INCLUSION CRITERIA

1. Confirmed diagnosis of one of the following:

a. Dermatomyositis (DM): Probability score of at least 55% under the 2017 EULAR/ACR classification criteria, corresponding to probable or definite DM.

b. Antisynthetase syndrome (ASyS): Diagnosis based on ACR/EULAR classification criteria.

1. Dermatomyositis or antisynthetase syndrome with muscle and/or skin involvement.

1. Disease refractory to standard therapy or intolerance to standard therapy.

1. Stable background immunosuppressive therapy for at least 8 weeks.

1. Adequate hematologic, renal, hepatic, and pulmonary function, including oxygen saturation (SpO2) of at least 92% on room air.

1. Able to provide informed consent and comply with study visits, contraception requirements, and vaccination requirements.

EXCLUSION CRITERIA

1. Isolated interstitial lung disease (ILD) without muscle or skin involvement.

1. Severe irreversible muscle damage or advanced weakness, such as being wheelchair-bound.

1. Interstitial lung disease requiring oxygen, severe pulmonary impairment (FVC of 45% or less or DLCO of 40% or less), or pulmonary hypertension.

1. Other inflammatory myopathies, including polymyositis (PM), immune-mediated necrotizing myopathy (IMNM), inclusion body myositis (IBM), cancer-induced or drug-induced myositis, or overlap myositis other than Sjogren's.

1. Other severe neuromuscular, cardiac, pulmonary, or systemic autoimmune diseases requiring immunosuppression.

1. Significant uncontrolled chronic illnesses or psychiatric conditions that interfere with study participation.

1. Pregnancy or lactation.

1. Recent use of prohibited immunosuppressants, biologics, or investigational agents within the applicable protocol-defined washout periods.

1. Live vaccination within 4 weeks.

1. History of primary immunodeficiency, organ transplant, or bone marrow transplant.

1. Active or uncontrolled infections, including hepatitis B (HBV), hepatitis C (HCV), HIV, or tuberculosis, or recurrent/severe infections.