Exosomes: recruits for tumour surveillance?

Extracellular vesicles were firstly described 50 years ago (1). Subsequently it was discovered that three different types could be distinguished: microvesicles and apoptotic bodies (larger than 100 nm) and exosomes (up to 150 nm in diameter) (2). Exosomes are small vesicles derived from, and formed inside, the endosomal compartment (Figure 1A). Endosomal vesicles containing exosomes are called Multivesicular Bodies (MVBs) and they fuse with the cell membrane releasing the exosomes outside the cell (2). Exosomes can subsequently be uptaken by other cells trough clathrin-independent pathways (Figure 1B) (3). In this way their content can be transferred from cell to cell (2,5). Firstly formally described in 1987 (6) they were, according to a pattern very common in science, first dismiss as artefact and subsequently as of no interest (7). It has been only after some years that their importance has been eventually acknowledged (2,5,7).