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In a phase 1 clinical study, a research team has tested the efficacy of an
oral vaccine produced by transgenic corn, obtaining encouraging preliminary
results, December 2004 by Angelika Kren, Checkbiotech .
In developing countries, many people fall ill with, and eventually
sometimes even die of, diseases they could have been easily protected from
with today?s available medical means such as vaccinations. However, access
for these people to vaccination often is restricted for logistical and
The production of vaccines, or vaccine antigens respectively, by common
technology is very expensive. Scientists around the world work on
technologies for the production and formulation of vaccine antigens in
alternative systems. The production of a vaccine antigen in transgenic
plants seems to be one of the most promising approaches with advantages
towards the production in bacterial, fungal, insect or other cell cultures.
First off, it is inexpensive, when compared to traditional methods. Second,
if the vaccine is produced in a plant, it might also function as an oral
vaccination. This is an important factor for people living in developing
countries that have never seen a vaccination before?for them, a needle stuck
under their skin can be a rather fearful event.
In her work published in the journal ?Vaccine? early this year, Dr. Carol O.
Tacket and her team from the University of Maryland School of Medicine,
tested whether an antigen (LT-B) produced and delivered by transgenic corn
would be well tolerated and could stimulate antibody immune responses.
Escherichia coli (E. coli) is a bacterium that is a common inhabitant of the
human intestine and normally, E. coli does not cause disease. However, some
strains can produce toxic proteins (toxins) causing various illnesses, as
for example cholera. Enterotoxic E. coli produces the heat-labile
enterotoxin (LT) that causes watery diarrhea among young children in
developing countries and travelers. The structure and mode of action of LT
is very similar to the Cholera Toxin. LT consist of two subunits, LT-A and
LT-B. Whereas the enzymatically active LT-A subunit is the one actually
causing the disease, LT-B (the binding subunit) is an enzymatically inactive
protein and does not cause any pathological situations, but is highly
immunogenic. Hence, LT-B potentially represents a very good vaccine antigen
that is safe for humans.
Dr. Tacket?s team prepared the transgenic corn, as defatted corn germ meal,
using standard commercial techniques. Thirteen volunteers were then fed
doses of transgenic corn meal (9 persons) or, a control (4 persons) of
defatted corn germ meal for three times that did not contain LT-B.
What Dr. Tacket found was seven (78%) of nine volunteers developed
significant rises in serum IgG anti-LT-antibody and four (44%) out of nine
developed significant rises in serum IgA anti-LT. Furthermore, seven (78%)
out of nine vaccines developed specific IgA antibody secreting cells (ASC)
and the same seven also developed IgG ASC. These results indicate that LT-B
produced in transgenic corn is well-tolerated and immunogenic in humans.
But what might be the reasons for some people not responding? ?There are
several explanations possible,? said Dr. Tacket.
?The antigen might have been damaged while passing through the stomach and
intestine. High levels of pre-existing immunity might be another explanation
for non-responders, and, of course, you can never rule out genetic factors.?
At the moment Dr. Tacket?s team is working on ensuring that a larger percent
of people is immunized. To increase the efficacy of the vaccine, Dr. Tackets
team is looking at a variety of adjuvants that can be attached to LT-B.
Adjuvants are substances that help enhance the pharmacological effect of a
drug, or increase the ability of an antigen to stimulate the immune system.
Until Dr. Tacket?s new vaccine will actually be commercially available, she
noted there is still some more work that needs to be done, ?These are phase
1 safety and immunogenicity studies. Phase 2 safety and immunogenicity
studies in larger numbers of people and phase 3 efficacy studies in the
filed must be done, we do not know yet whether the anti-LT response is
She hopes, though, that society might benefit from her research by
successfully using the transgenic corn for the production of very safe and
Angelika Kren is a Science Journalist with Checkbiotech, and is a graduate
student at the University of Basel, Switzerland.
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