Pedersen et al 2015

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Translational BiomedicineISSN 2172-0479

2015Vol. 6 No. 2:18

1© Copyright iMedPub Find this article in: www.transbiomedicine.com

Pedersen KW3

Kierulf B3,Manger I3,Oksvold MP1,2,Li M3,Vlassov A3,Roos N4,Kullmann A3,Neurauter A3

1 DepartmentofImmunology,Institutefor Cancer Research, Oslo University Hospital, Norway

2 Centre for Cancer Biomedicine, University of Oslo, Norway

3 ThermoFisherScientific,Oslo,Norway4 DepartmentofBiosciences,Sectionfor

Physiology and Cell Biology, University of Oslo, Norway

Corresponding author: KetilW.Pedersen

[email protected]

Life Technologies AS, Ullernchausseen 52, PO Box 114 Smestad 0379 Oslo, Norway

Tel: +47 22 06 11 63, +47 91 18 14 78

Direct Isolation of Exosomes from Cell Culture: Simplifying

Methods for Exosome Enrichment and Analysis

AbstractExosomes, (50-150 nm sized vesicles), are secreted by all cells and found in all body fluids investigated. Isolationandcharacterizationofexosomes fromcell culturesystemsandbodyfluidsprovidevaluableinformationaboutthebiologicalsystem.The level of exosomes in human serum will vary depending on many factors such as age, sex, timeof sample collection (circadian rhythm/nutrition status) , andofparticular interestduringdiseasedconditions.Suchinformationmaypossiblybe used for early detection of disease,monitoring of disease and/or effect oftreatment.

Theestablishedstandardforexosomeisolationisdifferentialultracentrifugationamethodwhichcannotdiscriminatebetweenexosomesubpopulationsorotherparticleswithsimilarsizeanddensity.

Herewehaveestablishedadirectmethodforspecificisolationofexosomesfromcellculturesupernatantsuitableforarangeofdifferentdownstreamapplications.MagneticbeadstargetinghumanCD9orCD81,commonexosomalmarkers,wereused tofirst isolate and characterizepre-enrichedexosomes addressing criticalfactors (volume, time and exosome concentrations) to establish optimal andcomparableisolationconditions.Finally,exosomeswereisolatedandcharacterizeddirectlyfromcellculturemedia.

In conclusion, the data demonstrates the ability to capture exosomes directly providing the possibility to characterize and compare exosomes from differentsourcesandincreasingthecompatibilityintermsofapplications.

Keywords: Exosomes; Direct isolation; Flow cytometry; Western blotting;Immunoassay;Magneticbeads;CD9;CD81

IntroductionExosomes (50-150 nm) are extracellular vesicular structures secretedbycellsincultureandfoundinbodyfluids[1].Exosomesare involved in different biological processes including antigenpresentation [2], apoptosis, angiogenesis, inflammation andcoagulation[3].Theycanactivatesignallingpathwaysordelivernucleicacidstodistantcells[4-6].Tumor-derivedexosomescanenhance cancer progression, suppressing the immune response and transfer oncogens from tumor host cells [7]. Targetingexosomescouldbeadvantageousinordertoincreasetheefficacyoftherapeuticantibodies.

Exosomes,formedbyinvaginationoftheendosomalmembraneforming multivesicular bodies contain miRNA and mRNA [6,8-11].Theproteincompositionmirrorstheirendocyticorigin,MVBformation machinery, tetraspanins (e.g. CD9, CD81), heat shockproteins in addition to lipid-related proteins and phospholipases[12,13]andtheirpossibleroleinintercellularcommunication[14].

Currently,exosomesareisolatedbydifferentialultracentrifugation,densitygradientsorcushions[15],sizeexclusion[16]orprecipitation[17-19].Toobtainultrapureexosomesorisolationofpotentialsub-populationofexosomes,animmunomagneticisolationstrategycanbeappliedbytargetingexosomalmarkers[20,21].

The aim of this studywas to address critical factors for direct

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exosomeisolationandtoimplementthisknowledgetoestablishaneasy,reliableanddirectmethodforexosomecharacterizationensuringcompatibilitywithdownstreamanalysis.

