Extracellular vesicles are secreted by many cells, of which the common ones are Mesenchymal Stromal Cells, Pericytes, CAR-T cells, human primary bronchial epithelial cell, epithelial cells, EBV(Epstein-Barr virus)-immortalized B cells, HUVECs (Human umbilical vein endothelial cells) Leukocytes, platelets, cancer cells and even neural cells. They are classified into three groups depending on their size.