CXCL12 and precursor B-cell acute lymphoblastic leukemia: Even if B-ALL cells in vitro co-cultured with HD-MSCs did not directly modulate CXCL12 secretion by MSCs [62], our group recently demonstrated that Activin A, a soluble mediator belonging to the TGFβ family, overexpressed in the B-ALL BM niche [63], is able to downregulate CXCL12 production by BM-MSCs [50].