Fig. 6: SAR’336 engages IL-2Rα with high affinity but does not measurably interact with the IL-2Rβ subunit.

a Biochemical characterization of SAR’336 interactions with IL-2 Rα and β receptor subunits using SPR demonstrates that SAR’336 engages the IL-2Rα with high affinity but does not measurably engage the IL-2Rβ subunit. Extracellular domains of the human IL-2Rα (top row) and β (bottom row) subunits were immobilized on the surface of a SPR sensor and probed with a dilution series of either rhIL-2 (left column) or SAR’336 (right column). Test samples were injected for 60 s to allow association, followed by buffer only to measure dissociation kinetics. Response units (RU, Y-axis) are plotted versus time (s, X-axis). The colors correspond to each test concentration as shown (inset). b Assessing pSTAT5 levels SAR’336 in human primary lymphocytes shows that SAR’336 potency on Tregs is reduced compared to IL-2, but highly specific for Treg signaling versus CD8 + T cells and NK cells. Human PBMC samples from 4 healthy donors were stimulated with concentration series of rhIL-2 or SAR’336. Treated cell populations were analyzed using multi-color flow cytometry to detect and quantify pSTAT5 levels in different cell subsets. The plots shown represent the average (+ SEM) pSTAT5 fluorescence intensity, fit to a baseline restrained 4 parameter logistic regression and normalized to maximum signal to facilitate comparison of potency on Treg, NK and CD8 + T cell subsets. Average EC50 values are shown. Individual EC50 values are reported in Supplementary Table 4. CD8 cluster of differentiation 8, EC50 half-maximal effective concentration, ECD extracellular ___domain, IL-2 interleukin-2, IL-2 Rα interleukin-2 receptor alpha, IL-2 Rβ interleukin-2 receptor beta, KD dissociation constant, MFI median fluorescence intensity, ND not determined, NK natural killer, PBMC peripheral blood mononuclear cells, rhIL-2 recombinant human interleukin 2, RU response units, pSTAT5 phosphorylated Signal Transducer and Activator of Transcription 5, S seconds, SEM standard error of mean, SPR surface plasmon resonance, Treg regulatory T cell.