What is the role of interferon in defense against disease

Failure of Interferon and Ribavirin With or Without NS3/4 Protease Inhibitor

The re-treatment of patients with genotype 1, 4, 5, or 6 infection who experienced failure of previous treatment with IFN and ribavirin with or without NS3/4 protease inhibitors (NS3/4 protease inhibitors were approved only for genotype 1 infection) is the same as the initial treatment of patients with these genotypes with a few exceptions. The 8-week option for ledipasvir-sofosbuvir is not applicable, because this applies only to patients who have never received therapy for their HCV infection. Furthermore, a meta-analysis of a phase II/III study of ledipasvir-sofosbuvir found that patients with genotype 1 infection who had experienced previous failure of IFN and ribavirin with or without an NS3/4 protease inhibitor and had cirrhosis had a lower SVR when treated for 12 weeks than those who received 12 weeks of therapy with ribavirin or 24 weeks of therapy.a The phase II SIRIUS trial randomized patients to ledipasvir-sofosbuvir with ribavirin for 12 weeks versus 24 weeks without ribavirin and reported similar SVRs (96% vs. 97%, respectively).784 With multiple ribavirin-free, 12-week options available for this subgroup of patients, this regimen is listed as an alternative, not a recommended, treatment option. This same approach is applied in patients with genotype 4 infection, but for genotype 5 and 6 infections, 12 weeks of ledipasvir-sofosbuvir is recommended regardless of the presence or absence of cirrhosis. This is based on very limited data. In addition, the elbasvir-grazoprevir regimen was studied (and approved) with ribavirin in patients with prior failure of an NS3/4- and IFN-containing regimen; thus, this regimen is an alternative, not a recommended, regimen in this re-treatment population.

The re-treatment of patients with genotype 2 infection in whom previous treatment with IFN and ribavirin failed is the same as initial treatment. Both glecaprevir-pibrentasvir and sofosbuvir-velpatasvir offer high efficacy for this patient population. However, the re-treatment of patients with genotype 3 infection who experienced previous failure of IFN and ribavirin has unique recommendations. As previously mentioned in the “Initial Treatment of Chronic Hepatitis C Virus Infection” section, there are subpopulations of patients with genotype 3 infection that present a therapeutic challenge. Consistently, across multiple DAA regimens, prior treatment failure and/or presence of cirrhosis increases the risk of treatment failure. It is also in the setting of these multiple baseline negative predictors that the presence of NS5A RASs has more impact on the risk of treatment failure. The ASTRAL-3 study, which investigated 12 weeks of sofosbuvir-velpatasvir in patients with genotype 3 infection, included 71 patients in whom therapy had previously failed and 80 patients with compensated cirrhosis. Although the overall SVR12 was 95%, lower SVR was reported for patients with previous failure (90%) and with cirrhosis (91%).825 As previously described, when a sofosbuvir plus NS5A (velpatasvir or daclatasvir) regimen is used, baseline NS5A RASs, especially when other negative predictors are present, affect DAA treatment response for genotype 3 infection, with the Y93H variant having the greatest impact. Meanwhile, glecaprevir-pibrentasvir, which is approved as an 8-week regimen for initial treatment of genotype 3 infection, regardless of presence of cirrhosis, had a lower SVR rate when studied for 12 versus 16 weeks among 44 patients without cirrhosis in whom prior therapy had failed (previously treated with IFN and ribavirin with or without sofosbuvir; those previously treated with NS5A or NS3/4A protease inhibitors were excluded).883 Owing to small numbers, the role of baseline NS5A RASs is less clear, but all patients who experienced treatment failure had RASs at baseline. In particular, two subjects (one in each arm) had the A30K substitution at baseline, and treatment failure occurred with the A30K plus emergence of the Y93H variant, a double RAS that confers 69-fold resistance to GLE-PIB. The phase III POLARIS-3 study randomized treatment-naïve patients with genotype 3 infection and cirrhosis to 8 weeks of sofosbuvir-velpatasvir-voxilaprevir versus sofosbuvir-velpatasvir for 12 weeks.792 The SVR12 was 96% in both arms.

Abstract

Interferons (IFNs) are proteins produced by a variety of cells in the inflammatory response to infections. Their production is triggered by the immune system in response to pathogens or cytokines. Once triggered, they induce numerous molecular changes that affect cellular responses including cell growth and inflammation. IFNs can play both pathological and beneficial roles in the nervous system. Endogenous IFNs play a role in viral infections of the nervous system, and therapeutic use of IFNs is common in the treatment of multiple sclerosis (MS). Research suggests that IFNs may also be beneficial in the treatment of other viral, autoimmune, and neoplastic conditions of the nervous system.

