Detection of functionally altered hepatitis C virus-specific CD4 T cells in acute and chronic hepatitis C

Blocking of monocyte-associated B7-H1 (CD274) enhances HCV-specific T cell immunity in chronic hepatitis C infection

The establishment of a chronic hepatitis C (CHC) infection is associated with defective HCV-specific T cell responses. Recent studies suggest that negative T cell regulators such as programmed death 1 (PD-1) contribute to the impairment of virus-specific T cell functions in chronic viral infections. However, the implication of peripheral monocytes from CHC patients in the inhibition of HCV-specific T cell responses is only partially defined. In this study, we found that B7-H1, a ligand of PD-1, was significantly up-regulated on monocytes of CHC patients. Proliferation of T cells in response to anti-CD3 antibody was directly suppressed by B7-H1+CD14+ monocytes, and this suppression was reversed by addition of antagonistic B7-H1 mAb. Furthermore, blocking of monocyte-associated B7-H1 (moB7-H1) significantly enhanced the frequency of IFN-gamma-producing, HCV-specific CD4+ and CD8+ effector T cells and the production of Th1 cytokines, such as IL-2 but not Th2 cytokines, including IL-4 and IL-10. Upon B7-H1 blockade, production of perforin was also increased in CD8+ T cells stimulated with HCV peptides. Our findings suggest that moB7-H1 inhibits HCV-specific CD4+ and CD8+ T lymphocyte proliferation and suppresses Th1 cytokine production and perforin secretion. Blockade of the B7-H1 pathway thus represents an attractive approach in the treatment of chronic HCV infection.

Immunobiology and pathogenesis of viral hepatitis

Among the many viruses that are known to infect the human liver, hepatitis B virus (HBV) and hepatitis C virus (HCV) are unique because of their prodigious capacity to cause persistent infection, cirrhosis, and liver cancer. HBV and HCV are noncytopathic viruses and, thus, immunologically mediated events play an important role in the pathogenesis and outcome of these infections. The adaptive immune response mediates virtually all of the liver disease associated with viral hepatitis. However, it is becoming increasingly clear that antigen-nonspecific inflammatory cells exacerbate cytotoxic T lymphocyte (CTL)-induced immunopathology and that platelets enhance the accumulation of CTLs in the liver. Chronic hepatitis is characterized by an inefficient T cell response unable to completely clear HBV or HCV from the liver, which consequently sustains continuous cycles of low-level cell destruction. Over long periods of time, recurrent immune-mediated liver damage contributes to the development of cirrhosis and hepatocellular carcinoma.

Hepatitis C virus E2 envelope protein induces dendritic cell maturation

Maturation is a critical process for dendritic cells (DC) to gain or enhance their functions in antigen presentation and T-cell activation. In this study, we investigated the effect of hepatitis C virus (HCV) envelope protein E2 on DC maturation and related functions. We show that binding of E2 protein to DC leads to a change from immature to mature phenotype as detected by an increased expression of cell surface molecules including CD83, CD80, CD86, CD11c and MHC class II. The E2-matured DC showed higher capacity to stimulate T-cell proliferation and interferon-gamma production and displayed higher levels of interleukin-12 production when compared with immature DC. The induction of DC maturation by E2 is both time- and dose-dependent and can be inhibited by anti-E2 antibodies. In addition, DC matured by E2 showed decreased uptake of bovine serum albumin and latex beads, indicating their decreased activities of endocytosis and phagocytosis upon maturation. Taken together, our results demonstrated that E2 protein is able to induce dendritic cell maturation and suggested that E2 protein may play an important role in regulation of immune responses during HCV infection.

Regulatory T cells in hepatitis C virus infection

Hepatitis C virus (HCV) is a highly mutable RNA virus with a high propensity for chronic infection, affecting over 3% of the world's population. Persistent infection is associated with chronic hepatitis that may progress to cirrhosis and hepatocellular carcinoma over many years of infection. While cellular immune response plays a key role in viral infection, HCV persistence is associated with antiviral effector T-cell dysfunction with increased CD4+ CD25+ Tregs and interleukin-10+ Tr1cells, raising the possibility that the balance between antiviral effector and regulatory T-cell subsets contributes to the outcome of HCV infection.

Innate immunity in hepatitis C virus infection: Interplay among dendritic cells, natural killer cells and natural killer T cells

Sequential activation of innate and adaptive immune response is crucial for virus elimination. We thus sought to clarify the role of innate immune system in the pathogenesis of hepatitis C virus (HCV) infection. Dendritic cells (DC) sense virus infection via toll-like receptors (TLR) or retinoic acid inducible gene-I (RIG-I), resulting in the secretion of type-I interferons (IFN) and inflammatory cytokines. Blood DC consist of two subsets; myeloid DC (MDC) and plasmacytoid DC (PDC). In MDC from HCV-infected patients, regardless of higher expression of TLR2, TLR4 and RIG-I compared to the controls, the levels of TLR/RIG-I-mediated IFN-beta or TNF-alpha induction are lower than those in uninfected donors. These results suggest that the signal transduction in the downstream of TLR/RIG-I in MDC is profoundly impaired in HCV infection. In response to IFN-alpha, DC are able to express MHC class-I related chain A/B (MICA/B) and activate natural killer (NK) cells following ligation of NKG2D. Interestingly, DC from HCV-infected patients are unresponsive to exogenous IFN-alpha to enhance MICA/B expression and fail to activate NK cells. Alternatively, NK cells from HCV-infected patients downregulate DC functions in the presence of human leukocyte antigen E-expressing hepatocytes by secreting interleukin (IL)-10 and transforming growth factor-beta1. Such functional alteration of NK cells in HCV infection is ascribed to the enhanced expression of inhibitory receptor NKG2A/CD94 compared to the healthy counterparts. Invariant NKT cells activated by CD1d-positive DC secrete both T-helper (Th)1 and Th2 cytokines, serving as immune regulators. The frequency of NKT cells in chronic HCV infection does not differ from those in healthy donors. Activated NKT cells produce higher levels of IL-13 but comparable levels of IFN-gamma with those from healthy subjects, showing that NKT cells are biased to Th2-type in chronic HCV infection. In conclusion, cross-talks among DC, NK cells and NKT cells are critical in shaping subsequent adaptive immune response against HCV.

CD4+ T cell responses in hepatitis C virus infection

Hepatitis C virus (HCV) infection is a major cause of liver damage, with virus-induced end-stage disease such as liver cirrhosis and hepatocellular carcinoma resulting in a high rate of morbidity and mortality worldwide. Evidence that CD4+ T cell responses to HCV play an important role in the outcome of acute infection has been shown in several studies. However, the mechanisms behind viral persistence and the failure of CD4+ T cell responses to contain virus are poorly understood. During chronic HCV infection, HCV-specific CD4+ T cell responses are relatively weak or absent whereas in resolved infection these responses are vigorous and multispecific. Persons with a T-helper type I profile, which promotes cellular effector mechanisms are thought to be more likely to experience viral clearance, but the overall role of these cells in the immunopathogenesis of chronic liver disease is not known. To define this, much more data is required on the function and specificity of virus-specific CD4+ T cells, especially in the early phases of acute disease and in the liver during chronic infection. The role and possible mechanisms of action of CD4+ T cell responses in determining the outcome of acute and chronic HCV infection will be discussed in this review.

Monocyte-derived dendritic cells from chronic HCV patients are not infected but show an immature phenotype and aberrant cytokine profile

BACKGROUND

Chronic hepatitis C virus (HCV) infection is characterized by an insufficient immune response, possibly owing to impaired function of antigen-presenting cells such as myeloid dendritic cells (DCs). Therapeutic vaccination with in vitro generated DCs may enhance the immune response. Subsets of DCs can originate from monocytes, but the presence of HCV in monocytes that develop into DCs in vitro may impair DC function. Therefore, we studied the presence of HCV RNA in monocytes and monocyte-derived DCs from chronic HCV patients.