Materials and MethodsReagentsFor isolation of CD9+ and CD81+ exosomes Dynabeads® coated with monoclonal anti-human CD81 (Thermo Fisher Scientific,Oslo, Norway) were applied. Primary antibodies for Westernblottinganalysis:mouseanti-CD81(10630D)andCD9(10626D,ThermoFisherScientific,Oslo,Norway).Primaryantibodies forflowcytometry:mouseanti-humanCD9PE(555372)and-CD81PE (555676,BDBiosciencesUSA).HRP-coupledanti-mouse IgGTrueblot was purchased from Rockland (US). AFP-substrate:DynaLightSubstratewithRapidGlow(4475406),LifeTechnologies.Chemiluminescence reader: BioTek Synergy (BioRad). AFP-conjugated antibodies (CD9 and CD81) for immunoassay (inhouse conjugation). Protein-A gold was obtained from CMC(Utrecht,Netherlands).

Cell cultureTheSW480cell line(ATCC)wasculturedtoconfluence inRPMI1640 (10% FCS, 1 mM Sodium-pyruvat) in cell culture bottles(37°C and 5% CO2) and medium was replaced with 50 mL fresh medium.Jurkatcells(ATCC)wereseededatadensityof0.4x106 cells per mL in fresh RPMI medium and grown for 3 days before harvest.

Exosome harvest and pre-enrichmentThe cell culture medium was replaced with fresh complete medium withFBS3daysbeforeexosomeharvesting.JurkatandSW480cells(5 x 107)wereculturedforeachexosomesamplepreparation.After24h,cellsanddebriswereremovedbycentrifugationat350xgfor10minutesand2,000xgfor30min.Forultracentrifugation,thesampleswere pre-enriched at 100.000 x g for 70min at 4°C using a Ti45rotor (Beckman) andBeckmanultracentrifugation tubes (355622)on a BeckmanOptimaXPN-100. For precipitation, Total ExosomeIsolationkit(ThermoFisherScientific,USA)wasaddedtothecell-and debris-free cellmedium (1:2with exosome isolation reagentand cell medium, respectively). Cell medium and the exosomeisolationreagentweremixedbybriefvortexingandincubatedat4°Covernightbeforecentrifugatedat4°Cat10,000xgfor1h.Thepelletcontainingpre-enrichedexosomeswasresuspendedinPBS(e.g.400µlfor10mlcellmediainput).

Size measurement of exosomesAnalysis of pre-enriched exosomes was performed as previously described[22]usingtheNanoSightLM10instrument.

Real time quantitative PCR

RNA isolation, reverse transcription and real time quantitativePCRanalysiswereperformedasdescribedearlier[23]usingthefollowing primers: Hs99999905_m1 (GAPDH), Hs03023880_g1(ACTB), Hs99999901_s1 (18S), Let7a: has-let-7a, 000377, andhas-miR-16,000391(miR16).

Immunolabeling and negative stain of exosomes for electron microscopy

Immunolabeling followed by negative stain and electronmicroscopy was carried out targeting CD81 as previouslydescribed [24] and analyzed at theUniversity ofOslo,NorwayonPhilipsCD100.Imageswererecordedat80kV.FurtherimageprocessingwasdonewithAdobePhotoshopsoftware.

Preparation of pre-enriched exosomes for Western immunoblotting analysis

The total pre-enriched exosome samples were prepared for WesternblottingasdescribedbyOksvoldetal[22].

Direct capture of exosomes from cell culture supernatant for flow cytometry, Western blotting analysis and immunoassay

20µLofmagneticbeads(1x107beads/mL1.3x108beads/mL,and0.5x 107beads/mLwereusedforflowcytometry,westernblottingandimmunoassay,respectively)andwashedin200µLPBS(0.1%BSA,0.2µmfiltered).0-100µLofcell-anddebris-freecellmediumcontainingexosomeswereaddedtothemagneticbeadsandincubatedfor16-20 h at 4oCwhilerotating/mixingunlessotherincubationtimesareindicated. After incubation, the tubes containingmagnetic beadscoated with exosomes were subjected to a short centrifugationfollowedbyapplyingamagneticfield.Washingtheexosomecoatedbeads twice were done by removing the supernatant while being on themagnetandreplacedthesupernatantwith0.3mLofPBS(0.1%BSA).SampleswerethenprocessedforflowcytometryorWesternblotting. For immunoassaywashingwas performed two to threetimesinmicrotitreplatesin100µLTBS(0.1%Tween-20)buffer.

