Expression and Manufacture of Pharmaceutical Proteins in Genetically Engineered Horticultural Plants - Transgenic Horticultural Crops: Challenges and Opportunities - page 107

a QuatIc p lantS
One. of. the. most.innovative. and.the. simplest. whole-plant. transgenic.expression.
systems.may.be.that.of.employing.the.common.duckweed,. Lemna ..Largely.devel-
oped. by. Biolex. Therapeutics. (Pittsboro,. NC),. Lemna -based. LEX. Systems. expres-
sion. technology. allows. rapid. pharmaceutical. product. development. and. potential.
seamless. transition. to. large-scale. manufacture. under. GMP. conditions.. This. tech-
nology. is. enabled. by. several. advantages. of. the. duckweed. plants. including. small.
genome.for.facile.molecular.manipulation,.ease.of.transformation.and.regeneration,.
rapid. clonal. propagation,. and. biomass. growth. requiring. only. water. and. inorganic.
nutrients..Furthermore,.smaller.pharmaceutical.proteins.produced.in.duckweed.can.
be. directly. secreted. into. the. culture. medium.. This. would. eliminate. the. need. for.
homogenization.of.plant.tissue.and.signiicantly.simplify.target.protein.puriication.
and,.in.turn,.reduce.the.overall.processing.cost..Since. Lemna .plants.produce.neither.
pollen. nor. seeds,. but. are. propagated. vegetatively. in. simple. containers,. the. system.
also.offers.high.degree.of.containment..The.clonal.nature.of. Lemna .plants.and.the.
feasibility.of.growing.them.in.a.controlled.environment.also.allow.better.batch-
to-batch.product.reproducibility..Like.any.other.bioreactor.or.container-based.pro-
duction.systems,.the.scalability.of.the.duckweed.system.could.be.limited.compared.
with. those. of. other. crops.. Biolex. Therapeutics. has. produced. 35. proteins. with.
their. LEX Systems. and. their. leading. drug. candidate,. Locteron ® ,. an. α-interferon.
for.the.treatment.of.hepatitis.C,.is.being.examined.in.a.Phase.2b.human.clinical.trial.
in. Europe. (http://www.biolex.com,. 2011).. Duckweeds. have. also.been. shown. as.an.
excellent.host.system.for.therapeutic.mAb.production..Because.of.its.small.genome,.
its.glycosylation.pathway.can.be.manipulated.with.relative.ease..This.added.advan-
tage.allows. Lemna -derived.mAbs. to. have. uniform.and. “humanized”. glycans. 136 .It.
was.shown.that. Lemna -produced.CD30.mAb.contained.only.a.single.major. N -glycan.
species.and.showed. more.superior.ADCC.and. effector. cell-binding. activities. than.
those.of.equivalent.mAb.produced.in.mammalian.cells..In.addition.to. Lemna minor .
used.by.Biolex,.other.species.in.the.Lemnaceae.family.such.as. Pirodela oligorhiza .
and. several. Wolfia . are. also. being. exploited. as. a. source. for. recombinant. protein.
production. 241
p lant S uSpenSIon c ell c ultureS and S InGle -c ell c ultureS of a lGae
Plant. suspension. cells. are. liquid. culture. of. cells. or. cell. aggregates. derived. from.
callus.tissue..Transgenic.plant.cell.cultures.can.be.established.by.transforming.sus-
pension. cells. with. Agrobacterium . or. by. using. stable. transgenic. plant. to. produce.
the. callus. tissue.. Since. these. suspension-cultured. plant. cell. lines. can. be. grown. in.
a.controlled.environment,.they.allow.better.product.reproducibility,.a.high.level.of.
containment,.and.the.potential.to.manufacture.protein.under.cGMP.similar.to.mam-
malian.cell.culture.practices..Even.though.these.culture.systems.share.similar.limita-
tions.in.scalability.with.current.bacterial,.yeast,.and.mammalian.cell.cultures,.they.
still.provide.useful.alternatives.in.producing.pharmaceutical.proteins.owing.to.the.
fact. that. plant. cell. lines. require. less. expensive. culture. media. to. grow.. Moreover,.
pharmaceutical.proteins.smaller.than.20.kDa.can.be.directly.secreted.into.the.culture.