Asthma Exacerbations and Interferon Biology in the Airway

Asthma exacerbations represent an acute worsening of airflow obstruction in the setting of chronic disease, due to worsening of airway smooth muscle contraction, airway wall edema, and luminal obstruction with mucus.283 The mucus plug pathology reflects formation of pathologic mucus gels characterized by increases in the elastic behavior of the mucus gels with consequences including poor clearance from the airway. As a result, the airways become occluded with mucus plugs. Autopsy studies indicate that mucus-plugged airways are especially prominent in fatal and near fatal asthma.284 Common upper respiratory tract viruses, especially rhinoviruses, are the most common and important cause of exacerbations in both children and adults.285,286 Airway mucosal remodeling increasessusceptibility to this acute reduction in airflow in asthmatics. Changes in the epithelium that increase mucin stores in airway smooth muscle that render it more hyper-reactive and in blood vessels that render them more leaky, predispose many asthmatics to exaggerated airway responses to inhaled environmental insults, such as viruses, allergens, or pollutants.283 Asthmatic airways are hyperreactive in several ways; concentric smooth muscle contraction from hyperresponsiveness is one element, but mucosal edema from vascular permeability and excess mucus from mucin hypersecretion are others. The efficacy of corticosteroids in preventing exacerbations likely relates to their effects not only in reducing inflammatory cell numbers (especially eosinophils) but also through improvements in pathologic changes to goblet cells, smooth muscle cells, and blood vessels.

Viral infections are among the most important of the environmental stimuli implicated in asthma initiation. Airway epithelial cells are considered active sentinels and master coordinators of antiviral responses in the lung, usually mediated by IFNs. There are three distinct IFN families.287 The type I IFN family mainly comprises IFN-α subtypes and IFN-β. The type II IFN family consists of just IFN-γ. The type III IFN family comprises IFN-λ subtypes with similar functions to type I IFN cytokines but restricted activity because their receptor is restricted to epithelial cell surfaces. Type I IFNs are important for host defense against viruses, and it has been hypothesized that dysregulation of IFNs in the airway may promote virus-induced exacerbations. Indeed, it has been shown that rhinovirus-induced IFN-λ induction is deficient in epithelial cells and alveolar macrophages from asthmatics.288,289 However, it is not clear whether these impaired IFN responses represent a feature of asthma or an effect of treatment. For example, corticosteroids—frequently used to treat asthma—impair IFN responses,290 and suppression of IFNs by corticosteroids during virus-induced exacerbations of airway disease may be a mechanism of infection and exacerbation risk. Also, mice deficient in the type I IFN-α/β receptor have suppressed antimicrobial peptide and enhanced mucin responses to rhinovirus infection.290 These data have provided rationale for inhaled IFN-β therapy to prevent exacerbations, but preliminary reports of the efficacy of this approach in asthma have not been encouraging. Much more encouraging have been the beneficial effects of therapeutic proteins targeting T2 immunity (IgE, IL-4Rα, and IL-5 pathways) on asthma exacerbation rates. Notably, genetic polymorphisms inIL4RA are associated with a history of severe asthma exacerbations.291 Potential mechanistic explanations include reversal of the inhibitory effect of T2 cytokines on production of type I IFNs, or improvement of inflammatory and remodeling features of asthma that render asthmatics more susceptible to viral infection, or exacerbations in general. Related to this, mice infected with influenza and mild asthmatics experimentally infected with rhinovirus produce IL-33 that subsequently suppresses production of type I IFN and antiviral immunity.292 Omalizumab reverses the inhibitory effect that IgE has on production of type I IFNs by plasmacytoid DCs, a mechanism that may explain how it reduces exacerbation frequency.293

Interferons (IFNs) are a family of cytokines that were first identified almost half a century ago through their antiviral properties. IFNs not only have important antiviral effects but also have a role in antitumor and immunomodulatory responses. There are two major classes of IFNs: type I (IFN-α subtypes, IFN-β, etc.) and type II (IFN-γ). Additional IFNs (IFN-like cytokines; IFN-λ subtype) have recently been discovered, but they are not as well characterized. Type I and II IFNs use distinct but similar receptor systems. Research on these receptor systems has helped to provide a fundamental base to understand the function and signal pathways of other cytokines and their receptors. The biological effects of IFNs result primarily from the IFN-inducible proteins in responsive cells. Type I IFNs were the first to be produced by recombinant DNA technology and used therapeutically for viral infections, cancers, and autoimmune diseases. IFN-γ plays important roles in controlling diseases caused by intracellular bacteria, parasites, and fungi by induction of reactive oxidant species. It may also be important in modulating adaptive immune responses in the lung and participates in the pathogenesis of pulmonary diseases such as pulmonary fibrosis and asthma.

