Alefacept (AMEVIVE®) is an immunosuppressive dimeric fusion protein that consists of the extracellular CD2-binding portion of the human leukocyte function antigen-3 (LFA-3) linked to the Fcof IgG1. Alefacept is produced by recombinant DNA technology in a Chinese Hamster Ovary (CHO) mammalian cell expression system. It was shown to interfere with lymphocyte activation. Alefacept was evaluated in two randomized, double-blind, placebo-controlled studies in adults with chronic plaque psoriasis. Each course consisted of once-weekly administration for 12 weeks of placebo or alefacept. The response to alefacept was significantly better in both studies. In both studies, onset of response to alefacept treatment (defined as at least 50% reduction of baseline Psoriasis Area and Severity Index (PASI)) began 60 days after the start of therapy. With one course of therapy, the median duration of response (defined as maintenance of a 75% or greater reduction in PASI) was 3.5 months for alefacept treated patients and 1 month for placebo-treated patients. Most patients who had responded to either alefacept or placebo maintained a 50% or greater reduction in PASI through the 3-month observation period.