Deletion of Vascular Endothelial Growth Factor in myeloid cells accelerates tumorigenesis

Angiogenesis and the development of a vascular network is required for tumor progression, and involves release of angiogenic factors, including vascular endothelial growth factor (VEGF), from both malignant and stromal cell types(1). Infiltration by cells of the myeloid lineage is a hallmark of many tumors, and in many cases the macrophages in these infiltrates express VEGF(2). Here we show that deletion of inflammatory cell-derived VEGF attenuates the formation of a typical high-density vessel network, thus blocking the angiogenic switch in solid tumors. Vasculature in tumors lacking myeloid cell-derived VEGF was less tortuous, with increased pericyte coverage and decreased vessel length, indicating vascular normalization. In addition, loss of myeloid-derived VEGF decreases VEGFR2 phosphorylation in tumors, even though overall VEGF levels in the tumors are unaffected. However, myeloid deletion of VEGF resulted in an accelerated tumor progression in multiple subcutaneous isograft models and an autochthonous transgenic model of mammary tumorigenesis, with less overall tumor cell death and decreased tumor hypoxia. Furthermore, loss of myeloid cell VEGF increased tumor susceptibility to chemotherapeutic cytotoxicity. This demonstrates that myeloid-derived VEGF is essential for tumorigenic alteration of vasculature and signaling to VEGFR2, and that these changes act to retard, not promote, tumor progression.