position 27 of the core protein: a mutation from a valine to an isoleucine (V27I). The mutant peptide (FLPSDFFPSI, I27) was found to bind to the HLA-A2 molecule with high affinity and elicit specific cytotoxic T lymphocyte (CTL) responses in acutely infected hepatitis B patients. In CTL assays using I27-specific pentamer staining, the V27 epitope showed a cross-reactive T cell response specific for the I27 epitope, but not vice versa. These findings provide important insights for the design of HBcAg18-27-based vaccines in the future.

Recombinant heat shock protein 65 carrying hepatitis B core antigen induces HBcAg-specific CTL response

Many studies have provided evidence that heat shock protein 65 (Hsp65) can elicit potent specific cellular adaptive immune responses (e.g. CD8(+) cytotoxic T-cell effectors or classic CTLs) based on their ability to chaperone antigenic peptides. Hsp65 is thus an effective carrier for heterologous peptide epitopes for therapeutic vaccines against cancer or chronic infectious diseases. The core antigen of hepatitis B virus (HBcAg) is extremely immunogenic, and functions as both a T-cell-dependent and a T-cell-independent antigen. Therefore, HBcAg may be a promising candidate target for therapeutic vaccine control of chronic HBV infection. Here, a chimeric protein, Hsp65Bc, was created by fusing the HBcAg sequence to the carboxyl terminus of the Hsp65 sequence in E. coli. Analysis of its antigenicity and immunogenicity revealed that HBc epitopes are surface accessible. Hsp65Bc induced moderate anti-HBc immune responses as well as a strong specific T-cell response in BALB/c mice. These results indicate that Hsp65Bc may have potential as a vaccine for treatment of HBV chronic infection.

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.

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.

Different composition of intrahepatic lymphocytes in the immune-tolerance and immune-clearance phase of chronic hepatitis B

Based on virological and biochemical parameters patients with chronic hepatitis B virus (HBV) are divided into distinct clinical phases: the immune-tolerance phase, the immune-clearance phase, and the inactive carrier state. Unclear is whether these phases have characteristic intrahepatic immune responses. The composition of liver-derived lymphocytes in patients with chronic HBV infection was studied. In 47 patients the composition of liver-derived lymphocytes was analyzed by flow cytometry of fine needle aspiration biopsies of the liver. The proportion natural killer (NK) cells in the liver was significantly higher in immune-tolerant than in immune-clearance patients and inactive carriers. No differences were found in proportion CD4+ T-cells and CD8+ T-cells, in these phases. However, when patients in the immune-clearance phase, with similar alanine transaminase (ALT), were grouped according to viral load, the proportion CD8+ T-cells was higher in those with high viral load. In contrast, the proportion CD4+ T-cells was increased in patients with low HBV-DNA. These differences were absent in the peripheral blood (PB). Intrahepatic HBV-specific CD8+ T-cells were mainly found in immune-clearance patients with low viral load. In conclusion, clear differences in the intrahepatic cellular infiltrate were found between the various clinical phases of chronic HBV infection. These findings are relevant to the design of new, individualized anti-viral strategies.

The impact of HBV-DNA fluctuations on virus-specific CD8+ T cells in HBeAg+ chronic hepatitis B patients treated with a steroid and lamivudine

Restoration of anti-viral immune response may be a requisite for sustained virological response to treatment in chronic hepatitis B patients. Over a 13-month period, we examined the dynamics of hepatitis B virus (HBV)-specific CD8+ cells in six human leucocyte antigen (HLA)-A2+ hepatitis B e antigen (HBeAg)+ 'immunotolerant' chronic hepatitis B patients treated sequentially with corticosteroid and lamivudine. Our results show that the combination treatment did not result in a sustained restoration of anti-viral specific CD8+ cells in five of the six patients studied. However, HBV-specific CD8+ cells, despite being severely compromised, were not totally deleted. Paradoxically, steroid treatment was not associated with inhibition but with a minimal increase of the HBV-specific CD8 response, and we observed that nucleocapsid-specific CD8 responses were not rescued by stable and prolonged inhibition but became detectable after rapid rebounds of HBV replication. In most patients, the transient and minimal restoration of HBV-specific immunity was not associated with clinical benefits. Our results describe a dynamic relationship between HBV-specific CD8+ cells and HBV-DNA values, that could potentially be used for a better design of HBV treatment in HBeAg+ 'immunotolerant' chronic hepatitis B patients.

