Ulcerative colitis (UC) is a subtype of inflammatory bowel disease (IBD) that causes relapsing and remitting inflammation in the colon and rectum. Numerous treatment options are available for patients with UC including biologics and small molecule inhibitors that target the immune system. Although these therapies have dramatically improved options for patients with IBD, there remains a modest ceiling for their overall efficacy. Currently there are no biomarkers that can guide treatment decisions in patients with UC. Some studies have reported certain molecules or immune populations that are associated with treatment resistance or as predictors of treatment response. However, their clinical utility have yet to be fully determined because there is a paucity of longitudinal studies examining the direct effects of current biologics and small molecule inhibitors approved for UC on the immune biology of the colon mucosa. In this study, we perform longitudinal immune phenotyping using flow cytometry in patients with UC before and after therapy. Colon biopsy tissue was taken prior to treatment from 10 UC patients who were then followed and repeat biopsies were obtained from the same patients after 6-12 months of treatment. Tissue was analyzed using high dimensional flow cytometry with a panel of 24 markers of both lymphoid and myeloid lineages. Pre-treatment samples with inflammation correlated with higher populations of CD4+ T cells and CD4+ FOXP3 regulatory T cells also positive for TIGIT and GITR. Inflammation also corresponded with the presence of a CD33+ HLA-DR- population classically known as myeloid-derived suppressor cells (MDSC). Overall, therapy significantly decreased immune cell infiltration in the colon, most notably in B and T cell populations. However, certain treatments increased the MDSC population along with the stromal compartment of non-immune cells. A comprehensive analysis of the populations present during active inflammation and the treatment-induced changes in mucosal immunity will help identify biomarkers to predict response to therapy. In addition, examining the interplay between immune cells and the surrounding stroma can may lead to important findings that improve our understanding of each drug’s mechanism and efficacy. Future experiments with single cell RNA and T cell receptor sequencing on the same patients will identify effects of biologic therapy on the T cell repertoire and interactions between immune, epithelial, and stromal cells in the colonic mucosa. With the advent of novel sequencing and immune profiling assays, we now have the ability to harness the power of precision medicine to make more informed therapeutic decisions for IBD patients that improve clinical outcomes.
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