CD4 and acute lymphoblastic leukemia: In vitro and in vivo experiments confirmed that the low expression of miR-539-5p in B-ALL could directly target and promote BMP2 expression, and the increased BMP2 could further promote the proliferation and inhibit apoptosis of Nalm-6 cells, and cooperate with TGF-β1 to stimulate the differentiation of human CD4+CD25-T cells into Treg.