Name: purification of high yield extracellular vesicle preparations away from virus
Uploaded: 2019-09-12T14:00:00
Description: Watch this Scientific Journal Video about Purification of High Yield Extracellular Vesicle Preparations Away from Virus at JoVE.com

We would like to thank all members of the Kashanchi lab, especially Gwen Cox. This work was supported by National Institutes of Health (NIH) Grants (AI078859, AI074410, AI127351-01, AI043894, and NS099029 to F.K.).

1. Filtration and Precipitation of Extracellular Vesicles (EVs)
<ol>
	<li>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 &#176;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 prepar...

<ol>
	<li>Taylor, D. D., Shah, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Methods+of+isolating+extracellular+vesicles+impact+down-stream+analyses+of+their+cargoes.">Methods of isolating extracellular vesicles impact down-stream analyses of their cargoes.</a> Methods (San Diego, Calif). 87, 3-10 (2015).</li><li>Konoshenko, M. Y., Lekchnov, E. A., Vlassov, A. V., Laktionov, P. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+of+Extracellular+Vesicles:+General+Methodologies+and+Latest+Trends.">Isolation of Extracellular Vesicles: General Methodologies and Latest Trends.</a> BioMed Research International. 2018, 8545347 (2018).</li><li>Momen-Heravi, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Current+methods+for+the+isolation+of+extracellular+vesicles.">Current methods for the isolation of extracellular vesicles.</a> Biological Chemistry. 394 (10), 1253-1262 (2013).</li><li>Th&#233;ry, C., Amigorena, S., Raposo, G., Clayton, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isolation+and+characterization+of+exosomes+from+cell+culture+supernatants+and+biological+fluids.">Isolation and characterization of exosomes from cell culture supernatants and biological fluids.</a> Current Protocols in Cell Biology. , (2006).</li><li>Boriachek, K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biological+Functions+and+Current+Advances+in+Isolation+and+Detection+Strategies+for+Exosome+Nanovesicles.">Biological Functions and Current Advances in Isolation and Detection Strategies for Exosome Nanovesicles.</a> Small (Weinheim an Der Bergstrasse, Germany). 14 (6), (2018).</li><li>DeMarino, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antiretroviral+Drugs+Alter+the+Content+of+Extracellular+Vesicles+from+HIV-1-Infected+Cells.">Antiretroviral Drugs Alter the Content of Extracellular Vesicles from HIV-1-Infected Cells.</a> Scientific Reports. 8 (1), 7653 (2018).</li><li>Van Deun, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+impact+of+disparate+isolation+methods+for+extracellular+vesicles+on+downstream+RNA+profiling.">The impact of disparate isolation methods for extracellular vesicles on downstream RNA profiling.</a> Journal of Extracellular Vesicles. 3, (2014).</li><li>Lobb, R. 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A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exosomes+from+uninfected+cells+activate+transcription+of+latent+HIV-1.">Exosomes from uninfected cells activate transcription of latent HIV-1.</a> The Journal of Biological Chemistry. 292 (28), 11682-11701 (2017).</li><li>Pleet, M. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ebola+VP40+in+Exosomes+Can+Cause+Immune+Cell+Dysfunction.">Ebola VP40 in Exosomes Can Cause Immune Cell Dysfunction.</a> Frontiers in Microbiology. 7, 1765 (2016).</li><li>Pleet, M. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ebola+Virus+VP40+Modulates+Cell+Cycle+and+Biogenesis+of+Extracellular+Vesicles.">Ebola Virus VP40 Modulates Cell Cycle and Biogenesis of Extracellular Vesicles.</a> The Journal of Infectious Diseases. , (2018).</li><li>Anderson, M. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Viral+antigens+detectable+in+CSF+exosomes+from+patients+with+retrovirus+associated+neurologic+disease:+functional+role+of+exosomes.">Viral antigens detectable in CSF exosomes from patients with retrovirus associated neurologic disease: functional role of exosomes.</a> Clinical and Translational Medicine. 7 (1), 24 (2018).</li><li>Vlassov, A. V., Magdaleno, S., Setterquist, R., Conrad, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exosomes:+current+knowledge+of+their+composition,+biological+functions,+and+diagnostic+and+therapeutic+potentials.">Exosomes: current knowledge of their composition, biological functions, and diagnostic and therapeutic potentials.</a> Biochimica Et Biophysica Acta. 1820 (7), 940-948 (2012).</li><li>Th&#233;ry, C., Zitvogel, L., Amigorena, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exosomes:+composition,+biogenesis+and+function.">Exosomes: composition, biogenesis and function.</a> Nature Reviews. Immunology. 2 (8), 569-579 (2002).</li><li>Schwab, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Extracellular+vesicles+from+infected+cells:+potential+for+direct+pathogenesis.">Extracellular vesicles from infected cells: potential for direct pathogenesis.</a> Frontiers in Microbiology. 6, 1132 (2015).</li><li>Narayanan, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exosomes+derived+from+HIV-1-infected+cells+contain+trans-activation+response+element+RNA.">Exosomes derived from HIV-1-infected cells contain trans-activation response element RNA.</a> The Journal of Biological Chemistry. 288 (27), 20014-20033 (2013).</li><li>Sami Saribas, A., Cicalese, S., Ahooyi, T. M., Khalili, K., Amini, S., Sariyer, I. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=HIV-1+Nef+is+released+in+extracellular+vesicles+derived+from+astrocytes:+evidence+for+Nef-mediated+neurotoxicity.">HIV-1 Nef is released in extracellular vesicles derived from astrocytes: evidence for Nef-mediated neurotoxicity.</a> Cell Death &amp; Disease. 8 (1), e2542 (2017).</li><li>Yang, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exosomal+miR-9+Released+from+HIV+Tat+Stimulated+Astrocytes+Mediates+Microglial+Migration.">Exosomal miR-9 Released from HIV Tat Stimulated Astrocytes Mediates Microglial Migration.</a> Journal of Neuroimmune Pharmacology: The Official Journal of the Society on NeuroImmune Pharmacology. 13 (3), 330-344 (2018).</li><li>Arakelyan, A., Fitzgerald, W., Zicari, S., Vanpouille, C., Margolis, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Extracellular+Vesicles+Carry+HIV+Env+and+Facilitate+Hiv+Infection+of+Human+Lymphoid+Tissue.">Extracellular Vesicles Carry HIV Env and Facilitate Hiv Infection of Human Lymphoid Tissue.</a> Scientific Reports. 7 (1), 1695 (2017).</li><li>Jaworski, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+T-lymphotropic+virus+type+1-infected+cells+secrete+exosomes+that+contain+Tax+protein.">Human T-lymphotropic virus type 1-infected cells secrete exosomes that contain Tax protein.</a> The Journal of Biological Chemistry. 289 (32), 22284-22305 (2014).</li><li>Heinemann, M. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Benchtop+isolation+and+characterization+of+functional+exosomes+by+sequential+filtration.">Benchtop isolation and characterization of functional exosomes by sequential filtration.</a> Journal of Chromatography. A. 1371, 125-135 (2014).</li><li>McNamara, R. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Large-scale,+cross-flow+based+isolation+of+highly+pure+and+endocytosis-competent+extracellular+vesicles.">Large-scale, cross-flow based isolation of highly pure and endocytosis-competent extracellular vesicles.</a> Journal of Extracellular Vesicles. 7 (1), 1541396 (2018).</li><li>Heinemann, M. L., Vykoukal, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sequential+Filtration:+A+Gentle+Method+for+the+Isolation+of+Functional+Extracellular+Vesicles.">Sequential Filtration: A Gentle Method for the Isolation of Functional Extracellular Vesicles.</a> Methods in Molecular Biology. 1660, 33-41 (2017).</li><li>Busatto, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tangential+Flow+Filtration+for+Highly+Efficient+Concentration+of+Extracellular+Vesicles+from+Large+Volumes+of+Fluid.">Tangential Flow Filtration for Highly Efficient Concentration of Extracellular Vesicles from Large Volumes of Fluid.</a> Cells. 7 (12), (2018).</li><li>Andriolo, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exosomes+From+Human+Cardiac+Progenitor+Cells+for+Therapeutic+Applications:+Development+of+a+GMP-Grade+Manufacturing+Method.">Exosomes From Human Cardiac Progenitor Cells for Therapeutic Applications: Development of a GMP-Grade Manufacturing Method.</a> Frontiers in Physiology. 9, 1169 (2018).</li><li>Pleet, M. 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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 &#181;L, 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...

