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

Incubation phase of acute hepatitis B in man: dynamic of cellular immune mechanisms

After hepatitis B virus (HBV) infection, liver injury and viral control have been thought to result from lysis of infected hepatocytes by virus-specific cytotoxic T cells. Patients are usually studied only after developing significant liver injury, and so the viral and immune events during the incubation phase of disease have not been defined. During a single-source outbreak of HBV infection, we identified patients before the onset of symptomatic hepatitis. The dynamics of HBV replication, liver injury, and HBV-specific CD8+ and CD4+ cell responses were investigated from incubation to recovery. Although a rise in alanine transaminase (ALT) levels was present at the time of the initial fall in HBV-DNA levels, maximal reduction in virus level occurred before significant liver injury. Direct ex vivo quantification of HBV-specific CD4+ and CD8+ cells, by using human leukocyte antigen (HLA) class I tetramers and intracellular cytokine staining, showed that adaptive immune mechanisms are present during the incubation phase, at least 4 weeks before symptoms. The results suggest that the pattern of reduction in HBV replication is not directly proportional to tissue injury during acute hepatitis B in humans. Furthermore, because virus-specific immune responses and significant reductions in viral replication are seen during the incubation phase, it is likely that the immune events central to viral control occur before symptomatic disease.

How can the cellular immune response control hepatitis B virus replication?

In this review we focus on aspects of the virus-specific cellular immune response, although we should point out that all the components of the innate and adaptive immune response are likely to play a role in successful control of hepatitis B virus (HBV) infection. We concentrate particularly on the relevance of the polyclonality and multispecificity of the HBV-specific cytotoxic T cell response to its antiviral activity. In this context, we discuss the possible role of viral escape mutations and highlight evidence from other models of the benefit of multispecificity in antiviral responses. We stress the contribution of CD4 help for effective CD8 responses and raise the possibility that HBV may produce factors inhibiting the antiviral response.

Nondeletional T-cell receptor transgenic mice: model for the CD4(+) T-cell repertoire in chronic hepatitis B virus infection

Chronicity after infection with the hepatitis B virus (HBV) can occur for a variety of reasons. However, once established, chronicity may be maintained by high levels of viral proteins circulating in the serum. To examine the characteristics of T cells capable of coexisting with the secreted hepatitis B e antigen (HBeAg), T-cell receptor (TCR) transgenic (Tg) mice were produced. To ensure that HBeAg-specific T cells would not be deleted in the presence of serum HBeAg, the TCR alpha- and beta-chain genes used to produce the TCR-Tg mice were derived from T-cell hybridomas produced from immunizing HBeAg-Tg mice. A TCR-Tg lineage (11/4-12) was produced that possessed a high frequency ( approximately 67%) of CD4(+) T cells that expressed a Tg TCR specific for the HBeAg. As predicted, when 11/4-12 TCR-Tg mice were bred with HBeAg-Tg mice no deletion of the HBeAg-specific CD4(+) T cells occurred in the thymus or the spleen. Functional analysis of the TCR-Tg T cells revealed that the HBeAg-specific CD4(+) T cells escaped deletion in the thymus and periphery by virtue of low avidity. Regardless of their low avidity, HBeAg-specific TCR-Tg T cells could be activated by exogenous HBeAg, as measured by cytokine production in vitro and T-helper-cell function for anti-HBe antibody production in vitro and in vivo. Furthermore, activated TCR-Tg HBeAg-specific T cells polarized to the Th1 subset were able to elicit liver injury when transferred into HBeAg or HBcAg-Tg recipients. Therefore, HBeAg-specific CD4(+) T cells that can survive deletion or anergy in the presence of circulating HBeAg nonetheless are capable of being activated and of mediating liver injury in vivo. The 11/4-12 TCR-Tg lineage may serve as a monoclonal model for the HBe/HBcAg-specific CD4(+) T-cell repertoire present in chronically infected HBV patients.

Properties of hepatitis B virus genome recovered from Vietnamese patients with fulminant hepatitis in comparison with those of acute hepatitis

Among the many mutations found in the hepatitis B virus (HBV) genome, some have been associated with fulminant hepatitis, as exemplified by precore-defective mutations. The aim of this study was to determine whether such mutations also are found in Vietnamese cases of fulminant hepatitis B. The full-genome nucleotide sequence of HBV in three patients with fulminant hepatitis (F-2, F-3, and F-6) and one with acute hepatitis (A-3), who were admitted to Cho Ray Hospital, Ho Chi Minh City, Vietnam was ascertained. Additionally, two patients with fulminant hepatitis (F-1 and F-7) and three with acute hepatitis (A-1, A-2, and A-5) were examined only for the precore/core region of HBV. Remarkably, the nonsense mutation at precore codon 28 (Trp82Stop) was found in four of the five patients with fulminant hepatitis, while all the acute hepatitis patients harbored wild type (one had a mixture of wild and mutant types). The missense mutations within the core region, Ile97Leu and Pro130Ile/Thr/Ser, were also remarkable in fulminant hepatitis. Only F-2 was free from these precore/core mutations, but F-2 was unique in that it possessed a chimeric genotype: it could be classified into genotype C as a whole, but its X region was of genotype B, like the other four fulminant hepatitis isolates (F-1, F-3, F-6, and F-7). The codon 41 of the X protein was Pro in all three fulminant hepatitis cases examined for this region, while it was Ser in the wild-type isolates of genotype B. Of note as negative data, the mutations C1653T and T1753M of the enhancer II (Enh II) and A1762T and G1764A of the precore/core promoter regions, once reported to be relevant to severe or fulminant hepatitis, were not found in the present cases. The results with the Vietnamese cases of fulminant hepatitis corroborated results of previous studies with respect to the mutations Trp28Stop of precore and Ile97Leu and Pro130Ile/Thr/Ser of core, but not for the mutations within Enh II and precore/core promoter region. Whether the Ser41Pro mutation in the X region of genotype B HBV is Vietnam-specific or disease-specific deserves further investigation.

Virus-specific lymphokine production differs quantitatively but not qualitatively in acute and chronic hepatitis B infection

Cytokines that are secreted as a response to viral antigen not only have direct antiviral properties but also crucially influence immune reactions determining the outcome of infection. As an advantageous alternative to the study of cytokines present in the supernatants of antigen-specific T cell clones and lines, we have used ELISPOT assays to determine the number of interferon-gamma (IFN-gamma)- and IL4-producing cells generated by peripheral blood mononuclear cells from patients with acute hepatitis B (AHB) and chronic hepatitis B (CHB) infection in response to HBcAg in a short-term culture (48 h). In response to HBcAg IFN-gamma was predominantly produced. In contrast to the results obtained in acute hepatitis B, the typical lymphokine pattern in CHB was characterized by a weak or absent antigen-specific IFN-gamma production. A predominance of IL-4-producing cells was not observed in either AHB or CHB. A significant number of IFN-gamma-producing cells was usually detectable during phases of viral elimination and the quality of the lymphokine response seemed to be epitope independent. Comparison of the results obtained in proliferation assays and ELISPOT assays clearly shows that lymphokine production upon stimulation with viral protein is totally independent of T cell proliferation and more sensitively reflects antiviral reactivity.

Comparison of the kinetics of the specific cellular immune response to duck hepatitis B virus in infected and immune ducks

The kinetics of the cell mediated immune response by ducks acutely and chronically infected with, or immune to infection by duck hepatitis B virus (DHBV) was determined. This was measured by an antigen specific blastogenesis assay to duck hepatitis B surface antigen (DHBsAg) and duck hepatitis B core antigen (DHBcAg) using peripheral blood mononuclear cells (PBMC). The three outcomes of acute infection by DHBV were either clearance from both serum and liver, clearance from serum but not liver, or the development of persistent viraemia. Acutely infected ducks that failed to clear the infection also failed to develop a significant cellular immune response to both antigens. Ducks with chronic infection acquired as neonates or as the result of the failure to clear acute infection had an increasing cellular immune response over time. Two groups of immune ducks were examined. These were either ducks that had become immune following infection or that had been vaccinated. Both groups of ducks demonstrated significant cellular responses following challenge with DHBV irrespective of the level of their responses before challenge. However, there was a reduction in the response of their PBMC over a 4-week-period postchallenge. The range of cellular immune responses to DHBV antigens observed in this study has a number of counterparts in hepatitis B infection of humans. Coupled with the defined clinical outcomes that can be established in the duck/DHBV model, further study of the cellular immune response to DHBV is warranted.

