siRNA mediated depletion of CD26 mRNA leads to enhanced T-cell proliferation. PBMCs from healthy subjects were isolated and placed in culture for 6 days in 96 round-well plates. To promote T-cell division, Accell culture medium was supplemented with PHA ± IL-12. Besides, a CD26-specific or a non-targeting Accell siRNAs pool was also used. (a) Expression of CD26 (MFI; mean fluorescence intensity) on PBMCs was assessed by flow cytometry. Three representative assays are shown. 2-way ANOVA with Tukey’s multiple comparison test: *P < 0.05, ***P < 0.001, ****P < 0.0001; n.s., non-significant. (b) PBMCs from 2 representative donors were labelled with CFSE and T-cell proliferation induced by PHA ± IL-12 was assessed by CFSE-dilution assays. Responder frequency is the percentage of T lymphocytes that divided at least once. 2-way ANOVA with Tukey’s multiple comparison test: *P < 0.05, **P < 0.01, ****P < 0.0001; n.s., non-significant.