A Safety and Efficacy Study to Evaluate Efalizumab in Combination With UVB for Moderate to Severe Psoriasis

Inclusion Criteria: * Subject has given informed consent * Subject is in generally good health, and an ambulatory male or female adult (18 years or older) * Subject has moderate to severe plaque psoriasis affecting greater than or equal to 5% body surface area * Subject is a candidate for efalizumab in combination with narrowband UVB phototherapy in the opinion of the assessing investigator * If a female of childbearing potential, a negative pregnancy test and commitment to the use of two forms of effective contraception (birth control) for the duration of the study are necessary * If a non-sterile male, commitment to the use of two forms of effective contraception (birth control) for the duration of the study is necessary. Exclusion Criteria: * Subject is not in generally good health in the opinion of the investigator * Subject has a history of a phototoxic reaction * Subject has a history of NB-UVB failure or severe side effects from UVB that resulted in discontinuation of treatment * Subject has erythrodermic, pustular, inverse or guttate psoriasis * Subject is currently using other psoriasis treatments * Subject has used other psoriasis treatments, including herbal products or alternative therapies within 2 months (biologics), 1 month (systemic therapies including methotrexate, cyclosporine and acitretin, PUVA, Broadband UVB, NB-UVB, and tanning beds), or 2 weeks (topical therapies) of first dose of efalizumab or NB-UVB * Subject is currently enrolled in any other study except non-treatment, biopsy studies * Subject has a history of any form of cancer, including lymphoma, with the exception of non-melanoma skin cancer * Subject has a genetic disorder that predisposes to cancer (e.g. xeroderma pigmentosum) * Subject has a history of squamous cell cancer within the past 5 years or basal cell cancer within the past 3 months in areas that will be treated with NB-UVB * Subject has a history of significant drug or alcohol abuse * Pregnant women, nursing mothers, or women planning to become pregnant during the study * Subject with congenital or acquired immunodeficiency * Subjects planning to have prolonged exposure to the sun or tanning beds during the study which, in the investigator's clinical judgement, may modify the subject's disease severity * Subject has a history of lupus erythematosus, bullous pemphigoid or any other photosensitive condition which may worsen with NB-UVB * Subject is taking a medication that causes photosensitivity at the discretion of the investigator * Subject has an active infection or sepsis prior history or serious infection or tendency to get infections easily * Subject has an untreated positive PD * Subject has a blood disorder, aplastic anemia, bleeding tendency * Subject is allergic to efalizumab or any of its components * Subject has any other condition that, in the opinion of the investigator, makes subject a poor candidate for entry into the study * Subject will be vaccinated with live vaccines (e.g. Flu-Mist) during the study period.