Induction of cytotoxic T lymphocytes with peptides in vitro: identification of candidate T-cell epitopes in hepatitis B virus X antigen

Hepatitis B x (HBx) as a Component of a Functional Cure for Chronic Hepatitis B

Patients who are carriers of the hepatitis B virus (HBV) are at high risk of chronic liver disease (CLD) which proceeds from hepatitis, to fibrosis, cirrhosis and to hepatocellular carcinoma (HCC). The hepatitis B-encoded X antigen, HBx, promotes virus gene expression and replication, protects infected hepatocytes from immunological destruction, and promotes the development of CLD and HCC. For virus replication, HBx regulates covalently closed circular (ccc) HBV DNA transcription, while for CLD, HBx triggers cellular oxidative stress, in part, by triggering mitochondrial damage that stimulates innate immunity. Constitutive activation of NF-κB by HBx transcriptionally activates pro-inflammatory genes, resulting in hepatocellular destruction, regeneration, and increased integration of the HBx gene into the host genome. NF-κB is also hepatoprotective, which sustains the survival of infected cells. Multiple therapeutic approaches include direct-acting anti-viral compounds and immune-stimulating drugs, but functional cures were not achieved, in part, because none were yet devised to target HBx. In addition, many patients with cirrhosis or HCC have little or no virus replication, but continue to express HBx from integrated templates, suggesting that HBx contributes to the pathogenesis of CLD. Blocking HBx activity will, therefore, impact multiple aspects of the host–virus relationship that are relevant to achieving a functional cure.

Whole genome deep sequencing analysis of viral quasispecies diversity and evolution in HBeAg seroconverters

Background & Aims

We aimed to investigate how viral quasispecies of the HBV whole genome evolves and diversifies in response to HBeAg seroconversion and viral control utilising next-generation sequencing (NGS).

Methods

Fifty HBeAg-positive chronic hepatitis B patients, including 18 treatment-naïve and 32 interferon (IFN)-treated individuals, were recruited. Serial HBV whole genomes in serum were analysed by NGS to determine sequence characteristics and viral quasispecies.

Results

HBV quasispecies diversity, measured by nucleotide diversity, was negatively correlated with viral load and hepatitis activity. Spontaneous HBeAg seroconverters exhibited significantly greater viral quasispecies diversity than treatment-naïve non-seroconverters from >1 year before seroconversion (0.0112 vs. 0.0060, p <0.01) to >1 year after seroconversion (0.0103 vs. 0.0068, p <0.01). IFN-induced HBeAg seroconverters tended to have higher viral genetic diversity than non-seroconverters along with treatment. Particularly, the IFN responders, defined as IFN-induced HBeAg seroconversion with low viraemia, exhibited significantly greater genetic diversity of whole HBV genome at 6 months post-IFN treatment than IFN non-responders (0.0148 vs. 0.0106, p = 0.048). Moreover, spontaneous HBeAg seroconverters and IFN responders exhibited significantly higher evolutionary rates and more intra-host single-nucleotide variants. Interestingly, in spontaneous HBeAg seroconverters and IFN responders, there were distinct evolutionary patterns in the HBV genome.

Conclusions

Higher HBV quasispecies diversity is associated with spontaneous HBeAg seroconversion and IFN-induced HBeAg seroconversion with low viraemia, conferring a favourable clinical outcome.

Lay summary

HBeAg seroconversion is a landmark in the natural history of chronic HBV infection. Using next-generation sequencing, we found that the nucleotide diversity of HBV was negatively correlated with viral load and hepatitis activity. Patients undergoing HBeAg seroconversion had more diverse HBV genomes and a faster viral evolution rate. Our findings suggest HBeAg seroconversion is driven by host selection pressure, likely immune selection pressure.

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Deep sequencing of whole HBV genome uncovers the quasispecies changes in chronic hepatitis B patients.

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The nucleotide diversity of HBV negatively correlates with viraemia during HBeAg loss/seroconversion.

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Viral quasispecies diversity is greater in spontaneous HBeAg seroconverters before and after seroconversion than in treatment-naïve non-seroconverters.

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Responders to IFN have greater viral quasispecies diversity than non-responders at 24 weeks after treatment.

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The genome positions of non-synonymous intra-host single nucleotide variants (iSNVs) of HBV tend to be located at possible T cell epitopes.

