Natural killer cell dynamic profile is associated with treatment outcome in patients with chronic HCV infection

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.

Immunomodulation of the Natural Killer Cell Phenotype and Response during HCV Infection

Hepatitis C virus (HCV) infection develops into chronic hepatitis in over two-thirds of acute infections. While current treatments with direct-acting antivirals (DAAs) achieve HCV eradication in >95% of cases, no vaccine is available and re-infection can readily occur. Natural killer (NK) cells represent a key cellular component of the innate immune system, participating in early defence against infectious diseases, viruses, and cancers. When acute infection becomes chronic, however, NK cell function is altered. This has been well studied in the context of HCV, where changes in frequency and distribution of NK cell populations have been reported. While activating receptors are downregulated on NK cells in both acute and chronic infection, NK cell inhibiting receptors are upregulated in chronic HCV infection, leading to altered NK cell responsiveness. Furthermore, chronic activation of NK cells following HCV infection contributes to liver inflammation and disease progression through enhanced cytotoxicity. Consequently, the NK immune response is a double-edged sword that is a significant component of the innate immune antiviral response, but persistent activation can drive tissue damage during chronic infection. This review will summarise the role of NK cells in HCV infection, and the changes that occur during HCV therapy.

Lymphocytes Negatively Regulate NK Cell Activity via Qa-1b following Viral Infection

NK cells can reduce anti-viral T cell immunity during chronic viral infections, including infection with the lymphocytic choriomeningitis virus (LCMV). However, regulating factors that maintain the equilibrium between productive T cell and NK cell immunity are poorly understood. Here, we show that a large viral load resulted in inhibition of NK cell activation, which correlated with increased expression of Qa-1b, a ligand for inhibitory NK cell receptors. Qa-1b was predominantly upregulated on B cells following LCMV infection, and this upregulation was dependent on type I interferons. Absence of Qa-1b resulted in increased NK cell-mediated regulation of anti-viral T cells following viral infection. Consequently, anti-viral T cell immunity was reduced in Qa-1b- and NKG2A-deficient mice, resulting in increased viral replication and immunopathology. NK cell depletion restored anti-viral immunity and virus control in the absence of Qa-1b. Taken together, our findings indicate that lymphocytes limit NK cell activity during viral infection in order to promote anti-viral T cell immunity.

Mapping Determinants of Virus Neutralization and Viral Escape for Rational Design of a Hepatitis C Virus Vaccine

Hepatitis C virus (HCV) continues to spread worldwide with an annual increase of 1.75 million new infections. The number of HCV cases in the U.S. is now greater than the number of HIV cases and is increasing in young adults because of the opioid epidemic sweeping the country. HCV-related liver disease is the leading indication of liver transplantation. An effective vaccine is of paramount importance to control and prevent HCV infection. While this vaccine will need to induce both cellular and humoral immunity, this review is focused on the required antibody responses. For highly variable viruses, such as HCV, isolation and characterization of monoclonal antibodies mediating broad virus neutralization are an important guide for vaccine design. The viral envelope glycoproteins, E1 and E2, are the main targets of these antibodies. Epitopes on the E2 protein have been studied more extensively than epitopes on E1, due to higher antibody targeting that reflects these epitopes having higher degrees of immunogenicity. E2 epitopes are overall organized in discrete clusters of overlapping epitopes that ranged from high conservation to high variability. Other epitopes on E1 and E1E2 also are targets of neutralizing antibodies. Taken together, these regions are important for vaccine design. Another element in vaccine design is based on information on how the virus escapes from broadly neutralizing antibodies. Escape mutations can occur within the epitopes that are involved in antibody binding and in regions that are not involved in their epitopes, but nonetheless reduce the efficiency of neutralizing antibodies. An understanding on the specificities of a protective B cell response, the molecular locations of these epitopes on E1, E2, and E1E2, and the mechanisms, which enable the virus to negatively modulate neutralizing antibody responses to these regions will provide the necessary guidance for vaccine design.

A Developed NK-92MI Cell Line with Siglec-7neg Phenotype Exhibits High and Sustainable Cytotoxicity against Leukemia Cells

Altered sialic acid processing that leads to upregulation of cell surface sialylation is recognized as a key change in malignant tissue glycosylation. This cancer-associated hypersialylation directly impacts the signaling interactions between tumor cells and their surrounding microenvironment, especially the interactions mediated by immune cell surface sialic acid-binding immunoglobulin-like lectins (Siglecs) to relay inhibitory signals for cytotoxicity. First, we obtained a Siglec-7^neg NK-92MI cell line, NK-92MI-S7N, by separating a group of Siglec-7^neg cell population from an eight-month-long-term NK-92MI in vitro culture by fluorescence-activated cell sorting (FACS). The effect of Siglec-7 loss on NK-92MI-S7N cells was characterized by the cell morphology, proliferation, and cytotoxic activity via FACS, MTS assay, cytotoxic assay, and natural killer (NK) degranulation assay. We found the expression levels of Siglec-7 in NK-92MI were negatively correlated with NK cytotoxicity against leukemia cells. This NK-92MI-S7N cell not only shared very similar phenotypes with its parental cells but also possessed a high and sustainable killing activity. Furthermore, this Siglec-7^neg NK line was unexpectedly capable of eliminating a NK-92MI-resistant leukemia cell, THP-1, through enhancing the effector-target interaction. In this study, a NK cell line with high and sustainable cytotoxicity was established and this cell may provide a potential application in NK-based treatment for leukemia patients.

The benefits of hepatitis C virus cure: Every rose has thorns

To examine mid-term benefits on hepatic complications, extrahepatic clinical syndromes and quality of life associated with HCV cure; to review the few safety issues linked to oral direct-acting antivirals (DAAs); and to discuss the potential population benefits of reducing the burden of HCV infection. DAAs cure HCV infection in more than 95% of patients. The halting of liver inflammation and fibrosis progression translates into both hepatic and extrahepatic benefits and reduces the need for liver transplantation. A reduction in the frequency of extrahepatic manifestations such as mixed cryoglobulinaemia and vasculitis and improvements in quality of life and fatigue have also been described. A few safety issues linked to DAAs such as the potential recurrence of aggressive HCC, the flares of hepatitis B virus in patients with overt or occult HBV infection are been discussed. Curing HCV infection also has a high potential to reduce the burden of HCV infection at the population level. With widespread scaling up of HCV treatment, several modeling studies suggest that major reductions in HCV prevalence and incidence are possible, and that elimination of viral hepatitis is an achievable target by 2030.

