Bone Marrow Stromal Cells for Inflammatory Bowel Diseases

Background: \- Bone marrow stromal cells (BMSCs) are cells that can develop into other tissue types, including bone, cartilage, marrow, and blood cells. However, BMSCs are not stem cells there is no evidence that after infusion into another person that BMSCs change into any other cells. Research suggests that BMSCs can travel to different parts of the body and work with immune cells to reduce inflammation and help repair damaged tissues. BMSC infusions have been used in tests to treat moderate to severe inflammatory bowel disease, like Crohn's disease (CD) or ulcerative colitis (UC). These tests have shown some good results, but more research is needed to study their safety and effectiveness. Researchers want to see how well BMSC infusions work to treat CD and UC. The BMSCs will be collected from volunteer donors. Objectives: \- To look at the safety and effectiveness of BMSC infusions for moderate to severe CD and UC. Eligibility: \- Individuals between 18 and 65 years old with moderate or severe inflammatory bowel disease (CD or UC) that has not responded to standard treatment. Design: * Participants will have two screening visits. The first will be 15 to 30 days before the first BMSC infusion. The second will be within 14 days of the first BMSC infusion. * At the first screening visit, participants will have a physical exam and medical history. They will provide blood, urine, and stool samples. They will also give information about their symptoms and quality of life. * At the second screening visit, participants will have their vital signs (like blood pressure and heart rate) measured. They will also provide blood samples, and have a colonoscopy with biopsies. * During treatment, participants will have one BMSC infusion per week for 4 weeks. Blood and urine samples will be collected at each treatment visit. * One week after the last infusion, participants will have a study visit. The tests from the first and second screening visits will be repeated. * Ther