This is a randomized, double-blind phase II clinical study to evaluate the efficacy and safety of AK139 in the treatment of patients with moderate-to-severe atopic dermatitis.

Inclusion Criteria:

1. Able to understand the study and voluntarily sign the ICF.
2. Atopic dermatitis (AD) diagnosed at least 6 months before screening.
3. Eczema Area and Severity Index (EASI) score ≥16, Investigator's Global Assessment (IGA) score ≥3, and Body surface area (BSA) involvement ≥10% at both screening and baseline.
4. A weekly average of daily Peak Pruritus Numerical Rating Scale (P-NRS) score ≥4 at baseline.
5. Inadequate response or intolerance to prior topical therapy for AD.
6. The patients agree to use highly effective contraception methods from the moment of signing of the ICF to 90 days after the last dose of the investigational product.

Exclusion Criteria:

1. Acute onset of AD within the first 4 weeks of randomization.
2. Received systemic corticosteroids, immunosuppressive/immunomodulatory drugs, phototherapy or other systemic therapies used for AD within the 4 weeks before randomization.
3. Received treatment with other clinical research drugs (non-biological agents) within the first 4 weeks or 5 half-lives of randomization (whichever is longer)
4. Received or planned to receive live vaccine treatment within the 12 weeks before randomization or during the study period.
5. Received allergen specific immunotherapy within the 12 weeks before randomization.
6. Have a history of allergies to any component of AK139 and/or severe allergic reactions to monoclonal antibodies.