TABLE 1.

Major features of exosomes.

Feature	Exosomes	References
Size	40–200 nm	Shao et al., 2018
Markers	ESCRT mechanism components (Alix, TSG101), tetraspanins (CD9, CD63, and CD81), heat shock proteins (Hsp70 and Hsp90), Rab GTPases, flotillin	Kalluri and LeBleu, 2020
Cargos	Proteins; lipids; DNA, mRNA, microRNA, and other non-coding RNAs	van Niel et al., 2018
Mechanism of release	ESCRT-dependent pathways
	ESCRT-0, I, II, and III: MVBs formation, vesicle budding, and protein cargo sorting	Zhang et al., 2019
	ESCRT-independent pathways
	Ceramides: RNA sorting in mammalian cells, spontaneous negative curvature of the endosomal membrane and inducing the budding of ILVs	Trajkovic et al., 2008; Kosaka et al., 2010
	Tetraspanins such as CD9, CD63, CD82: the sorting of cargos to ILVs	Chairoungdua et al., 2010; van Niel et al., 2011
	Rab family proteins such as Rab27A, Rab27B, and Rab35: inducing the transfer of MVBs to the cell surface	Hsu et al., 2010; Ostrowski et al., 2010
	Cytoskeleton, molecular switches (small GTPases), membrane fusion associated molecules (SNAREs, tethering factors): the docking and fusion process between MVBs and PM	Raposo and Stoorvogel, 2013
Mechanism of targeting recipient cells	Endocytosis (micropinocytosis, endocytosis mediated by clathrin, caveolin, or lipid rafts, phagocytosis of specialized cells such as macrophages)	van Niel et al., 2018
	Fusing directly with the PM of the recipient cells	van Niel et al., 2018
	Receptor-ligand interactions	Mulcahy et al., 2014
Physiological effect	Removing unnecessary components from cells: Modulating the expression and function of recipient cells by transferring bioactive molecules	Kalluri and LeBleu, 2020

ESCRT, endosomal sorting complex required for transport; SNAREs, soluble N-ethyl maleimide-sensitive factor attachment protein receptors.