Inhibition of alpha interferon signaling by hepatitis B virus

Alpha interferon (IFN-alpha) and pegylated IFN-alpha (pegIFN-alpha) are used for the treatment of chronic hepatitis B (CHB). Unfortunately, only a minority of patients can be cured. The mechanisms responsible for hepatitis B virus (HBV) resistance to pegIFN-alpha treatment are not known. pegIFN-alpha is also used to treat patients with chronic hepatitis C (CHC). As with chronic hepatitis B, many patients with chronic hepatitis C cannot be cured. In CHC, IFN-alpha signaling has been found to be inhibited by an upregulation of protein phosphatase 2A (PP2A). PP2A inhibits protein arginine methyltransferase 1 (PRMT1), the enzyme that catalyzes the methylation of the important IFN-alpha signal transducer STAT1. Hypomethylated STAT1 is less active because it is bound by its inhibitor, PIAS1. In the present work, we investigated whether similar molecular mechanisms are also responsible for the IFN-alpha resistance found in many patients with chronic hepatitis B. We analyzed the expression of PP2A, the enzymatic activity of PRMT1 (methylation assays), the phosphorylation and methylation of STAT1, the association of STAT1 with PIAS1 (via coimmunoprecipitation assays), the binding of activated STAT1 to interferon-stimulated response elements (via electrophoretic mobility shift assays), and the induction of interferon target genes (via real-time RT-PCR) in human hepatoma cells expressing HBV proteins as well as in liver biopsies from patients with chronic hepatitis B and from controls. We found an increased expression of PP2A and an inhibition of IFN-alpha signaling in cells expressing HBV proteins and in liver biopsies of patients with CHB. The molecular mechanisms involved are similar to those found in chronic hepatitis C.     

Protection of hepatocytes from cytotoxic T cell mediated killing by interferon-alpha

BACKGROUND: Cellular immunity plays a key role in determining the outcome of hepatitis C virus (HCV) infection, although the majority of infections become persistent. The mechanisms behind persistence are still not clear; however, the primary site of infection, the liver, may be critical. We investigated the ability of CD8+ T-cells (CTL) to recognise and kill hepatocytes under cytokine stimulation. METHODS/PRINCIPLE FINDINGS: Resting hepatocytes cell lines expressed low levels of MHC Class I, but remained susceptible to CTL cytotoxicity. IFN-alpha treatment, in vitro, markedly increased hepatocyte MHC Class I expression, however, reduced sensitivity to CTL cytotoxicity. IFN-alpha stimulated hepatocyte lines were still able to present antigen and induce IFN-gamma expression in interacting CTL. Resistance to killing was not due to the inhibition of the FASL/FAS- pathway, as stimulated hepatocytes were still susceptible to FAS-mediated apoptosis. In vitro stimulation with IFN-alpha, or the introduction of a subgenomic HCV replicon into the HepG2 line, upregulated the expression of the granzyme-B inhibitor-proteinase inhibitor 9 (PI-9). PI-9 expression was also observed in liver tissue biopsies from patients with chronic HCV infection. CONCLUSION/SIGNIFICANCE: IFN-alpha induces resistance in hepatocytes to perforin/granzyme mediate CTL killing pathways. One possible mechanism could be through the expression of the PI-9. Hindrance of CTL cytotoxicity could contribute to the chronicity of hepatic viral infections.     

Liver-specific alpha 2 interferon gene expression results in protection from induced hepatitis

The current therapy for hepatitis B and C is based on systemic administration of recombinant human alpha interferon (r-hIFN-alpha). However, systemic delivery of r-hIFN-alpha is associated with severe side effects, but more importantly, it is effective in only a small percentage of patients. In an effort to maximize IFN-alpha antiviral efficacy, we have explored the therapeutic potential of murine IFN-alpha2 (mIFNalpha2) selectively expressed in the liver. To this end, we have developed a helper-dependent adenovirus vector (HD) containing the mIFN-alpha2 gene under the control of the liver-specific transthyretin promoter (HD-IFN). Comparison with a first-generation adenovirus carrying the same mIFN-alpha2 expression cassette indicates that at certain HD-IFN doses, induction of antiviral genes can be achieved in the absence of detectable circulating mIFN-alpha2. Challenge of injected mice with mouse hepatitis virus type 3 showed that HD-IFN provides high liver protection. Moreover, liver protection was also observed in acute nonviral liver inflammation hepatitis induced by concanavalin A at 1 month postinfection. These results hold promise for the development of a gene therapy treatment for chronic viral hepatitis based on liver-restricted expression of IFN-alpha2.     

