In a world first, European biologists working together on a
Community project have made an important breakthrough in research
into producing vaccines from plants. The results of animal vaccine
trials are very promising, and may well herald some interesting developments
for the human race. The large-scale engineering of inexpensive "edible
vaccines" in plant hosts would usher in a genuine pharmaceutical revolution.
A common and easy to grow fodder crop, whose properties could
revolutionise methods of vaccination.
It all started with a modest fodder crop, the
cowpea (Vigna unguiculata) - also known in the English-speaking world
as the blackeye bean. Basing their work on a virus that commonly affects
the cowpea, European researchers taking part in a FAIR programme project
found a way of combating three viral diseases that mainly attack animals:
canine parvovirus, mink enteritis and the feline panleukopenia virus.
The virus that infects the cowpea has a feature that makes it eminently
attractive from the researchers' viewpoint: its surface is composed
of sixty copies of two proteins, one of which has a sort of molecular
loop projecting outward. The scientists proceeded in two stages. First,
they isolated a peptide - a short string of amino acids - common to
the proteins of the three viruses in question. Then, they managed
to insert the peptide into the multiple loops of the plant virus.
From plant to animal
Consequently, when the plant virus - now carrying sixty copies of
the peptide - infects the cowpea and multiplies there, the latter
becomes a very abundant source of an important element of the disease-causing
virus which can stimulate the animals' immune systems. Once it has
been administered to the animals, the modified plant virus will
act as an antigen, setting off the production of antibodies just
like a vaccination.
All that remains to be done is to harvest the leaves of the infected
plant, crush them, and isolate the modified plant virus for use.
The system could hardly be better: not only are production volumes
relatively very high (1 to 2 grams per kilo of undried material),
but the plant, having lost some leaves, carries on growing, thereby
ensuring sustained production.
Once purified, as controlled tests have confirmed, the modified
plant virus becomes a powerful vaccine when administered in appropriate
doses (from 100 micrograms to one milligram per animal treated).
Since a single kilo of plant material may yield 2 000 doses of vaccine,
one of the main advantages of the process is clear: its low cost.
The need for an international strategy
"Such research would have been impossible to carry out in a single
laboratory given the range of scientific expertise required - from
plant physiology to product development, not to mention animal and
plant virology, immunology, molecular biology and process development,"
explains Paul Rodgers, development director at Axis Genetics and
coordinator of the project. "To continue along this path, an international
research strategy was needed. Today, this openness policy brings
with it a second advantage - access to the largest markets. In this
respect, the European Union can assist by setting up laboratory
consortia that can be called on to focus on specific applications
for the technology we have developed."
In time, researchers believe it will be possible to administer
vaccines simply by oral ingestion of the active agent. "A practical
method which would help enormously in epidemiological prevention
campaigns," comments Paul Rodgers. For, it goes without saying,
that if so far the project has been limited to testing the process
for producing animal vaccines, the potential benefits for humankind
are just around the corner. Certain auto-immune diseases may be
preventable, even if not treatable, thanks to the somewhat artificially
induced, but renewable attributes of a simple fodder plant. Could
we be on the threshold of 21st century phytotherapy?