To assess whether BMDM phenotypic switching by MSC-derived CXCL12 might have an impact on tumor induction by 4T1 cells, a mixture of 4T1 cells plus BMDM co-cultured with MSCsCXCL12+/+ or MSCsCXCL12−/− was respectively injected into the left and right inguinal mammary fat pads (four fat pads in each group) (Fig. 4A). The gene discussed is CXCL12; the disease is neoplasm.