Mepolizumab for treatment of adolescents and adults with eosinophilic oesophagitis: a multicentre, randomised, double-blind, placebo-controlled clinical trial

Objective We aimed to determine whether mepolizumab, an anti-IL- 5 antibody, was more effective than placebo for improving dysphagia symptoms and decreasing oesophageal eosinophil counts in eosinophilic oesophagitis (EoE). Methods We conducted a multicentre, randomised, double-blind, placebo-controlled, trial. In the first part, patients aged 16-75 with EoE and dysphagia symptoms (per EoE Symptom Activity Index (EEsAI)) were randomised 1:1 to 3 months of mepolizumab 300 mg monthly or placebo. Primary outcome was change in EEsAI from baseline to month 3 (M3). Secondary outcomes included histological, endoscopic and safety metrics. In part 2, patients initially randomised to mepolizumab continued 300 mg monthly for 3 additional months (mepo/mepo), placebo patients started mepolizumab 100 mg monthly (pbo/mepo), and outcomes were reassessed at month 6 (M6). Results Of 66 patients randomised, 64 completed M3, and 56 completed M6. At M3, EEsAI decreased 15.4 +/- 18.1 with mepolizumab and 8.3 +/- 18.0 with placebo (p=0.14). Peak eosinophil counts decreased more with mepolizumab (113 +/- 77 to 36 +/- 43) than placebo (146 +/- 94 to 160 +/- 133) (p<0.001). With mepolizumab, 42% and 34% achieved histological responses of <15 and =6 eos/hpf compared with 3% and 3% with placebo (p<0.001 and 0.02). The change in EoE Endoscopic Reference Score at M3 was also larger with mepolizumab. At M6, EEsAI decreased 18.3 +/- 18.1 points for mepo/mepo and 18.6 +/- 19.2 for pbo/mepo (p=0.85). The most common adverse events were injection-site reactions. Conclusions Mepolizumab did not achieve the primary endpoint of improving dysphagia symptoms compared with placebo. While eosinophil counts and endoscopic severity improved with mepolizumab at 3 months, longer treatment did not yield additional improvement.