CXCR4 and leukemia: The results revealed that compared with the leukemia cells in the control group and EV group, up-regulating CXCR4 in leukemia cells obviously enhanced the promotion effect of TGF-β conditioned MSCs on the migration and invasion of Nalm-6/RS4;11 cells (P < 0.05; Supplementary Figures S3C,D).