Case report of lamivudine-resistant hepatitis B virus infection post liver transplantation from a hepatitis B core antibody donor

The use of allografts from donors with hepatitis B core antibody in liver transplantation (LT) is associated with the risk of de novo hepatitis B virus (HBV) infection. Prophylaxis using hepatitis B Immune globulin (HBIg) and lamivudine alone or in combination has been reported. Yet, there are no standardized regimens and long-term efficacy is not known. We report a case of a patient who underwent LT for alcoholic liver disease who received an allograft from a donor with Hepatitis B core antibody. The patient had no previous exposure to HBV, was vaccinated against HBV, and had demonstrated Hepatitis B surface antibody present in serum before and 6 months after transplantation. Prophylaxis with short-term HBIg (1 week) and indefinite lamivudine was given. De novo HBV infection developed more than 3 years after LT with a lamivudine-resistant polymerase mutant containing the rtM204I and rtl180L/M mutations. We reviewed the risk of de novo post-LT HBV infection in recipients of livers from hepatitis B core antibody positive donors. High risk were HBV naïve recipients, moderate risk recipients had isolated hepatitis B surface antibody (anti-HBs) or hepatitis B core antibody (anti-HBc), while low-risk recipients had both anti-HBs and anti-HBc. We reviewed prophylaxis protocols reported in the literature and made recommendations for management.

Tumor-associated carbohydrate antigens: a possible avenue for cancer prevention

Here we examine the use of glycopeptides containing tumour-associated carbohydrate antigens (TACA) as potential preventive vaccines for carcinomas. Our recent results suggest that CD8+ T cells (CTL) are capable of recognizing TACA in a conventional class I MHC-restricted fashion. The ThomsenFriedenreich antigen (TF), a disaccharide, and Tn, its immediate precursor, are TACA largely expressed in carcinomas. TF and Tn can be successfully used as Th-independent vaccines when conjugated to designer peptides with optimal binding affinity for class I MHC molecules. TF- and Tn-specific CTL generated using this strategy are capable of recognizing TACA-expressing tumours in vitro, suggesting that glycopeptides are as effectively presented by class I MHC molecules as non-glycosylated peptides. Because the exact sequences of endogenously synthesized glycopeptides are unknown, the TACA-specific T cell repertoire elicited by carbohydrate-based vaccines is assumed to be degenerate. Here we report that mice genetically manipulated to develop TACA-expressing mammary tumours are not tolerant to glycopeptide vaccination. Moreover, we tested the immunogenicity of designer glycopeptides capable of binding multiple HLA alleles as a novel approach for the development of vaccines potentially useful for vaccination of a large fraction of the general population. Our results have suggested that CTL derived from normal donors respond with high efficiency to glycopeptides in vitro, opening a new avenue for the design of prospective vaccines for cancer prevention.

