Notably, a submicromolar concentration of FoxO1 inhibitor (0.5 μM) decreased primary CLL cells’ viability by approximately 40% (n = 7, P = 0.001; Figure 6D and Supplemental Figure 9A), and FoxO1 inhibition combined with ibrutinib or idelalisib was more potent in inducing primary CLL cells and MEC1 cell apoptosis in vitro (P < 0.05, mostly additive effect; Figure 6, D–F). Here, FOXO1 is linked to B-cell chronic lymphocytic leukemia.