Interferons and their use in persistent viral infections

Myxovirus resistance protein A activates type I IFN signaling pathway to inhibit Zika virus replication

Myxovirus resistance protein A(MxA), one of the dynamin superfamily of large guanosine triphosphatase and a classical interferon stimulated gene (ISG) induced by type I interferons (IFNs), plays antiviral role in various virus infections. However, the effect of MxA on Zika virus (ZIKV) infection and its underlying mechanism remain elusive. In this study, we aimed to explore the role of MxA in ZIKV infection and its potential mechanisms. MxA overexpression was achieved by transfection with plasmid. The levels of MxA expression and ZIKV replication were assayed by both qRT-PCR and western blot. The activation status of Jak/STAT signaling pathway was evaluated at three levels: phosphorylation of STAT1 and STAT2(p-STAT1, p-STAT2) (western blot), activity of interferon sensitive response element (ISRE) (dual luciferase reporter gene assay), and the expression levels of ISGs (qRT-PCR). Our results showed that MxA overexpression inhibited ZIKV replication with no effect on virus entry. The expression levels of retinoic acid inducible gene I (RIG-I), melanoma differentiation-associated gene-5(MDA5), Toll-like receptor3(TLR3) and interferon regulatory Factor 3(IRF3), as well as IFNα and IFNβ, were increased in parallel with MxA upregulation. Interestingly, the inhibitory effect of MxA on ZIKV replication was abolished in type I IFN receptor (IFNAR) deficient cells (U5A). These data collectively supported that MxA inhibits ZIKV replication through activation of the type I IFN signaling pathway.

Zika Virus Pathogenesis: A Battle for Immune Evasion

Zika virus (ZIKV) infection and its associated congenital and other neurological disorders, particularly microcephaly and other fetal developmental abnormalities, constitute a World Health Organization (WHO) Zika Virus Research Agenda within the WHO’s R&D Blueprint for Action to Prevent Epidemics, and continue to be a Public Health Emergency of International Concern (PHEIC) today. ZIKV pathogenicity is initiated by viral infection and propagation across multiple placental and fetal tissue barriers, and is critically strengthened by subverting host immunity. ZIKV immune evasion involves viral non-structural proteins, genomic and non-coding RNA and microRNA (miRNA) to modulate interferon (IFN) signaling and production, interfering with intracellular signal pathways and autophagy, and promoting cellular environment changes together with secretion of cellular components to escape innate and adaptive immunity and further infect privileged immune organs/tissues such as the placenta and eyes. This review includes a description of recent advances in the understanding of the mechanisms underlying ZIKV immune modulation and evasion that strongly condition viral pathogenesis, which would certainly contribute to the development of anti-ZIKV strategies, drugs, and vaccines.

Interferon stimulated gene 15 promotes Zika virus replication through regulating Jak/STAT and ISGylation pathways

Zika virus is an emergent arbovirus that has caused a public health emergency in South America. Zika virus infection is known to cause microcephaly and other congenital defects and Guillain-Barré syndrome. Unfortunately no direct antiviral treatments are available at present. IFN-stimulated gene 15 (ISG15) is one of the most upregulated host genes following type I interferon treatment or virus infections. ISG15 has been shown to have antiviral effect on a wide variety of viruses although pro-HCV replication was observed. However, the effect of ISG15 on ZIKV infection is not well defined. In this study, we try to clarify the effect of ISG15 on ZIKV replication and to further dissect the underlying mechanism. Our results indicated that ZIKV infection led to the increased expression of ISG15 in A549, 2fTGH, U5A cells. Overexpression of ISG15 stimulated ZIKV replication although ISG15 did not affect the viral entry. Further studies showed that this proviral effect was mediated through Jak/STAT signaling pathway and was ISGylation-dependent. Taken together, our work demonstrates that ISG15 is an important host factor exploited by ZIKV to facilitate its replication and might serve as a potential target for the development of novel antiviral agents.

ADAR1 and PKR, interferon stimulated genes with clashing effects on HIV-1 replication

The induction of hundreds of Interferon Stimulated Genes (ISGs) subsequent to virus infection generates an antiviral state that functions to restrict virus growth at multiple steps of their replication cycles. In the context of Human Immunodeficiency Virus-1 (HIV-1), ISGs also possess antiviral functions, but some ISGs show proapoptotic or proviral activity. One of the most studied ISGs, the RNA activated Protein Kinase (PKR), shuts down the viral protein synthesis upon activation. HIV-1 has evolved to evade its inhibition by PKR through viral and cellular mechanisms. One of the cellular mechanisms is the induction of another ISG, the Adenosine Deaminase acting on RNA 1 (ADAR1). ADAR1 promotes viral replication by acting as an RNA sensing inhibitor, by editing viral RNA and by inhibiting PKR. This review challenges the orthodox dogma of ISGs as antiviral proteins, by demonstrating that two ISGs have opposing and clashing effects on viral replication.