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)

Monocytes inhibit hepatitis C virus-induced TRAIL expression on CD56bright NK cells

BACKGROUND & AIMS

Natural killer (NK) cells play an important role in the pathogenesis of hepatitis C virus (HCV) infection. We have previously shown that culture-derived HCV (HCVcc) enhance tumor necrosis-factor-related apoptosis-inducing ligand (TRAIL) expression on healthy NK cells, but not on those from patients infected with HCV, which was likely dependent on accessory cells. Here we sought to elucidate the mechanisms involved in altered TRAIL upregulation in this setting.

METHODS

Peripheral blood mononuclear cells (PBMC) from controls and patients infected with HCV were exposed to HCVcc. Cell depletions were performed to identify cells responsible for NK cell activation. Flow cytometry and ELISA were used to identify the cytokines involved in the NK activation process.

RESULTS

In patients infected with HCV, soluble factors secreted by control PBMC restored the ability of NK cells to express TRAIL. Of note, CD14+ cell depletion had identical effects upon virus exposure and promoted increased degranulation. Moreover, increased concentrations of interleukin (IL)-18 binding protein a (IL-18BPa) and IL-36 receptor antagonist (IL-36RA) were observed after PBMC exposure to HCVcc in patients with HCV. HCVcc-induced NK cell TRAIL expression was inhibited by IL-18BPa and IL-36RA in control subjects. There were statistically significant correlations between IL-18BPa and indices of liver inflammation and fibrosis, supporting a role for this protein in the pathogenesis of chronic HCV infection.

CONCLUSIONS

During chronic HCV infection, monocytes play a key role in negative regulation of NK cell activation, predominantly via secretion of inhibitors of IL-18 and IL-36.

LAY SUMMARY

Coordination and collaboration between immune cells are essential to fight pathogens. Herein we show that during HCV infection monocytes secrete IL-18 and IL-36 inhibitory proteins, reducing NK cell activation, and consequently inhibiting their ability to express TRAIL and kill target cells.

Higher expression of inhibitory CD158b and CD158e NK cell receptor and age predicts treatment response in children with chronic hepatitis C

Treatment with pegylated interferon-α and ribavirin (PEG-IFN/RBV) is the only choice for chronic hepatitis C (CHC) in children. Natural killer (NK) cells were described to play a vital role in CHC. The aim of this study was to analyze the expression of peripheral blood NK cell receptors in their relation to PEG-IFN/RBV treatment response. Study included 26 children with CHC-13 boys, age range 13.42 ± 3.28 years. Blood for biochemical, virological and cytometric testing was taken for evaluation prior to the antiviral treatment. NK cell receptors were detected by flow cytometry and the results were presented as proportion of cells and mean fluorescence intensity (MFI). Therapy consisted of PEG-IFNα-2b (60 μg/m² s.c 1×/week) and RBV (15 mg/kg p.o. daily). Treatment duration was response-related and varied from 12 to 72 weeks. Rapid virological response (RVR) was evaluated in the 4th week and sustained virological response (SVR) 6 months after completion of the therapy. RVR children were younger (11.67 ± 3.74 vs 15.35 ± 2.42; p = 0.001) and displayed higher CD158b (3.58 ± 0.16 vs 3.45 ± 0.13; p = 0.038) and CD158e expression (4.33 ± 0.21 vs 4.03 ± 0.16; p = 0.039). Density of CD158b (logMFI = 3.68 ± 0.22 vs 3.36 ± 0.16; p = 0.036) and CD158e expression was significantly higher (4.37 ± 0.14 vs 4.12 ± 0.21; p = 0.046) and NKG2D expression significantly lower (97.50 ± 3.46 vs 94.92 ± 5.93; p = 0.049) in SVR children. SVR children were also significantly younger (12.40 ± 3.66 vs 15.13 ± 2.83; p = 0.003). Significance of the age of patients, and expression of CD158b and CD158e were confirmed in univariate and multivariate analysis. Age of patients is negatively related to RVR and SVR. NK cell phenotype with higher expression density of CD158b and CD158e receptor was a positive predictor of SVR.

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.

Hepatitis C virus-induced NK cell activation causes metzincin-mediated CD16 cleavage and impaired antibody-dependent cytotoxicity

BACKGROUND & AIMS

The Fc receptor family for immunoglobulin (Ig)G type III (FcγRIII, CD16) is an activating receptor on natural killer (NK) cells and an essential mediator of antibody-dependent cellular cytotoxicity (ADCC). There is only limited information on its role during chronic hepatitis C virus (HCV) infection. We studied CD16 expression in relation to NK cell functional activity in HCV-infected patients and sought mechanistic insights into virus-induced modulation.

METHODS

NK cell CD16 expression and activation status were evaluated ex vivo by flow cytometry in HCV-infected patients and healthy controls (HC) as well as in vitro after co-culture with HCV-infected HuH7.5 cells. Rituximab-mediated ADCC was assessed in HC and HCV-infected patients using Daudi cells as a target. The role of metzincins in CD16 down-modulation was assessed using specific inhibitory molecules and by evaluating intracellular mRNA levels.

RESULTS

HCV-infected patients exhibited increased frequencies of ex vivo activated NK cells and a concomitantly decreased NK CD16 expression, which resulted in impaired ADCC activity. Moreover, exposure of NK cells to culture-derived HCV recapitulated the ex vivo findings of decreased CD16 expression and increased NK cell activation. Importantly, blockade of metzincin-mediated shedding activity, including selective a disintegrin and metalloproteinase 17 (ADAM-17) inhibition, restored NK CD16 expression. Successful treatment with direct-acting antivirals partially improved NK ADCC function despite delayed CD16 reconstitution.

CONCLUSION

Chronic HCV infection induces NK cell activation resulting in ADAM-17-dependent CD16 shedding and consequent impaired ADCC function. Altered ADCC may contribute to failure to eradicate HCV-infected hepatocytes.

