Quantitative and functional differences in CD8+ lymphocyte responses in resolved acute and chronic hepatitis C virus infection

CD8⁺ T lymphocyte responses are important in the clearance of viral infections. In chronic infections they may contribute to pathogenesis. To investigate the role of CD8⁺ T lymphocyte responses in viral clearance and chronic hepatitis C we have compared hepatitis C virus (HCV) specific cytotoxicity and interferon-gamma (IFN-γ) production in patients with resolved-acute, and chronic HCV infection. CD8⁺ T cell responses to a panel of 13 HCV T cell peptide epitopes were studied using Elispot assays of IFN-γ production and chromium release cytotoxicity assays. Responses of seven patients with resolved acute HCV infection were compared with those of 14 chronically infected patients. HCV-specific cytotoxicity differentiated the two populations of patients. The majority (71%) of patients with resolved acute infection tested positive to 42% of relevant peptides compared with the minority (28%) of patients with chronic hepatitis C ( P =0.03) who responded to only 8% of relevant peptides ( P =0.0009). In contrast, HCV-specific IFN-γ production was detected in 86% of patients with either resolved or chronic infection in response to 42% and 35%, respectively, of relevant peptides tested (not significant). In patients with chronic infection the magnitude of the HCV-specific IFN-γ production was inversely correlated to viral load ( R ²=0.52; P =0.042). Failure to clear HCV infection may be attributable to the presence of noncytolytic IFN-γ producing CD8⁺ T lymphocytes in chronically infected patients. However these CD8⁺ T cells may play a beneficial role in contributing to the control of viral load in chronic hepatitis C.     

Transient immunological control during acute hepatitis C virus infection: ex vivo analysis of helper T-cell responses

Summary.  Hepatitis C virus (HCV) readily sets up persistence after acute infection. Cellular immune responses are thought to play a major role in control of the virus. Failure of CD4+ T-cell responses in acute disease is associated with viral persistence but the dynamics of this are poorly understood. We aimed to assess such responses using a novel set of Class II tetrameric complexes (tetramers) to study helper T-cells ex vivo in acute disease. We analysed the HCV-specific CD4+ T-cell response in a patient with acute hepatitis c infection. We were able to track the virus-specific CD4+ T-cells directly ex vivo with HLA DR4 tetramers. Proliferative responses were absent initially, recovered as viral load dropped and were lost again during relapse. Longitudinal tetramer analyses showed expanded populations of antiviral CD4+ T-cells throughout acute infection despite lack of proliferation. A pattern of transient CD4+ T-cell proliferative responses as HCV is partially controlled is observed. Failure to control virus is associated with emergence of 'dysfunctional' CD4+ T-cell populations. Failure to control HCV in acute disease may relate to the capacity to sustain efficient immune responses as virus attempts to 'bounce back' after partial control.     

Sustained response to interferon-α plus ribavirin therapy for chronic hepatitis C is closely associated with increased dynamism of intrahepatic natural killer and natural killer T cells

Aim:  Previous studies have revealed that functional impairment of innate immune cells, including natural killer (NK) and natural killer T (NKT) cells, might be associated with the persistence of hepatitis C virus (HCV) infection. However, the involvement of innate immune cells, which predominate in the liver, in therapeutic HCV clearance is still unclear.
Methods:  To clarify the role of intrahepatic innate immune cells in the clinical outcome of patients with chronic hepatitis C (CHC) treated with interferon-α plus ribavirin (IFN/RBV), we prospectively investigated the status of NK and NKT cells in paired liver biopsy and peripheral blood (PB) samples obtained from 21 CHC patients before and immediately after IFN/RBV treatment by flow cytometry. Normal liver and PB samples were obtained from 10 healthy donors for living donor liver transplantation.
Results:  Before treatment, intrahepatic NK and NKT cells constituted a significantly lower proportion in CHC patients than in healthy individuals ( P  < 0.05). After IFN/RBV treatment, the proportions and absolute numbers of CD3^-CD161⁺ NK and CD3⁺CD56⁺ NKT cells in the liver, but not in PB, were significantly increased in sustained responders (SR) as compared with poor responders ( P  < 0.05). The proportion of CD3⁺CD161⁺ NKT cells was also increased in the liver of SR after the treatment. Moreover, there was a striking increase of activated CD152⁺ cells among CD3⁺CD56⁺ NKT cells in the liver of SR ( P  = 0.041).
Conclusion:  These findings demonstrate that sustained response to IFN/RBV treatment for patients with CHC is closely associated with increased dynamism of NK and NKT cells in the liver.     