Predictive value of early virological response to treatment with different interferon-based regimens plus ribavirin in patients with chronic hepatitis C

Early virological response (EVR) to different interferon-based regimens plus ribavirin and its ability to predict the outcome of therapy in patients with chronic hepatitis C were investigated. The study design was as follows: 64 naive patients were considered, 32/64 received pegylated interferon alpha-2b (Peg-IFN-alpha2b) plus ribavirin and the remaining 32 received leucocyte interferon alpha (IFN-alpha) plus ribavirin. At week 4 of treatment, EVR was present in 68.7% and 37.5% of patients treated with Peg-IFN-alpha2b plus ribavirin, and with leucocyte interferon alpha (IFN-alpha) plus ribavirin, respectively (p = 0.024). At week 12, the cumulative EVR rates did not differ between the two groups (71.9% vs 56.2%, p >0.05) because a higher proportion of patients achieved EVR for the first time after more than 4 weeks of therapy in the standard IFN-alpha group. Sustained virological response (SVR) rates, however, resulted significantly higher in the Peg-IFN-alpha2b group (65.6% vs 37.5%; p = 0.045) since a higher proportion of patients who received standard IFN-alpha relapsed during the follow-up. In the standard IFN-alpha group, HCV genotype 1 (p = 0.035), high baseline viral load (p = 0.035) and the presence of bridging fibrosis/cirrhosis (p = 0.011) were closely associated with significantly lower SVR rates. In the Peg-IFN-alpha2b group, only bridging fibrosis/cirrhosis (p = 0.02) negatively influenced the outcome of treatment. Overall, 33/41 (80.5%) patients with EVR at week 12 were sustained responders, yielding a positive predictive value (PPV) of 0.80. However, when SVR was related to the time taken to reach EVR, 32/34 (94.1%) patients with EVR at week 4 of therapy (PPV = 0.94) versus 1/7 (14.3%) patients who had EVR after more than 4 weeks of therapy (PPV = 0.14) resulted sustained responders (p = 0.000057). In conclusion, EVR at week 4 of treatment is strongly associated with the likelihood of achieving SVR, regardless of the therapeutic regimen. However, when compared with standard IFN-alpha plus ribavirin, treatment with Peg-IFN-alpha2b plus ribavirin significantly increases the probability of viral clearance within the first 4 weeks of treatment. Finally, patients who do not clear the virus within the first 12 weeks of treatment have no chance of achieving SVR, justifying discontinuation of therapy in these patients.     

Evolution of the Hepatitis C Virus Second Envelope Protein Hypervariable Region in Chronically Infected Patients Receiving Alpha Interferon Therapy

Sustained hepatitis C virus (HCV) RNA clearance is achieved in 8 to 12% of patients with chronic HCV infection treated with alpha interferon (IFN-alpha) at the approved dose of 3 MU three times a week for 6 months and in about 25% of those receiving this treatment for 12 months. We used single-strand conformation polymorphism analysis combined with cloning and sequencing strategies to characterize the genetic evolution of HCV second envelope gene hypervariable region 1 (HVR1) quasispecies during and after IFN therapy in patients who failed to clear HCV RNA. Sustained HCV RNA clearance was achieved in 6% of patients. Profound changes in HVR1 quasispecies major variants were estimated to occur in 70% of the patients during and after therapy. These changes were evolutionary and were characterized by shifts in the virus population, related to selection and subsequent diversification of minor pretreatment variants. The quasispecies changes appeared to be induced by changes in the host environment likely resulting from the IFN-induced enhancement and post-IFN attenuation of neutralizing and possibly cytotoxic responses against HVR1. The remaining patients had no apparent changes in HVR1 quasispecies major variants, suggesting selection of major pretreatment variants, but some changes were observed in other genomic regions. We conclude that IFN-alpha administration and withdrawal profoundly alters the nature of circulating HCV quasispecies, owing to profound changes in virus-host interactions, in patients in whom sustained HCV RNA clearance fails to occur. These changes are associated with profound alterations of the natural outcome of HCV-related liver disease, raising the hypothesis of a causal relationship.     