Histological changes during clearance of chronic hepatitis B virus infection by adoptive immunity transfer

BACKGROUND

Serological clearance of hepatitis B surface antigen (HBsAg) has been described after reception of hepatitis B surface antibody positive marrow, via allogeneic bone marrow transplantation (BMT). Histological changes during the clearance of HBsAg are unknown.

METHODS AND RESULTS

We described two chronic hepatitis B carriers (both hepatitis B e antigen negative), who cleared HBsAg after allogeneic bone marrow transplantation. Both received hepatitis B surface and core antibody positive human leucocyte antigen identical donors' marrow and had serological clearance of HBsAg 15 and 7 weeks after allogeneic BMT, respectively. Both events were preceded by hepatic flare. Both patients were also treated with famciclovir for the prevention of hepatitis B reactivation after BMT. Histological examination during the flare showed only mild necroinflammatory activity with multiple foci of confluent necrosis, associated with moderate lymphocytic infiltration. The majority of these lymphocytes were cluster of differentiation (CD) 8 positive. Using immunohistochemistry, there was no detectable hepatic expression of hepatitis B core antigen. However, HBsAg was positive, mainly in the area of confluent necrosis. Using in situ hybridization, hepatitis B virus (HBV) DNA was detected in the nucleus of 5% of hepatocytes, but not in the cytoplasm.

CONCLUSIONS

At their last follow up, 22 and 16 months after BMT, the serum of both patients remained HBsAg negative, hepatitis B surface antibody positive and HBV-DNA negative by branched DNA assay.

Differential antigen-processing pathways of the hepatitis B virus e and core proteins

BACKGROUND & AIMS

Hepatitis B e antigen (HBeAg) and hepatitis B core antigen (HBcAg) seem to play different roles in the induction and regulation of the antiviral immune response, although the two antigens share all major CD4(+) T-cell epitopes, and these epitopes can be processed from both antigens via the exogenous antigen-presenting pathway. The aim of this study was to test the ability of antigen-presenting cells to present epitopes from endogenously synthesized HBcAg/HBeAg on HLA class II molecules.

METHODS

Lymphoblastoid cell lines infected with recombinant vaccinia viruses containing various HBcAg or HBeAg constructs and stable transfectants were tested for their ability to stimulate HBcAg/HBeAg-specific CD4(+) T-cell clones.

RESULTS

Only antigen-presenting cells infected with HBeAg constructs but not those infected with HBcAg constructs were able to stimulate HBcAg/HBeAg-specific CD4(+) T-cell clones. T-cell activation by HBeAg constructs was completely inhibited by brefeldin A but not affected by chloroquin. In contrast, T-cell activation by exogenous, recombinant HBcAg was inhibited by chloroquin but not by brefeldin A.

CONCLUSIONS

The findings indicate that processing and HLA class II-associated presentation of endogenously synthesized HBeAg in virus-infected cells, including hepatocytes, may occur. This mechanism may be involved in the regulation of the CD4(+) T-cell response to HBcAg/HBeAg.

Antiviral cell-mediated immune responses during hepatitis B and hepatitis C virus infections

Cell-mediated immune responses to hepatitis B (HBV) and hepatitis C virus (HCV) antigens are vigorous and multispecific in acute, self-limited infections. Moreover, the prevalent cytokine pattern of circulating virus-specific T cells from patients who recover spontaneously from acute hepatitis is Th1-like. Longitudinal analysis of the T cell response to HCV antigens from the early stages of HCV infection in patients who recover from hepatitis and those who do not indicates that weaker responses and a prevalent Th2 pattern of cytokine production is associated with viral persistence and chronic evolution of disease. Although similar sequential studies are missing in hepatitis B, the observation that HBV-specific T cell responses are very weak or totally undetectable in the peripheral blood of patients with long-lasting chronic hepatitis B suggests that strength and quality of virus-specific T cell responses at the early stages of infection may influence the final outcome of both hepatitis B and C. While T cell hyporesponsiveness seems to be an important determinant for HBV persistence once chronic hepatitis has developed, this mechanism appears to be less critical in chronic HCV infection, because the vigor and quality of HCV-specific T cell responses seem to improve as a function of the duration of infection. This is shown by the finding that HCV-specific CD4- and CD8-mediated responses are easily detectable in the peripheral blood of patients with long-lasting chronic hepatitis C and that production of Th1 cytokines predominates within their livers. HCV therefore seems to be able to persist even in the face of an active T cell response and to acquire the capacity to survive within a host environment apparently unfavorable to its persistence. The high variability of HCV may explain its efficiency in escaping immune surveillance.

Kinetics of hepatitis B surface antigen-specific immune responses in acute and chronic hepatitis B or after HBs vaccination: stimulation of the in vitro antibody response by interferon gamma

Because cellular and humoral immune responses against the hepatitis B virus (HBV) surface antigen (HBs) might be crucial to overcome HBV infection, HBs-specific B- and T-cell responses of HBV patients and HBs vaccine recipients were analyzed quantitatively and functionally. In patients with acute hepatitis B (AHB), transient high anti-HBs-secreting B-cell frequencies were observed early after clinical onset, whereas 1 patient who probably developed chronic infection and chronic HBV carriers had absent or weak B- and T-cell responses. In HBs vaccine recipients, maximal HBs-specific B- and T-cell responses were detected after the first injection that decreased gradually before anti-HBs antibodies appeared in serum. Years after vaccination, anti-HBs-secreting B cells were enriched in the bone marrow. After in vitro stimulation with HBsAg, peripheral blood mononuclear cells (PBMC) of only 1 of 5 acute and 1 of 6 chronic HBV patients, but of all 6 vaccine recipients, secreted varying amounts of interferon gamma (IFN-gamma), but no interleukin-4 (IL-4) or IL-5. Furthermore, the addition of IFN-gamma, but not of IL-2, -4, -12, or IFN-alpha, resulted in strong increases of anti-HBs-secreting B cells in vaccine recipients and chronic carriers. In conclusion, circulating anti-HBs-secreting B cells were significantly higher in early acute hepatitis B or early after HBs vaccination than in chronic hepatitis B and decreased in the follow-up as a result of compartmentalization to lymphoid tissues. Release of IFN-gamma by antigen-stimulated T cells might be critical for anti-HBs formation.

Treatment of chronic hepatitis B virus infection: an Asia-Pacific perspective

Chronic hepatitis B infection is a serious health threat in the Asia-Pacific area. A consensus meeting on the treatment of chronic hepatitis B infection was conducted in Hong Kong, in August 1997. It was generally agreed that treatment of chronic hepatitis B infection should be based on the understanding of the natural history of chronic hepatitis B infection. To date, interferon alpha is the only Food and Drug Administration (FDA)-approved form of therapy for chronic hepatitis B infection. The overall response in Asian patients is unsatisfactory: approximately 15-20% will clear hepatitis B e antigen, but less than 5% will clear hepatitis B surface antigen. Newer immunomodulatory therapies are under trial. In contrast, nucleoside analogues, such as lamivudine (pending FDA approval) and famciclovir, have been shown to be potent suppressors of hepatitis B viral replication; however, their role as monotherapy in the treatment of chronic hepatitis B infection remains to be defined. Also, the issues of resistance to nucleoside analogues and withdrawal rebound need to be carefully studied. The future direction of therapy in chronic hepatitis B infection is probably a combination of nucleoside analogues or nucleoside analogues with immunomodulatory therapy.