Assessment of hepatitis C virus RNA and genotype from 6807 patients with chronic hepatitis C in the United States

Hepatitis C virus (HCV) RNA status and HCV genotype have become important tools in the diagnosis and monitoring of therapy in chronic HCV infection. To establish a database with respect to HCV genotype and serum HCV RNA concentrations in chronic hepatitis C patients in the United States, we analysed 6807 chronic hepatitis C patients who had HCV RNA and HCV genotype tests conducted at a central laboratory. The HCV RNA concentration cut-off for the lower 25th percentile of this population (low titre) was 0.9 × 10⁶ copies ml^–1. The median HCV RNA concentration was 3.5 × 10⁶ copies ml^–1 and the cut-off for the upper 25th percentile (high titre) was 5 × 10⁶ copies ml^–1. Male patients had a median HCV RNA concentration of 3.9 × 10⁶ copies ml^–1, which was significantly higher than the median HCV RNA level for females (2.75 × 10⁶ copies ml^–1; P  < 0.001). HCV genotype 1 was detected in 73% of patients; genotype 2 in 14%; genotype 3 in 8%; mixed genotype in 4%; and genotypes 4, 5 and 6 with a frequency of < 1%. Patients from the Northeast, Southeast and Midwest had significantly ( P  < 0.001) more infections with genotype 1 than patients from the Western and Southern regions. African–American patients were more likely to be infected with genotype 1 when compared with Caucasian, Hispanic or Asian Pacific Islanders ( P  < 0.001). Patients infected with HCV genotype 1 and mixed HCV genotypes had significantly higher serum HCV RNA concentrations when compared with HCV genotypes 2 and 3 ( P  < 0.001 for all comparisons).     

Peripheral virus-specific T-cell interleukin-10 responses develop early in acute hepatitis C infection and become dominant in chronic hepatitis

BACKGROUND /AIMS: Interleukin-10 (IL-10) has been ascribed pro-viral but anti-fibrotic properties in chronic hepatitis C virus (HCV) infection. In this study, we examined the role of HCV-specific T-cell IL-10 response in patients with acute and chronic HCV infection. METHODS: Peripheral HCV-specific T-cell IL-10 and IFNgamma responses were measured in cytokine Elispot assay using overlapping HCV-derived peptides in patients with chronic (n=61), resolved (n=15) and acute (n=8) hepatitis C, looking for their onset, quantity, breadth and durability relative to clinical and virological outcomes. The source and effect of HCV-specific IL-10 response were determined in depletion and IL-10 neutralization experiments. RESULTS: Both HCV-specific IL-10 and IFNgamma responses were detected early within 1-2 months of acute clinical hepatitis C. However, only HCV-specific IL-10 response correlated with elevated liver enzymes, increased viremia and suppressed HCV-specific CD4(+) T-cell proliferation in acute infection. While these associations were lost in established chronic infection, HCV-specific IL-10 responses were increased in patients without cirrhosis while IL-10 blockade enhanced antiviral effector IFNgamma responses. CONCLUSIONS: HCV-specific IL-10 Tr1 responses may play a dual role in HCV infection, dampening effector T-cells to promote viral persistence in acute infection but also protecting against progressive fibrosis in chronic infection.     

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.     

