Effect of tezepelumab on airway inflammatory cells, remodelling, and hyperresponsiveness in patients with moderate-to-severe uncontrolled asthma (CASCADE): a double-blind, randomised, placebo-controlled, phase 2 trial.

Background: Tezepelumab is a human monoclonal antibody that blocks the activity of thymic stromal lymphopoietin (TSLP), an epithelial cell-derived cytokine. In phase 2b and 3 studies, tezepelumab significantly reduced exacerbations versus placebo in patients with severe uncontrolled asthma, irrespective of baseline levels of type 2 inflammatory biomarkers. We investigated the mechanism of action of tezepelumab by assessing its effects on airway inflammatory cells, airway remodelling, and airway hyperresponsiveness.

Methods: CASCADE was an exploratory, double-blind, randomised, placebo-controlled, parallel-group, phase 2 study done in 27 medical centres in Canada, Denmark, Germany, the UK, and the USA. Adults aged 18-75 years with uncontrolled, moderate-to-severe asthma were randomly assigned (1:1) to receive tezepelumab 210 mg or placebo administered subcutaneously every 4 weeks for a planned 28 weeks, extended to up to 52 weeks if COVID-19-related disruption delayed participants' end-of-treatment assessments. Randomisation was balanced and stratified by blood eosinophil count. The primary endpoint was the change from baseline to the end of treatment in the number of airway submucosal inflammatory cells in bronchoscopic biopsy samples. Eosinophils, neutrophils, CD3 T cells, CD4 T cells, tryptase mast cells, and chymase mast cells were evaluated separately. This endpoint was also assessed in subgroups according to baseline type 2 inflammatory biomarker levels, including blood eosinophil count. Airway remodelling was assessed via the secondary endpoints of change from baseline in reticular basement membrane thickness and epithelial integrity (proportions of denuded, damaged, and intact epithelium). Exploratory outcomes included airway hyperresponsiveness to mannitol. All participants who completed at least 20 weeks of study treatment, had an end-of-treatment visit up to 8 weeks after the last dose of study drug, and had evaluable baseline and end-of-treatment bronchoscopies were included in the primary efficacy analysis. All participants who received at least one dose of study drug were included in the safety analyses. This study is registered with ClinicalTrials.gov, NCT03688074.

Findings: Between Nov 2, 2018, and Nov 16, 2020, 250 patients were enrolled, 116 of whom were randomly assigned (59 to tezepelumab, 57 to placebo). 48 in the tezepelumab group and 51 in the placebo group completed the study and were assessed for the primary endpoint. Treatment with tezepelumab resulted in a nominally significantly greater reduction from baseline to the end of treatment in airway submucosal eosinophils versus placebo (ratio of geometric least-squares means 0·15 [95% CI 0·05-0·41]; nominal p<0·0010), with the difference seen across all baseline biomarker subgroups. There were no significant differences between treatment groups in the other cell types evaluated (ratio of geometric least-squares means: neutrophils 1·36 [95% CI 0·94-1·97]; CD3 T cells 1·12 [0·86-1·46]; CD4 T cells 1·18 [0·90-1·55]; tryptase mast cells 0·83 [0·61-1·15]; chymase mast cells 1·19 [0·67-2·10]; all p>0·10). In assessment of secondary endpoints, there were no significant differences between treatment groups in reticular basement membrane thickness and epithelial integrity. In an exploratory analysis, the reduction in airway hyperresponsiveness to mannitol was significantly greater with tezepelumab versus placebo (least-squares mean change from baseline in interpolated or extrapolated provoking dose of mannitol required to induce ≥15% reduction in FEV from baseline: tezepelumab 197·4 mg [95% CI 107·9 to 286·9]; placebo 58·6 mg [-30·1 to 147·33]; difference 138·8 [14·2 to 263·3], nominal p=0·030). Adverse events were reported in 53 (90%) patients in the tezepelumab group and 51 (90%) patients in the placebo group, and there were no safety findings of concern.

Interpretation: The improvements in asthma clinical outcomes observed in previous studies with tezepelumab are probably driven, at least in part, by reductions in eosinophilic airway inflammation, as shown here by reduced airway eosinophil counts regardless of baseline blood eosinophil count. Tezepelumab also reduced airway hyperresponsiveness to mannitol, indicating that TSLP blockade might have additional benefits in asthma beyond reducing type 2 airway inflammation.

Funding: AstraZeneca and Amgen.