Expression and Manufacture of Pharmaceutical Proteins in Genetically Engineered Horticultural Plants - Transgenic Horticultural Crops: Challenges and Opportunities - page 97

opportunity.to.deliver.plant-derived.vaccines.in.the.developing.world,.considerations.
of.licensure.and.regulatory.issues.have.pointed.to.necessity.of.developing.process-
ing.technologies. to.produce. vaccines.and.therapeutics. with.deined.unit.dosage. 139 .
Developing.new.technologies.to.minimize.cost.associated.with.downstream.pro-
cessing. is. crucial. for. the. full. realization. of. economic. effectiveness. of. PMP. tech-
nology,.since.it.can.account.for.up.to.80%.of.the.total.cost.in.a.therapeutic.protein.
production. 140 . A. well-developed. downstream. process. will. increase. manufacturing.
productivity,.reduce.cost.of.goods,.enhance.scalability,.and.ensure.the.compliance.of.
the.manufacturing.procedures.with.FDA's.cGMP.regulations.
Similar.to.other.production.systems,.the.goal.of.PMP.downstream.processing.is.to.
recover.the.maximal.amount.of.highly.puriied.target.protein.with.minimal.number.of.
steps.including.tissue.harvesting,.protein.extraction,.puriication,.and.product.formula-
tion.(Figure.4.3)..The.unique.properties.of.plant.tissues,.however,.present.both.speciic.
challenges.and.opportunities.for.each.of.the.processing.steps..Column.chromatogra-
phy.has.been.extensively.employed.in. PMP.puriication,.while.nonchromatographic.
methods.are.being.explored.aiming.to.provide.alternatives.for.large-scale.manufacture.

c olumn c hromatoGraphy
Chromatography. has. been. the. method. of. choice. for. PMP. puriication. due. to. its.
resolving. power.. As. a. result,. many. PMPs. have. been. successfully. puriied. from.
a. diversity. of. host. plants. with. a. variety. of. chromatographic. techniques. tai-
lored. for. each. individual. PMP. protein. based. on. its. solubility,. size,. pI,. charge,.

Seed
bank

(A)

(B)

Agrobacterium production
Media

-80

Master
cell bank

(C)

1

2

3

Inoculum
preparation Fermentation

Working
cell bank

FIGURE 4.3 (See color insert.) .General.large-scale.production.steps.for.plant-made.pharma-
ceuticals.from.green.leafy.materials.using.deconstructed.viral.vector.transient.expression.strat-
egy..(A).Plant.cultivation..(B).Iniltration.and.growth.. (C).Downstream. processing.. (Adapted.
from.Chen,.Q..et.al.,.Subunit.vaccines.produced.using.plant.biotechnology,.in. New Generation
Vaccines ,.Levine,.M.M..Ed.,.4th.edn.,.Informa.Healthcare.USA,.Inc.,.New.York,.2009,.p..77..
Copyright.2009..With.permission.from.Informa.Healthcare.USA,.Inc.)