The food industry uses soybeans in products
ranging from baby formulas to salad dressing. Despite such broad use,
this crop isn't for everyone. Worldwide, 6% to 8% of children and 1% to
2% of adults suffer food allergies. Soy, in particular, is considered
one of the "big eight" foods that trigger potentially fatal reactions.
To prevent such reactions people allergic to soybeans must avoid eating
foods containing its proteins. Research suggests a single protein called
Gly m Bd 3s0K/P34 is to blame.
"Soybeans are in many processed foods, and here in the Western Hemisphere
it's hard to avoid them unless you're very proactive," said Eliot Herman,
who discovered P34 in the early 1990s. Now, using a biotech approach,
he and colleagues have shut off the gene that makes the allergenic protein
in the crop's seed.
"This is probably the first time a dominant human allergen has been knocked
out of a major food crop using biotechnology," says Herman, an ARS plant
physiologist. He'll publish the advance along with co-investigators Rick
Helm, an associate professor at the University of Arkansas for Medical
Sciences in Little Rock; Tony Kinney, a crop-genetics research leader
at the DuPont Experiment Station, Wilmington, DE; and Rudolf Jung at Pioneer
Hi-Bred International, a DuPont affiliate.
The team resorted to biotechnology after analysis of the soybean genome
revealed the P34 gene in domestic cultivars and in their wild cousins.
"The simplest approach would be to find a soybean without the protein,
but we found that all the domestic varieties and wild soybeans had it,"
said Herman, who recently transferred from Beltsville to the Donald Danforth
Plant Science Center in St. Louis, but is assigned to ARS' Plant Genetics
Research Unit, Columbia, Missouri.
More than just a sneeze
And while P34's exact function still isn't known, the researchers do know
it belongs to a class of proteins called cysteine proteases. It causes
65% or more of allergic reactions in soy-sensitive individuals and does
so by binding with IgE antibodies circulating in their bloodstreams. The
most severe form of allergic reaction is anaphylaxis. Here, a sensitized
person's airways rapidly constrict. More common reactions to soy include
nonfatal reactions such as hives, itching, and diarrhea.
"The only cure is avoidance of the food product. The difficulty with this
is the number of products derived from peanuts, soybeans, and other legumes,"
noted Helm, an immunologist specializing in food allergens at the Arkansas
Children's Hospital Research Institute.
Follow the biotech road
Although scientists appear to have shut off the gene for making P34, farmers
aren't likely to see the knockout soybeans commercialized just yet. More
tests are needed to prove they're indeed hypoallergenic, or less allergy
causing. So far, though, the researchers are encouraged by early results
from human blood serum tests in which antibodies that normally bind to
P34 couldn't detect the allergen in knockout beans.
The hypoallergenic beans will also have to pass muster on an agronomic
checklist that includes seed production, yield, pest resistance, oil and
protein composition, and other criteria important to soy farmers and processors.To
expedite research that could eventually yield a new commercial cultivar,
Pioneer Hi-Bred International is propagating the researchers' most promising
knockout strain on field plots in Hawaii. The tropical climate there allows
for two crops per season versus one on the U.S. mainland.
The knockout strain, derived from the soybean cultivar Jack, got its start
from a clump of embryonic plant cells called a callus. The scientists
cultured the material in the lab specifically for the purpose of knocking
out the P34 gene. To do this, they used a biotech method called gene-silencing.
Once they knew for sure they had silenced P34 in the callus, they regenerated
the cells into whole plants and propagated them further for their seed.
After obtaining a uniform plant population by selecting for three generations,
they checked the knockout beans' growth, development, and P34 activity
against those of an unaltered control group.
"The yield looks perfectly normal. The plants develop and grow at a normal
rate. The seeds set at a normal rate, and they all seem to have the same
kinds of protein, oil, and other good stuff in them," Herman reported.
"It looks like silencing P34 doesn't hurt the plant's agronomic characteristics."
Additionally, no new proteins emerged to take P34's place as a human allergen.
"We assayed the transgenic plants with antisera from people who were allergic
to soybeans. We wanted to see whether taking one allergen out caused any
new proteins to become allergenic. The answer is no," Herman said.
Besides making agronomic assessments, the researchers will use seed harvested
from the Hawaiian bean plots to begin trials with piglets, which require
lots of feed as they grow and develop. Helm will lead the studies at Little
Rock using part of a $784,000 grant that he, Herman, Glenn Furuta, and
Susan Hefle were awarded by USDA's Initiative for Future Agriculture and
Food Systems. They were recognized for their development of an animal
model to predict the allergenicity of genetically modified food. Furuta
is at Children's Hospital/Harvard Medical School. Hefle is with the University
Their study will include skin-prick allergenicity tests and feeding trials
using newborn piglets. "We'll use unaltered soybeans versus the knockout
soybeans to see what allergic reactions occur in the animals," Helm said.
Like human babies, he notes, piglets eventually outgrow their sensitivity
to soybean allergens. But until that time, an affected piglet can experience
vomiting, diarrhea, dehydration, and skin rashes. "Because this seems
to be a food allergy problem, it should be manageable by getting rid of
whatever the pigs are allergic to," added Herman. Information from the
pig studies and others could serve as the springboard for clinical trials
"We're doing human testing only in the in vitro sense," said Herman. "We
use human blood serum to test for P34 in the laboratory." But doing clinical
tests with human subjects is a responsibility that will ultimately rest
on the shoulders of whoever decides to commercialize the knockout beans
as a hypoallergenic variety, he adds.
Miracle crop market
The potential effect such beans could have on the industry and on consumers
may be far reaching, not so much because of the number of soy-sensitive
people there are, but because of the multitude of products derived from
the crop, which generated $12 billion in 2000 U.S. farm sales. Some products
that could potentially benefit from hypoallergenic soybeans include baby
formulas, soy milk, flour, cereals, grits, and pet food.
"You're never going to make a completely allergy-free soybean plant because
you're not going to be able to eliminate all the proteins in it," said
Helm. Rather, "we're looking to make a safer product." Many soy-sensitive
consumers are also allergic to other foods, particularly those among the
big eight. Singling out soy's major allergen could shorten the list of
products they need to avoid.
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