Etrasimod Treatment Modulates Circulating and Lymph Node-Derived Lymphocytes in Crohn’s Disease

Etrasimod is an oral selective sphingosine-1 phosphate receptor modulator, and its anti-inflammatory mechanism of action in inflammatory bowel diseases is not completely understood. It targets pro-inflammatory immune cells expressing sphingosine-1-phosphate receptors during their migration from the lymphatic system to the circulation and intestinal mucosa. Reductions in certain lymphocyte subsets in the peripheral blood have been reported, but its effects in lymph nodes remain unknown. This study investigated changes in leukocyte subpopulations in peripheral lymph nodes and blood in Crohn’s disease patients treated with etrasimod. Moderate-to-severe Crohn’s disease patients participated in this randomized, double-blind study, within the phase 2 CULTIVATE clinical trial. At baseline and after 14 weeks of etrasimod treatment, peripheral blood and inguinal lymph node biopsies were obtained. Isolated peripheral blood mononuclear cells and lymph node leukocyte populations were analyzed at single cell level using mass cytometry at both timepoints. The immunophenotyping revealed 15 innate and adaptive major immune cell populations, as well as 14 subpopulations of CD4+ and CD8+ T-cells. In peripheral lymph nodes, etrasimod resulted in significant accumulation of naïve, central memory, and effector memory CD4+ T-cells (+10.7%, +4.2%, and +2.3%, respectively; all p = 0.03), as well as naïve CD8+ T-cells (+4.2%; p = 0.03). Conversely, these subsets were reduced in peripheral blood (−6.2%, −6.0%, −2.0%, and −2.2%, respectively; all p = 0.03). Naïve and memory B-cells decreased in the circulation (−1.7%, p = 0.057; −0.6%, p = 0.03, respectively) but were unchanged in the lymph nodes. Innate immune cell populations remained mostly unaffected in both compartments. Our data indicate that etrasimod’s pharmacodynamic effect is related primarily with the attenuation of the T-cell mediated inflammation with minor changes in B-cells. However, additional follow-up studies are needed for the validation of these observations in the context of Crohn’s disease.