Comparison of Vedolizumab Treatment to Adalimumab Dose Intensification in Crohn's Disease Patients With Loss of Response or Biomarker Activity to Adalimumab on First Line With Therapeutic Drug Concentration.

Inclusion Criteria:

• Major patient and having given consent to participate in the study

• Patients with Crohn's disease who have responded primary to Adalimumab princeps orsimilar bio with loss of response to Adalimumab (40 mg every two weeks) withtherapeutically adequate levels of ADA (> 7.5 μg/mL).

• Patient affiliated to or entitled under a social security scheme

Exclusion Criteria:

• Pregnant woman

• Patient unable to perform MRI or VCE or ileocolonoscopy or ultrasound less than onemonth before inclusion

• Previous or current use of vedolizumab or ustekinumab for Crohn's disease orparticipation in a biological study

• Concomitant use of immunomodulators

• Patients on corticosteroid therapy

• History of cancer

• History of human immunodeficiency virus (HIV), immunodeficiency syndrome, centralnervous system (CNS) demyelinating disease (including myelitis), neurologicalsymptoms suggestive of demyelinating disease, chronic recurrent infection, activetuberculosis (received or untreated), severe infections such as sepsis andopportunistic infections

• Patient with ileoanal pouchitis or ileorectal anastomosis

• Patient with short small bowel syndrome as determined by investigator

• Patients receiving total parenteral nutrition (TPN)

• Patients receiving enteral nutrition

• Patient under legal protection or unable to give consent

• Hemorrhagic rectocolitis or indeterminate colitis

• Patients treated with concomitant immunosuppressive agents

• Patient treated with an optimized dose of adalimumab

• Primary non-responder to Adalimumab

• Patient previously treated with infliximab or ustekinumab before adalimumab

• Severe relapse defined by CDAI > 330

• Patient with anoperineal Crohn's disease

• Crohn's disease patient with transient or permanent stoma.