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...

The innate immune system is able to sense HBV infection, as shown by the early development of NK and NT cell responses, which probably contribute to contain the HBV infection and to allow timely induction of adaptive 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 ␥, interleukin ( S pontaneous clearance of hepatitis C virus infection occurs in a small percentage of acutely infected patients and is associated with a vigorous cellular immune response of a broad specificity. [1][2][3][4][5][6][7][8][9] In contrast, chronic infection is characterized by less vigorous and narrowly focused CD4 and CD8 T cell responses. The mechanisms responsible for immune failure in patients who do not succeed in clearing the virus spontaneously are still unclear. Although there have been several reports of the hepatitis C virus (HCV)-specific cellular immune response during acute illness, a comprehensive study analyzing simultaneously the contribution of each T cell subsets to the mechanisms of clearance or persistence has never been performed. Most recent reports used wide panels of 10-to 15-mer HCV peptides that cannot distinguish the relative contribution of CD4 and CD8 cells to the overall antiviral T cell response. [5][6][7][8][9][10][11] Alternatively, a small number of preselected epitopes of known HLA restriction or whole recombinant HCV proteins were tested. [12][13][14][15][16][17][18] Moreover, only limited information is available about the ex vivo profile of cytokine production in the acute phase of infection, because ELISPOT and intracellular cytokine staining (ICS) analysis were based on the measure of interferon-␥ (IFN-␥) only. 12,19 In the present study, we used panels of genotypematched, overlapping peptides covering the entire HCV sequence to obtain a reliable representation of the overall T cell response to HCV, associated with control of infec-

No abstract

No abstract