Inclusion Criteria:
1. Aged 18-75 years;
2. Diagnosed with SLE for ≥12 weeks prior to screening, met the 2019 ACR/EULAR diagnostic criteria for SLE screening period;
3. SELENA-SLEDAI ≥8 at screening;
4. Positive immunological markers within 12 months prior to baseline;
5. Currently receiving ≥1 stable doses of standard treatment: oral corticosteroids, antimalarials, or conventional immunosuppressive drugs;
6. All male participants or females of reproductive potential must agree to use reliable contraception with their partner from signing the ICF through 5 months after the last dose of the study drug
7. Understanding of the study procedures and voluntary signing of the informed consent form
Exclusion Criteria:
1. Severe active or unstable lupus-related neuropsychiatric disorders;
2. Combined with active infections, malignant tumors, or other autoimmune diseases;
3. Catastrophic antiphospholipid syndrome;
4. severe lupus nephritis;
5. Study participants who received a live or attenuated vaccine within 28 days prior to baseline or during the screening period;
6. Received any investigational treatment within 30 days prior to baseline or within 5 half-lives of the investigational drug (whichever is longer);
7. Patients at high risk of severe clinical bleeding, or those requiring plasma transfusion, intravenous immunoglobulin, or acute blood products;;
8. Patients who experienced any of the following cardiovascular or cerebrovascular events within 24 weeks prior to baseline: myocardial infarction, unstable angina, ventricular arrhythmia, New York Heart Association (NYHA) Class II or higher heart failure, stroke, etc.;
9. In accordance with the protocol requirements, participants with abnormal laboratory test results;
10. Participants with positive results of viral serology, including Treponema pallidum, HIV, HCV, and HBV;
11. participants with a history of tuberculosis or latent tuberculosis infection;
12. Diagnosed with type 1 or type 2 diabetes with poor control;
13. Uncontrolled hypertension;
14. Intolerance to the study drug or contraindications, including a history of severe allergic reactions to monoclonal antibodies or any component of SCTC21C injection;
15. Required hospitalization for major surgery within 4 weeks prior to screening or within 12 weeks post-study drug administration;
16. History of solid organ or hematopoietic stem cell/bone marrow transplant, or expected to undergo transplant surgery during the study;
17. Pregnant or breastfeeding;
18. Any other condition that the investigator deems unsuitable for participation in the study
