 It was the first integrin receptor antagonist, receiving FDA approval in 2004 for the treatment of Crohn's disease.It was approved for the treatment of multiple sclerosis as well, but there have been concerns due to reports of progressive multifocal leukoencephalopathy.Vedolizumab is very similar to natalizumab in that it is a humanized IgG monoclonal antibody, but vedolizumab is an IgG1 that specifically blocks the alpha 4 beta 7 integrin that is located primarily on cells in the gastrointestinal tract.