Purification of High Yield Extracellular Vesicle Preparations Away from Virus

Summary

This protocol isolates extracellular vesicles (EVs) away from virions with high efficiency and yield by incorporating EV precipitation, density gradient ultracentrifugation, and particle capture to allow for a streamlined workflow and a reduction of starting volume requirements, resulting in reproducible preparations for use in all EV research.

Abstract

One of the major hurdles in the field of extracellular vesicle (EV) research today is the ability to achieve purified EV preparations in a viral infection setting. The presented method is meant to isolate EVs away from virions (i.e., HIV-1), allowing for a higher efficiency and yield compared to conventional ultracentrifugation methods. Our protocol contains three steps: EV precipitation, density gradient separation, and particle capture. Downstream assays (i.e., Western blot, and PCR) can be run directly following particle capture. This method is advantageous over other isolation methods (i.e., ultracentrifugation) as it allows for the use of minimal starting volumes. Furthermore, it is more user friendly than alternative EV isolation methods requiring multiple ultracentrifugation steps. However, the presented method is limited in its scope of functional EV assays as it is difficult to elute intact EVs from our particles. Furthermore, this method is tailored towards a strictly research-based setting and would not be commercially viable.

Introduction

Research centered around extracellular vesicles (EVs), specifically exosomes, a type of EV ranging 30-120 nm and characterized by the presence of three tetraspanin markers CD81, CD9, and CD63, has largely been shaped by the development of methods to isolate and purify the vesicles of interest. The ability to dissect multifaceted mechanisms has been hindered due to complex and time-consuming techniques which generate samples composed of a heterogeneous population of vesicles generated via different pathways with a wide range of contents, sizes, and densities. While this is an issue for nearly all EV research, it is of particular importance when studying EVs in the cont....

Protocol

1. Filtration and Precipitation of Extracellular Vesicles (EVs)

1. To prepare the culture supernatant from infected or transfected cells (i.e., cell lines and/or primary cells), culture approximately 10 mL of late-log cells for 5 days at 37 °C and 5% CO₂ in appropriate culture medium (i.e., RPMI or DMEM with 10% fetal bovine serum [FBS]).
   NOTE: All culture medium reagents should be free of EVs, and can be either purchased (see Table of Materials) or prepared in-house by pre-ultracentrifugation of serum at 100,000 x g for 90 min. This protocol has been successful for several commonly-used cell l....

Results

PEG precipitation increases EV yield
Our combination approach to EV isolation is significantly more efficient in terms of EV recovery as compared to traditional ultracentrifugation, as evident by the 90% reduction in the volume of starting material required. Ultracentrifugation, the current gold standard in EV isolation, requires approximately 100 mL of culture supernatant to produce an adequate EV prep for downstream assays, whereas our novel protocol requires only 1.......

Discussion

The outlined method allows for enhanced EV yield and the separation of virus from EVs using a combination approach to isolation. Relatively large quantities of starting material (i.e., cell supernatant) can be filtered prior to EV isolation by precipitation, DG separation, and nanoparticle enrichment, resulting in a final volume of ~30 µL, allowing for immediate usage in a variety of downstream assays. The use of nanoparticle enrichment is essential as, compared to traditional ultracentrifugation, these EV-enriching.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
CEM CD4+ Cells	NIH AIDS Reagent Program	117	CEM
DPBS without Ca and Mg (1x)	Quality Biological	114-057-101
ExoMAX Opti-Enhancer	Systems Biosciences	EXOMAX24A-1	PEG precipitation reagent
Exosome-Depleted FBS	Thermo Fisher Scientific	A2720801
Fetal Bovine Serum	Peak Serum	PS-FB3	Serum
HIV-1 infected U937 Cells	NIH AIDS Reagent Program	165	U1
Nalgene Syringe Filter 0.2 µm SFCA	Thermo Scientific	723-2520
Nanotrap (NT80)	Ceres Nanosciences	CN1030	Reactive Red 120 core
Nanotrap (NT82)	Ceres Nanosciences	CN2010	Cibacron Blue F3GA core
Optima XE-980 Ultracentrifuge	Beckman Coulter	A94471
OptiPrep Density Gradient Medium	Sigma-Aldrich	D1556-250mL	Iodixanol
SW 41 Ti Swinging-Bucket Rotor	Beckman Coulter	331362
Ultra-Clear Tube, 14 mm x 89 mm	Beckman Coulter	344059