LAY SUMMARY

We show here that hepatitis C virus (HCV) activates natural killer (NK) lymphocytes which, as a consequence, loose their Fc receptor for IgG (CD16), an essential molecule for antibody binding. We show that this occurs through the action of enzymes named metzincins, resulting in altered NK-mediated antibody-dependent killing (ADCC) of target cells. This mechanism may contribute to HCV persistence and may represent a general phenomenon whereby some viruses can escape host's immune responses.

Alterations of the NK cell pool in HIV/HCV co-infection

BACKGROUND

A relevant proportion of human immunodeficiency virus (HIV) infected patients is co-infected with the hepatitis C virus (HCV). HCV co-infection in HIV-positive patients is associated with faster progression of liver disease in comparison to HCV mono-infection. Natural killer (NK) cells critically modulate the natural course of HCV infection. Both HIV and HCV mono-infection are associated with alterations of the NK cell pool. However, little data is available concerning phenotype and function of NK cells in HIV/HCV co-infection.

METHODS

A total of 34 HIV/HCV co-infected, 35 HIV and 39 HCV mono-infected patients and 43 healthy control persons were enrolled into this study. All HIV-positive patients were under effective antiretroviral therapy. NK cell phenotype, IFN-γ production and degranulation were studied by flow cytometry.

RESULTS

NK cell frequency in HIV/HCV co-infection was significantly lower than in healthy individuals but did not differ from HIV and HCV mono-infection. HIV/HCV co-infection was associated with significantly decreased expression of the maturation/differentiation markers CD27/62L/127 on NK cells but increased expression of CD57 compared to healthy controls. Of note, expression also differed significantly from HCV mono-infection but was similar to HIV mono-infection, suggesting a pronounced impact of HIV on these alterations. Similar findings were made with regard to the NK cell receptors NKG2A/C and NKp30. More importantly, NK cells in co-infection displayed a highly impaired functional activity with significantly lower IFN-γ production and degranulation than in healthy donors as well as HIV and HCV mono-infection, suggesting a synergistic effect of both viruses.

CONCLUSIONS

Our data indicate that HIV/HCV co-infection is associated with significant alterations of the NK cell pool, which might be involved in the rapid progression of liver disease in co-infected patients and which mainly reflect alterations observed in HIV mono-infection.

Immunological Predictors of Nonresponse to Directly Acting Antiviral Therapy in Patients With Chronic Hepatitis C and Decompensated Cirrhosis

BACKGROUND

Sustained virological response rates (SVRs) to directly acting antiviral (DAA) therapy for hepatitis C virus (HCV) are lower in decompensated cirrhosis. Markers of innate immunity predict nonresponse to interferon-based HCV treatment; however, whether they are associated with the response to DAAs in patients with decompensation is not known.

METHODS

Information on demographics, adherence, viral kinetics, and resistance were gathered prospectively from a cohort with decompensated cirrhosis treated with 12 weeks of DAAs. C-X-C motif chemokine-10 (CXCL-10) level and T-cell and natural killer (NK) cell phenotype were analyzed pretreatment and at 4 and 12 weeks of treatment.

RESULTS

Of 32 patients, 24 of 32 (75%) achieved SVR (responders). Eight of 32 (25%) experienced relapse after the end of treatment (nonresponders). There were no differences in demographics or adherence between groups. Nonresponders had higher CXCL-10; 320 pg/mL (179461) vs 109 pg/mL (88170) in responders (P < .001) and differential CXCL-10 dynamics. Nonresponders had lower NK cell frequency, higher expression of activation receptor NKp30, and lower frequency of the NK subset CD56^-CD16⁺.

CONCLUSIONS

Nonresponders to DAAs displayed a different NK phenotype and CXCL-10 profile to responders. Nonresponders did not have poorer adherence or baseline virological resistance, and this shows that immunological parameters are associated with treatment response to interferon-free treatment for HCV in individuals with decompensated cirrhosis.

Rapid decrease in hepatitis C viremia by direct acting antivirals improves the natural killer cell response to IFNα

OBJECTIVE

Chronic HCV infection is characterised by innate immune activation with increased interferon-stimulated genes (ISG) expression and by an altered phenotype of interferon-responsive natural killer (NK) cells. Here, we asked whether a rapid reduction in viremia by daclatasvir (DCV) and asunaprevir (ASV) improves the response to pegylated interferon (PegIFN) in patients who had previously failed a standard course of PegIFN/ribavirin (RBV) therapy.

DESIGN

Twenty-two HCV-infected non-responders to previous PegIFN/RBV therapy were studied for IFN-responsiveness of NK cells during quadruple (QUAD) therapy with DCV, ASV, PegIFN and RBV. A direct comparison of early NK cell responses in PegIFN/RBV therapy and QUAD therapy was performed for seven patients using paired cryopreserved peripheral blood mononuclear cells (PBMC) from both treatment courses. As a validation cohort, nine DCV/ASV-treated patients were studied for their NK cell response to in vitro stimulation with IFNα.

RESULTS

The 24 h virological response to QUAD therapy correlated with an increase in signal transducer and activator of transcription 1 (STAT1), phosphorylated STAT1 (pSTAT1) and tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) expression in NK cells, and the STAT1/pSTAT1/TRAIL induction was greater during QUAD therapy than during previous PegIFN/RBV therapy. Successful QUAD therapy as well as successful IFN-free DCV/ASV regimen resulted in an improved functional NK cell response (degranulation and TRAIL expression) to in vitro stimulation with IFNα.

CONCLUSIONS

IFN-responsiveness can be improved by inhibiting HCV replication and reducing the HCV-induced activation of the innate immune response. This may provide a rationale for clinical trials of a brief period of direct acting antiviral therapy followed by PegIFN/RBV therapy to reduce the overall treatment costs in low-income and middle-income countries.

TRIAL REGISTRATION NUMBERS

NCT01888900 and NCT00718172.

Lack of Siglec-7 expression identifies a dysfunctional natural killer cell subset associated with liver inflammation and fibrosis in chronic HCV infection

OBJECTIVE

Sialic-acid-binding immunoglobulin-like lectin-7 (Siglec-7) is a natural killer (NK) cell inhibitory receptor associated with NK phenotypic and functional abnormalities in HIV-1 infection. We investigated the significance of NK-expressed and serum soluble Siglec-7 in relation to NK functional ability and parameters of liver necroinflammation and fibrosis in chronic HCV infection.

