Fine characterization of intrahepatic NK cells expressing natural killer receptors in chronic hepatitis B and C

Peripheral NK cell phenotypic alteration and dysfunctional state post hepatitis B subviral particles stimulation in CHB patients: evading immune surveillance

Background

The relationship between chronic hepatitis B (CHB) infection and natural killer (NK) cell dysfunction is well-established, but the specific role of HBV viral antigens in driving NK cell impairment in patients with CHB remains unclear. This study investigates the modulatory effects of hepatitis B virus subviral particles (HBVsvp, a representative model for HBsAg) on the phenotypic regulation (activating and inhibitory receptors), cytokine production and cytotoxic potential of peripheral blood mononuclear cell-derived natural killer cells (PBMCs-derived NK cell), which contributes to NK cell dysfunction in CHB infection, potentially serving as an effective HBV immune evasion strategy by the virus.

Methods

NK cells were isolated from peripheral blood of patients with CHB (n=5) and healthy individuals (n=5), stimulated with HBVsvp. Subsequent flow cytometric characterization involved assessing changes in activating (NKp46 and NKG2D) and inhibitory (CD94) receptors expression, quantifying TNF-α and IFN- γ cytokine secretion, and evaluating the cytotoxic response against HepG2.2.15 cells with subsequent HBVsvp quantification.

Results

In CHB patients, in vitro exposure of PBMCs-derived NK cell with HBVsvp (represent HBsAg model) significantly reduced NK cell-activating receptors expression (P = 0.022), increased expression of CD94 + NK cells (p = 0.029), accompanied with a reduced TNF-α - IFN-γ cytokine levels, and impaired cytotoxic capacity (evidenced by increased cell proliferation and elevated HBVsvp levels in co-cultures with HepG2.2.15 cells in a time-dependent), relative to healthy donors.

Conclusion

These findings suggest that HBVsvp may induce dysfunctional NK cell responses characterized by phenotypic imbalance with subsequent reduction in cytokine and cytotoxic levels, indicating HBVsvp immunosuppressive effect that compromises antiviral defense in CHB patients. These data enhance our understanding of NK cell interactions with HBsAg and highlight the potential for targeting CD94 inhibitory receptors to restore NK cell function as an immunotherapeutic approach. Further clinical research is needed to validate these observations and establish their utility as reliable biomarkers.

Lower NKG2D expression in hepatic natural killer cells predicts poorer prognosis for chronic hepatitis B patients with cirrhosis

OBJECTIVE

Natural killer cells (NK) acts a central player of the immune system in liver cirrhosis. The aim of this study was to examine the expression of activating intra-hepatic NK cell group 2D (NKG2D) in patients with chronic hepatitis B (CHB) and analyzed the correlation between NKG2D expression and prognosis of liver cirrhosis in these patients.

METHODS

This was a cross-section study. Subjects with liver biopsy or sponge hemangioma surgery were included. The primary outcome was the NKG2D expression on intra-hepatic NK cells and their subtype cells in patients with CHB-related liver cirrhosis. Subsequently, the correlation of expression of NKG2D and clinical characteristic indicators were assayed RESULTS: Among 38 subjects, 11 (28.95%) normal liver sections adjacent the sponge hemangioma (healthy group) were collected during surgery, and 27 (71.05%) CHB-cirrhosis tissues (Cirrhosis group) were preserved after liver biopsy. Compared with healthy group, sections from cirrhosis group revealed more severe inflammation and collagen deposition and lower NKG2D expression in hepatic NK cells. The proportion of hepatic NK cells and the mean fluorescence intensity (MFI) of NKG2D on hepatic NK cells showed a positive correlation with serum albumin (Alb) level, platelet (Plt) count. Moreover, they had a significantly negative correlation with patient prothrombin time (PT), international standardized ratio (INR), the sirius red positive stained area and fibrosis stages.

CONCLUSIONS

Lower NKG2D expression in intra-hepatic NK cells may be predictive of poorer prognosis of CHB patients with cirrhosis.

Current and Future States of Natural Killer Cell-Based Immunotherapy in Hepatocellular Carcinoma

Natural killer (NK) cells are innate lymphoid cells that exhibit high levels of cytotoxicity against NK-specific targets. NK cells also produce various cytokines, and interact with T cells, B cells, and dendritic cells to effectively serve as frontliners of the innate immune system. Produce various cytokines, and interact with T cells, B cells, and dendritic cells to effectively serve as frontliners of the innate immune system. Moreover, NK cells constitute the second most common immune cell in the liver. These properties have drawn significant attention towards leveraging NK cells in treating liver cancer, especially hepatocellular carcinoma (HCC), which accounts for 75% of all primary liver cancer and is the fourth leading cause of cancer-related death worldwide. Notable anti-cancer functions of NK cells against HCC include activating antibody-dependent cell cytotoxicity (ADCC), facilitating Gasdermin E-mediated pyroptosis of HCC cells, and initiating an antitumor response via the cGAS-STING signaling pathway. In this review, we describe how these mechanisms work in the context of HCC. We will then discuss the existing preclinical and clinical studies that leverage NK cell activity to create single and combined immunotherapies.

The Role of Inflammation in Cholestatic Liver Injury

Cholestasis is a common clinical event in which bile formation and excretion are blocked, leading to retention of bile acids or bile salts; whether it occurs intra- or extrahepatically, primary or secondary, its pathogenesis is still unclear and is influenced by a combination of factors. In a variety of inflammatory and immune cells such as neutrophils, macrophages (intrahepatic macrophages are also known as Kupffer cells), mast cells, NK cells, and even T cells in humoral immunity and B cells in cellular immunity, inflammation can be a "second strike" against cholestatic liver injury. These cells, stimulated by a variety of factors such as bile acids, inflammatory chemokines, and complement, can be activated and accumulate in the cholestatic liver, and with the involvement of inflammatory mediators and modulation by cytokines, can lead to destruction of hepatocytes and bile duct epithelial cells and exacerbate (and occasionally retard) the progression of cholestatic liver disease. In this paper, we summarized the new research advances proposed so far regarding the relationship between inflammation and cholestasis, aiming to provide reference for researchers and clinicians in the field of cholestatic liver injury research.

Association of NK Cells with the Severity of Fibrosis in Patients with Chronic Hepatitis C

Some NK cell subpopulations may be involved in the modulation of fibrogenesis in the liver. The aim of the study was to evaluate the relationship between the number and phenotype of NK cell subsets in peripheral blood (PB) and total NK cell percentage, population density and the degree of liver fibrosis of patients infected with hepatitis C virus (HCV+). The study group consisted of 56 HCV+ patients, divided into two subgroups: patients with mild or moderate fibrosis and patients with advanced liver fibrosis or cirrhosis (F ≥ 3 in METAVIR classification). The preparations were stained with H-E and AZAN staining. NK cells were targeted with anti-CD56 antibody and identified automatically in situ using the DakoVision system. Assessment of different NK cell subsets in PB was performed with the flow cytometry technique. In the PB of HCV+ patients with advanced liver fibrosis, there was a lower proportion of CD62L+; CD62L+/CD94++; CD27+; CD127+/CD27+ and CXCR3+/CD27+ NK subsets, as compared to patients with mild/moderate liver fibrosis. The results also showed no association between total PB NK cell level and total intrahepatic NK cell population density between patients with mild/moderate fibrosis and with advanced liver fibrosis. However, positive correlations between the PB levels of CD94+ and CD62L+ NK cell subsets and the intrahepatic total NK cell percentage and population density in the liver, irrespectively to the extent of fibrosis, were observed. Additionally, positive correlation was found between the PB CXCR3+/CD94+ NK cell percentages and intrahepatic NK cell percentages in patients with advanced hepatic fibrosis. Lower blood availability of specific NK subsets in patients with chronic type C hepatitis might be a cause of progression of liver fibrosis via insufficient control over hepatic stellate cells.

Prospects for NK-based immunotherapy of chronic HBV infection

Effective and long-term treatment is required for controlling chronic Hepatitis B Virus (HBV) infection. Natural killer (NK) cells are antiviral innate lymphocytes and represent an essential arm of current immunotherapy. In chronic HBV (CHB), NK cells display altered changes in phenotypes and functions, but preserve antiviral activity, especially for cytolytic activity. On the other hand, NK cells might also cause liver injury in the disease. NK -based immunotherapy, including adoptive NK cell therapy and NK -based checkpoint inhibition, could potentially exploit the antiviral aspect of NK cells for controlling CHB infection while preventing liver tissue damage. Here, we review recent progress in NK cell biology under the context of CHB infection, and discuss potential NK -based immunotherapy strategies for the disease.

Effect of Antiviral Therapy During Pregnancy on Natural Killer Cells in Pregnant Women With Chronic HBV Infection

Objective

To study the effect of antiviral therapy during pregnancy on the frequency of natural killer (NK) cells in peripheral blood of women with HBV DNA positive chronic hepatitis B (CHB).

Method

In total 124 female subjects were divided into four groups: 11 healthy non-pregnant women (Normal group), 26 non-pregnant women in immune tolerance period of chronic hepatitis B virus (HBV) infection (CHB group), 41 pregnant CHB women without antiviral treatment during pregnancy (Untreated group), and 46 pregnant CHB women receiving antiviral treatment during pregnancy (Treated group). The frequency of NK cells in peripheral blood were detected by flow cytometry.

