CXCR4 and leukemia: It is suggested that after Nrf2 overexpressed MSCs were co-cultured with Nalm-6/RS4; 11 cells, CXCR4 on Nalm-6/RS4; 11 cell surface can be an important factor activating the SDF-1/CXCR4 axis within the leukemia microenvironment, which further promotes Nrf2 overexpressed MSCs to react with ALL cells (Teicher and Fricker, 2010).