A Study of Firsekibart Versus Anakinra in Adult-Onset Still's Disease

The purpose of this study is to compare the efficacy and safety of firsekibart versus anakinra in patients with AOSD.

Inclusion Criteria: * Age: This study will include subjects aged 18 to 75 years (inclusive), regardless of gender. * Subjects must be willing to participate in the study and voluntarily sign an informed consent form. * Diagnosis of AOSD will be based on the Yamaguchi criteria: Major criteria: (1) Fever ≥39°C lasting for ≥1 week; (2) Arthralgia lasting for ≥2 weeks; (3) Typical rash; (4) White blood cell count ≥10×10\^9/L with neutrophils ≥80%. Minor criteria: (1) Sore throat or pharyngitis; (2) Lymphadenopathy and/or splenomegaly; (3) Abnormal liver function; (4) Negative rheumatoid factor and antinuclear antibody. Exclusion criteria: (1) Infectious diseases (especially sepsis and EBV infection); (2) Malignancies (especially lymphoma); (3) Other rheumatic diseases (particularly systemic vasculitis). After excluding the above exclusion criteria, a diagnosis of AOSD requires meeting ≥5 of the above criteria (including at least 2 major criteria). * Active disease is defined as meeting 2 Yamaguchi criteria along with the presence of fever or CRP \>10 mg/L. * If currently receiving glucocorticoid therapy, the dose must have been stable for at least 1 week prior to randomization. The maximum allowed dose is 1 mg/kg/day. * Subjects (including their partners) must have no pregnancy plans from the screening period until 28 days after the last dose and must voluntarily use contraception. Exclusion Criteria: * Pre-randomization Medications: a) Received BTK inhibitors, JAK inhibitors, intravenous immunoglobulin, plasmapheresis, or traditional Chinese medicine within 4 weeks prior to screening or 5 half-lives of the known drug (whichever is shorter). b) Received anakinra therapy within 1 day prior to randomization. c) Received etoposide (VP-16) therapy within 12 weeks prior to the baseline visit. d) Increase in dose or addition of new non-biologic agents for treating rheumatic/autoimmune diseases (e.g., immunosuppressants, immunomodulators, antimalarials) within 3 days prior to the baseline visit, unless deemed ineffective by the investigator and discontinued prior to baseline. Specific agents include: i Immunosuppressants/Immunomodulators: Methotrexate, azathioprine, leflunomide, mycophenolate mofetil (or mycophenolate sodium), mizoribine, calcineurin inhibitors (e.g., tacrolimus, cyclosporine), sirolimus, oral cyclophosphamide, 6-mercaptopurine, thalidomide, total glucosides of paeony. ii Antimalarials: Hydroxychloroquine, chloroquine, quinacrine. * History of hypersensitivity to any component of the investigational product. * Presence or suspicion of hemophagocytic lymphohistiocytosis (HLH) at baseline, or diagnosis of HLH within 2 months prior to randomization. According to the HLH-2004 diagnostic criteria, the diagnosis can be established by meeting any one of the following two conditions: (1) Molecular diagnosis consistent with HLH. (2) Fulfillment of ≥5 of the following 8 criteria: a) Fever: Temperature \>38.5°C for \>7 days. b) Splenomegaly. c) Cytopenias (affecting ≥2 lineages): Hemoglobin \