Natural killer cells and hepatitis C: natural killer p46 expression linked to antiviral and antifibrotic activity

Increased expression of TIGIT and KLRG1 correlates with impaired CD56bright NK cell immunity in HPV16-related cervical intraepithelial neoplasia

BACKGROUND

The onset and progression of cervical intraepithelial neoplasia (CIN) are closely associated with the persistent infection of high-risk HPV (especially type16), which is mainly caused by immune escape. Natural killer (NK) cells play an important role against virally infected cells and tumor cells through a fine balance of signals from multiple surface receptors. Overexpression of non-MHC-I specific inhibitory receptors TIGIT, KLRG1, Siglec-7, LAIR-1, and CD300a on NK cells correlates with cellular exhaustion and immune evasion, but these receptors have not been investigated in CIN. The aim of the present study was to examine the potential role of NK cell non-MHC-I specific inhibitory receptors expression in immune escape from HPV16(+)CIN patients.

METHODS

The subset distribution, IFN-γ and TNF-α expression levels and immunophenotype of TIGIT, KLRG1, Siglec-7, LAIR-1, and CD300a of NK cells were investigated in peripheral blood mononuclear cell samples by flow cytometry from 82 women who were HPV16(+) with CIN grades 0, I, II-III or HPV(-) CIN 0. Immunohistochemistry was applied to detect the expression of ligands for NK receptors in the cervical tissues. HPV types were identified by PCR assays.

RESULTS

The HPV16(+) subjects with high-grade lesions had an increased number of circulating peripheral blood CD56^bright NK cells with reduced functionality and IFN-γ secretion. The expression levels of the inhibitory molecules TIGIT and KLRG1 on CD56^bright NK cells increased in parallel with increasing CIN grade. In addition, TIGIT and KLRG1 related ligands, Poliovirus receptor (PVR), N-Cadherin and E-Cadherin expression level was also elevated with increasing CIN grade.

CONCLUSIONS

Our results suggest that up-regulation of the inhibitory TIGIT, KLRG1 and their ligands may negatively regulate cervical CD56^bright NK-mediated immunity to HPV16 and contribute to the progression of CIN. These results may facilitate the development of early-warning immune predictors and therapeutic strategies for HPV16(+) CIN based on the TIGIT and KLRG1 inhibitory pathways of NK cells.

Differential inhibitory and activating NK cell receptor levels and NK/NKT-like cell functionality in chronic and recovered stages of chikungunya

The role of natural killer (NK; CD3^-CD56⁺)/NKT (CD3⁺CD56⁺)-like cells in chikungunya virus (CHIKV) disease progression/recovery remains unclear. Here, we investigated the expression profiles and function of NK and NKT-like cells from 35 chronic chikungunya patients, 30 recovered individuals, and 69 controls. Percentage of NKT-like cells was low in chronic chikungunya patients. NKp30⁺, CD244⁺, DNAM-1⁺, and NKG2D⁺ NK cell percentages were also lower (MFI and/or percentage), while those of CD94⁺ and NKG2A⁺ NKT-like cells were higher (MFI and/or percentage) in chronic patients than in recovered subjects. IFN-γ and TNF-α expression on NKT-like cells was high in the chronic patients, while only IFN-γ expression on NK cells was high in the recovered individuals. Furthermore, percentage of perforin⁺NK cells was low in the chronic patients. Lower cytotoxic activity was observed in the chronic patients than in the controls. CD107a expression on NK and NKT-like cells post anti-CD94/anti-NKG2A blocking was comparable among the patients and controls. Upregulated inhibitory and downregulated activating NK receptor expressions on NK/NKT-like cells, lower perforin⁺ and CD107a⁺NK cells are likely responsible for inhibiting the NK and NKT-like cell function in the chronic stage of chikungunya. Therefore, deregulation of NKR expression might underlie CHIKV-induced chronicity.

Hepatitis C Virus and Human Cytomegalovirus-Natural Killer Cell Subsets in Persistent Viral Infections

Hepatitis C virus (HCV) and human cytomegalovirus (HCMV) are prominent examples of RNA and DNA viruses, respectively, that establish a persistent infection in their host. HCV affects over 185 million patients worldwide, who are at high risk for developing liver fibrosis, liver cirrhosis, and ultimately hepatocellular carcinoma. Recent breakthroughs in HCV therapy, using direct-acting antivirals have provided the opportunity to monitor natural killer (NK) cells after clearance of a chronic infection. There is now increasing evidence that the individual NK cell repertoire before infection is predictive for the course of disease. HCMV affects the majority of the global population. While being asymptomatic in healthy individuals, HCMV represents a severe clinical challenge in immunocompromised patients. Both viral infections, HCV and HCMV, lead to long-lasting and profound alterations within the entire NK cell compartment. This review article, will discuss the diverse range of changes in the NK cell compartment as well as potential consequences for the course of disease.

