Expression and Manufacture of Pharmaceutical Proteins in Genetically Engineered Horticultural Plants - Transgenic Horticultural Crops: Challenges and Opportunities - page 95

protective.eficacy.in.humans.has.yet.to.be.determined.for.a.plant-derived.vaccine,.
challenge.studies.have.yielded.promising.results.in.animal.models.
Commercial.success.of.this.strategy,.however,.has.not.been.achieved.due.to.chal-
lenges.including.the.possible.degradation.of.vaccines.by.the.digestion.system,.poor.rec-
ognition.of.certain.antigen.at.mucosal.immune.effector.sites,.and.persistent.concerns.
about.whether.edible.vaccines.would.cause.inappropriate.antigenic.tolerance..Technical.
dificulties.also.contributed.to.the.lack.of.commercial.success..For.example,.challenges.
in.controlling.the.luctuation.of.antigen.content.among.individual.plants.or.plant.tissue.
often.cause.inconsistent.vaccine.protein.content.per.unit.of.plant.tissue..This,.in.turn,.
complicates.the.dosage.control.process.and.ultimately.hinders.the.commercial.applica-
tion.of.this.strategy. 115 .This.particular.problem,.however,.is.being.resolved.as.progress.
in.genetic.element.manipulations.has.allowed.more.precise.control.of.vaccine.expres-
sion.in.plants. 126 .While.oral.vaccines.still.offer.an.attractive.option.for.vaccine.delivery.
in.developing.countries,.the.application.of.this.strategy.in.the.United.States.will.face.
regulatory.obstacles,.since.a.vaccine.without.a.strictly.controlled.dose.would.have.tre-
mendous.dificulty.in.getting.approval.by.the.Food.and.Drug.Administration.(FDA)..
As.a.result,.increasing.efforts.have.been.shifted.to.downstream.processing.to.identify.
innovative.and.low-cost.ways.to.purify.or.partially.purify.vaccines.from.plant.tissue.
(see.below)..Puriied.vaccines.can.be.formulated.with.adjuvants.and.delivered.through.
different. immunization.routes. including.oral. and.other.mucosal. surfaces.. Thus,. this.
new.strategy.is.driven.not.only.by.the.necessity.to.develop.PMP.vaccines.with.deined.
dosage.content.but.also.to.address.the.needs.of.a.creative.formulation.with.adjuvants.to.
enhance.potency.as.well.as.creating.multivalent.and.multicomponent.vaccines. 77,127-129 .
On.going.research.by.our.group.has.allowed.us.to.establish.downstream.processing.
standard.operating.procedures.(SOPs).for.extracting.and.purifying.Norwalk.virus.cap-
sid.protein.(NVCP).from. N. benthamiana .plants.under.stringent.federal.current.Good.
Manufacturing.Practices.(cGMP).guidelines. 13 .We.anticipate.that.our.NVCP.material.
produced.under.the.cGMP.regulation.will.be.used.in.a.human.clinical.trial.as.a.vaccine.
candidate.for.sexually.transmitted.infections.later.in.2011. 130
Due.to.its.advantages.in.speed,.scale,.and.cost.for.subunit.vaccine.production,.the.
application.of.plant.expression.systems.has.recently.been.expanded.to.develop.and.
produce.vaccines.for.emerging.and.re-emerging.diseases,.cancers.as.well.as.agents.
of. biological. warfare.. For. example,. vaccines. for. smallpox, 104 . anthrax, 106 . dengue.
virus, 101 .avian.inluenza.A.virus, 131 .and.a.personalized.cancer.vaccine.for.follicular.
B-cell.lymphoma 67 .are.some.of.these.new.vaccine.candidates.produced.in.plants.
GLYCOSYLATION OF PLANT-MADE PHARMACEUTICALS
As. with. recombinant. proteins. produced. in. other. systems,. glycosylation. of. plant-
derived. pharmaceutical. proteins. is. a. critical. issue.. Glycosylation. is. depending. on.
a. series. of. posttranslational. modiication. steps. by. host. cells,. and. the. outcome. can.
seriously.impact.pharmacokinetics,.antigen/receptor.binding,.stability,.effector.func-
tions, and. eficacy. of. the. mAbs. and. other. PMPs.. As. such,. recombinant. proteins.
produced.by.heterologous.systems.may.have.appreciable.structural.and.functional.dif-
ferences.from.the.native.molecules.and.could.be.immunogenic.in.humans..In.general,.
the.glycosylation.of.proteins.in.plants.is.similar.to.that.of.mammalian.cells..However,.