Exosomes are a type of cell‐derived extracellular nanovesicle. They relay information between cells. Some known exosome functions
include immune modulation, promotion of angiogenesis, and tumor metastasis. To date, clinical use of exosomes has focused
predominantly on evaluating their efficacy as cancer vaccines or diagnostically as biomarker containers. However, few investigations
have explored their potential to serve as a platform for the development of semi‐synthetic nanovesicles. Given their nanoscale
size, potential to express targeting ligands in native conformations and deformable structure, exosomes offer a logical biological
vesicle platform for adapting and producing semi‐synthetic vesicles with excellent potential for nanomedicine applications.
However, there are obstacles associated with realizing this potential that must be addressed. Thus, a systematic approach
to isolating, modifying, and testing exosomes is presented to facilitate the introduction of exosome‐based translational nanomedicine.
WIREs Nanomed Nanobiotechnol 2012, 4:458–467. doi: 10.1002/wnan.1174
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Exosome production and contents. Exosomes are formed in multivesicular bodies (MVBs) that subsequently fuse with the inner plasma membrane surface resulting in exosome release into the extracellular microenvironment. Exosomes are approximately 30–200 nm in size and display a variety of surface receptors such as major histocompatibility complexes (MHCs) or contain heat shock proteins (HSPs)5 and exosome shuttle RNA (mRNA and miRNA).6 Exosome messages are transmitted to target cells by either receptor‐mediated uptake or possibly fusion.
A systematic approach to exosome‐based semi‐synthetic nanovesicle (EBSSN) production and testing. Cellular nanofactories are constructed by selecting cell lines of interest and programing them through traditional molecular biology techniques to produce EBSSNs expressing specific targeting ligands (receptors) or cargo (RNA). Non‐modified exosomes or EBSSNs are collected from cell culture supernatants using differential centrifugation. Immediately prior to the ultracentrifugation step of exosome or EBSSN isolation, dynamic light scattering (DLS) is employed to confirm the presence and size of exosomes or EBSSNs and fluorescent labels (carbocyanine dyes) added. Following ultracentrifugation, exosomes or EBSSNs are purified using sucrose density gradients and fractions collected. Rapid confirmation of exosome or EBSSN isolation, without sample loss, is achieved through the use of in gradient fluorescent detection (IGFD). Fluorescent‐labeled exosomes or EBSSNs are washed and purified by ultracentrifugation. Exosomes, or EBSSNs derived from intracellular modification steps, can be further exogenously modified using universal peptide cargo linkers43 or alternative strategies to add additional targeting ligands and/or therapeutics. EBSSNs are then washed in PBS and re‐isolated by ultracentrifugation. EBSSN properties are assessed using DLS and zeta potential analysis. Quantitative readouts such as ELISAs and/or RT‐RT PCR arrays are used to confirm EBSSN cargo content and induced effects using reducible 3D tissue culture14 or in vivo models such as bilateral lymph node exosome tracking.33
works at the interface of biotechnology and materials science. His lab is researching many topics, such as investigating the mechanism of release from polymeric delivery systems with concomitant microstructural analysis and mathematical modeling; studying applications of these systems including the development of effective long-term delivery systems for insulin, anti-cancer drugs, growth factors, gene therapy agents and vaccines; developing controlled release systems that can be magnetically, ultrasonically, or enzymatically triggered to increase release rates; synthesizing new biodegradable polymeric delivery systems which will ultimately be absorbed by the body; creating new approaches for delivering drugs such as proteins and genes across complex barriers such as the blood-brain barrier, the intestine, the lung and the skin; stem cell research including controlling growth and differentiation; and creating new biomaterials with shape memory or surface switching properties.
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