Alefacept (AMEVIVE®) is an immunosuppressive dimeric fusion protein. It was shown to interfere with lymphocyte activation by specifically binding to the lymphocyte antigen, CD2, and inhibiting LFA-3/CD2 interaction. Alefacept was evaluated in two randomized, double-blind, placebo-controlled studies in adults with chronic (>1 year) plaque psoriasis and a minimum body surface area involvement of 10% who were candidates for or had previously received systemic therapy or phototherapy. 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.