Result

The frequency of NK cells in healthy women [15.30 (12.80, 18.40)] was higher than that in women with HBV infection, but there was no significant statistical difference (p=0.436). The frequency of NK cells in CHB group [10.60 (6.00, 18.30)] was higher than those in pregnant CHB women [Untreated: 6.90 (4.89, 10.04), P=0.001; Treated: 9.42 (6.55, 14.10), P=0.047]. The frequency of NK cells in treated group was significantly higher than that in untreated group (P = 0.019). The frequencies of NK cells, CD56^bright NK cells and NKp46^dim NK cells at 12 and 24 weeks postpartum in the untreated group were increased significantly than those before delivery. In treated group, the frequencies of NK cells, CD56^bright NK cells, NKp46⁺ NK cells and NKp46^dim NK cells were significantly increased at 6 and 12 weeks than those before delivery. The frequencies of NK cells and CD56^bright NK cells postpartum were increased significantly in treated group than those in untreated group. The frequencies of CD56^dim NK cells decreased significantly after delivery in treated than those in untreated patients. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) significantly increased after delivery than those before delivery. The results showed that the postpartum ALT level was weak positive correlated with NKp46^high frequency (r=0.199) and was weak negative correlated with NKp46^dim frequency (r= -0.199).

Conclusion

Antiviral treatment during pregnancy could significantly increase the frequency of NK cells postpartum. Postpartum hepatitis may be related to the immune injury caused by change of NK cell frequency and HBV infection.

Chronic Hepatitis C Pathogenesis: Immune Response in the Liver Microenvironment and Peripheral Compartment

Chronic hepatitis C (CHC) pathogenic mechanisms as well as the participation of the immune response in the generation of liver damage are still a topic of interest. Here, we evaluated immune cell populations and cytokines in the liver and peripheral blood (PB) to elucidate their role in CHC pathogenesis. B, CTL, Th, Treg, Th1, Th17, and NK cell localization and frequency were evaluated on liver biopsies by immunohistochemistry, while frequency, differentiation, and functional status on PB were evaluated by flow cytometry. TNF-α, IL-23, IFN-γ, IL-1β, IL-6, IL-8, IL-17A, IL-21, IL-10, and TGF-β expression levels were quantified in fresh liver biopsy by RT-qPCR and in plasma by CBA/ELISA. Liver CTL and Th1 at the lobular area inversely correlated with viral load (r = −0.469, p =0.003 and r = −0.384, p = 0.040). Treg correlated with CTL and Th1 at the lobular area (r = 0.784, p < 0.0001; r = 0.436, p = 0.013). Th17 correlated with hepatic IL-8 (r = 0.52, p < 0.05), and both were higher in advanced fibrosis cases (Th17 p = 0.0312, IL-8 p = 0.009). Hepatic cytokines were higher in severe hepatitis cases (IL-1β p = 0.026, IL-23 p = 0.031, IL-8 p = 0.002, TGF-β, p= 0.037). Peripheral NK (p = 0.008) and NK dim (p = 0.018) were diminished, while NK bright (p = 0.025) was elevated in patients vs. donors. Naïve Th (p = 0.011) and CTL (p = 0.0007) were decreased, while activated Th (p = 0.0007) and CTL (p = 0.0003) were increased. IFN-γ production and degranulation activity in NK and CTL were normal. Peripheral cytokines showed an altered profile vs. donors, particularly elevated IL-6 (p = 0.008) and TGF-β (p = 0.041). Total hepatic CTLs favored damage. Treg could not prevent fibrogenesis triggered by Th17 and IL-8. Peripheral T-lymphocyte differentiation stage shift, elevated cytokine levels and NK-cell count decrease would contribute to global disease.

Human Hepatitis B Virus Negatively Impacts the Protective Immune Crosstalk Between Natural Killer and Dendritic Cells

BACKGROUND AND AIMS

Natural killer (NK) cells play a crucial role in the clearance of human viruses but their activity is significantly impaired in patients infected with chronic hepatitis B (CHB). Cooperation with dendritic cells (DCs) is pivotal for obtaining optimal NK cell antiviral function; thus, we investigated whether HBV might impact the ability of DCs to sustain NK cell functions.

APPROACH AND RESULTS

Human DCs were poor stimulators of interferon-gamma (IFN-γ) production by NK cells when exposed to HBV, while maintaining the capability to trigger NK cell cytotoxicity. HBV prevented DC maturation but did not affect their expression of human leukocyte antigen class I, thus allowing DCs to evade NK cell lysis. Tolerogenic features of DCs exposed to HBV were further supported by their increased expression of IL-10 and the immunosuppressive enzyme indoleamine 2,3-dioxygenase, which contributed to the impairment of DC-mediated NK cell IFN-γ production and proliferation, respectively. HBV could also inhibit the expression of inducible immunoproteasome (iP) subunits on DCs. In fact, NK cells could induce iP subunit expression on DCs, but they failed in the presence of HBV. Remarkably, circulating blood DC antigen1 (BDCA1)⁺ DCs isolated from patients with CHB were functionally compromised, hence altering, in turn, NK cell responses.

CONCLUSIONS

The abnormal NK-DC interplay caused by HBV may significantly impair the efficacy of antiviral immune response in patients with CHB.

Natural killer cells play an important role in virus infection control: Antiviral mechanism, subset expansion and clinical application

With the global spread of coronavirus disease 2019 (COVID-19), the important role of natural killer (NK) cells in the control of various viral infections attracted more interest, via non-specific activation, such as antibody-dependent cell-mediated cytotoxicity (ADCC) and activating receptors, as well as specific activation, such as memory-like NK generation. In response to different viral infections, NK cells fight viruses in different ways, and different NK subsets proliferate. For instance, cytomegalovirus (CMV) induces NKG2C + CD57 + KIR+ NK cells to expand 3-6 months after hematopoietic stem cell transplantation (HSCT), but human immunodeficiency virus (HIV) induces KIR3DS1+/KIR3DL1 NK cells to expand in the acute phase of infection. However, the similarities and differences among these processes and their molecular mechanisms have not been fully discussed. In this article, we provide a summary and comparison of antiviral mechanisms, unique subset expansion and time periods in peripheral blood and tissues under different conditions of CMV, HIV, Epstein-Barr virus (EBV), COVID-19 and hepatitis B virus (HBV) infections. Accordingly, we also discuss current clinical NK-associated antiviral applications, including cell therapy and NK-related biological agents, and we state the progress and future prospects of NK cell antiviral treatment.

Innate lymphocytes: pathogenesis and therapeutic targets of liver diseases and cancer

The liver is a lymphoid organ with unique immunological properties, particularly, its predominant innate immune system. The balance between immune tolerance and immune activity is critical to liver physiological functions and is responsible for the sensitivity of this organ to numerous diseases, including hepatotropic virus infection, alcoholic liver disease, nonalcoholic fatty liver disease, autoimmune liver disease, and liver cancer, which are major health problems globally. In the past decade, with the discovery of liver-resident natural killer cells, the importance of innate lymphocytes with tissue residency has gradually become the focus of research. In this review, we address the current knowledge regarding hepatic innate lymphocytes with unique characteristics, including NK cells, ILC1/2/3s, NKT cells, γδ T cells, and MAIT cells, and their potential roles in liver homeostasis maintenance and the progression of liver diseases and cancer. A better understanding of the immunopathogenesis of hepatic innate lymphocytes will be helpful for proposing effective treatments for liver diseases and cancer.

Control of HCV Infection by Natural Killer Cells and Macrophages

Host defense against invading pathogens within the liver is dominated by innate immunity. Natural killer (NK) cells have been implicated at all stages of hepatitis C virus (HCV) infection, from providing innate protection to contributing to treatment-induced clearance. Decreased NK cell levels, altered NK cell subset distribution, activation marker expression, and functional polarization toward a cytolytic phenotype are hallmarks of chronic HCV infection. Interferon α (IFN-α) is a potent activator of NK cells; therefore, it is not surprising that NK cell activation has been identified as a key factor associated with sustained virological response (SVR) to IFN-α-based therapies. Understanding the role of NK cells, macrophages, and other innate immune cells post-SVR remains paramount for prevention of disease pathogenesis and progression. Novel strategies to treat liver disease may be aimed at targeting these cells.

Cirrhosis Hampers Early and Rapid Normalization of Natural Killer Cell Phenotype and Function in Hepatitis C Patients Undergoing Interferon-Free Therapy

Background: Chronic hepatitis C virus (HCV) infection impairs natural killer (NK) cell phenotype and function. Whether restoration of NK cells occurs after successful interferon (IFN)-free therapies remains a controversial issue. Aim: To analyze how HCV-related liver cirrhosis impacts changes in NK cells prior and post-IFN-free therapies. Methods: NK cell analysis by multicolor flow cytometry was performed in HCV-infected patients with (n = 17) and without (n = 14) cirrhosis at baseline, week 4 during therapy, and weeks 12 and 48 after the end of therapy (FU12 and FU48, respectively). Non-HCV cirrhotic patients (n = 12) and healthy individuals (n = 12) served as controls. Results: At baseline, HCV cirrhotic patients presented an altered distribution of NK subsets (CD56dim and CD56bright) with higher expression of NKp46, HLA-DR, NKp30, KIR2DL2/L3, NKG2A, and CD85j receptors compared to healthy controls. All frequencies normalized by FU48, except for CD85j+ cells. Likewise, substantial alterations were detected in NK cell function assessed by (i) signal transducer and activator of transcription 1 (STAT1) and phosphorylated levels of STAT1 and STAT4, (ii) degranulation (CD107a), (iii) cytotoxicity [tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)], and (iv) cytokine production [IFN-γ and tumor necrosis factor-α (TNF-α)]. Of note, NK cell function at FU48 remained partially impaired. In contrast, non-cirrhotics showed normal baseline frequencies of HLA-DR-, NKG2A-, and CD85j-expressing NK cells. Importantly, altered baseline frequencies of NK cell subsets and NKp46+ CD56dim cells, as well as NK cell function, were rapidly and completely restored. Conclusions: NK cell phenotype alterations persist after HCV eradication in cirrhotic patients, while their function is only partially restored, compromising immune restoration and immunosurveillance.

