Direct-acting antivirals trump interferon-alpha in their capacity to rescue exhausted T cells upon HCV clearance
Authors: Mala K. Maini, Anna Schurich
Journal: Journal of Hepatology (2014)

Restoration of HCV-specific CD8+ T cell function by interferon-free therapyJournal of HepatologyVol. 61Issue 3PreviewChronic hepatitis C virus (HCV) infection is characterised by a failure of virus-specific CD8+ T cells that is mainly caused by viral escape and T cell exhaustion. Constant antigen stimulation has been suggested to contribute to HCV-specific CD8+ T cell exhaustion. However, IFN-based therapies failed to recover HCV-specific CD8+ T cell function suggesting that the damage to CD8+ T cells may be permanent even after antigen removal. It was therefore the objective of this study to analyse the impact of inhibition of ongoing viral replication by IFN-free therapy with direct acting antivirals (DAA) on the phenotype and function of HCV-specific CD8+ T cells. Full-Text PDF The treatment of HCV has been transformed by the capacity of direct acting antivirals (DAAs) to eliminate the infection by attacking the virus effectively. In this issue Martin et al. reveal that these drugs can also harness the immune system by releasing it from the burden of chronic antigen load [[1]Martin B. Hennecke N. Lohmann V. Kayser A. Neumann-Haefelin C. Kukolj G. et al.Restoration of HCV-specific CD8+ T-cell function by interferon-free therapy.J Hepatol. 2014; 61: 538-543Abstract Full Text Full Text PDF PubMed Scopus (196) Google Scholar]. Their important findings underscore a detrimental immunoregulatory component to the effects of interferon-alpha (IFN-α), which was not able to boost antiviral T cells in the manner now demonstrated with DAAs, even when it achieved viral clearance (Fig. 1). CD8 T cells are well-recognised to be critical for the control of viruses such as HCV but to be depleted and dysfunctional (exhausted) in chronic infection [2Wherry E.J. T cell exhaustion.Nat Immunol. 2011; 12: 492-499Crossref PubMed Scopus (2541) Google Scholar, 3Klenerman P. Hill A. T cells and viral persistence: lessons from diverse infections.Nat Immunol. 2005; 6: 873-879Crossref PubMed Scopus (348) Google Scholar, 4Park S.H. Rehermann B. Immune responses to HCV and other hepatitis viruses.Immunity. 2014; 40: 13-24Abstract Full Text Full Text PDF PubMed Scopus (201) Google Scholar, 5Rehermann B. Pathogenesis of chronic viral hepatitis: differential roles of T cells and NK cells.Nat Med. 2013; 19: 859-868Crossref PubMed Scopus (361) Google Scholar]. There are clear demonstrations of the inverse relationship between duration and level of viraemia and T cell responses in murine and human persistent viral infections [2Wherry E.J. T cell exhaustion.Nat Immunol. 2011; 12: 492-499Crossref PubMed Scopus (2541) Google Scholar, 3Klenerman P. Hill A. T cells and viral persistence: lessons from diverse infections.Nat Immunol. 2005; 6: 873-879Crossref PubMed Scopus (348) Google Scholar, 6Webster G.J. Reignat S. Brown D. Ogg G.S. Jones L. Seneviratne S.L. et al.Longitudinal analysis of CD8+ T cells specific for structural and nonstructural hepatitis B virus proteins in patients with chronic hepatitis B: implications for immunotherapy.J Virol. 2004; 78: 5707-5719Crossref PubMed Scopus (344) Google Scholar]. However it has been difficult to determine to what extent the persistent, high antigen load in these settings contributes to the failure of the T cell response [[7]Mueller S.N. Ahmed R. High antigen levels are the cause of T cell exhaustion during chronic viral infection.Proc Natl Acad Sci U S A. 2009; 106: 8623-8628Crossref PubMed Scopus (274) Google Scholar] or is rather a result of it. A vital issue in the attempt to cure persistent viral infection is whether removal of antigen will be sufficient to allow recovery of T cells with antiviral efficacy. Alternatively, T cells may be permanently scarred by, for example, stable imprinting of PD-1 [[8]Utzschneider D.T. Legat A. Fuertes Marraco S.A. Carrie L. Luescher I. Speiser D.E. et al.T cells maintain an exhausted phenotype after antigen withdrawal and population reexpansion.Nat Immunol. 2013; 14: 603-610Crossref PubMed Scopus (191) Google Scholar], or subject to other ongoing tolerising mechanisms, which are particularly prevalent in the liver environment [[9]Knolle P.A. Thimme R. Hepatic immune regulation and its involvement in viral hepatitis infection.Gastroenterology. 