NOD-Like Receptors, RIG-I–Like Receptors, the Cyclic GMP-AMP Synthase–Stimulator of Interferon Genes Sensing Pathway, and the Inflammasome

While TLRs predominantly respond to extracellular or to endosomal microbial ligands, NLR proteins detect microbial ligands in the cytosol.309 Among the best characterized of these, NOD1 and NOD2 respond to fragments of bacterial peptidoglycan, while NLRC4 responds to bacterial flagellin in the cytosol.328,329 NLRs activate NF-κB signaling, and assemble into multicomponent structures called inflammasomes that consist of an NLR, an adaptor protein, and caspase subunits.330 Inflammasomes activate a host cell apoptotic pathway and the expression of IL-1 and IL-18 by activating caspase-1 or caspase-8.164 Macrophage caspase-1 activity is also important for phagosomal maturation.331 Thus detection of microbial molecules in the cytosol induces an inflammatory response that has consequences for adaptive Th2 and Th2 cell responses.332

The RIG-I–like receptors (RLRs) retinoic acid–inducible gene 1 (RIG-I), melanoma differentiation–associated gene 5 (MDA5), and laboratory of genetics and physiology 2 (LGP2) are members of a family of molecules that detect cytosolic nucleic acids from RNA viruses (e.g., measles virus, influenza virus, hepatitis C virus, and West Nile virus).311 RLRs signal via the adaptor protein mitochondrial antiviral-signaling protein (MAVS, also known as IPS1/VISA/Cardif) on the mitochondrial surface and collaborate with other pattern recognition receptors to induce antiviral responses.333–337 For example, inherited MDA5 deficiency is linked to recurrent rhinovirus, influenza, and respiratory syncytial virus infections (seeTable 6.1).338 Influenza and other viruses can subvert cytosolic detection systems by inhibiting RLR signal transduction and targeting components of this pathway for degradation.

Detection of cytosolic DNA, specifically to cyclic dinucleotides, occurs via receptors that signal through the endoplasmic reticulum adaptor molecule stimulator of interferon genes (STING).339 A central regulator of cytosolic DNA sensing is cyclic GMP-AMP synthase (cGAS), an interferon-inducible nucleotidyl transferase that has broad antiviral activity against HSV-1, vaccinia virus, and Kaposi sarcoma–associated herpesvirus (seeFig. 6.11).340–343 Notably, these and other viruses can evade cytosolic sensing by disrupting DNA binding to cGAS or interfering with downstream STING phosphorylation, or both.313,314 RLR- and cGAS/STING-dependent signaling events, either alone or via their cross talk, turn on NF-κB and type I interferon signaling in both infected and bystander cells.313,314 The role of cytosolic sensors of viral nucleic acids in shaping B- and T-cell responses remains less well defined, although emerging evidence implicates the cGAS-STING pathway in DC maturation, development of antigen-specific Th2 cells, and immunoglobulin G2c production.344

Introduction

Interferons (IFNs) comprise a family of secreted α-helical cytokines induced in response to specific extracellular biomolecules through stimulation of Toll-like receptors (TLRs). Acting in paracrine or autocrine modes, IFNs stimulate intra- and intercellular networks for regulating innate and acquired immunity, resistance to viral infections, and normal and tumor cell survival and death (Table 53-1). Through high-affinity cell surface receptors, IFNs stimulate genes, employing signaling molecules also used in part by other cytokines first identified through studies of IFNs. Perturbations in these pathways can also make cells resistant to a given ligand, facilitating either progression or resistance of malignancy. IFNs act on almost every cell type and, through their cellular actions, can be effective in inhibiting tumor emergence and progression and in inducing regression (see Table 53-1).

