IL-4/IL-13 axis as therapeutic targets in allergic rhinitis and asthma

Biological characteristics of IL-4 and IL-13 receptor complexes

The genes encoding IL-4 and IL-13 are located in chromosome 5q31 where this genetic loci is home to a cluster of cytokine genes such as IL-3, IL-4, IL-5, IL-13 and granulocyte-macrophage colony stimulating factor (Giuffrida et al., 2019). IL-4 is produced by T cells, basophils and mast cells where it induces differentiation of T cells into Th2 subtype (Ptackova et al., 2018). IL-13 is produced by several immune cell populations including Th2 cells, mast cells, B cells, NK cells, innate lymphoid cells and granulocytes (Giuffrida et al., 2019; Joshi et al., 2006). IL-4 signaling pathway initiates immunoglobulin class switching toward IgE in B cells (Paul, 2015), while IL-13 triggers changes in epithelial and smooth muscle cell functions leading to hypersensitivity reactions (Ito et al., 2009; Wills-Karp & Finkelman, 2008).

IL-4 and IL-13 are structurally similar, multifunctional peptides and share a functional signaling receptor chain. IL-4 binds to two receptors i.e., the type I IL-4 receptor (IL-4R) composed of IL-4Rα and common γ-chain (γ_c), and type II IL-4R composed of IL-4Rα and IL-13Rα1. IL-4Rα is present on various types of cells including CD4⁺ and CD8⁺ T cells, lung epithelial cells, B cells, macrophages, airway goblet cells, and smooth muscle cells (Tan, Sugita & Akdis, 2016). On the other hand, IL-13R α1 is expressed by B cells, eosinophils, macrophages, lung epithelial cells, airway goblet cells, and endothelial cells (Tan, Sugita & Akdis, 2016).

The type I IL-4R complex is found on the surface of lymphoid T and NK cells, basophils, mast cells and most mouse B cells, while type II IL-4R is present on the surface of non-lymphoid and tumor cells (Koller et al., 2010; Wills-Karp & Finkelman, 2008). Another receptor that binds IL-13 only is IL-13Rα2 where it acts as a decoy receptor, and usually overexpressed as well as activated in tumor cells or fibrosis (Bartolome, Jaen & Casal, 2018; Fichtner-Feigl et al., 2006).

IL-4 and IL-13 activate the IL-4Rα /STAT6 pathway to induce allergic responses

Allergic response is triggered when DCs present allergen peptides to CD4⁺ T cells that then differentiate into Th2 cells to produce Th2 cytokines. Binding of IL-4 with its type I receptor which comprises of IL-4Rα and γ_c chain leads to activation of JAK1 and JAK3, respectively. For type II IL-4R, binding of IL-13 with IL-13Rα1 subunit activates TYK2/JAK2 (Nguyen et al., 2020; Wang et al., 2020). Activated JAKs facilitate tyrosine residues phosphorylation of the cytoplasmic tail of IL-4R. Following JAK3 activation, inflammatory mediators (e.g., histamines, leukotrienes) and cytokines (e.g., IL-4, IL-13 and IL-9) are released which influence the responses of neighboring cells (i.e B cells, mast cells, macrophages, dendritic cells and endothelial cells), triggering IgE production by plasma cells, eosinophils infiltration, airway inflammation, bronchoconstriction and tissue damage (Malaviya, Laskin & Malaviya, 2010).

The phosphorylated tyrosine residues serve as docking sites for STAT6 (a transcription factor selectively coupled to the IL-4Rα chain), activating IL-4 and IL-13 responsive genes in the subsequent signaling pathway of allergic responses. STAT6 induces Sonic hedgehog expression in the airway epithelium leading to goblet cell metaplasia and enhanced mucus production in asthma. pSTAT6 is associated with the production of Th9 cells and IL-9 during airway inflammation (Hoppenot et al., 2015). Activated macrophage marker Arginase 1 (Arg-1) can be induced by IL-4 and IL-13 which ultimately increase the production of L-ornithine and its downstream products polyamines and L-proline (i.e., inflammatory mediators causing airway remodeling) (Van Den Berg, Meurs & Gosens, 2018). Arg-1 inhibitors were recently patented for the treatment of AR and asthma (Meurs et al., 2019).