Endoplasmic reticulum targeting sequence enhances HBV-specific cytotoxic T lymphocytes induced by a CTL epitope-based DNA vaccine

CD8(+) T cells play a critical role in protective immunity against Hepatitis B Virus (HBV). Epitope-based DNA vaccines expressing HBV-dominant CTL epitopes can be used as candidate vaccines capable of inducing cytotoxic T Lymphocytes (CTL) responses. A plasmid DNA encoding a CTL epitope of HBV core antigen, HBc(18-27), was constructed. Intramuscular immunization of C57BL/6 mice with this DNA vaccine resulted in successful induction of HBV-specific CTL responses. In order to promote transportation of the peptide into endoplasmic reticulum (ER) to bind to MHC class I molecules for optimal class I antigen presentation, an ER targeting sequence (ERTS) was fused with the C(18-27) encoding gene. ERTS fusion significantly enhanced specific CD8(+) T cell responses in terms of CTL cytolysis as well as IFN-gamma secretion. This enhancement was correlated with promoted epitope presentation on target cell surface. We report here an enhanced immunogenicity of an epitope-based DNA vaccine using an ER targeting signal sequence, which has significant implications for future design of therapeutic HBV vaccine.

Oral attenuated Salmonella typhimurium vaccine against MG7-Ag mimotope of gastric cancer

AIM: To develop an oral attenuated Salmonella typhimurium vaccine against gastric cancer and to evaluate its efficacy in mice.

METHODS: A complementary sequence of Nco I site and a sequence coding for MG7-Ag mimotope were designed at the 5’ terminus of forward primer. Using p1.2 II-HBCAg plasmid as template, PCR was performed to get a fusion gene of the mimotope and a HBcAg gene. The fusion gene was then subcloned into the plasmid pYA3341 complementary to Salmonella typhimurium X4550, and the recombinant plasmid was then transformed into attenuated Salmonella typhimurium X4550. Balb/c mice were orally immunized with the recombinant Salmonella typhimurium X4550. The mice were immunized every 2 wk to reinforce the immunity. At the 6^th wk, serum titer of antibody was detected by ELISA, and at the 8^th wk, cellular immunity was detected by ⁵¹Cr release test. Ehrlich ascites carcinoma cells expressing MG7-Ag were used in tumor challenge assay as a model to evaluate the protective effect of the vaccine.

RESULTS: Serum titer of antibody against MG7-Ag was significantly higher in mice immunized with the vaccine than in control groups (0.9538±0.043 vs 0.6531±0.018, P<0.01; 0.9538±0.043 vs 0.6915±0.012, P<0.01), while in vitro⁵¹Cr release assay of the splenocytes showed no statistical difference in the three groups. Two weeks after tumor challenge, 1 in 5 immunized mice was tumor free, while all the mice in the control group presented tumor.

CONCLUSION: Oral attenuated Salmonella typhimurium vaccine against the MG7-Ag mimotope of gastric cancer is immunogenic. It can induce significant humoral immunity against tumors in mice, and has some protective effects.

Cellular immune responses to the hepatitis B virus polymerase

CD4 T cells play an important role in hepatitis B virus (HBV) infection by secretion of Th1 cytokines that down-regulate HBV replication, and by promoting CD8 T cell and B cell responses. We have identified and characterized 10 CD4 T cell epitopes within polymerase and used them to analyze the immunological effects of long-term antiviral therapy as compared with spontaneous recovery from HBV infection. Candidate epitopes were tested for binding to 14 HLA-DR molecules and in IFN-gamma ELISPOT and cytotoxicity assays using peripheral blood lymphocytes from 66 HBV-infected patients and 16 uninfected controls. All 10 epitopes bound with high affinity to the most prevalent HLA-DR Ags, were conserved among HBV genomes, and induced IFN-gamma responses from HBV-specific CD4+ T cells. Several epitopes contained nested MHC class I motifs and stimulated HBV-specific IFN-gamma production and cytotoxicity of CD8+ T cells. HBV polymerase-specific responses were more frequent during acute, self-limited hepatitis and after recovery (12 of 18; 67%) than during chronic hepatitis (16 of 48 (33%); p=0.02). Antiviral therapy of chronic patients restored HBV polymerase and core-specific T cell responses during the first year of treatment, but thereafter, responses decreased and, after 3 years, were no more frequent than in untreated patients. Decreased T cell responsiveness during prolonged therapy was associated with increased prevalence of lamivudine-resistant HBV mutants and increased HBV titers. The data provide a rationale for the combination of antiviral and immunostimulatory therapy. These newly described HBV polymerase epitopes could be a valuable component of a therapeutic vaccine for a large and ethnically diverse patient population.

