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 such as presence of at least 1 of the following criteria: abnormal enzyme levels assessed as secondary to IIM, or EMG demonstrating active disease, DM skin rash, muscle biopsy demonstrating active IIM, or MRI demonstrating active inflammation. 4. Participant must meet criteria for severe myositis such as presence of active muscle weakness. 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.