Trametinib suppresses phosphorylation of ERK1/2 in T and B cells. (A) PBMCs were isolated from patients and stimulated with PMA and ionomycin for 15 minutes. Expression of phosphorylated ERK1/2 by CD4⁺ T, CD8⁺ T cells, and CD19⁺ B cells was analyzed after treatment (or not) with trametinib and tacrolimus (10 nM, 100 nM, and 1 µM). The numbers represent the frequencies of phospho-ERK1/2 cells compared with controls. (B) Aggregated percentages of cells CD4⁺/CD8⁺ T and CD19⁺ B cells showing phosphorylated ERK1/2 expression with PMA/Ionomycin stimulation for 4 hours (data expressed as means ± SEMs; n = 4 per group, gray; PMA and ionomycin stimulation, red; unstimulated). *P < .05; **P < .01; ***P < .001; ****P < .0001 (unpaired 2-tailed Student t test).