METHODS

Monocytes were cultured with granulocyte macrophage colony-stimulating factor (GM-CSF) and interleukin 4 (IL-4) for 6 days, and then with GM-CSF, IL-4, tumour necrosis factor-alpha (TNF-alpha), prostaglandin E2, IL-1beta and IL-6 for 2 days to generate mature DCs. HCV RNA was assessed by polymerase chain reaction. Surface molecules were assessed by flow cytometry. Cytokine production was assessed by cytokine bead array.

RESULTS

HCV RNA was present in monocytes in 11 of 13 patients, but undetectable in mature DCs in 13 of 13 patients. The morphology of patient DCs was comparable with DCs from healthy controls, but the percentage of cells expressing surface molecules CD83 (P=0.001), CD86 (P=0.023) and human leucocyte antigen-DR (P=0.028) was lower in HCV patients. Compared with control DCs, patient DCs produced enhanced levels of IL-10 (P=0.0079) and IL-8 (P=0.0079), and lower levels of TNF-alpha (P=0.032), IL-6 (P=NS) and IL-1beta (P=0.0079). Patient and control DCs did not produce IL-12.

CONCLUSIONS

Monocyte-derived DCs from chronic HCV patients are not infected but show an immature phenotype and aberrant cytokine profile.

Hepatitis C virus core protein up-regulates anergy-related genes and a new set of genes, which affects T cell homeostasis

Hepatitis C virus (HCV) infection is the main cause for chronic hepatitis, leading to cirrhosis and hepatic carcinoma. Virally induced immune dysfunction has been called as the cause for viral persistence. Previous results demonstrate that CD4 Jurkat cells stably expressing the HCV core protein show an increased activation of NFAT transcription factor and an impaired IL-2 promoter activity, affecting intracellular signaling pathways in a manner that mimics clonal anergy. We had shown previously that NFAT activates a transcriptional program, ensuing in immunological tolerance. In the present work, we have engineered lentiviral vectors expressing the HCV core to analyze the events, which unfold in the initial phase of HCV core-induced anergy. We show that genes initially described to be up-regulated by ionomycin-induced anergy in mice are also up-regulated in humans, not only by ionomycin but also by HCV core expression. We also show that HCV core is sufficient to cause NFAT nuclear translocation and a slow-down in cell-cycle progression, and using whole genome microarrays, we identify novel genes up-regulated in Jurkat cells expressing HCV core. The relevance of our results is highlighted by the presence of HCV in CD4 T cells from HCV chronically infected patients.

Protective effect of HLA-B57 on HCV genotype 2 infection in a West African population

Recovery from Hepatitis C virus (HCV) infection is considered infrequent (<20%) in western populations but reaches 50% in West Africa where genotype 2 infection is predominant. To investigate the role of cellular immune responses and host genetics in this phenomenon, samples from 104 Ghanaian blood donors reactive with anti-HCV assays were collected between 2000 and 2005. HCV antibody was confirmed by Western blot using genotype 2 recombinant core, E2 and NS3 proteins. Viral load and genotype were determined. Samples were stratified into 37 chronic, 35 recovered infections and 32 false positive. Eighty-one percentage of subjects with chronic infection (RNA positive) carried genotype 2 HCV. Cellular immune response was investigated in 35 frozen peripheral blood mononuclear cell (PBMC) samples suitable for interferon-gamma ELISPOT assay. Twelve out of 24 confirmed recovered, 1 out of 5 chronically infected and none of the 6 false-positive controls reacted to recombinant proteins. HLA-A, -B and -DR types were determined by DNA methodology. HLA-B*57 was significantly more frequent in the group which had recovered from HCV infection compared with chronically infected subjects (P = 0.0053, OR = 8.02). In conclusion, it is hypothesized that the dominance of genotype 2 HCV strains may be an important factor explaining the high rate of recovery from HCV infections in Ghana via an efficient contribution of HLA-B*57 which is relatively frequent in the population.

Tracking virus-specific CD4+ T cells during and after acute hepatitis C virus infection

BACKGROUND

CD4+ T cell help is critical in maintaining antiviral immune responses and such help has been shown to be sustained in acute resolving hepatitis C. In contrast, in evolving chronic hepatitis C CD4+ T cell helper responses appear to be absent or short-lived, using functional assays.

METHODOLOGY/PRINCIPAL FINDINGS

Here we used a novel HLA-DR1 tetramer containing a highly targeted CD4+ T cell epitope from the hepatitis C virus non-structural protein 4 to track number and phenotype of hepatitis C virus specific CD4+ T cells in a cohort of seven HLA-DR1 positive patients with acute hepatitis C in comparison to patients with chronic or resolved hepatitis C. We observed peptide-specific T cells in all seven patients with acute hepatitis C regardless of outcome at frequencies up to 0.65% of CD4+ T cells. Among patients who transiently controlled virus replication we observed loss of function, and/or physical deletion of tetramer+ CD4+ T cells before viral recrudescence. In some patients with chronic hepatitis C very low numbers of tetramer+ cells were detectable in peripheral blood, compared to robust responses detected in spontaneous resolvers. Importantly we did not observe escape mutations in this key CD4+ T cell epitope in patients with evolving chronic hepatitis C.

CONCLUSIONS/SIGNIFICANCE

During acute hepatitis C a CD4+ T cell response against this epitope is readily induced in most, if not all, HLA-DR1+ patients. This antiviral T cell population becomes functionally impaired or is deleted early in the course of disease in those where viremia persists.

Analysis of the relationship between cytokine secretion and proliferative capacity in hepatitis C virus infection

CD4(+) T-cell responses are important for the outcome of hepatitis C virus (HCV) infection. However, the functional status of HCV-specific CD4(+) T cells in persistent infection is poorly understood. It is generally recognized that proliferative capacity of HCV-specific CD4(+) T cells is weak or absent in persistent infection, but whether this results from deletion of antigen-specific cells or represents maintenance of antigen-specific but poorly proliferative populations is not defined. We used a set of ex vivo assays to evaluate the functionality of HCV specific CD4(+) T cells in persistent and resolved infection. Peripheral blood mononuclear cells (PBMC) from 24 prospectively recruited HCV polymerase chain reaction (PCR) positive individuals, 12 spontaneously resolved individuals (i.e. anti-HCV+, PCR-) and 11 healthy controls were analysed for interferon-gamma (IFN-gamma) and interleukin 2 (IL-2) secretion by enzyme linked immunospot assays (ELISpot). HCV-specific CD4(+) proliferative responses of carboxy fluorescein succinimidyl ester-labelled PBMC were assessed using a sensitive single cell flow cytometric assay. Sustained IFN-gamma ELISpot responses were observed in the PCR+ group. However, proliferation of HCV-specific CD4(+) T cells in the PCR+ group was substantially reduced on a per cell basis, in parallel to IL-2 secretion, compared with responses in the PCR- group. In PCR- individuals, a strong relationship between cytokine secretion and proliferative capacity was seen. However, in PCR+ individuals, IFN-gamma secretion far exceeded proliferative capacity. During persistent HCV infection, some CD4(+) T-cell specificities appear to be lost, as measured using a range of techniques, but others, potentially important, are maintained as IFN-gamma secretors but with low proliferative capacity even using a highly sensitive assay. Such subsets may yet play a significant role in vivo and also provide a template for modulation in immunotherapeutic interventions.

Immunologic evidence for lack of heterologous protection following resolution of HCV in patients with non-genotype 1 infection

Chronic hepatitis C virus (HCV) infection is typically characterized by a lack of virus-specific CD4(+) T-cell-proliferative responses, but strong responses have been described in a subset of persons with persistent viremia. One possible explanation for these responses is that they were primed by an earlier resolved infection and do not recognize the current circulating virus. We defined all targeted epitopes using overlapping peptides corresponding to a genotype 1a strain in 44 patients chronically infected with different HCV genotypes (GT). Surprisingly, more HCV-specific CD4(+) T-cell responses were detected in patients with chronic non-GT1 infection compared with patients with chronic GT1 infection (P = .017). Notably, we found serologic evidence of a previous exposure to GT1 in 4 patients with non-GT1 infection, and these persons also demonstrated significantly more responses than non-GT1 patients in whom genotype and HCV serotype were identical (P < .001). Comparison of recognition of GT1-specific peptides to peptides representing autologous virus revealed the absence of cross-recognition of the autologous circulating virus. These data indicate that persistent HCV infection can occur in the presence of an HCV-specific T-cell response primed against a heterologous HCV strain, and suggest that clearance of 1 GT does not necessarily protect against subsequent exposure to a second GT.