Preparation of immunoisolated exosomes for Western immunoblotting analysis

Magnetic beads coated with anti-human CD9 or CD81 weremixed with exosome samples and incubated over night at 4°C while mixing. The beads were washed in PBS (0.1% BSA) andlysedin25µlRIPAbuffer(150mMsodiumchloride,1.0%NP-40,0.5%sodiumdeoxycholate,0.1%SDS,50mMTris,pH8.0)withproteinaseinhibitorsfollowedby15minincubationonice.Thelysatewasmixed1:1with2xTrislysisbufferundernon-reducingconditions.SampleswerefurtherprocessedforSDS-PAGE.

Flow cytometry

CD9orCD81positiveexosomescaptureddirectlyfromcellculturemediaorafterpre-enrichmentwereresuspendedin300µlPBSwith0.1%BSA.100µlwasusedperflowstainingandincubatedfor45-60minutesonashaker(1050rpm)atroomtemperature.The labelled exosomes were washed and analysed using BD LSRII andBDFACSDiva.

Immunoassay

CD9(alsopositiveforCD81)positiveexosomescaptureddirectlyfromcellculturemediawithmagneticbeadswerestainedwithAP conjugated CD81 or CD9 antibodies (1:1000 in TBS-T) for60minuteson a shaker (1050 rpm) at room temperature. Thelabelled exosomes were washed three times, transferred tonewwells, added substrate andanalysedusingBioTek Synergy(BioRad)chemiluminescensereader.

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ResultsAnalysis of exosome markers in pre-enriched exosome samplesPriortoanalysis,theRNAcontentoftheexosomeswasverified.SW480cellculturemediawasharvestedafter3daysfollowedbyprecipitationandanalysisofmRNA/rRNAandmicroRNAcontent.The exosomes contained full length mRNA/rRNA (GAPDHand 18S) and microRNAs (ACTb, Let7a and miR16) typical for exosomes (Figure 1A).Then,thesizedistributionwasestimated.Theprecipitatedexosomes fromSW480cellculturemediawasanalysedbytheNanosightLM10instrument.Thesizedistributionshowed a size range (top at 111 nm) (Figure 1B) comparable to standard exosome preparations by ultracentrifugation. Finally,thepre-enrichedvesicleswereidentifiedbyelectronmicroscopy.Pre-enrichedexosomeswereprepared fromSW480cells.Hereantigenslocatedonthesurfaceoftheexosomescanbinddetectionantibodies such as the tetraspanin protein CD81, commonlyidentified in exosomal preparations [25]. Immunoelectronmicroscopyconfirmedtheidentityofthevesiclesbothintermsof size and expression of CD81 (Figure 1C and 1D).

Pre-enrichedexosomeswerethensubjectedtoWesternblottinganalysistotargettheexosomalmarkersCD9andCD81.Currently,the most common method for exosome pre-enrichment is differential ultracentrifugation. Therefore, the presence ofthe exosomal marker CD9 and CD81 in exosomes preparedby ultracentrifugation were compared with CD9 and CD81expression in exosomes prepared by precipitation (Figure 2A and 2B).Exosomeswerepre-enrichedfromthesamecellculturemediumusingthesameamountofinputvolume.Inaddition,thesamevolumeofexosomesapplied toeachwellwas the same.Therefore, the results from these two pre-enrichment methods

should be comparable. The data showed equal amounts ofCD9fromSW480derivedexosomesusingthetwomethodsforexosome pre-enrichment (Figure 2A). Furthermore, CD81 wasalsodetectedinSW480derivedexosomesafterpre-enrichmentusingprecipitation(Figure 2A).CD81wasdetectedinexosomesderived from Jurkat pre-enriched by ultracentrifugation andprecipitation.CD9wasabsentinequaltothefindingsbyOksvoldetal.[22].Thepresenceofcontaminatingnon-exosomalvesicleswereexaminedbystaining forgp96,anendoplasmic reticulummarker.Gp96wasonlyobservedincelllysateandabsentinpre-enrichedexosomes(datanotshown).

