Vedolizumab, a gut-homing α4β7 integrin antagonist, has demonstrated efficacy in 
ulcerative colitis and Crohn's disease. Development of progressive multifocal 
leukoencephalopathy, a serious brain infection associated with natalizumab (an 
α4β7 and α4β1 integrin antagonist), has raised concern that vedolizumab may 
convey a similar risk. Natalizumab is believed to impair central nervous system 
immune surveillance by affecting cerebrospinal fluid (CSF) lymphocyte counts and 
the CD4:CD8 ratio. To determine if vedolizumab elicits similar effects, we 
examined CSF of healthy volunteers by flow cytometry for T-lymphocyte surface 
markers 5 weeks after administration of intravenous vedolizumab 450 mg. No 
significant changes were observed in CSF T-lymphocyte populations.