Purpose: Extracellular vesicles, small vesicles carrying inter alia proteins, miRNA and RNA, are important mediators of intercellular communication. The purpose of this study was to assess the distribution of extracellular vesicles from highly malignant breast cancer and their subsequent effect on the immune cell infiltrate in target organs of metastasis. Procedures: Extracellular vesicles were isolated from the tissue culture supernatant of highly malignant 4T1 breast cancer cells or the serum of healthy BALB/c mice. The purity of the isolate was verified by electron microscopy and western blotting. Extracellular vesicles were additionally subjected to proteome analysis. After labeling with the fluorescent dye DiR, extracellular vesicles were injected into healthy BALB/c mice and their in vivo distribution was assessed using fluorescence reflectance imaging (FRI). Following ex vivo imaging of the organs, lung tissue samples were analyzed for extracellular vesicle-mediated changes of myeloid cells and T cell numbers, using flow cytometry. Proteome analysis revealed major differences in the cargo of tumor cell-derived versus extracellular vesicles from healthy serum.

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