2014; 146: 1193-1207Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar]. Previous data from the HCV field had suggested that whilst T cells show variable recovery following spontaneous or therapeutic removal of antigen in acute infection, they might no longer be amenable to rescue in chronic infection [4Park S.H. Rehermann B. Immune responses to HCV and other hepatitis viruses.Immunity. 2014; 40: 13-24Abstract Full Text Full Text PDF PubMed Scopus (201) Google Scholar, 10Abdel-Hakeem M.S. Bedard N. Badr G. Ostrowski M. Sekaly R.P. Bruneau J. et al.Comparison of immune restoration in early vs. late alpha interferon therapy against hepatitis C virus.J Virol. 2010; 84: 10429-10435Crossref PubMed Scopus (54) Google Scholar, 11Missale G. Pilli M. Zerbini A. Penna A. Ravanetti L. Barili V. et al.Lack of full CD8 functional restoration after antiviral treatment for acute and chronic hepatitis C virus infection.Gut. 2012; 61: 1076-1084Crossref PubMed Scopus (49) Google Scholar]. Thus patients with IFN-α induced clearance of chronic HCV had no consistent recovery of virus-specific T cells [10Abdel-Hakeem M.S. Bedard N. Badr G. Ostrowski M. Sekaly R.P. Bruneau J. et al.Comparison of immune restoration in early vs. late alpha interferon therapy against hepatitis C virus.J Virol. 2010; 84: 10429-10435Crossref PubMed Scopus (54) Google Scholar, 11Missale G. Pilli M. Zerbini A. Penna A. Ravanetti L. Barili V. et al.Lack of full CD8 functional restoration after antiviral treatment for acute and chronic hepatitis C virus infection.Gut. 2012; 61: 1076-1084Crossref PubMed Scopus (49) Google Scholar, 12Barnes E. Gelderblom H.C. Humphreys I. Semmo N. Reesink H.W. Beld M.G. et al.Cellular immune responses during high-dose interferon-alpha induction therapy for hepatitis C virus infection.J Infect Dis. 2009; 199: 819-828Crossref PubMed Scopus (39) Google Scholar]. Now the Thimme group demonstrate that when the antigen load is reduced by IFN-free therapy, there is a striking recovery of the capacity of HCV-specific T cells to expand in culture. Responders to DAAs had a significant increase in the number of detectable HCV-specific responses, and in their frequencies after in vitro expansion, whereas non-responders did not. Three of the 25 responders had no detectable HCV-specific T cells and a further three showed no increase on therapy, but this could reflect the fact that the study was focused on 4 immunodominant epitopes, thereby under-estimating the full extent of reconstitution [[1]Martin B. Hennecke N. Lohmann V. Kayser A. Neumann-Haefelin C. Kukolj G. et al.Restoration of HCV-specific CD8+ T-cell function by interferon-free therapy.J Hepatol. 2014; 61: 538-543Abstract Full Text Full Text PDF PubMed Scopus (196) Google Scholar]. This focused approach did, however, allow the vital distinction between T cells directed against consensus vs. mutated viral sequences. HCV clearance had less impact on the expansion of responses to mutated epitopes [[1]Martin B. Hennecke N. Lohmann V. Kayser A. Neumann-Haefelin C. Kukolj G. et al.Restoration of HCV-specific CD8+ T-cell function by interferon-free therapy.J Hepatol. 2014; 61: 538-543Abstract Full Text Full Text PDF PubMed Scopus (196) Google Scholar], in line with the concept that these T cells have already escaped from the effects of continuous MHC/peptide stimulation [[13]Bengsch B. Seigel B. Ruhl M. Timm J. Kuntz M. Blum H.E. et al.Coexpression of PD-1, 2B4, CD160, and KLRG1 on exhausted HCV-specific CD8+ T cells is linked to antigen recognition and T cell differentiation.PLoS Pathog. 2010; 6: e1000947Crossref PubMed Scopus (305) Google Scholar]. Importantly, T cell responses directed against CMV and flu epitopes within HCV-infected patients were not augmented by therapy, arguing against a direct capacity of DAAs to boost T cells generally. Taken together, their findings support a role for viral clearance in driving a recovery of HCV-specific T cells. So why does IFN-α not have analogous effects on T cells even when it eliminates the virus? In addition to its direct antiviral effects, IFN-α has diverse effects on innate and adaptive immunity, with the dual potential to either enhance immune cell activation or to exert negative immunoregulatory effects [[14]Odorizzi P.M. Wherry E.J. Immunology. An interferon paradox.Science (New York, NY). 