P0838Single-cell profiling of peripheral blood mononuclear cells of ulcerative colitis patients treated with etrasimod

Background Etrasimod is an oral, once-daily, selective sphingosine 1-phosphate receptor 1,4,5 (S1PR) modulator approved for the treatment of moderately to severely active ulcerative colitis (UC). Its mechanism of action involves the retention of lymphocytes within lymphoid tissues, thereby reducing their migration to the gut and subsequent inflammation. However, the impact of etrasimod on circulating immune cell composition and function, as well as the extent to which treatment response correlates with distinct immune signatures, remains poorly understood. Methods Peripheral blood mononuclear cells (PBMCs) were collected at baseline (week 0) and at week 12 from UC patients enrolled in the ELEVATE UC 52 Phase 3 clinical trial. PBMCs from 12 patients in clinical remission at week 12 (modified Mayo score <2), 16 non-responders to etrasimod treatment (modified Mayo score >2), and 14 placebo-treated patients were analyzed by mass cytometry. A subset of patients (n = 5 per group) underwent single-cell RNA sequencing with paired TCR profiling. Previously generated plasma proteomics data from a matching subset of patients from the ELEVATE UC study were analyzed. Results In responders, etrasimod treatment reduced the frequency of circulating CD4+ T cells and B cells while increasing the frequency of monocytes and dendritic cells at week 12 compared to baseline (p value <0.05). Analysis of lymphocyte subsets revealed decreased frequencies of memory T and B cells and an expansion of CD4+ cytotoxic T lymphocytes (CTLs) at week 12 (p value <0.05). TCR analysis demonstrated reduced CD4+ T cell diversity and increased expansion of CD4+ CTLs and CD8+ effector memory T cells following etrasimod treatment (p value <0.05). In the plasma of responders, decreased levels of pro-inflammatory cytokines (IL-8, IL-17A) and chemokines (CCL20, CCL3) were observed at week 12 (p value <0.05). In comparison to non-responders, responders exhibited a higher baseline frequency of expanded CD4+ CTLs and upregulation of cytotoxic gene programs (p value <0.05), suggesting a pre-existing cytotoxic T cell signature associated with treatment response at week 12. Conclusion Single-cell analyses of circulating immune cells on a subset of patients from the ELEVATE UC 52 trial demonstrate that etrasimod treatment impacts lymphocyte composition and clonality, consistent with the role of S1PR signaling in lymphocyte trafficking. Moreover, a distinct baseline cytotoxic T cell signature was associated with clinical response to etrasimod. Given the limited number of samples analyzed, these findings should however be interpreted with caution and validated in larger patient cohorts. This study was conducted as a collaboration between Charité,Universitätsmedizin Berlin and Pfizer. Conflict of interest: Ms. Hecker, Julia: No conflict of interest Milek, Miha: No conflict of interest Haag, Lea Maxie: No conflict of interest Freise, Inka: No conflict of interest Obermayer, Benedikt: No conflict of interest Beule, Dieter: No conflict of interest Ryan, Rathi: No conflict of interest Crosby, Catherine: No conflict of interest Siegmund, Britta: Grant: Pfizer Other: Consultant: Abbvie, Abivax, Boehringer Ingelheim, Bristol Myers Squibb, Dr. Falk Pharma, Eli Lilly, Endpoint Health, Galapagos, Janssen/Johnson & Johnson, Materia Prima, MSD, Pfizer, Takeda, Wedbush Securities. Speaker: Abbvie, AlfaSigma, Bristol Myers Squibb, CED Service GmbH, Dr. Falk Pharma, Eli Lilly, Ferring, Galapagos, Janssen/Johnson & Johnson, MD Education, MSD, Pfizer, Tr1xBio. Weidinger, Carl: C.W. received grant support by Pfizer, served as consultant for Pfizer and received speaker’s fees from Falk, Ferring, Janssen.