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 context of viral infection, as virions and virus-like particles (VLPs) can be similar in diameter to the vesicles of interest. For example, the Human Immunodeficiency Virus Type 1 (HIV-1) is approximately 100 nm in diameter, which is roughly the same size as many types of EVs. For this reason, we have designed a novel EV isolation workflow to address these issues.
The current gold standard of EV isolation is ultracentrifugation. This technique makes use of the various vesicle densities, which allows the vesicles to be separated by centrifugation with differential sedimentation of higher density particles versus lower density particles at each stage 1,2. Several low-speed centrifugation steps are required to remove intact cells (300-400 x g for 10 min), cell debris (~2,000 x g for 10 min), and apoptotic bodies/large vesicles (~10,000 x g for 10 min). These initial purifications are followed by high speed ultracentrifugation (100,000-200,000 x g for 1.5-2 h) to sediment EVs. Wash steps are performed to further ensure EV purity, however, this results in the reduction of the number of isolated EVs, thereby lowering total yield 3,4. This method&#8217;s utility is further limited by the requirement of a large number of cells (approximately 1 x 108) and a large sample volume (&#62; 100 mL) to achieve adequate results.
To address the growing concerns, precipitation of vesicles with hydrophilic polymers has become a useful technique in recent years. Polyethylene glycol (PEG), or other related precipitation reagents, allows the user to pull down the vesicles, viruses, and protein or protein-RNA aggregates within a sample by simply incubating the sample with the reagent of choice, followed by a single low-speed centrifugation1,2,5. We have previously reported that use of PEG or related methods to precipitate EVs in comparison to traditional ultracentrifugation results in a significantly higher yield6. This strategy is fast, easy, does not require additional expensive equipment, is readily scalable, and retains EV structure. However, due to the promiscuous nature of this method, the resulting samples contain a variety of products including free proteins, protein complexes, a range of EVs, and virions thus requiring further purification to obtain the desired population1,2,7,8.
To overcome the heterogeneity of EVs obtained from various precipitation methods, density gradient ultracentrifugation (DG) is utilized to better separate particles based upon their density. This method is carried out using a stepwise gradient using a density gradient medium, such as iodixanol or sucrose, which allows for the separation of EVs from proteins, protein complexes, and virus or virus-like particles (VLPs). It is important to note that, while it was once thought that DG allowed for more precise separation of EV subpopulations, it is now known that sizes and densities of various vesicles can overlap. For example, exosomes are known to have flotation densities of 1.08-1.22 g/mL9, while vesicles isolated from the Golgi (COPI+ or clathrin+) have densities of 1.05-1.12 g/mL and those from the endoplasmic reticulum (COPII+) sediment at 1.18-1.25 g/mL1,2,3,4,9. Additionally, if one desires to compare exosomal fractions against fractions containing viral particles, this may become more difficult depending upon the density of the virus of interest&#8212;there are viruses other than HIV-1 that likely equilibrate at the same densities as exosomal positive fractions2.
Finally, enrichment of EV preps for downstream visualization and functional assays is vital to EV research. The use of EV-enriching nanoparticles, specifically, multi-functional hydrogel particles that range 700-800 nm in diameter, are a critical step in achieving concentrated EV preps. They possess a high affinity aromatic bait which encapsulated by a porous outer sieving shell to promote selectivity. The nanoparticles utilized in this study include two distinct preparations with different core baits (Reactive Red 120 NT80; and Cibacron Blue F3GA NT82) which have shown to increase capture of EVs from various reagents and biofluids (see the Table of Materials)6,10,11,12,13,14,15. The particles offer easy enrichment of EVs from numerous starting materials including iodixanol fractions, cell culture supernatant, as well as patient biofluids such as plasma, serum, cerebral spinal fluids (CSF), and urine6,13.
The method presented here improves the efficiency of current EV purification techniques by combining several technologies; EV precipitation, density gradient ultracentrifugation, and particle capture, to streamline the workflow, reduce sample requirements, and increase yield to obtain a more homogenous EV sample for use in all EV research. This method is particularly useful in the investigation of EVs and their contents during viral infection as it includes a 0.22 &#181;m filtration step to exclude large, unwanted vesicles and VLPs and separation of the total EV population based on density to effectively isolate EVs from virions.

