A Study in Patients With Moderate to Severe Plaque Psoriasis to Evaluate the Efficacy and Safety of ESK-001

Inclusion Criteria:

1. Males or females, age ≥18 years

2. Diagnosis of plaque psoriasis for ≥6 months

3. Plaques covering ≥10% of BSA

4. PASI ≥12

5. sPGA ≥3

6. Women of childbearing potential (WOCBP) and males who are sexually active with WOCBPmust agree to adhere to highly effective methods of contraception

Exclusion Criteria:

1. Nonplaque psoriasis or other inflammatory skin conditions

2. Immune-mediated conditions commonly associated with psoriasis (eg inflammatory boweldisease). Patients with psoriatic arthritis may participate

3. Pregnant, lactating, or planning to get pregnant during the study

4. Use of drugs prior to Study Day 1 that treat or may affect psoriasis:

• Topical within 2 weeks

• Phototherapy or any systemic treatments within 4 weeks

• Any biologic agent targeted to IL-12 or IL-23 within 6 months, oral IL-12 orIL-23 or TNFα inhibitor within 2 months, or IL-17 within 4 months

• Systemic immunosuppressants or immunomodulatory drugs within 4 weeks

• Modulators of B cells within 6 months, or T cells within 3 months

• JAK inhibitors or TYK2 inhibitors within 4 weeks

• PDE4 inhibitor within 2 months

• Any investigational agent, within 30 days or 5 half-lives or is currentlyenrolled in an investigational study

5. Lack of clinical response to a TYK2, IL-12, or IL-23 targeted psoriasis treatment

6. Patients with QTcF >450 msec (males) or >470 msec (females) at Screening

7. Unstable cardiovascular disease, defined as a recent clinical deterioration or acardiac hospitalization within the last 3 months

8. Evidence of recent or recurrent herpes zoster or herpes simplex viral infection

9. Evidence of active infection or positive test result for hepatitis B, hepatitis C,HIV or TB

10. History of serious bacterial, fungal, or viral infections that led tohospitalization, or any recent serious infection requiring antibiotic treatment

11. Any history of known or suspected congenital or acquired immunodeficiency state orcondition that would compromise the patient's immune status

12. Lab abnormalities indicating significant renal, hepatic or bone marrow dysfunction

13. History of any immune-mediated or inflammatory medical condition for which patientrequires current systemic corticosteroids