Anna Schurich

Blockade of Immunosuppressive Cytokines Restores NK Cell Antiviral Function in Chronic Hepatitis B Virus Infection

NK cells are enriched in the liver, constituting around a third of intrahepatic lymphocytes. We have previously demonstrated that they upregulate the death ligand TRAIL in patients with chronic hepatitis B virus infection (CHB), allowing them to kill hepatocytes bearing TRAIL receptors. In this study we investigated whether, in addition to their pathogenic role, NK cells have antiviral potential in CHB. We characterised NK cell subsets and effector function in 64 patients with CHB compared to 31 healthy controls. We found that, in contrast to their upregulated TRAIL expression and maintenance of cytolytic function, NK cells had a markedly impaired capacity to produce IFN-γ in CHB. This functional dichotomy of NK cells could be recapitulated in vitro by exposure to the immunosuppressive cytokine IL-10, which was induced in patients with active CHB. IL-10 selectively suppressed NK cell IFN-γ production without altering cytotoxicity or death ligand expression. Potent antiviral therapy reduced TRAIL-expressing CD56bright NK cells, consistent with the reduction in liver inflammation it induced; however, it was not able to normalise IL-10 levels or the capacity of NK cells to produce the antiviral cytokine IFN-γ. Blockade of IL-10 +/− TGF-β restored the capacity of NK cells from both the periphery and liver of patients with CHB to produce IFN-γ, thereby enhancing their non-cytolytic antiviral capacity. In conclusion, NK cells may be driven to a state of partial functional tolerance by the immunosuppressive cytokine environment in CHB. Their defective capacity to produce the antiviral cytokine IFN-γ persists in patients on antiviral therapy but can be corrected in vitro by IL-10+/− TGF-β blockade.

Role of the coinhibitory receptor cytotoxic T lymphocyte antigen‐4 on apoptosis‐Prone CD8 T cells in persistent hepatitis B virus infection

An excess of coinhibitory signals has been proposed to drive the T‐cell exhaustion characteristic of persistent viral infections. In this study we examined the contribution of the coinhibitory receptor cytotoxic T lymphocyte antigen‐4 (CTLA‐4) to CD8 T cell tolerance in chronic hepatitis B virus (HBV) infection (CHB). CD8 T cells in patients with CHB have an increased propensity to express the coinhibitory receptor CTLA‐4 and this correlates with viral load. CTLA‐4 is up‐regulated on those HBV‐specific CD8 T cells with the highest levels of the proapoptotic protein Bim, which we have previously shown mediates their premature attrition; abrogation of CTLA‐4‐mediated coinhibition can reduce Bim expression. Longitudinal study of CHB patients beginning antiviral therapy reveals that HBV DNA suppression induces transient reconstitution of HBV‐specific CD8 T cells but does not reprogram their CTLA‐4hiBimhi tolerogenic phenotype. Blocking CTLA‐4 is able to increase the expansion of interferon gamma (IFN‐γ)‐producing HBV‐specific CD8 T cells in both the peripheral and intrahepatic compartments. The rescue of anti‐HBV responses by either CTLA‐4 or PD‐L1 blockade is nonredundant. Conclusion: CTLA‐4 is expressed by HBV‐specific CD8 T cells with high levels of Bim and helps to drive this proapoptotic phenotype. CTLA‐4 blockade could form one arm of a therapeutic approach to modulate the diverse patterns of coregulation of T‐cell exhaustion in this heterogeneous disease. (HEPATOLOGY 2011;)

Tolerogenic maturation of liver sinusoidal endothelial cells promotes B7-homolog 1-dependent CD8(+) T cell tolerance

Liver sinusoidal endothelial cells (LSEC) are unique organ‐resident antigen‐presenting cells capable of cross‐presentation and subsequent tolerization of naïve CD8+ T cells. We investigated the molecular mechanisms underlying this tolerance induction in naive CD8+ T cells. MHC class I–restricted antigen presentation by LSEC led to initial stimulation of naïve CD8+ T cells, which up‐regulated CD69, CD25, CD44, and programmed death (PD)‐1 and proliferated similar to dendritic cell (DC)–activated CD8+ T cells. Importantly, cognate interaction with naïve CD8+ T cells triggered increased expression of co‐inhibitory B7‐H1 but not co‐stimulatory CD80/86 molecules exclusively on LSEC but not DC. This matured phenotype of B7‐H1high CD80/86low was critical for induction of CD8+ T cell tolerance by LSEC: B7‐H1–deficient LSEC, that failed to interact with PD‐1 on stimulated T cells, were incapable of inducing CD8+ T cell tolerance. Moreover, increased costimulation via CD28 interfered with tolerance induction, indicating that the noninducible low expression levels of CD80/86 on LSEC supported B7‐H1–dependent tolerance induction. LSEC‐tolerized CD8+ T cells had a distinctive phenotype from naïve and activated T cells with CD25low, CD44high, CD62Lhigh. They also expressed the homeostatic cytokine receptors CD127, CD122, and high levels of Bcl‐2, indicating survival rather than deletion of tolerant CD8+ T cells. On adoptive transfer into congenic animals, tolerized CD8+ T cells failed to show specific cytotoxicity in vivo. Conclusion: Cognate interaction of LSEC with naïve CD8+ T cells elicits a unique tolerogenic maturation of LSEC and permissiveness of T cells for tolerogenic signals, demonstrating that LSEC‐induced tolerance is an active and dynamic process. (HEPATOLOGY 2007.)