Hepatitis B virus X protein binding to hepsin promotes C3 production by inducing IL-6 secretion from hepatocytes

Hepatitis B virus (HBV) X protein (HBx) is an important effector for HBV-associated pathogenesis. In this study, we identified hepsin as an HBx-interacting protein and investigated the effects of hepsin on HBx-mediated complement component 3 (C3) secretion in hepatocytes. In vivo and in vitro binding between HBx and hepsin was confirmed by co-immunoprecipitation and Glutathione S-transferase pull-down assays. HBx synergized with hepsin to promote C3 production by potentiating interleukin-6 (IL-6) secretion. Knockdown of endogenous hepsin attenuated C3 and IL-6 secretion induced by HBx in hepatic cells. In addition, levels of hepsin protein correlated positively with C3 expression in human non-tumor liver tissues. Further exploration revealed that HBx and hepsin increased C3 promoter activity by up-regulating the expression and phosphorylation of the transcription factor CAAT/enhancer binding protein beta (C/EBP-β), which binds to the IL-6/IL-1 response element in the C3 promoter. HBx and hepsin synergistically enhanced IL-6 mRNA levels and promoter activity by increasing the nuclear translocation of nuclear factor kappaB (NF-κB). Our findings show for the first time that binding between HBx and hepsin promotes C3 production by inducing IL-6 secretion in hepatocytes.

Structural and functional distinctiveness of HLA-A2 allelic variants

Human leukocyte antigen (HLA) class I molecules are involved in the presentation of antigenic peptides to CD8(+) cytotoxic T lymphocytes (CTLs), which is important for the development of cellular immunity during viral infections and in cancers. HLA-A2 is one of the most frequent HLA class I specificities and thus is extensively studied structurally and functionally. Since its discovery, more than 300 allelic variants of this HLA specificity have been recorded. Among the HLA-A2 allelic variants, HLA-A*02:01 is the most prevalent, hence commonly used as a model to study HLA-A2-restricted CTL responses. However, HLA-A2 alleles are unevenly distributed globally such that HLA-A2 allelic variants besides A*02:01 are expressed at considerably high frequencies in Asian and African populations. Furthermore, increasing evidence of variations in the peptide-binding repertoire and CTL responses among HLA-A2 allelic variants suggests the need to understand these differences among various frequently expressed HLA-A2 molecules. In this review, the structural and functional distinctiveness of HLA-A2 allelic variants will be discussed.

Plasma soluble human leukocyte antigen-G expression is a potential clinical biomarker in patients with hepatitis B virus infection

The significance of upregulated soluble human leukocyte antigen-G (sHLA-G) expression under various pathologic conditions has been discussed. In this study, we evaluated the potential significance of plasma sHLA-G expression in patients with hepatitis B virus (HBV) infection. The study included 90 acute hepatitis B patients (AHB), 131 chronic hepatitis B patients (CHB), 152 resolved hepatitis B individuals (RHB), and 129 normal controls. sHLA-G were determined using enzyme-linked immunosorbent assay. A receiver operating characteristic (ROC) curve was used to evaluate the feasibility of plasma sHLA-G as a biomarker for distinguishing patients with HBV infection. sHLA-G levels in AHB (median, 193.1 U/mL; p < 0.001), CHB (median, 324.6 U/mL; p < 0.001), and RHB (median, 14.8 U/mL; p = 0.006) patients was much higher than that in normal controls (median, 9.0 U/mL). A significant difference for sHLA-G levels was also observed between patients with HBV infection (AHB vs CHB, AHB vs RHB, and CHB vs RHB; all p < 0.001). The area under the ROC curve for sHLA-G levels was 1.000 (p < 0.001) for AHB, 0.993 (p < 0.001) for CHB, and 0.604 (p = 0.003) for RHB patients versus normal controls, respectively. Data also indicated that the percentage of CD4(+)CD25(+)FoxP3(+) T regulatory cells and HLA-G(+)CD14(+) monocytes was significantly increased in AHB and CHB patients compared with normal controls (all p < 0.001). Our findings indicated that induction of HLA-G expression may play a role in HBV immune evasion and sHLA-G levels could be a useful biomarker in HBV infection.

Hepatitis B virus mutations associated with in situ expression of hepatitis B core antigen, viral load and prognosis in chronic hepatitis B patients

