High-dose Cyclophosphamide for Severe Refractory Crohn Disease

Inclusion Criteria: * ≥ 18 years of age, males and females will be eligible * Moderate to severe Crohn's Disease (CD) with CDAI \> 220, in addition to evidence of ulceration on ileocolonoscopy or active disease on small bowel imaging (in patients with an ostomy, CDAI criteria do not apply) * Disease progression (primary or secondary non-responder, or reaction to) to at least one anti-tumor necrosis factor (TNF) agent (infliximab, adalimumab, certolizumab pegol), and additionally had disease progression despite one of the following immunosuppressant drugs: azathioprine, 6-mercaptopurine, methotrexate, cyclosporine, natalizumab, vedolizumab * Willingness to participate in a clinical trial * Approval by Enrollment Panel, who will collectively decide on the appropriateness of possible study study participants Exclusion Criteria: * Pregnant or nursing women * Sexually active men and women who do not agree to use effective means of birth control during treatment period * Evidence of primarily fibrostenosing disease without active inflammatory disease on disease staging * Co-morbid conditions including cardiac disease with an ejection fraction of \< 45%, chronic renal failure with serum creatinine \> 2.0, liver disease with total bilirubin \> 2.0, (excluding hyperbilirubinemia secondary to Gilbert's disease) or transaminitis \> 3x upper limit of normal. * History of serious allergic reaction to cyclophosphamide * History of malignancy in the last 5 years (excluding non-melanomatous skin cancers) * Patients who are pre-terminal * Toxic megacolon * Active infection * White blood cell count \< 3000 cells/ul, platelets \< 100K / ul, hemoglobin \< 10.0 g/dL * Any use of thiopurines, methotrexate or anti-TNF agents in the previous four weeks prior to treatment