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Japanese
researchers have developed a genetically engineered rice
that protects against cholera, offering the hope of an
inexpensive, easily stored vaccine that could make a
major impact against diseases in third-world countries.
The
research, carried out by Hiroshi Kiyono and colleagues
at the University of Tokyo, was published online in the
Proceedings of the National Academy of Sciences.
The
scientists engineered the rice to produce a portion of
the cholera toxin protein in the grains. Mice that ate
the powdered rice did not get sick when later fed
complete cholera toxin.
Injected
vaccines are not typically effective for diseases of the
digestive system, such as cholera. Kiyono and his
coauthors designed their vaccine to target mucous
membranes such as the nose and mouth, where over 90
percent of infectious agents enter the body. This new
system for making vaccines, dubbed MucoRice, could
potentially be used for several diseases, such as
anthrax and the flu.
Scientists have been working on plant-based vaccines
since 1990, using plants such as tobacco, potatoes and
corn.
However,
food-based vaccines are tricky because the vaccine may
cause an allergic reaction to the food, or it may be
digested too quickly to stimulate an immune response.
“This is
the first time anyone has used rice,” said Charles
Arntzen, a plant biotechnologist at
Arizona State
University. “Rice is particularly useful because it is a
well-tolerated food crop and it is digested slowly.”
Kiyono
and his colleagues found that their rice-based vaccine
did not cause an immune response to rice proteins and
was digested slowly enough to allow immunity to develop.
Most
vaccines must stay cold during both storage and
transport, which makes delivery to developing nations
expensive. The cost to keep vaccines chilled is
estimated at $200-300 million each year.
The
rice-based cholera vaccine, in contrast, was still
effective after over a year stored at room temperature.
Such a
vaccine would be needle- and pain-free, probably
available as a tablet or capsule containing powdered
rice. This would diminish the accumulation of needles as
medical waste. |
