The role of plasma-derived small extracellular vesicles in pre-metastatic niche formation through modulation of macrophages in head and neck squamous cell carcinoma.

BACKGROUND: Metastases are associated with poor survival in head and neck squamous cell carcinoma (HNSCC) patients and tumour-associated macrophages (TAMs) are important drivers in tumour progression and metastasis formation. Small extracellular vesicles (sEVs) are another important factor that contribute to systemic immunosuppression and pre-metastatic niche formation. Here, we investigate the effect of plasma sEVs from HNSCC patients on pre-metastatic niche formation, directly or through modulation of macrophages. METHODS: Primary macrophages were incubated with sEVs from plasma of HNSCC patients or healthy donors (HD). RNA profiles and inflammatory properties of macrophages were evaluated. Direct and indirect effects of sEVs on chemotaxis, T cell activation, proliferation and epithelial-to-mesenchymal transition (EMT) of tumour cells were investigated. RESULTS: sEVs of HNSCC patients and HD induced different RNA profiles in macrophages. sEVs induced apoptosis and inhibition of T cell activation, while tumour cells were attracted by sEV-treated macrophages, but not sEVs directly. Proliferation was inhibited by both, sEVs and supernatant of EV-treated macrophages in HNSCC. Additionally, EMT in tumour cells was reversed by HNSCC sEV-treated macrophages. CONCLUSION: sEVs from plasma of HNSCC patients transformed macrophages into metastasis-promoting TAMs and inhibited anti-tumour T cells, highlighting the potential of sEVs and TAMs as targets for therapeutic approaches.