The purpose of the study is to evaluate an intravenous (by injection) investigational medication to treat severe ulcerative colitis refractory to steroid therapy. The research is being conducted at up to 8 clinical research sites in the US and is open to both men and women ages 18 to 70 years old. Participants in the study will have a number of visits to a research site. All study-related care and medication is provided to qualified participants at no cost: this includes all visits, examinations and laboratory work.