Conventional protein kinase C inhibition prevents alpha interferon-mediated hepatitis C virus replicon clearance by impairing STAT activation

Hepatitis C virus (HCV) has evolved complex strategies to evade host immune responses and establish chronic infection. The only treatment available for HCV infections, alpha interferon (IFN-alpha), is effective in a limited percentage of patients. The mechanisms by which IFN-alpha interferes with the HCV life cycle and the reasons for limited effectiveness of IFN-alpha therapy have not yet been fully elucidated. Using a cell-based HCV replication system and specific kinase inhibitors, we examined the role played by various signaling pathways in the IFN-alpha-mediated HCV clearance. We reported that conventional protein kinase C (cPKC) activity is important for the effectiveness of IFN-alpha treatment. In cells treated with a cPKC-specific inhibitor, IFN-alpha failed to induce an efficient HCV RNA degradation. The lack of cPKC activity leads to a broad reduction of IFN-alpha-stimulated gene expression due to a significant impairment of STAT1 and STAT3 tyrosine phosphorylation. Thus, modulation of cPKC function by either host or viral factors could influence the positive outcome of IFN-alpha-mediated antiviral therapies.     

Alpha interferon inhibits hepatitis C virus replication in primary human hepatocytes infected in vitro

Chronic hepatitis C is a common cause of liver disease, the complications of which include cirrhosis and hepatocellular carcinoma. Treatment of chronic hepatitis C is based on the use of alpha interferon (IFN-alpha). Recently, indirect evidence based on mathematical modeling of hepatitis C virus (HCV) dynamics during human IFN-alpha therapy suggested that the major initial effect of IFN-alpha is to block HCV virion production or release. Here, we used primary cultures of healthy, uninfected human hepatocytes to show that: (i) healthy human hepatocytes can be infected in vitro and support HCV genome replication, (ii) hepatocyte treatment with IFN-alpha results in expression of IFN-alpha-induced genes, and (iii) IFN-alpha inhibits HCV replication in infected human hepatocytes. These results show that IFN-alpha acts primarily through its nonspecific antiviral effects and suggest that primary cultures of human hepatocytes may provide a good model to study intrinsic HCV resistance to IFN-alpha.     

Polymorphisms in the IFNAR1 gene in patients with chronic hepatitis C: outcome of combined IFN-alpha therapy

AIMS: Interferon-alpha (IFN-alpha) alone or in combination with ribavirin has been used for the last decade in the treatment of chronic hepatitis C, although the achievement of a sustained virological response (SVR) has not been very satisfactory. The treatment outcome depends on viral genotypes and host genetic polymorphisms in genes involved in the IFN-alpha signaling cascade. In this paper, we investigated the distribution of two variants of the IFNAR1 gene, G17470C and L168V, in two patient groups having received IFN-alpha alone or in combination with ribavirin. METHODS: The analysis was performed using DNA sequencing of the relevant gene fragments. RESULTS AND CONCLUSIONS: This study suggests that when combination therapy with high dose IFN-alpha and ribavirin is administered, HCV genotypes and age rather than the IFNAR1 polymorphisms are the predictors of a sustained response.     