Virological and immunological determinants of intrahepatic virus-specific CD8+ T-cell failure in chronic hepatitis C virus infection

Virus-specific CD8+ T-cells play an important role in the outcome of acute hepatitis C virus (HCV) infection. In the chronic phase, however, HCV can persist despite the presence of virus-specific T-cell responses. Therefore, we set out to perform a full-breadth analysis of the intrahepatic virus-specific CD8+ T-cell response, its relation to the peripheral T-cell response, and the overall influence of viral escape and the genetic restriction on intrahepatic CD8+ T-cell failure. Intrahepatic and peripheral CD8+ T-cells from 20 chronically HCV infected patients (genotype 1) were comprehensively analyzed using overlapping peptides spanning the entire HCV polyprotein in concert with autologous viral sequences that were obtained for all targeted regions. HCV-specific CD8+ T-cell responses were detectable in most (90%) chronically HCV-infected patients, and two thirds of these responses targeted novel previously undescribed epitopes. Most of the responses were detectable only in the liver but not in the peripheral blood, indicating accumulation and enrichment at the site of disease. Of note, only approximately half of the responses were associated with viral sequence variations supported by functional analysis as viral escape mutations. Escape mutations were more often associated with HLA-B alleles. CONCLUSION: Our results show an unexpected high frequency of intrahepatic virus-specific CD8+ T-cells, a large part of which continue to target the present viral antigens. Thus, our results suggest that factors other than mutational escape contribute to the failure of intrahepatic virus-specific CD8+ T-cells.     

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

Aim:  Dendritic cells (DCs) pulsed with HBsAg efficiently reverse the immune tolerance to hepatitis B virus (HBV) and induce HBV-specific cytotoxic T lymphocyte (CTL) responses in transgenic mice and healthy volunteers. However, it is not clear whether HBV core antigen (HBcAg)-pulsed DCs can effectively induce CD4⁺ helper T cells polarization into Th1, which contribute to the induction and maintenance of HBV-specific CD8⁺ T cells in chronic hepatitis B (CHB) patients. To address this issue, we conducted this study and investigated whether HBcAg-pulsed DCs could polarize Th1 cells and induce an HBcAg-specific CTL response.
Methods:  HBcAg-pulsed DCs were generated from 21 CHB patients. The capacity of the HBcAg-pulsed DC vaccine to stimulate CD4⁺ and CD8⁺ T cells to produce IFN-γ and IL-4 was estimated by intercellular cytokine staining, and the HBcAg-pulsed DCs derived from 10 humam leucocyte antigen (HLA)-A2⁺ CHB patients were tested for the induction of HBV-specific CTLs from autologous T cells by pentamer staining. The cytotoxicity of these CTLs was evaluated in vitro by flow cytometry.
Results:  The HBcAg-pulsed DCs derived from CHB patients exhibited a stronger capacity to stimulate autologous CD4⁺ and CD8⁺ T cells to release IFN-γ rather than IL-4, which could induce HBV core 18-27 specific CTLs, suggesting a specific cytotoxicity against T2 cells that had been loaded with the HBV core 18-27 peptide in vitro .
Conclusion:  HBcAg-pulsed DC vaccine derived from CHB patients efficiently induced autologous T cell polarization to Th1 and generation of HBV core 18-27 specific CTLs.     

Hepatic inflammatory cytokine mRNA expression in hepatitis C virus-human immunodeficiency virus co-infection