Up-regulation of a death receptor renders antiviral T cells susceptible to NK cell–mediated deletion

Hepatic NK cells eliminate HBV-specific T cells dependent on TRAIL and TRAIL-R2 interactions to limit antiviral immunity in chronic infection.

Upregulation of the Tim-3/Galectin-9 Pathway of T Cell Exhaustion in Chronic Hepatitis B Virus Infection

The S-type lectin galectin-9 binds to the negative regulatory molecule Tim-3 on T cells and induces their apoptotic deletion or functional inactivation. We investigated whether galectin-9/Tim-3 interactions contribute to the deletion and exhaustion of the antiviral T cell response in chronic hepatitis B virus infection (CHB). We found Tim-3 to be expressed on a higher percentage of CD4 and CD8 T cells from patients with CHB than healthy controls (p<0.0001) and to be enriched on activated T cells and those infiltrating the HBV-infected liver. Direct ex vivo examination of virus-specific CD8 T cells binding HLA-A2/peptide multimers revealed that Tim-3 was more highly upregulated on HBV-specific CD8 T cells than CMV-specific CD8 T cells or the global CD8 T cell population in patients with CHB (p<0.001) or than on HBV-specific CD8 after resolution of infection. T cells expressing Tim-3 had an impaired ability to produce IFN-γ and TNF-α upon recognition of HBV-peptides and were susceptible to galectin-9-triggered cell death in vitro. Galectin-9 was detectable at increased concentrations in the sera of patients with active CHB-related liver inflammation (p = 0.02) and was strongly expressed by Kupffer cells within the liver sinusoidal network. Tim-3 blockade resulted in enhanced expansion of HBV-specific CD8 T cells able to produce cytokines and mediate cytotoxicity in vitro. Blocking PD-1 in combination with Tim-3 enhanced the number of patients from whom functional antiviral responses could be recovered and/or the strength of responses, indicating that these co-inhibitory molecules play a non-redundant role in driving T cell exhaustion in CHB. Patients taking antivirals able to potently suppress HBV viraemia continued to express Tim-3 on their T cells and respond to Tim-3 blockade. In summary, both Tim-3 and galectin-9 are increased in CHB and may contribute to the inhibition and deletion of T cells as they infiltrate the HBV-infected liver.

Differential boosting of innate and adaptive antiviral responses during pegylated-interferon-alpha therapy of chronic hepatitis B

BACKGROUND & AIMS A better understanding of the immunomodulatory effects of PegIFNα therapy could allow more rational optimisation of future therapeutic approaches in chronic HBV infection. In this study, we evaluated dynamic changes in the innate and adaptive arms of the immune system induced by PegIFNα. METHODS PBMC were obtained from a cohort of patients with eAg-negative CHB before, during and after PegIFNα treatment. The number, phenotype and function of global and virus-specific T cells and NK cells were analyzed by flow cytometry and serum cytokines by ELISA or CBA. RESULTS The absolute number of CD8 T cells was strikingly reduced on PegIFNα therapy (p<0.001), with a predominant loss of end-stage effectors, including CMV-specific CD8 T cells. There was no significant recovery of the exhausted HBV-specific CD8 T cell response. By contrast, PegIFNα was able to potently and cumulatively drive the proliferation and expansion in absolute numbers of CD56(bright) NK cell numbers (p<0.001), with induction of the pro-proliferative cytokine IL-15. Expanded CD56(bright) NK cells showed enhanced expression of activation markers and the activating receptor NKp46, accompanied by augmentation of TRAIL and IFN-γ expression (p<0.001). Peak virological response (temporal within individual patients and cross-sectional within the cohort) correlated with the degree of expansion of functional CD56(bright) NK cells. CONCLUSIONS IFN-α mediates divergent effects on the innate and adaptive arms of the immune system in vivo. The efficacy of PegIFNα may be limited by its depleting effect on CD8 T cells; conversely, it can cumulatively drive proliferation, activation and antiviral potential of CD56(bright) NK cells.

The molecular basis of the failed immune response in chronic HBV: therapeutic implications.

