IL21 and acute lymphoblastic leukemia: In the present study, we demonstrate that elevated frequencies of Th17 cells and Th17-related cytokines and reduced frequencies of Th1 cells are presented in PB and BM from B-ALL patients; Th17-secreted cytokines IL-17A and IL-21 activate the Akt signaling and Stat3 signaling, and subsequently stimulate the proliferation in B-ALL cell line Nalm-6 and primary B-ALL cells; IL-17A also promotes resistance to daunorubicin through activation of Akt signaling.