GUT-ASSOCIATED LYMPHOID TISSUE ATTRITION ASSOCIATES WITH RESPONSE TO ANTI-α4β7 THERAPY IN ULCERATIVE COLITIS

Induction of intestinal immune responses occurs in gut-associated lymphoid tissues (GALT). After priming in GALT, lymphocytes upregulate integrin α4β7, which drives their homing back to intestinal effector sites through engagement of MADCAM1. Tertiary lymphoid structures (TLS) such as ILF increase in inflamed intestines but their role in the pathogenesis of inflammation is unclear. Anti-α4β7 blockade using vedolizumab (VDZ) is a highly effective therapy for ulcerative colitis (UC), which was originally thought to reduce inflammation by preventing lymphocyte entry into effector sites. However, this mechanism has not been proven. Here, we investigated the effects of α4β7 blockade on gut immune responses and searched for correlates of response.

We studied a cohort of patients with UC (n=83) treated with VDZ or tumor necrosis factor inhibitors (TNFi). Intestinal biopsies and/or peripheral blood were longitudinally analyzed pre- and post-therapy by flow cytometry (FC). In peripheral blood, we observed a significant decrease in β7⁺ plasma cells (PC) post-VDZ. In the gut, we found a significant decrease in naïve B and T cells post-VDZ, but not post-TNFi. We confirmed these results in mice, where we observed a loss of naïve B cells (FC and single-cell RNAseq) and loss of GALT size after anti-α4β7 blockade. Using photoconvertible mice, we discovered that recruitment of naïve B cells into PPs was impaired by blocking α4β7. The induction of antigen-specific IgA after oral immunization was significantly decreased in anti-α4β7 treated mice.

To determine correlates of therapeutic response to VDZ, we investigated two cohorts of UC patients (n=60, n=21) where intestinal biopsies were obtained pre- and post-therapy with VDZ or TNFi. After therapy, lymphoid aggregates were significantly smaller in Responders compared to Non-Responders (NR) to VDZ, but not to TNFi. Longitudinal samples demonstrated a significant decrease in aggregate size and naïve B cell number in Responders, but not in NRs. Morphologically, lymphoid aggregates in Responders were less organized after therapy, while NRs retained GALT organization (demarcated B/T cell zones and germinal centers). Further, Responders (but not NRs) had reduced frequencies of circulating β7⁺IgG⁺ PCs and colonic IgG⁺ PCs post-VDZ. Finally, we evaluated the expression of genes from the FcγR-mediated phagocytosis pathway on two datasets from UC patients (n=406, n= 41). This pathway was enriched in inflamed tissues and significantly reduced after VDZ in Responders but not in NRs. Our work demonstrates a novel effect of anti-α4β7 blockade that results in GALT attrition through impaired recruitment of naïve B cells, leading to the suppression of inflammation-associated immune responses and FcγR signaling. These data highlight the targeting of GALT as a novel therapeutic paradigm in IBD.