Analysis of pre-enriched exosome sub-populationCommon methods for exosome sample preparation areultracentrifugation and precipitation. Both methods arechallengingintermsoflackofvesiclespecificityobtainingvesiclepopulationswithheterogeneoussizedistributionsindicatingthatothervesiclesareco-enriched[26].SizeofexosomeswillprovidelittleinformationonFACSgiventhelimitedresolution.Magneticbeads canprovide a solid support at a size detectable byflowcytometry.Increasedsensitivityandremovalofpotentialproteinaggregates and possibly isolate subpopulations of exosomeswere obtained by immunomagnetic separation strategyfollowedbydownstreamflowanalysis.Theforward/sidescatterplot demonstrated how the magnetic beads were displayedin flow cytometry (Figure 3A). Immunomagnetic isolation ofexosomes and staining with isotypic antibody demonstratingthe background (Figure 3B-3E, grey histograms) compared to specific signal obtained by relevant CD9 and CD81 staining ofbead isolated exosomes (Figure 3B-3E,redhistograms).Withthepurposeofmaximizetheflowsignalandbeabletocomparedatathe amount ofmagnetic beads and the isolation volumewerekept constant, ensuring equal binding kinetics. Pre-enriched

Analysisofprecipitatedexosomes.A)Precipitatedexosomes released fromSW480 cellswereanalysed for the contentofcharacteristic exosomal mRNA/rRNA (GAPDH, 18S) and miRNAs (ActB, Let7a, miR16) by qRT-PCR. Average Ct values forthree independentexperimentsare shown (n=3,SD).B)Precipitatedexosomes fromSW480culturemediawereanalysedbyNanosightLM10.ThesizedistributionoftotalexosomesresuspendedinPBSisshown.C-D)ImmunolabellingofexosomesderivedfromSW480cells.Bar.100nm.

Figure 1



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CD9+ SW480 derived exosomes were isolated using magneticbeadscoatedwithanti-humanCD9antibodiesfollowedbyCD9staining (Figure 3B).ThedatademonstratedsignificantstainingofCD9. IsolationofCD81+exosomes fromSW480cellsshowedthe presence of CD81 but at lower signal (Figure 3C).Likewise,pre-enrichedJurkatderivedexosomesconfirmedthepresenceofCD81 (Figure 3E).Finally,isolationofCD9+exosomesfromJurkatcellsresultedinsignalequivalenttobackground(Figure 3D).

Exosomes derived from Jurkat cellswere isolated usingmagneticbeads and prepared for downstream Western blotting analysis.Western blotting requires a larger total surface area for optimalsignal. A higher number ofmagneticbeadswere therefore used.In order to illustrate the isolation volume were kept constant incombination with increased amounts of beads. CD81+ exosomes derivedfromJurkatcells(Figure 4A)wereisolatedusingmagneticbeadscoatedwithanti-humanCD81antibodiesataconcentrationequaltotheconcentrationusedfordetectionbyflowcytometry(1x)inadditionto5x,10xand25xtheamountofbeadsusedforflowdetection.TheexosomeswereprocessedforSDS-PAGEandWesternblotting and labeled for CD81. The data showed that exosomesisolatedwithabeadconcentrationequaltowhat isusedforflowcytometry were not detectable by western blotting. However,increasing amount of CD81 was observed when the amount of beadswasincreased.Finally,isolationefficiencywasconfirmedbyanalysisoftheremainingexosomesinthesupernatantpostisolationmeasured by flow cytometry (Figure 4B). Increasing amounts ofmagneticbeadshavebeenusedforisolationstartingwithamountsequivalenttowhatisusedforflowcytometry(1x)uptoamountofbeadstypicallyusedforWesternblotting(25x).

Critical factors for direct isolation of exosomes from cell culture mediaIn order to provide a fast and scalable protocol compatiblewithmany downstream applications a direct approachwould bebeneficial. This requires attention to several factors. In order toillustrate this, exosomes derived from SW480 cells were isolatedwithmagneticbeadscoatedwithanti-humanCD9antibodiesandsubjectedtodifferentexperimentalconditions.First,theimpactofvolumeofexosomecontaining cell culturemediaduring isolationwasaddressed.Increasedamountofexosomecontainingcellculturemedia(175µl,350µl,700µl)keepingtheamountofmagneticbeadsconstant (20 µl) provided a non-linear (+) dose response curve (Figure 5A).Atveryhighvolumes,thereducedconcentrationofmagneticbeadsresultedinlowerbindingkinetics.Secondly,welookedattheeffectofincreasedincubationtime.Increasedincubationtimein combination with fixed amount of exosome containing cellculturemediaandmagneticbeads(20µl)alsogaveanon-linear(+) dose response curve (Figure 5B).Finally,wekepttheisolationvolumeandtheamountofmagneticbeadconstantandincreasedtheamountofexosomesinordertoensureequalbindingkinetics.The data demonstrated a linear (+) dose response curve (Figure 5C).Forsamplecomparisonsuchexperimentalsettingsarecriticalasitensuresequivalentbindingkinetics.

