The purpose of the study is to evaluate an intravenous (by injection) investigational medication to treat moderate to severe inflammatory, nonstricturing, nonpenetrating Crohn's disease. The research is being conducted at up to 5 clinical research sites in the US and Europe 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 up to 17 months. All study-related care and medication is provided to qualified participants at no cost: this includes all visits, examinations and laboratory work.

Visilizumab is a humanized antibody (antibodies are proteins that are normally made by the immune system to help defend the body from infections and other foreign substances) that is directed against T cells. Visilizumab selectively attacks problematic T cells and, in doing so, it may prevent them from causing inflammation. Visilizumab has also been observed to have a suppressive effect on the body's immune system (system in the body that reacts to foreign or occasionally one's own proteins).

PDL BioPharma, Inc. was formerly known as Protein Design Labs, Inc.

Inclusion Criteria:

• 18-70 years old
• Diagnosis of moderate-to-severe inflammatory, nonstricturing, nonpenetrating Crohn's disease, defined as Crohn's Disease Activity Index greater than or equal to 250, C-reactive protein greater than or equal to upper limit of normal, and endoscopic evidence of moderate-to-severe active inflammatory disease
• Test negative for Clostridium difficile within 3 weeks
• Signed informed consent, including permission to use protected health information

Exclusion Criteria:

• History of lymphoproliferative disorder or prior malignancy within 5 years or current malignancy
• Pregnant or nursing
• HIV, Hepatitis B or Hepatitis C infection
• Presence of obstructive symptoms, confirmed by endoscopy
• Serious infections within 12 months
• Active infections that require antibiotic therapy
• Started or changed dose of sulfasalazine, 5-aminosalicylic acid; or antibiotics, probiotics, or topical therapies for Crohn's within 2 weeks
• Serious infections that required IV antibiotic therapy or hospitalization within 8 weeks
• Increase dose of corticosteroid medication within 2 weeks
• Received a live vaccine within 6 weeks
• Received any monoclonal antibodies or investigational agents within 3 months
• Received cyclosporine or tacrolimus (FK506) within 4 weeks
• Dose change or discontinuation from 6-mercaptopurine, azathioprine, or methotrexate within 4 weeks
• Significant organ dysfunction
• Likely to require surgery in the next 6 months
• History of lymphoproliferative disorder
• History of tuberculosis or mycobacteria infection or positive chest x-ray
• History of thrombophlebitis or pulmonary embolus
• History of immune deficiency or autoimmune disorders other than Crohn's
• History of subtherapeutic blood levels of anticonvulsive medications within 1 week