Single-cell RNAseq of murine Peyer's patches after one dose of anti-α4β7 antibody or PBS

Targeting the α4β7-MAdCAM-1 axis with vedolizumab (VDZ) is a first-line treatment in ulcerative colitis (UC). However, mechanism(s) of action (MOA) of VDZ remain relatively undefined. Here, we examined five distinct cohorts of patients with UC (n=83, n=60, n=21, n=31, n=401), to determine the effect of VDZ on the mucosal and peripheral immune system. We found a significant decrease in colonic and ileal naïve B and T cells and circulating gut- homing plasmablasts (β7+) in VDZ-treated patients, pointing to gut-associated lymphoid tissue (GALT) targeting by VDZ. Murine Peyer’s patches (PP) demonstrated a significant loss cellularity associated with reduction in follicular B cells, including a unique population of epithelium-associated B cells, following anti-α4β7 antibody (mAb) administration. Photoconvertible (KikGR) mice demonstrated impaired cellular entry into PPs in anti-α4β7 mAb treated mice. In VDZ-treated, but not anti-tumor necrosis factor-treated UC patients, lymphoid aggregate size was significantly reduced in treatment responders compared to non- responders, with an independent validation cohort further confirming these data. Response to VDZ was associated with a significant decrease of naïve B cells and a reduction in B cell follicle organization in the GALT. Responders had a significant reduction of β7+IgG+ plasmablasts in circulation, as well as IgG+ plasma cells and FcgR-dependent signaling in the intestine. GALT targeting represents a previously unappreciated MOA of α4β7-targeted therapies, with major implications for this therapeutic paradigm in UC, and for the development of new therapeutic strategies. Peyer's patches were isolated from the small inthestine of treated mice and incubated with collagenase D, before mechanical homogenization to obtain a single-cell suspension.