Exploratory Clinical Study of Anti-CD19/BCMA Universal CAR-T Cell Injection for the Treatment of Refractory Autoimmune Diseases

Inclusion Criteria: * Common Inclusion Criteria 1. Voluntarily sign an informed consent form, understand the study, and be willing and capable of completing all trial procedures. 2. Aged 18 to 70 years, regardless of gender. 3. At screening, the number of peripheral blood CD19-positive B cells determined by flow cytometry \> 5 cells/μL. 4. For subjects previously treated with B-cell targeted therapy, peripheral blood B cell counts have returned to normal or above pre-treatment levels at the screening visit. 5. Complete blood counts within 7 days prior to lymphodepleting chemotherapy meet the following requirements in patients with Sjögren's disease (SjD): Absolute neutrophil count (ANC) ≥ 1.5×10⁹/L Hemoglobin (Hb) ≥ 80 g/L Platelet count (PLT) ≥ 50×10⁹/L 6. Subjects have adequate hepatic, renal, pulmonary and cardiac function at screening visit, defined as: Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) ≤ 2.5 × upper limit of normal (ULN) Total bilirubin (TBIL) ≤ 1.5 × ULN; except for patients with Gilbert syndrome, whose TBIL must be ≤ 3.0 × ULN Renal function: estimated glomerular filtration rate (eGFR) ≥ 30 mL/min/1.73m². Subjects with eGFR \< 30 mL/min/1.73m² and/or receiving renal replacement therapy may be enrolled if the investigator assesses benefits outweigh risks and full informed consent is obtained from the subject or guardian. Peripheral oxygen saturation (SpO₂) ≥ 92% under room air without oxygen supplementation; no clinically significant pleural effusion (excluding that related to the target indication). Left ventricular ejection fraction (LVEF) ≥ 50%; no pericardial effusion confirmed by echocardiography (excluding indication-related effusion); no clinically significant abnormalities on electrocardiogram (ECG). 7. During the screening period, serum pregnancy test must be negative for fertile female subjects. Females who have undergone surgical sterilization or natural menopause for at least 2 years are considered non-fertile. Fertile female and male subjects must adopt highly effective contraceptive methods throughout the clinical study and for 1 year after the last study treatment. They shall also agree not to donate oocytes or sperm for assisted reproductive technology within 1 year following the final study treatment. Specific Inclusion Criteria Relapsed/Refractory Rheumatoid Arthritis (RA) 8. Meet the 2010 ACR/EULAR classification diagnostic criteria, diagnosed with moderate to severe active rheumatoid arthritis, with a confirmed RA diagnosis for ≥ 6 months. 9. Swollen joint count ≥ 6 (based on 66-joint assessment) and tender joint count ≥ 6 (based on 68-joint assessment) at screening. 10. C-reactive protein (CRP) ≥ 10 mg/L or erythrocyte sedimentation rate (ESR) ≥ 28 mm/h at screening. 11. Definition of EULAR refractory rheumatoid arthritis: Treatment failure: Patients received treatment in accordance with EULAR recommended guidelines, and failed to respond to ≥ 2 biological/targeted synthetic disease-modifying antirheumatic drugs (b/tsDMARDs) following failure of conventional synthetic DMARDs (csDMARDs). ① Exclusions: Treatment access restricted to bDMARDs/tsDMARDs due to socioeconomic factors. ② If csDMARDs are contraindicated, treatment failure with ≥ 2 b/tsDMARDs with distinct mechanisms of action also qualifies. Both patients and physicians acknowledge persistent difficulties in managing RA symptoms. Presence of at least one of the following five indicators suggestive of active or progressive disease: 1. Moderate or higher disease activity (DAS28-ESR \> 3.2 or CDAI \> 10); 2. Clinical signs and/or symptoms indicative of active disease; 3. Inability to taper glucocorticoids to ≤ 7.5 mg/day prednisone or equivalent dose; 4. Rapid radiographic progression (increase in modified van der Heijde Sharp score ≥ 5 points within 1 year); 5. Impaired quality of life secondary to RA, despite seemingly adequate disease control. Dermatomyositis (DM) 12. Diagnosed with Dermatomyositis (DM) in accordance with the 2017 EULAR/ACR criteria for at least 24 weeks prior to informed consent (ICF) signing. 13. Meet the classification criteria for refractory DM, and satisfy criterion ① plus any one of criteria ②-⑤:① Insufficient response to glucocorticoids (prednisone 1-2 mg/kg/day or equivalent dose of other corticosteroids) combined or sequential treatment with at least two immunosuppressants, with glucocorticoid treatment lasting for no less than 3 months;② Rapid disease progression, and/or involvement of extrapulmonary organs including the heart and gastrointestinal tract, and/or significant interstitial lung disease;③ Calcification in subcutaneous, muscular and articular tissues;④ Recurrent rashes or cutaneous ulcers;⑤ Recurrent or persistent muscle weakness. MRI shows extensive diffuse muscle edema during the disease course, or CMAS score \< 48. At least two abnormal results among the five core parameters: Physician Global Assessment (PhGA) ≥ 2 cm, Patient Global Assessment (PtGA) ≥ 2 cm, Manual Muscle Test MDAAT ≥ 2, Health Assessment Questionnaire (HAQ) total score ≥ 0.25, muscle enzyme levels \> 1.5 × upper limit of normal (ULN). 14. Patients with anti-synthetase syndrome and positive anti-synthetase antibodies meet DM criteria and may be enrolled directly. 15. Patients with immune-mediated necrotizing myopathy positive for SRP or HMGCR antibodies meet DM criteria and may be enrolled directly. Systemic Lupus Erythematosus (SLE) 16. Diagnosed with adult systemic lupus erythematosus (SLE) in accordance with the 2019 EULAR/ACR SLE classification criteria for at least 12 weeks prior to signing the informed consent form (ICF). 17. Subjects with moderate to severe refractory SLE shall meet all of the following criteria: Positive antinuclear antibody (ANA) with a titer \>1:80 at screening visit; or anti-double