Description

Eligible participants will receive vedolizumab through an IV ("infusion") at week 0, then week 2, then week 6. Participants who respond well to the treatment after the first 3 infusions and are interested in continuing will receive vedolizumab every 8 weeks for about 1 year. At each visit, participants will be asked about their collagenous gastritis symptoms and any changes in their health or medications.

Blood samples will be collected from participants at every vedolizumab infusion. Some of these samples will be collected for safety purposes, some will be collected to monitor CG progression, and some will be collected for research purposes.

During the screening period and a few months after beginning treatment, the study doctor will perform an upper endoscopy to help determine whether vedolizumab has improved each participant's CG. An upper endoscopy is a procedure where the doctor inserts a small tube with a camera through the mouth and down the throat to look at the upper gastrointestinal tract (the esophagus, stomach, and part of the small intestine). During the procedure, biopsies will be collected to monitor CG and for research purposes. All participants will be given medication to make them comfortable throughout the duration of the procedure, which lasts approximately 10 to 30 minutes.