Hepatitis C virus infects T cells and affects interferon-gamma signaling in T cell lines

It has been reported that hepatitis C virus (HCV) may infect and replicate in human T cells, particularly in perihepatic lymph nodes, but the extent and consequence of T-cell infection in patients is unclear. This study is conducted to characterize the parameters and functional consequences of HCV infection in T lymphocytes. By using a lymphotropic HCV strain, we showed that HCV could infect T cell lines (Molt-4 and Jurkat cells) in vitro. Both positive- and negative-strand HCV RNA were detected for several weeks after infection. Viral proteins could also be detected by immunofluorescence studies. Moreover, infectious HCV particles were produced from Molt-4 cell cultures, and could be used to infect naïve T cell lines. HCV could also infect human primary CD4+ T cells, particularly naïve (CD45RA+CD45RO-) CD4+ cells, in culture. The amounts of STAT-1 and phosphorylated STAT-1 proteins in the infected Molt-4 cells were significantly less than those in uninfected cultures, suggesting the possibility of defect in interferon-gamma signaling. Indeed, T-bet and STAT-1 mRNA levels after interferon-gamma stimulation in infected Molt-4 were suppressed. In conclusion, HCV could infect and transiently replicate in T cells and that HCV replication suppressed the IFN-gamma/STAT-1/T-bet signaling due to the reduction of STAT-1 and inhibition of its activation (phosphorylation).

Hepatitis C virus (HCV)-specific CD8+ cells produce transforming growth factor beta that can suppress HCV-specific T-cell responses

Hepatitis C virus (HCV)-specific T-cell responses are rarely detected in peripheral blood, especially in the presence of human immunodeficiency virus (HIV) coinfection. Based on recent evidence that T-regulatory cells may be increased in chronic HCV, we hypothesized that functional blockade of regulatory cells could raise HCV-specific responses and might be differentially regulated in the setting of HIV coinfection. Three groups of subjects were studied: HCV monoinfected, HCV-HIV coinfected, and healthy controls. Frequencies of peripheral T cells specific for peptides derived from HCV core, HIV type 1 p24, and recall antigens were analyzed by gamma interferon (IFN-gamma) enzyme-linked immuno-spot assay. HCV-specific T-cell responses were very weak in groups with HCV and HCV-HIV infections. Addition of blocking antibodies against transforming growth factor beta1 (TGF-beta1), -2, and -3 and interleukin-10 specifically increased the HCV-specific T-cell responses in both infected groups; however, this increase was attenuated in the group with HCV-HIV coinfection compared to HCV infection alone. No increase in recall antigen- or HIV-specific responses was observed. Flow cytometric sorter analysis demonstrated that regulatory-associated cytokines were produced by HCV-specific CD3(+)CD8(+)CD25(-) cells. Enhancement of the IFN-gamma effect was observed for both CD4 and CD8 T cells and was mediated primarily by TGF-beta1, -2, and -3 neutralization. In conclusion, blockade of TGF-beta secretion could enhance peripheral HCV-specific T-cell responses even in the presence of HIV coinfection.

Monocyte-derived dendritic cell function in chronic hepatitis C is impaired at physiological numbers of dendritic cells

Monocyte-derived dendritic cells (MoDCs) are a promising cellular adjuvant for effector immune responses against tumours and chronic viral infections, including hepatitis C virus (HCV). If autologous DC therapeutic approaches are to be applied in persistent HCV infections in patients, it is important to have an unambiguous understanding of the functional status of the cell type used, namely MoDCs from patients with chronic hepatitis C (CHC) infection. Because of conflicting published reports of either impaired or normal MoDC function in CHC infection, we re-examined the ability of MoDCs from CHC and normal healthy donors (NHD) to mature to an inflammatory stimulus [tumour necrosis factor (TNF)-alpha] and their subsequent functional capabilities. Expression of maturation-associated phenotypic markers [human leucocyte antigen (HLA)-DR, CD83, CD86, CD40], allostimulatory capacity in mixed lymphocyte reactions (MLRs) and CD40-ligand-induced cytokine and chemokine generation were compared in CHC- versus NHD-MoDCs. TNF-alpha-stimulated CHC-MoDCs up-regulated phenotypic markers, but to significantly lower levels than NHD-MoDCs. At physiological ratios of DCs to T cells, CHC-MoDCs were less allostimulatory than NHD-MoDCs, but not when DC numbers were substantially increased. CHC- and NHD-MoDCs generated equivalent amounts of cytokines [TNF-alpha, interleukin (IL)-1beta, IL-6, IL-12p70, IL-15, IL-10] and chemokines [interferon-inducible protein (IP)-10, macrophage inflammatory protein (MIP)-1alpha, regulated upon activation, normal T expressed and secreted (RANTES)] after CD40 ligation. Because the functional defect was not apparent at high MoDC : T cell ratios, autologous MoDC therapy with sufficiently high numbers of DCs could, in theory, overcome any impairment of MoDC function in CHC.

Vaccine-induced early control of hepatitis C virus infection in chimpanzees fails to impact on hepatic PD-1 and chronicity

Broad T cell and B cell responses to multiple HCV antigens are observed early in individuals who control or clear HCV infection. The prevailing hypothesis has been that similar immune responses induced by prophylactic immunization would reduce acute virus replication and protect exposed individuals from chronic infection. Here, we demonstrate that immunization of naïve chimpanzees with a multicomponent HCV vaccine induced robust HCV-specific immune responses, and that all vaccinees exposed to heterologous chimpanzee-adapted HCV 1b J4 significantly reduced viral RNA in serum by 84%, and in liver by 99% as compared to controls (P=0.024 and 0.028, respectively). However, despite control of HCV in plasma and liver in the acute period, in the chronic phase, 3 of 4 vaccinated animals developed persistent infection. Analysis of expression levels of proinflammatory cytokines in serial hepatic biopsies failed to reveal an association with vaccine outcome. However, expression of IDO, CTLA-4 [corrected] and PD-1 levels in liver correlated with clearance or chronicity.

CONCLUSION

Despite early control of virus load, a virus-associated tolerogenic-like state can develop in certain individuals independent of vaccination history.

Immunopathogenesis in hepatitis C virus cirrhosis

HCV (hepatitis C virus) has a high propensity to persist and to cause chronic hepatitis C, eventually leading to cirrhosis. Since HCV itself is not cytopathic, liver damage in chronic hepatitis C is commonly attributed to immune-mediated mechanisms. HCV proteins interact with several pathways in the host's immune response and disrupt pathogen-associated pattern recognition pathways, interfere with cellular immunoregulation via CD81 binding and subvert the activity of NK (natural killer) cells as well as CD4(+) and CD8(+) T-cells. Finally, HCV-specific T-cells become increasingly unresponsive and apparently disappear, owing to several possible mechanisms, such as escape mutations in critical viral epitopes, lack of sufficient help, clonal anergy or expansion of regulatory T-cells. The role of neutralizing antibodies remains uncertain, although it is still possible that humoral immunity contributes to bystander damage of virally coated cells via antibody-dependent cellular cytotoxicity. Cytotoxic lymphocytes kill HCV-infected cells via the perforin/granzyme pathway, but also release Fas ligand and inflammatory cytokines such as IFNgamma (interferon gamma). Release of soluble effector molecules helps to control HCV infection, but may also destroy uninfected liver cells and can attract further lymphocytes without HCV specificity to invade the liver. Bystander damage of these non-specific inflammatory cells will expand the tissue damage triggered by HCV infection and ultimately activate fibrogenesis. A clear understanding of these processes will eventually help to develop novel treatment strategies for HCV liver disease, independent from direct inhibition of HCV replication.

