P738 Response to etrasimod treatment in ulcerative colitis is associated with a reduction of circulating B and pro-inflammatory T cells: a single-cell-based post-hoc sub-analysis of the ELEVATE UC 52 trial

Abstract

Abstract Background Etrasimod (ETR) is an oral, once-daily, selective sphingosine 1-phosphate receptor 1,4,5 (S1PR) modulator for the treatment of moderately to severely active ulcerative colitis (UC). The mechanism of action is based on a retention of lymphocytes in lymphatic tissue hindering circulating lymphocytes from entering the gut and causing inflammation. However, the effect of ETR on immune cell function and composition is not well characterized. In addition, it is unknown whether the response of UC patients to ETR treatment is associated with specific immune cell signatures. Methods Single-cell RNA sequencing (scRNAseq), mass cytometry (CyTOF) and clinical data integration were used to characterize the effects of 12 weeks of treatment with ETR on the immune composition and function of peripheral blood mononuclear cells (PBMCs) collected from 15 UC patients at weeks 0 and 12 during the ELEVATE UC Phase 3 clinical trial. As an exploratory cohort, PBMCs from 5 UC patients reaching the primary endpoint of clinical remission at week 12 (modified Mayo score <2), 5 UC patients not responding to ETR treatment (modified Mayo score >2) and 5 placebo-treated UC patients were included. 30 samples were processed for scRNAseq; additionally, 28 blood samples were ex-vivo stimulated with ionomycin/PMA for 4 h and cytokine production was assessed by CyTOF. To determine the effects of ETR in UC patients, immune cell function and composition were compared intra-individually between weeks 0 and 12. Subsequent comparisons between ETR responders, non-responders and placebo-treated UC patients were performed to discriminate responders from non-responders. Results Significant reductions in T and B cell subsets, along with increases in the abundance of dendritic and monocytic cells, were observed in responders by week 12 of -treatment. Importantly, ETR treatment significantly reduced circulating T cells producing pro-inflammatory cytokines, including TNFα and IFNγ, and S1PR modulation led to a mitigation of naïve and effector memory CD4 and CD8 T cells in ETR-treated UC patients achieving clinical remission. In contrast, patients not responding to ETR treatment had significantly higher frequencies of both naïve and TNFα-producing CD4 T cells by week 12. Conclusion In line with the described role of S1PR in lymphocyte trafficking, single-cell analyses of circulating immune cells from ETR-treated UC patients confirmed a significant reduction in B cells and pathogenic T cell subsets after ETR treatment providing an in-depth cellular characterization of S1PR modulation in UC patients thereby contributing to a better understanding of the key mechanism of action of ETR. However, these findings require validation in larger cohorts.