Long-Term One Year Use of Alefacept (Amevive®) in Moderate to Severe Chronic Plaque Type Psoriasis

Inclusion Criteria: * Must give written informed consent. * Subjects must be 18 years of age or older. * Subject must be adult males or non-pregnant, non-lactating females. * Female subjects of childbearing potential must state that they are using measures to avoid conception through active means including hormone replacement, intrauterine device, or abstinence. * Subjects must be in general good health with no other skin disease, disease state or physical condition which would impair evaluation of psoriasis or which would increase their health risk by study participation. * Subjects must be willing to receive an IM injection per protocol for 1 year. * Must require systemic therapy or phototherapy for their psoriasis, as determined by the investigator prior to Visit 1. Objectively this equates to Inclusion criteria of either: * IGA≥3 on a 0-5 scale and BSA≥10% * PASI ≥12 * Subjects may not be taking any other systemic therapies or receiving phototherapy during the duration of the study. Subjects are required a 4 week washout period from any systemic medication or phototherapy prior to enrolling in the study and starting treatment with alefacept. * There is no washout for topical corticosteroid medications. Stable dosing of topical corticosteroids may be used up until the first dosing visit. Exclusion Criteria: * Female subjects who are not postmenopausal for at least 1 year, surgically sterile, or willing to practice effective contraception during the study. Nursing mothers, pregnant women and women planning to become pregnant while on study are to be excluded. * Subjects have guttate, pustular, erythrodermic or rapidly flaring psoriasis. * Current enrollment in any research study. * Serious local infection (e.g., cellulitis, abscess) or systemic infection (e.g., pneumonia, septicemia) within the 3 months prior to the first dose of investigational drug. * Any subject who has a CD4\<250 cells/µL at study entry. * Treatment with another investigational drug or approved therapy within 28 days prior to study drug administration. * Treatment with systemic retinoids, systemic steroids, methotrexate, cyclosporine, azathioprine, thioguanine, etanercept, efalizumab, infliximab, adalimumab or mofetil or other systemic immunosuppressant agents within the 28 days prior to investigational drug administration. * Phototherapy, including Ultraviolet B (UVB) and Psoralen + Ultraviolet A (PUVA), within 28 days prior to investigational drug administration. * Known HIV+, known viral Hepatitis infection, known tuberculosis infection. * History of systemic malignancy.