Adoptive transfer of regulatory T cells (Treg) has successfully been used for blockade of experimental colitis in vivo, but their usage for treatment of patients with ulcerative colitis (UC) remains poorly studied. Gut homing and effects on the gut epithelium of these Treg are detrimental to suppress gut-specific inflammation. In this project, we will further define the molecular mechanisms of mucosal trafficking and retention of Treg in UC. We will combine the clinical assessment of our current GMP-approved Treg in a phase II clinical trial with in depth studies on their gut-homing potential. These studies will result in further refinement of the current GMP-approved Treg product in future studies.