Extracellular Vesicles in the Blood of Dogs with Cancer—A Preliminary Study

SIMPLE SUMMARY: Extracellular vesicles are a diverse population of submicron-sized structures released from cells under physiological and pathological conditions. Due to their size, their role in cell-to-cell communication in cancer is currently being discussed. In blood, the most abundant population is platelet-derived extracellular vesicles. The aim of this study was to estimate the absolute number and the origin of extracellular vesicles in the blood of healthy dogs and of dogs with various types of cancer. The number of extracellular vesicles derived from platelets, leukocytes, and T lymphocytes was significantly higher in dogs with cancer compared to healthy controls. Estimation of platelet-derived extracellular vesicle (PEV) and leukocyte-derived EV counts may provide a useful biological marker in dogs with cancer. ABSTRACT: Extracellular vesicles (EVs) are a heterogeneous population of submicron-sized structures released during the activation, proliferation, or apoptosis of various types of cells. Due to their size, their role in cell-to-cell communication in cancer is currently being discussed. In blood, the most abundant population of EVs is platelet-derived EVs (PEVs). The aim of this study was to estimate the absolute number and the origin of EVs in the blood of healthy dogs and of dogs with various types of cancer. The EV absolute number and cellular origin were examined by flow cytometry technique. EVs were classified on the basis of surface annexin V expression (phosphatidylserine PS+) and co-expression of specific cellular markers (CD61, CD45, CD3, CD21). The number of PEVs was significantly higher in dogs with cancer (median: 409/µL, range: 42–2748/µL vs. median: 170/µL, range: 101–449/µL in controls). The numbers of EVs derived from leukocytes (control median: 86/µL, range: 40–240/µL; cancer median: 443/µL, range: 44–3 352/µL) and T cells (control median: 5/µL, range: 2–66/µL; cancer median: 108/µL, range: 3–1735/µL) were higher in dogs with neoplasia compared to healthy controls. The estimation of PEV and leukocyte-derived EV counts may provide a useful biological marker in dogs with cancer.