A Prospective, Single Arm, Open Label, Proof of Concept Clinical Study of Sulfasalazine in the Treatment of Active Systemic Lupus Erythematosus

Inclusion Criteria: * Clinical diagnosis of SLE according to the 2012 SLICC SLE classification criteria. * 18 to 65 years old, regardless of gender. * Active SLE, i.e. SLEDAI-2K score ≥ 4 points at enrollment. * Receiving standard of care: 1. Prednisone dosage≤20mg/day, with or without hydroxychloroquine (HCQ,≤400mg/day), classic immunosuppressive agents (IS),ie, mycophenolate mofetil(≤2.0g/day), azathioprine (≤2mg/kg/day), cyclosporine(≤5.0mg/kg/day), tacrolimus(≤3.0mg/day), methotrexate(≤20mg/week), leflunomide(≤40mg/day), or biological agents such as belimumab(≤ 10mg/kg/month) and telitacicept (≤160mg/week); 2. No more than three types of combined classic IS or biological agents, not including HCQ. 3. Prednisone dosage should NOT be increased within one month of the screening period, and the immunosuppressants regimen should be stable for at least one month. * Agree to sign the informed consent form. * Agree to receive contraception through intrauterine devices or oral contraceptives (progesterone or compound progesterone) or condoms. Exclusion Criteria: * Severely active SLE: SLEDAI-2K \>12 at screening. * 24-hour urine protein≥ 3g/24 hours. * eGFR \< 60mL/min/1.73m2 (EPI formula). * Baseline prednisone dosage\>40mg/d at screening. * Other autoimmune diseases, such as rheumatoid arthritis, Sjogren's syndrome, myositis, scleroderma, autoimmune liver disease, etc. * Leukopenia or thrombocytopenia (WBC≤3×109/L or PLT≤50×109/L) not caused by SLE. * Liver dysfunction (ALT or AST more than twice the normal upper limit). * Allergic to sulfonamide drugs. * Pregnant or breast-feeding.