FOR MORE INFORMATION ON PLANT DERIVED VACCINES
October 13, 2005 SemBioSys Genetics Inc. (TSX:SBS), a biotechnology
company developing a broad pipeline of protein-based pharmaceutical and
non-pharmaceutical products, today announced it successfully completed
a milestone-based feasibility agreement with Dow AgroSciences LLC. The
agreement evaluated the utility of the StratosomeTM Biologics System for
production of an experimental animal vaccine. Financial details of the
agreement were not disclosed.
The completion of the
program with Dow AgroSciences demonstrates our ability to execute,
said Andrew Baum, President and CEO of SemBioSys Genetics Inc. We
continue to demonstrate the broad commercial utility of our oilbody-oleosin
technology and the ability of the SemBioSys organization to achieve its
objectives on schedule. The completion of the Dow AgroSciences program
demonstrates two important aspects of the StratosomeTM Biologics System
from which we can derive value; its flexibility to generate simple or
complex proteins, and its ability to address protein recovery and purification
simultaneously with bulk protein production.
During the program, SemBioSys
and Dow AgroSciences established the applicability of the StratosomeTM
Biologics System to produce plant derived proteins for use in the manufacture
of animal vaccines. The collaborative research project applied the StratosomeTM
Biologics System for the production, purification and formulation of an
animal vaccine. Dow AgroSciences is now evaluating the efficacy of the
vaccine in animal trials, and depending on the results, it has the option
to initiate negotiations toward a funded program with SemBioSys to develop
the animal vaccine product.
SemBioSys is developing other
animal health products with the StratosomeTM Biologics System including
the ImmunoSphereTM Feed Additive. ImmunoSphereTM targets the US$18 billion
shrimp production market. Viral disease is a major threat to commercial
shrimp aquaculture production. ImmunoSphere is an immunostimulatory
protein feed additive that enhances disease resistance in shrimp.
tobacco used against cervical cancer
Scientists at UCT are using
genetically altered tobacco plants to create vaccines against cervical
cancer. They aim to create vaccines that fight the virus not the wallet.
Rows of bright green, leafy tobacco plants grow in a humid greenhouse.
They look identical but one row is special. These are genetically altered
tobacco plants, carrying the shell of the human papilloma virus which
causes cervical cancer in women.
Tobacco leaves, dried, rolled and smoked, cause lung cancer. But these
genetically modified tobacco leaves are little factories, producing a
potentially inexpensive vaccine against cervical cancer, the biggest cancer
killer of women in Southern Africa and one which is particularly difficult
to catch early as it is buried deep within the female reproductive system.
The tobacco plant is an ideal crop for genetic modification. For a start,
the genetic alteration doesnít confer any survival advantage over plants
that have not been tweaked. In addition, tobacco and humans have been
around each other for so long that they have developed a reliance on each
other: the plant canít escape and grow wild. Just like maize, tobacco
requires human intervention to survive in Africa.
"Tobacco is a really well understood crop," says Professor Ed Rybicki
of the University of Cape Town. "All of the kinds of conditions that one
needs to use to grow it are very well understood indeed. It is relatively
tolerant of all sorts of conditions and you get an enormous volume of
leaf out of each plant, one hectare of mature tobacco gives you 20,000
kilograms or 20 metric tons of wet leaf. So that is an enormous volume
of plant material that you can actually make something out of."
What Rybicki and his team are trying to make out of tobacco is an affordable
vaccine against the virus which causes cancer in the cervix, the gateway
between the vagina and the uterus. (Men can transmit the virus. They can
also develop cancer of the penis. However, men have a far lower rate of
penile cancer, compared to cervical cancer in women, so itís not quite
the same public health issue.)
"You start with trying to make something that the immune system is going
to recognise instead of the virus. You cannot use the live virus because
you cannot culture these particular viruses, it is almost impossible,"
says the Zambia-born viral biotechnologist. "So what you do is make a
portion of the virus - that is, the protein coat - which is what the immune
system recognises. You can make this in a number of systems. And the nice
thing about it is however you make it, it usually self-assembles - that
is, it makes something that looks like the real virus. We can make it
in animal cell cultures, we can make it in insect cell cultures, we can
make it in plants. And we are trying to make plant production a reality."
The hollowed-out virus lacks nucleic acid, the trigger which makes the
virus infectious. Consider a jacket or coat without anyone inhabiting
it. It lies limp and flat. The same thing applies to this protein coat.
Give a human the hollowed-out virus, with the outside intact, and the
bodyís immune system goes on attack. If the real virus shows up, transmitted
by sex, it doesnít stand a chance.
Plant vaccine factories
"The primary reason for making things like vaccines in plants is that
it is potentially cheap," Rybicki said. "We may be able to cut costs by
orders of magnitude, because you do not need a fermentation plant which
you would for yeast or bacteria, you don't need huge tissue culture facilities
which you would need for human or insect or animal tissue culture. What
you need is a field or probably more likely a greenhouse."
The particles are also relatively easy to purify. They are "nice big stable
particles, which cannot do anything except provoke a response."
Like any vaccine developers, the team is far from their goal Ė and relatively
comfortable with that.
Vaccines that attack the virus not the wallet
"The usual vaccine production pathway from initiation of research to production
is about 10 years and there is a lot of reiteration because you have to
discover how to do things better or even how to do things at all," said
Rybicki. "We are still in the development phase. We have got candidates,
we know that we can make them. We need to make them on a bigger scale,
prove that we can make them economically and then stick them in a bottle.
Only then will we begin animal testing, let alone human testing."
South Africa used to have the capacity to generate its own polio virus
vaccine in the 1950s. Now it imports. In his office at the Department
of Molecular and Cell Biology, Rybicki notes that simply working on a
vaccine carries significant advantages for developing countries: "there
are a lot of orphan diseases out there that nobody wants to make a vaccine
for. Vaccines cost about one hundred million US dollars to take through
from beginning to human testing, just through to human testing, and this
is enormous money for big pharmaceutical companies. Drug development can
cost even more than vaccine development but because the vaccine market
is so much smaller than the drug market, the return is relatively low."
The number of vaccines being made today has dropped to its lowest in a
quarter of a century. Some vaccines have become a victim of their own
success: a one-off dose of polio drops generates considerably less money
than say, anti-depressant pills which have to be taken every day for the
rest of the patientís life.
But there are major international efforts underway in countries such as
India, Brazil, China and Argentina to make publicly funded vaccines. "Diseases
that don't occur in Europe or the United States do not get vaccines made
for them. Or they donít get the right type of vaccine. In Africa, we wonít
necessarily get the correct HIV subtype vaccine made for example."
Also, new vaccines made in Europe or the US are expensive. "The Hepatitis
B vaccine when it first came out was around 40$ a dose and it is now about
a dollar a dose but it took ten or 15 years to get to that point!" marvelled
Rybicki. The current push by big pharmaceutical companies for a vaccine
for cervical cancer Ė already well advanced, with the first human trials
accomplished - doesnít worry him. The vaccine will be too expensive for
third world health budgets, he predicts. His aim is to find something
that attacks the virus, not the wallet.
More information: Dr Ed Rybicki: www.mcb.uct.ac.za/staff/ed/htm
Copyright 2002, Science in Africa, Science magazine for Africa CC