• Age: ≥5 years and \<17 years old

• To meet the diagnostic criteria of JDM, four or five of the following criteria must be met:① symmetrical proximal muscle weakness; ②Characteristic skin changes, including positive dermatitis (purplish red rash on upper eyelid with periorbital edema) and Gottron papules (red patchy squamous papules on the back of knuckles); ③ The level of one muscle enzyme in serum was increased; ④ Positive myositis antibody; ⑤Electromyography shows denervation and myopathy; ⑥ Muscle biopsies showed necrosis and inflammation.

• The classification criteria of RJDM must meet ① and any of the criteria②-④: ① Patients who are intolerant or unresponsive to glucocorticoids and at least 2 immunosuppressants, adequate hormone therapy and duration of at least 6 months; ② The disease progresses rapidly and/or involves organs such as lungs, heart and gastrointestinal tract; ③ Calcification of subcutaneous or muscle and joint tissues; ④ Repeated rashes or skin ulcers.

• myositis specific antibody positive, defined as MDA-5, NXP2, TIF-1γ, Ro-52 and any other positive;

• If the patient has SRP or HMGCR antibody positive immune-mediated necrotizing myopathy equivalent to RJDM, the inclusion criteria of (2) - (4) can be met.

• The functions of important organs are basically normal:

• ① Cardiac function: left ventricular ejection fraction (LVEF) ≥55%, no obvious abnormality in electrocardiogram;

• ② Renal function: eGFR≥30ML/min/1.73m2;

• ③ Liver function: AST and ALT≤3.0 ULN, total bilirubin ≤2.0×ULN;

• ④ Lung function: Lung function is basically normal, SpO2≥92%;

• Have the criteria for simple or intravenous blood collection, and no other contraindications for cell collection;

• The subject of childbearing age has a negative urine pregnancy test result and agrees to take effective contraceptive measures during the test period until 1 year after the infusion;

• The patient or his/her guardian agrees to participate in this clinical trial and signs an informed consent indicating that he/she understands the purpose and procedure of this clinical trial and is willing to participate in the study.