Summary.  Although epidemiologic studies have documented that hepatitis C virus (HCV)/human immunodeficiency virus (HIV) co-infected patients have accelerated fibrogenesis, especially those with CD4⁺ cell counts <200 cells/mm³, the pathogenic mechanisms are poorly understood. We investigated whether severe immunodeficiency in co-infection is associated with changes in intrahepatic inflammatory cytokine mRNA levels. We measured interferon (IFN)-γ, tumour necrosis factor-α, transforming growth factor (TGF)-β₁, interleukin (IL)-4, IL-10, IL-12p35 and IL-12p40 mRNA levels by real-time PCR performed on liver samples from HCV mono-infected ( n  = 19) and HCV/HIV co-infected ( n  = 24) patients. Co-infected patients had decreased intrahepatic mRNA levels of IFN-γ ( P  = 0.09), IL-4 ( P  = 0.05) and IL-12p35 ( P  = 0.04) compared with mono-infected patients, while IL-10 was increased ( P  = 0.07). In co-infected patients, IFN-γ mRNA levels increased linearly with increasing peripheral CD4⁺ cell counts by 1.23 times relative to the calibrator for every 100 CD4⁺ cells/mm³ increase ( P  = 0.02). No other cytokines were significantly associated with CD4⁺ cell counts. In conclusion, HIV-induced lymphopenia may result in hepatic inflammatory cytokine suppression in HCV/HIV co-infection. Intrahepatic IFN-γ levels are significantly reduced in patients with advanced immunodeficiency. Further studies are needed to assess whether decreased IFN-γ secretion by HCV-specific CD4⁺ cells may account for accelerated fibrogenesis in these patients.     

Low interleukin-10 production by monocytes of patients with a self-limiting hepatitis C virus infection

Summary.  Host factors seem to be crucial for the spontaneous clearance of hepatitis C virus (HCV). Monocytes play a pivotal role in innate immunity and help regulate adaptive responses. This study assesses the characteristics of monocytes from patients with self-limiting HCV infections. We studied 35 consecutive patients [11 with a self-limiting HCV infection, 16 chronically infected with HCV and sustained virological responders (SVR) following antiviral therapy, and eight chronically infected HCV but untreated] and eight healthy donors (HD). The production of interleukin (IL)-10, tumour necrosis factor-alpha (TNF-α) and IL-12p40 by monocytes stimulated with lipopolysaccharides(LPS) or HCV Core protein was measured by enzyme-linked immunoassay. Monocyte surface markers were analysed by flow cytometry. LPS and Core protein triggered IL-10 and TNF-α production, but monocytes from self-limiting infection patients produced significantly less IL-10 and TNF-α than those of SVR, chronically infected or HD ( P  < 0.05), while IL-12p40 production was unchanged. This cytokine production profile did not appear to be due to expansion of the CD14⁺ CD16⁺ monocyte subset or to a classical or alternative activation monocyte profile. Monocytes from self-limiting infection patients had more CCR7 than those from SVR or chronically infected patients ( P  < 0.05). Monocytes of self-limiting infection patients appear to produce little IL-10 and TNF-α in response to viral or unspecific stimulation and to have a higher CCR7 expression. This profile seems to be independent to a particular monocyte subset or activation state. Low IL-10 production may help establish an effective immune response and spontaneous HCV clearance.     

Composition of peripheral blood lymphocyte populations during different stages of chronic infection with hepatitis B virus

To characterize the immunological populations associated with different stages of chronic infection with hepatitis B virus (HBV), we performed flow cytometric analyses on the peripheral blood leucocytes of 29 patients with various forms of chronic hepatitis B. The clinical spectrum of the patients ranged from asymptomatic infections, in the presence of high virus production, to intermittent or recurrent exacerbations of liver injury alternating with relatively normal liver function. Patients with partial resolution of disease who experienced an initial acute flare followed by prolonged seroconversion showed decreased percentages of CD3⁺ cells during the seroconversion phase when levels of serum alanine transferase (ALT) had normalized. These CD3⁺ cells were predominantly CD4⁺ cells bearing the αβ⁺ T-cell receptor (TCR). In addition, we saw an increase in CD4⁺ and CD8⁺ cells bearing the γδTCR in those patients who had seroconverted. No significant differences were seen between any of the groups with respect to percentage of cells with a naive (CD45RA) or memory (CD45RO) phenotype, or of cells displaying the activation markers CD38, HLA-DR or CD57. Longitudinal analyses of 15 patients failed to show any consistent pattern of changes in the immunophenotypic profile during acute flares and their resolution. Our results indicate that the turnover of circulating T lymphocytes during the apparent quiescent phase of chronic infections is higher than that during acute exacerbations, suggesting an active immunosurveillance role of T-cell subpopulations in maintaining low virus levels during seroconversion.     