Immunization of woodchucks with plasmids expressing woodchuck hepatitis virus (WHV) core antigen and surface antigen suppresses WHV infection

DNA vaccination can induce humoral and cellular immune response to viral antigens and confer protection to virus infection. In woodchucks, we tested the protective efficacy of immune response to woodchuck hepatitis core antigen (WHcAg) and surface antigen (WHsAg) of woodchuck hepatitis virus (WHV) elicited by DNA-based vaccination. Plasmids pWHcIm and pWHsIm containing WHV c- or pre-s2/s genes expressed WHcAg and WHsAg in transient transfection assays. Pilot experiments in mice revealed that a single intramuscular injection of 100 microgram of plasmid pWHcIm DNA induced an anti-WHcAg titer over 1:300 that was enhanced by boost injections. However, two injections of 100 microgram of pWHcIm did not induce detectable anti-WHcAg in woodchucks. With an increase in the dose to 1 mg of pWHcIm per injection, transient anti-WHcAg response and WHcAg-specific proliferation of peripheral mononuclear blood cells (PMBCs) appeared in woodchucks after repeated immunizations. Four woodchucks vaccinated with pWHcIm were challenged with 10(4) or 10(5) of the WHV 50% infective dose. They remained negative for markers of WHV replication (WHV DNA and WHsAg) in peripheral blood and developed anti-WHs in week 5 after challenge. In contrast, woodchucks not immunized or immunized with the control vector pcDNA3 developed acute WHV infection. Two woodchucks immunized with 1 mg of pWHsIm developed WHsAg-specific proliferative response of PBMCs but no measurable anti-WHsAg response. A rapid anti-WHsAg response developed during week 2 after virus challenge. Neither woodchuck developed any signs of WHV infection. These data indicate that DNA-based vaccination with WHcAg and WHsAg can elicit immunity to WHV infection.

Deletions in the hepatitis B virus core gene may influence the clinical outcome in hepatitis B e antigen-positive asymptomatic healthy carriers

To address the significance of mutations within the hepatitis B virus (HBV) core gene in chronic HBV infection, we followed prospectively HBe-antigen-positive asymptomatic healthy carriers, documented the onset of their disease based on serum alanine transaminase (ALT) concentrations, and analyzed sequentially serum samples from a quiescent phase through to an active phase of the chronic infection. In three female carriers, the first flare-up was documented during the follow-up period. Serial analysis by polymerase chain reaction, cloning, and sequencing of the HBV precore/core open reading frame genome demonstrated that clones with core gene deletions emerged during the quiescent phase and persisted subsequently during the active phase in two patients, who failed to seroconvert to anti-HBe and had persistently increased ALT levels despite interferon (IFN) therapy. The deletions were various, overlapping, and located in the mid-core region ranging from amino acid (aa) position 64 to 128. The remaining patient, who seroconverted with IFN therapy, did not have a core-gene-deletion HBV variant during follow-up, but had aa substitutions clustered in some restricted core regions. Two control asymptomatic carriers, who had no change in biochemical or virologic markers over a 15- to 19-year period, had no core-gene-deletion variants and few aa changes. These findings indicate that the mid-portion of the core gene is subject to deletion even during the quiescent phase. Thus, the immunologic interaction between the host and virus may occur insidiously, and the emergence of a core-gene-deletion HBV variant during the quiescent phase may be involved in the onset of hepatitis and the subsequent outcome of chronic infection.

Lamivudine treatment can restore T cell responsiveness in chronic hepatitis B

High viral and/or antigen load may be an important cause of the T cell hyporesponsiveness to hepatitis B virus (HBV) antigens that is often observed in patients with chronic HBV infection. Reduction of viral and antigen load by lamivudine treatment represents an ideal model for investigating this hypothesis. HLA class II restricted T cell responses and serum levels of HBV-DNA, HBsAg, and HBeAg were studied before and during lamivudine treatment in 12 patients with hepatitis B e antigen positive chronic active hepatitis B to assess possible correlations between viral and/or antigen load and vigor of the T cell response. Cell proliferation to HBV nucleocapsid antigens and peptides and frequency of circulating HBV nucleocapsid-specific T cells were assessed to characterize CD4-mediated responses. A highly significant enhancement of the CD4-mediated response to HBV nucleocapsid antigens was already detectable in most patients 7-14 d after the start of lamivudine treatment. This effect was dramatic and persistent in 10 patients but undetectable in 2. It occurred concomitant with a rapid and marked reduction of viremia. Interestingly, lamivudine also enhanced the responses to mitogens and recall antigens, showing that its effect was not limited to HBV-specific T cells. In conclusion, an efficient antiviral T cell response can be restored by lamivudine treatment in patients with chronic hepatitis B concurrently with reduction of viremia, indicating the importance of viral load in the pathogenesis of T cell hyporesponsiveness in these patients. Since lamivudine treatment can overcome T cell hyporeactivity, combining lamivudine with treatments directed to stimulate the T cell response may represent an effective strategy to induce eradication of chronic HBV infection.

Core variability does not affect response to interferon alpha in HBeAg negative chronic hepatitis B

BACKGROUND/AIMS

The pre-core stop codon variant (A 1896) of hepatitis B virus (HBV) has been associated with chronic active liver disease with acute exacerbations and a high relapse rate after an initial response to alpha-interferon (IFN-alpha) therapy. Poor sustained response has been correlated with a high prevalence of mutations in the core region, potentially enabling escape from the immune system. The aim of this study was to analyse the predictive factors of response to IFN-alpha in such patients.

METHODS

We studied the baseline clinical, biochemical, histological, serological and virological parameters in 30 hepatitis B s antigen positive (HBsAg-positive)/hepatitis B e antigen negative (HBeAg-negative) Greek patients with chronic liver disease. The patients were selected from a cohort who received IFN-alpha for 24 weeks. These were divided into three groups of ten sequential patients: those with no response to IFN-alpha treatment, those who relapsed after an initial response, and those with a sustained response. Serum HBV DNA was measured by a liquid hybridisation method, and the anti-HBc IgM was quantitated by the IMx analyser. The amino-acid sequence of core protein residues 40-89, a region where a clustering of mutations has been detected previously in severe hepatitis, was compared with a sequence from an HBeAg positive patient with chronic liver disease.

RESULTS

Multiple logistic regression analysis showed that the initial response to IFN-alpha could be predicted by pre-treatment absence of HBcAg staining in the liver and high ALT values, but no parameter could predict sustained response. The pre-treatment extent and pattern of aminoacid substitutions in the core region sequenced was similar in all groups studied and was not associated with IFN-alpha response.

CONCLUSIONS

In HBsAg-positive/HBeAg-negative patients with chronic liver disease, response to IFN-alpha therapy was not correlated with genomic variability of the core region. Other parameters such as pre-treatment HBcAg positivity in the liver and alanine aminotransferase values indicative of disease activity before treatment were associated with initial IFN-alpha response.

A vigorous virus-specific CD4+ T cell response may contribute to the association of HLA-DR13 with viral clearance in hepatitis B

A strong virus-specific CD4+ and CD8+ T lymphocyte response to hepatitis B virus (HBV) has been associated with viral clearance, but little is known about factors determining the individual's ability to mount such a T cell response. Recently a strong association between the HLA class II allele DR13 and a self-limited course of HBV infection has been described. In the present study of 33 patients with acute hepatitis B we show that individuals carrying HLA-DR13 mount a more vigorous CD4+ T cell response to HBV core (5706 ct/min (25th/75th percentile 3239 ct/min; 10,552 ct/min)) than patients without HLA-DR 13 (1365 ct/min (490 ct/min; 5334 ct/min); P = 0.006). However, peptide epitopes aa 50-69, aa 61-85, and aa 81-105 were recognized most frequently by both patient groups. Moreover, among 14 HBV core-specific CD4+ T cell clones from two patients with HLA-DR13, only one T cell clone was HLA-DR13-restricted. Our data suggest that the beneficial effect of the HLA-DR13 alleles on the outcome of HBV infection could be explained by a more vigorous HBV core-specific CD4+ T cell response, which may either be due to more proficient antigen presentation by the HLA-DR13 molecules themselves or a linked polymorphism in a neighbouring immunoregulatory gene.

