P127 Sphingosine-1-Phosphate Receptor Blockade with Etrasimod alters Lymphocyte Trafficking in Crohn's Disease: Insights from High-Dimensional Phenotypic Mapping

Abstract Background The blockade of lymphocyte trafficking from the lymph nodes (LNs) towards the intestinal mucosa is an effective approach for the treatment of ulcerative colitis (UC). Etrasimod is an oral, once-daily (QD), selective sphingosine 1-phosphate (S1P)1,4,5 receptor (S1PR) modulator, which is currently also under investigation for Crohn’s disease (CD). The therapeutic mechanism of action of S1PR modulators in the context of inflammatory bowel disease (IBD) is not completely understood. It is hypothesized that both B and T- cell populations are affected by this treatment and are retained in the peripheral LNs, reducing circulating lymphocytes and resulting in fewer immune cells available to traffic in the gastrointestinal tract. Etrasimod has been reported to induce a partial and selective reduction of lymphocyte subsets in the blood of healthy subjects, but the direct effect of S1PR modulators on LN leukocytes has not been evaluated. The aim of this study was to investigate changes in leukocyte subpopulations in peripheral LNs and peripheral blood (PB) in response to S1PR inhibition with etrasimod in patients with CD. Methods CD patients with moderate to severe disease activity, participating in the Phase 2, double-blinded, non-placebo-controlled portion of the CULTIVATE trial, were eligible for this sub-study. At baseline and after 14 weeks of etrasimod induction treatment (2 or 3 mg/day), 10cc of PB and 4 ultrasound guided biopsy samples of an inguinal LN were obtained. The isolated peripheral blood mononuclear cells (PBMCs) and LN leukocyte populations, were analyzed at single cell level via high-dimensional immunophenotyping through mass cytometry (CyTOF) at both timepoints. Results We observed that in the LNs, the numbers/percentages of naïve, central and effector memory T-helper cells, as well as, of CD8+ naïve T-cells were increased after treatment with etrasimod. There was a decrease in the proportion of these cell populations in peripheral blood. Circulating naïve and memory B-cells were reduced, while these subsets where also slightly reduced in the LN compartment. Innate immune cell populations were not significantly altered. Conclusion Etrasimod induction treatment resulted in an increase of both naïve and central memory T-lymphocyte subsets in inguinal LNs, with a corresponding decrease in the periphery. The effect on the frequency of B-cells was not consistent in the LNs and PB, while innate immunotypes and T-regs, were not signi