Cobimetinib, but not trametinib, inhibits both PI3K/AKT and MEK/ERK signaling. (A-B) PBMCs were stimulated with PMA and ionomycin, and phosphorylation of ERK1/2 within CD4⁺ and CD8⁺ T cells was evaluated by flow cytometry: representative data (A) and aggregate data (B). The line graph plots the mean value; error range, standard error of the mean (SEM). (C) PBMCs were stimulated with PMA and ionomycin, and total ERK1/2 and pERK1/2 were evaluated by western blotting. (D-E) B or T cells were stimulated with insulin, and phosphorylation of AKT was evaluated by flow cytometry: representative data (D) and aggregate data (E). Bars, MFI values with SEM. (F-G) PBMCs were exposed to trametinib, taselisib, or both drugs, and frequencies of CD20⁺CD23⁺CD69⁺ cells after stimulation with anti-CD40 antibody and IL-4 were evaluated: representative data (F) and aggregate data (G). Bars, mean values; error range, SEM. All experiments were performed 4 times, independently. A two-tailed unpaired t test was used for comparisons between 2 groups of continuous variables. ∗P < .05, ∗∗P < .01. Cobi, cobimetinib; N.S., not significant; pAKT, phosphorylated AKT; pERK, phosphorylated ERK; Tase, taselisib; Tra, trametinib.