Expression and Manufacture of Pharmaceutical Proteins in Genetically Engineered Horticultural Plants - Transgenic Horticultural Crops: Challenges and Opportunities - page 110

also.be.used.to.prevent.the.exposure.of.environment.to.the.transgene.and.transgenic.
products..For.example,.PMP.tobacco.plants.are.routinely.harvested.through.mowing.
before.reproductive.organs.are.formed,.and.transgenic.corn.is.detasseled.mechani-
cally.to.prevent.transgene.low.to.the.environment.through.pollen.outcrossing. 252 .In.
addition.to.meeting.the. traditional.requirements. such.as.high.PMP.yield.and.easy.
scalability,. many. new. expression. systems. were. developed. with. the. added. advan-
tage. for. containment.. For. example,. since. duckweeds. produce. no. pollen. or. seeds,.
but.propagate.vegetatively.and.can.grow.in.closed.containers,.the.duckweeds-based.
LEX.Systems.offers.a.higher.degree.of.containment.than.other.systems..Similarly,.
plant. suspension. cultures. are. also. grown. in. controlled. containers,. allowing. better.
biosafety.control..Furthermore,.the.feasibility.of.growing.aquatic.plant.and.plant.cell.
culture.in.a.controlled.environment.also.allows.better.batch-to-batch.product.repro-
ducibility.and.the.ability.of.protein.production.under.cGMP..In.fact,.these.advantages.
have.enabled.them.to.be.operated.similarly.to.conventional.bacterial.or.mammalian.
cell.cultures.and.to.achieve.considerable. commercial.success.ahead.of.other. PMP.
systems.. These. successes. include. that. tobacco. suspension. cells. produced. the. irst.
FDA-approved. plant-made. poultry. vaccine. and. that. PMPs. produced. by. Lemna . or.
carrot.cell.cultures.are.being.examined.in.Phase.2.or.Phase.3.human.clinical.trials.
(http://www.biolex.com,.2011).
The.transient.expression.technology.based.on.“deconstructed”.viral.vectors.also.
provides. advantages. in. biosafety. and. containment. because. it. does. not. involve. the.
production. of. transgenic. plants.. Since. high. level. of. PMP. product. can. be. obtained.
easily.with.this.system,.the.amount.of.biomass.required.for.the.production.of.a.given.
quantity.of.PMP.is.reduced,.which.provides.the.possibility.of.performing.the.pro-
cesses.in.contained.facilities..This,.in.turn,.will.eliminate.the.need.for.ield-grown.
plants,.and.the.environmental.concerns.for.the.use.of.“deconstructed”.viral.vectors..
Furthermore,.this.system.does.not.require.fermenters.or.containers.to.grow.biomass,.
giving.it.an.easier.scalability.than.fermenter-based.duckweed.or.plant.tissue.cultures..
This.transient.expression.technology,.therefore,.represents.one.of.the.most.promising.
PMP.platforms.for.commercialization.
Biological Containment
It.is.necessary.in.certain.circumstances.to.use.biological.containment,.which.is.less.
dependent.on.human.oversight.than.physical.containment.as.an.additional.measure.
to.ensure.the.biosafety.of.PMP.production..Biological.containment.usually.employs.
molecular. or. genetic. techniques. to. either. create. a. biological. barrier. against. trans-
gene.low.into.other.plants.or.organisms.or.to.prevent.the.production.of.transgenic.
products.before.host.plants.being.harvested.or.moved.into.a.controlled.environment.
Transgenes.can.low.from.PMP.transgenic.plants.in.two.major.forms—pollen.
and. seeds. carried. by. various. vectors.. Correspondingly,. molecular. genetic. strat-
egies. for. containing. transgene. outlow. have. been. focused. on. the. areas. of. male.
sterility,.maternal.inheritance,.transgene.mitigation,.and.seed.sterility.(also.called.
“terminator”.technology). 253 .Male.sterility.is.one.of.the.early.strategies.of.biologi-
cal.containment.and.is.the.only.strategy.that.has.been.applied.to.commercial.trans-
genic.plant.(rape.seeds).production.(Plant.Genetic.systems,.Ghent,.Belgium)..Male.
sterile. plants. are. unable. to. produce. mature,. viable. pollen,. therefore. preventing.