NK Cell Metabolism and TGFβ - Implications for Immunotherapy

NK cells are innate lymphocytes which play an essential role in protection against cancer and viral infection. Their functions are dictated by many factors including the receptors they express, cytokines they respond to and changes in the external environment. These cell processes are regulated within NK cells at many levels including genetic, epigenetic and expression (RNA and protein) levels. The last decade has revealed cellular metabolism as another level of immune regulation. Specific immune cells adopt metabolic configurations that support their functions, and this is a dynamic process with cells undergoing metabolic reprogramming during the course of an immune response. Upon activation with pro-inflammatory cytokines, NK cells upregulate both glycolysis and oxphos metabolic pathways and this supports their anti-cancer functions. Perturbation of these pathways inhibits NK cell effector functions. Anti-inflammatory cytokines such as TGFβ can inhibit metabolic changes and reduce functional outputs. Although a lot remains to be learned, our knowledge of potential molecular mechanisms involved is growing quickly. This review will discuss our current knowledge on the role of TGFβ in regulating NK cell metabolism and will draw on a wider knowledge base regarding TGFβ regulation of cellular metabolic pathways, in order to highlight potential ways in which TGFβ might be targeted to contribute to the exciting progress that is being made in terms of adoptive NK cell therapies for cancer.

Observed Changes in Natural Killer and T cell Phenotypes with Evaluation of Immune Outcome in a Longitudinal Cohort Following Sofosbuvir-Based Therapy for Chronic Hepatitis C Infection

Background

Chronic hepatitis C virus (HCV) infection diminishes immune function through cell exhaustion and repertoire alteration. Direct acting antiviral (DAA)-based therapy can restore immune cell subset function and reduce exhaustion states. However, the extent of immune modulation following DAA-based therapy and the role that clinical and demographic factors play remain unknown.

Methods

We examined natural killer (NK) cell, CD4⁺, and CD8⁺ T cell subsets along with activation and exhaustion phenotypes across an observational study of sofosbuvir-based treatment for chronic HCV infection. Additionally, we examined the ability of clinical variables and duration of infection to predict 12 weeks of sustained virologic response (SVR12) immune marker outcomes.

Results

We show that sofosbuvir-based therapy restores NK cell subset distributions and reduces chronic activation by SVR12. Likewise, T cell subsets, including HCV-specific CD8⁺ T cells, show reductions in chronic exhaustion markers by SVR12. Immunosuppressive CD4⁺ regulatory T cells decrease at 4-weeks treatment and SVR12. We observe the magnitude and direction of change in immune marker values from pretreatment to SVR12 varies greatly among participants. Although we observed associations between the estimated date of infection, HCV diagnosis date, and extent of immune marker outcome at SVR12, our regression analyses did not indicate any factors as strong SVR12 outcome predictors.

Conclusion

Our study lends further evidence of immune changes following sofosbuvir-based therapy. Further investigation beyond SVR12 and into factors that may predict posttreatment outcome is warranted.

The Influence of Hepatitis C Viral Loads on Natural Killer Cell Function

Background

Hepatitis C virus (HCV) infection has a high rate of chronicity, attributable to its capacity to alter host immunity, including natural killer (NK) cell function. In this study, the interaction between NK cell activity and HCV viral load was investigated.

Methods

Peripheral blood NK cells were examined for cytotoxicity and interferon (IFN)-γ expression in HCV infected low (LVL, < 800,000 IU/mL, n = 10) and high (HVL, > 800,000 IU/mL, n = 13) viral load patient cohorts.

Results

Spontaneous NK cell cytotoxicity was more robust in the LVL cohort resulting in a negative correlation with viral loads (spontaneous, r = -0.437, P = 0.037; IFN-α activated, r = -0.372, P = 0.081). Although the percent of IFN-γ+ NK cells did not associate with viral load, within the LVL cohort there was a marked increase in IFN-γ+ NK cells upon IFN-α activation relative to medium alone (P < 0.01). To examine the inability of NK cells derived from HVL patients to be further activated, the expression of the exhaustion marker programmed cell death protein (PD)-1 was evaluated. PD-1 expression upon NK cell activation correlated with viral load (r = 0.649, P = 0.009). In addition, HCV proteins upregulated PD-1 expression in vitro (P < 0.05), suggesting that HCV can directly promote NK cell exhaustion. Cells from HVL patients were also more likely to produce IFN-γ in response to HCV core protein. The finding that NK cell PD-1 and IFN-γ expression are linked (r = 0.542, P < 0.05) suggests that increased IFN-γ levels may induce PD-1 as a negative feedback mechanism.

Conclusions

High HCV loads appear to promote NK exhaustion in chronic HCV infection.

Peripheral lymphocytes analyses in children with chronic hepatitis C virus infection

BACKGROUND

Hepatitis C virus (HCV)-specific immune response is believed to play a crucial role in viral clearance. There is, nevertheless, no reliable parameter to monitor this immune response or predict chronic HCV infection development.

METHOD

An observational case-control study was performed to identify such parameters, peripheral blood mononuclear cells from 57 children with chronic HCV were systemically phenotyped, and the serum level of Interferon gamma and interleukin (IL) -17 was measured. The data were compared with 37 age-matched healthy volunteers (controls).

RESULTS

Children with chronic HCV infection had a lower frequency of natural killer cells (NK) cells, CD56Dim NK cells and expansion of CD56Bright NK cells compared with controls (P = 0.001, P < 0.0001 and P < 0.0001 respectively). Increased CD56Dim NK cells were negatively correlated with the higher viral load, R²  = 0.29, P = 0.05, while, increased NK T cells were positively correlated with high viral load, R²  = 0.17, P = 0.011. T helper cells, naive T cells, CD127 negative T cells, and HLA-DR-positive T cells significantly increased in patients than in controls. The frequency of CD4+CD25high+ T regulatory (Treg) cells increased in HCV-infected patients, compared with those in control, and FOXP3 was upregulated within them. Treg cells' increase was positively correlated with high viral load, R²  = 0.45, P = 0.004. The level of IL-17 was higher in HCV patients than that in control, P < 0.0001.

CONCLUSION

Although the contribution of those markers to the chronic HCV establishment in children remains elusive, the results may provide important clues for reliable indicators of HCV infection.

Natural Killer Cells in Liver Disease and Hepatocellular Carcinoma and the NK Cell-Based Immunotherapy

Nature killer (NK) cells play a critical role in host innate and adaptive immune defense against viral infections and tumors. NK cells are enriched in liver hematopoietic cells with unique NK repertories and functions to safeguard liver cells against hepatitis virus infection or malignancy transformation. However, accumulating evidences were found that the NK cells were modulated by liver diseases and liver cancers including hepatocellular carcinoma (HCC) and showed impaired functions failing to activate the elimination of the viral-infected cells or tumor cells and were further involved in the pathogenesis of liver injury and inflammation. The full characterization of circulation and intrahepatic NK cell phenotype and function in liver disease and liver cancer has not only provided new insight into the disease pathogenesis but has also discovered new targets for developing new NK cell-based therapeutic strategies. This review will discuss and summarize the NK cell phenotypic and functional changes in liver disease and HCC, and the NK cell-based immunotherapy approaches and progresses for cancers including HCC will also be reviewed.

Immune function of plasmacytoid dendritic cells, natural killer cells, and their crosstalk in HBV infection

Chronic hepatitis B virus infection is a major health problem, with over 245 million chronic carriers worldwide. This persistent infection is thought to be associated with inefficient innate and adaptive immune responses. Natural killer cells (NK cells) and plasmacytoid dendritic cells (pDCs) are the major innate immune cells which respond to viral infection at the early phase and are considered major components of the antiviral immune response. In this review, we summarize recent findings regarding the role of NK cells, pDCs, and their cross-talk in HBV infection and its chronicity. Although the data regarding the biological function of pDCs and NK cells in HBV infection is still controversial, many studies show that in chronic HBV infection, the cytotoxicity of NK cells is retained, while their capacity to secrete cytokines is strongly impaired. In addition, interferon-α production by pDCs is impaired during chronic HBV infection, and the virus interferes with pDC-NK cell interaction.

