Dancing with Trojan horses: an interplay between the extracellular vesicles and viruses

Extracellular vesicles (EVs) are membrane-encapsulated particles released by eukaryotic and prokaryotic cells into the extracellular environment. Depending on their origin, size, and composition, EVs are grouped in several classes, with one of them being exosomes, which are small EVs (SEVs) generated within the endosomal compartment of eukaryotic cells via the unique multivesicular body pathway. Being able to deliver their content (proteins, lipids, small molecules, and nucleic acids) to other cells, exosomes/SEVs are considered as bioactive vesicles with multiple biological functions. Importantly, the composition of exosomes/SEVs depends on the cell and tissue of origin including a set of specific proteins. However, the pathological conditions may lead to the appearance of diseases-specific exosomes/SEVs containing pathology-specific cargoes utilized in the malicious cell-cell communication and spread of malady. Viruses demonstrate complex 'dancing' around the exosome biogenesis system, being able to hijack the host systems responsible for the exosome biogenesis. They use the exosome biogenesis system to promote packaging of their capsids, regulate virion production, and virus secretion. They also utilize a Trojan horse stratagem to place virions inside the SEVs and thereby to spread beyond their normal range of cell hosts using the normal EV uptake process. Another illustration of the virus-based utilization of Trojan horse strategy is given by the ability of human viruses to use exosomes/SEVs as carriers of their exogenous miRNA or viral proteins to the non-infected cells. Taken together, these strategies of dancing with Trojan horses can help viruses to fight with the host defense and to spread the infection. Communicated by Ramaswamy H. Sarma