Exosomes as bio-inspired nanocarriers for RNA delivery

Nanocarriers as drug/biomolecule delivery systems have been significantly developed during recent decades. Given the stability, reasonable delivery efficiency, and safety of nanocarriers, there are several barriers in the fulfillment of successful clinical application of these delivery systems. These challenges encouraged drug delivery researchers to establish innovative nanocarriers with longer circulation time, high stability, and high compatibility. Exosomes are extracellular nanometer-sized vesicles released through various cells. These vesicles serve as nanocarriers, possessing great potential to overcome some obstacles encountered in gene and drug delivery due to their natural affinity to recipient cells and the inherent capability to shuttle the genes, lipids, proteins, and RNAs between cells. So far, there has been a lot of valuable research on drug delivery by exosomes, but research on RNA delivery, especially mRNA, is very limited. Since mRNA-based vaccines and therapies have recently gained particular prominence in various diseases, it is essential to find a suitable delivery system due to the large size and destructive nature of these nucleic acids. Researchers take a look at the unique features of exosomes and their isolation and loading methods, to embrace this idea that exosome-mediated mRNA-based therapies would be introduced as a very efficient strategy in disease treatment within the near future.

Schematic diagram of isolation methodology of exosomes

a Size exclusion chromatography which separates particles based on size, is one of the most common methods for obtaining a large volume of exosomes due to the lack of protein contamination and the ability to purify the exosome on a large scale. b Ultracentrifuge separation, despite being dependent on expensive equipment, has been widely used to isolate exosomes based on size and sedimentation properties or density in sucrose gradients. c Microfluidics-based methods rely on physical properties such as size and density, or chemical properties such as binding to exosome surface antigens. d In immunoaffinity methods, exosomes are captured based on their specific binding to antibodies or magnetic nanoparticles. As a result, the surface chemical properties are critical in these techniques. e In ultrafiltration, the particles are centrifuged through the filter and separated based on the pore size of the filter. f In the polymer co-percipitation method, based on steric exclusion, particles are gathered by PEG to form clumps that can be easily precipitated by low-speed centrifugation. g In field flow fractionation, particles accumulate at different position of the membrane depending on their size. Separation occurs when the diffusing and cross-flow forces are balanced