A Phase 2 Proof of Concept Study to Evaluate the Efficacy and Safety of Daxdilimab in Participants With Dermatomyositis (DM) or Anti-synthetase Inflammatory Myositis (ASIM)

The study will enroll 96 participants with 2 idiopathic inflammatory myositis populations: - Population 1 or dermatomyositis (DM): participants with DM with definite or probable myositis according to the American College of Rheumatology/European League Against Rheumatism 2017 (ACR/EULAR 2017) criteria and a DM rash. - Population 2 or anti-synthetase inflammatory myositis (ASIM): participants with ASIM with definite or probable myositis according to ACR/EULAR 2017 criteria and a positive ASIM associated antibody. Participants will be randomized by population in a 1:1 ratio and receive investigational product (IP) daxdilimab or placebo by subcutaneous injection. The estimated total study duration will be up to 60 weeks. Acquired from Horizon in 2024.