Study Overview- This study aims to evaluate the efficacy, safety and tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and immunogenicity of efgartigimod PH20 SC in participants with active, moderate-to-severe TED, compared with placebo PH20 SC.

After the screening period, eligible participants will be randomized in a 2:1 ratio to receive efgartigimod PH20 SC or placebo PH20 SC, respectively during the double-blinded treatment period (DBTP). At the end of the DBTP, participants may enter a follow-up observational period while off study drug. Some participants may also enter the open-label treatment period with efgartigimod PH20 SC. The study duration varies from approximately 60-110 weeks

A Phase 3, Randomized, Double-Masked, Placebo-Controlled, Multicenter Study to Evaluate the Efficacy, Safety, Tolerability, Pharmacokinetics, Pharmacodynamics, and Immunogenicity of Efgartigimod PH20 SC Administered by Prefilled Syringe in Adult Participants With Thyroid Eye Disease

Total Number of treatments – 24-weeks Double-Blinded Treatment Period; Follow-up observational period while off drug or open-label treatment period with efgartigimod PH20 SC. Complete study duration varies from approximately 60-110 weeks.