DESIGN

NK-expressed and serum Siglec-7 were evaluated in 130 and 166 HCV-infected individuals by flow cytometry and ELISA, respectively. NK cell degranulation and cytokine secretion were determined by flow cytometry. 65 patients with chronic HBV infection, 84 with chronic biliary disorders and 168 healthy donors served as controls.

RESULTS

Expression of Siglec-7 was significantly decreased on NK cells from HCV-infected and HBV-infected patients and, conversely, serum Siglec-7 was significantly increased in these patients compared with controls. The frequency of Siglec-7pos NK cells was significantly higher at baseline in sustained virological responders to pegylated interferon-α/ribavirin treatment than in non-responders. Activating receptor expression was significantly higher in Siglec-7pos NK cells and was associated with increased degranulation and cytokine secretion compared with Siglec-7^neg cells. In chronic HCV infection, there was an inverse correlation between Siglec-7 expression and serum aminotransferases, γ-glutamyl transpeptidase, liver stiffness, aspartate aminotransferase to platelet ratio index and fibrosis-4 scores, and a positive correlation between serum Siglec-7 and the same clinical parameters, including histological staging.

CONCLUSIONS

These findings identify Siglec-7^neg NK cells as a dysfunctional subpopulation associated with severe liver disease in chronic HCV infection.

Immune regulation in chronic hepatitis C virus infection

The immunological result of infection with Hepatitis C virus (HCV) depends on the delicate balance between a vigorous immune response that may clear the infection, but with a risk of unspecific inflammation and, or a less inflammatory response that leads to chronic infection. In general, exhaustion and impairment of cytotoxic function of HCV-specific T cells and NK cells are found in patients with chronic HCV infection. In contrast, an increase in immune regulatory functions is found primarily in form of increased IL-10 production possibly due to increased level and function of anti-inflammatory Tregs. Thus, the major immune players during chronic HCV infection are characterized by a decrease of cytotoxic function and increase of inhibitory functions. This may be an approach to diminish intrahepatic and systemic inflammation. Finally, there has been increasing awareness of regulatory functions of epigenetic changes in chronic HCV infection. A vast amount of studies have revealed the complexity of immune regulation in chronic HCV infection, but the interplay between immune regulation in virus and host remains incompletely understood. This review provides an overview of regulatory functions of HCV-specific T cells, NK cells, Tregs, IL-10, and TGF-β, as well as epigenetic changes in the setting of chronic HCV infection.

IL15 polymorphism is associated with advanced fibrosis, inflammation-related biomarkers and virological response in human immunodeficiency virus/hepatitis C virus coinfection

BACKGROUND & AIMS

IL15 is an essential cytokine in both innate and adaptive immune response against hepatitis C virus (HCV) infection. The aim was to analyze whether IL15 rs10833 is associated with liver disease severity and response to pegylated-interferon-alpha plus ribavirin (pegIFN-alpha/RBV) therapy in human immunodeficiency virus (HIV)-/HCV-co-infected patients.

METHODS

A retrospective study was performed in 315 patients who started pegIFN-alpha/RBV therapy. Liver fibrosis stage was characterized in 286 patients. IL15 rs10833 and IL28B rs12980275 were genotyped by GoldenGate. The primary outcomes were: (a) advanced liver fibrosis evaluated by liver biopsy (F3-F4) or transient elastography (liver stiffness values ≥9.5 Kpa); (b) sustained virological response (SVR). The secondary outcome variable was the levels of serum biomarkers of inflammation.

RESULTS

Patients with rs10833 AA genotype had increased odds of having advanced fibrosis (adjusted odds ratio (aOR) = 2.30; P = 0.019), particularly in males (aOR = 2.24; P = 0.040), patients with HCV serum viral load (HCV-RNA) <500 000 IU/ml (aOR = 5.14; P = 0.018) and patients with IL28B rs12980275 AG/GG genotypes (aOR = 2.51; P = 0.046). Moreover, rs10833 AA genotype was significantly associated with higher levels of hepatocyte growth factor (adjusted arithmetic mean ratio (aAMR) = 1.50; P = 0.016), sICAM-1 (aAMR = 1.57; P = 0.025) and sVCAM-1 (aAMR = 1.56; P = 0.007). Finally, patients with rs10833 AA genotype had increased odds of achieving SVR (aOR = 3.12; P = 0.006), particularly in males (aOR = 3.69; P = 0.005), GT1/4 patients (aOR = 3.59; P = 0.006), patients with advanced fibrosis (aOR = 4.64; P = 0.021), HCV-RNA ≥500 000 IU/ml (aOR = 3.92; P = 0.007) and patients with IL28B rs12980275 AG/GG genotype (aOR = 2.98; P = 0.041).

CONCLUSIONS

The presence of IL15 rs10833 AA genotype in HIV-/HCV-co-infected patients was associated with advanced liver fibrosis, inflammation-related biomarkers and increased rates of SVR to pegIFN-alpha/RBV therapy.

Herpes virus reactivation after initiation of interferon-free antiviral agents in HIV-HCV-coinfected subjects: a new immune restoration disease?

We report four HCV-HIV-coinfected patients who developed herpes zoster or muco-cutaneous herpes virus disease shortly after starting interferon-free antiviral treatment for HCV. We suggest that in our patients the prompt clearance of HCV following direct-acting antivirals leads to a paradoxical effect on the innate and adaptive immune system mediating the reactivation of herpetic infection.

Improved Survival Among all Interferon-α-Treated Patients in HCV-002, a Veterans Affairs Hepatitis C Cohort of 2211 Patients, Despite Increased Cirrhosis Among Nonresponders

BACKGROUND

As the era of interferon-alpha (IFN)-based therapy for hepatitis C ends, long-term treatment outcomes are now being evaluated.

AIM

To more fully understand the natural history of hepatitis C infection by following a multisite cohort of patients.

METHODS

Patients with chronic HCV were prospectively enrolled in 1999-2000 from 11 VA medical centers and followed through retrospective medical record review.

