CXCR4 and leukemia: CXCL12 is produced in the BM microenvironment, activates CXCR4 on leukemic cells, facilitates leukemia cell trafficking and homing in the BM microenvironment, and maintains close contact of leukemic cells with stromal cells and the extracellular matrix that constitutively generate growth-promoting and anti-apoptotic signals [13].