This is a Phase I dose-escalation study of MDX-1100. patients with ulcerative colitis will be enrolled into one of four dose cohorts, to receive of MDX-1100 at 0.3, 1.0, 3.0 or 10mg/kg. Three to six patients will be enrolled at each dose level, starting at the lowest dose level, for a maximum of 24 patients to be enrolled into the study. The study is designed to establish the safety and tolerability of single doses of MDX-1100 administered in dose-escalating cohorts to patients with ulcerative colitis. Other study objectives include characterizing a pharmacokinetic profile and pharmacodynamic effects of MDX-1100 and determination of immunogenic response to MDX-1100.