Tumor-Derived Macrophage Colony Stimulating Factor Mediates Tumor Immunosuppression

The mechanisms through which tumors evade immune surveillance remain incompletely understood. In our previous study, immunosuppressive soluble factor(s) secreted by murine mammary tumor (4T1) cells was shown to be a protein between 10-100 kDa. In the current study, identification of the protein in the active fractions revealed the presence of macrophage colony stimulating factor (M-CSF). M-CSF is a cytokine that plays an essential role in the regulating survival, proliferation and differentiation of macrophages and monocytes. Although the involvement of M-CSF in enhancing tumor metastasis has been reported, its involvement in tumor growth is not well reported. Here we show that genetic ablation of M-CSF in 4T1 cells reduces the rate of tumor growth and the rate of splenomegaly which have been shown to be high in 4T1 tumor-bearing mice. These data argue that, M-CSF is a key player in suppressing immune response against tumor and may be explored to boost immune based tumor therapy