• To evaluate the preliminary efficacy of AIN457 when administered as a single dose infusion to patients with stable plaque psoriasis; proof-of-concept study comparing 3mg/kg of AIN457 to placebo [ Time Frame: at week 4 ] [ Designated as safety issue: No ]
• The comprimary efficacy endpoints will be the Psoriasis Area and Severity Index (PASI) measure at 4 weeks after the infusion and the number of responses as determined by the Investigator's global assessment (IGA). [ Time Frame: At week 5 ] [ Designated as safety issue: No ]

• Efficacy of AIN457 will be evaluated by comparing the coprimary endpoint of the reduction in PASI score between the placebo and treatment arms
• This study will have two primary endpoints which are the reduction in PASI score from baseline to 4 weeks of follow-up and the number of responses as determined by an IGA.

• Characterize compound in blood, in plaque [ Time Frame: throughout the duration of the study ] [ Designated as safety issue: No ]
• Perform exploratory analysis [ Time Frame: throughout the duration of the study ] [ Designated as safety issue: No ]

• To evaluate the safety of AIN457 when administered as a single dose infusion to patients with stable plaque psoriasis
• To evaluate the population pharmacokinetics of AIN457 when administered as a single dose infusion to patients with stable plaque psoriasis
• Characterize the binding kinetics of IL-17/AIN457 complex in blood
• Characterize the pharmacodynamics of AIN457 in a sentinel plaque
• Conduct exploratory genomic, proteomic and metabolomic studies to identify gene expression patterns, proteins, and metabolites of blood that are associated with treatment response to AIN457.
• Perform exploratory analysis of soluble protein markers (by multiplex based immunoassay in serum) and, when applicable, exploratory Pharmacogenomic analysis of skin biopsy if clinical and/or histological response has been demonstrated

This is a two-arm, parallel group, double-blind, placebo-controlled proof-of-concept study comparing 3 mg/kg of AIN457 to placebo. Subjects with a diagnosis of moderate to severe stable plaque psoriasis will be randomized to receive either AIN457 or placebo. AIN457 or placebo will be administered by single infusion at baseline and subjects will be observed for up to 26 weeks following the infusion.

• Biological: AIN457
• Biological: Placebo

Inclusion Criteria:

• Males or females, aged 18-69 at time of consent.
• Post menopausal or surgically sterile female patients are allowed. Male patients must be willing to use contraception method at least for 3 months following the completion of the study. Women of child-bearing potential will not be allowed to participate.

• Diagnosis of plaque psoriasis for at least 6 months prior to screening. The patients must meet both of the following criterion:

  1. Coverage of the body surface area (BSA) of 10% or more with plaques
  2. A score of 3 or more on the IGA scale
• Stable plaque psoriasis at screening and randomization.
• PASI score of 12 or greater at randomization.
• Able to communicate well with the investigator, and to understand and comply with the requirements of the study. Understand and sign the written informed consent.
• Patients must have normal laboratory values for screening laboratory test results of hematological (hemoglobin, WBCs, neutrophils, platelets) and renal (serum creatinine) assessments. For the transaminases, aspartate aminotransferase and alanine aminotransferase, levels 1.5 times the upper limit of normal will be accepted. For the additional hepatic laboratory results (alkaline phosphatase, gamma-glutamyltransferase, bilirubin), patients must have non-clinically significant values.

Exclusion Criteria:

• Currently have any of the nonplaque forms of psoriasis: erythrodermic, guttate, or pustular.
• Currently have drug-induced psoriasis (new onset or exacerbation of psoriasis from beta blockers, calcium channel blockers, or lithium).
• Men who are planning to initiate a pregnancy while enrolled in the study or for 3 months following completion of the study.
• Women of child-bearing potential are not allowed in the study.
• Used any investigational drug within the previous 4 weeks.

• Recent previous treatment with anti-TNF-α therapy (or other biological therapy), immunosuppressive agents such as cyclosporine, mycophenolate, pimecrolimus, or tacrolimus. The following washout period will be required for such patients to be eligible to participate in the trial.

  1. 2 months washout prior to screening for etanercept, adalimumab, or infliximab.
  2. 1 month washout prior to screening for cyclosporine, mycophenolate, tacrolimus, and any systemic immunosuppressants including, but not limited to, methotrexate, azathioprine, 6-thioguanine, mercaptopurine, and hydroxyurea

Other protocol-defined inclusion/exclusion criteria may apply