Phase 2 Study of Rapcabtagene Autoleucel in Myositis

Key Inclusion Criteria: 1. Men and women, aged ≥ 18 and ≤75 years, with a diagnosis of probable or definite myositis according to American College of Rheumatology/European League Against Rheumatism 2017 (ACR/EULAR 2017) criteria 2. Participants who had inadequate response to prior therapy 3. Diagnosed with active disease 4. Participant must meet criteria for severe myositis Key Exclusion Criteria: 1. Any condition during Screening that could prevent a complete washout of medications or could otherwise make the participant ineligible for anti-CD19 CAR-T therapy and further participation in the study 2. BMI at Screening of ≤17 or ≥40 kg/m2 3. Severe muscle damage at Screening 4. Inadequate organ function 5. Hypersensitivity and/or contraindications to any product (including its ingredients) to be given to the participant as per the study protocol 6. Other inflammatory and non-inflammatory myopathies 7. Any medical conditions that are not related to IIM that would jeopardize the ability of the participant to tolerate CD19 CAR-T cell therapy Other protocol-defined inclusion/exclusion criteria may apply.