Enhanced expression of interferon-regulated genes in the liver of patients with chronic hepatitis C virus infection: detection by suppression-subtractive hybridization

Hepatitis C virus (HCV) infection causes acute and often also chronic liver disease. Worldwide, prevalence of infection is estimated to exceed that of human immunodeficiency virus infection fourfold. Because of the lack of appropriate animal models, knowledge of interactions between virus and host is still limited. Assumptions regarding pathogenesis or the activation status of innate antiviral host responses, for instance, derive mainly from clinical observations and from expression analyses of selected genes. To obtain a more objective insight into virus-host interrelationships, we used suppression-subtractive hybridization to compare gene expression in HCV-infected and non-HCV-infected liver tissues samples. Four differentially expressed genes were found: (i) the gamma interferon (IFN-gamma)-inducible chemokine IP-10 gene; (ii) the IFN-alpha/beta-inducible antiviral MxA gene; (iii) the gene encoding IFN-alpha/beta-inducible p44, shown to be associated with ultrastructural cytoplasmic entities within hepatocytes of non-A, non-B hepatitis-infected chimpanzees; and (iv) the gene encoding IFN-alpha/beta/gamma-inducible IFI-56K, a protein recently shown to interact with the eukaryotic translation initiation factor eIF-3. Compared to hepatic gene expression in patients with liver diseases unrelated to viral infections, expression in patients with chronic HCV infection was up to 50-fold higher. While in patients with chronic HBV infection IP-10 was slightly activated as well, the IFN-alpha/beta-regulated genes were not. Revealing a dominance of hepatic interferon-regulated processes in chronic HCV infection, data on the enhanced expression of the IFN-gamma regulated IP-10 support earlier findings and may explain the composition of the hepatic cellular infiltrate. The data on enhanced expression of IFN-alpha/beta inducible genes might be germane to therapeutic considerations.     

Ribavirin enhances interferon-γ levels in patients with chronic hepatitis C treated with interferon-α

Some patients with chronic hepatitis C respond to interferon (IFN)-alpha treatment, and the efficiency can be improved by combining it with ribavirin. The mechanism of this improvement is unknown. To investigate the effects of these two regimens on the immune responses in 51 patients with chronic hepatitis C, we examined the hepatitis C core antigen-specific proliferative response and cytokine production profiles, natural killer (NK) cell cytotoxicity and cytotoxic T cell function during treatment. The results are as follows: (1) both viral clearance and biochemical normalization occurred more frequently in patients receiving combination therapy; (2) the function of NK cells increased after treatment in the responders of both groups (p < 0.05); (3) the level of IFN-gamma produced by hepatitis C core antigen-stimulated peripheral blood mononuclear cells was higher in patients receiving combination therapy, especially in responders; (4) the core antigen-specific proliferative response decreased after treatment, and (5) in addition, the core-specific cytotoxic T cell activities of five responder patients also increased significantly after therapy. In conclusion, enhancement of immune responses, especially those related to type-1 T helper cell activity, may contribute to better efficacy in combining ribavirin with IFN-alpha for treatment of chronic hepatitis C.     

Lambda interferon inhibits hepatitis B and C virus replication

Lambda interferon (IFN-lambda) induces an intracellular IFN-alpha/beta-like antiviral response through a receptor complex distinct from the IFN-alpha/beta receptor. We therefore determined the ability of IFN-lambda to inhibit hepatitis B virus (HBV) and hepatitis C virus (HCV) replication. IFN-lambda inhibits HBV replication in a differentiated murine hepatocyte cell line with kinetics and efficiency similar to IFN-alpha/beta and does not require the expression of IFN-alpha/beta or IFN-gamma. Furthermore, IFN-lambda blocked the replication of a subgenomic and a full-length genomic HCV replicon in human hepatocyte Huh7 cells. These results suggest the possibility that IFN-lambda may be therapeutically useful in the treatment of chronic HBV or HCV infection.     

Interleukin-29 functions cooperatively with interferon to induce antiviral gene expression and inhibit hepatitis C virus replication