Hepatitis C virus: standard-of-care treatment

Hepatitis C virus (HCV) infection is curable by therapy. The antiviral treatment of chronic hepatitis C has been based for decades on the use of interferon (IFN)-α, combined with ribavirin. More recently, new therapeutic approaches that target essential components of the HCV life cycle have been developed, including direct-acting antiviral (DAA) and host-targeted agents (HTA). A new standard-of-care treatment has been approved in 2011 for patients infected with HCV genotype 1, based on a triple combination of pegylated IFN-α, ribavirin, and either telaprevir or boceprevir, two inhibitors of the HCV protease. New triple and quadruple combination therapies including pegylated IFN-α, ribavirin, and one or two DAAs/HTAs, respectively, are currently being evaluated in Phase II and III clinical trials. In addition, various options for all-oral, IFN-free regimens are currently being evaluated. This chapter describes the characteristics of the different drugs used in the treatment of chronic hepatitis C and those currently in development and provides an overview of the current and future standard-of-care treatments of chronic hepatitis C.

Susceptibility of different hepatitis B virus isolates to interferon-alpha in a mouse model based on hydrodynamic injection

Interferon alpha (IFN-α) is commonly used for the treatment of chronic hepatitis B (CHB) patients. Many factors including viral genetics may determine the outcome of IFN-α therapy. In this study, we tested whether the expression of IFN-α directly in the liver inhibits HBV gene expression and replication using a HBV hydrodynamic injection (HI) mouse model. Two replication-competent clones from different HBV isolates that belonging to HBV genotype A and B based on a pAAV vector (pAAV-HBV-A and pAAV-HBV-B) were compared for their susceptibility to IFN-α. HBV clones were injected into mice either alone or in combination with a murine (m) IFN-α expression plasmid (pmIFN-α). HBsAg and HBeAg concentrations and HBV DNA levels in mice differed after injection of these two HBV clones. Co-application of pmIFN-α together with the two distinct isolates resulted in markedly different kinetics of decline of HBsAg, HBeAg, and HBV DNA levels in the mice. Immunohistochemical staining of liver sections with anti-HBc showed that mIFN-α application completely inhibited the expression of HBcAg in mice inoculated with pAAV-HBV-B, whereas the expression of HBcAg was only reduced in mice with pAAV-HBV-A. Consistently, mice injected with pAAV-HBV-B and pmIFN-α showed higher expression levels of the IFN-stimulated genes (ISGs) ISG15, OAS, PKR as well as proinflammatory cytokine IL-6 in the liver. In addition, expression levels of anti-inflammatory cytokine IL-10 was down-regulated significantly in liver of the mice injected with pAAV-HBV-B and pmIFN-α. Our data demonstrate that IFN-α exerts antiviral activity in HBV mouse model, but different HBV isolates may have diverse susceptibility to IFN-α.

What are the pros and cons of the use of host-targeted agents against hepatitis C?

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Host-targeted agents block hepatitis C virus production by interacting with host cell components.

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Blocking the interaction of a cell component involved in the HCV lifecycle results in blockade of viral production.

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Cyclophilin A inhibitors and antagonists of microRNA-122 have reached clinical development.

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Host-targeted agents represent ideal “backbones” for pangenotypic drug combinations.

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Research on host-targeted approaches to combat viral infections other than HCV should be encouraged.

Hepatitis C virus (HCV) therapy is living a revolution. Host-targeted agents (HTAs) block HCV production by interacting with host cell components. Because they target conserved host proteins, not variable viral proteins, HTAs have the potential for pangenotypic antiviral activity and a high barrier to resistance. Only two HTAs have reached clinical development, including specific inhibitors of cyclophilin A peptidyl-prolyl cis/trans isomerase activity and antagonists of microRNA-122. Cyclophilin inhibitors have proven to be relatively well tolerated and can be confidently used as backbones of all-oral, interferon-free regimens. In addition, HTAs such as cyclophilin inhibitors offer opportunities for “panviral” approaches when they target mechanisms common to viruses of the same or different families. This article forms part of a symposium in Antiviral Research on “Hepatitis C: next steps toward global eradication.”

