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

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 (inclusive) 3. Diagnosed with moderate-to-severe inactive 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 ≤ 2 points in each eye * CAS ≤ 2 in each eye for 6 months prior to screening (based on medical records); or meets all of the following criteria for ≥ 6 months prior to screening (based on patient self-report or medical records): no progression of proptosis, no new-onset or progressive TED-related diplopia, no new-onset inflammatory TED symptoms * The time since initial TED diagnosis is ≥ 2 years and \< 10 years 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. 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 4. Prior/concomitant treatments: * Use of oral or intravenous glucocorticoids within 30 days prior to screening * Periorbital/periocular corticosteroid injection within 90 days of screening * Oral or IV non-steroidal immunosuppressants within 90 days of screening * Corticosteroid or non-steroidal immunosuppressant eye drops within 7 days of screening * Received teprotumumab or teprotumumab N01 at any time prior to screening * Received anti-CD20 antibody therapy within 12 months prior to screening * Received anti-interleukin-6 receptor (anti-IL-6R) antibody therapy within 6 months prior to screening * Received any other investigational therapy for TED at any time prior to screening (including, but not limited to, biologics targeting IGF-1R, FcRn, or TSHR) * Received any other monoclonal antibody therapy within 90 days prior to screening * Need for selenium or vitamin supplementation for TED treatment from 21 days pre-dose through study end (multivitamins are permitted) 5. Medical history/conditions: * Medical conditions that contraindicate study drug use, including: suspected or confirmed inflammatory bowel disease (IBD), coagulopathy, Cerebrovascular accident (CVA) or transient ischemic attack (TIA) within 180 days, acute myocardial infarction (MI), unstable angina, or CABG/PCI within 180 days, severe arrhythmia, or severe systemic infection * Malignancy (treated or untreated) within 5 years prior to screening, except for the following cured or non-metastatic conditions: cutaneous squamous cell carcinoma (SCC) or basal cell carcinoma (BCC), cervical or prostate carcinoma in situ (CIS), papillary thyroid carcinoma * Uncontrolled diabetes (HbA1c ≥8.0% at screening, or initiation of a new diabetes medication, or a \>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 \<50 or \>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 6. 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) \<30 mL/min/1.73 m² (MDRD formula) 7. Clinically significant ear disease, prior ear surgery, hearing impairment, or abnormal pure-tone audiometry (defined as a mean bone conduction threshold ≥25 dB at 0.5, 1, 2, 4 kHz, or ≥40 dB at any frequency) 8. Positive for HBsAg with HBV-DNA \>1000 IU/mL or currently receiving anti-HBV therapy; positive for HIV antibody or HCV antibody; or active syphilis 9. 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 10. Female subjects who are pregnant or lactating 11. Any other condition deemed by the investigator as inappropriate for study participation