Use of Complete Eluted Peptide Sequence Data from HLA-DR and -DQ Molecules to Predict T Cell Epitopes, and the Influence of the Nonbinding Terminal Regions of Ligands in Epitope Selection

In diseases with a strong association with an HLA haplotype, identification of relevant T cell epitopes may allow alteration of the pathologic process. In this report we use a reverse immunogenetic approach to predict possible HLA class II-restricted T cell epitopes by using complete pool sequencing data. Data from HLA-DR2(B1*1501), -DR3(B1*0301), -DQ2(A1*0501, B1*0201), and -DQ8(A1*0301, B1*0302) alleles were used by a computer program that searches a candidate protein to predict ligands with a relatively high probability of being processed and presented. This approach successfully identified both known T cell epitopes and eluted single peptides from the parent protein. Furthermore, the program identified ligands from proteins in which the binding motif of the HLA molecule was unable to do so. When the information from the nonbinding N- and C-terminal regions in the pool sequence was removed, the ability to predict several ligands was markedly reduced, particularly for the HLA-DQ alleles. This suggests a possible role for these regions in determining ligands for HLA class II molecules. Thus, the use of complete eluted peptide sequence data offers a powerful approach to the prediction of HLA-DQ and -DR peptide ligands and T cell epitopes.

T-Cell response to woodchuck hepatitis virus (WHV) antigens during acute self-limited WHV infection and convalescence and after viral challenge

The infection of woodchucks with woodchuck hepatitis virus (WHV) provides an experimental model to study early immune responses during hepadnavirus infection that cannot be tested in patients. The T-cell response of experimentally WHV-infected woodchucks to WHsAg, rWHcAg, and WHcAg peptides was monitored by observing 5-bromo-2'-deoxyuridine and [2-3H]adenine incorporation. The first T-cell responses were directed against WHsAg 3 weeks after infection; these were followed by responses to rWHcAg including the immunodominant T-cell epitope of WHcAg (amino acids 97 to 110). Maximal proliferative responses were detected when the animals seroconvered to anti-WHs and anti-WHc (week 6). A decrease in the T-cell response to viral antigens coincided with clearance of viral DNA. Polyclonal rWHcAg-specific T-cell lines were established 6, 12, 18, and 24 weeks postinfection, and their responses to WHcAg peptides were assessed. Five to seven peptides including the immunodominant epitope were recognized throughout the observation period (6 months). At 12 months after infection, T-cell responses to antigens and peptides were not detected. Reactivation of T-cell responses to viral antigens and peptides occurred within 7 days after challenge of animals with WHV. These results demonstrate that a fast and vigorous T-cell response to WHsAg, rWHcAg, and amino acids 97 to 110 of the WHcAg occurs within 3 weeks after WHV infection. The peak of this response was associated with viral clearance and may be crucial for recovery from infection. One year after infection, no proliferation of T cells in response to antigens was observed; however, the WHV-specific T-cell response was reactivated after challenge of woodchucks with WHV and may be responsible for protection against WHV reinfection.

Analysis of hepatitis B virus populations in an interferon-alpha-treated patient reveals predominant mutations in the C-gene and changing e-antigenicity

It is largely unknown whether hepatitis B virus (HBV) sequence variation during chronic infection hampers HBV immune recognition or the antiviral effect of cytokines on HBV production. Here we have analyzed which region of the HBV genome changes most drastically during an interferon-alpha (IFNalpha)-stimulated immune response. In addition, we have investigated whether the mutations affect viral replication, gene expression, and immune recognition of the mutant viral proteins. The study was performed with full-length HBV genomes taken longitudinally from a patient who transiently cleared HBV and seroconverted to anti-HBe during a long-term IFNalpha treatment. We found a replacement of the predominant virus population during IFNalpha therapy The virus populations differed mainly by a cluster of nucleotide changes in the C-gene and a pre-S2 deletion. Most of the newly emerging mutations localized within core/HBe B-cell epitopes, changed HBe antigenicity toward mono- and polyclonal antibodies, and also influenced the reactivity of the anti-HBc/e antibodies of the patient. All genomes tested expressed less HBeAg than wild-type HBV, while replication and IFNalpha susceptibility were similar. These data indicate that IFNalpha therapy can lead to the emergence of HBV variants with mutations mainly affecting recognition of the core/HBe proteins by antibodies. Taken together, the type of core/HBe-specific B-cell immune response, the sequence of the corresponding epitopes, and the HBe expression level appear to contribute to the decision on viral clearance or persistence.

Several Common HLA-DR Types Share Largely Overlapping Peptide Binding Repertoires

The peptide binding specificities of HLA-DRB1*0401, DRB1*0101, and DRB1*0701 have been analyzed by the use of large collections of synthetic peptides corresponding to naturally occurring sequences. The results demonstrated that nearly all peptides binding to these DR molecules bear a motif characterized by a large aromatic or hydrophobic residue in position 1 (Y, F, W, L, I, V, M) and a small, noncharged residue in position 6 (S, T, C, A, P, V, I, L, M). In addition, allele-specific secondary effects and secondary anchors were defined, and these parameters were utilized to derive allele-specific motifs and algorithms. By the combined use of such algorithms, peptides capable of degenerate DRB1*0101, DRB1*0401, and DRB1*0701 binding were identified. Additional experiments utilizing a panel of quantitative assays specific for nine additional common DR molecules identified a large set of DR molecules, which includes at least the DRB1*0101, DRB1*0401, DRB1*0701, DRB5*0101, DRB1*1501, DRB1*0901, and DRB1*1302 allelic products, characterized by overlapping peptide-binding repertoires. These results have implications for understanding the molecular interactions involved in peptide-DR binding, as well as the genetic and structural basis of MHC polymorphism. These results also have potential practical implications for the development of epitope-based prophylactic and therapeutic vaccines.

Functional characterization of naturally occurring variants of human hepatitis B virus containing the core internal deletion mutation

Naturally occurring variants of human hepatitis B virus (HBV) containing the core internal deletion (CID) mutation have been found frequently in HBV carriers worldwide. Despite numerous sequence analysis reports of CID variants in patients, in the past decade, CID variants have not been characterized functionally, and thus their biological significance to HBV infection remains unclear. We report here two different CID variants identified from two patients that are replication defective, most likely due to the absence of detectable core protein. In addition, we were unable to detect the presence of the precore protein and e antigen from CID variants. However, the production of polymerase appeared to be normal. The replication defect of the CID variants can be rescued in trans by complementation with wild-type core protein. The rescued CID variant particles, which utilize the wild-type core protein, presumably are enveloped properly since they can be secreted into the medium and band at a position similar to that of mature wild-type Dane particles, as determined by gradient centrifugation analysis. Our results also provide an explanation for the association of CID variants with helper or wild-type HBV in nature. The significance of CID variants in HBV infection and pathogenesis is discussed.

The optimization of helper T lymphocyte (HTL) function in vaccine development

Helper T lymphocyte (HTL) responses play an important role in the induction of both humoral and cellular immune responses. Therefore, HTL epitopes are likely to be a crucial component of prophylactic and immunotherapeutic vaccines. For this reason, Pan DR helper T cell epitopes (PADRE), engineered to bind most common HLA-DR molecules with high affinity and act as powerful immunogens, were developed. Short linear peptide constructs comprising PADRE and Plasmodium-derived B cell epitopes induced antibody responses comparable to more complex multiple antigen peptides (MAP) constructs in mice. These antibody responses were composed mostly of the IgG subclass, reactive against intact sporozoites, inhibitory of schizont formation in liver invasion assays, and protective against sporozoite challenge in vivo. The PADRE HTL epitope has also been shown to augment the potency of vaccines designed to stimulate a cellular immune response. Using a HBV transgenic murine model, it was found that CTL tolerance was broken by PADRE-CTL epitope lipopeptide, but not by a similar construct containing a conventional HTL epitope. There are a number of prophylactic vaccines that are of limited efficacy, require multiple boosts, and/or confer protection to only a fraction of the immunized population. Also, in the case of virally infected or cancerous cells, new immunotherapeutic vaccines that induce strong cellular immune responses are desirable. Therefore, optimization of HTL function by use of synthetic epitopes such as PADRE or pathogen-derived, broadly crossreactive epitopes holds promise for a new generation of highly efficacious vaccines.

