Poster Session II – Poster of Distinction II - A207 EXPANSION OF PERIPHERAL RORγT+ POLYMORPHONUCLEAR MYELOID-DERIVED SUPPRESSOR CELLS (PMN-MDSCS) SIGNALS EARLY IMMUNE DYSREGULATION LINKED TO CROHN’S DISEASE RISK

Abstract Background Crohn’s disease (CD) is a chronic inflammatory bowel disease thought to be driven, in part, by an exaggerated immune response to intestinal microbes. While impaired epithelial barrier function, and anti-microbial antibodies can be detected years before CD onset; the immunological changes preceding CD onset remains unexplored Aims To identify immune signatures associated with CD risk by phenotyping the peripheral immune landscape during the preclinical phase of CD Methods In a nested case-control cohort of the CCC-GEM Project, which prospectively follows healthy first-degree relatives (FDRs) of CD patients, 80 FDRs who developed CD (pre-CD) were matched by age, sex, follow-up duration, and location with FDRs who remained healthy (HMC, n = 310). PBMCs collected at recruitment were analyzed by single-cell mass cytometry using 40 phenotypic and functional markers. Immune subsets were identified by automated unbiased clustering, and their associations with future CD, faecal calprotectin (FCP), serum proteomics (Olink®), and antimicrobial antibodies (Prometheus®) were assessed using conditional logistic regression, generalized estimating equations, or partial Spearman correlation as appropriate. ROC analyses evaluated performance of immune subsets to stratify future CD cases from controls Results A distinct peripheral immune landscape, characterized by increased myeloid and reduced lymphoid subsets, was associated with FCP and future CD (p = 0.00003-0.05). Subgroup analysis based on median follow-up time to diagnosis revealed temporal immune alterations during the preclinical phase, with early expansion of RORγt+ PMN-MDSCs and CCR9+ dendritic cells occurring more than 2.5 years prior to CD onset, preceding the peripheral loss of α4β7+ activated naïve-like T and B cells observed within 2.5 years before diagnosis. Early expansion of these myeloid subsets correlated with elevated serum ASCA- or ompc-IgA levels. Although RORγt+ PMN-MDSCs remained elevated until CD onset, proteomic analysis revealed a shift from regulatory to proinflammatory phenotypes approaching CD onset. Finally, ROC analysis identified RORγt+ PMN-MDSCs as having the highest potential for CD risk stratification (AUC=0.821). Conclusions This study delineates the immune cell alterations associated with future CD and identifies RORγt+ PMN-MDSCs as a potential early immune marker for CD risk stratification and target for preventive intervention. Funding Agencies CCC