The goal of this interventional study is to learn if TRIV-509 works to treat moderate to severe atopic dermatitis in adults. It will also evaluate the safety of TRIV-509.

Participants will receive 4 doses of the study intervention that they are randomized to (TRIV-509 or placebo), and at Week 16 will cross over and receive 4 doses of the other study intervention.

The study duration for individual participants is up to 57 weeks, including a Screening period of up to 30 days.

Inclusion Criteria:

• Has Atopic Dermatitis.
• Has moderate to severe, active and symptomatic AD

Exclusion Criteria:

• Severe or uncontrolled medical conditions.
• Use of topical treatments, phototherapy, systemic immunosuppressives or immunomodulatory therapies, or immunomodulatory biologics, within stated washout periods.