<table>
	<tbody>
		<tr>
			<td>CEM CD4+ Cells</td>
			<td>NIH AIDS Reagent Program</td>
			<td>117</td>
			<td>CEM</td>
		</tr>
		<tr>
			<td>DPBS without Ca and Mg (1X)</td>
			<td>Quality Biological</td>
			<td>114-057-101</td>
			<td></td>
		</tr>
		<tr>
			<td>ExoMAX Opti-Enhancer</td>
			<td>Systems Biosciences</td>
			<td>EXOMAX24A-1</td>
			<td>PEG precipitation reagent</td>
		</tr>
		<tr>
			<td>Exosome-Depleted FBS</td>
			<td>Thermo Fisher Scientific</td>
			<td>A2720801</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Peak Serum</td>
			<td>PS-FB3</td>
			<td>Serum</td>
		</tr>
		<tr>
			<td>HIV-1 infected U937 Cells</td>
			<td>NIH AIDS Reagent Program</td>
			<td>165</td>
			<td>U1</td>
		</tr>
		<tr>
			<td>Nalgene Syringe Filter 0.2 &#181;m SFCA</td>
			<td>Thermo Scientific</td>
			<td>723-2520</td>
			<td></td>
		</tr>
		<tr>
			<td>Nanotrap (NT80)</td>
			<td>Ceres Nanosciences</td>
			<td>CN1030</td>
			<td>Reactive Red 120 core</td>
		</tr>
		<tr>
			<td>Nanotrap (NT82)</td>
			<td>Ceres Nanosciences</td>
			<td>CN2010</td>
			<td>Cibacron Blue F3GA core</td>
		</tr>
		<tr>
			<td>Optima XE-980 Ultracentrifuge</td>
			<td>Beckman Coulter</td>
			<td>A94471</td>
			<td></td>
		</tr>
		<tr>
			<td>OptiPrep Density Gradient Medium</td>
			<td>Sigma-Aldrich</td>
			<td>D1556-250mL</td>
			<td>Iodixanol</td>
		</tr>
		<tr>
			<td>SW 41 Ti Swinging-Bucket Rotor</td>
			<td>Beckman Coulter</td>
			<td>331362</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultra-Clear Tube, 14x89mm</td>
			<td>Beckman Coulter</td>
			<td>344059</td>
			<td></td>
		</tr>
	</tbody>
</table>

purification of high yield extracellular vesicle preparations away from virus

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.

