This trial aims to evaluate the safety and tolerability of the patient's mesenchymal stromal cells (MSCs) in the treatment of young adults with moderate to severe Crohn's Disease. The trial is being conducted at Emory University in Atlanta in conjunction with the Atlanta Clinical and Translational Science Institute. Participants in the trial will receive an intravenous (IV) infusion of MSCs obtained from their own bone marrow. The cells will be expanded in the laboratory before infusion and participants will randomly divided into different groups. Each group will receive a different dose of cells. Participants will be monitored for complications and changes in their clinical condition. The trial seeks to enrol 16 participants between July 2012 and July 2013.