State-of-the-art-gene-based-therapies-the-road-ahe

Theideaofgene-basedtherapeuticshasbeenaroundforsometime,butitonlyreceivedseriousattentionwiththeadventofrecombinantDNAtechnologyandtheabilitytotransferandexpressexogenousgenesinmammaliancells.Thefirstclinicaltrialswerecarriedoutinthelate1980s,andatthatstageitwaspredictedthatgenetherapywouldbecomeatreatmentforseri-ousdiseasesinjustamatterofyears.However,duringtheensuingtwodecades,numerousobstacleshavetem-peredtheenthusiasmforgenetherapy.Morerecently,someimportanttechnicalbarriershavebeenovercometothepointwheresuccessfulexamplesexistoftreatingspecificdiseases,aswellasencouragingnewpreclini-caltrialsthatwillexpandonthenumberoftreatabledisease-targets.ThisReviewprovidesinsightsintothestate-of-the-artaccomplishmentsmadewithgene-basedtherapiesandthemajorbarriersthatneedtobeovercomebeforetheyaremorewidelyimplementedbythemedi-calcommunity.TheReviewstartsbydescribingthegeneralapproachesused—highlightingthegrowingapplicationoftherapiesinvolvingthetranscriptionofnon-codingRNA—andsomeofthepracticalconsider-ationsthatarecommontoallgenetransferstudies.Themostclinicallyrelevantvectorsarediscussed,provid-ingexamplesofcurrentsuccesses(suchashighergenetransferefficiencyandlowerimmunologicalresponses)andtheareasinwhichmoreeffortisrequiredtoover-cometechnicalbarriers.ThereaderisreferredtothreeotherReviewsinthisFocusissuethatcovertheuseofviralvectors1,silencing-basedtherapies2andcell-basedtherapies3ingreaterdetail.Iendwithsomethoughtsontheprospectsforthefutureapplicationsofgenetherapyintheeraofpersonalizedgenomicmedicine.Althoughgenetherapyhashadarockycourse—whichhasbeenexacerbatedinpartowingtoscepticismfromsomepartsofthescientificcommunity—itisnowemergingasapromisingdisciplineasaresultoftech-nicaladvancesandthesuccessfultreatmentofseveraldevastatingmedicalconditions.ThegoalsofgenetherapyGene-basedtherapeuticsisbroadlydefinedastheintro-duction,usingavector,ofnucleicacidsintocellswiththeintentionofalteringgeneexpressiontoprevent,haltorreverseapathologicalprocess.Here,Irestrictthedefinitiontoincludeexogenousnucleicacidsthatpro-videatranscriptionaltemplatefortheexpressionofaprotein-codingornon-codingnucleic acid.Genetherapycanbecarriedoutbythreeroutes—geneaddition,genecorrection/alterationandgeneknockdown—thataresometimesusedincombination.Thevectorscanbeadministeredin vivoorex vivousingautologouscellsderivedfromanindividualpatient.Dependingonthevector,thetherapeuticDNAeitherintegratesintohostchromosomalDNAorexistsasanepisomal vector.Geneadditionandcorrection.Oftheapproachesmen-tionedabove,geneadditionisthemostcommonlyattemptedincurrentpreclinicalandclinicalstudies;itisusedtoprovidetherapeuticbenefitortosupplyaproteinthatismissingowingtogeneticmutation.Theleastcommonofthetechniques,genecorrection/alteration,hasgainedalotofattentionandhasbeencoveredinarecentReview4:inthisapproach,zincfingernucleasesandDNArecombinationtechnolo-giesareusedtoaltergenomicsequencestocorrectaDepartmentsofPediatricsandGenetics,AssociatePediatricChairforBasicResearch,StanfordUniversity,269CampusDrive,Room2105,Stanford,California94305,USA.e‑mail:[e-mail]:10.1038/nrg2971Publishedonline6April2011ZincfingernucleasesEngineeredDNA-bindingproteinsthatproducedouble-strandbreaksatspecificsequences.TheycanbeusedtocorrectorinducemutationsingenomicDNA.State-of-the-artgene-basedtherapies:theroadaheadMarkA. KayAbstract|Improvementsinthegenetransfervectorsusedintherapeutictrialshaveledtosubstantialclinicalsuccessesinpatientswithseriousgeneticconditions,suchasimmunodeficiencysyndromes,blindnessandsomecancertypes.Severalbarriersneedtobeovercomebeforethistypeoftherapybecomesawidelyacceptedtreatmentforabroadgroupofmedicaldiseases.However,recentprogressinthefieldisfinallyrealizingsomeofthepromisesmademorethan20 yearsago,providingoptimismforadditionalsuccessesinthenearfuture.REVIEWS316|MAY2011|VOLUME12©2011MacmillanPublishersLimited.AllrightsreservedRNAi(RNAinterference).TheprocessbywhichtheintroductionorexpressionwithincellsofdsRNAleadstothesequence-specificcleavageanddegradationofatargetmRNAandthereforetogenesuppression.miRNAspongesExogenouslydeliveredorexpressednon-codingRNAsthatbindandinhibitmicroRNAfunctioninasequence-specificmanner.RNAaptamersShortRNAsselectedfromlargelibrariesthat,owingtotheirthree-dimensionalstructure,bindtoandactivateorinterferewithproteinfunctionand/ordirectamacromolecularcargo(forexample,smallinterferingRNAs)intocellsviaatargetedreceptor.mutationorcreateamutation(forexample,amutationinC-Cchemokinereceptortype5(CCR5)canmakecellsresistanttoHIVinfection).Geneknockdown.Newertoolsformodulatingsinglegenesorcomplexgenenetworkshaverenewedenthu-siasmingene-basedtherapeuticsowingtotheelucida-tionofmicroRNA(miRNA)-mediatedgeneregulationcircuitsandtheabilitytovirtuallyeliminateageneprod-uct usingRNAi.RNAicanbeinducedbyexpressingshorthairpinRNAs(shRNAs)orbydeliveringshortdsRNAsthathavecompletecomplementaritytoatargetmRNA.miRNAsgeneratesimilarsmallRNAsbutdownregulategenesbyanon-cleavage-dependentdegradationpath-w