The interferon (IFN)-related cytokine interleukin (IL)-29 (also known as IFN-lambda1) inhibits virus replication by inducing a cellular antiviral response similar to that activated by IFN-alpha/beta. However, because it binds to a unique receptor, this cytokine may function cooperatively with IFN-alpha/beta or IFN-gamma during natural infections to inhibit virus replication, and might also be useful therapeutically in combination with other cytokines to treat chronic viral infections such as hepatitis C (HCV). We therefore investigated the ability of IL-29 and IFN-alpha or IFN-gamma to cooperatively inhibit virus replication and induce antiviral gene expression. Compared with the individual cytokines alone, the combination of IL-29 with IFN-alpha or IFN-gamma was more effective at blocking vesicular stomatitis virus and HCV replication, and this cooperative antiviral activity correlated with the magnitude of induced antiviral gene expression. Although the combined effects of IL-29 and IFN-alpha were primarily additive, the IL-29/IFN-gamma combination synergistically induced multiple genes and had the greatest antiviral activity. Two different mechanisms contributed to the enhanced gene expression induced by the cytokine combinations: increased activation of ISRE promoter elements and simultaneous activation of both ISRE and GAS elements within the same promoter. These findings provide new insight into the coregulation of a critical innate immune response by functionally distinct cytokine families.     

Virus-specific CD8+ lymphocytes share the same effector-memory phenotype but exhibit functional differences in acute hepatitis B and C

Hepatitis B and hepatitis C viruses (HBV and HCV) are both noncytopathic and can cause acute and chronic infections of the liver. Although they share tropism for the same organ, development of chronic hepatitis is much more frequent following HCV infection, suggesting different mechanisms of viral persistence. In this study, we show that circulating HBV- and HCV-specific tetramer-positive CD8 cells during the acute phase of hepatitis B and C belong almost entirely to an effector-memory subset (CCR7(-) CD45RA(-)). Despite this phenotypic similarity, HBV- and HCV-specific CD8 cells show striking functional differences. HBV-specific tetramer-positive CD8 cells express high perforin content ex vivo, expand vigorously, and display efficient cytotoxic activity and gamma interferon (IFN-gamma) production upon peptide stimulation. A comparable degree of functional efficiency is maintained after the resolution of hepatitis B. In contrast, HCV-specific CD8 cells in the acute phase of hepatitis C express significantly lower levels of perforin molecules ex vivo and show depressed CD8 function in terms of proliferation, lytic activity, and IFN-gamma production, irrespective of the final outcome of the disease. This defect is transient, because HCV-specific CD8 cells can progressively improve their function in patients with self-limited hepatitis C, while the CD8 function remains persistently depressed in subjects with a chronic evolution.     

Free fatty acids induce ER stress and block antiviral activity of interferon alpha against hepatitis C virus in cell culture

ABSTRACT: BACKGROUND: Hepatic steatosis is recognized as a major risk factor for liver disease progression and impaired response to interferon based therapy in chronic hepatitis C patients. The mechanism of response to interferon-alpha (IFN-alpha) therapy under the condition of hepatic steatosis is unexplored. We investigated the effect of hepatocellular steatosis on hepatitis C virus (HCV) replication and IFN-alpha antiviral response in a cell culture model. METHODS: Sub-genomic replicon (S3-GFP) and HCV infected Huh-7.5 cells were cultured with a mixture of saturated (palmitate) and unsaturated (oleate) long-chain free fatty acids (FFA). Intracytoplasmic fat accumulation in these cells was visualized by Nile red staining and electron microscopy then quantified by microfluorometry. The effect of FFA treatment on HCV replication and IFN-alpha antiviral response was measured by flow cytometric analysis, Renilla luciferase activity, and real-time RT-PCR. RESULTS: FFA treatment induced dose dependent hepatocellular steatosis and lipid droplet accumulation in the HCV replicon cells was confirmed by Nile red staining, microfluorometry, and by electron microscopy. Intracellular fat accumulation supports replication more in the persistently HCV infected culture than in the sub-genomic replicon (S3-GFP) cell line. FFA treatment also partially blocked IFN-alpha response and viral clearance by reducing the phosphorylation of Stat1 and Stat2 dependent IFN-beta promoter activation. We show that FFA treatment induces ER stress response and down regulates the IFNAR1 chain of the type I IFN receptor leading to defective Jak-Stat signaling and impaired antiviral response. CONCLUSION: These results suggest that intracellular fat accumulation in HCV cell culture induces ER stress, defective Jak-Stat signaling, and attenuates the antiviral response, thus providing an explanation to the clinical observation regarding how hepatocellular steatosis influences IFN-alpha response in chronic hepatitis C (CHC).     