RESULTS

A total of 2211 patients were followed for an average of 8.5 years after enrollment. Thirty-one percent of patients received HCV antiviral therapy, 15 % with standard IFN/ribavirin only, 16 % with pegylated IFN/ribavirin, and 26.7 % of treated patients achieved sustained virologic response (SVR). Cirrhosis developed in 25.8 % of patients. Treatment nonresponders had a greater than twofold increase in the hazard of cirrhosis and hepatocellular carcinoma, compared to untreated patients, whereas SVR patients were only marginally protected from cirrhosis. Nearly 6 % developed hepatocellular carcinoma, and 27.1 % died during the follow-up period. Treated patients, regardless of response, had a significant survival benefit compared to untreated patients (HR 0.58, CI 0.46-0.72). Improved survival was also associated with college education, younger age, lower levels of alcohol consumption, and longer duration of medical service follow-up-factors typically associated with treatment eligibility.

CONCLUSIONS

As more hepatitis C patients are now being assessed for all-oral combination therapy, these results highlight that patient compliance and limiting harmful behaviors contribute a significant proportion of the survival benefit in treated patients and that the long-term clinical benefits of SVR may be less profound than previously reported.

Elevated on-treatment levels of serum IFN-gamma is associated with treatment failure of peginterferon plus ribavirin therapy for chronic hepatitis C

Chronic hepatitis C virus (HCV) infection had been associated with cytokine imbalance. Cytokine dynamics in response to peginterferon/ribavirin therapy have an impact on the treatment efficacy for HCV patients. Ninety-two treatment-naive chronic hepatitis C patients were treated with 24 or 48 weeks of peginterferon/ribavirin therapy according to their viral genotypes. Sustained virologic response (SVR) is defined as undetectable HCV RNA throughout a 24-week post-treatment follow-up period. Dynamic serum levels of the following cytokines: (1) Th1-mediated cytokines: IFN-γ, interleukin-2, and TNF-alpha; (2)Th2-mediated cytokines: interleukin-4, interleukin-5, interleukin-6, and interleukin-10 and (3)immuno-modulatory cytokines: interleukin-1β, interleukin-8, and interleukin-12 were determined by Fluorescent Bead immunoassay. Serial dynamic cytokine expression demonstrated that not only elevated IFN-γ concentrations at specific time points but also the total IFN-γ amount was strongly linked to non-response in peginterferon/ribavirin therapy. IFN-γ levels could serve as an independent predictor for SVR analyzed by multivariate logistic regression test. The accuracy of discriminating responders from non-responders was acceptable when IFN-γ cut-off levels were set at 180, 120, and 40 pg/ml at the 4th week, 12th week, and end-of-treatment of therapy, respectively. Elevated on-treatment IFN-γ concentration was significantly associated with treatment failure among interleukin-28B rs8099917TT carriers and those patients failed to achieve rapid virologic response.

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.

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.

NK cells lacking FcεRIγ are associated with reduced liver damage in chronic hepatitis C virus infection

A novel subset of human natural killer (NK) cells, which displays potent and broad antiviral responsiveness in concert with virus-specific antibodies, was recently uncovered in cytomegalovirus (CMV)+ individuals. This NK-cell subset (g-NK) was characterized by a deficiency in the expression of FcεRIγ adaptor protein and the long-lasting memory-like NK-cell phenotype, suggesting a role in chronic infections. This study investigates whether the g-NK-cell subset is associated with the magnitude of liver disease during chronic hepatitis C virus (HCV) infection. Analysis of g-NK-cell proportions and function in the PBMCs of healthy controls and chronic HCV subjects showed that chronic HCV subjects had slightly lower proportions of the g-NK-cell subset having similarly enhanced antibody-dependent cellular cytotoxicity responses compared to conventional NK cells. Notably, among CMV+ chronic HCV patients, lower levels of liver enzymes and fibrosis were found in those possessing g-NK cells. g-NK cells were predominant among the CD56(neg) NK cell population often found in chronic HCV patients, suggesting their involvement in immune response during HCV infection. For the first time, our findings indicate that the presence of the g-NK cells in CMV+ individuals is associated with amelioration of liver disease in chronic HCV infection, suggesting the beneficial roles of g-NK cells during a chronic 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.

Natural Killer Cells in Viral Hepatitis

Natural killer (NK) cells are traditionally regarded as first-line effectors of the innate immune response, but they also have a distinct role in chronic infection. Here, we review the role of NK cells against hepatitis C virus (HCV) and hepatitis B virus (HBV), two agents that cause acute and chronic hepatitis in humans. Interest in NK cells was initially sparked by genetic studies that demonstrated an association between NK cell-related genes and the outcome of HCV infection. Viral hepatitis also provides a model to study the NK cell response to both endogenous and exogenous type I interferon (IFN). Levels of IFN-stimulated genes increase in both acute and chronic HCV infection and pegylated IFNα has been the mainstay of HCV and HBV treatment for decades. In chronic viral hepatitis, NK cells display decreased production of antiviral cytokines. This phenotype is found in both HCV and HBV infection but is induced by different mechanisms. Potent antivirals now provide the opportunity to study the reversibility of the suppressed cytokine production of NK cells in comparison with the antigen-induced defect in IFNγ and tumor necrosis factor-α production of virus-specific T cells. This has implications for immune reconstitution in other conditions of chronic inflammation and immune exhaustion, such as human immunodeficiency virus infection and cancer.

Altered effector functions of NK cells in chronic hepatitis C are associated with IFNL3 polymorphism

Interferon α-mediated effector functions of NK cells may contribute to the control of HCV replication and the pathogenesis of liver disease. The single-nucleotide polymorphism rs12979860 near IFNL3 (previously known as IL28B) is important in response to IFN-α treatment and in spontaneous resolution of acute hepatitis C. The role of the IFNL3 polymorphism in NK cell function is unclear. Thus, we investigated the role of IFNL3 polymorphism in type I IFN-dependent regulation of NK cell functions in patients with cHC and healthy control subjects. We demonstrated a marked polarization of NK cells toward cytotoxicity in response to IFN-α stimulation in patients with hepatitis C. That TRAIL up-regulation was present, particularly in patients with the IFNL3-TT allele, was supported by a shift in the pSTAT-1:pSTAT-4 ratios toward pSTAT-1. In patients bearing the IFNL3-TT allele, NK cell effector function correlated with liver disease activity. In contrast, higher cytokine production of NK cells was observed in healthy individuals with the IFNL3-CC genotype, which may support spontaneous HCV clearance in acute infection. Overall, these findings show that the role of NK cells may differ in chronic infection vs. early antiviral defense and that the IFNL3 genotype differentially influences NK cell function.

