Safety, Efficacy and Pharmacokinetics of an Antibody for Psoriatic Arthritis

Inclusion criteria: * Diagnosed with PsA as defined by: * Presence of psoriasis with at least one 2 cm plaque AND * One of the five functional classifications of PsA * Functional Class I, II, or III as defined by the ACR Classification of Functional Status in Rheumatoid Arthritis * Moderate to severe disease, defined as follows: * At least 3 tender and 3 swollen joints (78 joint count for tenderness and 76 joints for swelling; AND * Either ESR ≥ 28 mm/hr, CRP ≥ 1.5 mg/dL, or morning stiffness for ≥ 30 minutes. * Currently taking at least one of the following systemic therapies for PsA: pre-existing stable doses of NSAIDs, corticosteroids (≤ 10 mg/day), and either sulfasalazine (≤ 3 gm/day) or methotrexate (≥ 7.5 and ≤ 30 mg/week) but not both. * 18 to 80 years of age. * Body weight ≤ 125 kg (275 lbs). * Candidate for systemic immunomodulatory therapy. * Using an acceptable method of birth control. * If female, must have a negative serum pregnancy test during screening period, must be surgically sterile, or must be at least five years postmenopausal. * Informed about the study and signed an informed consent prior to performance of any study-related procedure. Exclusion criteria: * Previous treatment with efalizumab. * Rheumatoid Factor positive without dactylitis or positive X-rays of the hands or feet, or with rheumatoid nodules. * History of joint replacement surgery within 60 days prior to the start of study drug dosing. * Joint replacement therapy planned within nine months subsequent to the start of study drug dosing. * Intra-articular cortisone injections within 28 days prior to the start of study drug dosing. * Pregnancy or lactation. * History of severe allergic or anaphylactic reactions to humanized or murine monoclonal antibodies. Respiratory distress (dyspnea, oxygen desaturation with pO2 \< 90% or onset of acute respiratory distress syndrome), flank or back pain, and/or hypotension may be signs of anaphylaxis. * Active bacterial, viral, fungal, mycobacterium tuberculosis or atypical mycobacterium infection. * Positive PPD test unless subject with positive PPD test completed a course of treatment for tuberculosis * History of any opportunistic infection. * History of a malignancy within the past five years. Subjects with a history of fully resolved, resected, basal or squamous cell carcinoma may be enrolled. * Received any vaccine within 28 days prior to the start of study drug dosing. * Chronic disorders apart from PsA affecting the joints, such as systemic lupus erythematosus, rheumatoid arthritis, gout, scleroderma or known reactive arthritis (e.g., Reiter's syndrome). * COPD, asthma, or other pulmonary disease requiring more therapy than using one inhaler 4× daily. * Failed to respond or maintain response to Enbrel. * Received any DMARD other than methotrexate or sulfasalazine during the 28 days prior to the start of study drug dosing. * Approved biologic PsA therapy during the 28 days or seven half-lives of the drug prior to the start of study drug dosing, whichever is the greater length of time; Enbrel within 42 days prior to the start of study drug dosing. * Investigational drug and/or treatment during the 28 days or 7 half-lives of the drug prior to the start of study drug dosing, whichever is the greater length of time. * Any condition which, in the opinion of the Investigator, would jeopardize the subject's safety following exposure to efalizumab. * Liver disease (e.g., hepatitis, cirrhosis) or abnormal hepatic function (AST or ALT ≥ 2.5 * ULN). * Serum creatinine level ≥ 1.5 mg/dL * Platelet count ≤ 125,000 cells/mm3 * WBC count ≤ 3,500 cells/mm3 * Total lymphocyte count ≤ 1000 cells/mm3 * Seropositive for hepatitis B * Seropositive for hepatitis C antibody * Seropositive for HIV * Antinuclear antibodies titer ≥ 1:80 * History of inflammatory bowel disease