A Study to Assess the Efficacy and Safety of Two Dosing Regimens of Alefacept in Subjects Weighing Between 100kg and 150kg With Moderate to Severe Chronic Plaque Psoriasis

Inclusion Criteria: * Body weight between 100kg and 150kg * Diagnosis of Chronic Plaque Psoriasis with Body Surface Area (BSA) involvement of ≥ 10% * Candidate for phototherapy or systemic therapy for Psoriasis * CD4 + T lymphocyte counts \> lower limit of normal Exclusion Criteria: * Clinically significant abnormal hematology values or blood chemistry values * ALT or AST value of ≥ 3x the upper limit of normal * Other types of Psoriasis * Serious infection within 3 months prior to 1st dose of study drug * Antibody positive for HIV * History of malignancy * History of severe allergic or anaphylactic reactions * History of any clinically significant cardiac, endocrinologic, hematologic, hepatic, immunologic, metabolic, urologic, pulmonary, neurologic, dermatologic, psychiatric, renal and/or other major disease