Hepatic irradiation persistently eliminates liver resident NK cells

Hepatic irradiation for the treatment of hepatobiliary malignancies often indirectly damages liver tissue and promotes the development of liver fibrosis. However, little is known concerning the effects of hepatic irradiation on the liver immune system, including natural killer (NK) cells. The aim of this study was therefore to investigate how hepatic irradiation influences the functions and characteristics of liver resident NK cells. An established murine hepatic irradiation model was used to examine the specific effects of hepatic irradiation on immune cell populations and metastasis. This analysis demonstrated that hepatic irradiation decreased the number of liver resident NK cells (DX5^–TRAIL⁺), but did not affect the total NK number or proportions of NK cells in the liver or spleen. This effect was correlated with the hepatic irradiation dose. Surprisingly, the liver resident NK population had not recovered by two months after hepatic irradiation. We also found that hepatic irradiation limited the cytotoxic effects of liver-derived lymphocytes against a mouse hepatoma cell line and promoted hepatic metastases in an in vivo model, although adoptive transfer of activated NK cells could alleviate metastatic growth. Finally, we demonstrated that hepatic irradiation disrupted the development of liver-resident NK cells, even after the adoptive transfer of precursor cells from the bone marrow, liver, and spleen, suggesting that irradiation had altered the developmental environment of the liver. In summary, our data demonstrated that hepatic irradiation abolished the DX5^–TRAIL⁺ liver-resident NK cell population and dampened antitumor activities in the liver for at least two months. Additionally, hepatic irradiation prevented differentiation of precursor cells into liver-resident NK cells.

Liver sampling: a vital window into HBV pathogenesis on the path to functional cure

In order to optimally refine the multiple emerging drug targets for hepatitis B virus (HBV), it is vital to evaluate virological and immunological changes at the site of infection. Traditionally liver biopsy has been the mainstay of HBV disease assessment, but with the emergence of non-invasive markers of liver fibrosis, there has been a move away from tissue sampling. Here we argue that liver biopsy remains an important tool, not only for the clinical assessment of HBV but also for research progress and evaluation of novel agents. The importance of liver sampling has been underscored by recent findings of specialised subsets of tissue-resident immune subsets capable of efficient pathogen surveillance, compartmentalised in the liver and not sampled in the blood. Importantly, the assessment of virological parameters, such as cccDNA quantitation, also requires access to liver tissue. We discuss strategies to maximise information obtained from the site of infection and disease pathology. Fine needle aspirates of the liver may allow longitudinal sampling of the local virus/host landscape. The careful utilisation of liver tissue and aspirates in conjunction with blood will provide critical information in the assessment of new therapeutics for the functional cure of HBV.

Early and late changes in natural killer cells in response to ledipasvir/sofosbuvir treatment

Chronic hepatitis C virus (HCV) infection is characterized by dysregulated natural killer (NK) cell responses. NKs play a critical role in achieving sustained responses to interferon (IFN)‐α‐based therapy. Rapid sustained HCV‐RNA clearance is now achieved with direct‐acting antivirals (DAAs). Studies of patients receiving first‐wave DAAs suggest NK functional restoration. Here, we investigate the effect of mainstream DAA treatment on NKs. We collected a prospective cohort of male HCV genotype 1‐infected patients treated with ledipasvir/sofosbuvir (n = 22). Peripheral blood was obtained at treatment start, week 2 (W2), W4, W8, and W12 of treatment and 12 weeks posttreatment. Flow cytometry was used to characterize NK responses to therapy. Mean baseline viral load was 1.75 million IU/mL. All subjects rapidly cleared virus and remained HCV RNA‐negative posttreatment. No change was seen in total NK levels; however, the frequency of immature NKs (clusters of differentiation [CD]56^bright) decreased by W2 and was maintained throughout the study. Phenotypic changes were evident by W2/W4, coincident with rapid viral clearance. At W2, T‐cell immunoglobulin and mucin‐domain containing‐3 and CD161 were significantly increased, returning to pretreatment levels by W12. Some changes were not evident until late (W12 or posttreatment). Down‐regulation of several activation markers, including NKp30 and tumor necrosis factor–related apoptosis‐inducing ligand, was observed at W12 and sustained posttreatment. No difference was observed in IFN‐γ production or cytokine‐mediated killing of NK‐sensitive cell line K562 posttreatment compared to pretreatment. Conclusion: Our phenotype data suggest transient activation followed by dampening of NK cell activity to pretreatment levels. The NK response to ledipasvir/sofosbuvir is not universal in a homogeneous patient cohort. More studies are needed to elucidate the roles of NK cells in IFN‐free regimens, which will have implications for protection from re‐infection and fibrosis progression. (Hepatology Communications 2018;2:364‐375)

Interferon-α-Enhanced CD100/Plexin-B1/B2 Interactions Promote Natural Killer Cell Functions in Patients with Chronic Hepatitis C Virus Infection

Background

CD100, also known as Sema4D, is an immune semaphorin constitutively expressed on natural killer (NK) cells and T cells. As an immune activation molecule, CD100 has important immunoregulatory effects on NK functions by enhancing the interactions between NK cells and target cells. The aim of this study was to investigate whether hepatitis C virus (HCV) infection affects CD100 expression, and whether interferon-α treatment enhances NK killing activity to facilitate HCV clearance via CD100.

Methods

Expression of CD100 on NK cells was evaluated by flow cytometry in patients with chronic HCV infection, with or without pegylated interferon-α-based therapy. NK cell cytotoxicity and interferon (IFN)-γ production were measured by flow cytometry upon culturing the NK cells with K562 and Huh7.5 or HCV JFH-1-infected Huh7.5 cells.

Results

The frequency of CD100⁺ NK cells in HCV-infected individuals was slightly suppressed compared to healthy subjects. IFN-α treatment could significantly upregulate CD100 expression, which was confirmed by in vitro studies using peripheral blood mononuclear cells cocultured with HCV-expressing Huh7.5 cells or IFN-α. Importantly, the expression of CD100 on NK cells from HCV patients was inversely associated with the HCV-RNA levels in the early phase of IFN-α therapy, and the IFN-α upregulated CD100 led to an enhanced NK killing activity through ligations with its receptors plexin-B1/B2 on target cells.

Conclusion

These results implied a novel mechanism by which IFN-α enhanced CD100/Plexin-B1/B2 interaction plays an important role in promoting NK functions in patients with chronic hepatitis C.

NK cells in self-limited HCV infection exhibit a more extensively differentiated, but not memory-like, repertoire

Natural killer (NK) cells have long been thought of as a purely innate immune cell population, but increasing reports have described developmental and functional qualities of NK cells that are commonly associated with cells of the adaptive immune system. Of these features, the ability of NK cells to acquire functional qualities associated with immunological memory and continuous differentiation resulting in the formation of specific NK cell repertoires has recently been highlighted in viral infection settings. By making use of a unique cohort of monitored, at-risk intravenous drug users in this study, we were able to dissect the phenotypic and functional parameters associated with NK cell differentiation and NK cell memory in patients 3 years after acute HCV infection and either the subsequent self-clearance or progression to chronicity. We observed increased expression of cytolytic mediators and markers CD56^bright and NKp46⁺ of NK cells in patients with chronic, but not self-limited HCV infection. Patients with a self-limited infection expressed higher levels of differentiation-associated markers CD57 and KIRs, and lower levels of NKG2A. A more extensively differentiated NK cell phenotype is associated with self-clearance in HCV patients, while the NK cells of chronic patients exhibited more naïve and effector NK cell phenotypic and functional characteristics. The identification of these distinct NK cell repertoires may shed light on the role NK cells play in determining the outcome of acute HCV infections, and the underlying immunological defects that lead to chronicity.

Veritable antiviral capacity of natural killer cells in chronic HBV infection: an argument for an earlier anti-virus treatment

Background

There is limited information on innate immunity, especially natural killer (NK) cell function, in different chronic hepatitis B (CHB) stages. Therefore, we examined whether the clinical staging strategy accurately reflects veritable NK cell immunity.

Methods

A total of 237 eligible CHB patients and 22 healthy controls were enrolled in our study. Demographic and clinical data were collected, and the CHB phases (immune active-IA, immune tolerant phase-IT, inactive CHB-IC, and grey zone-GZ) were classified according to the latest American Association for the Study of Liver Disease guidelines. Peripheral blood mononuclear cells from patients and healthy controls were tested for NK cell frequency, phenotype and function using flow cytometry.

Results

A significant decrease in activating receptor NKp44 and NKp46 expression and significant increase of exhaustion molecule Tim-3 expression were observed in NK cells from CHB patients. Reduced cytokine secretion and preserved or elevated cytotoxic function were also observed. Patients in the IT group exhibited comparable cytokine secretion and cytolytic capacity as age-matched IA patients. NK cell anti-viral functions were preserved in GZ patients. Some of the NK cell function in patients who were excluded from treatment by the current treatment guidelines was less compromised than patients who qualified for treatment.

Conclusion

Our findings provide evidence of veritable NK cell immunity during different natural history phases in treatment-naïve patients with chronic HBV Infection. Chronic HBV infection hindered NK cell function in CHB patients. However, the presumed IT and GZ statuses of CHB patients based on the clinical parameters may not accurately reflect the inner immune status of these patients and should be reconsidered. Some patients excluded from treatment by the current treatment guidelines may be able to be selected as candidates for treatment.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-017-1318-1) contains supplementary material, which is available to authorized users.

