STEM CELL-DERIVED EXOSOMES: BIOGENESIS, CHARACTERIZATION, ISOLATION AND PRECONDITIONING
Abstract
Introduction. Exosomes are nanoscale extracellular vesicles of endosomal origin (approximately 30–150 nm) secreted by almost all cell types, which mediate intercellular communication by carrying proteins, lipids and nucleic acids. Because stem cell-derived exosomes reproduce much of the paracrine activity of the parent cell without the drawbacks of cell transplantation, they offer a promising option in cell-free regenerative medicine. The aim of the study – to summarise current data on the structure, molecular markers, cellular sources and isolation of stem cell-derived exosomes, and on the preconditioning strategies used to modulate their properties. Research Methods. The peer-reviewed literature was searched in the PubMed, Web of Science and Scopus databases, with priority given to primary experimental studies, widely cited reviews and the international reporting framework for extracellular vesicles. Results and Discussion. The review distinguishes exosomes from microvesicles and apoptotic bodies; describes exosome structure (the lipid bilayer, the tetraspanins CD9, CD63 and CD81, the proteins ALIX and TSG101, and the internal contents); sets out identification by positive and negative markers; outlines the main stem cell types (mesenchymal cells from bone marrow, adipose tissue, umbilical cord and dental tissues; pluripotent, including induced pluripotent, cells; and neural and other progenitors) and how they are obtained; and compares the isolation methods (ultracentrifugation, size-exclusion chromatography, precipitation and filtration) with reported figures. Exosome composition depends strongly on the source cell and culture conditions. Conclusions. Both the stem cell source and the preconditioning regimen (hypoxia, cytokines, threedimensional culture and pharmacological agents) markedly influence exosome properties. Standardised production remain essential if exosomes are to progress from a research material toward a clinically applicable, cell-free therapeutic.