Granulocyte-macrophage colony-stimulating factor has been widely used as an adjuvant therapy for cancer patients exhibiting myelosuppression induced by chemotherapy or radiotherapy. However, the effects of granulocyte-macrophage colony-stimulating factor on tumor growth, as well as its precise mechanism, are still controversial due to inconsistent evidence. This study investigated the effect of exogenous granulocyte-macrophage colony-stimulating factor on the growth of B16 melanoma, S180 sarcoma, and U14 cervical carcinoma in mice. The angiogenesis and recruitment of bone-marrow-derived cells were analyzed in tumor tissues. Interactions among granulocyte-macrophage colony-stimulating factor, bone-marrow-derived cells, and B16 tumor cells were investigated in vitro. Proangiogenic types of bone-marrow-derived cells in blood were assessed both in vivo and in vitro. The results showed that granulocyte-macrophage colony-stimulating factor markedly facilitated the growth of B16 and S180 tumors, but not U14 tumors. Granulocyte-macrophage colony-stimulating factor increased the densities of blood vessels and the number of bone-marrow-derived cells in B16 tumor tissues. The granulocyte-macrophage colony-stimulating factor–induced enhancement of tumor cell proliferation was mediated by bone-marrow-derived cells in vitro. Meanwhile, a distinct synergistic effect on endothelial cell function between granulocyte-macrophage colony-stimulating factor and bone-marrow-derived cells was observed. After separating two types of bone-marrow-derived cells, granulocyte-macrophage colony-stimulating factor–induced enhancement of tumor growth and angiogenesis in vivo was mediated by proangiogenic cells in granulocytes, but not monocytes, with CD11b+, vascular endothelial growth factor receptor 2, and C-X-C chemokine receptor 4 granulocytes possibly involved. These data suggest that granulocyte-macrophage colony-stimulating factor contributes to the growth and angiogenesis of certain types of tumor, and these mechanisms are probably mediated by proangiogenic cells in granulocytes. Applying granulocyte-macrophage colony-stimulating factor may attenuate the antitumor effects of chemotherapy and radiotherapy in certain types of tumor.
Tumor Growth Inhibition by Intratumoral Inoculation of Defective Herpes Simplex Virus Vectors Expressing Granulocyte–Macrophage Colony-Stimulating Factor