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.

Therapeutic polypeptides based on HBV core 18-27 epitope can induce CD8+ CTL-mediated cytotoxicity in HLA-A2+ human PBMCs

AIM: To explore how to improve the immunogenicity of HBcAg CTL epitope based polypeptides and to trigger an HBV-specific HLA I-restricted CD₈⁺ T cell response in vitro.

METHODS: A new panel of mimetic therapeutic peptides based on the immunodominant B cell epitope of HBV PreS2 18-24 region, the CTL epitope of HBcAg18-27 and the universal T helper epitope of tetanus toxoid (TT) 830-843 was designed using computerized molecular design method and synthesized by Merrifield’s solid-phase peptide synthesis. Their immunological properties of stimulating activation and proliferation of lymphocytes, of inducing T_H1 polarization, CD₈⁺ T cell magnification and HBV-specific CD₈⁺ CTL mediated cytotoxicity were investigated in vitro using HLA-A2⁺ human peripheral blood mononuclear cells (PBMCs) from healthy donors and chronic hepatitis B patients.

RESULTS: Results demonstrated that the therapeutic polypeptides based on immunodominant HBcAg18-27 CTL, PreS2 B- and universal T_H epitopes could stimulate the activation and proliferation of lymphocytes, induce specifically and effectively CD₈⁺ T cell expansion and vigorous HBV-specific CTL-mediated cytotoxicity in human PBMCs.

CONCLUSION: It indicated that the introduction of immunodominant T helper plus B-epitopes with short and flexible linkers could dramatically improve the immunogenicity of short CTL epitopes in vitro.

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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.

New options in the treatment of chronic hepatitis

The short-term aim of chronic hepatitis B treatment is the suppression of Hepatitis B Virus (HBV) replication, as shown by the loss of HBV DNA by DNA hybridization and the loss of Hepatitis B e Antigen (HBeAg). Loss of Hepatitis B s Antigen (HBsAg) and HBV DNA as assayed by Polymerase Chain Reaction (PCR) is very difficult to achieve. There are two important treatment approaches. The first is immunomodulation, comprising Interferon (IFN) and other cytokine treatment and therapeutic vaccination. The second is antiviral treatment, which mainly includes treatment with nucleoside analogs. There are many limitations to IFN treatment, because it has succeeded only in a small number of patients with a high level of transaminase and a low level of HBV DNA. The theoretical basis of therapeutic vaccination is the use of a vaccine that contains epitopes known to stimulate Human Leucocyte Antigen (HLA)-restricted cytotoxic T cell activity in order to lyse the HBV-infected hepatocytes. Several strategies of hepatitis vaccination are the incorporation of both pre-S and S antigen, the incorporation of a Cytotoxic T Lymphocyte (CTL)-specific antigen, the use of an HBV vaccine complexed to Hepatitis B Immune Globulin (HBIG), and DNA vaccination. One of the limitations of therapeutic vaccination is the short duration of immunity to the CTL antigen. Lamivudine is an oral nucleoside analog with potent antiviral action. It rapidly reduces the HBV DNA level, a level that soon returns to pretreatment level after drug administration is terminated. This drug does not affect the covalently bond closed circular (ccc)DNA of infected hepatocytes; it only inhibits the formation of new viruses. One-year of Lamivudine treatment significantly improved necroinflammation and reduced the progression of fibrosis and the histologic activity index. HBeAg seroconversion occurred after prolonged treatment. The emergence of a tyrosine-methionine asparagine aspargine YMDD mutant is one of the drawbacks of lamivudine treatment. Therefore a combination with other antiviral agents or immune modulators, such as therapeutic vaccination, is likely to be more effective.