Discordant role of CD4 T-cell response relative to neutralizing antibody and CD8 T-cell responses in acute hepatitis C

BACKGROUND & AIMS

Acute hepatitis C virus (HCV) infection becomes chronic in the majority of patients. Although HCV-specific CD4 T-cell response is associated with HCV clearance, less is known about virus-specific CD8 T-cell or neutralizing antibody (nAb) responses and the role of CD4 help in their induction during acute infection.

METHODS

HCV-specific CD4, CD8, and HCV pseudoparticle (HCVpp) nAb responses were monitored in acutely HCV-infected patients to define their relative contributions to viral clearance.

RESULTS

Our results show that the outcome of acute hepatitis C is associated with a functional hierarchy in HCV-specific CD4 T-cell response and the scope of virus-specific, total T-cell interferon-gamma response. HCV-specific CD8 T-cell response was readily detectable in acutely HCV-infected patients regardless of virologic outcome or virus-specific CD4 T-cell response. In contrast, HCVpp-specific nAbs were readily detected in patients with chronic evolution and impaired virus-specific CD4 T-cell response but not in patients who cleared infection with robust virus-specific CD4 T-cell response.

CONCLUSIONS

The outcome of acute hepatitis C is associated with efficient virus-specific CD4 T-cell response(s) without which HCV-specific CD8 T-cell and heterologous nAb responses may develop but fail to clear viremia. Furthermore, HCV-specific nAb responses may not be induced despite robust virus-specific CD4 T-cell response.

Hepatitis C virus continuously escapes from neutralizing antibody and T-cell responses during chronic infection in vivo

BACKGROUND & AIMS

Broadly reactive neutralizing antibodies (nAbs) and multispecific T-cell responses are generated during chronic hepatitis C virus (HCV) infection and yet fail to clear the virus. This study investigated the development of autologous nAb and HCV-glycoprotein-specific T-cell responses and their effects on viral sequence evolution during chronic infection in order to understand the reasons for their lack of effectiveness.

METHODS

Numerous E1E2 sequences were amplified and sequenced from serum samples collected over a 26-year period from patient H, a uniquely well-characterized, chronically infected individual. HCV pseudoparticles (HCVpp) expressing the patient-derived glycoproteins were generated and tested for their sensitivity to neutralization by autologous and heterologous serum antibodies.

RESULTS

A strain-specific nAb response developed early in infection (8 weeks postinfection), whereas cross-reactive antibodies able to neutralize HCVpp-bearing heterologous glycoproteins developed late in infection (>33 wk postinfection). The humoral response continuously failed to neutralize viruses bearing autologous glycoprotein sequences that were present in the serum at a given time. The amplified glycoprotein sequences displayed high variability, particularly in regions corresponding to defined linear B-cell epitopes. Mutations in defined neutralizing epitopes were associated with a loss of recognition by monoclonal antibodies against these epitopes and with decreased neutralization of corresponding HCVpp. Viral escape from CD4 and CD8 T-cell responses also was shown for several novel epitopes throughout the glycoprotein region.

CONCLUSIONS

During chronic infection HCV is subjected to selection pressures from both humoral and cellular immunity, resulting in the continuous generation of escape variants.

Differential dysfunction in dendritic cell subsets during chronic HCV infection

Hepatitis C virus (HCV) infection is a leading cause of chronic liver disease with over 200 million individuals infected worldwide. The vast majority of acutely infected humans develop chronic infection, which is characterized by attenuated antiviral T-cell responses. The mechanisms leading to such attenuation/suppression are poorly understood. It has been proposed that dysfunction of antigen-presenting cells (APC) may underlie the downregulation of antiviral immune responses. However, studies using bulk or in vitro-derived APC populations have resulted in conflicting reports. In this study, we evaluated the functional and immunophenotypic features of ex vivo-purified dendritic cell (DC) subsets during chronic HCV infection. We found that plasmacytoid DC (PDC) from HCV-infected patients (HCV-PDC) showed a striking deficit in IFN-alpha production in response to CpG stimulation. In addition, we found that myeloid DC (MDC) from these patients showed a diminished capacity to induce a mixed lymphocyte response (MLR), correlating with lower levels of HLA-DR and CD86 expression and higher IL-10 production in response to poly-IC stimulation. In contrast, HCV-PDC showed increased ability to stimulate an MLR. Of note, within the HCV-PDC preparation, we noted a distinctly expanded DC subset that expressed some markers of MDC, but showed significantly lower HLA-DR and CD86 expression, suggesting an expansion of DC at an immature/intermediate stage of differentiation. Our studies demonstrate distinct and contrasting dysfunctional features in DC subsets and underscore the importance of evaluating APC subpopulations separately.

Modulation of the immune response induced by gene electrotransfer of a hepatitis C virus DNA vaccine in nonhuman primates

Induction of multispecific, functional CD4+ and CD8+ T cells is the immunological hallmark of acute self-limiting hepatitis C virus (HCV) infection in humans. In the present study, we showed that gene electrotransfer (GET) of a novel candidate DNA vaccine encoding an optimized version of the nonstructural region of HCV (from NS3 to NS5B) induced substantially more potent, broad, and long-lasting CD4+ and CD8+ cellular immunity than naked DNA injection in mice and in rhesus macaques as measured by a combination of assays, including IFN-gamma ELISPOT, intracellular cytokine staining, and cytotoxic T cell assays. A protocol based on three injections of DNA with GET induced a substantially higher CD4+ T cell response than an adenovirus 6-based viral vector encoding the same Ag. To better evaluate the immunological potency and probability of success of this vaccine, we have immunized two chimpanzees and have compared vaccine-induced cell-mediated immunity to that measured in acute self-limiting infection in humans. GET of the candidate HCV vaccine led to vigorous, multispecific IFN-gamma+CD8+ and CD4+ T lymphocyte responses in chimpanzees, which were comparable to those measured in five individuals that cleared spontaneously HCV infection. These data support the hypothesis that T cell responses elicited by the present strategy could be beneficial in prophylactic vaccine approaches against HCV.

Defining target antigens for CD25+ FOXP3 + IFN-gamma- regulatory T cells in chronic hepatitis C virus infection

The mechanism behind the apparent lack of effective antiviral immune responses in chronic hepatitis C virus (HCV) patients is poorly understood. It remains unclear if natural regulatory T cells (Treg) contribute to the induction and maintenance of HCV persistence. We herein report for the first time that CD25(high)IFN-gamma(-)FOXP3(high) Tregs can be rapidly induced by culturing peripheral blood mononuclear cells (PBMCs) of HCV-positive patients with HCV protein-derived peptides. The HCV-specific Tregs, generally CD4(+)CD45RO(+), did not proliferate in response to HCV peptide and failed to produce interferon (IFN)-gamma, in distinct contrast to antiviral effector cells. Stimulation of healthy donor PBMCs with HCV peptides did not result in CD25 and FOXP3 upregulation above non-antigen background. To further investigate the antigen specificity of these potentially disease-associated natural Tregs, CD25(+) cells were isolated from PBMCs, labeled with carboxyfluorescein diacetate succinimidylester and added back to CD25-depleted PBMCs, and the co-cultures were then stimulated with individual peptides derived from the HCV core protein. We found that the actual peptide that can stimulate Treg varied between patients, but within any given subject only a small number of the peptides were able to stimulate Treg, suggesting the existence of dominant Treg epitopes. Although functional experiments for these peptides are ongoing in our laboratory, data presented here suggests that HCV-specific natural Tregs are abundant in infected individuals, in contrast to the extremely low frequency of anti-HCV effector T cells, supporting the view that natural Treg may be implicated in host immune tolerance during HCV infection.

Flying under the radar: the immunobiology of hepatitis C

The hepatitis C virus (HCV) is a remarkably successful pathogen, establishing persistent infection in more than two-thirds of those who contract it. Its success is related to its abilities to blunt innate antiviral pathways and to evade adaptive immune responses. These two themes may be related. We propose that HCV takes advantage of the impaired innate response to delay the organization of an effective adaptive immune attack. The tolerogenic liver environment may provide cover, prolonging this delay. HCV's error-prone replication strategy permits rapid evolution under immune pressure. Persistent high levels of viral antigens may contribute to immune exhaustion. Finally, the virus may benefit from the efficient enlistment of memory T and B cells in the pursuit of a moving target.