A comparison of the antitumor effects of interferon-alpha and beta on human hepatocellular carcinoma cell lines

The antiviral, antiproliferative and immunomodulatory effects of type I interferons (IFNs) are well documented, however, few studies have been published concerning differences in the antitumor effects of IFN-alpha and beta. In the present study, differences in antitumor effect, including the antiproliferative effect, cell cycle change, apoptosis, and the IFN-stimulated gene (ISG) were examined by flow cytometry between IFN-alpha and beta on three human hepatocellular carcinoma (HCC) cell lines (HepG2, Huh7 and JHH4). The antiproliferative effect of both IFNs on the HCC cell lines was time- and dose-dependent, and IFN-beta was significantly stronger than IFN-alpha. The cell cycle effect by both IFNs was an S-phase accumulation, with IFN-beta having a tendency to increase the S-phase ratio more strongly than IFN-alpha, especially in Huh7. Apoptosis marker expression, Fas antigen and intracellular active caspase-3, was increased after the addition of IFNs, especially of IFN-beta. The expression of human leukocyte antigen-class I molecules, ISG-encoded protein, was increased after the addition of IFNs, especially of IFN-beta. These data suggest that IFN-beta has a greater antitumor effect than IFN-alpha on HCC of a very early stage in patients with chronic hepatitis C.     

Increased expression of perforin and granzyme B genes in patients with metastatic melanoma treated with recombinant interleukin-2

The frequency of peripheral blood cells expressing the perforin gene or the granzyme B gene was evaluated by in situ hybridization in nine patients suffering from metastatic melanoma and treated with recombinant interleukin-2 (rIL-2). A spontaneous expression of both genes was detected in five to seven patients, rIL-2 administration increased the frequency of positive cells in all patients (P<0.03 for each gene), the highest frequency being reached in the patients who already expressed these genes prior to rIL-2 treatment (P<0.02). Expressions of the granzyme B gene and of the perforin gene were strongly correlated before IL-2 treatment and they were similarly affected by rIL-2 administration. In contrast, their modification under treatment did not correlate with that of CD56⁺ cell counts, of natural killer activity and of sCD8 release. This indicates that perforin and granzyme B gene expressions are markers of cytotoxic cell activation independent of those previously described, and that they should be further evaluated in patients with malignancies to delineate their potential value in predicting clinical outcome.     

Molecular characterization of woodchuck type I interferons and their expression by woodchuck peripheral blood lymphocytes

Interferon (IFN)-alpha and -beta are important antiviral mediators. IFN-alpha is widely used for the treatment of chronic hepatitis B. In our previous studies, a subtype of woodchuck IFN-alpha (wIFN-alpha) was characterized and has been shown to be active in suppressing the replication of woodchuck hepatitis virus (WHV) in vitro and vivo. Here, we refined the analysis of the IFN-alpha/beta system of the woodchuck and studied the expression of wIFN-alpha/beta in peripheral blood lymphocytes (PBLs) from na?ve and WHV-infected woodchucks. A number of wIFN-alpha genes were sequenced and could be classified into 10 subtypes and 3 pseudotypes. The biological activity of different subtypes of wIFN-alpha was demonstrated by their ability to protect woodchuck cells against encephalomyocarditis virus infection and to induce MxA expression in woodchuck cells. Additionally, a partial sequence of wIFN-beta was characterized. A subtyping method for wIFN-alpha based on restriction length polymorphism analysis was developed. Further, the expression of wIFN by woodchuck PBLs after stimulation with polyI/C was investigated. The maximal production of wIFN by woodchuck PBLs occurred within the first 48 h after addition poly I/C. The wIFN-alpha subtypes 1, 4, and 5 were found to be produced by poly I/C-stimulated woodchuck PBLs, indicating a selective expression of wIFN-alpha subtypes. PBLs from chronically WHV-infected woodchucks showed a reduced ability to produce wIFN when stimulated with poly I/C. The results suggest that woodchucks with chronic WHV infection have impaired immunological responses to poly I/C.