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 stranded DNA antibody level above the laboratory normal reference range (excluding borderline values); or anti-Sm antibody level above the laboratory normal reference range. BILAG score showing Grade A involvement in ≥1 organ system, or Grade B involvement in ≥2 organ systems at both screening and baseline visits. SLEDAI-2000 score ≥ 8 at both screening and baseline visits. Insufficient clinical response following adequate standard-dose glucocorticoids, antimalarials, immunosuppressants, and at least one biological agent administered in combination or sequentially for ≥ 3 months prior to screening. 18. Subjects receiving hematopoietic growth factor supportive therapy, including erythropoietin (EPO), granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF) and thrombopoietin (TPO), must have an interval of at least 2 weeks between the last dose of growth factor therapy and screening assessments.For subjects receiving blood product transfusions: platelet assessments at screening shall be separated by at least 1 week from the last platelet transfusion; hemoglobin assessments at screening shall be separated by at least 2 weeks from the last red blood cell transfusion. Systemic Sclerosis (SSc) 19. Meet the 2013 ACR/EULAR classification criteria for systemic sclerosis, with disease duration ≤ 60 months. 20. Positive for antinuclear antibody (ANA) or any SSc-specific autoantibody. 21. Modified Rodnan Skin Score (mRSS) ≥ 15 (full score: 51). 22. Meet the definition of refractory disease: * Significant progressive involvement of skin and visceral organs; ② No obvious disease remission after more than 3 months of combined or sequential treatment with glucocorticoids and/or cyclophosphamide, plus one or more immunomodulatory agents including but not limited to antimalarials, azathioprine, mycophenolate mofetil, methotrexate, leflunomide, tacrolimus, ciclosporin, and biological agents such as rituximab, belimumab, telitacicept.Alternatively, subjects meeting criteria for rapidly progressive disease with no response to conventional standard clinical therapy may be enrolled if the investigator determines that clinical benefits outweigh risks and full informed consent is obtained from the subject or legal guardian. Exclusion Criteria: * Common Exclusion Criteria 1. History of malignant tumors (excluding cured and completely resected basal cell carcinoma, squamous cell skin carcinoma or cervical carcinoma in situ with a disease-free interval of at least 5 years post resection), or concurrent malignant tumors. 2. Complicated severe pulmonary diseases, including pulmonary hypertension graded ≥ Grade 3 per WHO functional classification, requirement for oxygen therapy via oxygen reservoir mask, non-invasive or invasive mechanical ventilation support at screening. 3. Known allergy, hypersensitivity, intolerance or contraindication to CD19/BCMA CAR-NK cells or any investigational medicinal ingredients (including fludarabine, cyclophosphamide and tocilizumab), or history of severe anaphylactic reactions. 4. Evidence of severe active viral, bacterial infection or uncontrolled systemic fungal infection at screening or baseline visit. 5. Cardiac insufficiency classified as NYHA Class Ⅲ or Ⅳ according to New York Heart Association criteria (see Appendix). 6. Congenital heart disease prior to screening, history of acute myocardial infarction within 6 months, severe arrhythmia (including multifocal frequent supraventricular tachycardia, ventricular tachycardia, etc.), moderate to massive pericardial effusion, severe myocarditis; unstable vital signs requiring vasopressor support. 7. Active or uncontrolled infection requiring parenteral antimicrobial therapy at screening or baseline visit. 8. Positive hepatitis B surface antigen (HBsAg) or hepatitis B core antibody (HBcAb) with peripheral HBV DNA level above upper limit of normal; positive HCV antibody with peripheral HCV RNA level above upper limit of normal; positive HIV antibody, positive syphilis serology, or positive cytomegalovirus (CMV) DNA. 9. History of severe herpes infection such as herpes encephalitis, ocular herpes or disseminated herpes; signs of herpes or varicella-zoster virus infection (particularly varicella and herpes zoster) within 12 weeks prior to screening. 10. Active tuberculosis, history of active tuberculosis, or negative interferon-gamma release assay for tuberculosis infection not achieved during screening period. 11. History of epilepsy or other active central nervous system disorders. 12. Subjects with acquired or congenital immunodeficiency diseases. 13. Any clinically significant cardiac, endocrine, hematological, hepatic, immune, metabolic, urinary, pulmonary, neurological, dermatological, psychiatric, renal disorders or major medical history that may interfere with KN3601 administration, as judged by the investigator. 14. Solid organ transplantation or hematopoietic stem cell transplantation within 3 months prior to screening; acute graft-versus-host disease (GVHD) Grade ≥2 within 2 weeks prior to screening. 15. Administration of live vaccines within 4 weeks prior to screening. 16. Receipt of the following treatments within specified time windows before baseline visit: B-cell depleting therapy within 26 weeks Anti-CD40 monoclonal antibody, belimumab, abatacept, anti-tumor necrosis factor-α biologics, immunoglobulin therapy or plasma exchange within 24 weeks JAK inhibitors or other kinase inhibitors within 12 weeks, unless explicitly permitted by the protocol Traditional Chinese medicines and proprietary Chinese medicines for Sjögren's disease within 4 weeks (including Tripterygium wilfordii, Tripterygium hypoglaucum, Tripterygium hypoglaucum root, Paeonia lactiflora, and preparations/supplements containing the above ingredients) Prior treatments within 3 elimination half-lives, 4 weeks, or ongoing pharmacodynamic effect, whichever is longer Post prior B-cell depleting therapy with B lymphocyte count below lower limit of normal or baseline value, whichever is lower 17. Participation in other clinical trials within 3 months, excluding subjects confirmed not to receive investigational drugs or devices. 18. Any conditions that, in the investigator's opinion, may elevate subject risk or confound trial outcomes. Specific Exclusion Criteria Relapsed/Refractory Rheumatoid Arthritis (RA) 19. ACR functional class Grade 4 for rheumatoid arthritis. Dermatomyositis (DM) 20. Paraneoplastic myositis, defined as myositis diagnosed within 2 years following cancer diagnosis, or subjects categorized as high-risk for malignancy. 21. Subjects with overlap syndrome (excluding overlap with Sjögren's syndrome), connective tissue disease-associated DM other than primary DM, inclusion body myositis, polymyositis, or drug-induced myopathy. 22. Subjects with severe systemic musculoskeletal disorders other than DM, which interfere with adequate investigator assessment of disease activity. Systemic Lupus Erythematosus (SLE) 23. Renal pathological diagnosis of Class V lupus nephritis (excluding Class III or IV lupus nephritis complicated with Class V lupus nephritis); active nephritis requiring treatment with protocol-prohibited medications, or requirement for hemodialysis. Systemic Sclerosis (SSc) 24. Concurrent rheumatic autoimmune diseases other than SSc, including but not limited to rheumatoid arthritis, systemic lupus erythematosus, mixed connective tissue disease, polymyositis and dermatomyositis, as determined by the investigator.Note: Subjects with fibromyalgia, secondary Sjögren's syndrome, and scleroderma-associated myopathy at screening will not be excluded. 25. Non-SSc cutaneous lesions that impair accurate investigator evaluation of disease activity. 26. History of scleroderma renal crisis occurring within 2 years prior to screening visit.