 Patients will be enrolled in the study when they are selected to initiate vedolizumab therapy. Vedolizumab is an intravenous infusion given at increasing intervals. The first infusion of vedolizumab will be considered baseline. Patients may be enrolled at baseline or at colonoscopy prior to the first scheduled infusion of vedolizumab pre-treatment visit. The standard induction protocol for vedolizumab consists of infusions at week 0 baseline, week 2, and week 6. Vedolizumab, as per standard-of-care, is then continued at an interval of every 8 weeks following induction therapy. Vedolizumab treatment will be prescribed as per standard practice and will be prescribed regardless of participation in this study. Patients will not receive medication for the sole purpose of this research. Treatment decisions including timing of wash out period between anti-TNf and vedolizumab will be made by the subjects physician and not per the research protocol. There will not be a protocolized washout period for patients previously receiving anti-TNF therapy because treatment will be standard of care and per the directing physician. 