The primary objective of this study is to evaluate the efficacy and safety of ustekinumab (CNTO 1275) in the treatment of patients with moderate to severe plaque psoriasis.

Although numerous therapeutic options exist for the treatment of psoriasis, there is still a significant unmet medical need due to the limited effectiveness and/or significant side effect profile of current treatment options. Preclinical studies and early phase clinical studies suggest that interleukins-12 and -23, two molecules that are part of the communication network in the immune system, may play an important role in psoriasis. Ustekinumab (CNTO 1275) is a monoclonal antibody directed against interleukins -12 and -23. This is a randomized (study drug assigned by chance like flipping a coin), double blind (neither physician nor patient knows the name of the assigned drug), parallel-group, multicenter study to determine the effectiveness and safety of two different doses of ustekinumab (CNTO 1275) administered subcutaneously (under the skin) as compared with placebo in patients with moderate to severe plaque-type psoriasis (the most common type of psoriasis). The hypothesis is that ustekinumab (CNTO 1275) will be more effective in treatment of psoriasis than placebo, that the improvement in psoriasis will result in an improved quality of life for treated patients and that ustekinumab (CNTO 1275) will be generally well tolerated. Patients will receive ustekinumab (CNTO 1275), 45 or 90 mg, or placebo administered subcutaneously at weeks 0 and 4 weeks then every 12 weeks thereafter until week 52. For patients who partially respond to the starting regimen, the dosing interval may be adjusted to every 8 weeks. Patients will enter long term extension portion of the study at week 52 during which patients will continue to receive treatment with ustekinumab (CNTO 1275) and will be followed for a total of up to 264 weeks from the initial (week 0) administration of study agent.

The dose of ustekinumab (CNTO 1275) will be 45 or 90 mg or placebo administered subcutaneously at weeks 0 and 4 weeks then every 12 weeks thereafter. For patients who partially respond to the starting regimen, the dosing interval may be adjusted to every 8 weeks.

Inclusion Criteria:

• Plaque-type psoriasis diagnosed >= 6 months prior
• Plaque-type psoriasis covering at least 10% of total body surface areas
• Psoriasis area-and-severity index score of >=12 at screening and baseline
• Considered by treating dermatologist to be a candidate for phototherapy or systemic treatment of psoriasis
• Women of childbearing potential and all men must agree to use adequate birth control measures throughout the trials and for 12 months following the last injection of study agent
• Have no history of latent or active tuberculosis (TB)

Exclusion Criteria:

• Currently have nonplaque forms of psoriasis or drug-induced psoriasis
• Women who are pregnant or nursing, or men and women planning pregnancy while enrolled in the study
• Patients who have used any therapeutic agent targeted at reducing IL-12 or IL-23
• Patients who have had a Bacillus Calmette-Guerin (BCG) vaccination within the previous 12 months prior to screening
• Patients who have a history of chronic or recurrent infectious disease or who have or have had a serious infection requiring hospitalization or intravenous antibiotics within the previous 2 months prior to screening
• Patients who have or ever have had a nontuberculous mycobacterial infection or opportunistic infection
• Patients known to be infected with human immunodeficiency virus (HIV), hepatitis B, or hepatitis C
• Patients who have current signs or symptoms of severe, progressive, or uncontrolled renal, hepatic, hematological, gastrointestinal, endocrine, pulmonary, cardiac, neurologic, cerebral, or psychiatric disease
• Patients with a malignancy or who have a history of malignancy (with the exception of certain skin cancers and pre-invasive cervical cancer)
• Patients participating in another trial using an investigational agent or procedure
• Systemic immunosuppressants within 4 weeks of the first administration of study agent