Ozanimod Differentially Impacts Circulating Lymphocyte Subsets in Patients with Moderately to Severely Active Crohn’s Disease

Background: Ozanimod showed efficacy and safety in the phase 2 STEPSTONE study conducted in patients with moderately to severely active Crohn’s disease. Aims: This analysis assessed the effects of ozanimod on circulating lymphocytes in Crohn’s disease. Methods: Patients received ozanimod 0.92 mg for 12 weeks. Lymphocyte subtypes were evaluated using multicolor flow analysis on blood samples collected before treatment and on Week 12. Absolute lymphocyte count changes were analyzed by Wilcoxon signed rank tests. Disease activity changes and efficacy outcomes were evaluated at Week 12, and associations with lymphocyte subtype levels were assessed using Spearman’s correlation and logistic regression. Results: Reductions in median total T, Th, and cytotoxic T cells occurred at Week 12 (45.4%–76.8%), with reductions in most subtypes of 47.5% to 91.3% (P < 0.001). CD8⁺ terminally differentiated effector memory cells were largely unaffected (median change, − 19%; P = 0.44). Reductions in median total B cells occurred at Week 12 (76.7%), with reductions in subtypes of 71.4% to 81.7% (P < 0.001). Natural killer and monocyte cell counts were unchanged. Greater baseline levels and changes in nonswitched memory B cells were significantly associated with clinical, endoscopic, and histologic efficacy (P < 0.05, all comparisons). Conclusions: Ozanimod reduced circulating levels of all B-cell and most T-cell subsets but not monocytes or natural killer cells. Key subsets relevant to immune surveillance were not reduced, supporting the low risk of infection and malignancy with ozanimod in chronic inflammatory diseases. Levels of nonswitched memory B cells were associated with efficacy, providing a potential marker for ozanimod response. Trial Registration: ClinicalTrials.gov: NCT02531113, EudraCT: 2015–002025–19 Graphical Abstract: (Figure presented.).