By Cyrill Götz
There are 6.6 billion people in the world and about 350 million of
them are infected with the Hepatitis B Virus. This makes it the most common
virus infection in the world and it occurs all over the globe. Vaccines
already exist, but they have several disadvantages such as pain after
injection and high costs. New approaches are needed to succeed in bringing
this virus under control - genetically modified plants may be a promising
attempt.
Xiao-Ming Lou of the Shanghai Key Laboratory of Agricultural Genetics
and Breeding and his team modified the genome of a tomato in a way that the
plant is able to produce a special antigen of the Hepatitis B virus
envelope, called the large surface antigen. The idea is that the modified
tomato becomes an edible-vaccine, which will create a good immune response
and be less expensive than the existing vaccines.

To create such a tomato plant they constructed the gene which encodes
for the human Hepatitis B virus large surface antigen and transferred it
into Agrobacterium tumefaciens. Afterwards they co-cultivated the bacteria
with a special cell-complex of the tomato fruit - the callus ? which has the
ability to develop into a mature tomato plant.

The bacteria then insert their enhanced genome into the plant cells.
The bacterial genome, which contains the gene of the Hepatitis B virus
antigen, will be integrated in the genome of the plant cell.

This process has the effect that afterwards the tomato can produce the
antigen of the Hepatitis B virus. This fact makes the fruit a possible
edible-vaccine, which is also often referred to as an oral-vaccine.

But to be able to act as a vaccine, the concentration of the antigen
in the tomato has to be high enough; otherwise the immune system will not be
stimulated.

The tomatoes that Lou and his team have created showed significant
differences in concentration during different stages of maturity. Smaller,
unripe fruits contained low concentrations of the antigen, where as ripe
fruits showed much higher amounts of the large surface antigen. In different
organs of the plant the concentration also varied. For example, the fruit
showed high concentrations when compared to the leafs, where the antigen is
found in lower quantities.

Lou and his team then wanted to find out where the Hepatitis B protein
appears in the plant cell. Analyses indicated that the large surface antigen
accumulates near the Endoplasmatic Reticulum ? a system of canals which pass
through the whole cell and is mainly responsible for transport and synthesis
of different molecules.

Checkbiotech learned that the next stage of research for Lou and his
team is to find out if the modified tomatoes are able to stimulate the
immune system. To prove this, experiments with mice will be done. The
results then will provide needed information to move onto testing in humans
if successful.

Cyrill Götz is a Science Writer for Checkbiotech in Basel,
Switzerland, and is currently studying biology at the University of Basel.


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