1. Subjects who have been on ADA monotherapy (40 mg eow or greater) for at least 16 weeks but who in the opinion of the Investigator have shown a sub-optimal response to treatment and have a PGA of > 3 and a PASI of > 5; or Subjects who after an initial positive response to ADA monotherapy (40 mg eow or greater) have failed to maintain an optimal level of response, based on the opinion of the Investigator, and have a PGA of > 3 and a PASI of > 5;