Sphingosine-1 phosphate receptor-1 (S1P ) activation maintains endothelial barrier integrity whereas S1P desensitization induces peripheral blood lymphopenia. The latter is exploited in the approval and/or late-stage development of receptor-desensitizing agents targeting the S1P receptor in multiple sclerosis, such as siponimod, ozanimod and ponesimod. SAR247799 is a recently described G protein-biased S1P agonist that activates S1P without desensitization, and thus has endothelial-protective properties in patients without reducing lymphocytes. As SAR247799 demonstrated endothelial-protective effects at sub-lymphocyte-reducing doses, the possibility exists that other S1P modulators could also exhibit endothelial-protective properties at lower doses. To explore this possibility, we sought to quantitatively compare the biased properties of SAR247799 with the most advanced clinical molecules targeting S1P . In this study, we define the b-arrestin pathway component of the impedance profile following S1P activation in a human umbilical vein endothelial cell line (HUVEC) and report quantitative indices of the S1P activation-to-desensitization ratio of various clinical molecules. In a label-free impedance assay assessing endothelial barrier integrity and disruption, the mean estimates (95% confidence interval) of the activation-to-desensitization ratios of SAR247799, ponesimod, ozanimod and siponimod were 114 (91.1-143), 7.66 (3.41-17.2), 6.35 (3.21-12.5) and 0.170 (0.0523-0.555), respectively. Thus, we show that SAR247799 is the most G protein biased S1P agonist currently characterized. This rank-order of bias amongst the most clinically advanced S1P modulators provides a new perspective on the relative potential of these clinical molecules for improving endothelial function in patients in relation to their lymphocyte-reducing (desensitization) properties.This article is protected by copyright. All rights reserved.