Phase 1/2, multicenter, multiple dose clinical study designed to evaluate lonigutamab in subjects with 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.

Double-masked, placebo-controlled and open label