In this retrospective study, we investigated the prevalence and significance of mutations in part of the hepatitis B virus (HBV) x gene, and tried to clarify their relationship with clinicopathological or histopathological characteristics and prognosis in patients with chronic hepatitis B (CHB). A total of 83 consecutive CHB patients (1986-1994) were chosen for the present study. Sequence analysis was performed using polymerase chain reaction (PCR) and the direct sequencing method. The histological activity index was described using Scheuer scores. Two-step immunohistochemical staining showed the expression of viral antigens in situ. Tissue HBV DNA levels were determined by fluorescence quantitative real-time PCR. For the prognostic study, all the patients were followed up using clinical and laboratory data. Mutation at nt1726-1730 correlated significantly with decreased expression of HBcAg in situ (P = 0.006) and with lower HBV DNA levels in the liver (P = 0.004). In particular, the CTGAC mutation showed the strongest decrease of the viral load (P = 0.007). By contrast, nt1762/1764 mutation correlated with increased HBcAg (P = 0.005) and higher HBV DNA levels (P = 0.006). The mutants with the wild-type of nt1726-1730 or nt1762/1764 mutation were more prevalent in hepatocellular carcinoma (HCC) patients than in CHB patients. Although the mutations did not correlate with cirrhosis, the frequency of nt1762/1764 mutation in patients with hepatocarcinogenesis was significantly higher than in those without hepatocarcinogenesis (P = 0.011). Mutations at nt1726-1730 and nt1762/1764 are associated with in situ expression of HBcAg and viral load. Higher HBV DNA levels in the liver may be associated with hepatocarcinogenesis. Mutation at nt1762/1764 remarkably increases the risk of hepatocarcinogenesis.

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.

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.

Hepatitis B virus-related hepatocellular carcinoma: paradigms for viral-related human carcinogenesis

As discussed in detail in other chapters of this review, chronic hepatitis B (HBV) infection is a major risk factor for hepatocellular carcinoma (HCC). Most HCCs complicate the evolution of an active or inactive cirrhosis. However, some tumors occur on livers with minimal histological changes; the prevalence of such cases varies from one geographical region to the other, being much higher in the southern half of Africa (around 40% of HCCs) than in Asia, America and Europe, where at least 90% of HCCs are associated with the cirrhosis. This heterogeneity is probably a reflection of different environmental and genetic factors. This review will summarize the current knowledge on the mechanisms involved in HBV-related liver carcinogenesis. It will show in particular how viruses can be viewed as tools to discover and dissect new cellular pathways involved in cancer development and emphasize the potential synergistic effects between HBV and hepatitis C virus, as well as between viral infections and other environmental factors, such as alcohol.

In vivo hierarchy of immunodominant and subdominant HLA-A*0201-restricted T-cell epitopes of HBx antigen of hepatitis B virus

A polyepitopic CD8+ T-cell response is critical for the control of hepatitis B virus (HBV) infection. The HBV X protein (HBx) is a multifunctional protein that is important for the viral life cycle and for host-virus interactions. The aim of this study was to analyze the immunogenicity and dominance of various HLA-A*0201-restricted HBx-derived epitopes. For this purpose, we immunized HLA-A*0201-transgenic mice with HBx-derived peptides and DNA. This is a powerful model for studying the induction of HLA-A*0201-restricted immune responses in vivo, as these mice possess a cytotoxic T lymphocyte (CTL) repertoire representative of HLA-A2.1 individuals. We used cytotoxic tests and enzyme-linked immunosorbent spot (ELISPOT) assays to study the induction of specific cytotoxic and interferon (IFN)-gamma-secreting T cells. This allowed us to classify the HBx epitopes according to their T-cell activation capacity. After endogenous processing of the antigen synthesized in vivo after DNA-based immunization, we found that the HBx-specific T-cell response is targeted against one immunodominant epitope. Furthermore, following peptide immunization, we identified six additional novel subdominant T-cell epitopes. Inclusion of well-characterized epitopic sequences of HBx in a new vaccine for chronic HBV infections could help to broaden the T-cell response.

Dominant mutations of hepatitis B virus variants in hepatoma accumulate in B-cell and T-cell epitopes of the HBx antigen

Hepatitis B virus (HBV) X gene, encoding a pleotropic transactivator of HBx protein, has been associated with the development of hepatocellular carcinoma (HCC). Molecular information on liver-derived HBV variants isolated from HCC among Taiwanese population was studied. Amplification of the HBV X genes of 20 HCC patients in high stringency with HBV specific primers was observed. The resulting amplified HBV X genes were purified and individually-cloned into pUC-T vector. Sequences of the eight liver-derived X gene were aligned and compared with the wild type, the ayw HBV serotype. Results indicate that the HBx protein of variants were found predominantly within the regions of amino acid positions 26-45 in N-terminus, and positions 87, 88, 116, 118, 119, 127 and 144. Sequences from six out of the eight variants were found to be identical. These accumulated sequence mutations among the eight HBx variants were found to coincide within the B-cell epitopes (positions 29-48), particularly in the HBx proline and serine rich (PSR) domain, and the T-cell epitopes regions (positions 116-127). These frequent mutations of HBV variants, rather than subtype-specific polymorphic sites, may be involved in immunoevasion.

