Efficacy and Safety of the Anti-mucosal Addressin Cell Adhesion Molecule-1 Antibody Ontamalimab in Patients with Moderate-to-Severe Ulcerative Colitis or Crohn's Disease

Background and Aims: Ontamalimab is a fully human immunoglobulin G2 monoclonal antibody against mucosal addressin cell adhesion molecule-1, developed as treatment for inflammatory bowel disease. Methods: Six phase 3, multicentre, randomised, double-blind, placebo-controlled clinical trials compared efficacy and safety of ontamalimab [25 mg and 75 mg once every 4 weeks] with placebo in patients with moderate-to-severe ulcerative colitis or Crohn's disease [two induction studies and one re-randomised maintenance study per condition]. This clinical trial programme was discontinued in 2020 for reasons unrelated to drug safety/efficacy; Crohn's disease studies are described in the Supplementary data. Results: The induction [12-week] and maintenance [52-week] studies included 659 and 366 randomised patients, respectively. More patients who received ontamalimab induction than placebo achieved the primary endpoint of clinical remission at Week 12 [25 mg, 18.5% vs 15.8%, p=0.617, 27.0% vs 12.5%, p=0.027; 75 mg, 29.8% vs 15.8%, p=0.018, 29.5% vs 12.5% p=0.014]; significantly more patients who received ontamalimab maintenance therapy than placebo achieved Week 52 clinical remission [25 mg, 53.5% vs 8.2%, p<0.001; 75 mg, 40.2% vs 12.8%, p<0.001]. Endoscopic improvement was generally significantly different vs placebo [induction: 25 mg, 27.8% vs 21.1%, p=0.253, 35.1% vs 12.5%, p=0.001; 75 mg, 41.1% vs 21.1%, p=0.002, 33.9% vs 12.5%, p=0.003; maintenance: 25 mg, 56.3% vs 9.6%, p<0.001; 75 mg, 48.8% vs 15.1%, p<0.001]. Adverse event rates were similar between ontamalimab and placebo groups. Conclusions: Ontamalimab 75 mg was effective, with no safety concerns, as induction and maintenance therapy for patients with moderate-to-severe ulcerative colitis.