2013; 340: 155-156Crossref PubMed Scopus (50) Google Scholar]. The effects of interferon on T cells are particularly pleiotropic, varying from beneficial (promoting their expansion) to detrimental (inhibiting their proliferation and driving apoptosis), depending on timing, T cell phenotype and prior antigen experience [[15]Welsh R.M. Bahl K. Marshall H.D. Urban S.L. Type 1 interferons and antiviral CD8 T-cell responses.PLoS Pathog. 2012; 8: e1002352Crossref PubMed Scopus (132) Google Scholar]. However a number of studies have pointed to IFN-α signalling exerting a predominantly negative effect on T cells in persistent viral infections [[14]Odorizzi P.M. Wherry E.J. Immunology. An interferon paradox.Science (New York, NY). 2013; 340: 155-156Crossref PubMed Scopus (50) Google Scholar]. These unexpected findings have been reinforced by the recent discovery that IFN-α blockade in vivo enhances T cell-dependent resolution of LCMV by reducing excessive immune activation and accompanying immune suppressive mechanisms [[14]Odorizzi P.M. Wherry E.J. Immunology. An interferon paradox.Science (New York, NY). 2013; 340: 155-156Crossref PubMed Scopus (50) Google Scholar]. The emerging concept that IFN-α predominantly suppresses antiviral T cells in persistent viral infection is congruent with their lack of convincing reconstitution following IFN-α (in comparison to DAA)-mediated viral clearance in HCV [1Martin B. Hennecke N. Lohmann V. Kayser A. Neumann-Haefelin C. Kukolj G. et al.Restoration of HCV-specific CD8+ T-cell function by interferon-free therapy.J Hepatol. 2014; 61: 538-543Abstract Full Text Full Text PDF PubMed Scopus (196) Google Scholar, 10Abdel-Hakeem M.S. Bedard N. Badr G. Ostrowski M. Sekaly R.P. Bruneau J. et al.Comparison of immune restoration in early vs. late alpha interferon therapy against hepatitis C virus.J Virol. 2010; 84: 10429-10435Crossref PubMed Scopus (54) Google Scholar, 11Missale G. Pilli M. Zerbini A. Penna A. Ravanetti L. Barili V. et al.Lack of full CD8 functional restoration after antiviral treatment for acute and chronic hepatitis C virus infection.Gut. 2012; 61: 1076-1084Crossref PubMed Scopus (49) Google Scholar, 12Barnes E. Gelderblom H.C. Humphreys I. Semmo N. Reesink H.W. Beld M.G. et al.Cellular immune responses during high-dose interferon-alpha induction therapy for hepatitis C virus infection.J Infect Dis. 2009; 199: 819-828Crossref PubMed Scopus (39) Google Scholar] and HBV [16Penna A. Laccabue D. Libri I. Giuberti T. Schivazappa S. Alfieri A. et al.Peginterferon-alpha does not improve early peripheral blood HBV-specific T-cell responses in HBeAg-negative chronic hepatitis.J Hepatol. 2012; 56: 1239-1246Abstract Full Text Full Text PDF PubMed Scopus (67) Google Scholar, 17Boni C. Laccabue D. Lampertico P. Giuberti T. Vigano M. Schivazappa S. et al.Restored function of HBV-specific T cells after long-term effective therapy with nucleos(t)ide analogues.Gastroenterology. 2012; 143: e969Abstract Full Text Full Text PDF Scopus (279) Google Scholar]. In fact in both these infections, IFN-α therapy can profoundly decrease global and virus-specific T cells [12Barnes E. Gelderblom H.C. Humphreys I. Semmo N. Reesink H.W. Beld M.G. et al.Cellular immune responses during high-dose interferon-alpha induction therapy for hepatitis C virus infection.J Infect Dis. 2009; 199: 819-828Crossref PubMed Scopus (39) Google Scholar, 18Micco L. Peppa D. Loggi E. Schurich A. Jefferson L. Cursaro C. et al.Differential boosting of innate and adaptive antiviral responses during pegylated-interferon-alpha therapy of chronic hepatitis B.J Hepatol. 2012; 58: 225-233Abstract Full Text Full Text PDF PubMed Scopus (192) Google Scholar]. In contrast, IFN-α therapy potently expands activated, TRAIL-expressing NK cells [5Rehermann B. Pathogenesis of chronic viral hepatitis: differential roles of T cells and NK cells.Nat Med. 2013; 19: 859-868Crossref PubMed Scopus (361) Google Scholar, 18Micco L. Peppa D. Loggi E. Schurich A. Jefferson L. Cursaro C. et al.Differential boosting of innate and adaptive antiviral responses during pegylated-interferon-alpha therapy of chronic hepatitis B.J Hepatol. 