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[SANET-MG] plant based vaccines not ready for production



The article below notes that plant based vaccines are not ready for
commercial production. However, the danger of the careless field tests
done in US, Canada and third world countries is not mentioned.
Development of oral tolerance would assist the spread of disease along
with numerous other problems certainly threaten to contaminate the food
supply.
Nature medicine sept. 2004
NEWS Edible vaccines not ready for main course
Edible vaccines produced in genetically
modified crops promise cheap and effective
protection against infectious diseases in the
developing world. But vaccine manufacturers
are reluctant to take a bite out of the projects.
Since 1992, when biologist Charles Arntzen
proposed genetically modifying bananas to
serve as cheap vaccines against infectious
diseases, research on plant-based pharmaceuticals
has grown rapidly. In July, the European
Union promised €12 million to European and
South African scientists developing vaccines or
antibodies against HIV/AIDS, rabies and
tuberculosis.Work is further ahead in the US,
where several acres of crops, most of them still
experimental, are planted each year.
Researchers have thus far produced more
than 45 different antigens in a wide range of
plants.“In 10–15 years,” says Hilary Koprowski,
a veteran vaccine researcher at Thomas
Jefferson University, “plant-derived vaccines
will be fully appreciated.”
At least in theory, plant-based vaccines
would be safer than those produced in animal
tissues because the chances of unknown
human pathogens hitching a ride would be
extremely small. Costs per dose would be low,
and scaling up would just mean planting a
larger crop. During transport and storage,
vaccine-containing seeds or dried leaves would
not need refrigeration, a significant advantage
in developing countries. Oral vaccines
especially, administered as juices or tablets to
circumvent dose variability,would pave the way
for mass vaccinations in those countries.
But even Arntzen now says his original idea
of distributing vaccine-bearing fruit
was naive, because regulatory agencies
will not approve vaccines with
variable dosing.
Many in the field say that, at least in
animals, plant-based oral vaccines
have been proven to be safe and
effective. For instance, corn loaded
with proteins from a gastroenteritis
virus is effective, at least when used as
a booster, in protecting pigs against
the disease, says John Howard,
founder of the Texas-based firm
ProdiGene.
In humans, several vaccines have passed
safety trials. Arntzen’s group at Arizona
State University tried vaccines produced in
genetically modified potatoes and corn against
enterotoxic Escherichia coli and Norwalk virus.
Koprowski’s group fed volunteers spinach
containing a rabies booster vaccine. Both
groups have tested oral hepatitis B vaccines,
either as primary or booster vaccine, in lettuce,
spinach and potatoes.
Although small phase 1 trials like these can’t
prove protection, volunteers in the studies
showed an “appropriate,” though not always
strong,immune response,Arntzen says.
Arntzen is collaborating with companies in
Egypt, South Africa and South Korea, but
outside developing nations, where there is an
urgent need for such vaccines, finding
manufacturers willing to finance larger trials
to demonstrate efficacy has been a formidable
challenge. “I’ve talked to all of the [big
companies],” says Koprowski, “and so far I
regard it a waste of time.”
Vaccine manufacturers have little reason to
replace existing production lines, as most
vaccines are economically unattractive. The
medical community is also focused on
high-tech approaches, making farm-grown
vaccines a tough sell, Koprowski says. But
smaller companies, led by young people
willing to take risks, could challenge the current
thinking, he says.“Then, others will follow.”
Part of the hesitation stems from the fact
that plant-based oral vaccines constitute a
new technology from both a regulatory
and scientific perspective, says renowned
vaccinologist Stanley Plotkin, who now
advises Aventis Pasteur.
Before they can be approved, Plotkin says,
plant-based vaccines will have to consistently
generate stronger immune responses, which
would need to be studied carefully for every
crop. “If vaccines are intimately presented
together with food, the gut’s immune system
faces a conundrum,” he notes. The gut is
designed not to react to antigens in food, but
must produce a useful response against the
vaccine. Instead of being immunized, patients
could even end up being ‘tolerized,’ meaning an
immune response against future invaders
would be weakened, not intensified.
Researchers say they have not yet seen signs
of such tolerance, but Plotkin says experiments
to convince regulators have yet to be designed.
“Immunologists will have to figure out how the
gut can do this, and do it right 99.9999% of the
time,” he says. Producing veterinary vaccines
first, followed by human booster vaccines,
could be the sensible way forward, he adds.
Convincing the general public that it is safe to
grow vaccines in fields poses a bigger challenge.
Citing fears over supermarket shelves stocked
with vaccine-contaminated foods, consumer
groups have called for a ban on using food crops
to produce pharmaceuticals. Some companies
are avoiding the issue by developing injectable
plant-based vaccines,by using nonfood crops or
by not using genetically modified crops.
For instance, California-based Large Scale
Biology uses genetically engineered mosaic
viruses to infect tobacco plants. A few weeks
later, says Larry Grill, the company’s chief
scientific officer, antibodies can be
purified from the harvested leaves.
The company has produced patientspecific
antibodies against cancer cells
just months after biopsies were taken.
Once the scientific and regulatory
hurdles are cleared, convincing
skeptics will be easier, researchers
note. “If I could save millions of lives
in developing countries,” says
Arntzen, “I think I’d have a pressure
group that could stand up even
against Greenpeace in Europe.”
Peter Vermij,Amsterdam

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