BUFFALO, NY--Vaccines in bananas? The idea may not be farfetched, as
researchers at the Roswell Park Cancer Institute have successfully
tested transgenic plants that express a hepatitis B virus (HBV) antigen.
HBV infection is the leading cause of liver cancer and is epidemic in
developing third-world countries. It is estimated that 300 million
people are carriers of HBV worldwide. While an effective HBV vaccine
exists, it is expensive, requires refrigeration to maintain its
potency, and must be given in three needle injections over a 6-month period.
"Global immunization programs are more difficult with vaccines
that require a cold chain or multiple inoculations,"
said Yasmin Thanavala, PhD, Molecular Immunology, Roswell Park.
Her laboratory is trying to find a way to make vaccines that can be
shipped easily, kept fresh without refrigeration, and made affordable
for countries where HBV is endemic. "While our ultimate goal is
the banana, we have had success using the potato," she said at
the first meeting of the Regional Cancer Center Consortium for
Biological Therapy of Cancer, hosted by Roswell Park.
In pilot studies, researchers placed DNA from the hepatitis B virus
into tobacco leaves by infecting the leaves with Agrobacterium
containing the hepatitis B surface antigen (HBsAg) gene. The bacteria
transferred the gene to the plant where it was incorporated into the
DNA of the plant itself.
Much is known about the tobacco leaf, making it useful for testing
purposes, Dr. Thanavala said. Thus, she and her colleagues used the
tobacco leaf in their first experiments to establish proof of concept
that plants are capable of expressing viral antigen, and, if
expressed, the immune system will recognize the antigen.
These tests showed indeed that plants could take up an antigen and
create a product that would elicit an immune response when injected
into mice. The researchers then moved on to an edible plant--the potato.
Potatoes were transgenically altered (by Dr. Charles Arntzen of the
Institute for Plant Research, Ithaca, NY) to express the HBsAg gene.
Dr. Thanavala tested the immune function of the potatoes by feeding
them to mice. Each mouse was fed 5 g of potato containing roughly 5.5
µg of HBsAg.
When the observed immune response to HBsAg declined, the mice were
challenged with 0.5 µg of a commercially purchased vaccine. All
of the mice had seroconverted and responded to the challenge by
making a secondary immune response.
"While it was encouraging to see that the potato could also be
used to create an appropriate immune response, very few people eat
their potatoes raw. We tested the potatoes after they were boiled and
found that boiling did decrease the efficacy substantially, although
we could generate a reduced response to the cooked potato," Dr.
The goal now for Dr. Thanavalas lab is to recreate the success
of the tobacco leaves and potatoes in the banana. Bananas are common
in many developing countries and can be stored without refrigeration.
"This research opens the door to possibly eradicate many of the
diseases that plague third-world countries and harm their children.
What child, or adult for that matter, wouldnt prefer a banana
to a needle?" Dr. Thanavala asked.