Evaluation of Molecular Mechanisms of Non-response to Therapy in Patients With Inflammatory Bowel Disease

Inclusion Criteria: * Male and female patients ≥ 18 years of age (at the time of signing the Informed Consent) * Person informed about study organization and having signed the informed consent. * Established diagnosis of Crohn's dsease or ulcerative colitis with a minimum disease duration of 3 months * Moderate to severe disease activity * UC : Mayo Score ≥ 6 including endoscopy score of ≥ 2 * CD : CDAI score betwenn 220 and 450 (inclusive) * Indication to start any biological or small molecule agent (anti-TNF, anti-IL 21/23, anti-integrin and JAK-inhibitors) * In case of treatment with corticosteroid : stable dose for at least 3 weeks prior to baseline, dosage ≤ 20 mg prednisone * Indication for colonoscopy for the assessment of disease activity as for standards of care and current guidelines * Person affiliated to or beneficiary of a social security plan Exclusion Criteria: * Diagnosis of indeterminate colitis, microscopic colitis, ischaemic colitis, infectious colitis, radiation colitis * Absolute contraindications to colonoscopy procedures, complication during previous endoscopy * Bleeding disorders * Indication for surgery for UC * Rectal topical therapy (enemas or suppositories) ≤ 2 weeks prior to baseline * Treatment with \> 20 mg prednisone within 3 weeks prior to baseline * Anaemia (haemoglobbin \< 10g/dl) at baseline * Subject unable to comply with the study procedures * Person referred in articles L.1121-5, L. 1121-7 and L.1121-8 of the Public Health Code: * Pregnant, parturient or breastfeeding woman * Minor person (non-emancipated) * Adult person under legal protection (any form of public guardianship) * Adult person incapable of giving consent and not under legal protection * Person deprived of liberty for judicial or administrative decision, person under psychiatric care as referred in articles L. 3212-1 and L. 3213-1.