CXCL12 and leukemia: Loss of normal hematopoiesis is a classical event during human myeloproliferative neoplasias and leukemias where the niche downregulate essential HSPC retention factors as CXCL12, SCF, LepR, Angpt1, Cdh2, Slit2, and TGF-β1 though pro-inflammatory factors secreted by leukemia-initiating cells (64).