Association between frequency of amino acid changes in core region of hepatitis B virus (HBV) and the presence of precore mutation in Japanese HBV carriers

To elucidate the relationship between the frequency of core mutations and precore mutation of hepatitis B virus (HBV) in Japanese HBV carriers, we investigated the nucleotide sequence of the precore/core region of HBV in 26 Japanese HBV carriers [15 who were HBe antigen-negative (HBeAg-) and 11 who were HBeAg-positive (HBeAg+)]. The number of amino acid changes (5.9 +/- 3.8) in the core region of HBV in HBeAg-carriers was significantly greater than that in the HBeAg+ carriers (1.5 +/- 1.0; P < 0.005). The precore stop codon mutation was found in 93.3% of HBeAg-negative HBV carriers, while no precore mutation was found in the HBeAg-positive HBV carriers, suggesting that the frequency of core mutations may be associated with the presence of the precore stop codon mutation. However, there was no significant difference in the frequency of amino acid changes among HBeAg-HBV carriers. The mean number of core amino acid changes of liver cirrhosis patients, chronic active hepatitis patients, chronic persistent hepatitis patients, and asymptomatic carriers were 2.7 +/- 1.5, 6.0 +/- 2.2, 4.7 +/- 1.2, and 8.4 +/- 5.3, respectively. We detected hot spots for core mutations, which showed characteristic localizations and specific substitutions: Gly-87, Leu-97, and Thr-130 were detected exclusively in patients with chronic liver disease with or without HBeAg. To address further the relationship between frequency of core mutations and the presence of the precore stop codon mutation, we investigated the precore/core nucleotide sequence serially along with seroconversion in three patients with chronic hepatitis B in whom the hepatitis either became inactive or remained active after the seroconversion. Emergence of the precore stop codon mutation and a significant increase in core amino-acid changes after seroconversion were noted in all three patients. Our results suggest a close association between the frequency of core amino acid changes and the presence of the precore stop codon mutation; some characteristic core mutations may be associated with the clinical course of chronic hepatitis B in Japanese patients.

Human histocompatibility leukocyte antigen-binding supermotifs predict broadly cross-reactive cytotoxic T lymphocyte responses in patients with acute hepatitis

The present study was designed to determine if highly conserved hepatitis B virus (HBV)-derived peptides that bind multiple HLA class I alleles with high affinity are recognized as cytotoxic T lymphocyte (CTL) epitopes in acutely infected patients. Peripheral blood mononuclear cells from 67 patients with acute hepatitis B, and 12 patients convalescent from acute hepatitis B, were stimulated with three panels of peptides, each of which bind with high affinity to several class I alleles from the HLA-A2-, HLA-A3-, or HLA-B7-supertypes. In these patients, 8 of the 19 peptides tested were found to represent CTL epitopes recognized by two or more alleles in each supertype. Two sets of nested peptides were recognized in the context of alleles with completely unrelated peptide binding specificities. Finally, promiscuous recognition by the same CTL of a given peptide presented by target cells expressing different A2 subtypes was also commonly observed. In conclusion, several HBV-specific CTL epitopes, recognized by acutely infected or convalescent patients in the context of a wide range of HLA alleles have been identified. These results demonstrate the functional relevance of the supertype grouping of HLA class I molecules in a human viral disease setting. Furthermore, they represent a significant advance in the development of a totally synthetic vaccine to terminate chronic HBV infection and support the feasibility of a systematic approach to development of similar vaccines for prevention and treatment of other chronic viral infections.

Peptide-specific CTL induction in HBV-seropositive PBMC by stimulation with peptides in vitro: novel epitopes identified from chronic carriers

Cytotoxic T lymphocytes (CTL) recognize and destroy virus-infected cells, and it has been established that epitope-based peptides could induce such CTL in vivo as well as in vitro. In this study attempts were made to define the epitopes that are recognized by the CTL, and thus a series of 9- to 10-mer peptides derived from the amino acid sequences of hepatitis B virus (HBV) proteins were synthesized on the basis of the previously described HLA-A2 peptide binding motif. The binding assay of the synthetic peptides using transporter-associated with antigen processing (TAP)-deficient human cell line, T2, showed that eight out of 11 peptides tested enhanced the expression of HLA-A2 molecules on the T2 cell surface. Some of these peptides triggered activation of CTL in peripheral blood mononuclear cells of HBV-seropositive chronic carriers. The activated CTL in turn recognized and killed the T2 cells pulsed with the same peptides. This study shows that novel HLA-A2-restricted epitopes exist in the natural repertoire of immunity against HBV. These findings can be useful in developing peptide-based therapeutics against viral infections.

Effect of hepatitis B virus on tumour necrosis factor (TNF alpha) gene expression in human THP-1 monocytic and Namalwa B-cell lines

In response to viruses, monocytes and B cells produce TNF alpha. Therefore, we investigated TNF alpha gene expression and protein secretion in a human monocytic cell line, THP-1, and a Burkitt's lymphoma B-cell line, Namalwa, in response to hepatitis B virus (HBV). Stimulation by phorbol myristate acetate (PMA) (100 ng/ml for 48 h) induced TNF alpha secretion in THP-1 and Namalwa cells (100 to 300 pg/ml). In THP cells, the optimum response (> 2000 pg/ml) was obtained in the presence of a second mitogenic signal such as lipopolysaccharide (LPS) (10 microg/ml for 24 h). In our activation conditions, Northern blot analysis revealed a marked accumulation of TNF alpha mRNA species at 1.7 kb in both cell lines. When PMA- or PMA+LPS-stimulated THP-1 cells were exposed to HBV, TNF alpha protein and mRNA significantly decreased (> 50%). In contrast, HBV exposure of PMA-activated Namalwa cells resulted in strongly increased TNF alpha protein secretion (1 ng/ml). In this case, HBV induced TNF alpha mRNA accumulation that consisted of two types: a regular 1.7 kb and two novel high molecular weight (HMW) species at 3.7 and 4.3 kb. Exposure of stimulated THP-1 and Namalwa cells to HBV resulted in HBs and pre-S1 antigen production in the supernatants. In addition, HMW HBV DNA forms were detected in both cell lines, but with distinct HindIII restriction patterns. These findings indicate that TNF alpha gene expression may be differently regulated by HBV in activated human macrophages and B cells, and thus TNF alpha may be involved in the pathogenesis of HBV.

Mapping of the cellular immune responses to woodchuck hepatitis core antigen epitopes in chronically infected woodchucks

T-cell responses to hepatitis B virus nucleocapsid antigens (HBcAg and HBeAg) play an important role in disease outcome in those infected with hepatitis B virus (HBV). The woodchuck is naturally infected in the wild with woodchuck hepatitis virus (WHV), which shows a high degree of genetic homology to HBV and produces a similar pattern of infection in its natural host. Twenty-three overlapping peptides were constructed to cover the entire WHV core region and used to identify immunodominant cellular epitopes in the nucleocapsid antigen using peripheral blood lymphocytes from 12 chronic WHV carrier and 4 uninfected control animals. A peripheral blood lymphocyte response was seen in all of the chronic WHV carrier animals to at least one peptide, and in 8 of the 12 chronic carrier animals a response was observed to 5 common peptides: peptide analogues of amino acids 16-30, 38-52, 50-69, 76-90 and 91-105. Peptide 91-105 produced maximal proliferation in 5 out of 12 infected animals. In addition, a difference in response was observed between wild and laboratory infected animals; the latter appeared to have a lower response to peptides than animals infected in the wild. This study provides evidence that the woodchuck has a population of peripheral blood cells which are sensitised to epitopes within the nucleocapsid protein and provides a basis on which to develop the use of the woodchuck as an immunological model of HBV infection for testing therapeutic means of enhancing this response.

