Exploratory Clinical Study on the Safety and Efficacy of Anti- CD19/BCMA CAR-NK Cell Injection for the Treatment of Refractory Pediatric Rheumatic Diseases

Common Inclusion Criteria: 1. . Gender unrestricted, age ≥5 years; 2. . The patient or their legal guardian agrees to participate in this clinical trial and signs the informed consent form, indicating their understanding of the trial's purpose and procedures and willingness to participate; 3. . Peripheral blood B cells confirmed by flow cytometry to express CD19, with a B cell count \>5 cells/uL; 4. . If previously treated with B cell-targeted therapy, peripheral blood B cell count at screening has returned to normal or above the pre-treatment level; 5. . Echocardiography indicates basically normal cardiac structure and left ventricular ejection fraction (LVEF) ≥55%; electrocardiogram shows no significant abnormalities; 6. . Liver function: aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤3.0×ULN, total bilirubin (TBIL) ≤2.0×ULN; 7. . Renal function: estimated glomerular filtration rate (eGFR) ≥30 mL/min/1.73m²; (If eGFR \<30 mL/min/1.73m² and/or undergoing renal replacement therapy, the subject may be considered for enrollment after the investigator's assessment that the benefit outweighs the risk and with full informed consent from the patient/guardian); 8. . Pulmonary function: No severe pulmonary lesions, blood oxygen saturation (SpO₂) ≥92%; 9. . Female subjects of childbearing potential must have a negative urine pregnancy test and agree to use effective contraception during the trial until 1 year after infusion. Polyarticular Juvenile Idiopathic Arthritis (pJIA): 1. . Onset before age 16, disease duration ≥6 weeks, diagnosed as polyarticular JIA according to the 2001 International League of Associations for Rheumatology (ILAR) classification criteria, and positive for rheumatoid factor (RF) and/or anti-citrullinated peptide/protein antibody (ACPA): positive on ≥2 occasions at least 3 months apart during the first 6 months of illness; 2. . Judged by the investigator to have active disease despite adequate standard-dose treatment prior to screening, meeting the following adequacy of treatment conditions: a. Treatment with conventional disease-modifying antirheumatic drugs (DMARDs) for at least 6 months, with stable doses of 2 DMARDs for ≥12 weeks; b. Treatment with at least 2 biologic agents, with stable doses for ≥12 weeks; 3. . Juvenile Arthritis Disease Activity Score-27 (JADAS-27) \>8.5; 4. . Must have at least 5 active joints (defined as the presence of joint swelling; or in the absence of swelling, the presence of limited range of motion accompanied by pain on motion and/or tenderness) as per the American College of Rheumatology (ACR) definition at both screening and baseline; 5. . No occurrence of macrophage activation syndrome within 1 month prior to screening. Sjögren's Syndrome (SS): 1. . Diagnosed with childhood-onset primary SS at least 24 weeks prior to signing the ICF, according to the 2002 American-European Consensus Group (AECG) classification criteria / 2016 EULAR/ACR classification criteria and the 2021 Japanese classification criteria for childhood primary SS; 2. . Meet the classification criteria for SS, and Intolerance or inadequate response to glucocorticoids (prednisone 1-2 mg/kg/day or equivalent doses of other corticosteroids) and at least 2 immunosuppressants, with a duration of glucocorticoid treatment of at least 6 months; 3. . EULAR Sjögren's Syndrome Disease Activity Index (ESSDAI) score ≥5 in at least 1 of the following 8 domains at screening: constitutional, lymphadenopathy, glandular, articular, cutaneous, renal, hematological, and serological; 4. . EULAR Sjögren's Syndrome Patient Reported Index (ESSPRI) score ≥5 at screening; 5. . Positive for anti-SSA/Ro antibody. Juvenile Dermatomyositis (JDM): 6. . Diagnosed with JDM at least 24 weeks prior to signing the ICF according to the 2017 EULAR/ACR classification criteria; 7. . Meet the classification criteria for Refractory JDM (RJDM), and had Intolerance or inadequate response to glucocorticoids (prednisone 1-2 mg/kg/day or equivalent doses of other corticosteroids) and at least 2 immunosuppressants, with a duration of glucocorticoid treatment of at least 6 months; 8. . Patients with anti-synthetase syndrome who are anti-synthetase antibody positive and meet the criteria for RJDM can be directly enrolled; 9. . Patients with immune-mediated necrotizing myopathy who are signal recognition particle (SRP) or 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibody positive and meet the criteria for RJDM can be directly enrolled. Systemic Sclerosis (SSc): 1. . Meet the 2013 ACR/EULAR classification criteria for SSc, with first non-Raynaud's phenomenon occurring at age \<18 years and disease duration ≤60 months; 2. . Positive for antinuclear antibody (ANA) or any SSc-specific antibody; 3. . Modified Rodnan Skin Score (mRSS) ≥15 (total score 51); 4. . Meet the definition of treatment-refractory disease: inadequate response to glucocorticoids (≥0.5 mg/kg/day) and cyclophosphamide and at least 1 other immunomodulatory drug for over 3 months; 5. . Diagnosed with refractory UCTD-ILD: UCTD typically refers to patients with symptoms and signs suggestive of CTD and serologic evidence of autoimmunity, but not fulfilling classification criteria for any defined CTD. Presence of ILD-related clinical manifestations: e.g., dry cough, exertional dyspnea, bibasral crackles, clubbing, OR chest high-resolution CT consistent with ILD features (often symmetric, subpleural), OR pulmonary function tests showing impaired diffusion capacity and restrictive ventilatory defect. All patients must have no improvement in symptoms like dyspnea or cough after at least 1 month of glucocorticoid therapy (prednisone ≥1 mg/kg/day or equivalent). Systemic Lupus Erythematosus (SLE): (1. Diagnosed with childhood-onset SLE according to the 2012 Systemic Lupus International Collaborating Clinics (SLICC) or 2019 EULAR/ACR classification criteria for SLE; (2). Must meet one of the following adequacy of treatm