Fig. 1

Schematic depicting the biogenesis, structure, and major molecular components of exosomes. Exosomes are lipid bilayer extracellular vesicles with diameters typically between 30 and 120 nm. Exosome biogenesis initiates when a portion of the plasma membrane buds into the cell to create an early endosome that transforms into late endosomes termed multivesicular bodies (MVB) containing a large number of exosomes. In the meantime, transmembrane and surface proteins located on the plasma membrane are placed into the invaginating membrane, while the cytosolic biologics are enveloped within the exosomes. After fusion with the plasma membrane and through the exocytosis, MVBs release the exosomes into the extracellular space. The payload of exosomes can include proteins, cytoskeletal proteins, signaling molecules, receptors, ligand, tetraspanins, miRs, mRNAs, and other bioactive compounds. They can also carry various immunoregulatory (like miRs) and immunosuppressive (like surface proteins) as well as anti-tumor (like miRs) and tumorigenic (like surface proteins) mediators