Successful Interferon-Free Therapy of Chronic Hepatitis C Virus Infection Normalizes Natural Killer Cell Function

BACKGROUND & AIMS

Chronic hepatitis C virus infection activates an intrahepatic immune response, leading to increased expression of interferon (IFN)-stimulated genes and activation of natural killer (NK) cells-the most prevalent innate immune cell in the liver. We investigated whether the elimination of hepatitis C virus with direct-acting antiviral normalizes expression of IFN-stimulated genes and NK cell function.

METHODS

We used multicolor flow cytometry to analyze NK cells from the liver and blood of 13 HCV-infected patients who did not respond to treatment with pegylated interferon and ribavirin. Samples were collected before and during IFN-free treatment with daclatasvir and asunaprevir and compared with samples from the blood of 13 healthy individuals (controls). Serum levels of chemokine C-X-C motif ligand (CXCL) 10 or CXCL11 were measured by enzyme-linked immunosorbent assay.

RESULTS

Before treatment, all patients had increased levels of CXCL10 or CXCL11 and a different NK cell phenotype from controls, characterized by increased expression of HLA-DR, NKp46, NKG2A, CD85j, signal transducer and activator of transcription 1 (STAT1), phosphorylated STAT1, and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). NK cells from patients also had increased degranulation and decreased production of IFNγ and tumor necrosis factor α compared with NK cells from controls. Nine patients had an end-of-treatment response (undetectable virus) and 4 had virologic breakthrough between weeks 4 and 12 of therapy. A rapid decrease in viremia and level of inflammatory cytokines in all patients was associated with decreased activation of intrahepatic and blood NK cells; it was followed by restoration of a normal NK cell phenotype and function by week 8 in patients with undetectable viremia. This normalized NK cell phenotype was maintained until week 24 (end of treatment).

CONCLUSIONS

Direct-acting antiviral-mediated clearance of HCV is associated with loss of intrahepatic immune activation by IFNα, which is indicated by decreased levels of CXCL10 and CXCL11 and normalization of NK cell phenotype and function.

Inherent transcriptional signatures of NK cells are associated with response to IFNα + rivabirin therapy in patients with Hepatitis C Virus

BACKGROUND

Differences in the expression of Natural Killer cell receptors have been reported to reflect divergent clinical courses in patients with chronic infections or tumors. However, extensive molecular characterization at the transcriptional level to support this view is lacking. The aim of this work was to characterize baseline differences in purified NK cell transcriptional activity stratified by response to treatment with PEG-IFNα/RBV in patients chronically infected with HCV.

METHODS

To this end we here studied by flow cytometer and gene expression profile, phenotypic and transcriptional characteristics of purified NK cells in patients chronically infected with HCV genotype-1 virus who were subsequently treated with PEG-IFNα/RBV. Results were further correlated with divergent clinical response obtained after treatment.

RESULTS

The pre-treatment transcriptional patterns of purified NK cells from patients subsequently undergoing a sustained virologic response (SVR) clearly segregated from those of non-responder (NR) patients. A set of 476 transcripts, including molecules involved in RNA processing, ubiquitination pathways as well as HLA class II signalling were differently expressed among divergent patients. In addition, treatment outcome was associated with differences in surface expression of NKp30 and NKG2D. A complex relationship was observed that suggested for extensive post-transcriptional editing. Only a small number of the NK cell transcripts identified were correlated with chronic HCV infection/replication indicating that inherent transcriptional activity prevails over environment effects such as viral infection.

CONCLUSIONS

Collectively, inherent/genetic modulation of NK cell transcription is involved in setting the path to divergent treatment outcomes and could become useful to therapeutic advantage.

Contribution of genes for killer cell immunoglobulin-like receptors (KIR) to the susceptibility to chronic hepatitis C virus infection and to viremia

BACKGROUND

Natural killer (NK) cells are an important element of innate immunity against viruses, although their numbers decrease in the liver during chronic HCV infection. NK cells express a large panel of inhibitory and activating receptors. The most polymorphic of these are killer cell immunoglobulin-like receptors (KIRs) which are encoded by multiple genes that may be present or absent in given individuals depending on their genotype. This variability results in differential susceptibility to viral infections and diseases, including HCV infection and its consequences.

AIMS AND METHODS

The aim of this study was to test whether chronical infection with HCV and the viremia levels are associated with any KIR gene in the Polish population. We typed 301 chronically HCV-infected patients and 425 non-infected healthy individuals for the presence or absence of KIR genes and their ligands, HLA-C C1 and C2 groups as well as HLA-B and HLA-A Bw4-positive alleles.

RESULTS

We found that males, but not females, possessing KIR2DS2 and KIR2DL2 genes had a 1.7 higher probability to become chronically HCV-infected than males negative for these genes (p=0.0213). In accord with this, centromeric B region, containing KIR2DS2 and KIR2DL2 genes, was also associated with chronic HCV infection in males. In addition, patients of both genders possessing KIR2DS3 but not KIR2DS5 gene exhibited, on average, 2.6 lower level of viremia than HCV-infected individuals with other genotypes (p=0.00282). This was evident in those infected at a young age. KIR2DS3-positive patients also had lower mean levels of bilirubin than KIR2DS3-negative ones (p=0.02862).

CONCLUSION

Our results suggest a contribution of the KIR2DS2 and KIR2DL2 genes (cenB haplotype) to the susceptibility to chronic HCV infection, and an association of the KIR2DS3 gene in the absence of KIR2DS5 with low viremia levels.

NK cells and interferons

The role of Natural Killer cells in host defense against infections as well as in tumour surveillance has been widely appreciated for a number of years. Upon recognition of "altered" cells, NK cells release the content of cytolytic granules, leading to the death of target cells. Moreover, NK cells are powerful producers of chemokines and cytokines, particularly Interferon-γ (IFN-γ), of which they are the earliest source upon a variety of infections. Despite being armed to fight against pathogens, NK cells become fully functional upon an initial phase of activation that requires the action of several cytokines, including type I IFNs. Type I IFNs are now recognized as key players in antiviral defense and immune regulation, and evidences from both mouse models of disease and in vitro studies support the existence of an alliance between type I IFNs and NK cells to ensure effective protection against viral infections. This review will focus on the role of type I IFNs in regulating NK cell functions to elicit antiviral response and on NK cell-produced IFN-γ beneficial and pathological effects.