Strategies for loading dendritic cells with hepatitis C NS5a antigen and inducing protective immunity

Summary.  Dendritic cell (DC)-based vaccination strategies are promising for the treatment of cancers and infectious diseases including hepatitis C virus (HCV). As the induction of T cell-mediated immune responses by DC vaccination is highly dependent on efficient antigen loading of the DCs, the purpose of this study was to identify an optimal nonviral DC loading strategy for HCV NS5a. Furthermore, the efficacy of immunization with the NS5a-loaded DCs in comparison to plasmid encoding NS5a and NS5a protein was evaluated. Transfection of DCs with mRNA was most efficient with close to 100% of DCs expressing NS5a, whereas approximately 10% of protein-pulsed DCs and <1% of plasmid-transfected DCs expressed NS5a, suggesting remarkably different loading efficiencies. Vaccination of mice with NS5a mRNA-transfected DCs or NS5a protein-pulsed DCs resulted in significantly stronger CD4⁺ and CD8⁺ T-cell responses and protection from challenge with vaccinia virus expressing NS3/NS4/NS5, in comparison to vaccination with NS5a DNA-transfected DCs, plasmid encoding NS5 or rNS5a protein formulated with alum. Furthermore, vaccination with NS5a mRNA-transfected DCs was superior to vaccination with rNS5a-pulsed DCs. These data have important clinical implications, with mRNA-transfected DCs providing a safe and effective vaccination strategy against hepatitis C and possibly other pathogens.     

Hepatitis G virus infection in patients with bleeding disorders

Eighty-two patients with bleeding disorders registered with our centre were screened for infection with hepatitis G virus (HGV). 80 patients were positive for hepatitis C (HCV) antibodies, 66 of whom (83%) were HCV PCR positive. 11 patients (13%) were HGV RNA-positive, a similar prevalence rate to that of other studies of patients with bleeding disorders who received factor concentrates prior to the introduction of viral inactivation procedures. There was no significant difference in histological activity index (HAI) between the 10 HGV RNA-positive and the 31 HGV RNA-negative patients who underwent liver biopsy for assessment of HCV infection (median HAI scores 5.5, range 2–10 and four, range 0–10 respectively, P  = 0.07). One patient in each group had established cirrhosis. In patients who underwent HCV quantitation there was no significant difference in HCV viral titre between HGV RNA-positive and negative patients (median HCV titre in HGV RNA-positive patients 2.10 × 10⁵ DNA copies /ml ( n  = 8) range 4.17 × 10² to 4.17 × 10⁶, median HCV titre in HGV RNA-negative patients 3.33 × 10⁵ ( n  = 31) range 1.00 × 10³ to 6.67 × 10⁶, P  = 0.68). In this study there was no evidence that individuals co-infected with HGV and HCV have more severe liver disease than those infected with HCV alone.     

High resolution analysis of cellular immune responses in resolved and persistent hepatitis C virus infection