This activates B cells to produce circulating IgE that binds to specific Fcɛ receptors on mast cells and basophils. Signaling activation from Th2-type cytokines are important survival signals for mast cells, basophils, and eosinophils. Degranulation of mast cells results in the release of inflammatory mediators such as histamine, tryptase, chymase, kininogenase (generates bradykinin), heparin, prostaglandin D2 and the sulfidopeptidyl leukotrienes (Skoner, 2001). In AR, these mediators induce mucosal edema and watery rhinorrhea, while histamine activates its H1 receptors on sensory nerve endings that causes sneezing, pruritus, and reflex secretory responses. Moreover, histamine-mediated activation of H1 and H2 receptors on mucosal blood vessels leads to nasal congestion and plasma leakage (Sin & Togias, 2011). During the late phase in AR, nasal mucosal inflammation occurs with the influx and activation of a variety of inflammatory cells (i.e., T cells, eosinophils, basophils, neutrophils, and monocytes) into nasal mucosa that depends on Th2 cytokines e.g., IL-4, IL-5 and IL-13 (Sin & Togias, 2011). In asthma, the provocative discharges can spread from the upper airway to lungs, which triggers inflammation and bronchoconstriction (Stone, Prussin & Metcalfe, 2010). Airway hyperresponsiveness is a hallmark feature of asthma due to exaggerated bronchoconstrictor response (Sinyor & Perez, 2020). 

Furthermore, IL-4 and IL-13 are not only responsible for initiating inflammatory responses, but they also play important roles in disrupting nasal epithelial barrier integrity. The cytokines may accumulate within the sinonasal microenvironment surrounding sinonasal epithelial cells, activating IL-4/IL-13 axis signaling cascade that impairs epithelial TJ composition (Capaldo & Nusrat, 2009; London Jr, Tharakan & Ramanathan Jr, 2016). The signaling cascade deregulates the expression and assembly of epithelial TJ molecules, leading to increased nasal epithelial permeability to allergens (Capaldo & Nusrat, 2009; Steelant et al., 2018). The cytokines also obstruct the epithelial barrier from resealing which preserves the contact with inflammatory allergens (London Jr, Tharakan & Ramanathan Jr, 2016).

Association of IL-4/IL-13 axis with impaired nasal epithelial barrier integrity has been observed in both AR and asthma patients. In AR patients, treatment with anti-IL-4Rα monoclonal antibodies (mAbs) successfully restored epithelial barrier integrity and function (Steelant et al., 2018). IL-4 could disrupt epithelial integrity of primary nasal epithelial cells by reducing TJ molecules expression including zonula occludens-1 (ZO1) and occludin (OCLN) (Steelant et al., 2016a). Reduced expression of these TJ molecules in nasal epithelial cells are frequently observed in AR patients (Nur Husna et al., 2021a;Siti Sarah et al., 2020; Steelant et al., 2016a; Wang Ms et al., 2021). Addition of IL-4 and IL-13 to reconstructed human epidermis (RHE) cells resulted in downregulation of CLDN1 expression in AR (Gruber et al., 2015).

The IL-4/IL-13 axis also plays important roles in the pathophysiology of inflammatory arthritis especially rheumatoid arthritis (RA). In RA, IL-4/IL-13 cytokines promote the production of proinflammatory cytokines such as IL-1β and TNF-α, as well as macrophage polarization from classically activated (M1) phenotype into the alternatively activated (M2) phenotype (Iwaszko, Biały & Bogunia-Kubik, 2021). These collectively promote inflammation of the joints in RA patients. On the other hand, in AR patients, IL-4/IL-13 axis primarily induces the recruitment of mDCs, eosinophils and overproduction of IgE by plasma cells, as well as repressing the expression of TJs by nasal epithelial cells. The pathophysiological differences of IL-4/IL-13 axis in RA and AR patients are likely due to distinct causative factors in both diseases whereby in AR, allergens are the key trigger while RA is multifactorial (i.e., hormones, genetics and environmental factors), leading to dissimilar clinical manifestations.

IL-4/IL-13 axis is a promising therapeutic target in AR and asthma. Development of novel therapies targeting IL-4/IL-13 axis can be achieved by disrupting its signaling axis at various molecular levels such as inhibition of the soluble cytokines and their receptors on cell surfaces. Several therapeutic mAbs targeting IL-4 and IL-13 and their receptors have been developed to date and are discussed in the next sections.

Therapeutic antibodies targeting IL-4/IL-13 axis in AR

Anti-IL-13 mAb in AR

Dectrekumab (also known as QAX-576) is a fully human investigational anti-IL-13 mAb with anti-inflammatory potential. It is widely investigated in immune disorders including AR asthma, eosinophilic esophagitis (EoE), Crohn’s disease and keloids (Rothenberg et al., 2015). A phase II double-blind study on dectrekumab (QAX576) aimed to evaluate the effects of the anti–IL-13 mAb (n = 16) compared with placebo (n = 15) on repeated nasal allergen challenge responses in AR patients out of season (Kariyawasam et al., 2009; Nicholson et al., 2011).

A significant decrease in IL-13 levels was observed in patients administered with anti–IL-13 mAb compared with the placebo group after nasal allergen challenge on day 5 and day 7. However, there were no obvious effects of dectrekumab on nasal lavage eosinophil numbers or total nasal symptom scores compared to placebo. Dectrekumab treatment only managed to decrease total nasal symptom scores in a subgroup with high late-phase nasal IL-13 levels. The antibody inhibited nasal IL-13 responses but failed to inhibit nasal symptoms and eosinophils, suggesting that anti-IL-13 is not critical for acute nasal allergic response (Kariyawasam et al., 2009).

