April 8, 2002
Researchers make advance toward
low-cost treatments, edible vaccines
a tomato, one day, keep cholera away? Or produce therapeutic
antibodies to treat cancer? Scientists at California State
University, Sacramento have taken an important step toward
developing tomatoes as a possible source of edible vaccines
and other proteins such as therapeutic antibodies. Biological
sciences professor Nicholas Ewing and graduate student Seungil
Ro have identified and recently patented a portion of a gene
that could turn tomatoes into low-cost, disease-relieving
Currently, animal cell cultures are used to produce highly
effective but expensive vaccines and anti-cancer antibodies,
such as Genentech's herceptin antibody. Since this is such
a costly method, a number of groups are using plants to produce
the antibodies, including Vacaville's Large Scale Biology.
The novelty of Ewing and Ro's approach was the choice of the
tomato as a production system.
Their discovery - Promoter of the Tomato Expansion Gene LeEXP-1
- is a genetic "switch" that can be used to trigger
the activation of any gene placed adjacent to it. To produce
antibodies, the antibody gene is cloned from an animal cell
line and placed adjacent to the LeEXP-1 promoter. When this
new gene is transferred back into tomato plants, the antibody
gene is turned on in tomato fruit, which leads to the accumulation
of antibodies. The antibodies can then be purified from the
For edible vaccines, a different gene - one from the organism
being vaccinated against - would be inserted adjacent to the
LeEXP-1 promoter and transferred in the tomato. These fruit
would then contain the protein of the organism. Consumption
of the fruit then could generate an immune response that protects
the individual from exposure to the organism itself in the
Ewing notes that they still have a way to go toward their
long-range goal of a tomato-based vaccine. They are just beginning
to test the levels of protein they may be able to produce.
But if the work comes to fruition, Ewing foresees a great
potential for use, especially in developing countries.
"Regular vaccines are often too expensive - they have
to be refrigerated, you have to have clean needles,"
Ewing says. "While the edible vaccines would still need
to be administered by a health professional, they would be
The process could be used for an existing vaccine or as a
way to develop vaccines. "I'd like to see it used for
vaccines that pharmaceutical companies don't devote much time
and money to, such as in developing countries where there's
not a lot of money to be made in fighting diseases that impact
large numbers of people," Ewing says.
The discovery of the promoter of the LeEXP-1 gene isn't the
only reason Ewing is pursing the tomato as his potential source.
Previous efforts to produce edible vaccines using potatoes
would have required subjects to eat the tubers raw, since
cooking would alter the chemistry. Ewing thought it might
be better to try something that people will eat uncooked,
so he looked at the tomato.
Also for proteins that may later be purified, tomatoes may
be superior to sources being used now such as tobacco, corn
or soybeans, so they could produce larger amounts for lower
costs, he says. There is also less pollen transfer than with
other plants and therefore less risk of cross-contamination.
By next fall Ewing expects to be able to put some test plants
in greenhouses to test how well the system will work. Eventually
he hopes to test some in a field near a local biotech facility,
buffered from other plants.
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office at (916) 278-6156.
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