Inclusion Criteria:
1. Age 18-60 (age ≥18 years at first symptom onset), gender not limited;
2. The diagnosis meets the criteria for IIM according to the 2017 EULAR/ACR criteria and is confirmed to be of the following subtype:
a. Dermatomyositis: i. Presence of Gottron's rash or sunspot rash; ii. At least one serological result is positive: anti-transcriptional mediator (TIF1-gamma/P155) antibody, anti-matrix protein 2 (NXP2/P140) antibody, anti-Mi2 antibody, anti-melanoma differentiation-associated gene 5 (MDA5) antibody, anti-small ubiquitin-like modifier-1 activator (SAE1) antibody and/or SAE2 antibody, anti-histyl-tRNA synthetase (Jo-1) antibody, anti-alanyl-tRNA synthetase (PL-12) antibody, anti-threonyl-tRNA synthetase (PL-7) antibody, anti-glycyl-tRNA synthetase (EJ) antibody, anti-leucyl-tRNA synthetase (0J) antibody; b. Immune-mediated necrotizing myopathy: i. No characteristic skin manifestations of dermatomyositis were observed (i.e. Gottron's rash or sun-facing rash); ii. Muscle weakness characterized by IIM (e.g., symmetrical proximal muscle weakness of the upper/lower limbs; or more pronounced weakness of the neck flexors than the neck extensors; or more pronounced proximal muscle weakness of the lower limbs than distal muscle weakness).
iii. At least one serological result must be positive: anti-human signal recognition particle (SRP) antibody, or trihydroxytrimethylcoenzyme A reductase (HMGCR) antibody; c. Antisynthetic enzyme syndrome: i. At least one of the following clinical manifestations must be present: Raynaud's phenomenon, arthritis, interstitial lung disease, fever (with no other cause of fever found), or technician's hand (thickened and cracked skin on the hands, especially the fingertips).
ii. At least one serological result is positive: anti-histyl-tRNA synthetase (Jo-1) antibody, anti-threonyl-tRNA synthetase (PL-7) antibody, anti-alanyl-tRNA synthetase (PL-12) antibody, anti-glycyl-tRNA synthetase (EJ) antibody, anti-leucyl-tRNA synthetase (OJ) antibody, anti-aspartyl-tRNA synthetase (KS) antibody, anti-phenylalanyl-tRNA synthetase (Zo) antibody, anti-glutamyl-tRNA synthetase (JS) antibody, anti-lysyl-tRNA synthetase (SC) antibody, anti-tyrosyl-tRNA synthetase (YRS) antibody;
3. Refractory IIM: At least one round of high-dose corticosteroid therapy and/or intravenous immunoglobulin, and at least two immunosuppressants (including but not limited to cyclophosphamide, mycophenolate mofetil, tacrolimus, cyclosporine, and azathioprine) have been used in adequate doses for more than 6 months;
4. At the time of enrollment, participants must be receiving background medication at a stable dose, defined as: receiving background therapy with one oral glucocorticoid and/or one immunosuppressant at a stable dose for ≥ 12 weeks;
5. Severity of enrollment met the following criteria:
1. MMT-8 score ≤141 (out of 150);
2. Students must meet at least one of the following CSM numerical scale criteria based on abnormal visual analog scale (VAS) scores: Overall activity assessed by study participants ≥2; overall disease activity assessed by physicians ≥2; extra-muscular activity (MDAAT) ≥2; HAQ-DI ≥0.25;
3. At least one muscle enzyme level \>1.5 times ULN;
6. Through examinations such as tumor markers, lung and abdominal CT scans, thyroid ultrasound, breast ultrasound, and gastroscopy and colonoscopy, possible potential tumors have been ruled out.
Exclusion Criteria:
1. During the screening period, individuals with active viral, bacterial, or other infections requiring systemic treatment are excluded.
2. The presence of a serious, poorly controlled comorbidity that the investigator considers clinically significant, such as (but not limited to) neurological, cardiovascular, renal, hepatic, endocrine, or gastrointestinal disorders;
3. Patients with severe organ dysfunction:
1. The estimated glomerular filtration rate (eGFR) using the MDRD formula is \<40 ml/min/1.73m² ; \[eGFR = 186 × (age) - 0.203 × SCr - 1.154 (mg/dl), for women, the result is multiplied by 0.742\].
2. Study participants with total bilirubin \>1.5 times the upper limit of normal (no specific restrictions are made for liver enzymes because inflammatory myopathy can cause elevated ALT/AST).
3. Cardiovascular: Assessed by echocardiography (ECHO) or cardiac radionuclide angiography (MUGA), with a left ventricular ejection fraction (LVEF) \<50% and oxygen saturation \<94%. Alternatively, patients may have poorly controlled hypertension or other conditions, or have NYHA class III or IV heart failure, myocardial infarction, unstable angina, uncontrolled or symptomatic atrial arrhythmias, any ventricular arrhythmias, or other clinically significant heart disease.
4. Bone marrow function: Absolute neutrophil count (ANC) \<1×10⁹/L; Absolute lymphocyte count (ALC) \<0.1×10⁹/L; Platelet count \<50×10⁹/L; Hemoglobin \<8.0 g/dL;
4. Research participants who have a history of or current malignancy;
5. Infectious diseases: Research participants with active hepatitis B (defined as positive hepatitis B surface antigen or positive hepatitis B core antibody, with hepatitis B virus DNA detection value \>1000 copies/mL) or hepatitis C (HCV RNA positive); research participants with positive HIV antibody or positive treponema pallidum antibody and positive non-treponemal syphilis antibody test; active tuberculosis (negative interferon release; if positive, chest X-ray or CT scan is required to rule out active infection);
6. Central nervous system diseases, including cerebrovascular diseases, epilepsy, etc.;
7. Allergies to components of treatment or pre-conditioning.
8. Those with elective surgery planned during the study period;
9. Those who do not wish to take necessary contraceptive measures during the research period;
10. Any other situation that researchers deem unsuitable for participation in the study including poor compliance and being involved in another clinical study.