Therapeutic antibodies targeting IL-4/IL-13 axis in asthma

Dupilumab as a dual IL-4/IL-13 blockade antibody in AR and asthma

The recent failure of the IL-13 inhibitor tralokinumab to show efficacy in phase III trials of asthma patients underscores the need for other more effective IL-4/IL-13 inhibitors. Dupixent (dupilumab) is a fully human mAb (Macdonald et al., 2014). It is a first-in-class biologic that binds to both monomeric and dimeric human IL-4Rα (type I and type II receptors), with K_D values of 33 pM and 12 pM, respectively, preventing both IL-4- and IL-13-mediated signaling pathways. The antibody has demonstrated clinical benefits for patients with type 2 signature diseases, leading to its approval for the treatment of asthma, chronic sinusitis patients with nasal polyposis, and moderate-to-severe atopic dermatitis (Beck et al., 2014; Blauvelt et al., 2017; Hamilton et al., 2014; Le Floc’h et al., 2020; Rabe et al., 2018; Simpson et al., 2016; Thaci et al., 2016; Wenzel et al., 2013).

In preclinical investigation utilizing primary cell assays and murine model of house dust mite (HDM)–induced asthma, the efficacy of IL-4 vs IL-13 vs IL-4Rα blockers was assessed (Le Floc’h et al., 2020). Dupilumab was responsible to reduce thymus and activation-regulated chemokine (TARC) and IgE levels (i.e., two effector molecules implicated in type 2 diseases), and fully blocked CD23 upregulation on B cells and IL-12p70 secretion from monocyte-derived DCs (Le Floc’h et al., 2020). Dupilumab also suppressed the infiltration of pathogenic cells such as ST2⁺CD4⁺ T cells (i.e., key cells that express the IL-33 receptor, ST2, IL-5 and IL-13 during allergic inflammation) and eosinophils, as well as repressing activated B cells both locally and systemically (Endo et al., 2014; Mato et al., 2017; Wambre et al., 2017). Moreover, dupilumab also inhibited HDM-induced expression of CCL26 (eotaxin 3), CCL2 (MCP-1), IL-6 and goblet cell metaplasia responsible for mucus production (Le Floc’h et al., 2020). Strikingly, treatment of HDM-exposed mice with dupilumab demonstrated an improvement in lung functions (FEV1) (Gandhi et al., 2016; Gandhi, Pirozzi & Graham, 2017).

In clinical trials, dupilumab therapy was able to improve lung functions and reduced levels of Th2-driven inflammatory markers (e.g., TARC, eotaxin-3, and IgE) compared to placebo group in phase II clinical trial of dupilumab in patients with persistent, moderate-to-severe asthma with increased levels of eosinophil (n = 52) (Wenzel et al., 2013). A greater benefit was observed in patients with higher baseline levels of eosinophil in phase III clinical trial (Liberty Asthma QUEST). In the study, moderate-to-severe asthma patients (n = 1,902) were randomly assigned to receive dupilumab (dose of 200 or 300 mg every two weeks) (n = 631) or matched-volume placebos (n = 317) for 52 weeks (Castro et al., 2018). Significantly lower rates of severe asthma exacerbation and improved FEV1 were observed in patients who received dupilumab compared to placebo. Patients with higher baseline levels of eosinophils exhibited better responses in terms of both exacerbations and the FEV1.

In an accompanying trial, assessment of dupilumab efficacy versus placebo was conducted in a phase III trial (LIBERTY ASTHMA VENTURE) in oral glucocorticoid-dependent severe asthma patients (n = 210) (Rabe et al., 2018). Add-on therapy with dupilumab significantly reduced OCS dose used and severe exacerbation rate together with improved FEV1 in the dupilumab group. The first real life cohort study (DUPI-France) (Dupin et al., 2020) on dupilumab in steroid-dependent severe asthmatic patients (n = 64) resulted in improved asthma control, lung functions and reduced oral steroids use. Further improvement in the lung function from these three studies showed a potential effect of dupilumab in airway remodeling. In the most recent phase III clinical trial (TRAVERSE) of dupilumab (Wechsler et al., 2021), the long-term safety and efficacy of dupilumab was assessed in moderate-to-severe or oral corticosteroid-dependent severe asthma (n = 2,282). Long-term safety profile in terms of severe asthma exacerbations and lung functions were achieved. The IL-4/IL-13 axis signaling pathway is summarized in Fig. 1. Schematic representation of the cellular effects of IL-4/IL-13 axis in AR and asthma are summarized in Fig. 2. In addition, completed and ongoing clinical trials of anti-IL-4/IL-13 axis mAbs in AR and asthma patients are presented in Table 1.