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

Cytotoxic T-lymphocyte (CTL) activity appears to play an important role in resolving hepatitis B virus (HBV) infection, and the ability to induce such responses remains an important goal for developing effective immunotherapeutics. A panel of recombinant retrovirus vectors expressing different forms of the HBV core antigen (HBcAg) or e antigen (eAg) were found to induce antigen-specific major histocompatibility complex-restricted CTL responses in both mice and macaques. In addition, a novel retrovirus vector expressing an HBcAg-neomycin phosphotransferase II (HBc-Neo) fusion protein [LHBc-NEO(6A3)], which allows the measurement of the anti-Neo antibody response as a means of directly tracking biological activity of the vector, was generated. Doses greater than 10(7) CFU were necessary to induce CTL responses in H-2(k) mice. Intramuscular injections with 10(8) CFU of the LHBc-NEO(6A3) retrovirus vector into rhesus monkeys induced HBc/eAg-specific antibody production and CD8+ CTLs. The CTL response from one of the two responder rhesus monkeys was directed against a 9-residue peptide, GELMTLATW, at positions 63 to 71 of the HBc/eAg sequence. The CTL response is long lived, being detectable as late as 16 weeks after immunization, and can be boosted upon reimmunization. The potent ability of recombinant retrovirus vectors to induce HBcAg- and eAg-specific CTL responses may prove beneficial as a therapeutic treatment for chronic hepatitis B infection.

Emergence and selection of HBV variants in an anti-HBe positive patient persistently infected with quasi-species

BACKGROUND/AIMS

Infection with the hepatitis B e antigen (HBeAg) negative variant of hepatitis B virus (HBV) causes chronic liver disease characterised by occasional acute exacerbations. This virus exhibits a high prevalence of mutations in the core region. Our aim was to study the changes in the pre-core/core region of the virus in relation to exacerbations of the disease.

METHODS/RESULTS

We performed direct sequencing on DNA amplified from 7 sequential sera taken over a 5-year period from a hepatitis B surface antigen (HBsAg) and anti-HBe positive Greek patient infected with the HBeAg negative variant. The patient had chronic hepatitis with several acute exacerbation episodes and underwent interferon therapy twice. We found significant variability in the core region at different time points. To determine whether these variants were present in the initial serum sample and subsequently selected under immune pressure or whether they arose de novo during the course of the disease, we cloned the pre-core/core region from 4 sera before and after episodes of acute exacerbation. Fifteen clones from each time point were sequenced. Fourteen nucleotide mutations in the pre-core/core region were recorded, 7 (50%) of which led to amino-acid substitutions. All the amino-acid changes occurred at recognised B- and CD4+ epitopes. The cloning results indicate the presence of quasi-species in all the samples investigated. Some of the variants present as a minor population in the first sample appear to have been selected and become dominant in subsequent sera. However, the emergence of novel variants, not present at a detectable level in earlier samples, during the course of the disease, was also established. The quasi-species nature of HBV only became apparent after the cloning experiments and was not obvious from the direct sequencing results.

CONCLUSIONS

New dominant variants occurring during the course of the disease arose either by the selection of pre-existing mutants that were not detected by direct sequencing or by mutation of existing strains. All changes were located within B- and CD4+ epitopes. The continuous production and selection of variants may enable virus to evade elimination by the immune system, resulting in persistent infection.

Characterization of T-cell response to woodchuck hepatitis virus core protein and protection of woodchucks from infection by immunization with peptides containing a T-cell epitope

Specific activation of T cells appears to be a prerequisite for viral clearance during hepatitis B virus (HBV) infection. The T-cell response to HBV core protein is essential in determining an acute or chronic outcome of HBV infection, but how this immune response contributes to the course of infection remains unclear. This is due to results obtained from humans, which are restricted to phenomenological observations occurring during the clinical onset after HBV infection. Thus, a useful animal model is needed. Characterization of the T-cell response to the core protein (WHcAg) of woodchuck hepatitis virus (WHV) in woodchucks contributes to the understanding of these mechanisms. Therefore, we investigated the response of woodchuck peripheral blood mononuclear cells (PBMCs) to WHcAg and WHcAg-derived peptides, using our 5-bromo-2'-deoxyuridine assay. We demonstrated WHcAg-specific proliferation of PBMCs and nylon wool-nonadherent cells from acutely WHV-infected woodchucks. Using a cross-reacting anti-human T-cell (CD3) antiserum, we identified nonadherent cells as woodchuck T cells. T-cell epitope mapping with overlapping peptides, covering the entire WHcAg, revealed T-cell responses of acutely WHV-infected woodchucks to peptide1-20, peptide100-119, and peptide112-131. Detailed epitope analysis in the WHcAg region from amino acids 97 to 140 showed that T cells especially recognized peptide97-110. Establishment of polyclonal T-cell lines with WHcAg or peptide97-110 revealed reciprocal stimulation by peptide97-110 or WHcAg, respectively. We vaccinated woodchucks with peptide97-110 or WHcAg to prove the importance of this immunodominant T-cell epitope. All woodchucks immunized with peptide97-110 or WHcAg were protected. Our results show that the cellular immune response to WHcAg or to one T-cell epitope protects woodchucks from WHV infection.

Anergic TH1 clones specific for hepatitis B virus (HBV) core peptides are inhibitory to other HBV core-specific CD4+ T cells in vitro

A strong and transient hepatitis B virus core (HBc)-specific CD4+ T-cell response has been shown to be associated with viral elimination in acute self-limited hepatitis B but to be absent in chronic hepatitis B. So far, little is known about immunological mechanisms involved in the regulation of the HBc-specific CD4+ T-cell response. We studied 28 patients with acute hepatitis B, and frequently a sudden decrease in the HBc-specific CD4+ T-cell response was found between 4 and 8 weeks after disease onset. Thirty-two CD4+ T-cell clones specific for amino acids 50 to 69, 81 to 105, 117 to 131, or 141 to 165 of HBc were isolated from a patient shortly before the peripheral blood mononuclear cell response to most HBc-derived peptides abruptly disappeared. TH1 clones, but not TH0 clones, could be anergized in vitro by stimulation with specific peptides even in the presence of costimulatory cells. Moreover, when anergic cells were mixed with responsive cells, the proliferation of HBc-specific TH1 or TH0 clones was inhibited antigen specifically by anergic cells. The unusual susceptibility of HBc-specific TH1 clones to anergy induction in vitro as well as their potential to inhibit other HBc-specific TH1 and TH0 clones suggests that anergy induction may be involved in the downregulation of the virus-specific immune response during acute hepatitis B in vivo.

Plasmid DNA and protein vaccination of mice to the outer surface protein A of Borrelia burgdorferi leads to induction of T helper cells with specificity for a major epitope and augmentation of protective IgG antibodies in vivo

Plasmid DNA-based vaccination is an efficient way to evoke various forms of protective immunity in laboratory animals. Our previous experiments have shown that mice immunized with either plasmid DNA encoding the outer surface lipoprotein A (pOspA) of Borrelia burgdorferi or the respective lipoprotein (Lip-OspA) produce protective antibodies against subsequent challenge with virulent spirochetes. In the present study, we compared the specificity and function of T cells generated in AKR/N mice previously immunized to either pOspA or Lip-OspA. T cell populations derived by either of the two protocols consistently responded by proliferation in vitro to one (residues 186-203; B4) out of a panel of 27 overlapping 20-mer peptides spanning the entire OspA molecule of strain ZS7. B4 was shown to express allele-specific ligand motifs for I-Ek. Most of the other peptides produced variable and much less pronounced or marginal proliferative T cell responses. T cells reactive to B4 as well as to some minor epitopes were CD4+CD8- T cells which produced IFN-gamma but no detectable IL-4 upon antigen stimulation in vitro. Priming of AKR/N mice with B4 but not with inactive peptides of OspA led to an enhanced production of IgG antibodies, mainly of the IgG1 isotype, including those to a prominent protective epitope (LA-2) upon subsequent challenge with Lip-OspA or intact spirochetes. The data demonstrate that both plasmid DNA and protein immunization with OspA results in T cell responses with specificity for a dominant OspA epitope and suggest that priming of mice with immunodominant peptides accelerates the appearance of protective antibodies in vivo. The identification of T helper cell epitopes relevant for the induction of protective antibodies will also facilitate the design of more potent vaccines against Lyme disease.

