Descartes-08 in Autoantibody Myositis

Inclusion Criteria: * Confirmed diagnosis of one of the following: Dermatomyositis (DM): Probability score ≥55% on the 2017 EULAR/ACR (European Alliance of Associations of Rheumatology/ American College of Rheumatology) criteria for classification of dermatomyositis (corresponding to diagnosis of 'probable or definite' DM). OR Antisynthetase Syndrome (ASyS): Diagnosis based on ACR/EULAR Classification Criteria (1)." * Participants must have dermatomyositis or antisynthetase syndrome with muscle and/or skin involvement. * Refractory or intolerance to standard therapy. * Stable background immunosuppressive therapy for ≥8 weeks. * Adequate hematologic, renal, hepatic, and pulmonary function (SpO₂ ≥92% on room air). * Informed consent, compliance with visits, contraception, and vaccinations required. Exclusion Criteria: * Isolated interstitial lung disease (ILD) without muscle or skin involvement * Severe irreversible muscle damage or advanced weakness (e.g., wheelchair-bound). * Interstitial lung disease (ILD) requiring oxygen, severe pulmonary impairment (FVC ≤45%, DLCO ≤40%), or pulmonary hypertension. * Other inflammatory myopathies (PM, IMNM, IBM, cancer- or drug-induced myositis, overlap myositis except Sjögren's). * Other severe neuromuscular, cardiac, pulmonary, or systemic autoimmune diseases requiring immunosuppression. * Significant uncontrolled chronic illnesses or psychiatric conditions interfering with participation. * Pregnancy or lactation. * Recent use of prohibited immunosuppressants/biologics or investigational agents (per washout periods). * Live vaccination within 4 weeks. * History of primary immunodeficiency, organ or bone marrow transplant. * Active or uncontrolled infections: HBV, HCV, HIV, tuberculosis, or recurrent/severe infections.