Inclusion Criteria:

- A diagnosis of dermatomyositis according to 2017 EULAR/ACR Classification Criteria for
Idiopathic Inflammatory Myopathies

- Adult subjects (18-75 years old)

- Active muscle and skin disease at screening and baseline

- Prior therapy OR current therapy with corticosteroids, hydroxychloroquine, and/or one
non-steroid immunosuppressant

- Weight > 40 kg to < 130 kg, and with a body mass index (BMI) < 40 kg/m2.

Exclusion Criteria:

- Dermatomyositis with end-stage organ involvement

- Dermatomyositis with irreversible muscle involvement

- History of:

- Any lymphoproliferative disorder

- Active malignancy;

- History of cancer within 5 years prior to screening (exceptions for basal cell
carcinoma, squamous cell carcinoma, ductal carcinoma in situ of the breast,
carcinoma in situ of the uterine cervix, or thyroid carcinoma.)

- Cancer-associated dermatomyositis

- Overlap myositis/connective tissue disease (except for overlap with Sjögren's
syndrome)

- Participants at a risk of thrombosis and cardiovascular disease

- Participants with a high risk for herpes zoster reactivation

- Participants with active or recent infections

Note: Other protocol defined Inclusion/Exclusion criteria may apply.

Eligibility last updated 5/1/23. Questions regarding updates should be directed to the study team contact.