A Phase III Study of KHN939 in Chinese Patients With Moderate-to-Severe Active Thyroid Eye Disease

This is a multicenter, randomized, double-masked, placebo-controlled Phase 3 study to evaluate the efficacy, safety, immunogenicity, and population pharmacokinetic (PopPK) characteristics of KHN939 in Chinese patients with moderate-to-severe active thyroid eye disease (TED). Approximately 60 participants who meet the study eligibility criteria will be randomized in a 2:1 ratio (stratified by smoking status) to receive 8 infusions of KHN939 or placebo q3W.

Inclusion Criteria: 1. Aged 18-70 years (inclusive) at the time of signing the informed consent form (ICF), male or female 2. Weight between 45 kg and 100 kg 3. Diagnosed with moderate-to-severe active TED: * Proptosis ≥18 mm, accompanied by at least one of the following: (a) eyelid retraction ≥2 mm; (b) moderate to severe soft tissue involvement; (c) intermittent or continuous diplopia * CAS ≥ 3 points * Duration of active TED symptoms ≤12 months prior to screening (documented by patient history or medical records) 4. Female participants of childbearing potential must have a negative serum pregnancy test during screening and agree to use an effective method of contraception from screening until 90 days after the last dose of the study drug. (Note: Women of non-childbearing potential, defined as surgically sterile or postmenopausal, are exempt.) Male participants must agree to use birth control from screening until at least 90 days after the dose of study drug. 5. Able to comply with all protocol-required procedures, examinations, and symptom reporting. Exclusion Criteria: 1. Known hypersensitivity to any component of the study drug formulation, or prior hypersensitivity to any monoclonal antibodies 2. Proptosis at Day 1 (pre-dose) that has decreased by ≥2 mm relative to screening 3. CAS at Day 1 (pre-dose) that has decreased by ≥2 points relative to screening 4. Ocular conditions: * Prior or investigator-assessed diagnosis of dysthyroid optic neuropathy (DON) at screening * Corneal involvement in the study eye without improvement after appropriate treatment * Prior orbital radiotherapy or surgery for TED in the study eye (including orbital decompression, strabismus correction, eyelid correction) * Requires immediate or planned ophthalmic surgical intervention during the study period * Has any pre-existing ocular condition (e.g., high myopia, anticipated cataract surgery) that, as determined by the investigator, would preclude study participation or complicate the interpretation of study results; 5. Prior/concomitant treatments: * Cumulative corticosteroid use for TED ≥1 g methylprednisolone equivalent. \[Note: Participants receiving \10% dose adjustment to an existing diabetes medication within 60 days prior to screening) * Poorly controlled thyroid function: defined as FT3 or FT4 deviating ≥50% from local laboratory normal range (≥1.5×ULN or ≤0.5×LLN) * Uncontrolled hypertension: defined as SBP ≥160 mmHg or DBP ≥100 mmHg; renal artery stenosis; or other evidence of clinically unstable blood pressure * 12-lead ECG with a heart rate \100 bpm and evidence of active cardiac disease; or any screening ECG abnormality that, in the investigator's opinion, confounds subsequent interpretation, particularly QTcF \>450 ms in males or \>470 ms in females 7. Laboratory exclusions at screening: * Alanine aminotransferase (ALT) \>3 × ULN * Aspartate aminotransferase (AST) \>3 × ULN * Serum creatinine(Cr) ≥1.5 × ULN, or glomerular filtration rate (GFR) \1000 IU/mL or currently receiving anti-HBV therapy; positive for HIV antibody or HCV antibody; or active syphilis 10. Participation in any drug, vaccine, or device clinical trial within 3 months prior to screening, or currently within follow-up or within 5 half-lives of another study 11. Female subjects who are pregnant or lactating 12. Any other condition deemed by the investigator as inappropriate for study participation