Studies on the mechanisms by which IFNs exert their antitumor activity have helped to understand host resistance to tumor emergence and also define cellular actions of interferon-stimulated gene (ISG) products (see Table 53-1). These latter proteins underlie not only the antitumor and immunoregulatory actions but also the antiviral effects of IFNs. More than a thousand genes regulated through IFN signaling pathways now have been identified.1,2 Suppression of IFNs and influences on their regulated gene products in and by malignant cells is emerging as an important contributor to the development of some human cancers (Table 53-2). Germ-cell mutation of an ISG RNASEL increases risk for prostate, breast, head and neck, and pancreatic carcinomas.3-6 Gene expression profiling and cytogenetic analyses have identified somatic homozygous deletions in the locus for IFNs at 9p21 and mutations of ISGs in melanoma, colon, lung, and hematologic malignancies.7-12 Epigenetic and genetic silencing of IFN signaling also likely influences tumor development.11,13-15 Activated natural killer (NK) and T cells have a critical role in the production and action of IFNs for potent immunomodulatory roles in the protection from chemical carcinogenesis and in controlling the growth of syngeneic and transplanted tumors. In addition to being a primary source for the production of IFNs-α and IFN-β, dendritic cell maturation is also influenced by IFNs.16-19 These actions of endogenous IFNs-α, IFN-β, and IFN-γ are probably the basis for the effectiveness of IFNs and/or inducers in suppressing tumor emergence and progression.20-22 These immunomodulatory actions, however, may or may not be identical to those resulting in clinical tumor regression with IFNs administered as single agents or in conjunction with other modalities of therapy.

Before the development of recombinant DNA technology for protein synthesis in prokaryotes, only limited quantities of impure IFNs were available. IFNs were, indeed, the first proteins produced by recombinant technology that were not previously available for wide use in clinical medicine. A long-awaited milestone, U.S. Food and Drug Administration (FDA) approval for a defined human protein with potent cell regulatory effects for the treatment of human malignancy, was subsequently realized.23,24 IFNs thus became the prototypic biologic response modifiers for clinical oncologic therapy. With an emphasis on studies in human cells, this chapter reviews the structure of this family of cytokines, receptor interactions, signal transduction pathways, mechanisms of action, the ISGs, and clinical antitumor activity.

Summary

Interferons are a large family of related cytokines first identified by their ability to confer resistance to viral infections. They are firmly established as components of the innate arm of the immune system providing rapid and broad protection against a wide variety of invading pathogens. Of the three subfamilies, Type I IFN show the greatest diversity with over 20 family members. Interestingly, one member of this class, interferon tau, evolved to function as a signaling molecule between the early conceptus and the maternal uterus in ruminant ungulates. This interferon, IFNT, is necessary and sufficient to rescue the function of the corpus luteum during early pregnancies in these species. In addition, it is clear that other IFN family members, including IFNA, IFNB, IFNG, and IFND, are produced by placentae of rodents, humans, and swine. Their functions are less well-understood, but they likely play roles in modulating the immune function at the fetal–maternal interface and protecting the fetus against infection by maternal pathogens.

Conclusion

The interferons are the classic example of the two-edged sword. On one side, they have a remarkable ability to promote both innate and acquired immune responses to viral infections. On the other, their pleiotropic effects often promote unwanted inflammatory responses in diseases such as MS. Because of their tremendous capacity for upregulating immune responses, however, they have been tested as potential therapies for a number of diseases. IFN-α has been used for treatment of hepatitis C, hepatitis B, and in several cancers, including hairy cell leukemia, chronic myelogenous leukemia, and Kaposi's sarcoma. IFN-β, perhaps through its inhibition of IL-12 production as well as induction of IL-10, an immunosuppressive cytokine, is the first drug shown to promote clinical improvement in MS. Finally, IFN-γ has been used in the treatment of chronic granulomatous disease, a rare hereditary disease in which the phagocytic cells have an impaired ability to kill ingested microbes, resulting in recurring bacterial and fungal infections. IFNs, probably in conjunction with other cytokines, will continue to hold a prominent role in various therapies in human diseases due in large part to their incredible wide-ranging and pronounced immunological properties.

