Study Of The Mechanism Of Action Of CP-690,550 In The Skin Of Subjects With Moderate To Severe Chronic Plaque Psoriasis

• Drug: (CP-6890,550) Tofacitinib
  
  2 x 5 mg oral capsules taken twice daily (every 12 hours) for 12 consecutive weeks
• Drug: Placebo
  
  2 matching oral capsules taken twice daily (every 12 hours) for 12 consecutive weeks
• Drug: (CP-690,550) Tofacitinib
  
  2 x 5 mg oral capsules taken twice daily (every 12 hours) for 12 weeks

• Experimental: Cohort 1
  
  Interventions:
  

  • Drug: (CP-6890,550) Tofacitinib
  • Drug: Placebo
• Experimental: Cohort 2
  
  Interventions:
  

  • Drug: (CP-690,550) Tofacitinib
  • Drug: Placebo

Inclusion Criteria:

• Adults over 18 years of age with a diagnosis of chronic moderate to severe plaque psoriasis for at least 12 months; in generally good health; on stable dose of non-prohibited medications; able to stop current psoriasis therapy (systemic or topical) for several weeks prior to and during study participation.

Exclusion Criteria:

• Serious underlying disease including viral disorders such as hepatitis or HIV or skin condition that would interfere with skin biopsies or evaluation of psoriasis; conditions that could interfere with drug absorption after oral administration; history of malignancy or auto-immune disease.
• Use of oral or injected corticosteroids (steroids).