Here, we show that Th17 cells and IL-17A are highly elevated in Ph+ B-ALL patients, which in turn promote the progression of Ph+ B-ALL by activating BCR-ABL, IL6/JAK/STAT3 and NF-kB signalling pathways and increasing the secretion of the chemokine CXCL16 by leukemia cells. Here, STAT3 is linked to precursor B-cell acute lymphoblastic leukemia.