Dysfunction and functional restoration of HCV-specific CD8 responses in chronic hepatitis C virus infection

Abstract

The functional impairment of HCV-specific T cell responses is believed to be an important determinant of HCV persistence, but the functional T cell defects of patients with chronic hepatitis C (CH-C) are only partially defined. CD8 responses to HLA-A2-restricted epitopes of HCV and other unrelated viruses were studied in 23 HLA-A2-positive patients both ex vivo and after in vitro culture. Degranulation capacity, intracellular perforin, and granzyme-A content and cytokine production (IFN-␥, TNF-␣) by HCV-and non-HCV-specific CD8 cells were tested both ex vivo and in vitro, whereas cytolytic activity was studied after 10 days' expansion in vitro. Memory maturation and role of exhaustion were assessed ex vivo by HCV-specific CD8 staining for CD127 and PD-1, and in vitro after peripheral blood mononuclear cells (PBMC) culture in the presence of anti-PD-L1 monoclonal antibodies. IFN-␥ production and cytolytic activity were expressed less efficiently by HCV-specific than by non-HCV specific CD8 cells derived from the same CH-C patients. The amount of stored granzyme-A within single cells was always lower in HCV-specific CD8 cells, which were less efficient also in the release of lytic granules and in the production of TNF-␣. The CD8 dysfunction was associated with high PD-1 expression by most HCV-specific CD8 cells, and PD-1/PD-L1 blockade by anti-PD-L1 antibodies in vitro was able to improve the HCVspecific CD8 function. Conclusion: Our study characterizes CD8 defects that may be important in maintaining HCV persistence; identification of strategies to correct these defects may help to define novel approaches to treat HCV infection. (HEPATOLOGY 2007;45:588 -601.) H epatitis C virus infection is a major public health problem, affecting more than 200 million people worldwide and causing chronic liver disease, with possible evolution to cirrhosis and HCC. 1 Available therapies can cure no more than 50% of infected patients, making essential the development of new therapeutic strategies for nonresponders. 1 Restoration of efficient antiviral T cell responses is one of the possible approaches to improve the efficacy of available antiviral drugs. This is suggested by the observation that HCVspecific CD4 and CD8 cells are hyporesponsive in patients with chronic hepatitis C (CH-C). 2,3 However, the functional basis of these defective T cell responses remains largely undefined.To better characterize the immune defects underlying chronic viral persistence, in this study we focused our analysis of the adaptive immune response in patients with chronic HCV infection on CD8 lymphocytes, given the central role played by these cells in the control of viral infections. Despite the low frequency of peripheral blood HCV-specific CD8 cells at this stage of infection, functional studies were carried out not only on in vitro expanded CD8 cells, but also ex vivo when HCV-specific CD8 frequencies were sufficient for a reliable analysis. This is particularly important to avoid incorrect conclusions based on the study of limited CD8 subsets s...

Selection of high-avidity CD8 T cells correlates with control of hepatitis C virus infection

“…17,21 Accordingly our HCV-specific T cell lines displayed heterogeneous functional properties that closely mimicked those of ex vivo specific T cells. 6,12,13,[22][23][24] Finally, because this study focused on peripheral blood mononuclear cell-derived T cell lines, we cannot rule out a specific trapping of high-avidity T cells within the liver in chronically infected patients. Although an in-depth analysis of liver-derived HCV-specific T cells would be required to directly address this issue, the assumption that high-avidity T cells are enriched in patients having recovered from HCV infection would better fit with studies reporting a correlation between selection of high-avidity T cells and clearance of several other viral infections.…”

“…[6][7][8] Mechanisms contributing to this progressive functional defect remain unclear but could involve (1) lack of CD4 T cell help, 7,9 (2) defective antigen-presenting cell function, 10 (3) impairment of HCV-specific immunity by regulatory T cells, 11 (4) expression of inhibitory receptors, 12,13 or (5) T cell exhaustion caused by chronic antigenic stimulation. The overall weak T cell responses observed along with viral persistence could also result from "holes" in the HCV-specific T cell repertoire or a preexisting functional defect of HCV-specific T cells before infection.…”

Programmed death 1 expression during antiviral treatment of chronic hepatitis B: Impact of hepatitis B e-antigen seroconversion

“…25 The advantage of the present study design is that by monitoring longitudinally the impact of treatment-induced suppression of HBV replication with direct antivirals (telbivudine or lamivudine), we were able to define the causeeffect relationship between the viral load and PD-1 expression. The results demonstrate a close positive correlation between HBV-DNA levels and PD-1 expression on total CD8ϩ T-cells, virus-specific CD8ϩ T-cells, and 10,11,12,14,[25][26][27] The lack of sufficient numbers of PBMCs precluded us from testing for this well-established effect. The blockade of the PD-1/PD L-1 pathway has been suggested as a possible immunomodulatory approach for enhancing immune control of viral replication.…”

Acute hepatitis C virus infection: A chronic problem

“…Blocking the PD-1/programmed death ligand 1 interaction improved the functional activity of HCV-specific CD8 ϩ T cells and restored CD8 function in vitro. 118 Supporting data for the role of PD-1 expression in chronic HCV infection has been recently published with chimpanzees models. 119 However, there are also data suggesting that most intrahepatic CD8 ϩ T cells are toleragenic and express PD-1.…”