Changes of soluble CD26 and CD30 levels correlate with response to interferon plus ribavirin therapy in patients with chronic hepatitis C

BACKGROUND

Clearance of hepatitis C virus (HCV) is attributed to host cellular immune responses, in which T helper cells play a critical role. The purpose of the present paper was therefore to study the serial changes of serum soluble markers released from T helper 1 (Th1) and 2 (Th2) and their correlations with treatment responses in chronic hepatitis C patients receiving interferon-alpha plus ribavirin for 24 weeks.

METHODS

Serum markers (soluble CD26 and CD30 levels) of T helper cells were quantified before and 6 months after combination therapy in 33 chronic hepatitis C patients and in 20 healthy controls.

RESULTS

Compared to healthy controls, chronic hepatitis C patients had significantly lower serum soluble CD26 levels before (140.4 +/- 63.9 ng/mL vs 200.6 +/- 60.3 ng/mL, P < 0.0001) and after (115.9 +/- 32.9 ng/mL vs 200.6 +/- 60.3 ng/mL, P < 0.0001) combination therapy. The level was even lower in those with non-sustained virologic response (non-SVR; 139.0 +/- 50.9 ng/mL vs 117.7 +/- 40.3 ng/mL, P = 0.039). In contrast, soluble CD30 levels at 6 months after combination therapy were significantly lower in patients with SVR than those with non-SVR (6.4 +/- 3.5 U/mL vs 10.4 +/- 5.4 U/mL, P = 0.021).

CONCLUSION

Chronic hepatitis C patients have a weak Th1 response as reflected by lower soluble CD26 levels and the levels are even lower in non-sustained responders. In sharp contrast, downregulation of Th2 response with serial changes of soluble CD30 level is associated with successful treatment of HCV infection.

Host and viral factors in the immunopathogenesis of primary hepatitis C virus infection

Individuals infected with hepatitis C virus (HCV) have two possible outcomes of infection, clearance or persistent infection. The focus of this review is the host mechanisms that facilitate clearance. The interaction between HCV viral components and the immune system ultimately determines the balance between the virus and host. Strong evidence points to the aspects of cellular immune response as the key determinants of outcome. The recent discovery of viral evasion strategies targeting innate immunity suggests that the interferon-alpha/beta induction pathways are also critical. A growing body of evidence has implicated polymorphisms in both innate and adaptive immune response genes as determinants of viral clearance in individuals infected with HCV.

Hepatitis C Virus (HCV) Core Protein-Induced, Monocyte-Mediated Mechanisms of Reduced IFN-α and Plasmacytoid Dendritic Cell Loss in Chronic HCV Infection

IFN-alpha production by plasmacytoid dendritic cells (PDCs) is critical in antiviral immunity. In the present study, we evaluated the IFN-alpha-producing capacity of PDCs of patients with chronic hepatitis C virus (HCV) infection in treatment-naive, sustained responder, and nonresponder patients. IFN-alpha production was tested in PBMCs or isolated PDCs after TLR9 stimulation. Treatment-naive patients with chronic HCV infection had reduced frequency of circulating PDCs due to increased apoptosis and showed diminished IFN-alpha production after stimulation with TLR9 ligands. These PDC defects correlated with the presence of HCV and were in contrast with normal PDC functions of sustained responders. HCV core protein, which was detectable in the plasma of infected patients, reduced TLR9-triggered IFN-alpha and increased TNF-alpha and IL-10 production in PBMCs but not in isolated PDCs, suggesting HCV core induced PDC defects. Indeed, addition of rTNF-alpha and IL-10 induced apoptosis and inhibited IFN-alpha production in PDCs. Neutralization of TNF-alpha and/or IL-10 prevented HCV core-induced inhibition of IFN-alpha production. We identified CD14+ monocytes as the source of TNF-alpha and IL-10 in the HCV core-induced inhibition of PDC IFN-alpha production. Anti-TLR2-, not anti-TLR4-, blocking Ab prevented the HCV core-induced inhibition of IFN-alpha production. In conclusion, our results suggest that HCV interferes with antiviral immunity through TLR2-mediated monocyte activation triggered by the HCV core protein to induce cytokines that in turn lead to PDC apoptosis and inhibit IFN-alpha production. These mechanisms are likely to contribute to HCV viral escape from immune responses.

Repression of interferon regulatory factor 1 by hepatitis C virus core protein results in inhibition of antiviral and immunomodulatory genes

Hepatitis C virus (HCV) proteins are known to interfere at several levels with both innate and adaptive responses of the host. A key target in these effects is the interferon (IFN) signaling pathway. While the effects of nonstructural proteins are well established, the role of structural proteins remains controversial. We investigated the effect of HCV structural proteins on the expression of interferon regulatory factor 1 (IRF-1), a secondary transcription factor of the IFN system responsible for inducing several key antiviral and immunomodulatory genes. We found substantial inhibition of IRF-1 expression in cells expressing the entire HCV replicon. Suppression of IRF-1 synthesis was mainly mediated by the core structural protein and occurred at the transcriptional level. The core protein in turn exerted a transcriptional repression of several interferon-stimulated genes, targets of IRF-1, including interleukin-15 (IL-15), IL-12, and low-molecular-mass polypeptide 2. These data recapitulate in a unifying mechanism, i.e., repression of IRF-1 expression, many previously described pathogenetic effects of HCV core protein and suggest that HCV core-induced IRF-1 repression may play a pivotal role in establishing persistent infection by dampening an effective immune response.

Virus-specific T-cell responses associated with hepatitis C virus (HCV) persistence in the liver after apparent recovery from HCV infection

Hepatitis C virus (HCV) RNA persistence in the liver has been described even after apparent resolution of HCV infection. Because T-cell reactivity plays a role in recovery from HCV infection, virus-specific T-cell responses were investigated in apparently recovered individuals in whom hepatic HCV RNA persistence was documented: 15 sustained virological responders to interferon (IFN)-treatment and 9 asymptomatic aviremic anti-HCV carriers. HCV-specific CD4(+) T-cell proliferative responses were detected significantly more often in apparently recovered individuals (sustained virological responders: 60%; asymptomatic anti-HCV carriers: 66%) compared with 50 chronic hepatitis C patients (28%; P < 0.05). However, T-cell frequencies and numbers tended to decline over time and the number of HCV proteins targeted by CD4(+) T-cell proliferative responses was limited. Interestingly, liver viral load correlated inversely with virus-specific immune responses. Thus, CD4(+) T-cell responders showed significantly lower hepatic HCV RNA levels (P < 0.05). HCV-specific IFN-gamma-secreting CD4(+) T-cells were not detected in all the apparently recovered patients although they were found significantly more often compared with chronic hepatitis C patients (P < 0.05). Also, HCV NS3-specific CD8(+) T-cells were detected in 11 HLA-A2-positive apparently recovered individuals (8 sustained virological responders and 3 asymptomatic anti-HCV carriers); T-cell frequencies tended to be greater in those patients who had lower hepatic viral levels. In conclusion, HCV-specific T-cells are detectable in apparently recovered individuals in whom HCV RNA can persist in the liver indicating that HCV replication may be prolonged in the face of an insufficient or inadequate virus-specific CD4(+) and CD8(+) T-cell response.

Vitamin E and C supplementation prevents decrease of eicosapentaenoic acid in mononuclear cells in chronic hepatitis C patients during combination therapy of interferon alpha-2b and ribavirin

OBJECTIVE

We investigated the effects of vitamin E and C supplementation on the fatty acid composition of mononuclear cells and on the clinical observations in patients who had chronic hepatitis C and received interferon-alpha-2b (IFN-alpha-2b) and ribavirin combination therapy.

METHODS

Patients were randomly allocated to receive daily 500 mg of vitamin E and 750 mg of vitamin C (vitamin group, n = 14) or no supplement (non-vitamin group, n = 16) in addition to IFN-alpha-2b and ribavirin therapy. The fatty acid composition of mononuclear cell phospholipids was analyzed before and at 2, 4, and 8 wk after treatment.