Innate and adaptive immune responses in HCV infections

Hepatitis C virus has been identified a quarter of a decade ago as a leading cause of chronic viral hepatitis that can lead to cirrhosis and hepatocellular carcinoma. Only a minority of patients can clear the virus spontaneously during acute infection. Elimination of HCV during acute infection correlates with a rapid induction of innate, especially interferon (IFN) induced genes, and a delayed induction of adaptive immune responses. However, the majority of patients is unable to clear the virus and develops viral persistence in face of an ongoing innate and adaptive immune response. The virus has developed several strategies to escape these immune responses. For example, to escape innate immunity, the HCV NS3/4A protease can efficiently cleave and inactivate two important signalling molecules in the sensory pathways that react to HCV pathogen-associated molecular patterns (PAMPs) to induce IFNs, i.e., the mitochondrial anti-viral signalling protein (MAVS) and the Toll-IL-1 receptor-domain-containing adaptor-inducing IFN-β (TRIF). Despite these escape mechanisms, IFN-stimulated genes (ISGs) are induced in a large proportion of patients with chronic infection. Of note, chronically HCV infected patients with constitutive IFN-stimulated gene (ISG) expression have a poor response to treatment with pegylated IFN-α (PegIFN-α) and ribavirin. The mechanisms that protect HCV from IFN-mediated innate immune reactions are not entirely understood, but might involve blockade of ISG protein translation at the ribosome, localization of viral replication to cell compartments that are not accessible to anti-viral IFN-stimulated effector systems, or direct antagonism of effector systems by viral proteins. Escape from adaptive immune responses can be achieved by emergence of viral escape mutations that avoid recognition by antibodies and T cells. In addition, chronic infection is characterized by the presence of functionally and phenotypically altered NK and T cell responses that are unable to clear the virus but most likely contribute to the ongoing liver disease. In this review, we will summarize current knowledge about the role of innate and adaptive immune responses in determining the outcome of HCV infection.

Patients co-infected with hepatitis C virus (HCV) and human immunodeficiency virus recover genotype cross-reactive neutralising antibodies to HCV during antiretroviral therapy

When severely immunodeficient HIV/HCV co-infected patients are treated with antiretroviral therapy, it is important to know whether HCV-specific antibody responses recover and whether antibody profiles predict the occurrence of HCV-associated immune restoration disease (IRD). In 50 HIV/HCV co-infected patients, we found that antibody reactivity and titres of neutralising antibodies (nAb) to JFH-1 (HCV genotype 2a virus) increased over 48 weeks of therapy. Development of HCV IRD was associated with elevated reactivity to JFH-1 before and during the first 12 weeks of therapy. Individual analyses of HCV IRD and non-HCV IRD patients revealed a lack of an association between nAb responses and HCV viral loads. These results showed that increased HCV-specific antibody levels during therapy were associated with CD4(+) T-cell recovery. Whilst genotype cross-reactive antibody responses may identify co-infected patients at risk of developing HCV IRD, neutralising antibodies to JFH-1 were not involved in suppression of HCV replication during therapy.

NK cells and virus-related cancers

Natural killer (NK) cells become activated during viral infections and can play roles in such infections by attacking virus-infected cells or by regulating adaptive immune responses. Experimental models suggest that NK cells may also have the capacity to restrain virus-induced cancers. Here, we discuss the seven viruses linked to human cancers and the evidence of NK cell involvement in these systems.

Truncated CXCL10 is associated with failure to achieve spontaneous clearance of acute hepatitis C infection

The pathogenesis of hepatitis C virus (HCV) infection is strongly influenced by the nature of the host's antiviral immunity. Counterintuitively, elevated serum concentrations of C-X-C chemokine 10 (CXCL10), a potent chemoattractant for antiviral T-cells and NK-cells, are associated with poor treatment outcomes in patients with chronic HCV. It has been reported that an N-terminal truncated form of CXCL10, generated by the protease dipeptidylpeptidase 4 (DPP4), can act as chemokine antagonist. We sought to investigate CXCL10 antagonism in the clinical outcome and evolution of acute HCV infection. We collected serial blood samples from 16 patients, at the clinical onset of acute HCV infection and at 12 standardized follow-up timepoints over the first year. Intact and truncated CXCL10 and DPP4 activity were quantified in all longitudinal samples. In addition, NK-cell frequency/phenotype, and HCV-specific T-cell responses were assessed. Subjects developing chronicity (n = 11) had higher concentrations of CXCL10 (P < 0.001), which was predominantly in a truncated form (P = 0.036) compared to patients who spontaneously resolved infection (n = 5). Truncated CXCL10 correlated with HCV-RNA (r = 0.40, P < 0.001) and DPP4 activity (r = 0.53, P < 0.001). Subjects who resolved infection had a higher frequency of HCV-specific interferon-gamma (IFNγ)-producing T-cells (P = 0.017) and predominance of cytotoxic NK-cells (P = 0.005) compared to patients who became chronic. Patients who became persistently infected had higher proportions of cytokine-producing NK-cells, which were correlated with concentrations of truncated CXCL10 (r = 0.92, P < 0.001).

CONCLUSION

This study provides the first evidence of chemokine antagonism during acute HCV infection. We suggest that the DPP4-CXCL10 axis inhibits antiviral innate and adaptive host immunity and favors establishment of viral persistence.

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.

Type I interferon protects antiviral CD8+ T cells from NK cell cytotoxicity

Despite development of new antiviral drugs, viral infections are still a major health problem. The most potent antiviral defense mechanism is the innate production of type I interferon (IFN-I), which not only limits virus replication but also promotes antiviral T cell immunity through mechanisms, which remain insufficiently studied. Using the murine lymphocytic choriomeningitis virus model system, we show here that IFN-I signaling on T cells prevented their rapid elimination in vivo. Microarray analyses uncovered that IFN-I triggered the expression of selected inhibitory NK-cell-receptor ligands. Consequently, T cell immunity of IFN-I receptor (IFNAR)-deficient T cells could be restored by NK cell depletion or in NK-cell-deficient hosts (Nfil3(-/-)). The elimination of Ifnar1(-/-) T cells was dependent on NK-cell-mediated perforin expression. In summary, we identified IFN-I as a key player regulating the protection of T cells against regulatory NK cell function.