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...

Watch this Scientific Journal Video about Purification of High Yield Extracellular Vesicle Preparations Away from Virus at JoVE.com

Purification of High Yield Extracellular Vesicle Preparations Away from Virus

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.

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 ...

This protocol is significant because it concentrates extracellular vesicles, EVs, through a combination of technologies, while allowing for separation of virions away from EVs. This method maximizes EV recovery above the current gold standard of ultracentrifugation for multiple downstream analysis and characterization of virus-free EV preps. This protocol is ideal for the study of EV's and viral infections.This method can be adapted to other virus systems, such as HTLV, Ebola, Zika, and more. I would expect a first time user of this method to struggle with nanoparticle preparation, so we recommend carefully following our specifications. Some optimization may be necessary, depending on the system.Visual demonstration of this method is important for illustrating the overall work flow and nuances of the protocol, which will reduce time and mistakes for first time users. Start by preparing culture supernatant from infected or transfected cells. Culture approximately 10 milliliters of late log cells for five days at 37 degrees Celsius and 5%carbon dioxide, making sure that all medium reagents are free of extracellular vesicles.When the culture is ready, pellet the cells by centrifugation at 3, 000 times G for five minutes and discard the pellet. Filter the supernatant with a sterile 0.22 micrometer filter and collect the filtrate in a clean tube. Add an equal volume of PEG precipitation reagents to the filtrate, and invert the tube several times to mix.Incubate the mixture at four degrees Celsius overnight. After the incubation, centrifuge the mixture at 1500 times G for 30 minutes, to yield a heterogeneous extracellular vesicle, or EV, pellet. Discard the supernatant, and re-suspend the pellet in 150 to 300 microliters of 1X PBS, without calcium and magnesium.Keep the pellet on ice, while preparing a density gradient. Prepare the iodixanol density gradient medium with 11 density fractions, ranging from six to 18%iodixanol, as described in the manuscript. Mix each tube by vortexing and layer the density fractions into a clean and dry swinging bucket ultracentrifuge tube.Add the re-suspended EV pellet to the top of the layered gradient and ultracentrifuge the tube at 10, 000 times G, and four degrees Celsius for 90 minutes. Carefully transfer each fraction from the ultracentrifuge tube to a new microcentrifuge tube. Prepare a 30%slurry of nanoparticles for EV fraction enrichment, by mixing equal volumes of NT80, NT82 and 1X-PBS.Vortex the nanoparticle mixture to ensure homogeneity. Add 30 microliters of the slurry to each density fraction and mix by either pipetting or inverting the tubes. The most critical step is the addition of the nano-articles to concentrate EV's, following the density gradient separation.Without this, EV recovery is poor. Rotate the nanoparticle containing density fractions overnight, at four degrees Celsius. Then centrifuge the density fractions at 20, 000 times G for five minutes at room temperature.Discard the liquid and wash the EV pellet twice with 1X-PBS. To prepare the pellet for RNA isolation, re-suspend it 50 microliters of autoclaved, deionized water, filtered and treated with depsy, according to the manuscript directions. The RNA can then be isolated, using a commercial kit.For analysis with gel electrophoresis, re-suspend the pellet in 15 microliters of Laemmli buffer. Heat the sample to 95 degrees Celsius for three minutes. Repeat the heating step two more times, vortexing gently and spinning the sample down between heat cycles.Centrifuge the sample for 15 seconds at 20, 000 times G, and load the supernatant directly onto the gel. For best results, limit the amount of particles loaded onto the gel, and run it at 100 volts, to prevent any loaded nanoparticles from entering the gel. PEG precipitation allows for significantly more efficient EV recovery, than traditional ultracentrifugation.When using 10 milliliters of culture, this approach results in an approximately 500 fold higher yield than ultracentrifugation. This approach also results in an increased isolation efficiency of exosomes, which is evident through higher levels of exosome marker proteins. Western PLA analysis shows, a 3000 fold increase in CD81, a four fold increase in CD63 and a 40 fold increase in CD9.Furthermore, this protocol allows for downstream studies of EV mediated mechanisms in HIV1 infection, by isolating EV's from verions. Western PLA analysis shows that EV's are found in three fraction populations. While the virus is present in only two of them.EV's infraction 10.8 through 12 are free of virus contamination. The most important thing to remember is that the nanoparticles are crucial for optimal EV enrichment. Their addition is a must.Many downstream assays, such as western blot, PCR, pure diomech analysis by mass spectrometry in plate-based cellular assays can be performed. These allow for characterization, mechanistic, and/or functional studies. This technique allows for specific studies that examine EV cargo and functionality without contaminating viral background.This provides a foundation for studying EV's in pathogenesis and development of potential therapeutics. To overcome the limitations of this technique, and to apply EV preparation and isolation to large volumes, we recommend the use of advanced systems, such as tangential flow filtration. The most hazardous instrument to use is the ultracentrifuge, during the density gradient separation.Make sure that all centrifuge tubes weight the same, to avoid imbalance and potential rotor failure.

