This is a randomized, double-blind, placebo-controlled, multi-center Phase II clinical study to evaluate the efficacy and safety of AK111 for the treatment of moderate to severe plaque psoriasis.

This is a randomized, double-blind, placebo-controlled, multi-center Phase II clinical study to evaluate the efficacy and safety of AK111 in subjects with moderate to severe plaque psoriasis. The study will consist of 4 periods: up to 4 weeks screening period, 12 weeks placebo-controlled period,12 weeks crossover treatment period,44 weeks long-term treatment period.

Key Inclusion Criteria:

1. Male or female, 18 to 75 years of age

2. Moderate to severe plaque-type psoriasis diagnosed for at least 6 months

3. Moderate-to-severe plaque psoriasis as defined at baseline by meeting all three criteria:

   1. Clinical diagnosis of stable plaque psoriasis with involvement of ≥ 10% body surface area.
   2. Psoriasis area and severity index(PASI) ≥12.
   3. Static Physicians Global Assessment score ≥3.

4. Subjects with a history of an inadequate response, intolerable or medically inappropriate use of systemic therapy and/or phototherapy.

5. Subjects who are women of childbearing potential must have a negative urine pregnancy test at screening and must be practicing an adequate, medically acceptable method of birth control for at least 8 months after the last study drug administration.

Key Exclusion Criteria:

1. Forms of psoriasis other than chronic plaque-type psoriasis.
2. History or evidence of active TB, Patients with evidence of latent tuberculosis may enter the trial after sufficient treatment according to protocol.
3. Positive results of confirmatory serology test for hepatitis B, hepatitis C, HIV or syphilis at screening.
4. History of a serious or systemic infection within 2 months before screening.
5. History of malignancy of any organ system within the past 5 years.
6. Inadequate washout period for prior drug therapy.
7. Previous use of secukinumab, ixekizumab or any other drug that targets IL-17 or IL-17 receptor.
8. Any medical conditions, in the opinion of the Investigator or the Sponsor's medical monitor, would place the subject at risk, interfere with study participation or study results interpretation.