This is a randomized, double-blind phase II clinical study to evaluate the efficacy and safety of AK111 in the treatment of subjects with moderate to severe plaque psoriasis.

This is a randomized, double-blind phase II clinical study to evaluate the efficacy and safety of AK111 in the treatment of subjects with moderate to severe plaque psoriasis. The study has 2 parts: first part (randomized double-blind) and second part (open).

Inclusion Criteria:

1. Male or female subjects aged ≥18 years old.
2. Subjects with moderate to severe plaque psoriasis with or without psoriatic arthritis.
3. At screening and baseline, PASI score ≥ 12, BSA ≥ 10%, sPGA ≥ 3.
4. Suitable for systematic therapy assessed by investigators.
5. Subjects who are women of childbearing potential must be practicing an adequate, medically acceptable method of birth control during the study and for at least 6 months after the last investigational drug administration.

Exclusion Criteria:

1. Types of psoriasis other than chronic plaque-type psoriasis.
2. Drug-induced psoriasis.
3. Evidence of active TB. Patients with evidence of latent tuberculosis may enter the trial after sufficient treatment had initiated and maintained according to protocol.
4. Positive results of confirmatory test for hepatitis B, hepatitis C, human immunodeficiency virus (HIV) or syphilis.
5. History of repeated chronic infection, had any serious infection or systemic infection within 2 months before screening.
6. Progressive or uncontrolled symptoms or signs of circulatory, respiratory, digestive, neuropsychiatric or psychological,hematological, endocrine and other systems before randomization.
7. History of malignant tumour within 5 years before screening.
8. Previous or current autoimmune diseases.
9. Allergic to any component of the investigational drug, or have had severe allergic reactions to monoclonal antibodies.