1. Phototherapy (PUVA (within 4 weeks of the Baseline Visit) and/or UVB (within 2 weeks of the Baseline Visit); 2. Other biologic therapies (including any other anti-TNF) within 4 weeks of the Baseline Visit; 3. Any investigational agents of chemical or biologic nature within a minimum of 30 days or 5 half-lives (whichever is longer) of the drug prior to the Baseline visit ; 4. Any other systemic drug therapies for Ps within 4 weeks of the Baseline Visit; 5. Oral or injectable corticosteroids, new prescription topical therapies, or changes in the concentration of current prescription topical therapies (including corticosteroids) that are being used, within 2 weeks of the Baseline Visit. Subjects may continue using previously prescribed topical therapies (including corticosteroids) during the study. 15. Prior exposure to biologics that have a potential or known association with Progressive multifocal leukoencephalopathy PML (i.e., natalizumab (Tysabri®) or rituximab (Rituxan®)); 16. Subjects with any active viral infection that based on the investigator's clinical assessment makes the subject an unsuitable candidate for the study;