purification-high-yield-extracellular-vesicle-preparations-away-from

Research

JoVE Journal

Immunology and Infection

Generation of Recombinant Influenza Virus from Plasmid DNA

Efforts by a number of influenza research groups have been pivotal in the development and improvement of influenza A virus reverse genetics. Originally established in 1999 1,2 plasmid-based reverse genetic techniques to generate recombinant viruses have revolutionized the influenza research field because specific questions have been answered by genetically engineered, infectious, recombinant influenza viruses. Such studies include virus replication, function of viral proteins, the contribution of specific mutations in viral proteins in viral replication and/or pathogenesis and, also, viral vectors using recombinant influenza viruses expressing foreign proteins 3.

Rescue of influenza A viruses from plasmid DNA is a basic and essential experimental technique that allows influenza researchers to generate recombinant viruses to study multiple aspects in the biology of influenza virus, and to be used as potential vectors or vaccines.

Efforts by a number of influenza research groups have been pivotal in the development and improvement of influenza A virus reverse genetics. Originally ...

High-throughput Detection Method for Influenza Virus

Influenza virus is a respiratory pathogen that causes a high degree of morbidity and mortality every year in multiple parts of the world. Therefore, precise diagnosis of the infecting strain and rapid high-throughput screening of vast numbers of clinical samples is paramount to control the spread of pandemic infections. Current clinical diagnoses of influenza infections are based on serologic testing, polymerase chain reaction, direct specimen immunofluorescence and cell culture 1,2.
Here, we report the development of a novel diagnostic technique used to detect live influenza viruses. We used the mouse-adapted human A/PR/8/34 (PR8, H1N1) virus 3 to test the efficacy of this technique using MDCK cells 4. MDCK cells (104 or 5 x 103 per well) were cultured in 96- or 384-well plates, infected with PR8 and viral proteins were detected using anti-M2 followed by an IR dye-conjugated secondary antibody. M2 5 and hemagglutinin 1 are two major marker proteins used in many different diagnostic assays. Employing IR-dye-conjugated secondary antibodies minimized the autofluorescence associated with other fluorescent dyes. The use of anti-M2 antibody allowed us to use the antigen-specific fluorescence intensity as a direct metric of viral quantity. To enumerate the fluorescence intensity, we used the LI-COR Odyssey-based IR scanner. This system uses two channel laser-based IR detections to identify fluorophores and differentiate them from background noise. The first channel excites at 680 nm and emits at 700 nm to help quantify the background. The second channel detects fluorophores that excite at 780 nm and emit at 800 nm. Scanning of PR8-infected MDCK cells in the IR scanner indicated a viral titer-dependent bright fluorescence. A positive correlation of fluorescence intensity to virus titer starting from 102-105 PFU could be consistently observed. Minimal but detectable positivity consistently seen with 102-103 PFU PR8 viral titers demonstrated the high sensitivity of the near-IR dyes. The signal-to-noise ratio was determined by comparing the mock-infected or isotype antibody-treated MDCK cells.
Using the fluorescence intensities from 96- or 384-well plate formats, we constructed standard titration curves. In these calculations, the first variable is the viral titer while the second variable is the fluorescence intensity. Therefore, we used the exponential distribution to generate a curve-fit to determine the polynomial relationship between the viral titers and fluorescence intensities. Collectively, we conclude that IR dye-based protein detection system can help diagnose infecting viral strains and precisely enumerate the titer of the infecting pathogens.

This method describes the use of Infrared dye based imaging system for detection of H1N1 in bronchioalveolar lavage (BAL) fluid of infected mice at a high sensitivity. This methodology can be performed in a 96- or 384-well plate, requires &lt;10 &mu;l volume of test material and has the potential for concurrent screening of multiple pathogens.

Influenza virus is a respiratory pathogen that causes a high degree of morbidity and mortality every year in multiple parts of the world. Therefore, ...

