UBC and leukemia: To further assess whether CXCL12, provided by the microenvironment, affects the growth and survival of leukemia cells, we transplanted c-Kit+MLL-AF9 leukemia cells into Cxcl12f/f-Ubc-Cre+ (referred to as Cxcl12−/−) mice (Figure 6D; Figure S6D), which are devoid of CXCL12 expression in all tissues.