T-ALL: Home Is where the CXCL12 Is.

T cell acute lymphoblastic leukemia (T-ALL) is caused by mutations affecting cell survival, proliferation, and differentiation. In addition to requiring these mutations, Passaro and colleagues and Pitt and colleagues in this issue of Cancer Cell demonstrate that T-ALL initiating cells residing in bone marrow depend on the CXCR4/CXCL12 signaling axis for disease maintenance and progression.