Anti-cancer chicken eggs produced*

UK scientists have developed genetically modified chickens capable of
laying eggs containing proteins needed to make cancer-fighting drugs.

The breakthrough has been announced by the same research centre that
created the cloned sheep, Dolly.

The Roslin Institute, near Edinburgh, says it has produced five
generations of birds that can produce useful levels of life-saving
proteins in egg whites.

The work could lead to a range of drugs that are cheaper and easier to make.

Professor Harry Griffin, director of the institute, told the BBC: "One
of the characteristics of lots of medical treatments these days is that
they're very expensive.

"The idea of producing the proteins involved in treatments of flocks of
laying hens means they can produce in bulk, they can produce cheaply and
indeed the raw material for this production system is quite literally
chicken feed."

Roslin has bred some 500 modified birds. Their existence is the result
of more than 15 years' work by the lead scientist on the project, Dr
Helen Sang.

But it could be another five years before patient trials get the
go-ahead and 10 years until a medicine is fully developed, the Roslin
Institute cautioned.

Anti-viral approach

Therapeutic proteins such as insulin have long been produced in
bacteria; but there are some complex proteins that can only be made in
the more sophisticated cells of larger organisms.

Scientists have successfully made a range of these molecules in the milk
of genetically modified sheep, goats, cows and rabbits.

The work at Roslin shows it is now possible to use chickens as
"biofactories", too.

A transgenic goat (GTC Biotherapeutics)
A number of GM animals are now being used as drug factories

Go-ahead for 'pharmed' goat
Some of the birds have been engineered to lay eggs that contain miR24, a
type of antibody with potential for treating malignant melanoma, or skin
cancer. Others produce human interferon b-1a, which can be used to stop
viruses replicating in cells.

The proteins are secreted into the whites of the eggs. It is a fairly
straightforward process then to extract and purify them.

Dr Sang said the team was highly encouraged by the level of the birds'
productivity, but further improvements were required.

"We're probably getting a high enough productivity if you want to make a
very active protein like interferon, but not enough yet if you want to
make an antibody because people need large doses of these over long
periods; so one of our next challenges is to try to increase the yield
in egg white," she told BBC News.

Wider role

Chickens had some advantages over other animals for "pharming" because
their lifecycles were shorter, said Dr Sang.

"Once you've made the transgenic birds, then it's very easy; once you've
got the gene in, then you can breed up hundreds of birds from one
cockerel - because they can be bred with hundreds of hens and you can
collect an egg a day and have hundreds of chicks in no time," she explained.

The Roslin research is part of the Avian Transgenic Project, a joint
venture with biotechnology firms Viragen and Oxford BioMedica.

Details of the latest work are to be published this week in the US
journal Proceedings of the National Academy of Sciences (PNAS).

The Roslin team also expects its engineered chickens to provide new
insights into aspects of reproductive biology.

It says the ability to modify birds' embryos will allow researchers to
study fundamental processes that control the very early development of
vertebrates.

It is just over 10 years since the Finn Dorset lamb called Dolly was
born at the institute.

She was the first mammal to be cloned from an adult cell - making her a
genetic replica of a six-year-old ewe. She was put down in 2003 after
contracting a common lung disease.