Immune Evasion Strategies during Chronic Hepatitis B and C Virus Infection

Both hepatitis B virus (HBV) and hepatitis C virus (HCV) infections are a major global healthcare problem with more than 240 million and 70 million infected, respectively. Both viruses persist within the liver and result in progressive liver disease, resulting in liver fibrosis, cirrhosis and hepatocellular carcinoma. Strikingly, this pathogenesis is largely driven by immune responses, unable to clear an established infection, rather than by the viral pathogens themselves. Even though disease progression is very similar in both infections, HBV and HCV have evolved distinct mechanisms, by which they ensure persistence within the host. Whereas HCV utilizes a cloak-and-dagger approach, disguising itself as a lipid-like particle and immediately crippling essential pattern-recognition pathways, HBV has long been considered a "stealth" virus, due to the complete absence of innate immune responses during infection. Recent developments and access to improved model systems, however, revealed that even though it is among the smallest human-tropic viruses, HBV may, in addition to evading host responses, employ subtle immune evasion mechanisms directed at ensuring viral persistence in the absence of host responses. In this review, we compare the different strategies of both viruses to ensure viral persistence by actively interfering with viral recognition and innate immune responses.

Innate immunity related pathogen recognition receptors and chronic hepatitis B infection

Innate immunity consists of several kinds of pathogen recognition receptors (PRRs), which participate in the recognition of pathogens and consequently activation of innate immune system against pathogens. Recently, several investigations reported that PRRs may also play key roles in the induction/stimulation of immune system related complications in microbial infections. Hepatitis B virus (HBV), as the main cause of viral hepatitis in human, can induce several clinical forms of hepatitis B and also might be associated with hepatic complications such as cirrhosis and hepatocellular carcinoma (HCC). Based on the important roles of PRRs in the eradication of microbial infections including viral infections and their related complications, it appears that the molecules may be a main part of immune responses against viral infections including HBV and participate in the HBV related complications. Thus, this review article has brought together information regarding the roles of PRRs in immunity against HBV and its complications.

On-treatment decrease of NKG2D correlates to early emergence of clinically evident hepatocellular carcinoma after interferon-free therapy for chronic hepatitis C

Background and aims

Interferon (IFN)- free direct antiviral agents (DAAs) with rapid HCV eradication might evoke immunological reconstitutions, and some early recurrences of HCC after IFN-free DAAs have been reported. This study aimed to investigate whether natural killer group 2, member D (NKG2D) predicts early emergence of HCC after IFN-free DAAs.

Methods

We conducted a clinical practice-based observational study of 101 patients infected with genotype 1 HCV who received IFN-free (DAAs), and stratified them into those who did or did not develop early (i.e., during the 6-month surveillance period following treatment.) recurrence or occurrence of clinically evident HCC. We also analyzed the peripheral blood mononuclear cells, both before treatment and at end of treatment (EOT), of 24 of the patients who received IFN-free DAAs, and 16 who received IFN-combined protease inhibitor.

Results

We found early emergence of clinically evident HCC after IFN-free DAAs in 12 (12%) patients. Higher pre-treatment NKG2D expression, higher FIB-4 score, previous HCC history and failure to achieve sustained viral response were significant factors correlating to early HCC emergence. After IFN-free DAAs, a rapid decrease of NKG2D at EOT correlated with early HCC emergence in the IFN-free DAA-treated patients, but not in patients treated with the IFN-combined regimen. The decrease of NKG2D until EOT was predictive of early HCC emergence at a cut-off of -52% (AUC = 0.92).

Conclusions

On-treatment decrease of NKG2D may be a useful predictor of early emerging HCC in patients treated with IFN-free DAAs.

Hepatitis B virus infection and the immune response: The big questions

Clinical events and the host immune response during hepatitis B virus (HBV) infection are intricately linked. Despite decades of research, important questions concerning the immunopathogenesis of chronic HBV infection remain unanswered. For example, it is unclear which immune parameters facilitate persistence, and if HBV can be completely cleared from the human liver. Recent technological breakthroughs now allow researchers to address these seemingly basic, but essential questions surrounding HBV immunity. It will be important to better define the molecular underpinnings of immune cell function and dysfunction during chronic disease and in controlled infection, with particular focus on the liver, as little information is available on the intrahepatic compartment. In the near future, it may be possible to solve some of the controversy surrounding the immune responses to HBV, and establish the features of both the innate and adaptive arms of the immune system required to achieve sustained control of HBV infection.

Dynamic Changes of the Frequency of Classic and Inflammatory Monocytes Subsets and Natural Killer Cells in Chronic Hepatitis C Patients Treated by Direct-Acting Antiviral Agents

OBJECTIVE

Up to now, little was known about the immunological changes of chronic hepatitis C (CHC) patients treated with direct-acting antiviral agents (DAAs); we try to explore the effect of DAAs on the frequency of monocytes, NK cells, and cytokines that promote their activation.

METHODS

15 treatment-naive CHC patients and 10 healthy controls were recruited. Patients were examined before DAAs therapy (0 w) and at week 4 (4 w) and week 12 (12 w) of therapy. Percentage of monocytes and NK cells of the peripheral blood was analyzed by flow cytometry. Serum cytokines IL-12, IL-18, CXCL10, CXCL11, sCD14, and sCD163 were measured by enzyme linked immunosorbent assay.

RESULTS

The frequency of CD3-CD16+CD56+ NK cells and classic CD14++CD16- monocytes decreased, while CD14+CD16+ monocytes and cytokines IL-12, IL-18, CXCL10, CXCL11, sCD14, and sCD163 increased at 0 w compared to healthy controls. During DAAs treatment, the decreased NK cells and classic monocytes gradually increased to normal levels; the increased inflammatory monocytes and cytokines IL-12 and CXCL11 decreased to normal levels, but the increased cytokines IL-18, CXCL10, sCD14, and sCD163 still remained at high levels at 12 w though they decreased rapidly from 0 w.

CONCLUSION

Our results showed that DAAs treatment attenuated the activation of monocytes and NK cells in CHC patients. Trial registration number is NCT03063723.

Hepatitis C virus impairs natural killer cell activity via viral serine protease NS3

Hepatitis C virus (HCV) infection is characterized by a high frequency of chronic cases owing to the impairment of innate and adaptive immune responses. The modulation of natural killer (NK) cell functions by HCV leads to an impaired innate immune response. However, the underling mechanisms and roles of HCV proteins in this immune evasion are controversial, especially in the early phase of HCV infection. To investigate the role of HCV nonstructural proteins especially NS3 in the impairment of NK functions, NK cells were isolated from the PBMCs by negative selection. To assess the direct cytotoxicity and IFN-γ production capability of NK cells, co-cultured with uninfected, HCV-infected, HCV-NS3 DNA-transfected Huh-7.5, or HCV-NS replicon cells. To determine the effect of an NS3 serine protease inhibitor, HCV-infected Huh-7.5 cells were treated with BILN-2061. Then, NK cells were harvested and further co-cultured with K-562 target cells. NK cell functions were analyzed by flow cytometry and enzyme-linked immunosorbent assay. When co-cultured with HCV-infected Huh-7.5 cells, the natural cytotoxicity and IFN-γ production capability of NK cells were significantly reduced. NK cell functions were inhibited to similar levels upon co-culture with HCV-NS replicon cells, NS3-transfected cells, and HCV-infected Huh-7.5 cells. These reductions were restored by BILN-2061-treatment. Furthermore, BILN-2061-treatment significantly increased degranulation against K-562 target cells and IFN-γ productivity in NK cells. Consistent with these findings, the expression levels of activating NK cell receptors, such as NKp46 and NKp30, were also increased. In HCV-infected cells, the serine protease NS3 may play a role in the abrogation of NK cell functions in the early phase of infection through downregulation of NKp46 and NKp30 receptors on NK cells. Together, these results suggest that NS3 represents a novel drug target for the treatment of HCV infections.

Frequency and role of NKp46 and NKG2A in hepatitis B virus infection

Background and Aim

Natural Killer (NK) cells are involved in the control of viral infection. However, the role of NK cells in chronic hepatitis B (CHB) remains unclear. This study investigated the frequencies and roles of NK cells in CHB, with a focus on activating receptor NKp46 and inhibitory receptor NKG2A.

Patients/Method

Peripheral blood lymphocytes were obtained from 71 CHB patients and 37 healthy subjects (HS). The expressions of NKp46 and NKG2A were analyzed using flow cytometry. The role of NKp46-ligand was assessed using an in vitro co-culture system. Cytotoxicity and IFN-γ production in NK cells were evaluated using RT-PCR and flow cytometry.

Results

CHB patients were classified into treatment-naïve patients with low HBV DNA titer (CHB-L; n = 28), high HBV DNA titer (CHB-H; n = 24) by the cut-off level of serum HBV DNA 4 log copies/ml, and patients receiving nucleos(t)ide analogue (CHB-NA; n = 19). The expressions of NKp46 and NKG2A were higher in CHB-H than in HS/CHB-L/CHB-NA. HepG2.2.15 had higher NKp46-ligand expression than HepG2. When NK cells from HS were co-cultured with HepG2.2.15, inhibition of the NKp46 and NKp46-ligand interaction by anti-NKp46 antibody significantly reduced cytolysis of HepG2.2.15 and IFN-γ production. However, those reductions were not observed in co-culture with HepG2. Additionally, NK cells that highly expressed NKp46 also highly expressed NKG2A (NKp46^highNKG2A^high subset). The frequencies of NKp46^highNKG2A^high subset in CHB-H were higher than those in HS/CHB-L/CHB-NA. Among treatment-naïve CHB patients, the frequencies of NKp46^highNKG2A^high subset were positively correlated with serum ALT (P<0.01, r = 0.45) and HBV DNA (P<0.01, r = 0.59) levels. The expressions of Fas-L, STAT1, TRAIL and CD107a were higher and IFN-γ expression was lower in the NKp46^highNKG2A^high subset than in the other subsets.