2012; 58: 225-233Abstract Full Text Full Text PDF PubMed Scopus (192) Google Scholar] that have the potential to delete virus-specific T cells [[19]Peppa D. Gill U.S. Reynolds G. Easom N.J. Pallett L.J. Schurich A. et al.Up-regulation of a death receptor renders antiviral T cells susceptible to NK cell-mediated deletion.J Exp Med. 2013; 210: 99-114Crossref PubMed Scopus (254) Google Scholar], providing one putative mechanism for the lack of antiviral T cell reconstitution. In addition, T cells in IFN-treated patients continue to be inhibited by PD-1 [11Missale G. Pilli M. Zerbini A. Penna A. Ravanetti L. Barili V. et al.Lack of full CD8 functional restoration after antiviral treatment for acute and chronic hepatitis C virus infection.Gut. 2012; 61: 1076-1084Crossref PubMed Scopus (49) Google Scholar, 16Penna A. Laccabue D. Libri I. Giuberti T. Schivazappa S. Alfieri A. et al.Peginterferon-alpha does not improve early peripheral blood HBV-specific T-cell responses in HBeAg-negative chronic hepatitis.J Hepatol. 2012; 56: 1239-1246Abstract Full Text Full Text PDF PubMed Scopus (67) Google Scholar, 18Micco L. Peppa D. Loggi E. Schurich A. Jefferson L. Cursaro C. et al.Differential boosting of innate and adaptive antiviral responses during pegylated-interferon-alpha therapy of chronic hepatitis B.J Hepatol. 2012; 58: 225-233Abstract Full Text Full Text PDF PubMed Scopus (192) Google Scholar], whereas initial data from Martin et al. suggest that expression of this co-inhibitory receptor is reduced by IFN-free viral clearance. The contrasting T cell reconstitution seen with these two different approaches underscores the need to modulate the immunosuppressive effects of IFN-α in order to capitalize on its potential benefits in the therapy of HBV. The data presented by Martin et al. raise a number of interesting questions. As the Thimme group has previously shown, it is not just the number of virus-specific T cells but also their functional profile that determine antiviral efficacy [9Knolle P.A. Thimme R. Hepatic immune regulation and its involvement in viral hepatitis infection.Gastroenterology. 2014; 146: 1193-1207Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar, 20Seigel B. Bengsch B. Lohmann V. Bartenschlager R. Blum H.E. Thimme R. Factors that determine the antiviral efficacy of HCV-specific CD8(+) T cells ex vivo.Gastroenterology. 2013; 144: 426-436Abstract Full Text Full Text PDF PubMed Scopus (36) Google Scholar]. In the present study they had sufficient cells from one patient to elegantly demonstrate an increase in their antiviral efficacy against a hepatoma cell line with an HCV reporter replicon [[1]Martin B. Hennecke N. Lohmann V. Kayser A. Neumann-Haefelin C. Kukolj G. et al.Restoration of HCV-specific CD8+ T-cell function by interferon-free therapy.J Hepatol. 2014; 61: 538-543Abstract Full Text Full Text PDF PubMed Scopus (196) Google Scholar]. It will be interesting in future studies to see whether a full functional restoration and reversal of exhausted phenotype is achieved in most DAA responders. It is tempting to speculate that the recovery of T cells achieved using IFN-free regimens may contribute to the high sustained cure rates and lack of off-treatment relapses seen with these drugs. This would imply that the extent of T cell reconstitution might be able to be used as a guide to personalize DAA therapy. Could a lack of induction of T cells signal the need for therapy intensification and conversely, could good T cell recovery allow shorter treatment duration in some patients, with the expectation that any residual virus will be cleared by T cells? The authors suggest that induced T cells may even be able to provide some protection against reinfection with a new strain of HCV, although this might be limited by virus variability and the possibility that recovered T cells will lack the capacity of memory cells to survive long-term in the absence of antigen [[2]Wherry E.J. T cell exhaustion.Nat Immunol. 2011; 12: 492-499Crossref PubMed Scopus (2541) Google Scholar]. In conclusion, Martin et al. make the rather ironic observation that drugs designed purely to target the hepatitis C virion have turned out to have better potential to indirectly boost antiviral T cell immunity than the standard “immunomodulatory” therapy with interferon. Their study highlights how vital ongoing antigenic stimulation is in driving T cell exhaustion and suggests an encouraging degree of reversibility to this process. It will stimulate efforts to move towards a functional cure in other persistent infections such as HBV and HIV by finding ways to further reduce antigen load, thereby potentially unleashing effective antiviral T cells. MKM has carried out consultancy for Roche, Gilead, BMS, Transgene and ITS and received an unrestricted educational grant from BMS.