Affinity Purification of Influenza Virus Ribonucleoprotein Complexes from the Chromatin of Infected Cells

Like all negative-strand RNA viruses, the genome of influenza viruses is packaged in the form of viral ribonucleoprotein complexes (vRNP), in which the single-stranded genome is encapsidated by the nucleoprotein (NP), and associated with the trimeric polymerase complex consisting of the PA, PB1, and PB2 subunits. However, in contrast to most RNA viruses, influenza viruses perform viral RNA synthesis in the nuclei of infected cells. Interestingly, viral mRNA synthesis uses cellular pre-mRNAs as primers, and it has been proposed that this process takes place on chromatin1. Interactions between the viral polymerase and the host RNA polymerase II, as well as between NP and host nucleosomes have also been characterized1,2.
Recently, the generation of recombinant influenza viruses encoding a One-Strep-Tag genetically fused to the C-terminus of the PB2 subunit of the viral polymerase (rWSN-PB2-Strep3) has been described. These recombinant viruses allow the purification of PB2-containing complexes, including vRNPs, from infected cells. To obtain purified vRNPs, cell cultures are infected, and vRNPs are affinity purified from lysates derived from these cells. However, the lysis procedures used to date have been based on one-step detergent lysis, which, despite the presence of a general nuclease, often extract chromatin-bound material only inefficiently. 
Our preliminary work suggested that a large portion of nuclear vRNPs were not extracted during traditional cell lysis, and therefore could not be affinity purified. To increase this extraction efficiency, and to separate chromatin-bound from non-chromatin-bound nuclear vRNPs, we adapted a step-wise subcellular extraction protocol to influenza virus-infected cells. Briefly, this procedure first separates the nuclei from the cell and then extracts soluble nuclear proteins (here termed the "nucleoplasmic" fraction). The remaining insoluble nuclear material is then digested with Benzonase, an unspecific DNA/RNA nuclease, followed by two salt extraction steps: first using 150 mM NaCl (termed "ch150"), then 500 mM NaCl ("ch500") (Fig. 1). These salt extraction steps were chosen based on our observation that 500 mM NaCl was sufficient to solubilize over 85% of nuclear vRNPs yet still allow binding of tagged vRNPs to the affinity matrix.
After subcellular fractionation of infected cells, it is possible to affinity purify PB2-tagged vRNPs from each individual fraction and analyze their protein and RNA components using Western Blot and primer extension, respectively. Recently, we utilized this method to discover that vRNP export complexes form during late points after infection on the chromatin fraction extracted with 500 mM NaCl (ch500)3.

Influenza viruses replicate their RNA genome in association with host-cell chromatin. Here, we present a method to purify intact viral ribonucleoprotein complexes from the chromatin of infected cells. Purified viral complexes can be analyzed by both Western blot and primer extension of protein and RNA content, respectively.

Like all negative-strand RNA viruses, the genome of influenza viruses is packaged in the form of viral ribonucleoprotein complexes (vRNP), in which the ...

Purification of Pathogen Vacuoles from Legionella-infected Phagocytes

The opportunistic pathogen Legionella pneumophila is an amoeba-resistant bacterium, which also replicates in alveolar macrophages thus causing the severe pneumonia "Legionnaires' disease"1. In protozoan and mammalian phagocytes, L. pneumophila employs a conserved mechanism to form a specific, replication-permissive compartment, the "Legionella-containing vacuole" (LCV). LCV formation requires the bacterial Icm/Dot type IV secretion system (T4SS), which translocates as many as 275 "effector" proteins into host cells. The effectors manipulate host proteins as well as lipids and communicate with secretory, endosomal and mitochondrial organelles2-4.
The formation of LCVs represents a complex, robust and redundant process, which is difficult to grasp in a reductionist manner. An integrative approach is required to comprehensively understand LCV formation, including a global analysis of pathogen-host factor interactions and their temporal and spatial dynamics. As a first step towards this goal, intact LCVs are purified and analyzed by proteomics and lipidomics.
The composition and formation of pathogen-containing vacuoles has been investigated by proteomic analysis using liquid chromatography or 2-D gel electrophoresis coupled to mass-spectrometry. Vacuoles isolated from either the social soil amoeba Dictyostelium discoideum or mammalian phagocytes harboured Leishmania5, Listeria6, Mycobacterium7, Rhodococcus8, Salmonella9 or Legionella spp.10. However, the purification protocols employed in these studies are time-consuming and tedious, as they require e.g. electron microscopy to analyse LCV morphology, integrity and purity. Additionally, these protocols do not exploit specific features of the pathogen vacuole for enrichment.
The method presented here overcomes these limitations by employing D. discoideum producing a fluorescent LCV marker and by targeting the bacterial effector protein SidC, which selectively anchors to the LCV membrane by binding to phosphatidylinositol 4-phosphate (PtdIns(4)P)3,11 . LCVs are enriched in a first step by immuno-magnetic separation using an affinity-purified primary antibody against SidC and a secondary antibody coupled to magnetic beads, followed in a second step by a classical Histodenz density gradient centrifugation12,13 (Fig. 1).
A proteome study of isolated LCVs from D. discoideum revealed more than 560 host cell proteins, including proteins associated with phagocytic vesicles, mitochondria, ER and Golgi, as well as several GTPases, which have not been implicated in LCV formation before13. LCVs enriched and purified with the protocol outlined here can be further analyzed by microscopy (immunofluorescence, electron microscopy), biochemical methods (Western blot) and proteomic or lipidomic approaches.

