• Participant has provided informed consent before initiation of any study-specific activities/procedures.

• Male or female aged 18 to 55 years (Part A).

• Female participants must be of non-childbearing potential.

• Body mass index (BMI) between 18 and 30 kg/m\^2, inclusive, at screening.

• The participant has adequate venous access and can receive intravenous (IV) therapy.

• The participant is considered by the investigator or designee to be in good general health as determined by medical history, clinical laboratory test results, vital sign measurements, 12-lead electrocardiogram (ECG) results, and physical examination findings at screening.

• Healthy Japanese participants in cohort 4 only. Japanese participants must meet all the following as confirmed by interview: Descendants of 4 ethnic Japanese grandparents who were born in Japan; Both parents are ethnic Japanese who were born in Japan; Hold a Japanese passport or identity papers; Have lived outside Japan for less than 10 years at the time of screening and lifestyle including diet has not changed significantly since leaving Japan.

• Male or female aged 18 to 65 years.

• Moderate-to-severe active TED.

• The participant had onset of active TED within 15 months prior to baseline.

• Clinical diagnosis of Graves' disease associated with active TED with a Clinical Activity Score (CAS)≥3 for the most severely affected eye at screening and baseline.

• Proptosis ≥18mm in the study eye at baseline.

• Participants with baseline subjective binocular diplopia score \>0.

• Does not require immediate surgical ophthalmological intervention and is not planning corrective surgery/irradiation during the trial.