PEG-IFN alpha but not ribavirin alters NK cell phenotype and function in patients with chronic hepatitis C

Background

Ribavirin (RBV) remains part of several interferon-free treatment strategies even though its mechanisms of action are still not fully understood. One hypothesis is that RBV increases responsiveness to type I interferons. Pegylated Interferon alpha (PEG-IFNa) has recently been shown to alter natural killer (NK) cell function possibly contributing to control of hepatitis C virus (HCV) infection. However, the effects of ribavirin alone or in combination with IFNa on NK cells are unknown.

Methods

Extensive ex vivo phenotyping and functional analysis of NK cells from hepatitis C patients was performed during antiviral therapy. Patients were treated for 6 weeks with RBV monotherapy (n = 11), placebo (n = 13) or PEG-IFNa-2a alone (n = 6) followed by PEG-IFNa/RBV combination therapy. The effects of RBV and PEG-IFNa-2a on NK cells were also studied in vitro after co-culture with K562 or Huh7.5 cells.

Results

Ribavirin monotherapy had no obvious effects on NK cell phenotype or function, neither ex vivo in patients nor in vitro. In contrast, PEG-IFNa-2a therapy was associated with an increase of CD56^bright cells and distinct changes in expression profiles leading to an activated NK cell phenotype, increased functionality and decline of terminally differentiated NK cells. Ribavirin combination therapy reduced some of the IFN effects. An activated NK cell phenotype during therapy was inversely correlated with HCV viral load.

Conclusions

PEG-IFNa activates NK cells possibly contributing to virological responses independently of RBV. The role of NK cells during future IFN-free combination therapies including RBV remains to be determined.

Between Scylla and Charybdis: The role of the human immune system in the pathogenesis of hepatitis C

Hepatitis C virus (HCV) frequently elicits only mild immune responses so that it can often establish chronic infection. In this case HCV antigens persist and continue to stimulate the immune system. Antigen persistence then leads to profound changes in the infected host’s immune responsiveness, and eventually contributes to the pathology of chronic hepatitis. This topic highlight summarizes changes associated with chronic hepatitis C concerning innate immunity (interferons, natural killer cells), adaptive immune responses (immunoglobulins, T cells, and mechanisms of immune regulation (regulatory T cells). Our overview clarifies that a strong anti-HCV immune response is frequently associated with acute severe tissue damage. In chronic hepatitis C, however, the effector arms of the immune system either become refractory to activation or take over regulatory functions. Taken together these changes in immunity may lead to persistent liver damage and cirrhosis. Consequently, effector arms of the immune system will not only be considered with respect to antiviral defence but also as pivotal mechanisms of inflammation, necrosis and progression to cirrhosis. Thus, avoiding Scylla - a strong, sustained antiviral immune response with inital tissue damage - takes the infected host to virus-triggered immunopathology, which ultimately leads to cirrhosis and liver cancer - the realm of Charybdis.

The natural killer cell response to HCV infection

In the last few years major progress has been made in better understanding the role of natural killer (NK) cells in hepatitis C virus (HCV) infection. This includes multiple pathways by which HCV impairs or limits NK cells activation. Based on current genetic and functional data, a picture is emerging where only a rapid and strong NK cell response early on during infection which results in strong T cell responses and possible subsequent clearance, whereas chronic HCV infection is associated with dysfunctional or biased NK cells phenotypes. The hallmark of this NK cell dysfunction is persistent activation promoting ongoing hepatitis and hepatocyte damage, while being unable to clear HCV due to impaired IFN-γ responses. Furthermore, some data suggests certain chronically activated subsets that are NKp46^high may be particularly active against hepatic stellate cells, a key player in hepatic fibrogenesis. Finally, the role of NK cells during HCV therapy, HCV recurrence after liver transplant and hepatocellular carcinoma are discussed.

Pathogenesis of chronic viral hepatitis: differential roles of T cells and NK cells

Chronic hepatitis B virus (HBV) and hepatitis C virus (HCV) infections account for 57% of cases of liver cirrhosis and 78% of cases of primary liver cancer worldwide and cause a million deaths per year. Although HBV and HCV differ in their genome structures, replication strategies and life cycles, they have common features, including their noncytopathic nature and their capacity to induce chronic liver disease, which is thought to be immune mediated. However, the rate of disease progression from chronic hepatitis to cirrhosis varies greatly among infected individuals, and the factors that regulate it are largely unknown. This review summarizes our current understanding of the roles of antigen-specific and nonspecific immune cells in the pathogenesis of chronic hepatitis B and C and discusses recent findings that identify natural killer cells as regulators of T cell function and liver inflammation.

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?

Interferon- α -Induced Changes to Natural Killer Cells Are Associated with the Treatment Outcomes in Patients with HCV Infections

Aim. We analyzed the pretreatment natural killer (NK) cell functions with the aim of predicting the sustained virological response (SVR) or the interleukin (IL) 28B polymorphism that is strongly associated with the treatment response. Methods. The peripheral NK cells from chronic hepatitis patients with HCV genotype 1 and high virus titers were activated using a Toll-like receptor (TLR) 4 ligand and IFN-α. The cell surface markers were evaluated using a flow cytometric analysis, and IFN-γ production was evaluated using an enzyme-linked immunosorbent assay (ELISA). The genotyping of the polymorphisms in the IL28B gene region (rs8099917) on chromosome 19 was performed on the DNA collected from each patient. Results. The production of IFN-γ was significantly higher in the SVR patients compared with the no-response (NR) patients, whereas the cell surface markers were similar between the SVR and the NR patients. There were no significant differences found in the IL28B genotype distribution associated with the production of IFN-γ. Conclusion. Differences in the NK cell functions were observed between the SVR patients and the NR patients, suggesting that NK cells play a potential role in the treatment response independent of the IL28B genotype.