Extracellular vesicles (EVs) are nanosized vesicles released by virtually all cell types. Increasing data suggest that EVs function in the regulation of intercellular communication both in physiological and pathological states. In cancer biology, mounting evidence suggests that cancer cell-derived EVs directly modulate several aspects of tumour progression by acting on both cancer cells and tumour-associated stromal cells.
In addition to cancer cells, the tumour microenvironment (TME) also features an intertwined ensemble of recruited host-derived cells. Tumour-associated macrophages (TAMs) often infiltrate tumours in high numbers, thus representing one of the major host-derived cell populations. The involvement of TAMs in cancer progression has been extensively documented. It is well established that according to their polarisation state, TAMs can exert both pro- and anti-tumoural functions. However, under the influence of cancer cell-derived factors TAMs often acquire a phenotype that fosters tumour progression by supporting angiogenesis, metastasis and immunosuppression. While the role of secreted soluble factors contributing to the pro- and anti-tumoural functions of TAMs is well characterised, the molecular composition, properties, and effects of TAM-derived EVs (TAM-EVs) in the TME are poorly understood.
In this thesis, I studied TAM-EVs produced in intact mouse tumours. We developed a methodology for the enrichment, quantification, and selective isolation of TAM-EVs produced in the TME. Furthermore, we performed comprehensive proteomic and lipidomic analyses of tumour-derived EVs and identified molecular signatures indicative of a role for TAM-EVs in immune response and lipid metabolism. Whereas source TAMs display a phenotype consistent with immunosuppressive functions, TAM-EVs have a pro-inflammatory and immune-stimulatory molecular signature. Indeed, TAM-EV-enriched preparations promoted T-cell proliferation and activation ex vivo and modulated arachidonic acid metabolism of cancer cells by inhibiting the production of the immunosuppressive PGE2 while favouring the secretion of pro-inflammatory thromboxane. Therefore, TAM-EVs might have the potential to stimulate, rather than limit, anti-tumour immunity. I also showed that while portraying some similarities with EVs of in vitro-polarised macrophages, TAM-EVs isolated from the TME present distinctive molecular profiles, suggesting that simplistic in vitro models do not faithfully recapitulate the complexity of the TME dynamics.
Overall, this work emphasises the importance of studying TAM-EVs in their physiological context and identifies a potential role for TAM-EVs in favouring the development of an anti-tumoural immune microenvironment. Findings from this work extend our knowledge of the multifaceted role of TAMs in tumour biology.