Hepatitis E virus (HEV) infection is usually self-limited but may lead to acute hepatitis and rarely to fulminant hepatic failure. Persistent HEV infections have recently been described in organ transplant recipients receiving immunosuppressive medications, suggesting that HEV is controlled by adaptive immune responses. However, only few studies have investigated HEV-specific T-cell responses and immune correlates for the failure to clear HEV infection have not been established so far. We investigated T-cell responses against HEV in 38 subjects including anti-HEV-positive (exposed, n = 9) and anti-HEV-negative (n = 10) healthy controls, 12 anti-HEV-positive but HEV RNA-negative organ transplant recipients, and seven transplant recipients with chronic hepatitis E. Proliferation as well as cytokine production of CD4+ and CD8+ T cells was studied after stimulation with overlapping peptides spanning all proteins encoded by HEV-open reading frame (ORF)2 and HEV-ORF3. We show that (1) strong and multispecific HEV-specific T-cell responses are present in exposed healthy controls, and to a lesser extent also in recovered patients after transplantation; (2) that these responses are absent in patients with chronic hepatitis E but become detectable after viral clearance; and (3) that HEV-specific T-cell responses can be restored in vitro by blocking the PD-1 or CTLA-4 pathways. However, a combination of PD-1 and CTLA-4 blockade had no synergistic effects. We conclude that chronic hepatitis E is associated with impaired HEV-specific T-cell responses and suggest that enhancing adaptive cellular immunity against HEV might prevent persistent HEV infections.

Approximately 130 million people worldwide are infected chronically with the hepatitis C virus (HCV).¹ x 1 Shepard, C.W., Finelli, L., and Alter, M.J. Global epidemiology of hepatitis C virus infection. Lancet Infect Dis. 2005; 5: 558–567 Abstract | Full Text | Full Text PDF | PubMed | Scopus (2003) | Google Scholar See all References HCV-related liver disease is one of the leading causes of liver failure, liver transplantation, and hepatocellular carcinoma in the Western world.² x 2 Hoofnagle, J.H. Course and outcome of hepatitis C. Hepatology. 2002; 36: S21–S29 Crossref | PubMed | Scopus (0) | Google Scholar See all References After acute infection, only 10%–50% of patients are able to clear the virus spontaneously,³ x 3 Wiegand, J., Deterding, K., Cornberg, M. et al. Treatment of acute hepatitis C: the success of monotherapy with (pegylated) interferon alpha. J Antimicrob Chemother. 2008; 62: 860–865 Crossref | PubMed | Scopus (43) | Google Scholar See all References and it is widely accepted that HCV-specific T-cell responses are associated with the outcome of acute and persistent HCV infection.⁴ x 4 Rehermann, B. Hepatitis C virus versus innate and adaptive immune responses: a tale of coevolution and coexistence. J Clin Invest. 2009; 119: 1745–1754 Crossref | PubMed | Scopus (379) | Google Scholar See all References Natural killer (NK) cells also have been suggested to contribute to the early control of HCV infection as well as being involved in the pathogenesis of chronic liver disease. Both T cells and NK cells are known to be impaired functionally in patients with chronic hepatitis C.⁵ x 5 Wedemeyer, H., He, X.S., Nascimbeni, M. et al. Impaired effector function of hepatitis C virus-specific CD8+ T cells in chronic hepatitis C virus infection. J Immunol. 2002; 169: 3447–3458 PubMed | Google Scholar See all References ^{, 6} x 6 Crotta, S., Stilla, A., Wack, A. et al. Inhibition of natural killer cells through engagement of CD81 by the major hepatitis C virus envelope protein. J Exp Med. 2002; 195: 35–41 Crossref | PubMed | Scopus (372) | Google Scholar See all References

The outcome of viral infections is dependent on the function of CD8+ T cells which are tightly regulated by costimulatory molecules. The NK cell receptor 2B4 (CD244) is a transmembrane protein belonging to the Ig superfamily which can also be expressed by CD8+ T cells. The aim of this study was to analyze the role of 2B4 as an additional costimulatory receptor regulating CD8+ T cell function and in particular to investigate its implication for exhaustion of hepatitis C virus (HCV)-specific CD8+ T cells during persistent infection. We demonstrate that (i) 2B4 is expressed on virus-specific CD8+ T cells during acute and chronic hepatitis C, (ii) that 2B4 cross-linking can lead to both inhibition and activation of HCV-specific CD8+ T cell function, depending on expression levels of 2B4 and the intracellular adaptor molecule SAP and (iii) that 2B4 stimulation may counteract enhanced proliferation of HCV-specific CD8+ T cells induced by PD1 blockade. We suggest that 2B4 is another important molecule within the network of costimulatory/inhibitory receptors regulating CD8+ T cell function in acute and chronic hepatitis C and that 2B4 expression levels could also be a marker of CD8+ T cell dysfunction. Understanding in more detail how 2B4 exerts its differential effects could have implications for the development of novel immunotherapies of HCV infection aiming to achieve immune control. Infection with the hepatitis C Virus (HCV) is a world-wide health burden, the infection becomes persistent in the majority of cases. In chronic patients HCV-specific immune responses are weak, HCV-specific CD8+ T cells were shown to be functionally exhausted and to be negatively controlled by costimulatory molecules like PD-1. Here, we show that the costimulatory molecule 2B4 (CD244) is also involved in the regulation of HCV-specific CD8+ T cell responses and that 2B4 expression is selectively upregulated on virus-specific CD8+ T cells in persistent infections. Proliferation of HCV-specific CD8+ T cells from chronic patients increased by 2B4 cross-linking only if the ex vivo 2B4 expression was low, while we could observe no effect on samples with high 2B4 expression levels. Of note, expression of the intracellular 2B4 adaptor molecule SAP, which leads to an activation of the cell, decreased with higher 2B4 expression levels. Finally, we were able to show that 2B4 cross-linking can counter-act enhanced proliferation of HCV-specific CD8+ T cells seen upon PD-1 blockade. Thus, our study provides new insights into the regulation of CD8+ T cell responses demonstrating an implication of the costimulatory molecule 2B4.