MELD and Child-Pugh Scores Are Related to Immune Status of Intrahepatic Natural Killer Cells in Liver Transplant Candidates

BACKGROUND

The role and phenotypic alterations of intrahepatic natural killer (NK) cells in liver disease were investigated. Although intrahepatic NK cells reportedly functionally deteriorate in the fibrotic liver, it remains unclear how the clinical severity of liver disease affects intrahepatic NK cells in patients with advanced liver failure.

METHODS

We analyzed the phenotypic properties of intrahepatic NK cells by using mononuclear cells extracted from ex vivo liver perfusate effluents from patients who underwent liver transplantation. The relationship between the clinical severity of liver disease and the phenotype of intrahepatic NK cells in these patients was also evaluated. To estimate the immunological responsiveness of intrahepatic NK cells, phenotypic enhancement after interleukin-2 stimulation was analyzed.

RESULTS

Intrahepatic NK cells from patients with advanced liver failure exhibited down-regulated monomodal expression of NKp46, a major activating molecule. Notably, the expression level of NKp46 decreased depending on the severity of liver disease, Model for End-Stage Liver Disease score, and Child-Pugh score rather than the etiology. After in vitro recombinant interleukin-2 stimulation, the enhancement of expression of cytotoxic molecules, NKp44, and tumor necrosis factor-related apoptosis-inducing ligand was significantly impaired in intrahepatic NK cells from patients with liver failure, concurrently with decreased expression of CD122 and interleukin-2 receptor beta.

CONCLUSIONS

Our results suggest that terminal deterioration of liver environments by chronic liver disease impairs the potential of local NK cells, depending on the severity of the deterioration. These influences of advanced liver failure on intrahepatic NK cells may be attributed to multicentric carcinogenesis in patients with liver failure.

Interferon Alpha Induces Sustained Changes in NK Cell Responsiveness to Hepatitis B Viral Load Suppression In Vivo

NK cells are important antiviral effectors, highly enriched in the liver, with the potential to regulate immunopathogenesis in persistent viral infections. Here we examined whether changes in the NK pool are induced when patients with eAg-positive CHB are 'primed' with PegIFNα and importantly, whether these changes are sustained or further modulated long-term after switching to nucleos(t)ides (sequential NUC therapy), an approach currently tested in the clinic. Longitudinal sampling of a prospectively recruited cohort of patients with eAg+CHB showed that the cumulative expansion of CD56bright NK cells driven by 48-weeks of PegIFNα was maintained at higher than baseline levels throughout the subsequent 9 months of sequential NUCs. Unexpectedly, PegIFNα-expanded NK cells showed further augmentation in their expression of the activating NK cell receptors NKp30 and NKp46 during sequential NUCs. The expansion in proliferating, functional NK cells was more pronounced following sequential NUCs than in comparison cohorts of patients treated with de novo NUCs or PegIFNα only. Reduction in circulating HBsAg concentrations, a key goal in the path towards functional cure of CHB, was only achieved in those patients with enhancement of NK cell IFNγ and cytotoxicity but decrease in their expression of the death ligand TRAIL. In summary, we conclude that PegIFNα priming can expand a population of functional NK cells with an altered responsiveness to subsequent antiviral suppression by NUCs. Patients on sequential NUCs with a distinct NK cell profile show a decline in HBsAg, providing mechanistic insights for the further optimisation of treatment strategies to achieve sustained responses in CHB.

Natural Killer p46 Controls Hepatitis B Virus Replication and Modulates Liver Inflammation

Natural killer (NK) cells play an important role in hepatitis B virus (HBV) infection control, and are regulated by a complex network of activating and inhibitory receptors. However, NK cell activity in HBV patients remains poorly understood. The objective of this study was to investigate the phenotypic and functional characteristics of circulating NK cells in patients during different chronic hepatitis B (CHB) infection stages. We investigated NK cell phenotypes, receptor expression and function in 86 CHB patients and 20 healthy controls. NK cells were purified and NK cell subsets were characterized by flow cytometry. Cytotoxic activity (CD107a) and interferon-gamma (IFN-γ) secretion were examined, and Natural Killer p46 (NKP46) blockade and spontaneous NK cell cytolytic activity against K562, HepG2 and HepG2.215 cell lines was studied. Activating NKp46 receptor expression was higher in inactive HBsAg carriers when compared with other groups (p = 0.008). NKp46 expression negatively correlated with HBV DNA (R = -0.253, p = 0.049) and ALT (R = -0.256, p = 0.045) levels. CD107a was higher in immune-activated groups when compared with immune-tolerant groups (p = 0.039). CD107a expression was related to viral load (p = 0.02) and HBeAg status (p = 0.024). In vitro NKp46 blockade reduced NK cell cytolytic activity against HepG2 and HepG2.215 cell lines (p = 0.02; p = 0.039). Furthermore, NK cells from high viral load CHB patients displayed significantly lower specific cytolytic activity against anti-NKp46-loaded K562 targets (p = 0.0321). No significant differences were observed in IFN-γ secretion (p > 0.05). In conclusion, NKp46 expression regulates NK cell cytolytic function. NKp46 may moderate NK cell activity during HBV replication suppression and HBV-associated liver damage and may be critical for NK cell activity during CHB infection.

