Efficacy and Safety of Lonigutamab in Subjects With Thyroid Eye Disease (TED)

Key Inclusion Criteria: * Male or female, ≥18 and ≤75 years of age. * Proptosis defined in the study eye as ≥3 mm above normal. * Clinical Activity Score (CAS) ≥4 (using a 7-item scale) for the most severely affected eye * Onset of active TED symptoms prior to baseline * Must agree to use highly effective contraception as specified in the protocol Key Exclusion Criteria: * Pathology related to inflammatory bowel disease or irritable bowel syndrome. * Clinically significant pathology related to hearing or history of hearing impairment * Optic neuropathy * Corneal decompensation unresponsive to medical management. * Previous orbital irradiation (for any cause) or any previous surgical treatment for TED. * Subjects with diabetes or hemoglobin A1c \>6.0% at screening * Any steroid use (intravenous \[IV\] or oral) with a cumulative dose equivalent to \>3 g of methylprednisolone for the treatment of TED within the last year. * Previous steroid use (IV or oral) specifically for the treatment of TED not to exceed 1 g total dose in the 8 weeks prior to Screening. * Previous use of teprotumumab or any other IGF-1 receptor (IGF-1R) inhibitor. * Any previous treatment with a biologic drug for the treatment of TED (eg, rituximab and tocilizumab) * Any other immunosuppressive agent within 1 month of screening. * Cohort 4 only: Prior history of craniofacial surgery or medical conditions that could alter orbital or facial features.