Conclusion

The NKp46 and NKp46-ligand interaction contributes to NK cell activation. A novel NK cell subset, the NKp46^highNKG2A^high subset, may be associated with liver injury and HBV replication.

Immunoregulatory Role of NK Cells in Tissue Inflammation and Regeneration

NK cells represent an important first line of defense against viral infection and cancer and are also involved in tissue homeostasis. Studies of NK cell activation in the last decade have revealed that they are able to respond to the inflammatory stimuli evoked by tissue damage and contribute to both progression and resolution of diseases. Exacerbation of the inflammatory response through interactions between immune effector cells facilitates the progression of non-alcoholic fatty liver disease (NAFLD) into steatosis, cirrhosis, and hepatocellular carcinoma (HCC). When hepatic damage is incurred, macrophage activation is crucial for initiating cross talk with neighboring cells present in the liver, including hepatocytes and NK cells, and the importance of this interaction in shaping the immune response in liver disease is increasingly recognized. Inflicted structural damage can be in part regenerated via the process of self-limiting fibrosis, though persistent hepatic damage will lead to chronic fibrosis and loss of tissue organization and function. The cytotoxic activity of NK cells plays an important role in inducing hepatic stellate cell apoptosis and thus curtailing the progression of fibrosis. Alternatively, in some diseases, such as HCC, NK cells may become dysregulated, promoting an immunosuppressive state where tumors are able to escape immune surveillance. This review describes the current understanding of the contributions of NK cells to tissue inflammation and metabolic liver diseases and the ongoing effort to develop therapeutics that target the immunoregulatory function of NK cells.

Changes in cellular proliferation and plasma products are associated with liver failure

AIM

To study the differences in immune response and cytokine profile between acute liver failure and self-limited acute hepatitis.

METHODS

Forty-six patients with self-limited acute hepatitis (AH), sixteen patients with acute liver failure (ALF), and twenty-two healthy subjects were involved in this study. The inflammatory and anti-inflammatory products in plasma samples were quantified using commercial enzyme-linked immunoassays and quantitative real-time PCR. The cellular immune responses were measured by proliferation assay using flow cytometry. The groups were divided into viral- and non-viral-induced self-limited AH and ALF. Thus, we worked with five groups: Hepatitis A virus (HAV)-induced self-limited acute hepatitis (HAV-AH), HAV-induced ALF (HAV-ALF), non-viral-induced self-limited acute hepatitis (non-viral AH), non-viral-induced acute liver failure (non-viral ALF), and healthy subjects (HC). Comparisons among HAV and non-viral-induced AH and ALF were performed.

RESULTS

The levels of mitochondrial DNA (mtDNA) and the cytokines investigated [interleukin (IL)-6, IL-8, IL-10, interferon gamma, and tumor necrosis factor] were significantly increased in ALF patients, independently of etiology (P < 0.05). High plasma mtDNA and IL-10 were the best markers associated with ALF [mtDNA: OR = 320.5 (95%CI: 14.42-7123.33), P < 0.0001; and IL-10: OR = 18.8 (95%CI: 1.38-257.94), P = 0.028] and death [mtDNA: OR = 12.1 (95%CI: 2.57-57.07), P = 0.002; and IL-10: OR = 8.01 (95%CI: 1.26-50.97), P = 0.027]. In the cellular proliferation assay, NK^bright, NKT and regulatory T cells (TReg) predominated in virus-specific stimulation in HAV-induced ALF patients with an anergic behavior in the cellular response to mitotic stimulation. Therefore, in non-viral-induced ALF, anergic behavior of activated T cells was not observed after mitotic stimulation, as expected and as described by the literature.

CONCLUSION

mtDNA and IL-10 may be predictors of ALF and death. TReg cells are involved in immunological disturbance in HAV-induced ALF.

Natural Killer Group 2A Expressed on Both Peripheral CD3-CD56+NK Cells and CD3+CD8+T Cells Plays a Pivotal Negative Regulatory Role in the Progression of Hepatitis B Virus-Related Acute-on-Chronic Liver Failure

To explore the role of surface receptors natural killer group 2A (NKG2A) and natural killer group 2D (NKG2D) on CD3⁺CD8⁺T cells and CD3^-CD56⁺NK cells in the progression of hepatitis B virus (HBV)-related acute-on-chronic liver failure (ACLF), we measured the expression of NKG2A and NKG2D on the surface of these 2 types of circulating cells by flow cytometry in 3 groups. One group consists of 36 patients with chronic hepatitis B (CHB), another one consists of 22 patients with HBV-related ACLF, and the last one has 12 normal controls (NC). The experimental result indicated that there was no significant difference in the proportion of CD3⁺CD8⁺T cells in total lymphocytes between the 3 groups. However, the percentage of CD3^-CD56⁺NK cells in ACLF group was evidently higher than that in the CHB group (P < 0.05). In addition, the expression of NKG2D on CD3⁺CD8⁺T cells in the ACLF group was significantly lower than that in the CHB group (P < 0.05), but there were no statistically significant differences in its percentages on CD3^-CD56⁺NK cells between the 3 groups. The expression of NKG2A on CD3⁺CD8⁺T cells in the ACLF group was significantly higher than that in the NC group (P < 0.05), and on NK cells was significantly higher than that in the CHB group (P < 0.05) and NC group (P < 0.01). The increase in ratios of NKG2A to NKG2D on CD3⁺CD8⁺T cells and CD3^-CD56⁺NK cells in the ACLF group was significantly more than that in the CHB group and NC group. The results indicate that the imbalance between NKG2A and NKG2D may contribute to the progression of HBV-related ACLF mediated by CD3^-CD56⁺NK cells and CD3⁺CD8⁺T cells. Compared with NKG2D, NKG2A expressed on both peripheral CD3^-CD56⁺NK cells and CD3⁺CD8⁺T cells plays a more pivotal negative regulatory role in the progression of HBV-related ACLF.

Functional Behavior of NKp46-Positive Intrahepatic Natural Killer Cells Against Hepatitis C Virus Reinfection After Liver Transplantation

BACKGROUND

NKp46 expression in natural killer (NK) cells has recently been shown to affect the responsiveness to antiviral treatment in hepatitis C virus (HCV)-infected patients. However, the density of NKp46 on intrahepatic NK cells is remarkably higher than that on peripherally circulating NK cells, whereas the biophylactic function of intrahepatic NK cells against HCV reinfection remains unclear.

METHODS

We analyzed the phenotypic and functional properties of intrahepatic NK cells using mononuclear cells extracted from ex vivo liver perfusates from living liver transplantation donors. To investigate the role of intrahepatic NK cells in relation to HCV infection, we evaluated posttransplant HCV load kinetics in HCV-related patients.

RESULTS

Intrahepatic NK cells from healthy donors showed a distinctive phenotype even in each of the CD56 and CD56 fractions compared with peripheral blood NK cells. In the assays using a Huh7-HCV replicon system, anti-HCV activity was induced via recognition of the NK cell receptors, including NKp46, NKp30, and NKG2D, which was demonstrated by the use of monoclonal antibodies that neutralized neutralizing molecules. Unexpectedly, the density of NKp46 on intrahepatic NK cells varied considerably among individuals, allowing us to demonstrate that HCV reload in the early posttransplant period was delayed in recipients of liver allografts containing a higher proportion of NKp46 NK cells.

CONCLUSIONS

Intrahepatic NKp46 NK cells exhibited anti-HCV activity via cell-to-cell contact. The variation of the NKp46 proportion in individuals could be attributed to the diversity of HCV resistance observed in these individuals, which possibly reflects the clinical outcome of infection in patients.

Modulation of innate immunity in the tumor microenvironment

A recent report from the Center for Disease Control identified melanoma as being among the highest causes of cancer-related mortalities in the USA. While interventions such as checkpoint blockade have made substantial impact in terms of improving response rates and overall survival, a significant number of patients fail to respond to treatment or become resistant to therapy. A better understanding of the tumor microenvironment in these patients becomes imperative for identifying immune suppressive mechanisms that impact the development of effective anti-tumor immune responses. We have investigated innate immune cells (dendritic cells, NK cells) in the tumor microenvironment (TME) in order to devise effective targeted anticancer immune therapies. We find that matrix metalloproteinase-2 (MMP-2), secreted from melanoma cells and stromal cells, cleaves IFNAR1 and stimulates TLR-2 on dendritic cells (DC) within the TME. Both these events independently culminate in programing the DCs to promote pro-tumorigenic TH2 T cell differentiation. In addition, we have shown that NK cells become functionally exhausted in melanoma patients. We identified the expression of Tim-3 as one of the factors responsible for NK cell exhaustion and showed that anti-Tim3 antibodies partially reversed this exhaustion. We have initiated local intervention strategies such as intra-tumoral administration of DC activating Poly-ICLC and compared the efficacy of different TLR agonists and melanoma antigens for use as combination tumor vaccine in clinical trials. Such approaches will provide a unique insight into tumor biology and will facilitate in development of highly effective and cell type-specific immune therapies.