Delivery of synthetic RNA can enhance the immunogenicity of vaccines against foot-and-mouth disease virus (FMDV) in mice

We have recently described the antiviral effect in mice of in vitro-transcribed RNAs mimicking structural domains in the non-coding regions of the foot-and-mouth disease virus (FMDV) genome RNA. These small, synthetic and non-infectious RNA molecules (ncRNAs) are potent type-I interferon (IFN) inducers in vivo. In this work, the immunomodulatory effect of the ncRNA corresponding to the internal ribosome entry site (IRES) on immunization with two different FMD vaccine formulations, both based on inactivated virus, including or not a commercial adjuvant, was analyzed in the mice model. The effect of the time interval between RNA inoculation and immunization was also studied. RNA delivery consistently increased the titers of specific anti-FMDV antibodies, including neutralizing antibodies, elicited after vaccination. Moreover, at day 2 after immunization, significant differences in mean antibody titers could be detected between the groups of mice receiving either vaccine co-administered with the RNA and the control group, unlike those immunized with the vaccine alone. When vaccinated mice were challenged with FMDV, the mean values of viral load were lower in the groups receiving the RNA together with the vaccine. Our results show the enhancing effect of the IRES RNA on the immune response elicited after vaccination and suggest the potential of this molecule as an adjuvant for new FMD vaccine design.

Hepatitis C variability, patterns of resistance, and impact on therapy

Hepatitis C (HCV), a leading cause of chronic liver disease, cirrhosis, and hepatocellular carcinoma, is the most common indication for liver transplantation in the United States. Although annual incidence of infection has declined since the 1980s, aging of the currently infected population is expected to result in an increase in HCV burden. HCV is prone to develop resistance to antiviral drugs, and despite considerable efforts to understand the virus for effective treatments, our knowledge remains incomplete. This paper reviews HCV resistance mechanisms, the traditional treatment with and the new standard of care for hepatitis C treatment. Although these new treatments remain PEG-IFN-α- and ribavirin-based, they add one of the newly FDA approved direct antiviral agents, telaprevir or boceprevir. This new “triple therapy” has resulted in greater viral cure rates, although treatment failure remains a possibility. The future may belong to nucleoside/nucleotide analogues, non-nucleoside RNA-dependent RNA polymerase inhibitors, or cyclophilin inhibitors, and the treatment of HCV may ultimately parallel that of HIV. However, research should focus not only on effective treatments, but also on the development of a HCV vaccine, as this may prove to be the most cost-effective method of eradicating this disease.

Therapeutic implications of hepatitis C virus resistance to antiviral drugs

Treatment of chronic hepatitis C is currently based on a combination of pegylated interferon-o! and ribavirin. Neither drug exerts direct selective pressure on viral functions, meaning that interferon-a/ribavirin treatment failure is not due to selection of interferon-a- or ribavirin-resistant viral variants. Several novel antiviral approaches are currently in preclinical or clinical development, and most target viral enzymes and functions, such as hepatitis C virus protease and polymerase. These new drugs all potentially select resistant viral variants both in vitro and in vivo, and resistance is therefore likely to become an important issue in clinical practice.

Recombinant chicken interferon-α inhibits H9N2 avian influenza virus replication in vivo by oral administration

Chicken interferon-alpha (ChIFN-α) has been demonstrated to be an important cytokine in antiviral immunity. However, the preventive or therapeutic effect of ChIFN-α as an oral antiviral agent on avian influenza virus (AIV) infection has not been fully clarified in chickens systemically. In the present study, we investigated the anti-H9N2 AIV effect of ChIFN-α on a cohort of 7- and 33-day-old specific pathogen-free (SPF) chickens by oral administration. Results showed that both the ChIFN-α preventive and therapeutic groups exhibited significantly reduced viral load in trachea when compared with the virus-challenged control group. The therapeutic effect was better than the preventive effect on 7-day-old SPF chickens, which is opposite to 33-day-old SPF chickens. We speculated that T-dependent lymphocyte system of 33-day-old SPF chickens might be easier to be stimulated by ChIFN-α than that of 7-day-old SPF chickens. In addition, there was no side effect on the body weight of chickens treated with ChIFN-α. We also found that IFN-stimulated genes (ISGs) (2',5'-oligoadenylate synthetase and Mx1) were upregulated in groups treated by ChIFN-α and/or virus, indicating that these 2 ISGs not only participated in anti-AIV response in vivo but also could be induced by oral administration of ChIFN-α. The present study suggested that ChIFN-α could be used as a potential preventive and therapeutic antiviral agent against H9N2 AIV infection by oral administration.