BACKGROUND & AIMS: Cellular immune responses are thought to play a key role in the resolution of primary HCV infection. Although it has been consistently shown that CD4+ T-cell responses are maintained in those with spontaneous resolution but lost in those with persistent infection, the role of CD8+ T-cell responses remains controversial. Previous studies have largely focused on limited HLA alleles and predefined CD8+ T-cell epitopes, and, thus, comprehensive studies remain to be performed. METHODS: To understand the composition of the immune response associated with spontaneous resolution, we comprehensively mapped CD8+ T-cell responses in 20 HLA-diverse persons with resolved HCV infection, using HCV peptides spanning the entire genome. We analyzed the magnitude, breadth, function, and phenotype using ELISpot, class-I tetramers, intracellular cytokine staining, and cytolytic assays. We studied in parallel HCV-specific responses and viral sequence variation in persistent infection. RESULTS: Responses in individuals with resolved infection were strong and broad with robust proliferation in response to antigen. Responses in those persistently infected were rarely detected ex vivo and, when present, were narrowly directed and weak. However, they also proliferated in vitro. Dominant target epitopes differed among individuals in both cohorts, despite frequently shared HLA-alleles. CONCLUSIONS: These data indicate that persisting, strong CD8+ T-cell responses are observed in the majority of persons with resolved HCV infection and provide support for strategies to boost CD8+ T-cell responses for the prevention or treatment of HCV infection but also highlight the diversity of responses that may need to be elicited to provide protection.     

Monitoring of CD95 and CD38 expression in peripheral blood T lymphocytes during active human cytomegalovirus infection after orthotopic liver transplantation

Aim:  The aim of the present study was to quantitatively monitor the response of CD95 molecules expressed on CD3⁺ T cells (CD95⁺CD3⁺ cells) and CD38 molecules expressed on CD8⁺ T cells (CD38⁺CD8⁺ cells) to ganciclovir treatment after orthotopic liver transplant (OLT) in recipients with active human cytomegalovirus (HCMV) infection.
Methods:  Blood samples were collected from 20 liver transplanted recipients with active HCMV infection and 24 recipients without HCMV infection. CD95⁺CD3⁺ cells and CD38⁺CD8⁺ cells were quantitatively detected with QuantiBRITE bead methods by dual-color flow cytometry analysis during the post-transplantation period.
Results:  CD95⁺CD3⁺ cells and CD38⁺CD8⁺ cells were not significantly different among different ages of healthy adults ( P  > 0.05). CD95⁺CD3⁺ cells and CD38⁺CD8⁺ cells were drastically increased in the active HCMV infection group compared with that in the stable group or in the healthy group ( P  < 0.001), and then they were gradually decreased within the next several weeks after ganciclovir treatment when compared with active HCMV infection recipients ( P  < 0.001).
Conclusions:  The present study showed that CD38⁺CD8⁺ T cells can be an appropriate immunological marker for early detection and antiviral therapeutic monitoring of HCMV infection. The evaluation of CD95 molecule levels may be used routinely in clinical practice to assess the level of immunosuppression.     

Spontaneous resolution of chronic hepatitis C virus infection after antiviral treatment and relapse

Clearance of acute hepatitis C virus (HCV) infection is associated with strong and multi-specific cellular immune responses which are often weak in chronic hepatitis C. We here report a case of spontaneous and sustained resolution of chronic hepatitis C virus infection in the absence of apparent HCV-specific immunity. The patient received standard antiviral therapy for chronic HCV infection and was HCV-RNA negative at the end of treatment but relapsed between follow-up week 4 and 12. Surprisingly, from follow-up week 28 on, he persistently was HCV-RNA negative in serum, even when being tested with the highly sensitive TMA-assay (cut-off 5-10 IU/ml). ALT levels were within the normal range throughout follow-up. Virus-specific CD4+ T cell responses were prospectively analysed during the relapse period and during spontaneous resolution by interferon-gamma ELISPOT assays. Importantly, no HCV-specific cellular immune responses were detectable at any time-point. The patient suffered from an acute respiratory tract infection before HCV clearance and serum IL-8 levels were significantly increased during this period.Thus, spontaneous resolution of hepatitis C after antiviral treatment and relapse may occur even in the absence of hepatitis flares and apparent HCV-specific immune responses in single cases. The role of heterologous infections for HCV clearance requires further investigation.     