Promiscuous CTL recognition of viral epitopes on multiple human leukocyte antigens: biological validation of the proposed HLA A24 supertype

Multiple HLA class I alleles can bind peptides with common sequence motifs due to structural similarities in the peptide binding cleft, and these groups of alleles have been classified into supertypes. Nine major HLA supertypes have been proposed, including an A24 supertype that includes A*2301, A*2402, and A*3001. Evidence for this A24 supertype is limited to HLA sequence homology and/or similarity in peptide binding motifs for the alleles. To investigate the immunological relevance of this proposed supertype, we have examined two viral epitopes (from EBV and CMV) initially defined as HLA-A*2301-binding peptides. The data clearly demonstrate that each peptide could be recognized by CTL clones in the context of A*2301 or A*2402; thus validating the inclusion of these three alleles within an A24 supertype. Furthermore, CTL responses to the EBV epitope were detectable in both A*2301(+) and A*2402(+) individuals who had been previously exposed to this virus. These data substantiate the biological relevance of the A24 supertype, and the identification of viral epitopes with the capacity to bind promiscuously across this supertype could aid efforts to develop CTL-based vaccines or immunotherapy. The degeneracy in HLA restriction displayed by some T cells in this study also suggests that the dogma of self-MHC restriction needs some refinement to accommodate foreign peptide recognition in the context of multiple supertype alleles.

HBcAg-specific CD8 T cells play an important role in virus suppression, and acute flare-up is associated with the expansion of activated memory T cells

We analyzed the prevalence and longitudinal fluctuation of hepatitis B virus (HBV)-specific CD8 T cells in chronic HBV infection using an HLA-A2-HBc18-27 tetramer. Thirty-five HLA-A2-positive patients with chronic HBV infection were divided into 17 HBe antigen (HBeAg)-positive and 18 anti-HBe antibody (anti-HBe)-positive patients. Five HLA-A2-positive normal subjects, five HLA-A2-negative patients with chronic HBV infection, and two HLA-A2-positive patients with acute HBV infection were included as controls. HBc18-27-specific CD8 T cells (c18-27-CD8Ts) were detected at a significantly higher prevalence in patients with anti-HBe (6/18) than in those with HBeAg (1/17), and their frequency reached 0.28% of the total CD8 T cells. The prevalence was significantly higher in patients with HBV DNA below 4.0 log genome equivalents (LGE)/ml (5/12) than in those with HBV DNA above 4.0 LGE/ml (2/23). The frequency of c18-27-CD8Ts was consistently higher in liver-infiltrating lymphocytes, ranging from 0.18 to 1.28%, than in autologous peripheral blood lymphocytes. Longitudinal analysis of patients with acute flare-up demonstrated that the elevation of alanine aminotransferase (ALT) was intimately associated with the expansion of c18-27-CD8Ts. Phenotypic analysis revealed that most c18-27-CD8Ts during acute flare-up expressed HLA-DR and CCR5, while those during low-ALT periods showed low expression. Furthermore, most liver-infiltrating c18-27-CD8Ts were positive for HLA-DR and CCR5, suggesting selective recruitment of activated c18-27-CD8Ts into the liver. In conclusion. HBV-specific CD8 T cells play an important role in the suppression of virus replication, and acute flare-up is associated with the expansion and activation of HBV-specific memory cells.

Cross-binding between Plasmodium falciparum CTL epitopes and HLA class I molecules

Plasmodium falciparum CTL epitope minigenes containing HLA-A2 and HLA-B7 subtype supermotifs were cloned into a plasmid expression vector; this expression was measured in eight human HLA class I molecule specific cell lines. Three assays for in vitro antigen presentation analysis were developed to examine the cross-binding between CTL epitopes and HLA class I molecules, including cell surface peptide-MHC class I binding assay, binding stabilization assay and MHC class I assembling assay. The results demonstrated that the HLA-B51 restricted CTL epitope of Plasmodium falciparum could be presented by other HLA class I molecules; however, no other presentation was found for HLA-A2.1 CTL epitope. This work suggests the possibility for improved vaccine-coverage rates by development of a CTL vaccine which contains epitopes capable of cross-binding among different MHC class I alleles.