Purification of Pathogen Vacuoles from Legionella-infected Phagocytes

This article describes a method for the isolation and purification of intact Legionella-containing vacuoles (LCVs) from amoeba and macrophages. The two-step protocol comprises LCV enrichment by immuno-magnetic separation using an antibody against a bacterial LCV marker and further purification by density gradient centrifugation.

The opportunistic pathogen Legionella pneumophila is an amoeba-resistant bacterium, which also replicates in alveolar macrophages thus causing the severe ...

High Yield Purification of Plasmodium falciparum Merozoites For Use in Opsonizing Antibody Assays

Plasmodium falciparum merozoite antigens are under development as potential malaria vaccines. One aspect of immunity against malaria is the removal of free merozoites from the blood by phagocytic cells. However assessing the functional efficacy of merozoite specific opsonizing antibodies is challenging due to the short half-life of merozoites and the variability of primary phagocytic cells. Described in detail herein is a method for generating viable merozoites using the E64 protease inhibitor, and an assay of merozoite opsonin-dependent phagocytosis using the pro-monocytic cell line THP-1. E64 prevents schizont rupture while allowing the development of merozoites which are released by filtration of treated schizonts. &#160;Ethidium bromide labelled merozoites are opsonized with human plasma samples and added to THP-1 cells. Phagocytosis is assessed by a standardized high throughput protocol. Viable merozoites are a valuable resource for assessing numerous aspects of P. falciparum biology, including assessment of immune function. Antibody levels measured by this assay are associated with clinical immunity to malaria in naturally exposed individuals. The assay may also be of use for assessing vaccine induced antibodies. &#160;

High Yield Purification of Plasmodium falciparum Merozoites For Use in Opsonizing Antibody Assays

Measuring antibody function is key to understanding immunity to Plasmodium falciparum malaria. This method describes the purification of viable merozoites, and measurement of opsonization-dependent phagocytosis by flow cytometry.

Plasmodium falciparum merozoite antigens are under development as potential malaria vaccines. One aspect of immunity against malaria is the removal of ...

An Efficient and High Yield Method for Isolation of Mouse Dendritic Cell Subsets

Dendritic cells (DCs) are professional antigen-presenting cells primarily responsible for acquiring, processing and presenting antigens on antigen presenting molecules to initiate T-cell-mediated immunity. Dendritic cells can be separated into several phenotypically and functionally heterogeneous subsets. Three important subsets of splenic dendritic cells are plasmacytoid, CD8&#945;Pos and CD8&#945;Neg cells. The plasmacytoid DCs are natural producers of type I interferon and are important for anti-viral T cell immunity. The CD8&#945;Neg DC subset is specialized for MHC class II antigen presentation and is centrally involved in priming CD4 T cells. The CD8&#945;Pos DCs are primarily responsible for cross-presentation of exogenous antigens and CD8 T cell priming. The CD8&#945;Pos DCs have been demonstrated to be most efficient at the presentation of glycolipid antigens by CD1d molecules to a specialized T cell population known as invariant natural killer T (iNKT) cells. Administration of Flt-3 ligand increases the frequency of migration of dendritic cell progenitors from bone marrow, ultimately resulting in expansion of dendritic cells in peripheral lymphoid organs in murine models. We have adapted this model to purify large numbers of functional dendritic cells for use in cell transfer experiments to compare in vivo proficiency of different DC subsets.

Distinct dendritic cell subsets exist as rare populations in lymphoid organs, and therefore are challenging to isolate in sufficient numbers and purity for immunological experiments. Here we describe a high efficiency, high yield method for isolation of all of the currently known major subsets of mouse splenic dendritic cells.

Dendritic cells (DCs) are professional antigen-presenting cells primarily responsible for acquiring, processing and presenting antigens on antigen ...

Neutrophil Isolation and Analysis to Determine their Role in Lymphoma Cell Sensitivity to Therapeutic Agents

Neutrophils are the most abundant (40% to 75%) type of white blood cells and among the first inflammatory cells to migrate towards the site of inflammation. They are key players in the innate immune system and play major roles in cancer biology. Neutrophils have been proposed as key mediators of malignant transformation, tumor progression, angiogenesis and in the modulation of the antitumor immunity; through their release of soluble factors or their interaction with tumor cells. To characterize the specific functions of neutrophils, a fast and reliable method is coveted for in vitro isolation of neutrophils from human blood. Here, a density gradient separation method is demonstrated to isolate neutrophils as well as mononuclear cells from the blood. The procedure consists of layering the density gradient solution such as Ficoll carefully above the diluted blood obtained from patients diagnosed with chronic lymphocytic leukemia (CLL), followed by centrifugation, isolation of mononuclear layer, separation of neutrophils from RBCsby dextran then lysis of residual erythrocytes. This method has been shown to isolate neutrophils &#8805; 90 % pure. To mimic the tumor microenvironment, 3-dimensional (3D) experiments were performed using basement membrane matrix such as Matrigel. Given the short half-life of neutrophils in vitro, 3D experiments with fresh human neutrophils cannot be performed. For this reason promyelocytic HL60 cells are differentiated along the granulocytic pathway using the differentiation inducers dimethyl sulfoxide (DMSO) and retinoic acid (RA). The aim of our experiments is to study the role of neutrophils on the sensitivity of lymphoma cells to anti-lymphoma agents. However these methods can be generalized to study the interactions of neutrophils or neutrophil-like cells with a large range of cell types in different situations.