Extracellular HCV-core protein induces an immature regulatory phenotype in NK cells: implications for outcome of acute infection

Background

Hepatitis C viral (HCV) proteins, including core, demonstrate immuno-modulatory properties; however, the effect of extracellular core on natural killer (NK) cells has not previously been investigated.

Aims

To characterise NKs in acute HCV infection over time, and, to examine the effect of exogenous HCV-core protein on NK cell phenotype and function.

Methods

Acute HCV patients (n = 22), including 10 subjects who spontaneously recovered, were prospectively studied. Flow-cytometry was used to measure natural cytotoxicity and to phenotype NKs directly ex vivo and after culture with HCV-core protein. Microarray analysis was used to identify pathways involved in the NK cell response to exogenous HCV-core.

Results

Direct ex vivo analysis demonstrated an increased frequency of immature/regulatory CD56^bright NKs early in acute HCV infection per se which normalized with viral clearance. Natural cytotoxicity was reduced and did not recover after viral clearance. There was a statistically significant correlation between the frequency of CD56^bright NKs and circulating serum levels of HCV core protein. In vitro culture of purified CD56^bright NK cells with HCV-core protein in the presence of IL-15 maintained a significant proportion of NKs in the CD56^bright state. The in vitro effect of core closely correlates with NK characteristics measured directly ex vivo in acute HCV infection. Pathway analysis suggests that HCV-core protein attenuates NK interferon type I responses.

Conclusions

Our data suggest that HCV-core protein alters NK cell maturation and may influence the outcome of acute infection.

Emerging concepts in immunity to hepatitis C virus infection

Since the discovery of hepatitis C virus (HCV) by molecular cloning almost a quarter of a century ago, unprecedented at the time because the virus had never been grown in cell culture or detected serologically, there have been impressive strides in many facets of our understanding of the natural history of the disease, the viral life cycle, the pathogenesis, and antiviral therapy. It is apparent that the virus has developed multiple strategies to evade immune surveillance and eradication. This Review covers what we currently understand of the temporal and spatial immunological changes within the human innate and adaptive host immune responses that ultimately determine the outcomes of HCV infection.

Natural killer cells: multifaceted players with key roles in hepatitis C immunity

Natural killer cells (NKs) are involved in every stage of hepatitis C viral (HCV) infection, from protection against HCV acquisition and resolution in the acute phase to treatment-induced clearance. In addition to their direct antiviral actions, NKs are involved in the induction and priming of appropriate downstream T-cell responses. In the setting of chronic HCV, overall NK cell levels are decreased, subset distribution is altered, and changes in NK receptor (NKR) expression have been demonstrated, although the contribution of individual NKRs to viral clearance or persistence remains to be clarified. Enhanced NK cell cytotoxicity accompanied by insufficient interferon-γ production may promote liver damage in the setting of chronic infection. Treatment-induced clearance is associated with activation of NK cells, and it will be of interest to monitor NK cell responses to triple therapy. Activated NK cells also have anti-fibrotic properties, and the same hepatic NK cell populations that are actively involved in control of HCV may also be involved in control of HCV-associated liver damage. We still have much to learn, in particular: how do liver-derived NKs influence the outcome of HCV infection? Do NK receptors recognize HCV-specific components? And, are HCV-specific memory NK populations generated?

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.

Natural killer cells are characterized by the concomitantly increased interferon-γ and cytotoxicity in acute resolved hepatitis B patients

Natural killer (NK) cells are abundant in the liver and have been implicated in inducing hepatocellular damage in patients with chronic hepatitis B virus (HBV) infection. However, the role of NK cells in acute HBV infection remains to be elucidated. We comprehensively characterized NK cells and investigated their roles in HBV clearance and liver pathology in 19 chronic hepatitis B (CHB) patients and 21 acute hepatitis B (AHB) patients as well as 16 healthy subjects. It was found that NKp46⁺ NK cells were enriched in the livers of AHB and CHB patients. We further found that peripheral NK cells from AHB patients expressed higher levels of activation receptors and lower levels of inhibitory receptors than those from CHB patients and HC subjects, thus displaying the increased cytolytic activity and interferon-γ production. NK cell activation levels were also correlated positively with serum alanine aminotransferase levels and negatively with plasma HBV DNA levels in AHB patients, which is further confirmed by the longitudinal follow-up of AHB patients. Serum pro-inflammatory cytokine and chemokine levels were also increased in AHB patients as compared with CHB and HC subjects. Thus, the concomitantly increased interferon-γ and cytotoxicity of NK cells were associated with liver injury and viral clearance in AHB patients.