Direct isolation of exosomes from cell culture mediaThe optimized conditions were used for direct isolation fromSW480 cell culture media for flow analysis. SW480 derivedexosomeswereisolatedtargetingCD9followedbyCD9staining.Forcomparisonwerelateddirect(Direct)isolationwithexosomes

Expression of exosome surface proteins in pre-enriched exosomes. A) Exosomes from SW480 cells pre-enriched byultracentrifugation(UC)orprecipitation(Prec.)andB)exosomes fromJurkatcellspre-enrichedbyultracentrifugation(UC)orprecipitation (Prec.)wereanalysedbyWestern immunoblottingwithantibodiesagainstCD9andCD81.Shown isaonerepresentativeresultoutofthreeindependentexperiments.Thewesternblotsareallfromonesinglegel.

Figure 2

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Flowcytometricanalysisofexosomesisolatedwithmagneticbeads.SW480derivedexosomes(BandC)andJurkatderivedexosomes(DandE)wereimmunoisolatedfrompre-enrichedexosomesamplesusingmagneticbeadscoatedwithanti-humanCD9orCD81.ExosomeswerestainedforexosomalantigensCD9(BandD)andCD81(CandE)followedflowcytometricanalysisandpresentedasMedianFluorescenceIntensity(MFI).A)Scatterplotofexosomesisolatedwithanti-CD81andlabelledforCD9todemonstrategating.Shownisonerepresentativeresultoutofthreeindependentexperiments.

Figure 3

pre-enrichedbyultracentrifugation(UC)andprecipitation(Prec).To enable direct comparison of the flow analysis the exosomeinputwasnormalizedforthethreewaysofprocessingconditionedcellculturemediumbasedontheconcentrationfactorachievedforUCandprec.,respectively.

Theresultsobtainedbyflowcytometry(Figure 6A) were supported byWesternblotting(Figure 6B)demonstratingCD9stainingafterdirect isolation of CD9+ exosomes (lane 1). Furthermore, CD9staining was somewhat reduced for UC pre-enriched samples comparedtodirect isolationindicatinglossofexosomesduringUC pre-enrichment (lane 2). For isolation from exosomes pre-enrichedbyprecipitation(lane3),CD9stainingwascomparabletodirectisolation(lane1).Theisolationefficiencywasconfirmedby flow cytometry analysis. The supernatant after isolation forWesternblottinginFigure 6B was subjected to a second round of isolationfordownstreamflowcytomtery(Figure 6C).

Finally, CD9+ exosomes isolated with magnetic beads were subjected to immunoassay (Figure 7). First, the correlationbetweenresultsobtainedbyflowcytometryand immunoassay

were established.CD9+ exosomes stained for CD81 (Figure 7A) and CD9 (Figure 7B)showedhighdegreeofcorrelation.Secondly,the dose responsewas investigated. Increasing amount of cellculture media containing exosomes (two separate exosome batches (Batch A and Batch B) were isolated using magneticbeadstargetingCD9followedbyCD81(Figure 7C) or CD9 (Figure 7D)detection.Asobservedforflowcytometry,adoseresponsewasobservedforimmunoassay.

DiscussionIsolation and analysis of nano-sized exosomes is challenging.Todaythegeneralapproachforexosomeisolationisdifferentialcentrifugation.Theprotocolisnotstandardizedasmanyvariantswith potential effect on the outcome are used and published.Also, several centrifugation steps are labour intensive, requirecostly equipment, increase risk for loss of exosomes and doesnot discriminate well between exosomes and contaminatingstructures such as larger vesicles and protein/lipid aggregates[26].Theinclusionofmagneticbeadswithantibodiesspecificfor



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exosomesurfaceproteins inthe isolationprotocoldownstreamof pre-enrichment has successfully overcome the issue of low purity.

Here we provide a simplified exosome isolation workflowby omitting the commonly used pre-enrichment step. Wedemonstrate that capturing exosomes directly from cell culture supernatant provides sufficient amounts of exosome fordownstream analysis while dramatically simplify the samplepreparation/handling.

Directisolationwithmagneticbeadsrequiresminimalhands-on,provides highly pure exosomes with minimal loss and enables future automation opportunities as it is compatible with theimmunoassayformat.