DNA-mediated immunization in a transgenic mouse model of the hepatitis B surface antigen chronic carrier state

Transgenic mice expressing the sequences coding for the envelope proteins of the hepatitis B virus (HBV) in the liver have been used as a model of the HBV chronic carrier state. We evaluated the possibility of inducing a specific immune response to the viral envelope antigens and thus potentially controlling chronic HBV infection. Using HBV-specific DNA-mediated immunization in this transgenic model, we show that the immune response induced after a single intramuscular injection of DNA resulted in the complete clearance of circulating hepatitis B surface antigen and in the long-term control of transgene expression in hepatocytes. This response does not involve a detectable cytopathic effect in the liver. Adoptive transfer of fractionated primed spleen cells from DNA-immunized mice shows that T cells are responsible for the down-regulation of HBV mRNA in the liver of transgenic mice. To our knowledge, this is the first demonstration of a potential immunotherapeutic application of DNA-mediated immunization against an infectious disease and raises the possibility of designing more effective ways of treating HBV chronic carriers.

Immunopathogenesis of viral hepatitis

More than 500 million people world-wide suffer from viral hepatitis which can be caused by a variety of distinct infectious agents. The spectrum of disease, which ranges from acute self-limited hepatitis to liver cirrhosis, not only reflects the different biological properties and pathogenicity of the hepatitis viruses, but is also the result of the specific interaction between each virus and the immune system of the infected host. The immune response plays a crucial role in the elimination of the infecting virus as well as in disease pathogenesis and is described in detail for acute and chronic hepatitis B and C virus infection. Acute hepatitis B virus infection is characterized by a vigorous, polyclonal cytotoxic T lymphocyte response against HBV that is not readily detectable in patients with chronic hepatitis B, suggesting that resolution of disease is mediated by the HBV-specific CTL response in these patients. Because traces of virus as well as HBV-specific CTL can persist for decades after clinical recovery, continuous priming of new CTL by minute traces of virus is thought to protect from reactivation of disease. In contrast, the hepatitis C virus causes chronic liver disease despite a polyclonal and multispecific immune response, suggesting that distinct immunological and viral mechanisms determine the different clinical outcome of HBV and HCV infection. Their implications for the development of immunomodulatory vaccines to cure patients with chronic viral hepatitis are discussed.

Long-lasting memory T cell responses following self-limited acute hepatitis B

The molecular and cellular basis of long-term T cell memory against viral antigens is still largely undefined. To characterize anti-viral protection by memory T cells against non-cytopathic viruses able to cause acute self-limited and chronic infections, such as the hepatitis B virus (HBV), we studied HLA class II restricted responses against HBV structural antigens in 17 patients with acute hepatitis B, during the acute stage of infection and 2.2 to 13 yr after clinical resolution of disease. Results indicate that: (a) significant T cell proliferative responses to HBV nucleocapsid antigens were detectable in all patients during the acute phase of infection and in 14/17 also 2-13 yr after clinical resolution of disease; b) long-lasting T cell responses were sustained by CD45RO+T cells, predominantly expressing the phenotype of recently activated cells; c) limiting dilution analysis showed that in some patients the frequency of HBV-specific T cells was comparable to that observed in the acute stage of infection and, usually, higher than in patients with chronic HBV infection; d) the same amino acid sequences were recognized by T cells in the acute and recovery phases of infection; and e) HBV-DNA was detectable by nested-PCR in approximately half of the subjects. to conclusion, our results show that vigorous anti-viral T cell responses are detectable in vitro several years after clinical recovery from acute hepatitis B. Detection of minute amounts of virus in some recovered subjects suggests that long-term maintenance of an active anti-viral T cell response could be important not only for protection against reinfection but also for keeping the persisting virus under tight control.

Different clinical behaviors of acute hepatitis C virus infection are associated with different vigor of the anti-viral cell-mediated immune response

The anti-viral T cell response is believed to play a central role in the pathogenesis of hepatitis C virus infection. Since chronic evolution occurs in > 50% of HCV infections, the sequential analysis of the T cell response from the early clinical stages of disease may contribute to define the features of the T cell response associated with recovery or chronic viral persistence. For this purpose, 21 subjects with acute hepatitis C virus infection were sequentially followed for an average time of 44 wk. Twelve patients normalized transaminase values that remained normal throughout the follow-up period; all but two cleared hepatitis C virus-RNA from serum. The remaining nine patients showed persistent viremia and elevated transaminases. Analysis of the peripheral blood T cell proliferative response to core, E1, E2, NS3, NS4, and NS5 recombinant antigens and synthetic peptides showed that responses to all hepatitis C virus antigens, except E1, were significantly more vigorous and more frequently detectable in patients who normalized transaminase levels than in those who did not. By sequential evaluation of the T cell response, a difference between the two groups of patients was already detectable at the very early stages of acute infection and then maintained throughout the follow-up period. The results suggest that the vigor of the T cell response during the early stages of infection may be a critical determinant of disease resolution and control of infection.

Serial analysis of hepatitis B virus core nucleotide sequence of patients with acute exacerbation during chronic infection

Recent studies suggest that hepatitis B virus (HBV) core region could be an immunological target and that amino acid (aa) substitutions are mostly restricted to a small segment located in the middle of the core region. We sequenced the middle portion of HBV core gene during the course of acute exacerbation of chronic hepatitis B, and compared aa variations between the region including ideal HLA-A2 binding motifs and the nonbinding region. Five HBeAg+ chronic hepatitis patients with subtype adr (three with HLA-A2 and two without HLA-A2) were selected and using polymerase chain reaction (PCR) and cloning system, the central part of core region (nt 2063 to 2365, 303 bp) was sequenced in sera from each patient at three time points; before, at the peak of, and after exacerbation of hepatitis. The second set of sera showed higher aa substitution rates in five and in three out of five patients compared with those of the first and third sera, respectively. No significant difference was found in the aa substitution rates for the region with ideal HLA-A2 binding motifs between patients with and without HLA-A2. In asymptomatic HBV carriers with persistently normal aminotransferase values, alterations of the aa sequence were not observed within the same time frame. The results suggest that aa substitutions often occur at some particular positions in the middle of HBV core region during acute exacerbation of the disease under possible host immune pressures. Furthermore, unidentified epitopes appear to exist in the central part of HBV core region and HLA-unrestricted lymphocytes may play a role in the immune response of chronic HBV carriers.

Liver-infiltrating and circulating CD4+ T cells in chronic hepatitis C: immunodominant epitopes, HLA-restriction and functional significance

The aim was to assess the specificity and functional significance of liver-infiltrating and peripheral blood T cells in chronic hepatitis C. Peripheral blood mononuclear cells hepatitis C virus from 50 of 58 (86.2%) patients with chronic hepatitis C virus infection and 6 of 28 (21.4%) controls showed a proliferative T cell response to at least one of 16 synthetic peptides covering highly conserved regions of the core, envelope (El) and non-structural regions (NS4) of hepatitis C virus. However, six immunodominant peptides were exclusively recognized by the proliferating blood mononuclear cells from 46 patients with chronic hepatitis C virus infection (79.3%). Fine specificity and HLA-restriction were studied with 15 peptide-specific CD4+ T cell lines and 23 T cell clones isolated from liver tissue and peripheral blood of 12 patients with chronic hepatitis C. It was demonstrated that the peptide-specific response of CD4+ T cells was restricted to the presence of autologous accessory cells and HLA-DR and -DP molecules. Eight peptide-specific T cell lines and five T cell clones derived from liver tissue and peripheral blood, released interferon-gamma (200-6600 pg/ml) and tumor necrosis factor-alpha (100-400 pg/ml) and no or little interleukin-4 (< 140 pg/ml) after peptide-specific or mitogeneic stimulation, thus resembling a Th1-like cytokine profile. Patients with active liver disease showed significantly higher proliferative responses to hepatitis C virus core peptides than asymptomatic hepatitis C virus carriers or complete responders to interferon therapy. In conclusion, class II-restricted CD4+ T cell responses to some immunodominant epitopes within the hepatitis core region correlated with disease activity in chronic hepatitis C virus infection. Functionally, liver-infiltrating and peripheral blood T cells released Th1-like cytokines in response to the specific stimulus. Thus, it can be suggested that CD4+ T cells can mediate the pathogenesis of chronic hepatitis C virus induced liver disease.