Majority of peptides binding HLA-A*0201 with high affinity crossreact with other A2-supertype molecules

The A*0201, A *0202, A*0203, A*0206, and A*6802 binding capacity of single amino acid substitution analogs of known A2-supertype binding peptides and of large nonredundant peptide libraries was measured. The results were utilized to rigorously define the peptide binding specificities of these A2-supertype molecules. Although each molecule was noted to have unique preferences, large overlaps in specificity were found. The presence of L, I, V, M, A, T, and Q residues in position 2, and L, I, V, M, A, and T residues at the C-terminus of peptide ligands were tolerated by all molecules. Likewise, whereas examination of secondary influences on peptide binding revealed allele specific preferences, shared features could also be identified. These shared features were utilized to define an A2-supermotif and were noted to correlate with crossreactivity. Over 70% of the peptides that bound A *0201 with high affinity were found to bind at least two other A2-supertype molecules. Because the A2-supertype molecules studied herein cover the variants most common in different major ethnicities, these findings have important implications for epitope-based approaches to vaccination, immunotherapy, and the monitoring of immune responses.

Induction of strong hepatitis B virus (HBV) specific T helper cell and cytotoxic T lymphocyte responses by therapeutic vaccination in the trimera mouse model of chronic HBV infection

Humanized BALB/c mice (termed trimera mice) conditioned by lethal total body irradiation and bone marrow transplantation from SCID mice have been described to support rapid engraftment of human peripheral blood mononuclear cells (PBMC) and the induction of strong B and T cell responses after immunization in vivo. Moreover, these mice can be infected with the hepatitis B and C viruses (HBV, HCV). The current study employed this model to study therapeutic vaccination approaches against the HBV. Thus, strong primary Th cell responses against the HBV core (HBc) and the Borrelia burgdorferi control antigen were induced by transfer of antigen-loaded dendritic cells together with autologous PBMC from HBV-naive donors as well as by vaccination with high doses of antigen or a DNA plasmid encoding for HBcAg. Moreover, primary peptide-specific CTL responses against the immunodominant epitope HBc(18 - 27) were induced by HBc particle or DNA vaccination of chimera engrafted with HBV-naive PBMC. Finally, strong HBc-specific Th cell and antibody responses were induced by HBc or DNA vaccination of mice reconstituted with PBMC from a chronic HBV patient. Thus, since HBc represents the immunodominant antigen in self-limited HBV infection, HBc particles or DNA vectors are good candidates for therapeutic vaccination, that will be further studied in our model and clinical studies.

Identification of hepatitis B virus-specific CTL epitopes presented by HLA-A*2402, the most common HLA class I allele in East Asia

BACKGROUND/AIMS

The aim of this study was to identify and characterize hepatitis B virus (HBV)-specific cytotoxic T lymphocytes (CTL) epitopes presented by human leukocyte antigen (HLA)-A*2402, most common HLA class I allele in East Asia.

METHODS

HLA-A*2402-restricted CTL epitopes were identified by reverse immunogenetics. Immunogenecity of these epitopes was investigated using peripheral blood mononuclear cell (PBMC) from HLA-A24+ patients with acute hepatitis B.

RESULTS

An HLA-A*2402 stabilization assay demonstrated that 36 of 63 HBV peptides carrying HLA-A*2402 anchor residues have high- and medium-HLA-A*2402 binding affinity. Two (C117-125 and P756-764) of the 36 peptides induced peptide-specific CTLs. CTL clones and lines specific for these peptides killed HBV recombinant vaccinia virus-infected target cells expressing HLA-A*2402, indicating that these two peptides are CTL epitopes presented by HLA-A*2402. These two peptides were able to induce specific CTLs in 7 and 11 of 12 HLA-A24+ patients with acute hepatitis B, respectively.