AcknowledgementsTheauthorswould like to thankLisbethLarsen (ThermoFisherScienfic)fortechnicalassistance.B.Kierulfwasresponsibleforthe

Western blot analysis of exosome surface markerCD81. Exosomes derived from SW480were isolatedby magnetic beads coated with anti-human CD81processed for Western immunoblot analysis (A).For comparison pre-enriched exosomes prior to bead isolation was included (pre). Shown is onerepresentative Western immunoblot out of threeindependentexperiments.B)Depletionefficiencywasmeasuredbyflowcytometryassignal tonoise (S/N)ofthesupernatantafterisolationforWesternblotting.25xrepresenttheamountofmagneticbeadsusedforWesternblotting.

Figure 4

Flow cytometric analysis of the effect of incubationvolume (A), incubation time (B) and exosome input(C)keeping theamountofmagneticbeadsconstant.Exosomes derived from SW480 cells were isolatedusing magnetic beads coated with anti-humanCD9 followed by CD9 staining and analysis by flowcytometryandpresentedassignal tonoise (S/N).A)CD9+ exosomes were isolated in 175 µL, 350 µL or 700 µLofcellculturemediausing20µLofmagneticbeads.B) CD9+ exosomes were isolated from 100 µL of cell culturemediabyincubating20µLofmagneticbeadsin 5, 16, 19 or 21 hours at 4°C. C) CD9+ exosomeswere isolated from 25 µL, 50 µL or 100 µL of added exosomes in a 100 µL total volume using 20 µL of magneticbeads.

Figure 5

flowassaydevelopmentandanlysis,flowassayvalidationflowcytanalysisanddatainterpretation.A.Kullmanwasresponsibleforthewesternblottingandflowcytometryanalysis.M.P.Oksvoldwas responsible for western blotting and data interpretation.M.Li was responsible for the miRNA analysis. Norbert Rooswas responsible for the electronmicroscopy. A.V. Vlassov was

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Flow analysis of CD9-positive exosomes isolated with magnetic beads from cell culture media, after pre-enrichment byultracentrifugationorprecipitation.SW480cellsweregrownforthreedaysbeforetheconditionedcellculturesupernatantwasharvestedandprocessedinthreedifferentways(A)nopre-enrichment(Direct),pre-enrichedbyultracentrifugation(UC)orprecipitation(Prec.)followedbyisolationusingmagneticbeadscoatedwithanti-humanCD9.TheexosomeswereanalysedbyflowcytometryafterstainingwithCD9-PE(redhistogram)orisotype-control(grayhistogram).B)CD9positiveexosomeswereisolatedfromcellculturemedia(Direct),pre-enrichedbyultracentrifugation(UC)orprecipitation(Prec),processedforWesternblottingandlabelledforCD9.Thewesternblotspresentedwereallfromthesamegel.C)ExosomeswereisolatedforWesternblottingusingmagneticbeadsspecificforCD9(25xtheamountofbeadsusedforflowanalysis)andtheremainingsupernatantwassubjectedtoasecondroundofexosomecaptureforflowanalysisasdescribedaboveandpresentedassignaltonoise(S/N).Theredandbluebarsrepresenttheflowanalysispre-andpost-exosomeisolationforWesternblotting,respectively.

Figure 6

CD9 positive exosomeswere isolated directly from conditioned cell culture supernatant harvested from SW480 cells andprocessedfor immunoassaydetectionusingeitherCD9-orCD81-AFP(A-D).A-B)Strongcorrelationbetweendataobtainedbyflowcytometry(medianfluorescenceintensity)andimmunoassay(meanluminescence)aredemonstratedforexosomesisolatedwithDynabeads®andstainedforCD81(A)orCD9(B).Immunoassayprovidedhighsignaltonoise(S/N)comparedtoflowanalysis(C-D)Doseresponsebetweenamountofexosomesaddedandsignalobtainedbyimmunoassaywasshown.

Figure 7



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responsible for the experimental design and miRNA analysis.Ingrid Manger was responsible for the experimental design of immunoassay and analysis of immunoassay. A.Neurauter wasresponsiblefortheexperimentaldesignanddatainterpretation.K.W. Pedersen was the project lead, and responsible for theexperimentaldesign,microscopy,datainterpretationandwritingofthemanuscript.

Conflicts of interestAnetteKullmann,BenteKierulf,AxlNeurauter,MuLi,AlexanderV. Vlassov, Ingrid Manger and Ketil W. Pedersen are full-timeemployeesofThermoFisherScienfic,Oslo,Norway.Theauthorshave indicated that they have no other conflicts of interestregardingthecontentofthisarticle.

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