Hepatitis B virus precore/core variation and interferon therapy

Precore/core genes from hepatitis B e antigen (HBeAg)-positive and antibody to HBeAg (anti-HBe) positive individuals with active hepatitis have been analyzed to search for correlations with response to interferon before and after treatment. Pretreatment, no precore stop codon mutants were detected, even at the 3% level, in HBeAg-positive responders or nonresponders. In anti-HBe-positive patients, precore mutants did not influence response. No significant core amino acid variability was observed in HBeAg-positive patients, irrespective of interferon response. However, anti-HBe-positive cases had multiple core protein substitutions, mostly in B- ant T-helper cell epitopes, but responders had fewer (P = .02 for responders versus nonresponders and reactivators). None of four responders, three of seven reactivators, and three of three nonresponders had mutations within the major T-helper epitope from aa50 to aa69 (P = .03). Precore mutants appeared in eight of nine natural seroconverters compared with 3 of 10 interferon-induced anti-HBe seroconverters (P = .01). Those in whom precore wild-type remained after treatment often tested negative in the last available sample using polymerase chain reaction (PCR), whereas emergence of mutants led to ongoing viremia in all cases. In anti-HBe-positive cases, precore sequences remained stable during therapy, except for 2 cases in whom a precore mutant appeared accompanied by reactivation. In the core protein, anti-HBe-positive cases selected a mean of 3.5, 1.6, and 1.7 amino acid substitutions in responders, nonresponders, and reactivators respectively (P = NS). In conclusion, core but not precore sequence before therapy may predict response. Appearance of precore mutants during therapy usually predicts failure to clear virus but substitution in core does not influence outcome.

Induction of T-helper cell response to hepatitis B core antigen in chronic hepatitis B: a major factor in activation of the host immune response to the hepatitis B virus

The T helper (Th) cell response to hepatitis B core antigen (HBcAg) was analyzed in 76 chronic hepatitis B virus (HBV) carriers with varying degrees of hepatic inflammation and HBV replication. Fifty-five patients had active viral replication, 28 with minimal histological changes and normal alanine transaminase (ALT) and 27 with active hepatic inflammation and elevated ALT. The remaining 21 chronic hepatitis B surface antigen (HBsAg) carriers had undetectable HBV replication, minimal histological activity, and normal ALT. In addition, 34 chronic HBV carriers were studied prospectively during treatment with alpha-interferon. The HBcAg-specific Th cell response was evaluated by a proliferative assay using 3H-thymidine uptake and gamma-interferon production by peripheral blood mononuclear cells. The proliferative response and gamma-interferon production of patients with active hepatic inflammation were significantly higher than in patients with minimal histological changes and in controls. In the longitudinal analysis during alpha-interferon treatment, 22 of 34 patients sustained an ALT flare accompanied by a parallel, significant Th cell response, which preceded or coincided with the ALT flare. The elevation in the Th cell response and the ALT flare were followed by a significant rise in the serum immunoglobulin (Ig) M anti-HBc index. Ten of twenty-two patients with an enhanced Th cell response and an ALT flare seroconverted after alpha-interferon treatment. The Th cell activity in the 10 responders rapidly subsided after hepatitis B e antigen (HBeAg) to anti-HBe seroconversion, whereas in the 12 nonresponders it remained elevated.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatitis B virus immunopathology

Approximately 5% of the world population is infected by the hepatitis B virus (HBV) which causes a necroinflammatory liver disease of variable duration and severity. Chronically infected patients with active liver disease carry a high risk of developing cirrhosis and hepatocellular carcinoma. The immune response to HBV-encoded antigens is responsible both for viral clearance and for disease pathogenesis during this infection. While the humoral antibody response to viral envelope antigens contributes to the clearance of circulating virus particles, the cellular immune response to the envelope, nucleocapsid and polymerase antigens eliminates infected cells. The class I- and class II-restricted T cell responses to the virus are vigorous, polyclonal and multispecific in acutely infected patients who successfully clear the virus, and they are relatively weak and more narrowly focussed in chronically infected patients who do not. The pathogenetic and antiviral potential of the cytotoxic T lymphocyte (CTL) response to HBV have been demonstrated by the induction of a severe necroinflammatory liver disease following the adoptive transfer of HBV surface antigen-specific CTL into HBV transgenic mice, and by the noncytolytic suppression of viral gene expression and replication in the same animals by a post-transcriptional mechanism mediated by interferon-gamma, tumor necrosis factor-alpha and interleukin-2. The dominant cause of viral persistence during HBV infection is the development of a weak antiviral immune response to the viral antigens. While neonatal tolerance probably plays an important role in viral persistence in patients infected at birth, the basis for poor responsiveness in adult onset infection is not well understood and requires further analysis. Viral evasion by epitope inactivation and T cell receptor antagonism may contribute to the worsening of viral persistence in the setting of an ineffective immune response, as can the incomplete down-regulation of viral gene expression and the infection of immunologically privileged tissues. Chronic liver cell injury and the attendant inflammatory and regenerative responses create the mutagenic and mitogenic stimuli for the development of DNA damage that can cause hepatocellular carcinoma. Elucidation of the immunological and virological basis for HBV persistence may yield immunotherapeutic and antiviral strategies to terminate chronic HBV infection and reduce the risk of its life-threatening sequellae.

Proliferative response of CD4+ T cells and hepatitis B virus clearance in chronic hepatitis with or without hepatitis B e-minus hepatitis B virus mutants

To assess the significance of cell-mediated immunity, T cells were derived from the peripheral blood and liver tissue of hepatitis B virus (HBV)-infected patients and controls. The analysis of the 3H-thymidine-uptake in response to a panel of recombinant HBV antigens revealed that peripheral blood mononuclear cells (PBMC) of the 25 viremic patients with inflammatory active, chronic hepatitis B, 16 with wild-type and nine with HBe-minus HBV mutant infection, showed stronger proliferative responses to HBc and HBe antigens than 16 asymptomatic nonviremic HBsAg carriers with normal aminotransferase levels (HBc: SI 19.3 +/- 3.9 vs. 13.0 +/- 3.2 vs. 8.0 +/- 1.2; P < .01 and HBe: SI 16.6 +/- 4.0 vs. 10.7 +/- 3.5 vs. 6.9 +/- 1.5; P < .05). In 15 patients with acute self-limited hepatitis B, however, significantly stronger HBc antigen-specific T-cell responses were observed during HBV clearance and HBe/anti-HBe seroconversion, whereas in nine completely HBV-immunized patients only minor proliferative responses to HBV antigens were observed. Six HBe/HBcAg- and two HBeAg-specific CD4+ T-cell lines could be expanded from liver tissue and peripheral blood of six viremic patients with chronic hepatitis B. Irrespectively of HBV mutations the HBV-specific activation of the T-cell lines was restricted by the presence of HLA-DR molecules and resulted in the release of Th1-like cytokine patterns. Follow-up of interferon (IFN) recipients showed simultaneous short-term increase of HBc/HBe-specific T-cell reactivities in responder patients during HBV clearance and HBe/anti-HBe seroconversion, whereas in nonresponders high virus load and HBV-specific immune responses were in imbalance.(ABSTRACT TRUNCATED AT 250 WORDS)