RESULTS

After vitamin supplementation, plasma and red blood cell alpha-tocopherol and plasma ascorbic acid levels increased in the vitamin group. Serum levels of alanine aminotransferase decreased significantly after 2 wk of treatment in both groups. At the start of treatment, a lower level of eicosapentaenoic acid (EPA) and a higher level of the molar ratio of arachidonic acid to EPA in mononuclear cells were observed in the present patients compared with healthy volunteers, and a significant correlation between the molar ratio and serum alanine aminotransferase level was found. The EPA level of mononuclear cells was maintained in the vitamin group during treatment, whereas a significant decrease was observed in the non-vitamin group at 4 and 8 wk after treatment.

CONCLUSIONS

Antioxidant vitamin supplementation during IFN-alpha-2b and ribavirin therapy prevented a decrease in EPA of mononuclear cell phospholipids. If a further decrease in the ratio of arachidonic acid to EPA can be achieved by using oral EPA supplementation, the efficacy of IFN-alpha-2b and ribavirin therapy may be improved.

Mechanism of T cell hyporesponsiveness to HBcAg is associated with regulatory T cells in chronic hepatitis B

AIM

To study the mechanisms of hyporesponsiveness of HBV-specific CD4+ T cells by testing TH1 and TH2 commitment and regulatory T cells.

METHODS

Nine patients with chronic hepatitis B were enrolled. Peripheral blood mononuclear cells were stimulated with HBcAg or HBsAg to evaluate their potential to commit to TH1 and TH2 differentiation. HBcAg-specific activity of regulatory T cells was evaluated by staining with antibodies to CD4, CD25, CTLA-4 and interleukin-10. The role of regulatory T cells was further assessed by treatment with anti-interleukin-10 antibody and depletion of CD4+CD25+ cells.

RESULTS

Level of mRNAs for T-bet, IL-12R beta2 and IL-4 was significantly lower in the patients than in healthy subjects with HBcAg stimulation. Although populations of CD4+CD25highCTLA-4+ T cells were not different between the patients and healthy subjects, IL-10 secreting cells were found in CD4+ cells and CD4+CD25+ cells in the patients in response to HBcAg, and they were not found in cells which were stimulated with HBsAg. Addition of anti-IL-10 antibody recovered the amount of HBcAg-specific TH1 antibody compared with control antibody (P < 0.01, 0.34% +/- 0.12% vs 0.15% +/- 0.04%). Deletion of CD4+CD25+ T cells increased the amount of HBcAg-specific TH1 antibody when compared with lymphocytes reconstituted using regulatory T cells (P < 0.01, 0.03% +/- 0.02% vs 0.18% +/- 0.05%).

CONCLUSION

The results indicate that the mechanism of T cell hyporesponsiveness to HBcAg includes activation of HBcAg-induced regulatory T cells in contrast to an increase in TH2-committed cells in response to HBsAg.

Protective immunity against hepatitis C virus infection

There is increasing evidence that a small percentage of individuals exposed to the hepatitis C virus have the capacity to generate a strong cellular immune response against the virus and avoid persistent infection, and perhaps do so repeatedly after re-exposure. This article reviews the evidence that the responses identified in this unique group of individuals represent the protective immunity that will need to be elicited by hepatitis C virus vaccines.

Outcome of acute hepatitis C is related to virus-specific CD4 function and maturation of antiviral memory CD8 responses

A timely, efficient, and coordinated activation of both CD4 and CD8 T cell subsets following HCV infection is believed to be essential for HCV control. However, to what extent a failure of the individual T cell subsets can contribute to the high propensity of HCV to persist is still largely undefined. To address this issue, we analyzed the breadth, vigor, and quality of CD4 and CD8 responses simultaneously with panels of peptides covering the entire HCV sequence or containing the HLA-A2-binding motif, and with recombinant HCV proteins in 16 patients with acute HCV infection by tetramer staining, ELISPOT, and intracellular cytokine staining for interferon gamma, interleukin (IL)-2, IL-4, and IL-10. Our results indicate that at clinical onset, CD8 responses are similarly weak and narrowly focused in both self-limited and chronically evolving infections. At this stage, CD4 responses are deeply impaired in patients with a chronic outcome as they are weak and of narrow specificity, unlike the strong, broad and T helper 1-oriented CD4 responses associated with resolving infections. Only patients able to finally control infection show maturation of CD8 memory sustained by progressive expansion of CD127+ CD8 cells. Thus, a poor CD8 response in the acute stage of infection may enhance the overall probability of chronic viral persistence. In conclusion, the presence of functional CD4 responses represents one of the factors dictating the fate of infection by directly contributing to control of the virus and by promoting maturation of protective memory CD8 responses.

Prospective study of viral clearance and CD4(+) T-cell response in acute hepatitis C primary infection and reinfection

BACKGROUND

The outcome of acute hepatitis C is determined by early host-virus interactions, particularly involving the antiviral T-cell response.

OBJECTIVES

To identify early prognostic markers of spontaneous resolution of acute hepatitis C by performing a comprehensive analysis of viral and immunological factors during the natural course of acute HCV infection and reinfection.

STUDY DESIGN

20 patients were investigated prospectively during acute HC or confirmed reinfection and 18 of them during follow up after spontaneous or treatment-induced elimination of the virus and resolution of the disease. Multiparameter flow cytometry was used to functionally characterize virus-specific CD4(+) T-cell responses relative to the virologic outcome.

RESULTS

Parallel immunologic and virologic monitoring of patients with acute HC identified distinct patterns of host-virus interaction related to HCV persistence or clearance. The highest frequency of antiviral Th1 cytokine-producing CD4(+) T-cells was observed in patients with HCV reinfection, preceding rapid viral clearance within 3 weeks after disease onset. In all patients who subsequently cleared viremia, CD4(+) T-cells produced Th1 cytokines following stimulation with non-structural HCV antigens (NS3 and NS4). In contrast, a chronic course of disease was associated with the absence of antiviral Th1 cytokine producing cells from the first weeks after onset of disease (acute persistent HC), or with fluctuating RNA levels (yo-yo pattern) and gradual waning of antiviral Th1 cells.

CONCLUSIONS

The results highlight the variability of immune response pattern in acute hepatitis C. Most importantly, "acute persistent hepatitis C" and a lack of TH1 effector cells within the first months of acute hepatitis C represent efficacious predictors of viral persistence and could thus be used as criteria in selecting candidates for early antiviral treatment.

Defective IL-2 production by HIV-1-specific CD4 and CD8 T cells in an adolescent/young adult cohort

Here we investigate the effect of viremia and the influence of HAART on the frequency and quality of HIVspecfic T cells in an adolescent/young adult cohort. Measurements of viral loads and the magnitude and quality of antiviral cellular immune responses were performed on 14 HAART-naive and 8 treated HIV-1-infected adolescents. Cross-sectional correlations between viral load and cellular immune responses were determined and data were analyzed by viral load (<4000, 4000-40,000, and >40,000 copies/ml plasma) and patient treatment status. All 22 patients showed a broad IFN-gamma ELISPOT response that was proportional to viral load (r = 0.53, p = 0.02), recognizing an average of five to eight peptide pools throughout Gag, Pol, Env, Tat, Rev, and Nef. Intracellular cytokine staining was performed with pools of overlapping peptides corresponding to HIV Gag to distinguish CD8 response from CD4 response. Among untreated patients with increased viral load there was a constant IFN-gamma CD8 response but a declining IFN-gamma CD4 response. HIV-specific IL-2 production was consistently low in CD8 cells but inversely related to viral load in CD4 cells (r = -0.52, p = 0.02). In this crosssectional analysis, time on HAART was associated with an increased frequency of antiviral IFN-gamma- and IL-2-coproducing CD4 cells (r = 0.98, p <0.001), but not of antiviral CD8 cells. Our results suggest that T cells coproducing IL-2 and IFN-gamma are a better marker for immunological competence than T cells producing IFN-gamma alone. They also suggest that HAART may be associated with an improved capacity for IL-2 production by antiviral CD4 T cells in a time-dependent manner. Longitudinal studies are clearly necessary to assess the impact of HAART on these parameters.

