From the Allergic Cascade to the Epithelium-Driven Disease: The Long Road of Bronchial Asthma

The Direct and Indirect Role of IgE on Airway Epithelium in Asthma

Asthma is a chronic airway inflammatory disorder, affecting over 350 million people worldwide, with allergic asthma being the most common form of the disease. Allergic asthma is characterized by a type 2 (T2) inflammatory response triggered by numerous allergens beginning in the airway epithelium, which acts as a physical barrier to allergens as well as other external irritants including infectious agents, and atmospheric pollutants. T2 inflammation is propagated by several key cell types including T helper 2 (Th2) cells, eosinophils, mast cells, and B cells. Immunoglobulin E (IgE), produced by B cells, is a key molecule in allergic airway disease and plays an important role in T2 inflammation, as well as being central to remodeling processes within the airway epithelium. Blocking IgE with omalizumab has been shown to be efficacious in treating allergic asthma however, the role of IgE on airway epithelial cells is less communicated. Developing a deeper explanation of the complex network of interactions between IgE and the airway epithelium will facilitate an improved understanding of asthma pathophysiology. This review discusses the indirect and direct roles of IgE on airway epithelial cells, with a focus on allergic asthma disease.

Tezepelumab in patients with allergic and eosinophilic asthma

Asthma is a heterogeneous disease commonly driven by allergic and/or eosinophilic inflammation, both of which may be present in severe disease. Most approved biologics for severe asthma are indicated for specific phenotypes and target individual downstream type 2 components of the inflammatory cascade. Tezepelumab, a human monoclonal antibody (immunoglobulin G2λ), binds specifically to thymic stromal lymphopoietin (TSLP), an epithelial cytokine that initiates and sustains allergic and eosinophilic inflammation in asthma. By blocking TSLP, tezepelumab has demonstrated efficacy across known asthma phenotypes and acts upstream of all current clinically used biomarkers. In a pooled analysis of the phase 2b PATHWAY (NCT02054130) and phase 3 NAVIGATOR (NCT03347279) studies, compared with placebo, tezepelumab reduced the annualized asthma exacerbation rate over 52 weeks by 62% (95% confidence interval [CI]: 53, 70) in patients with perennial aeroallergen sensitization (allergic asthma); by 71% (95% CI: 62, 78) in patients with a baseline blood eosinophil count ≥300 cells/μL; and by 71% (95% CI: 59, 79) in patients with allergic asthma and a baseline blood eosinophil count ≥300 cells/μL. This review examines the efficacy and mode of action of tezepelumab in patients with allergic asthma, eosinophilic asthma and coexisting allergic and eosinophilic phenotypes.

The Incredible Adventure of Omalizumab

The basis of our current understanding of allergies begins with the discovery of IgE in the mid-1960s. The whole theory of the physiology and pathophysiology of allergic diseases, including rhinitis and asthma, dates from that period. Among the key regions of IgE identified were the FAB (fragment antigen binding) portion that has the ability to capture allergens, and the Cε3 domain, through which IgE binds to its membrane receptor. It was then postulated that blocking IgE at the level of the Cε3 domain would prevent it from binding to its receptor and thus set in motion the allergic cascade. This was the beginning of the development of omalizumab, a monoclonal antibody with an anti-IgE effect. In this article, we review the pathophysiology of allergic disease and trace the clinical development of omalizumab. We also review the benefits of omalizumab treatment that are apparently unrelated to allergies, such as its effect on immunity and bronchial remodeling.

Omalizumab in Severe Asthma: Effect on Oral Corticosteroid Exposure and Remodeling. A Randomized Open-Label Parallel Study

INTRODUCTION

Data on the clinical efficacy and remodeling of omalizumab therapy in patients on oral corticosteroids (OC) are limited.

OBJECTIVE

The purpose of the study is to show that in patients with corticosteroid-dependent asthma, omalizumab is a corticosteroid-sparing therapy able to inhibit airway remodeling and to reduce disease burden (lung function impairment, exacerbations).

METHODS

This study is a randomised open-label study evaluating the addition of omalizumab to the standard of care in patients with severe asthma receiving oral corticosteroids. The primary endpoint was represented by the change in OC monthly dose by the end of treatment and secondary endpoints included spirometry changes, airway inflammation (FeNO), number of exacerbations and airways remodelling assessed by bronchial biopsies studied by transmission electron microscopy. As a safety variable, adverse effects were recorded.

RESULTS

Efficacy was assessed for 16 patients in the omalizumab group and 13 in the control group. The final cumulative mean monthly OC doses were 34.7 mg and 217 mg for the omalizumab and control group, respectively; the mean difference between groups adjusted for baseline was -148.1 [95% confidence interval (CI) -243.6, -52.5; p = 0.004]. OC withdrawal of 75% versus 7.7% (p = 0.001) was observed in the omalizumab and control group, respectively. Omalizumab provided a slowing of forced expiratory volume in one second (FEV₁) loss (70 mL versus 260 mL), a significant decrease in FeNO values and a reduction in the annual relative risk of clinically significant exacerbations of 54%. The treatment was well tolerated. The morphological study showed a significant decrease in basement membrane thickness in the omalizumab group (6.7 µm versus 4.6 µm) compared with controls (6.9 µm versus 7 µm) [mean difference between groups adjusted for baseline was -2.4 (95% CI -3.7, -1.2; p < 0.001], as well as a decrease in intercellular spaces (1.18 µm versus 0.62 µm and 1.21 µm versus 1.20 µm, p = 0.011, respectively). A qualitative improvement was also observed in the treated group.

CONCLUSIONS

Omalizumab showed a marked OC-sparing capacity and was associated with an improvement in clinical management that correlated with bronchial epithelial repair. In OC-dependent asthma, reversibility of remodelling is possible; the concepts that basement membrane enlargement is detrimental and that chronic airway obstruction is systematically irreversible are outdated (EudraCT: 2009-010914-31).