EFFICACY AND SAFETY ENDPOINTS: Safety and efficacy will be based on clinical assessments, laboratory testing, and gastrointestinal endoscopy and histology at baseline, at day 100 post-transplant, and yearly for 5 years. The primary endpoint is event-free survival at 1 year, defined as alive and free of active CD by endoscopy and biopsy. Transplant-related mortality is death occurring at any time after start of allogeneic HCT. Disease activity will be evaluated using CDAI. Quality of Life will be measured using the Short Inflammatory Bowel Disease Questionnaire.