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Background: Eosinophilic chronic rhinosinusitis is an often treatment‐resistant inflammatory disease mediated by type‐2 cytokines, including interleukin (IL)‐5. Mepolizumab, a monoclonal antibody drug targeting IL‐5, has demonstrated efficacy and safety in inflammatory airway disease, but there is negligible evidence on direct tissue response. The study's aim was to determine the local effect of mepolizumab on inflammatory biomarkers in sinonasal tissue of eosinophilic chronic rhinosinusitis patients. Methods: Adult patients with eosinophilic chronic rhinosinusitis received 100mg mepolizumab subcutaneously at four‐weekly intervals for 24 weeks in this prospective phase 2 clinical trial. Tissue eosinophil counts, eosinophil degranulation (assessed as submucosal eosinophil peroxidase deposition by immunohistochemistry) and cytokine levels (measured in homogenates by immunoassay) were evaluated in ethmoid sinus tissue biopsies collected at baseline and at weeks 4, 8, 16 and 24. Results: Twenty patients (47.7 ± 11.7 years, 50% female) were included. Sinonasal tissue eosinophil counts decreased after 24 weeks of treatment with mepolizumab (101.64 ± 93.80 vs 41.74 ± 53.76 cells per 0.1 mm2; p =.035), eosinophil degranulation remained unchanged (5.79 ± 2.08 vs 6.07 ± 1.20, p =.662), and type‐2 cytokine levels increased in sinonasal tissue for IL‐5 (10.84 ± 18.65 vs 63.98 ± 50.66, p =.001), IL‐4 (4.48 ± 3.77 vs 9.38 ± 7.56, p =.004), IL‐13 (4.02 ± 2.57 vs 6.46 ± 3.99, p =.024) and GM‐CSF (1.51 ± 1.74 vs 4.50 ± 2.97, p =.001). Conclusion: Mepolizumab reduced eosinophils in sinonasal tissue, demonstrating that antagonism of IL‐5 suppresses eosinophil trafficking. With reduced tissue eosinophils, a local type‐2 inflammatory feedback loop may occur. The study exposes mechanistic factors which may explain incomplete treatment response. [ABSTRACT FROM AUTHOR]

Background: Monoclonal antibody therapies have a growing role in treating refractory airway disease. Objective: The review aimed to summarize the response of respiratory mucosa to monoclonal antibody treatments in inflammatory airway conditions. Design: We conducted a systematic review including risk of bias assessment. Data sources: MEDLINE, EMBASE and PubMed from 1 January 2000 to 16 November 2019 were searched. Eligibility criteria: Eligible studies assessed the immunological and histological response of airway mucosa to monoclonal antibody therapy compared with baseline or a comparison group in patients with respiratory diseases (asthma, chronic rhinosinusitis and allergic rhinitis). Any prospective interventional studies, including randomized controlled trials (RCTs) and single‐arm trials, were eligible. Results: There were 4195 articles screened, and full‐text analysis produced n = 11 studies with extractable data. Nine were RCTs, and two were single‐arm trials. These studies focused on asthma (n = 9 articles), chronic rhinosinusitis (n = 1) and allergic rhinitis (n = 1). Five monoclonal antibody drugs were assessed (omalizumab, mepolizumab, dupilumab, benralizumab and tralokinumab). Risk of bias was low (n = 6) or unclear (n = 3) in the RCTs and moderate in the single‐arm trials. Omalizumab reduced the mucosal concentration of its target, IgE. Dupilumab reduced the concentration of one of its targets, IL‐13, but not IL‐4. Omalizumab, mepolizumab and benralizumab reduced tissue eosinophil cell density. Dupilumab decreased mucosal eosinophil granule proteins. Tralokinumab did not affect airway mucosa. Conclusions: Knowledge of the expected biological response of monoclonal antibody therapy on biomarkers in disease tissue provides an important supplement to data about clinical outcomes. An understanding of the biological effect is essential to identify likely responders, reasons for treatment failure and necessary adjustments to monoclonal antibody treatment. Further investigation into the effect of monoclonal antibody therapy on disease mucosa and more precise endotyping are required to move closer to achieving personalized medicine. [ABSTRACT FROM AUTHOR]