A simple scalable extracellular vesicle isolation method using polyethylenimine polymers for use in cellular delivery

Extracellular vesicles (EVs) are gaining interest as efficient, biocompatible vehicles for cellular delivery of therapeutic cargo. Precipitation-based methods for the isolation of EVs remain popular due to ease of use and lack of requirements for specialized equipment. We describe here a novel charge-based EV isolation method that is simple, scalable, and uses inexpensive polyethylenimine (PEI) polymers. GFP-expressing EVs were isolated from the conditioned cell culture (CCM) media of HEK293-GFP cells using either branched 10 kDa PEI (B-PEI) or linear 25 kDa PEI (L-PEI). Isolated EVs were characterized by Western blotting, nanoparticle tracking analysis, transmission electron microscopy (TEM), and flow cytometry. Western blotting for common EV markers, including CD63, CD9, flotillin-1, and heat shock protein 70 were positive, while GRP94, a marker for cellular contamination, was negative. Isolated EVs had a mean diameter of 146 nm for B-PEI and 175 nm for L-PEI, while TEM revealed a spherical cup-shaped appearance typical of EVs. In addition, we determined that PEI-based EV isolation methods were scalable up to volumes of at least 50 mL. EVs isolated from CCM collected from SUM159 cells that express CD63 fused to a dual EGFP-Renilla-split tag were tested for their ability to reconstitute functional luciferase by delivering the CD63-EGFP-Renilla-split tag to SUM159 recipient cells loaded with a cytopermeable Renilla luciferase substrate. Although EVs isolated using L-PEI behaved similarly to EVs isolated using ultracentrifugation, we observed that EVs isolated using B-PEI produced a more rapid uptake and delivery of active luciferase. In this study we demonstrate that both branched and linear PEI polymers can precipitate EVs from CCM. Furthermore, once eluted from the polymers, the isolated EVs were able to deliver functional protein cargo to recipient cells. Overall, our data support PEI-based isolation of EVs as a simple, rapid method for the recovery of functional EVs.