Dysfunctional CD8⁺T cells present in chronic virus infections can express programmed death 1 (PD-1) molecules, and the inhibition of the engagement of PD-1 with its ligand (PD-L1) has been reported to enhance the antiviral function of these T cells. We took advantage of the wide fluctuations in levels of viremia which are typical of chronic hepatitis B virus (HBV) infection to comprehensively analyze the impact of prolonged exposure to different virus quantities on virus-specific T-cell dysfunction and on its reversibility through the blocking of the PD-1/PD-L1 pathway. We confirm that chronic HBV infection has a profound effect on the HBV-specific T-cell repertoire. Despite the use of a comprehensive panel of peptides covering all HBV proteins, HBV-specific T cells were rarely observed directly ex vivo in samples from patients with chronic infection, in contrast to those from patients with acute HBV infection. In chronic HBV infection, virus-specific T cells were detected mainly in patients with lower levels of viremia. These HBV-specific CD8⁺T cells expressed PD-1, and their function was improved by the blocking of PD-1/PD-L1 engagement. Thus, a broad spectrum of anti-HBV immunity is expressed by patients with chronic HBV infection and this spectrum is proportional to HBV replication levels and can be improved by blocking the PD-1/PD-L1 pathway. This information may be useful for the design of immunotherapeutic strategies to complement and optimize available antiviral therapies.

Hepatitis B virus (HBV) causes self-limited infections in the majority of adult patients; however, in less than 5% of infected adults and in a larger proportion of children, HBV infection evolves into a chronic liver disease, which may lead to severe sequelae. Available data indicate a vigorous and broad T-cell response in patients with acute self-limited hepatitis B, which is in contrast with the much weaker and often barely detectable T-cell response observed during chronic HBV infections, in which HBV-specific T-lymphocytes have been described to be deeply dysfunctional.¹ x 1 Bertoletti, A. and Ferrari, C. Kinetics of the immune response during HBV and HCV infection. Hepatology. 2003; 38: 4–13 Google Scholar See all References ^{, 2} x 2 Rehermann, B. and Nascimbeni, M. Immunology of hepatitis B virus and hepatitis C virus infection. Nat Rev Immunol. 2005; 5: 215–229 Google Scholar See all References ^{, 3} x 3 Das, A., Hoare, M., Davies, N. et al. Functional skewing of the global CD8 T-cell population in chronic hepatitis B virus infection. J Exp Med. 2008; 205: 2111–2124 Google Scholar See all References Among the different mechanisms proposed to explain such a functional T-cell impairment, exhaustion by persistent exposure to high antigen concentrations represents a possible cause,⁴ x 4 Chang, J.J., Thompson, A.J.V., Visvanathan, K. et al. The phenotype of hepatitis B virus-specific T cells differs in the liver and blood in chronic hepatitis B virus infection. Hepatology. 2007; 46: 1332–1340 Google Scholar See all References ^{, 5} x 5 Zhang, Z., Zhang, J.-Y., Wherry, E.J. et al. Dynamic programmed death 1 expression by virus-specific CD8 T cells correlates with the outcome of acute hepatitis B. Gastroenterology. 2008; 134: 1938–1949 Abstract | Full Text | Full Text PDF | Scopus (94) | Google Scholar See all References ^{, 6} x 6 Boni, C., Fisicaro, P., Valdatta, C. et al. Characterization of hepatitis B virus (HBV)-specific T-cell dysfunction in chronic HBV infection. J Virol. 2007; 81: 4215–4225 Google Scholar See all References and T-cell attrition through Bcl2 signalling⁷ x 7 Lopes, A.R., Kellam, P., Das, A. et al. Bim-mediated deletion of antigen-specific CD8+ T cells in patients unable to control HBV infection. J Clin Invest. 2008; 118: 1835–1845 Google Scholar See all References as well as impaired T-cell receptor signaling through the ζ-chain³ x 3 Das, A., Hoare, M., Davies, N. et al. Functional skewing of the global CD8 T-cell population in chronic hepatitis B virus infection. J Exp Med. 2008; 205: 2111–2124 Google Scholar See all References have been shown to be involved.

Background and Aim: Innate immunity appears to be silent in acutely heptitis B virus (HBV)-infected chimpanzees, as shown by microarray analysis of intrahepatic gene expression. Whether this observation also applies to HBV pathogenesis in man remains undefined. The aim of this study was thus to characterise natural killer (NK) and CD56⁺ natural T (NT) cell responses early after human HBV infection and their relationship to the induction of adaptive immunity. Methods: Two HBV-seronegative blood donors who became hepatitis B surface antigen (HBsAg) and HBV DNA positive but had persistently normal alanine aminotransferase (ALT) were followed from a very early stage of HBV infection. The phenotype (CD69 and NKG2D) and function (cytotoxicity and interferon γ (IFNγ) production) of NK and NT cells were analysed. CD4- and CD8-mediated responses were studied in parallel with overlapping peptides covering the entire HBV sequence by ex vivo intracellular cytokine staining (ICS) for IFNγ, interleukin 2 (IL2), IL4 and IL10, and by ex vivo Elispot for IFNγ. Healthy subjects, and patients with chronic and acute HBV infection were studied for comparison. Results: An early induction of both innate and adaptive responses was observed. NK and NT cells showed faster kinetics than HBV-specific T cells with an earlier peak of activity, while CD4⁺ and CD8⁺ cell responses were mounted with a similar profile, with higher frequencies of IFNγ-producing CD8⁺ cells at the peak of the response. Conclusions: 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.

Background & Aims Natural killer (NK) cells are essential early after infection, not only for viral containment but also for timely and efficient induction of adaptive responses. An inhibitory effect of hepatitis C virus (HCV)-E2 proteins on NK cells has been reported, but the features of NK cell responses in the acute phase of hepatitis C are still largely undefined. Therefore, the aim of this study was to characterize the function and phenotype of NK cells in the acute phase of infection and compare individuals with chronic and self-limited outcomes. Methods Twenty-two individuals with acute HCV infection, 14 with chronic evolution, and 8 with self-limited infection, were studied using NK phenotypic and functional assays. Results An increased expression of NKG2D on both CD56^bright and CD56^dim NK cells was detected in patients with acute HCV, irrespective of the outcome, as compared with healthy controls. Also, interferon gamma production and cytotoxicity by NK cells were higher in individuals with acute HCV infection than in healthy controls. Subset analysis showed increased interferon gamma production in both NK cell subsets carrying group 1 and group 2 HLA-C–specific killer cell immunoglobulin-like receptors. However, increased CD107a was noted only on NK cells expressing the group 1 HLA-C–specific killer cell immunoglobulin-like receptor and was maximal in self-limited infection. Conclusions Our data show that in the acute phase of HCV infection, NK cells are activated regardless of outcome, with no evidence of a suppressive effect of HCV on NK cell function.

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 γ, 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.