BG9273 is a recombinant protein that has been designed to modulate immune responses through interaction with the CD2 receptor. The interaction of BG9273 with CD2 has been shown to inhibit in vitro human T lymphocyte responses, and therefore has potential as an effective therapy for psoriasis. Pre-clinical and clinical data suggest that BG9723 should be safe and well tolerated at dosing of .025 mg/kg to .150 mg/kg weekly for 12 weeks. This study was a multicenter, randomized, double-blind placebo-controlled, parallel-group dose response study comparing three dose levels of BG9273 in subjects with moderate to severe plaque psoriasis. All subjects were between 18 and 70, with moderate to severe plaque psoriasis and a body surface involvement of 10% or greater. The primary study objective was to determine the relationship of clinical response to the dose and plasma concentration of BG9273 when administered once a week for a total of up to 12 doses.