Eggs With A Little Extra

(REUTERS)  Sheep that produce human proteins in their milk, goats that can be milked for spider web proteins, and other genetically engineered animals just got some competition -- chickens that can produce useful drugs in their eggs, researchers reported Monday.

Because chickens grow up to lay eggs faster than sheep, goats or cattle begin producing milk, the researchers said, the birds potentially could be a quicker source of biologically produced drugs.

Genetically engineered chickens produced reliable levels of an enzyme in their eggs, suggesting they could be used as living "bioreactors" to make proteins used in human medicine, the team at the University of Georgia and AviGenics, Inc., reported.

"A modern, genetically selected White Leghorn hen lays up to 330 eggs per year, each containing about 6.5 grams of protein," the researchers wrote in their report, published in the April issue of the journal Nature Biotechnology.

The researchers, led by Alex Harvey of AviGenics, used a virus to genetically engineer chickens that produced a "marker" enzyme, beta-lactamase, in their eggs. The enzyme is not used in medicine but is easy to detect for laboratory tests.

Wrinkles still need to be ironed out -- they tried their method on 546 incubating eggs, from which 126 chicks hatched. Only 10 percent of these carried the new gene.

They mated the birds that had the highest levels of the beta-lactamase gene in their own egg and sperm cells and produced birds that reliably carried working copies of the gene.

Several generations of these chickens laid eggs that carried the gene, Harvey's team reported.

They could join sheep, goats, rabbits and other animals that produce human proteins in their milk, proteins that are used to treat a range of diseases from cystic fibrosis to diabetes.

Scientists have long used bacteria to create proteins, human and otherwise, that treat disease, but proteins made by mammals are considered superior in many cases.

In January, Canadian scientists said they had bred goats that can produce spider silk in their milk, which might be used to make armor and other strong materials. Weight for weight, spider silk, a protein, is much stronger and more flexible than steel.

But it takes a long time to breed mammals, Harvey and colleagues said. "Goats, for example, take 18 months from the creation of founder transgenic (genetically engineered) embryos to the production of milk by progeny," they wrote.

Chickens mature faster and they reproduce prolifically when artificial insemination is used, they said. "The hen has many advantages over other systems as a bioreactor," they added.

"Unlike cows, goats and sheep, chickens have been raised for many generations as specific pathogen-free animals in biosecure facilities," they wrote. For example, eggs are used to make vaccines, which must be pure.

Human drugs that might be made using eggs include serum albumin, which is used, for example, to treat blood loss, and antibodies, used to treat infections and cancer, the researchers said.