Vaccination with protein-transduced dendritic cells elicits a sustained response to hepatitis C viral antigens

BACKGROUND & AIMS

Professional antigen-presenting dendritic cells are capable of eliciting a vigorous antiviral response in naive T cells. The administration of antigen-loaded dendritic cells offers a potential approach to induce high-level immunity against hepatitis C virus.

METHODS

The dendritic cell population in mice was expanded in vivo by hydrodynamic delivery of naked DNA that encoded the secreted form of human fms-like tyrosine kinase 3 ligand. The CD11c-enriched dendritic cell population obtained from the spleen was transduced in vitro with recombinant hepatitis C virus core and nonstructural 5 proteins by using macromolecular-based protein delivery. Vaccine efficacy was assessed with a cytotoxic T-lymphocyte assay, cytokine enzyme-linked immunosorbent assays, and intracellular cytokine staining in vitro and by a tumor challenge model in vivo.

RESULTS

Relative to mice inoculated with nontransduced dendritic cells, splenocytes derived from mice immunized with either hepatitis C virus core-transduced or nonstructural 5-transduced dendritic cells showed 3- to 5-fold greater antigen-specific cytotoxic T lymphocyte activity. The CD4(+) T cells obtained from mice immunized with nonstructural 5-transduced dendritic cells produced interferon gamma, but not interleukin 4, when stimulated with nonstructural 5. In contrast, T cells derived from mice immunized with hepatitis C virus core-transduced dendritic cells produced neither interferon gamma nor interleukin 4 when stimulated with core protein. Mice vaccinated with nonstructural 5-transduced dendritic cells, but not a nonstructural 5-expressing plasmid, showed a sustained antiviral response to nonstructural 5 as evidenced by reduced growth of nonstructural 5-expressing tumor cells inoculated 10 weeks after vaccination.

CONCLUSIONS

These findings suggest that vaccination with protein-transduced dendritic cells may constitute an important antiviral strategy for hepatitis C virus.

Immunopathogenesis of hepatitis C virus infection: multifaceted strategies subverting innate and adaptive immunity

Hepatitis C virus (HCV) infection is one of the major causes of chronic liver disease worldwide. The critical role of innate as well as adaptive immunity has been reported in HCV persistence and liver injury. In the early phase of acute infection, HCV continues to replicate in the liver, suggesting the HCV capability of inhibiting innate immunity. The sustained, vigorous and multiepitope-specific CD4+ and CD8+ T cell responses are essential for spontaneous HCV clearance. HCV-specific CD8+ T cells are primary elements for HCV clearance by inducing hepatocyte apoptosis, in which Fas/CD95 is fundamentally involved. However, once HCV persistency develops, HCV utilizes multifaceted arms to subvert various immune effectors. During IFNalpha-based therapy, the enhancement of HCV-specific CD4+ T cell response followed by HCV eradication has been reported, however, it remains obscure whether the therapeutic HCV clearance is able to restore the durable immune competency to HCV. Further investigation is still warranted to establish the means to direct HCV-specific immune responses in the desired way.

Differences in HCV-specific T cell responses between chronic HCV infection and HIV/HCV co-infection

Hepatitis C virus (HCV)-specific CD4+ and CD8+ T cell responses were investigated using a panel of 728 overlapping peptides spanning the whole HCV genome in 47 HCV mono-infected and 26 HIV/HCV co-infected individuals using the IFN-gamma ELISPOT assay and flow cytometry. The frequency of HCV-specific T cell responses was similar (approximately 40%) in both groups, but the breadth of the T cell responses tended to be reduced in HIV/HCV co-infected individuals. Of interest, 23 new HCV-derived epitopes were identified, and CD4+ HCV-specific T cell responses were detected overall in a proportion similar to CD8+ T cell responses. A tendency towards a dominant CD8+ T cell response was associated with HIV/HCV co-infection. HCV-specific CD8+ T cells secreted both IL-2 and IFN-gamma, although a reduction in the percentage of IL-2/IFN-gamma-secreting cells was observed in HIV/HCV co-infected individuals. The increase in CD4+ T cell counts after antiretroviral therapy in HIV/HCV co-infected individuals was not associated with restoration of HCV-specific T cell responses. Altogether, these results provide new insights into the characterization of HCV-specific T cell responses in HCV mono-infected and HIV/HCV co-infected individuals.

The Impairment of CD8 Responses Limits the Selection of Escape Mutations in Acute Hepatitis C Virus Infection

Evasion from protective CD8 responses by mutations within immunodominant epitopes represents a potential strategy of HCV persistence. To investigate the pathogenetic relevance of this mechanism, a careful search for immunodominant CD8 epitopes was conducted in six patients with chronic evolution of HCV infection by analyzing their global CD8 response with a panel of overlapping synthetic peptides covering the overall HCV sequence and by studying the CD8 frequency by tetramer staining. Immunodominant responses were followed longitudinally from the time of acute onset in relation to the evolution of the epitopic sequences. Although intensity of CD8 responses and frequency of HCV-specific CD8 cells declined over time in all patients, mutations emerged in only three of the six acute patients studied. Variant sequences were less efficiently recognized by CD8 cells than parental epitopes and were poorly efficient in inducing a CD8 response in vitro. CD8 epitopes undergoing mutations were targeted by high avidity CD8 cells more efficient in effector function. Our data support the view that immunodominant CD8 responses are affected by inhibitory mechanisms operating early after infection and that the emergence of escape mutations represents an additional mechanism of virus evasion from those CD8 responses that are functionally preserved.

Increase of CD4+CD25+ regulatory T cells in peripheral blood of patients with chronic hepatitis C

AIM: To investigate the role of CD4⁺CD25⁺ regulatory T cells in the immune responses of patients with chronic hepatitis C.

METHODS: The number of CD4⁺CD25⁺ regulatory T cells in the peripheral blood of chronic HC patients was detected by flow cytometry. Then the CD4⁺CD25⁺ regulatory T cells were co-cultured with CD4⁺CD25^-T cells, and their inhibitory effect was analyzed. Flow cytometry was also used to examine the effect of CD4⁺CD25⁺ regulatory T cells on the synthesis of Interferon-g and Interleukin-4 in CD4⁺CD25^-T cells. The expression of Foxp3 in CD4⁺CD25⁺ regulatory T cells was detected by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS: The percentage of CD4+CD25+ regulatory T cells in the peripheral CD4+ T cells of the chronic HC patients was significantly higher than that of the healthy controls (14.1 ± 1.6% vs 5.3 ± 0.8%, P<0.01). CD4+CD25+ regulatory T cells significantly inhibited the proliferation of CD4⁺CD25^-T cells (P = 0.002) and the synthesis of IFN-g. Foxp3 was highly expressed in CD4⁺CD25⁺ regulatory T cells.

CONCLUSION: The level of CD4+CD25⁺ regulatory T cells increases in patients with chronic hepatitis C virus infection, which can specifically inhibit the response of Th1 cells.

Hepatitis C virus and the immune system: a concise review

Hepatitis C Virus (HCV) induces a chronic infection in 50%-80% of infected individuals, which can lead to cirrhosis and hepatocellular carcinoma. The inefficiency of the immune system in eliminating the virus is not well understood as humoral and cellular immune responses are induced. While a persistent infection is generally associated with a weak CD4+ and CD8+ T cell response during the acute phase, there is no good explanation as to why this response is strong enough in 20% of acutely infected people such that they spontaneously resolve the infection. However, the immune system partially controls the viral infection but due to a long-lasting inflammatory milieu, hepatic damage occurs. During the chronic phase of the infection, HCV does not seem to be cytopathic. This aspect is still controversial as the virus was linked to the development of cholestatic syndrome or acute lobular hepatitis after liver transplant in HCV infected patients. The development of new experimental systems such as HCV pseudoparticles, genomic replicon and transfected cell lines have improved our vision of the virus cycle as well as the understanding of the mechanism of persistence. However, a convincing explanation for the chronicity of the infection in the presence of a functional immune response is still missing and is an important area of research to understand HCV immune pathogenesis. Future research should dissect mechanisms that lead to quantitatively or qualitatively inadequate immune responses, the role of the high variability of the virus, the relevance of host's genetic factors and mechanisms of immunosuppression induced by the virus.

