This is a randomized, double-blind, placebo-controlled, parallel-group study to evaluate the safety and efficacy of 611 when used in combination with topical corticosteroid (TCS) treatment compared with placebo in combination with TCS treatment for moderate-to-severe atopic dermatitis.

Inclusion Criteria:

• Male or female adults ages 18 to 75 years old when signing the informed consent.
• AD (according to Hanifin-Rajka Criteria) that had been present for at least 1 years before the screening visit.
• Moderate to Severe Atopic Dermatitis.
• Recent history of inadequate response to treatment with topical medications.

Exclusion Criteria:

• Participation in a prior 611 clinical study.
• Treatment with the following prior to the baseline visit: 1) Systemic corticosteroid or Immunosuppressants / Immunomodulators within 4 weeks or within 5 half-lives (if known), whichever is longer. 2) Monoclonal antibody within 5 half-lives (if known) or 4 months, whichever is longer. 3) Cell-depleting within 6 months.
• Treatment with a live (attenuated) vaccine within 2 months of the baseline visit or planned during the study.
• Serious or Uncontrolled diseases that may affect the safety of participants during the study period or hinder their completion of the study.
• Evidence of active acute or chronic hepatitis.
• History of malignancy within 5 years before the screening visit or currently.
• Pregnant or breastfeeding women, or women planning to become pregnant.
• Any history of vernal keratoconjunctivitis (VKC) and atopic keratoconjunctivitis (AKC).