We have previously described a murine leukemia model that exhibits the characteristics of microenvironment-mediated drug resistance, and we showed that the interaction between leukemia cells and the stroma can be blocked in vivo by AMD3100, a small molecule inhibitor of CXCR4 that mobilizes normal hematopoietic stem cells and leukemic blasts from hematopoietic niches into the peripheral blood. Here, CXCR4 is linked to leukemia.