• Age ≥5 years old.

• To meet the diagnostic criteria of refractory B-cell-related pediatric rheumatic diseases, including but not limited to juvenile dermatomyositis, polyarticular juvenile idiopathic arthritis, systemic sclerosis, and primary Sjogren's syndrome.

‣ Diagnosed as juvenile dermatomyositis(JDM) according to the criteria of Bohan and Peter, and meeting the following conditions:

• The classification criteria of RJDM must meet (1) and any one of (2)-(5): (1) Patients who are intolerant or unresponsive to glucocorticoids and at least 2 immunosuppressants, and the duration of adequate hormone therapy should be 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; (5) Repeated or persistent myasthenia(muscle MRI indicates extensive, diffuse edema or the Childhood Myositis Assessment Scale(CMAS) should be less than 48 points, and at least two of the following five core measurement indicators should have abnormal results: Physician Global Assessment(PhGA) ≥2cm, Patient Global Assessment(PtGA) ≥2cm, Disease Activity Score(DAS) ≥2 points, Childhood Health Assessment Questionnaire(C-HAQ) ≥0.25 points, muscle enzyme level \> 1.5×upper limit of normal);

∙ RJDM with anti-synthetase syndrome who are positive for anti-synthetase antibody and those with immune-mediated necrotizing myopathy who are positive for SRP or HMGCR antibody can be included.

⁃ Meet the classification criteria for polyarticular juvenile idiopathic arthritis as defined by the International League of Associations for Rheumatology(ILAR) classification in 2001, and meeting the following conditions: After at least 6 months of traditional DMARDS treatment and at least one stable dose of DMARDS or biologic agent for ≥12 weeks, the disease is still active, that is, there are at least 2 active joints (defined as swollen joints; if there is no swelling, there must be limited passive range of motion, accompanied by pain during movement or joint tenderness).

⁃ Meet the classification criteria for Systemic sclerosis (SSc) as defined by the 2013ACR/EULAR standards, and meeting the following conditions:

• Meet the definition of intractable disease: Glucocorticoids (≥0.5mg/kg/d) and cyclophosphamide, as well as one or more of the following immunomodulators (including antimalarial drugs, azathioprine,mycophenolate mofetil, methotrexate, leflunomide, tacrolimus, cyclosporine, and biologics including rituximab, beliumab, and telitacicept, etc.), did not show significant remission of the disease for more than 3 months; Or meet the criteria for rapid disease progression , clinical routine treatment is ineffective, and the benefits outweigh the risks as determined by the investigator and the patient's or guardian's full and informed consent can be considered for inclusion;

∙ Modified Rodnan Skin Score (mRSS) ≥15 points (total 51 points).

⁃ Meet the classification criteria for primary Sjogren's syndrome as defined by the 2002 ACEG classification criteria /2016 EULAR/ACR classification criteria, and meeting the following conditions:

• Meet (1) and any one of (2)-(6): (1) For those who are intolerant or have an insufficient response to glucocorticoid (prednisone 1-2 mg/kg/d or an equivalent dose of other hormones) and at least two immunosuppressants, the duration of hormone treatment should be at least 6 months; (2) The disease progresses rapidly and/or involves organs such as the kidneys, nervous system, and lungs; (3) Repeated parotid gland swelling or repeated parotitis; (4) Recurrent rashes or skin ulcers; (5) Involvement of the blood system, repeated leukopenia, anemia or thrombocytopenia; (6) cryoglobulinemia;

∙ Positive for anti-SSA /Ro antibody;

∙ ESSDAI score ≥5 points or clinESSDAI score ≥5 points.

• Positive expression of CD19 in peripheral blood B cells determined by flow cytometry, and B cells \> 5 per/uL.

• Previously not treated with CAR-T; or recurrence or poor efficacy after previous autologous or universal CD19-targeted CAR-T treatment (evaluated by the researcher).

• The functions of important organs are basically normal:

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

⁃ Renal function: eGFR≥30mL/min/1.73m2;

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

⁃ Lung function: SpO2≥92%.

• Meet standards for leukapheresis or intravenous blood collection, and no other contraindications for leukapheresis.

• 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.