Overexpression of GM-CSF in tumors prevents generation of DC-derived macrophages. B16 tumor cells stably transduced with a retroviral vector encoding murine GM-CSF or wild-type B16 tumor cells were injected into CD11c-Cre⁺Rosa26-EGFP mice or CD11c-Cre⁻ littermate controls. (A) Expression of EGFP on CD45⁺ cells in tumor and spleen. Vertical black lines indicate background EGFP expression by Lin⁻CD45⁺ from control mice. (B-C) Expression of indicated markers by Lin⁻CD45⁺ EGFP⁺ cells in tumors (B) and spleen (C). Vertical black lines indicate staining with isotype control for CD11c. Data are representative of 2 independent experiments with 8 mice per group.