Multiple levels of PKR inhibition during HIV-1 replication

Recent therapeutic approaches against HIV-1 include IFN in combination therapy for patients with coinfections or as an alternative strategy against the virus. These treatment options require a better understanding of the weak efficacy of the IFN-stimulated genes, such as the protein kinase RNA-activated (PKR), which results in viral progression. Activated PKR has a strong antiviral activity on HIV-1 expression and production in cell culture. However, PKR is not activated upon HIV-1 infection when the virus reaches high levels of replication, due to viral and cellular controls. PKR is activated by low levels of the HIV-1 trans-activation response (TAR) RNA element, but is inhibited by high levels of this double-stranded RNA. The viral Tat protein also counteracts PKR activation by several mechanisms. In addition, HIV-1 replicates only in cells that have a high level of the TAR RNA binding protein (TRBP), a strong inhibitor of PKR activation. Furthermore, increased levels of adenosine deaminase acting on RNA (ADAR1) are observed when HIV-1 replicates at high levels and the protein binds to PKR and inhibits its activation. Finally, the PKR activator (PACT) also binds to PKR during HIV-1 replication with no subsequent kinase activation. The combination of all the inhibiting pathways that prevent PKR phosphorylation contributes to a high HIV-1 production in permissive cells. Enhancing PKR activation by counteracting its inhibitory partners could establish an increased innate immune antiviral pathway against HIV-1 and could enhance the efficacy of the IFN treatment.

Silibinin and related compounds are direct inhibitors of hepatitis C virus RNA-dependent RNA polymerase

BACKGROUND & AIMS

Silymarin is a mixture of flavonolignans extracted from the milk thistle. Silymarin contains several molecules, including silibinin A, silibinin B, isosilibinin A, isosilibinin B, silicristin, and silidianin. Intravenous infusion of silibinin induces dose-dependent reduction of hepatitis C virus (HCV) RNA levels. The aim of this study was to test the principal isomers contained in silymarin preparations for their ability to inhibit HCV enzymatic functions and replication in different models.

METHODS

The inhibitory activity of silymarin components was tested in HCV RNA-dependent RNA polymerase and NS3/4A protease enzyme assays. Their ability to inhibit replication of an HCV genotype 1b replicon model and the JFH1 infectious HCV model in cell culture was also studied.

RESULTS

Silibinin A, silibinin B, their water-soluble dihydrogen succinate forms and Legalon SIL, a commercially available intravenous preparation of silibinin, inhibited HCV RNA-dependent RNA polymerase function, with inhibitory concentrations 50% of the order of 75-100 microM. Silibinin A and silibinin B also inhibited HCV genotype 1b replicon replication and HCV genotype 2a strain JFH1 replication in cell culture. None of these compounds inhibited HCV protease function.

CONCLUSIONS

Silibinin A and silibinin B, as well as Legalon SIL, inhibit HCV replicon and JFH1 replication in cell culture. This effect is at least partly explained by the ability of these compounds to inhibit HCV RNA-dependent RNA polymerase activity. Our results provide a basis for the optimization and subsequent development of members of the Flavonoid family as specific HCV antivirals.

The evolution of the major hepatitis C genotypes correlates with clinical response to interferon therapy

BACKGROUND

Patients chronically infected with hepatitis C virus (HCV) require significantly different durations of therapy and achieve substantially different sustained virologic response rates to interferon-based therapies, depending on the HCV genotype with which they are infected. There currently exists no systematic framework that explains these genotype-specific response rates. Since humans are the only known natural hosts for HCV-a virus that is at least hundreds of years old-one possibility is that over the time frame of this relationship, HCV accumulated adaptive mutations that confer increasing resistance to the human immune system. Given that interferon therapy functions by triggering an immune response, we hypothesized that clinical response rates are a reflection of viral evolutionary adaptations to the immune system.

METHODS AND FINDINGS

We have performed the first phylogenetic analysis to include all available full-length HCV genomic sequences (n = 345). This resulted in a new cladogram of HCV. This tree establishes for the first time the relative evolutionary ages of the major HCV genotypes. The outcome data from prospective clinical trials that studied interferon and ribavirin therapy was then mapped onto this new tree. This mapping revealed a correlation between genotype-specific responses to therapy and respective genotype age. This correlation allows us to predict that genotypes 5 and 6, for which there currently are no published prospective trials, will likely have intermediate response rates, similar to genotype 3. Ancestral protein sequence reconstruction was also performed, which identified the HCV proteins E2 and NS5A as potential determinants of genotype-specific clinical outcome. Biochemical studies have independently identified these same two proteins as having genotype-specific abilities to inhibit the innate immune factor double-stranded RNA-dependent protein kinase (PKR).

CONCLUSION

An evolutionary analysis of all available HCV genomes supports the hypothesis that immune selection was a significant driving force in the divergence of the major HCV genotypes and that viral factors that acquired the ability to inhibit the immune response may play a role in determining genotype-specific response rates to interferon therapy.