Vigorous peripheral blood cytotoxic T cell response during the acute phase of hepatitis C virus infection.

After infection by hepatitis C virus (HCV), a minority of patients develop acute symptomatic disease and some of them are able to clear the virus. In this study, we analyzed peripheral blood mononuclear cells from nine patients with acute symptomatic disease with respect to their cytotoxic T lymphocyte (CTL) response using a panel of HCV-derived peptides in a semiquantitative secondary in vitro culture system. We could detect early CTL responses in 67% of these patients. The CTL responses were directed against multiple viral epitopes, in particular within the structural (core 2-9, core 35-44, core 131-140, and core 178-187) and nonstructural regions of the virus (NS3 1073-1081, NS3 1406-1415, NS4 1807-1816, NS5 2252-2260, and NS5B 2794-2802). We compared the CTL responses displayed by recently and chronically infected HLA-A2-positive patients. Virus-specific CTLs were detectable in chronic carriers but the percentage of positive peptide-specific CTL responses was significantly higher in recently infected patients (P = 0.002). Follow-up of recently infected patients during subsequent disease development showed a significant decrease in the values and proportions of positive peptide-specific CTL responses (P = 0.002 and 0.013, respectively). Patients with limited viral replication exhibited significantly more vigorous early responses (P = 0.024). These data suggest a protective role for the early antiviral CTL response in HCV infection.

Association of hepatitis C virus-specific CD8+ T cells with viral clearance in acute hepatitis C.

CD8+ T lymphocytes play a major role in antiviral immune defense. Their significance for acute hepatitis C is unclear. Our aim was to correlate the CD8+ T cell response with the outcome of infection. Eighteen patients with acute hepatitis C and 19 normal donors were studied. Hepatitis C virus (HCV)-specific CD8+ T cells were identified in the enzyme-linked immunospot assay by their interferon-gamma (IFN-gamma) production after specific stimulation. The highest numbers of IFN-gamma-producing HCV-specific CD8+ T cells were found in patients with acute hepatitis C and a self-limited course of disease during the first 6 months after onset of disease, but these numbers dropped thereafter to undetectable levels. The differences in responsiveness between patients with self-limited disease versus patients with a chronic course were statistically significant (P<.001). Our data show that the number of IFN-gamma-producing HCV-specific CD8+ T cells during the first 6 months after onset of disease is associated with eradication of the HCV infection.

Role of the specific T-cell response for clearance and control of hepatitis C virus.

T cells are believed to be the main players in antiviral defence. To investigate the role of the specific CD4+ T cell response for clearance and control of the hepatitis C virus we studied patients with acute hepatitis C (AHC) during the phase of spontaneous viral clearance and during follow up after elimination of the virus and resolution of disease. Symptomatic AHC has a self-limited course in 50% of patients, whereas the other half show virus persistence and develop chronic course of disease. Patients who were able to mount a vigorous, polyclonal, multispecific, TH1 lymphokine dominated CD4+ T-cell response showed viral clearance and a self-limited course of disease. In contrast, absence of this T-cell response in patients with AHC invariably led to viral persistence and chronic hepatitis. The characteristics of the T-cell response were as follows: it was mainly directed against nonstructural proteins of the virus, it was multispecific and demonstrated immunodominant epitopes, and the majority of T-cell clones established from our patients responded to a single peptide (NS3 amino acid 1248-1261) within the helicase region of HCV. Presentation of the peptide was HLA DR specific, the peptide showed promiscuous binding, and it had high binding affinity to 10 of the most common 13 HLA DR alleles, thus patients with diverse HLA DR backgrounds could mount an immune response. Furthermore, the epitope was conserved in 100% of 33 HCV strains published in databases. This strong initial CD4+ T-cell response is not sufficient for a definitive recovery from AHC, it has to be maintained to control the hepatitis C virus. Loss of the response after initial resolution of disease is followed by relapse. Even 20 years after an episode of self-limited AHC with elimination of HCV, we have observed a significant virus-specific CD4+ T-cell response. Our data indicate the decisive role of the virus-specific CD4+ T-cell response for clearance and control of HCV, and contribute to our understanding of immune mechanisms by which the host defends the HCV virus. This is a prerequisite for the development of new strategies to efficiently defend the virus by manipulating or modulating the immune response.

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

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