Ulcerative colitis (UC) is a chronic inflammatory disorder that affects the colon. There are multiple types of cells that drive inflammation and injury to the lining of the colon. Vedolizumab (VDZ) is a medication that blocks circulating immune cells from gaining access to the colon, but there are conflicting data about the primary cell types affected by this treatment. To identify the inflammatory cells that contribute to colitis and respond to VDZ, we performed a comprehensive single-cell transcriptomic and proteomic analysis of peripheral blood and colonic biopsies of patients with and without UC. We identified inflammatory cells called mononuclear phagocytes (MNPs) as a primary target of VDZ. We then used four new, complementary methods to look at where these cells are located in fixed tissue sections, and we discovered increased density and proximity of MNP and fibroblast subsets in UC biopsies when compared to HC, with inhibition by VDZ. We now want to confirm and extend these findings by looking in more detail at these cell types in tissue sections before and after therapy. We also want to culture epithelial cells from patients with MNPs and fibroblasts to see how these cells interact when grown in the lab.