Accumulation of Intrahepatic TNF-α-Producing NKp44+ NK Cells Correlates With Liver Fibrosis and Viral Load in Chronic HCV Infection

In the setting of chronic hepatitis C virus (HCV) infection, changes in natural killer (NK) cells have been shown to reflect activation in response to virus stimulation. The contribution of individual natural cytotoxicity receptors to HCV infection remains to be clarified. NKp44 is the sole specific natural cytotoxicity receptor expressed only on activated NK cells.In this study, peripheral blood and liver NK-cell subsets were purified from 31 patients with chronic C hepatitis or nonalcoholic steatohepatitis, and then characterized by flow cytometry. Their polyfunctional activity was determined by expression of the CD107a degranulation marker, together with intracellular cytokine production.Unlike the patients with nonalcoholic steatohepatitis, patients with chronic HCV infection had a higher frequency of NKp44 NK cells in the liver than in their peripheral blood (P < 0.0001). Intrahepatic NKp44 NK cells from HCV individuals produced higher levels of tumor necrosis factor-α than did NKp44 NK cells (P = 0.0011). Importantly, the frequency of intrahepatic NKp44 NK cells was correlated with both HCV-RNA levels (P = 0.0234) and stage of fibrosis (P = 0.0003).Our findings suggest that the accumulation of intrahepatic tumor necrosis factor-α-producing NKp44 resident NK cells play a role in the liver damage associated with chronic HCV infection.

Impact of natural killer cells on chronic hepatitis C and hepatocellular carcinoma

Natural killer (NK) cells are involved in the pathogenesis of hepatitis C viral (HCV) infection and hepatocellular carcinoma (HCC). Recent immunological progresses have revealed the molecular mechanisms of activation or inhibition of NK cells. In patients infected with HCV, the percentages of NK cells are decreased and the NK receptor expression and function of NK cells including cytotoxicity and cytokine production are altered. These alterations in NK cells are associated with persistent infection with HCV, liver injury, liver fibrosis and liver carcinogenesis. In HCV treatment, NK cells play a role in the eradication of HCV in both interferon (IFN)-based therapy and IFN-free therapy using direct-acting antivirals (DAA). In HCC patients, the exhaustion of NK cells that represents lower cytotoxicity and impaired cytokine production may contribute to the progression of HCC. Several immunotherapies targeting NK cells have been reported. NK cell transfer and NK-activating gene therapy have been demonstrated to be effective in mouse liver cancer models and several clinical trials are ongoing. Recently, the role of major histocompatibility complex class I-related chain A (MICA), a human ligand of NKG2D, has attracted attention in the development of HCC. The expression of MICA could be controlled by anti-HCC drugs including sorafenib. A new chemo-immunotherapy may be expected in the treatment of HCC. In this review, we summarize the impact of NK cells on chronic hepatitis C and HCC.

Liver-infiltrating CD8(+) lymphocytes as prognostic factor for tumour recurrence in hepatitis C virus-related hepatocellular carcinoma

BACKGROUND

Chronic liver inflammation and immune/inflammatory response promote hepatocellular carcinoma. The aim of this study was to characterize the immune status of HCV-related cirrhosis in patients with hepatocellular carcinoma (HCV-HCC) as compared to HCV patients without hepatocellular carcinoma.

METHOD

Immune markers (CD3, CD4, CD8, CD20, CD56, TCRγδ, FoxP3) and gene expression profiles (CD8α, CD8β, FoxP3, IL-6, IFN-γ, perforin, RANTES) were analysed in a test cohort by immunohistochemistry and quantitative RT-PCR analysis on serial non-tumorous and tumorous tissues.

RESULTS

Immune micro-environment was more inflammatory in HCV-HCC than HCV cirrhotic livers. The number of CD3(+) , CD4(+) , CD8(+) and CD20(+) liver-infiltrating lymphocytes was significantly higher, whereas the number of CD56(+) cells was significantly lower in HCV-HCC compared to HCV cirrhotic parenchyma. These differences were restricted to fibrous septa for CD4(+) and CD20(+) cells and to nodular parenchyma for CD8(+) cells. Gene expressions of CD8α, FoxP3 and RANTES were also significantly higher in HCV-HCC than in HCV cirrhosis. Interestingly, in a large cohort of 63 HCV-HCC patients. The number of CD8(+) cells ≥100/field was associated with significant higher tumour recurrence (P = 0.003) and lower overall survival (P = 0.05) at 5 years.

CONCLUSION

High densities of liver-infiltrating lymphocytes in HCV-HCC cirrhotic parenchyma prevail inflammatory conditions and could contribute to tumorigenesis and tumour recurrence. These results could contribute towards better clinical evaluation of patients susceptible for HCC recurrence after curative surgery.

Natural killer cells in hepatitis C: Current progress

Patients infected with the hepatitis C virus (HCV) are characterized by a high incidence of chronic infection, which results in chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. The functional impairment of HCV-specific T cells is associated with the evolution of an acute infection to chronic hepatitis. While T cells are the important effector cells in adaptive immunity, natural killer (NK) cells are the critical effector cells in innate immunity to virus infections. The findings of recent studies on NK cells in hepatitis C suggest that NK cell responses are indeed important in each phase of HCV infection. In the early phase, NK cells are involved in protective immunity to HCV. The immune evasion strategies used by HCV may target NK cells and might contribute to the progression to chronic hepatitis C. NK cells may control HCV replication and modulate hepatic fibrosis in the chronic phase. Further investigations are, however, needed, because a considerable number of studies observed functional impairment of NK cells in chronic HCV infection. Interestingly, the enhanced NK cell responses during interferon-α-based therapy of chronic hepatitis C indicate successful treatment. In spite of the advances in research on NK cells in hepatitis C, establishment of more physiological HCV infection model systems is needed to settle unsolved controversies over the role and functional status of NK cells in HCV infection.

Altered natural killer cells subsets distribution in children with hepatitis C following vertical transmission

BACKGROUND

Natural killer (NK) cells number, phenotypes and function have been evaluated in many studies in adults with hepatitis C as compared with healthy controls or dynamically during interferon-based and interferon-free treatments. Overall, in adults with chronic infection number of circulating NK cells has been reported to be lower when compared to spontaneous resolvers and healthy subjects. Different studies yielded inconsistent findings due to patient and virus heterogeneity.

AIM

To evaluate NK cells in children according to the different outcomes of the infection.

METHODS

In this cross-sectional study, we examined numbers and phenotypes of circulating NK cells from a homogenous cohort of Italian children with vertically acquired hepatitis C.

RESULTS

We compared 31 children who developed chronic infection with nine who presented spontaneous clearance and 13 controls. CD56(+) CD3(-) NK cell numbers were consistently lower in the persistently infected group (P = 0.03 and 0.04). This decrease was due to depletions of CD56(dim) NK cells (P = 0.03 chronic infection vs. spontaneous clearance), while CD56(bright) NK cells were expanded (P = 0.03). No significant difference was found in the frequencies of CD56(+) CD16(+) and CD56(dim) CD16(-) cells. Perforin expression was higher in children with chronic infection (P = 0.03 vs. spontaneous clearance).

CONCLUSIONS

Altered NK cells number and phenotypes could impact the outcome of HCV infection in children following vertical transmission. This study suggests for the first time that NK cells cytolytic function, featured by CD56(dim) cells, contributes to the elimination of HCV in children presenting spontaneous clearance.

Altered Immune Profiles of Natural Killer Cells in Chronic Hepatitis B Patients: A Systematic Review and Meta-Analysis

BACKGROUND

Natural killer (NK) cells are the main effective component of the innate immune system that responds to chronic hepatitis B (CHB) infection. Although numerous studies have reported the immune profiles of NK cells in CHB patients, they are limited by inconsistent results. Thus, we performed a meta-analysis to characterize reliably the immune profiles of NK cells after CHB infection, specifically frequency, phenotype, and function.

METHODS

A literature search of the computer databases MEDLINE, PUBMED, EMBASE, and Cochrane Center Register of Controlled Trails was performed and 19 studies were selected. The standard mean difference (SMD) and 95% confidence interval (CI) of each continuous variable was estimated with a fixed effects model when I2 < 50% for the test for heterogeneity, or the random effects model otherwise. Publication bias was evaluated using Begg's and Egger's tests.

RESULTS

The meta-analysis of publications that reported frequency of peripheral NK cells showed that NK cell levels in CHB patients were significantly lower compared with that of healthy controls. A higher frequency of CD56bright NK subsets was found in CHB patients, but the CD56dim NK subsets of CHB patients and healthy controls were similar. CHB patients before and after antiviral therapy with nucleotide analogues (NUCs) showed no statistical difference in NK frequency. The activating receptors were upregulated, whereas inhibitory receptors were comparable in the peripheral NK cells of CHB individuals and healthy controls. NK cells of CHB patients displayed higher cytotoxic potency as evidenced by CD107a protein levels and conserved potency to produce interferon-gamma (IFNγ), compared with their healthy counterparts.

