Biomedical Engineering Reference
In-Depth Information
in.the.number.of.macrophages,.a.77-fold.increase.in.the.number.of.dendritic.cells,.and.a.
2-.to.6-fold.increase.in.the.number.of.B.and.T.cells.at.the.site.of.injection,
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.supporting.the.
hypothesis.that.electroporation.itself.induces.inlammation.
However,.there.is.some.synergy,.speciically.between.DNA.injection.and.electroporation,.
which.may.aid.in.the.overall.induction.of.the.immune.system..For.example,.electropora-
tion.following.peptide.immunization.did.not.increase.vaccine-speciic.immune.responses,.
suggesting.that.electroporation.alone.is.not.suficient.to.augment.vaccine.potency.
19,29
.The.
exact.nature.of.this.synergy.is.not.completely.understood..The.vaccine.plasmids,.which.
are. bacterial. expression. vectors,. contain. unmethylated. CpG. sequences,. which. activate.
immune.cells.through.Toll-like.receptor.9.(TLR9).
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.However,.mice.deicient.in.TLR9
are.
equally. as. effective. as. the. wild-type. control. mice. are. in. responding. to. DNA. immuni-
zations;. thus,. DNA. vaccination. with. electroporation. can. stimulate. the. immune. system.
through.TLR9
-
independent
mechanisms.
30
.Another.reason.for.the.DNA/electroporation.
synergy. may. be. that. the. kinetics. of. DNA. immunization. and. electroporation. cooperate.
more.effectively.than.do.the.kinetics.of.peptide.and.electroporation..Antigen.expression.
from. plasmids. takes. a. few. hours,. allowing. electroporation-induced. inlammation. and.
antigen.expression.to.overlap,.while.peptide.injection.provides.antigen.in.a.ready.form.
29
.
Although. a. clear. mechanism. is. preliminary,. a. combination. of. these. effects—increased.
transfection. and. synergy. of. gene. expression. and. inlammation—is. likely. important. for.
increasing.the.immunogenicity.of.DNA.vaccines.via.electroporation.(Figure 14.2b).
14.3.3 Electroporation of DNA Vaccines Increases Immunogenicity in Larger Animals
Working.with.the.observation.that.electroporation.could.dramatically.increase.DNA.vac-
cine.eficacy.in.mice,.Babiuk.et.al..tested.this.vaccine.modality.in.pigs.weighing.between.
9. and. 18. kg.
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. The. authors. reported. dramatic. increases. in. both. antibody. and. cellular.
responses,. especially. in. pigs. that. were. not. boosted. with. recombinant. protein.. The. total.
antigen-speciic. T. cell. response. with. DNA. and. electroporation. was. comparable. to. that.
observed.with.DNA.prime.and.protein.boost.
31
.Subsequent.work.from.a.number.of.groups.
investigated.the.effect.of.DNA.vaccination.followed.by.electroporation.in.nonhuman.pri-
mates.. In. one. report,. Luckay. et. al.. reported. a. 50-. to. 200-fold. increase. in. DNA. vaccine.
potency.with.electroporation,.and.even.increased.immune.responses.against.less.immu-
nogenic.antigens.
32
.The.effect.of.electroporation.is.also.immediate;.Hirao.et.al..reported.
that. even. after. a. single. immunization,. the. addition. of. electroporation. induced. a. sixfold.
increase.in.T.cell.responses.against.HIV.antigens.
33
.After.the.second.immunization,.the.
increase.with.electroporation.was.nearly.20-fold.(Figure 14.3a)..The.overall.increase.in.cel-
lular.immune.response.was.associated.with.not.only.more.antigen-speciic.T.cells,.but.also.
more.T.cells.with.increased.capacity,.such.as.production.of.IL-2.and.tumor.necrosis.factor.
(TNF)-α.. These. increases. also. had. a. lasting. effect,. as. antigen-speciic. T. cells. were. pres-
ent.even.5.months.after.the.last.immunization,.suggesting.a.boost.in.the.memory.T.cell.
response..But.perhaps.the.most.interesting.consequence.of.electroporation.was.the.induc-
tion.of.strong.antibody.responses..A.historical.weakness.of.DNA.vaccine.technology.has.
been.its.inability.to.induce.clear.antibody.responses.in.nonhuman.primates.and.in.human.
clinical.studies.
34
.While.immunization.with.DNA.alone.induced.negligible.to.no.antigen-
speciic.antibody.responses,.the.addition.of.electroporation.increased.antibody.titers.tre-
mendously.
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.The.overall.consequence.was.not.only.an.increase.in.total.cellular.immune.
responses,.but.also.a.balance.in.the.response.by.stimulating.both.arms.of.the.immune.sys-
tem..As.will.be.discussed.further,.this.ability.to.activate.both.arms.of.the.immune.system.
will.have.numerous.beneits.in.targeting.various.diseases.and.conditions.
