Extracellular vesicle

Extracellular vesicles (EVs) are lipid bilayer-delimited particles that are naturally released from a cell and, unlike a cell, cannot replicate. EVs range in diameter from near the size of the smallest physically possible unilamellar liposome (around 20-30 nanometers) to as large as 10 microns or more, although the vast majority of EVs are smaller than 200 nm. They carry a cargo of proteins, nucleic acids, lipids, metabolites, and even organelles from the parent cell. Most cells that have been studied to date are thought to release EVs, including some bacterial, fungal, and plant cells that are surrounded by cell walls. A wide variety of EV subtypes have been proposed, defined variously by size, biogenesis pathway, cargo, cellular source, and function, leading to a historically heterogenous nomenclature including terms like exosomes and ectosomes.'a) physical characteristics of EVs, such as size (“small EVs” (sEVs) and “medium/large EVs” (m/lEVs), with ranges defined, for instance, respectively, <100nm or <200nm , or >200nm ) or density (low, middle, high, with each range defined); b) biochemical composition (CD63+/CD81+- EVs, Annexin A5-stained EVs, etc.); or c) descriptions of conditions or cell of origin (podocyte EVs, hypoxic EVs, large oncosomes, apoptotic bodies).' Extracellular vesicles (EVs) are lipid bilayer-delimited particles that are naturally released from a cell and, unlike a cell, cannot replicate. EVs range in diameter from near the size of the smallest physically possible unilamellar liposome (around 20-30 nanometers) to as large as 10 microns or more, although the vast majority of EVs are smaller than 200 nm. They carry a cargo of proteins, nucleic acids, lipids, metabolites, and even organelles from the parent cell. Most cells that have been studied to date are thought to release EVs, including some bacterial, fungal, and plant cells that are surrounded by cell walls. A wide variety of EV subtypes have been proposed, defined variously by size, biogenesis pathway, cargo, cellular source, and function, leading to a historically heterogenous nomenclature including terms like exosomes and ectosomes. Numerous functions of EVs have been established or postulated. The first evidence for the existence of EVs was enabled by the ultracentrifuge, the electron microscope, and functional studies of coagulation in the mid-20th century. A sharp increase in interest in EVs occurred in the first decade of the 20th century following the discovery that EVs could transfer nucleic acids such as RNA from cell to cell. Associated with EVs from certain cells or tissues, nucleic acids could be easily amplified as markers of disease and also potentially traced back to a cell of origin, such as a tumor cell. The discovery also implied that EVs could be used for therapeutic purposes, such as delivering nucleic acids or other cargo to diseased tissue. This growing interest was paralleled by formation of companies and funding programs focused on development of EVs as biomarkers or therapies of disease, the founding of an International Society for Extracellular Vesicles (ISEV), and establishment of a scientific journal devoted to the field, the Journal of Extracellular Vesicles. Evidence for the existence of EVs and their functions was first gathered by combined applications of ultracentrifugation, electron microscopy, and functional studies during the mid-20th century. Ultracentrifuged pellets from blood plasma were reported to have procoagulant properties by Erwin Chargaff and Randolph West in 1946. The platelet derivation and lipid-containing nature of these particles was further articulated by Peter Wolf. Around the same time, H. Clarke Anderson and Ermanno Bonucci separately described the calcifying properties of EVs in bone matrix. Although the extracellular and vesicular properties of EVs had been recognized by numerous groups by the 1970s, the term “extracellular vesicle” was first used in a manuscript title in 1971. This electron microscopy study of the flagellate freshwater alga 'Ochromonas danica' reported release of EVs from membranes including those of flagella. Soon thereafter, EVs were seen to be released from follicular thyroid cells of the bat during arousal from hibernation, suggesting the possible involvement of EVs in endocrine processes. Reports of EVs in intestinal villi samples and, for the first time, in material from human cancer (adenoma) referred back to even earlier publications that furnished similar evidence, although conclusions about EV release had not then been drawn. EVs were also described in bovine serum and cell culture conditioned medium with distinctions made between “vesicles of the multivesicular body” and “microvesicles.” These studies further noted the similarities of EVs and enveloped viruses. In the early- to mid-1980s, the Stahl and Johnstone labs forged a deeper understanding of the release of EVs from reticulocytes, while progress was also made on EVs shed from tumor cells. The reticulocyte research, in particular, showed that EVs could be released not only from the plasma membrane or surface of the cell, but also by fusion of the multivesicular body with the plasma membrane. During this time, EVs were described by many names, sometimes in the same manuscript, such as 'shedding vesicles,' 'membrane fragments,' 'plasma membrane vesicles,' 'micro-vesicles/microvesicles,' 'exosomes,' (previously used for mobile, transforming DNA elements in model organisms Drosophila and Neurospora), 'inclusion vesicles,' and more, or referred to by organ of origin, such as 'prostasomes' that were found to enhance sperm motility in semen. The involvement of EVs in immune responses became increasingly clear in the 1990s with findings of the group of Graça Raposo and others. A clinical trial of dendritic cell-derived EVs was performed in France just before the turn of the century. Cells of the immune system were found capable of transferring transmembrane proteins via EVs. For example, the HIV co-receptors CCR5 and CXCR4 could be transferred from an HIV-susceptible cell to a refractory cell by 'microparticles,' rendering the recipient cell permissive to infection. Beginning in 2006, several laboratories reported that EVs contain nucleic acids and have the ability to transfer them from cell to cell. Some RNAs were even found to be function in the recipient cell. Whether carrying RNA, surface molecules, or other factors, the involvement of EVs in cancer progression aroused considerable interest, leading to hypotheses that specific EVs could target specific cells due to 'codes' displayed on their surface; create or enhance a metastatic niche; betray the presence of specific cancers; or be used as a therapy to target cancer cells. Meanwhile, strides were made in the understanding of vesicle biogenesis and subtypes. Rapid growth of the EV research community in the early 2000s led to the creation of the International Society for Extracellular Vesicles (ISEV), which has led efforts for rigor and standardization in the field including establishment of the Journal of Extracellular Vesicles. A plethora of national and regional EV societies have also been formed. In 2012, the Director’s Office of the US National Institutes of Health (NIH) announced a program for funding of EV and extracellular RNA studies, the Extracellular RNA Communication Consortium (ERCC), which subsequently invested >USD 100 million in EV research. A second round of funding was announced in 2018. Commercial investment in EV diagnostics and therapeutics also grew during this time. Exosome Diagnostics has developed several cancer diagnostic assays based in part on EV RNA. Codiak Biosciences is a company with intellectual property in the pancreatic cancer space. Diverse EV subtypes have been proposed, with names such as ectosomes, microvesicles, microparticles, exosomes, oncosomes, apoptotic bodies, and more. These EV subtypes have been defined by various, often overlapping, definitions, based mostly on biogenesis (cell pathway, cell or tissue identity, condition of origin). However, EV subtypes may also be defined by size, constituent molecules, function, or method of separation. Because of the bewildering and sometimes contradictory definitions of different EV subtypes, the current scientific consensus is that “extracellular vesicle” and variations thereon are the preferred nomenclature unless specific biogenetic origin can be demonstrated. Subtypes of EVs may be defined by: