A Study of Imvotamab in Active, Refractory Idiopathic Inflammatory Myopathies

Key Inclusion Criteria: * Age ≥ 18 years at the time of signing ICF * Diagnosis of probable or definite IIM according to the 2017 European League Against Rheumatism (EULAR)/American College of Rheumatology (ACR) classification criteria for IIM with subgroup classification of either DM, polymyositis (PM), anti-synthetase syndrome, or immune-mediated necrotizing myositis (IMNM). * Active IIM despite treatment with corticosteroids and at least 1 immunosuppressive or immunomodulatory standard-of-care agent determined at the discretion of the investigator after at least 3 months of treatment. * If using oral corticosteroids (OCS), must be on a stable dose equivalent to ≤ 30 mg/day of prednisone for at least 4 weeks prior to first study treatment Key Exclusion Criteria: * Pregnant or breastfeeding or intending to become pregnant during the study or within 3 months after the final dose of imvotamab. * Receipt of an investigational therapy less than 12 weeks or 5 drug-elimination half-lives (whichever is longer) prior to first administration of study treatment and during the study. * Has inclusion body myositis or myositis-associated with other connective tissue disease.