ELEVATED OSM/OSMR EXPRESSION IN INFLAMED MUCOSAL TISSUE REFLECTS AN INFLAMMATORY CASCADE MEDIATED BY NEUTROPHIL:STROMAL INTERACTIONS ASSOCIATED WITH RESIDUAL DISEASE IN TREATMENT-REFRACTORY UC PATIENTS

OSM-OSMR signaling is associated with IBD disease severity and non-response to anti-TNFs, and OSMR expression is associated with inflammatory fibroblasts. We investigated OSM/OSMR signaling in primary fibroblasts, and their cellular expression in gut biopsies and interactions within the stromal and immune populations of moderate to severe UC patients. Additionally, we evaluated OSM/OSMR expression changes following treatment with etrolizumab and adalimumab to understand the specificity of these changes and their relationship to treatment response. RNASeq was applied to measure OSM, and TNF-a signaling changes in 1) OSM, TNF-a and OSM+TNF-a stimulated primary intestinal fibroblasts and 2) pre and post-treatment mucosal biopsies from HIBISCUS I/II Ph3 induction studies assessing the efficacy of etrolizumab (n=259) and adalimumab (n= 263). Downstream pSTAT3 signaling was measured to evaluate the effect of OSM induction and OSMR inhibition. A scRNA-seq atlas was generated from mucosal biopsies of moderate to severe UC patients in an independent cohort (n=20). In vitro stimulation of primary intestinal fibroblasts with OSM was used to establish an OSM-induced gene signature (PDPN, CXCL5, CXCL6, and CXCL8). Similar genes were induced in response to TNF-a stimulation and increased in OSM+TNF-a treated cells. OSM signaling was shown to be blocked by vixarelimab (anti-OSMR) treatment, through reduction in pSTAT3. In biopsy samples, OSMR expression and the OSM-induced gene signature were enriched in a subcluster of stromal cells characterized by high CHI3L1, IL11, and THY1 and low PDGFRA expression, consistent with previous reports. OSM was observed to be highly expressed by neutrophils and monocytes-derived macrophages, both of which were elevated in inflamed relative to uninflamed tissue. Within neutrophils, an OSMhi subset was identified and predicted to have abundant ligand:receptor interactions with inflammatory fibroblasts. OSM/OSMR expression was significantly reduced after ten weeks of etrolizumab (anti-beta7) or adalimumab (anti-TNF) treatment; however, less change was observed in non-remitters. Taken together, single-cell expression analysis of UC biopsies and in vitro OSM induction changes support a pro-inflammatory role of OSM/OSMR signaling between infiltrating neutrophils and inflammatory fibroblasts. Moreover, OSM/OSMR expression is associated with residual disease despite induction therapy with either etrolizumab or adalimumab. Blockade of OSMR to decrease pro-inflammatory mediators of inflammatory fibroblasts and dampen the inflammatory cycle in UC is a viable strategy for achieving benefits in clinical disease. Vixarelimab, an OSMR-targeted monoclonal antibody that blocks OSM/OSMR signaling, is currently in Ph2 clinical development for UC (NCT06137183).