TGFβ+ small extracellular vesicles from head and neck squamous cell carcinoma cells reprogram macrophages towards a pro-angiogenic phenotype

Transforming growth factor β (TGFβ) is a major component of tumor-derived small extracellular vesicles (TEX) in cancer patients. Mechanisms utilized by TGFβ+ TEX to promote tumor growth and pro-tumor activities in the tumor microenvironment (TME) are largely unknown. TEX produced by head and neck squamous cell carcinoma (HNSCC) cell lines carried TGFβ and angiogenesis-promoting proteins. TGFβ+ TEX stimulated macrophage chemotaxis without a notable M1/M2 phenotype shift and reprogrammed primary human macrophages to a pro-angiogenic phenotype characterized by the upregulation of pro-angiogenic factors and functions. In a murine basement membrane extract plug model, TGFβ+ TEX promoted macrophage infiltration and vascularization (p < 0.001), which was blocked by using the TGFβ ligand trap mRER (p < 0.001). TGFβ+ TEX injected into mice undergoing the 4-nitroquinoline-1-oxide (4-NQO)-driven oral carcinogenesis promoted tumor angiogenesis (p < 0.05), infiltration of M2-like macrophages in the TME (p < 0.05) and ultimately tumor progression (p < 0.05). Inhibition of TGFβ signaling in TEX with mRER ameliorated these pro-tumor activities. Silencing of TGFβ emerges as a critical step in suppressing pro-angiogenic functions of TEX in HNSCC.