Ulcerative colitis (UC) is a chronic inflammatory bowel disease (IBD) that results from immune dysregulation. Arguably, the development of Tumor Necrosis Factor (TNF) antagonists (including infliximab, adalimumab and golimumab) revolutionized the management of immune-mediated chronic diseases in the past two decades.||However, about one third of patients will not respond to a first anti-TNF treatment and 10% to 30% will loose response to anti-TNF during the follow-up.||Historically, a switch between anti-TNF was performed to recapture remission and response to anti-TNF. Recently, a new biologic therapy blocking another target has been approved and is now reimbursed during ulcerative colitis, namely vedolizumab. Vedolizumab is an anti-integrin agent avoiding the recruitment of lymphocytes specifically in inflamed gut tissue.||Emerging data suggest that a switch of therapeutic class (meaning a change of biologic target with Non-TNF-targeted biologic) in case of clinical failure or insufficient response to anti-TNF may be the best choice. This idea of a switch out of the anti-TNF class is also supported by data on drug monitoring that may help physician decision making in case of loss of response. However, no trial is currently available and ongoing to assess the best therapeutic strategy. The aim of the proposed study is to assess the best biological based strategy in patient losing response to a first subcutaneous anti-TNF (golimumab and/or adalimumab).