Extracellular vesicles (EVs) are nano-sized lipid bilayer vesicles released by virtually every cell type. EVs have diverse biological activities, ranging from roles in development and homeostasis to cancer progression, which has spurred the development of EVs as disease biomarkers and drug nanovehicles. Owing to the small size of EVs, however, most studies have relied on isolation and biochemical analysis of bulk EVs separated from biofluids. Although informative, these approaches do not capture the dynamics of EV release, biodistribution, and other contributions to pathophysiology. Recent advances in live and high-resolution microscopy techniques, combined with innovative EV labeling strategies and reporter systems, provide new tools to study EVs in vivo in their physiological environment and at the single-vesicle level. Here we critically review the latest advances and challenges in EV imaging, and identify urgent, outstanding questions in our quest to unravel EV biology and therapeutic applications.
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The authors acknowledge financial support from the International Society for Extracellular Vesicles, the French Society of Extracellular vesicles, the Société Française des Microscopies, the ITMO BCDE for their support for the organization of the ISEV workshop ‘EV imaging in vivo’ that provided the basis for this review. We thank the workshop organizing committee members G.D.’A., V.H., E.-M.K.-A., X.L., and K.W. for their help. We thank P. Stahl (Washington University School of Medicine, USA) for stimulating discussions and insight. F.J.V. is supported by INCa 2019-125, E.B.C. thanks M. Dustin for support through ERC AdG 670930. D.R.F.C. is supported by the BBSRC (BB/P006205/1) and Cancer Research UK (A28052). V.H. and J.G.G. are funded by La Ligue contre le Cancer, by INCa (PLBIO19-291), by Plan Cancer (Nanotumor) and through institutional funds from University of Strasbourg and INSERM. K.R. is supported by the UEF Cell and Tissue Imaging Unit, Biocenter Kuopio and Biocenter Finland. We apologize to colleagues for any relevant work that could not be cited due to space restrictions.
D.R.F.C. is employed by Evox Therapeutics. S.E.A. serves on the Scientific Advisory Board of EVOX Therapeutics. All other authors have no competing interests.
Peer review information Rita Strack was the primary editor on this article and managed its editorial process and peer review in collaboration with the rest of the editorial team.
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Verweij, F.J., Balaj, L., Boulanger, C.M. et al. The power of imaging to understand extracellular vesicle biology in vivo. Nat Methods 18, 1013–1026 (2021). https://doi.org/10.1038/s41592-021-01206-3