A major limitation of current leukemia treatment is that most patients ultimately relapse. Leukemia cells show heterogeneous potential and response to treatment. We have shown that primitive leukemia stem cells (LSC) in chronic myelogenous leukemia resist elimination by treatment, and persist as a source of relapse. The bone marrow microenvironment (BMM) plays a critical role in of hematopoietic stem cell maintenance and regulation. There is increasing interest in the role of the BMM in promoting LSC maintenance, resistance to therapy, and ultimately disease relapse. Recent studies have shown that leukemia-induced changes in the BMM provide a competitive growth advantage to LSC, and support their preservation after treatment. We are studying mechanisms of niche regulation of LSC to guide development of novel approaches to target LSC and enhance cures.