Adaptive immune responses in acute and chronic hepatitis C virus infection

The hepatitis C virus (HCV) persists in the majority of infected individuals and is a significant cause of human illness and death globally. Recent studies have yielded important insights into immunity to HCV, in particular revealing the central role of T cells in viral control and clearance. Other key features of adaptive immune responses remain obscure, including mechanisms by which T cells control HCV replication, the role of antibodies in conferring protection and how cellular and humoral immunity are subverted in persistent infection.

Hepatitis C virus-specific reactivity of CD4+-lymphocytes in children born from HCV-infected women

BACKGROUND/AIMS

T-lymphocyte reactivity against viral antigens may represent the only immunological marker of host contact with a virus. Aim of the present study was to investigate whether vertical exposure to hepatitis C virus (HCV) could activate HCV-specific T-cell responses that may represent a biomarker of previous contact with the virus, and possibly contribute to the low rate of vertical HCV transmission.

METHODS

We studied 28 children born from chronically HCV-infected mothers. HCV-specific activation and proliferation of CD4+-lymphocytes and cytokine production were evaluated in cultures of peripheral blood mononuclear cells (PBMCs) stimulated in vitro with HCV-peptides.

RESULTS

HCV-specific CD4+-cell reactivity was observed in 20 out of the 28 children (71%). The proliferation of HCV-specific CD4+-cells was more frequent and vigorous in children than in their mothers. In children, but not in the mothers, activation of CD4+-cells upon stimulation with HCV-peptides was directly correlated with proliferation. Early upon stimulation with HCV-peptides, lymphocytes from children produced lower levels of IL-10 than lymphocytes from the mothers.

CONCLUSIONS

Vertical exposure to HCV induces the development of viral-specific CD4+-cell-mediated immune responses, possibly endowed with protective function against infection, which may contribute to the low rate of vertical HCV transmission.

Hepatitis C virus core protein induces an anergic state characterized by decreased interleukin-2 production and perturbation of mitogen-activated protein kinase responses

Alterations of cytokine responses are thought to favor the establishment of persistent hepatitis C virus (HCV) infections, enhancing the risk of liver cirrhosis and hepatocellular carcinoma. Here we demonstrate that the expression of the HCV core (C) protein in stably transfected T cells correlates with a selective reduction of interleukin-2 (IL-2) promoter activity and IL-2 production in response to T-cell receptor triggering, whereas the activation of IL-4, IL-10, gamma interferon, and tumor necrosis factor alpha was moderately increased. This altered cytokine expression profile was associated with a perturbation of mitogen-activated protein (MAP) kinase responses. Extracellular regulated kinase and p38 were constitutively phosphorylated in C-expressing cells, while triggering of the costimulatory c-Jun N-terminal kinase (JNK) signaling cascade and activation of the CD28 response element within the IL-2 promoter appeared to be impaired. The perturbations of MAP kinase phosphorylation could be eliminated by cyclosporine A-mediated inhibition of nuclear factor of activated T cells, suggesting that the inactivation of JNK signaling and hyporesponsiveness to IL-2 induction were downstream consequences of C-induced Ca(2+) flux in a manner that mimics the induction of clonal anergy.

T cells with a CD4+CD25+ regulatory phenotype suppress in vitro proliferation of virus-specific CD8+ T cells during chronic hepatitis C virus infection

Chronic hepatitis C virus (HCV) infection is associated with impaired proliferative, cytokine, and cytotoxic effector functions of HCV-specific CD8(+) T cells that probably contribute significantly to viral persistence. Here, we investigated the potential role of T cells with a CD4(+)CD25(+) regulatory phenotype in suppressing virus-specific CD8(+) T-cell proliferation during chronic HCV infection. In vitro depletion studies and coculture experiments revealed that peptide specific proliferation as well as gamma interferon production of HCV-specific CD8(+) T cells were inhibited by CD4(+)CD25(+) T cells. This inhibition was dose dependent, required direct cell-cell contact, and was independent of interleukin-10 and transforming growth factor beta. Interestingly, the T-cell-mediated suppression in chronically HCV-infected patients was not restricted to HCV-specific CD8(+) T cells but also to influenza virus-specific CD8(+) T cells. Importantly, CD4(+)CD25(+) T cells from persons recovered from HCV infection and from healthy blood donors exhibited significantly less suppressor activity. Thus, the inhibition of virus-specific CD8(+) T-cell proliferation was enhanced in chronically HCV-infected patients. This was associated with a higher frequency of circulating CD4(+)CD25(+) cells observed in this patient group. Taken together, our results suggest that chronic HCV infection leads to the expansion of CD4(+)CD25(+) T cells that are able to suppress CD8(+) T-cell responses to different viral antigens. Our results further suggest that CD4(+)CD25(+) T cells may contribute to viral persistence in chronically HCV-infected patients and may be a target for immunotherapy of chronic hepatitis C.

Strain-specific T-cell suppression and protective immunity in patients with chronic hepatitis C virus infection

Hepatitis C virus (HCV) frequently persists with an apparently ineffective antiviral T-cell response. We hypothesized that some patients may be exposed to multiple HCV subtypes and that strain-specific T cells could contribute to the viral dynamics in this setting. To test this hypothesis, CD4 T-cell responses to three genotype 1a-derived HCV antigens and HCV antibody serotype were examined in chronically HCV infected (genotypes 1a, 1b, 2, 3, and 4) and spontaneously HCV recovered subjects. Consistent with multiple HCV exposure, 63% of patients infected with genotypes 2 to 4 (genotypes 2-4) and 36% of those infected with genotype 1b displayed CD4 T-cell responses to 1a-derived HCV antigens, while 29% of genotype 2-4-infected patients showed serotype responses to genotype 1. Detection of 1a-specific T cells in patients without active 1a infection suggested prior self-limited 1a infection with T-cell-mediated protection from 1a but not from non-1a viruses. Remarkably, CD4 T-cell responses to 1a-derived HCV antigens were weakest in patients with homologous 1a infection and greater in non-1a-infected patients: proportions of patients responding were 19% (1a), 36% (1b), and 63% (2-4) (P = 0.0006). Increased 1a-specific CD4 T-cell responsiveness in non-1a-infected patients was not due to increased immunogenicity or cross-reactivity of non-1a viruses but directly related to sequence divergence. We conclude that the T-cell response to the circulating virus is either suppressed or not induced in a strain-specific manner in chronically HCV infected patients and that, despite their ability to clear one HCV strain, patients may be reinfected with a heterologous strain that can then persist. These findings provide new insights into host-virus interactions in HCV infection that have implications for vaccine development.

T-cell response relative to genotype and ethnicity during antiviral therapy for chronic hepatitis C

Viral genotype and host ethnicity are important predictors of viral clearance during antiviral therapy for chronic hepatitis C virus (HCV) infection. Based on the role of T cells in natural HCV clearance, we hypothesized that T cells may contribute to the genotypic and ethnic difference in treatment outcome. To test this hypothesis, T-cell response to HCV antigens (core, nonstructural NS3/4 and NS5) and control phytohemagglutinin (PHA) was monitored prospectively and was correlated with virological outcome in 41 patients chronically infected with HCV (27 genotype 1, 14 genotype 2 or 3; 19 black persons, 22 white persons) undergoing combined interferon alfa and ribavirin therapy. Interestingly, in patients with genotype 2 or 3 infection, enhanced virological response coincided with a greater T-cell response to HCV NS3/4 antigen at baseline (50% vs. 15%; P = .026) that augmented further during therapy (29% vs. 4%; P = .035) compared with genotype 1-infected patients. However, HCV-specific T-cell response remained weak in genotype 1-infected patients regardless of virological outcome or ethnicity. Furthermore, virological outcome was associated with a suppressed baseline proliferative response to phytohemagglutinin (P < .03) that increased during therapy (P < .003) independent of ethnicity or genotype. In conclusion, HCV-specific T-cell response was associated with HCV genotype but not with therapeutic clearance of HCV infection. The association between treatment outcome and phytohemagglutinin response suggests more global and antigen-nonspecific mechanisms for therapeutic HCV clearance.