CONCLUSION

Our results revealed that CHB patients had a lower frequency of NK cells compared with healthy individuals not treatable with antiviral NUC therapy. With an activating phenotype, NK cells in CHB patients showed better cytotoxic potency and conserved IFNγ production.

Memory re-differentiation and reduced lymphocyte activation in chronic HCV-infected patients receiving direct-acting antivirals

Recently, the treatment of HCV has advanced significantly due to the introduction of direct-acting antivirals (DAAs). Studies using interferon (IFN)-containing regimens failed to consistently show restoration of immunologic responses. Therefore, IFN-free DAA formulations provide a unique opportunity to dissect the immunologic effect of HCV cure. This study investigates the restoration of the immune compartment as a consequence of rapid viral clearance in patients successfully treated with DAAs and in the absence of IFN and ribavirin. Here, we evaluate the immunologic changes that occurred following DAA-mediated HCV cure. Peripheral blood from nineteen previously treatment-naïve patients with chronic HCV genotype 1a/1b who received an IFN and ribavirin-free regimen of daclatasvir, asunaprevir and BMS-791325 was evaluated. Immune reconstitution occurs in patients in whom HCV was successfully eradicated via DAA therapy. Restoration of the CD4(+) T-cell compartment in the peripheral blood and a re-differentiation of the T lymphocyte memory compartment resulted in a more effector memory cell population and a reduction in expression in the co-inhibitory molecule TIGIT in bulk T lymphocytes. Furthermore, we observed a partial reversal of the exhausted phenotype in HCV-specific CD8(+) T cells and a dampening of the activation state in peripheral NK cells. Collectively, our data provide the groundwork for dissecting the effect of DAA therapy on the immune system and identifying novel mechanisms by which chronic HCV infection exerts immunosuppressive effects on T cells through the recently described co-inhibitory molecule TIGIT.

Immunopathogenesis of Hepatitis C Virus Infection

Despite advances in therapy, hepatitis C virus infection remains a major global health issue with 3 to 4 million incident cases and 170 million prevalent chronic infections. Complex, partially understood, host-virus interactions determine whether an acute infection with hepatitis C resolves, as occurs in approximately 30% of cases, or generates a persistent hepatic infection, as occurs in the remainder. Once chronic infection is established, the velocity of hepatocyte injury and resultant fibrosis is significantly modulated by immunologic as well as environmental factors. Immunomodulation has been the backbone of antiviral therapy despite poor understanding of its mechanism of action.

Hypoxia impairs anti-viral activity of natural killer (NK) cells but has little effect on anti-fibrotic NK cell functions in hepatitis C virus infection

BACKGROUND & AIMS

Natural killer (NK) cells have been shown to exert anti-viral as well as anti-fibrotic functions in hepatitis C virus (HCV) infection. Previous studies, however, analyzed NK cell functions exclusively under atmospheric oxygen conditions despite the fact that the liver microenvironment is hypoxic. Here, we analyzed the effects of low oxygen tension on anti-viral and anti-fibrotic NK cell activity.

METHODS

Peripheral (n=34) and intrahepatic (n=15) NK cells from HCV(+) patients as well as circulating NK cells from healthy donors (n=20) were studied with respect to anti-viral and anti-fibrotic activity via co-culture experiments with HuH7 replicon cells and hepatic stellate cells, respectively.

RESULTS

Anti-viral activity of resting NK cells from healthy controls was not affected by hypoxia. However, hypoxia significantly reduced the response of healthy NK cells to cytokine stimulation. In contrast to healthy controls, we observed resting and cytokine activated peripheral NK cells from HCV patients to display a significantly decreased anti-viral activity when cultured at 5% or 1% oxygen, suggesting HCV NK cells to be very sensitive to hypoxia. These findings could be confirmed when intrahepatic NK cells were tested. Finally, we show that anti-fibrotic NK cell activity was not affected by low oxygen tension.

CONCLUSIONS

Our results show that anti-viral function of NK cells from HCV(+) patients is critically affected by a hypoxic microenvironment and, therefore, indicate that in order to obtain an accurate understanding of intrahepatic NK cell anti-HCV activity, the laboratory modelling should take into account the liver specific levels of oxygen.

Contradicting roles of miR-182 in both NK cells and their host target hepatocytes in HCV

BACKGROUND AND AIM

Natural killer cells are part of the innate immunity involved in viral eradication and were shown to be greatly affected by HCV infection. Epigenetic regulation of NK cell function by microRNAs was not efficiently studied before and was never studied in HCV infection; therefore the aim of this study was to assess for the first time the role of microRNAs in regulating the function of NK cells of HCV-infected patients and hence viral replication in the target HCV-infected Huh7 cells.

METHODOLOGY

NK cells were isolated from PBMCs of HCV-infected patients as well as controls, and HCV-infected liver biopsies as well as Huh7 cells infected with the virus were used. For the infection of Huh7 cells, first viral vector was in-vitro transcribed into viral RNA that was then used to infect naїve Huh7 cells. Supernatant from the infected cells was then collected and used for further infection. For manipulation of NK cells or Huh7 cells, miR-182 mimics and inhibitors were transfected via lipofection method. RNA was extracted from each cell population, reverse transcribed. Gene expression as well as viral load was quantified using qPCR.

RESULTS

Screening of NKG2A and NKG2D between patients and controls showed no difference in expression of NKG2A, while NKG2D was found to be downregulated. In view of that, bioinformatics analysis was performed and showed that miR-182 has potential binding sites on both the inhibitory receptor NKG2A and the activating receptor NKG2D, and on its ligand ULBP2, as well as on the viral genome itself. In NK cells of HCV-infected patients, miR-182 was found to be over-expressed compared to controls; its ectopic expression was found to decrease NKG2D mRNA level, while miR-182 inhibitors were able to decrease NKG2A mRNA compared to untransfected cells. In addition, co-culturing genotype 4 or 2 HCV-infected Huh7 cells with miR-182 mimicked NK cells of HCV-infected patients showed decreased viral replication, suggesting an enhanced NK cell function. On the other hand, miR-182 and ULBP2 were both found to be downregulated in HCV liver tissues and HCV-infected Huh7 cells compared to their controls. miR-182 mimics were found to decrease ULBP2 mRNA and increase viral replication in genotypes 4 and 2 HCV-infected target (Huh7) cells compared to controls, while miR-182 inhibitor decreased viral replication in the cell models.

CONCLUSION

miR-182 was never investigated before, neither in HCV infection nor in NK cells, and we found it to have dysregulated expression in both liver tissues and NK cells of HCV-infected patients compared to control. In addition to that, miR-182 was found to have a contradicting effect in both effector cell and its HCV-infected target cell regarding HCV replication.

Natural killer cell dysfunction in hepatocellular carcinoma and NK cell-based immunotherapy

The mechanisms linking hepatitis B virus (HBV) and hepatitis C virus (HCV) infection to hepatocellular carcinoma (HCC) remain largely unknown. Natural killer (NK) cells account for 25%–50% of the total number of liver lymphocytes, suggesting that NK cells play an important role in liver immunity. The number of NK cells in the blood and tumor tissues of HCC patients is positively correlated with their survival and prognosis. Furthermore, a group of NK cell-associated genes in HCC tissues is positively associated with the prolonged survival. These facts suggest that NK cells and HCC progression are strongly associated. In this review, we describe the abnormal NK cells and their functional impairment in patients with chronic HBV and HCV infection, which contribute to the progression of HCC. Then, we summarize the association of NK cells with HCC based on the abnormalities in the numbers and phenotypes of blood and liver NK cells in HCC patients. In particular, the exhaustion of NK cells that represents lower cytotoxicity and impaired cytokine production may serve as a predictor for the occurrence of HCC. Finally, we present the current achievements in NK cell immunotherapy conducted in mouse models of liver cancer and in clinical trials, highlighting how chemoimmunotherapy, NK cell transfer, gene therapy, cytokine therapy and mAb therapy improve NK cell function in HCC treatment. It is conceivable that NK cell-based anti-HCC therapeutic strategies alone or in combination with other therapies will be great promise for HCC treatment.

NK cell function and receptor diversity in the context of HCV infection

Hepatitis C virus (HCV) infects over 170 million people in the world. While a minority of individuals are able to naturally clear this hepatotropic virus using their immune system, most people go on to develop a lifetime chronic infection that can result in severe liver pathology, potentially leading to liver cirrhosis and hepatic cellular carcinoma. Investigations into acute immune responses and spontaneous clearance of the virus are severely hampered by difficulties in identification of relevant patient cohorts. While the role for the adaptive immune response in viral clearance is well established, it is becoming clear that the innate immune system also impacts on HCV outcome. The innate immune response to infection is likely to influence the type of adaptive immune response that develops and will ultimately influence if the virus is cleared or develops into a chronic infection. Natural Killer (NK) cells are lymphocytes that have important anti-viral functions including direct cytotoxicity of infected cells and the production of inflammatory cytokines, e.g., IFN-γ. They are generally considered to be cells of the innate immune system, although there is increasing evidence that NK cells adapt and persist in response to particular viral infections. NK cells are altered in patients with acute and chronic HCV infection. There is increasing evidence from both cellular and genetic studies that NK cells modulate HCV outcome. This review will describe and discuss the current experimental and clinical evidence of a role for NK cells in HCV infection and describe recent discoveries that are likely to play a role in future research.