There is a pressing need to develop new immunotherapeutic interventions in chronic hepatitis B virus (HBV) infection in order to limit the high costs and risks of toxicity or viral resistance associated with maintenance antiviral treatment. Here we review recent advances in our understanding of the molecular defects underlying the profound T cell depletion characteristic of these patients. We propose that T cells are driven to apoptosis by the combination of a persistent, high antigen load and excessive inhibitory signals encountered in the hepatic microenvironment. The feasibility of boosting sustained antiviral control by targeted reversal of key tolerising mechanisms is discussed.

Metabolic regulation of hepatitis B immunopathology by myeloid-derived suppressor cells

Infection with hepatitis B virus (HBV) results in disparate degrees of tissue injury: the virus can either replicate without pathological consequences or trigger immune-mediated necroinflammatory liver damage. We investigated the potential for myeloid-derived suppressor cells (MDSCs) to suppress T cell–mediated immunopathology in this setting. Granulocytic MDSCs (gMDSCs) expanded transiently in acute resolving HBV, decreasing in frequency prior to peak hepatic injury. In persistent infection, arginase-expressing gMDSCs (and circulating arginase) increased most in disease phases characterized by HBV replication without immunopathology, whilst L-arginine decreased. gMDSCs expressed liver-homing chemokine receptors and accumulated in the liver, their expansion supported by hepatic stellate cells. We provide in vitro and ex vivo evidence that gMDSCs potently inhibited T cells in a partially arginase-dependent manner. L-arginine–deprived T cells upregulated system L amino acid transporters to increase uptake of essential nutrients and attempt metabolic reprogramming. These data demonstrate the capacity of expanded arginase-expressing gMDSCs to regulate liver immunopathology in HBV infection.

The Third Signal Cytokine IL-12 Rescues the Anti-Viral Function of Exhausted HBV-Specific CD8 T Cells

Optimal immune activation of naïve CD8 T cells requires signal 1 mediated by the T cell receptor, signal 2 mediated by co-stimulation and signal 3 provided by pro-inflammatory cytokines. However, the potential for signal 3 cytokines to rescue anti-viral responses in functionally exhausted T cells has not been defined. We investigated the effect of using third signal cytokines IL-12 or IFN-α to rescue the exhausted CD8 T cell response characteristic of patients persistently infected with hepatitis B virus (HBV). We found that IL-12, but not IFN-α, potently augmented the capacity of HBV-specific CD8 T cells to produce effector cytokines upon stimulation by cognate antigen. Functional recovery mediated by IL-12 was accompanied by down-modulation of the hallmark inhibitory receptor PD-1 and an increase in the transcription factor T-bet. PD-1 down-regulation was observed in HBV but not CMV-specific T cells, in line with our finding that the highly functional CMV response was not further enhanced by IL-12. IL-12 enhanced a number of characteristics of HBV-specific T cells important for viral control: cytotoxicity, polyfunctionality and multispecificity. Furthermore, IL-12 significantly decreased the pro-apoptotic molecule Bim, which is capable of mediating premature attrition of HBV-specific CD8 T cells. Combining IL-12 with blockade of the PD-1 pathway further increased CD8 functionality in the majority of patients. These data provide new insights into the distinct signalling requirements of exhausted T cells and the potential to recover responses optimised to control persistent viral infections.

Dynamic Regulation of CD8 T Cell Tolerance Induction by Liver Sinusoidal Endothelial Cells

Cross-presentation of soluble Ag on MHC class I molecules to naive CD8 T cells by liver sinusoidal endothelial cells (LSECs) leads to induction of T cell tolerance that requires interaction between coinhibitory B7-H1 on LSECs and programmed cell death-1 on CD8 T cells. In this study, we investigate whether cross-presentation of high as well as low Ag concentrations allowed for LSEC-induced tolerance. Ag concentration directly correlated with the cross-presentation capacity of murine LSECs and thus strength of TCR stimulation. Although LSEC cross-presentation at low-Ag concentrations resulted in tolerance, they induced differentiation into effector T cells (CTL) at high-Ag concentrations. CTL differentiation under these conditions was not caused by increased expression of costimulatory CD80/86 on cross-presenting LSECs but was determined by early IL-2 release from naive CD8 T cells. B7-H1 signals from LSECs and TCR avidity reciprocally controlled early T cell release of IL-2 and CTL differentiation. B7-H1 expression directly correlated with cross-presentation at low- but not high-Ag concentrations, indicating an imbalance between TCR and coinhibitory signals regulating T cell release of IL-2. Exogenous IL-2 overrode coinhibitory B7-H1–mediated signals by LSECs and induced full CTL differentiation. Our results imply that LSEC-mediated T cell tolerance can be broken in situations where T cells bearing high-avidity TCR encounter LSECs cross-presenting high numbers of cognate MHC class I peptide molecules, such as during viral infection of the liver. Furthermore, we attribute a novel costimulatory function to IL-2 acting in a T cell autonomous fashion to promote local induction of immunity in the liver even in the absence of CD80/86 costimulation.