CONCLUSIONS

We identified two immunodominant CTL epitopes restricted by HLA-A*2402. Because HLA-A*2402 is the most common allele in East Asia, a region in which there are approximately 200 million HBV carriers, these epitopes will be useful for analysis of CTL responses in patients from East Asia.

Degenerate immunogenicity of an HLA-A2-restricted hepatitis B virus nucleocapsid cytotoxic T-lymphocyte epitope that is also presented by HLA-B51

The recent identification of hepatitis B virus (HBV) epitopes restricted by multiple HLA alleles has greatly expanded the epitope repertoire available for T-cell-mediated therapeutic vaccine development. The HLA-B51-restricted peptide HBc19-27 is particularly interesting because it is located entirely within the HLA-A2-restricted HBc18-27 epitope. Here we show that HLA-B51-restricted cytotoxic T lymphocytes specific for HBc19-27 from a patient with acute HBV infection were also able to lyse HLA-B51-positive target cells pulsed with HBc18-27 and to produce gamma interferon when stimulated by that peptide, implying that HBc18-27 can be presented by HLA-B51 as well as by HLA-A2. These results demonstrate the concept of degenerate immunogenicity across HLA class supertype boundaries in a human viral disease setting. In addition, they could facilitate the development of an epitope-based therapeutic vaccine to terminate chronic HBV infection that could provide a broad and diverse population coverage with a single peptide.

T cell receptor usage of virus-specific CD8 cells and recognition of viral mutations during acute and persistent hepatitis B virus infection

T cells specific for a single viral epitope, but using different T cell receptors, should have flexibility in their epitope recognition to protect the infected host against the emergence of viral escape mutants. Therefore, polyclonality of the hepatitis B virus (HBV)-specific cytotoxic T lymphocyte response has been hypothesized to be a major determinant in the control of infection. We analyzed the Vbeta chain composition of the core 18-27-specific CD8 cells in acute and persistently HBV-infected patients using HLA-A2 tetrameric complexes and a panel of Vbeta antibodies. Different T cell receptors were utilized by core 18-27-specific CD8 cells both in patients with acute and chronic infection. The functional ability of these epitope-specific T cells to respond to potential viral mutations was then tested. The polyclonal HBV-specific CD8 response present in patients with acute hepatitis displayed a limited efficiency to recognize mutations introduced within the epitope. The ability of core 18-27-specific CD8 to tolerate epitope mutations was found only during persistent HBV infection. The data suggest that although a clonally heterogeneous CD8 response can be largely inhibited by the occurrence of single epitope mutations in primary HBV infection, preferential selection of T cells able to counteract the emergence of viral mutations can occur during persistent infection.

Immunization with the HBV core 18-27 epitope elicits CTL responses in humans expressing different HLA-A2 supertype molecules

The human leukocyte antigen (HLA)-A2 restricted HBV core 18-27 epitope is immunodominant in the context of HLA-A2.1 and subdominant in the context of the other HLA-A2 supertype molecules, as defined by frequency of recognition by memory cytotoxic T lymphocyte (CTL) responses from acute hepatitis B virus (HBV) patients, and on the basis of its binding affinity to purified HLA molecules in vitro. Herein, we show that immunization with a lipopeptide containing HBV core 18-27 epitope induces CTL responses in patients expressing different HLA-A2 supertype molecules, with indistinguishable frequency and magnitude. No difference in responses was noted between patients expressing either one or two different HLA-A2 supertype molecules. Thus, complexes of HBV core 18-27 bound to different HLA-A2 supertype alleles do not appear to act as altered peptide ligands, and do not cross antagonize CTL responses. These results substantiate the immunological relevance of the HLA supertypes concept, and illustrate its potential usefulness for the development of vaccines.