Extracellular Vesicles and Exosomes

Extracellular vesicles (EVs) are emerging as promising new biological drug modalities. They are starting to supersede other touted technologies with considerable heft in the biotechnology world. Monoclonal antibody technology is probably the leading topic still but EVs are pushing at that pinnacle.

The Nature of Extracellular Vesicles

Extracellular vesicles (EVS) are derived from cells and are nanometers in size.   Three types of cell derived extracellular vesicles are formed (Li et al., 2017) which are characterised by their respective size and source:-

• exosomes (30-150nm) (derived from intracellular vesicular traffic )
• microvesicles (100-1000nm) (derived from plasma membrane shedding)
• apoptotic vesicles or blebs (100 – 5000nm) (end death products)

The most interesting are the exosomes and the remainder of this article is devoted to them.

Exosomes

Exosomes are a discrete population of small vesicles produced by multivesicular bodies (MVBs) and are classified as nanostructures. Produced by most cells into their extracellular surroundings they have a diameter of between 30 and 150 nm (Simpson et al., 2009; Bobrie et al., 2011) although that can be narrowed to between 40 and 100 nm.

The exosomes are composed of a lipid bilayer with membrane proteins and various other proteins, lipids and RNAs in the cytosol (Li et al., 2017; Zhang et al., 2016). The topology is almost that of a cell. They have a role in various physiological and pathological processes.

They were identified in 1986 by Eberhard G. Trams and R.M. Johnstone who saw very small vesicles with a membrane structure in the culture supernatant of red blood cells collected from sheep’s blood. The name exosome was coined.

Purification and isolation are of extracellular vesicles (EVs) and exosomes one of the leading research areas. Most of the downstream processing activity has centred on characteristics of EVS generally such as  morphology, flotation density, vesicle size and the presence of marker proteins including Alix, TSG101, HSP70 and CD9 (Simpson et al., 2009).

They are viewed as useful drug delivery vehicles as well as offering considerable potential in dealing with various disease states including sepsis. They are also markers for biopsy because of the presence of marker proteins mentioned previously.

Purification

Ultracentrifugation is one of the main approaches still for isolating exosomes even though there are issues associated with it as a method. It’s often employed in combination with sucrose density gradients or sucrose cushions where the relatively low-density exosomes float.

EVs are promising vehicles for drug delivery. They can be sourced from many different tissues. Therapeutics (EV-Tx) can be derived from mesenchymal stromal cells (MSC) where they exert a potent mix of anti-inflammatory, anti-fibrotic and regenerative effects. MSC-EV-Tx could optimize healing after acute traumatic injury for example.

References

Bobrie, A., Colombo, M., Raposo, G., & Théry, C. (2011). Exosome secretion: molecular mechanisms and roles in immune responses. Traffic, 12(12), pp. 1659-1668.

Kalluri, R., & LeBleu, V. S. (2020). The biology, function, and biomedical applications of exosomes. Science, 367(6478), eaau6977.

Li, P., Kaslan, M., Lee, S. H., Yao, J., & Gao, Z. (2017). Progress in exosome isolation techniques. Theranostics. 7, pp. 789–804 (Article).

Pegtel, D. M., & Gould, S. J. (2019). Exosomes. Annual Review of Biochemistry, 88, pp. 487-514.

Simpson, R. J., Lim, J. W., Moritz, R. L., & Mathivanan, S. (2009). Exosomes: proteomic insights and diagnostic potential. Expert Review of Proteomics, 6(3), pp. 267-283.

Tauro, B. J., Greening, D. W., Mathias, R. A., Ji, H., Mathivanan, S., Scott, A. M., & Simpson, R. J. (2012). Comparison of ultracentrifugation, density gradient separation, and immunoaffinity capture methods for isolating human colon cancer cell line LIM1863-derived exosomes. Methods (San Diego, Calif.), 56(2), pp. 293–304 (Article)

Théry, C., Amigorena, S., Raposo, G., & Clayton, A. (2006). Isolation and characterization of exosomes from cell culture supernatants and biological fluids. Current Protocols in Cell Biology, 30(1), pp. 3-22

Zhang, M., Viennois, E., Xu, C., & Merlin, D. (2016). Plant derived edible nanoparticles as a new therapeutic approach against diseases. Tissue Barriers, 4, e1134415. (Article)