General adverse effects and adverse reactions

Adverse reactions to interferons are multifarious and the natural products seem to be less toxic than the pure synthetic compounds. Influenza-like symptoms with fever, chills, fatigue, myalgia, arthralgia, nausea, and lethargy, starting within 1 week after the start of treatment and lasting 1–7 days, seem to be very common [7,8]. Adverse reactions also include neurotoxicity (paresthesia, polyneuropathy), hepatic toxicity, renal toxicity, and an increase in eyelash growth [9–13]. Neutralizing antibodies can lead to resistance in patients with hairy cell leukemia and chronic myeloid leukemia [14,15]. The route of administration influences the provocation of an antibody response, and recombinant interferon beta is more likely to be immunogenic when given subcutaneously or intramuscularly than when given intravenously [16]. Raynaud’s phenomenon has been described after treatment with interferon alfa [17], and exacerbation of multiple sclerosis has been observed after treatment with interferon gamma.

The most common adverse effects and reactions reported in two large multicenter studies were fever (60%), leukopenia (43%), increased serum aspartate aminotransferase activity (30%), anorexia (30%), thrombocytopenia (25%), fatigue (21%), nausea, and vomiting (17%) [18,19]. Compared with subcutaneous administration, intravenous interferon alfa is associated with similar adverse effects of greater severity and frequency [20,21].

Interferon Genes, Proteins, and Their Induction

There are several types and families of interferons, all of which have antiviral effects. Current classification is based on primary structures as well as target receptors. By the latter criterion, there are three types of IFNs. Type I IFNs include the multiple subtypes of the IFN-α family, IFN-β, IFN-ω, IFN-τ, IFN-κ and IFN-ɛ (35–39). The sole type II IFN is IFN-γ. The newly discovered type III IFNs are also known as IFN-λ or IL-28/29; there are three known members, λ1 (IL-29) and λ2/3 (IL-28 A/B; 40). The type III IFNs share structural homology and induction characteristics with type I IFNs although function through a different receptor.

The genes for type I IFN lack introns; 17 human type I IFN genes, including many encoding subspecies of IFN-α, are clustered on chromosome 9 (36–39). The corresponding 13 murine genes are clustered on chromosome 4. At the protein level, the human IFN-α subspecies share about 50% sequence identity; IFN-β is 22% and IFN-ω is 37% identical to the IFN-α. Those conserved residues are thought to mediate similar receptor recognition by these proteins. IFN-α proteins have 186 to 190 amino acid residues and contain a cleavable signal peptide resulting in secreted protein of 165 or 166 amino acids. Two Cys-Cys disulfide bonds are conserved among the proteins.

The gene encoding IFN-γ, located on human chromosome 12 and mouse chromosome 10, has three introns and encodes a protein of 146 residues function as a dimmer (41,42). The structural homology of IFN-γ with type I IFNs is minimal. NK cells are the major source of IFN-γ whereas all cell types can produce IFNs-α and IFN-β.

Type I IFNs are produced however predominantly by dendritic cells but also by T cells, monocytes, fibroblasts, and epithelial cells. The choice of specific family members that are induced depends on both the cell type and the inducing agent. Virus infection or viral gene products, such as dsRNA, ssRNA, dsDNA or viral envelope proteins, can trigger type I IFN synthesis (43–45). These viral pathogen-associated molecular patterns (PAMPs) are recognized by specific membrane-bound proteins called Toll-like receptors (TLRs) that initiate the signaling process culminating in IFN synthesis (Table 52-3). Double-stranded (ds) RNA, a common byproduct of viral replication, is recognized by TLR3, a protein present in endosomal membrane (46). dsRNA can also be recognized by two cytosolic RNA-helicases, RIG-I and Mda5. Viral single-stranded (ss) RNAs are recognized by TLR7 and TLR8 and viral DNA by TLR9, all of which are also present in endosomal membrane (43,45). Different adaptor proteins connect these receptor proteins to specific protein kinases, such as TBK1 and IKK, which activate transcription factors including NF-κB, IRF-3, IRF-7, and AP-1. For IFN-β gene induction, NF-κB, the AP-1 complex composed of ATF2/c-jun and either IRF-3 or IRF-7 is needed. They form the enhancosome complex at the gene promoter (47,48). Synthesis of different members of the IFN-α family and IFN-β can be temporally staggered. IFN-β induces IRF-7 synthesis, which, in turn, induces transcription of IFN-α1 and other IFN-α genes. IFN synthesis and IFN action are, therefore, intimately linked; inhibition of IFN signaling blocks robust production of IFN-α. IRF5 can also participate in IFN-α gene induction in specific situations. Bacterial PAMPs can induce IFN synthesis using other TLRs, such as TLR4, which use different adapter proteins but activate the same transcription factors as TLR3.