Intrahepatic CD8+ T-cell failure during chronic hepatitis C virus infection

The precise mechanisms responsible for the failure of intrahepatic hepatitis C virus (HCV)-specific CD8+ T cells to control the virus during persistent infection have not been fully defined. We therefore studied the CD8+ T-cell response in 27 HLA-A2-positive patients using four previously well-defined HLA-A2-restricted HCV epitopes. The corresponding HCV sequences were determined in several patients and compared with the intrahepatic HCV-specific CD8+ T-cell response. The results of the study indicate: (1) intrahepatic HCV-specific CD8+ T cells are present in the majority of patients with chronic HCV infection and overlap significantly with the response present in the peripheral blood. (2) A large fraction of intrahepatic HCV-specific CD8+ T cells are impaired in their ability to secrete interferon gamma (IFN-gamma). This dysfunction is specific for HCV-specific CD8+ T cells, since intrahepatic Flu-specific CD8+ T cells readily secrete this cytokine. (3) T-cell selection of epitope variants may have occurred in some patients. However, it is not an inevitable consequence of a functional virus-specific CD8+ T-cell response, since several patients with IFN-gamma-producing CD8+ T-cell responses harbored HCV sequences identical or cross-reactive with the prototype sequence. (4) The failure of intrahepatic virus-specific CD8+ T cells to sufficiently control the virus occurs despite the presence of virus-specific CD4+ T cells at the site of disease. In conclusion, different mechanisms contribute to the failure of intrahepatic CD8+ T cells to eliminate HCV infection, despite their persistence and accumulation in the liver.     

Recurrence of hepatitis C virus after loss of virus-specific CD4(+) T-cell response in acute hepatitis C.

BACKGROUND & AIMS: The prospective comparison of patients with acute hepatitis C virus (HCV) who spontaneously clear the virus with those who cannot achieve viral elimination and progress to chronic hepatitis offers the unique opportunity to analyze natural mechanisms of viral elimination. METHODS: We studied the HCV-specific CD4(+) T-cell response in 38 patients with acute HCV and correlated the clinical course with the antiviral immune response. The individual HCV-specific T-cell response was assessed in a proliferation assay ((3)H-thymidine uptake) and an enzyme-linked immunospot assay. RESULTS: Patients were classified according to their clinical course and pattern of CD4(+) T-cell responses in 3 categories: first, patients mounting a strong and sustained antiviral CD4(+)/Th1(+) T-cell response who cleared the virus (HCV RNA-negative; n = 20); second, patients who were unable to mount an HCV-specific CD4(+) T-cell response and developed chronic disease (n = 12); and third, patients who initially displayed a strong CD4(+) T-cell response and eliminated the virus (HCV PCR-negative) but subsequently lost this specific T-cell response (n = 6). The loss of the HCV-specific CD4(+) T-cell response was promptly followed by HCV recurrence. CONCLUSIONS: The results indicate that a virus-specific CD4(+)/Th1(+) T-cell response that eliminates the virus during the acute phase of disease has to be maintained permanently to achieve long-term control of the virus. The induction and/or maintenance of virus-specific CD4(+) T cells could represent a promising therapeutic approach in HCV infection.     

Immune and non-immune responses to hepatitis C virus infection

The host innate and adaptive immune systems are involved in nearly every step of hepatitis C virus(HCV) infection. In patients,the outcome is determined by a series of complex host-virus interactions,whether it is a natural infection or results from clinical intervention. Strong and persistent CD8+ and CD4+ T-cell responses are critical in HCV clearance,as well as cytokineinduced factors that can directly inhibit virus replication. Newly available direct-acting antivirals(DAAs) are very effective in viral clearance in patients. DAA treatment may further result in the down-regulation of programmed death-1,leading to rapid restoration of HCV-specific CD8+ T cell functions. In this review,we focus on recent studies that address the host responses critical for viral clearance and disease resolution. Additional discussion is devoted to the prophylactic vaccine development as well as to current efforts aimed at understanding the host innate responses against HCV infection. Current theories on how the ubiquitin system and interferon-stimulated genes may affect HCV replication are also discussed.