Neutrophils are the most abundant type of white blood cells. The isolation of neutrophils from human blood by density gradient separation method and the differentiation of human promyelocytic (HL60) cells along the granulocytic pathway are described here; to test their role on sensitivity of lymphoma cells to anti-lymphoma agents.

Neutrophils are the most abundant (40% to 75%) type of white blood cells and among the first inflammatory cells to migrate towards the site of ...

Detection and Removal of Nuclease Contamination During Purification of Recombinant Prototype Foamy Virus Integrase

The integrase (IN) protein of the retrovirus prototype foamy virus (PFV) is a model enzyme for studying the mechanism of retroviral integration. Compared to IN from other retroviruses, PFV IN is more soluble and more amenable to experimental manipulation. Additionally, it is sensitive to clinically relevant human immunodeficiency virus (HIV-1) IN inhibitors, suggesting that the catalytic mechanism of PFV IN is similar to that of HIV-1 IN. IN catalyzes the covalent joining of viral complementary DNA (cDNA) to target DNA in a process called strand transfer. This strand transfer reaction introduces nicks to the target DNA. Analysis of integration reaction products can be confounded by the presence of nucleases that similarly nick DNA. A bacterial nuclease has been shown to co-purify with recombinant PFV IN expressed in Escherichia coli (E. coli). Here we describe a method to isolate PFV IN from the contaminating nuclease by heparin affinity chromatography. Fractions are easily screened for nuclease contamination with a supercoiled plasmid and agarose gel electrophoresis. PFV IN and the contaminating nuclease display alternative affinities for heparin sepharose allowing a nuclease-free preparation of recombinant PFV IN suitable for bulk biochemical or single molecule analysis of integration.

Recombinant prototype foamy virus integrase protein is often contaminated with a bacterial nuclease during purification. This method identifies nuclease contamination and removes it from the final preparation of the enzyme.

The integrase (IN) protein of the retrovirus prototype foamy virus (PFV) is a model enzyme for studying the mechanism of retroviral integration. Compared ...

Evaluation of Extracellular Vesicle Function During Malaria Infection

Malaria is a life-threatening disease caused by Plasmodium parasites, with P. falciparum being the most prevalent on the African continent and responsible for most malaria-related deaths globally. Several factors including parasite sequestration in tissues, vascular dysfunction, and inflammatory responses influence the evolution of the disease in malaria-infected people. P. falciparum-infected red blood cells (iRBCs) release small extracellular vesicles (EVs) containing different kinds of cargo molecules that mediate pathogenesis and cellular communication between parasites and host. EVs are efficiently taken up by cells in which they modulate their function. Here we discuss strategies to address the role of EVs in parasite-host interactions. First, we describe a straightforward method for labeling and tracking EV internalization by endothelial cells, using a green cell linker dye. Second, we report a simple way to measure permeability across an endothelial cell monolayer by using a fluorescently labeled dextran. Finally, we show how to investigate the role of small non-coding RNA molecules in endothelial cell function.

In this work, we describe protocols to investigate the role of extracellular vesicles (EVs) released by Plasmodium falciparum infected erythrocytes. In particular, we focus on the interactions of EVs with endothelial cells.

Malaria is a life-threatening disease caused by Plasmodium parasites, with P. falciparum being the most prevalent on the African continent and responsible ...

Assembly and Purification of Prototype Foamy Virus Intasomes

A defining feature and necessary step of the retrovirus life cycle is the integration of the viral genome into the host genome. All retroviruses encode an integrase (IN) enzyme that catalyzes the covalent joining of viral to host DNA, which is known as strand transfer. Integration may be modeled in vitro with recombinant retroviral IN and DNA oligomers mimicking the ends of the viral genome. In order to more closely recapitulate the integration reaction that occurs in vivo, integration complexes are assembled from recombinant IN and synthetic oligomers by dialysis in a reduced salt concentration buffer. The integration complex, called an intasome, may be purified by size exclusion chromatography. In the case of prototype foamy virus (PFV), the intasome is a tetramer of IN and two DNA oligomers and is readily separated from monomeric IN and free oligomer DNA. The integration efficiency of PFV intasomes may be assayed under a variety of experimental conditions to better understand the dynamics and mechanics of retroviral integration.

Recombinant retroviral integrase and DNA oligomers mimicking viral DNA ends can form an enzymatically active complex known as an intasome. Intasomes may be used for biochemical, structural, and kinetic studies. This protocol details how to assemble and purify prototype foamy virus intasomes.

A defining feature and necessary step of the retrovirus life cycle is the integration of the viral genome into the host genome. All retroviruses encode an ...