Cancer metastasis accounts for most of the cancer-related deaths. Metastatic progression culminates in the formation of secondary tumors in distant organs. This process, which involves the dissemination and survival of circulating tumor cells (CTCs) via the bloodstream, is facilitated by the priming of pre-metastatic niches (PMN) by tumor-secreted factors, including extracellular vesicles (EVs). Tumor EVs, which contain different cargos such as RNA, proteins or lipids, favor metastasis by inducing microenvironmental changes that are prone to survival and growth of disseminating tumor cells. Among these stromal changes, EVs are known to modulate the immune system, yet their precise mode of action remains unclear. In this study, we used a murine model of triple negative breast cancer (4T1) to dissect the immune response to tumor-derived EVs in the context of an experimental lung metastasis model. This characterization is achieved by a global myeloid and lymphoid cells immunophenotyping using flow cytometry combined to imaging approaches with immunofluorescence staining and an innovative ex vivo lung imaging strategy. Intravenous injection of 4T1-derived EVs in mice lead to the recruitment of neutrophils to the lungs, where CTCs would metastasize. Strikingly, this recruitment occurs within an hour after tumor EVs injection while other populations remain stable, although recruited interstitial macrophages seem affected. Interestingly, priming mice with tumor EVs shortly before tumor injections increases the lung metastatic burden, but this effect is substantially reduced when neutrophils are depleted prior to the injections. Altogether, our results suggest that 4T1 secreted-EVs favor neutrophil recruitment to the PMN and thereby facilitate early metastatic seeding in an experimental lung metastasis model. Using ex vivo imaging, we are currently investigating the mechanisms at the basis of neutrophil recruitment and dissecting the mechanistic events favoring lungs colonization and metastatic outgrowth.