Tumor eradication by hepatitis B virus X antigen-specific CD8+ T cells in xenografted nude mice

We have previously reported several CTL epitopes derived from the hepatitis B viral X Ag (HBx). In this study, we evaluated whether HBx-specific CTLs can be effectively used in adoptive cancer immunotherapy. To validate the possibility, four peptides containing a HLA-A2.1-restricted binding consensus motif were identified from the HBx protein and tested for their ability to activate CTL from PBMCs isolated from chronic carriers of HBV (n = 12). We selected two highly potent epitopes, HBx 52-60 (HLSLRGLFV) and HBx 115-123 (CLFKDWEEL), that are capable of inducing Ag-specific cytotoxic T cells in patient PBMCs. For adoptive immunotherapy using HBx-specific CTLs, we generated CTL clones restricted to the HBx 52-60 or HBx 115-123 peptide using a limiting dilution technique. LC-46, an HBx 52-60-specific clone, is CD62L(-)CD69(+)CD45RO(+)CD45RA(-)CD25(dim) and is stained by IFN-gamma (approximately 92%), IL-2 (30%), and TNF-alpha (56%), but not by IL-5, IL-10, IL-12, or TNF-beta, indicating that the cells are fully activated T cytotoxic 1-type cells. When LC-46 cells were adoptively transferred into xenografted nude mice bearing human hepatomas expressing HLA-A2.1 molecules and intracellular HBx proteins, the tumors were eradicated. Taken together, our data provide solid evidence for the feasibility of adoptive immunotherapy with HBx-sensitized CTLs in hepatitis disease, including hepatocellular carcinoma (HCC).

HLA-A2 1 restricted peptides from the HBx antigen induce specific CTL responses in vitro and in vivo

The HBx-derived, HLA-A2.1 restricted peptides, XEP-3, XEP-4, and XEP-6, induced activation of specific CTLs from patients with HBV in vitro. XEP-6 peptide induced the strongest response among the three peptides in CTLs from the blood samples of patients that were HBsAg positive. It was not clear whether the stage of disease (chronic infection, cirrhosis or hepatoma) was related to the responsiveness of the CTLs to each peptide. We vaccinated HLA-A2/K(b) transgenic mice with these peptides encapsulated in pH-sensitive liposomes at various concentrations and tested their ability to protect against challenge with rVV-HBx. Mice immunized with encapsulated peptides were protected against viral challenge whereas those immunized with empty liposomes were not. In general, 5 micro g of each peptide per head inoculation was sufficient to give protection after 2 weeks. After 3 weeks, this protective effect was increased. This effect of time was more important on the level of protection than the initial dose of the peptide. To explain the protective effect, IFN-gamma secreting CD8(+) cells isolated from mice 3 weeks after immunization were analyzed ex vivo. There was little dose dependency of peptide on IFN-gamma secretion except for XEP-3. The variations in the results may reflect the chemical properties of the peptides, such as solubility and binding affinity. In conclusion, epitope peptides derived from HBx can induce specific CTL activation and lead to cellular immunity in vitro and in vivo by inducing the peptide-specific CD8(+) CTLs. Thus, pH-sensitive liposomes increase the immune response following immunization with a peptide vaccine. This could be used for the treatment of HBV-related disease.

Immunology of hepatitis B infection

The immune response initiated by the T-cell response to viral antigens is thought to be fundamental for viral clearance and disease pathogenesis in hepatitis B virus (HBV) infection. The T-cell response during acute self-limited hepatitis B in people is characterised by a vigorous, polyclonal, and multispecific cytotoxic and helper-T-cell response. By contrast, the immune response in chronic carriers, not able to eliminate the virus, is weak or undetectable. Thus a dominant cause of viral persistence could be the existence of a weak antiviral immune response. Methodological progress in animal models allows more precise investigation of the mechanisms by which the immune system resolves viral infection or develops chronic infection. Although clearance of most virus infections is widely thought to indicate the killing of infected cells by virus-specific T cells, data suggest that non-cytolytic intracellular viral inactivation by cytokines released by virus-inactivated lymphomononuclear cells could have an important role in the clearance of this virus without killing the infected cell. Additional factors that could contribute to viral persistence, which have been partly proven in animal models, are viral inhibition of antigen processing or presentation, modulation of the response to cytotoxic mediators, immunological tolerance to viral antigens, viral mutations, and infection of immunologically privileged sites. In view of the central role of cellular immunity in disease pathogenesis, strategies have been proposed to manipulate this cellular immune response in favour of protection from disease.