Crack open an egg and cure a disease

November 09, 1999

WHY did the geneticist cross the chicken? To turn it into a cheap pharmaceuticals factory, it seems. Comical as it may sound, two companies are planning a pilot test of drugs in eggs laid by genetically engineered chickens.

GeneWorks of Ann Arbor, Michigan, announced this month that it has a flock of between 50 and 60 genetically engineered birds. Some carry a gene that enables them to make a human growth factor in their eggs, while others produce a human antibody.

Although the company will not name the proteins, it says that both have great potential for treating disease. According to its chief operating officer Steve Sensoli, GeneWorks has deals to make 14 proteins for six drug companies around the world.

Meanwhile, AviGenics of Athens, Georgia, has produced a human interferon for treating cancer in its flock of birds. It claims to have a slight lead on its rival because it has already managed to pass on the interferon gene to further generations of birds. With hens producing an average of 200 eggs each per year, and 100 milligrams or more of a drug in each egg, both companies believe the yields could be large and lucrative.

The companies smuggle genes into the birds using harmless forms of viruses that are engineered so they cannot replicate. The gene that makes the protein is inserted in the virus.

GeneWorks uses the reticulo endotheliosis virus as a ferry. The company uses a genetic switch that restricts production of the protein to the egg white. "We put it in a one-day-old chicken embryo by microinjecting it into a cavity called the blastoderm," explains Sensoli. He and his colleagues hope that some virus reaches primordial cells in the blastoderm which develop into sperm and eggs, so the gene for the protein can be passed down to future generations of chickens, rather than having to repeat the injection in each generation. But the company can already harvest the proteins from hens that have been injected and next year plans to open a production plant capable of making "metric tonnes" of protein.

AviGenics already has transgenic cockerels producing new generations of GM birds. "They're very busy," says Carl Marhaver, the company's president. AviGenics uses the avian leukosis virus as a gene shuttle. "We microinject it into the pronucleus in the egg yolk," says Marhaver. The gene is then expressed in all the chicken's cells. AviGenics plans to contract out production and protein purification to companies which already produce vaccines in chicken eggs-a long-established practice in the pharmaceuticals industry.

Helen Sang, a chicken biotechnology researcher at the Roslin Institute in Edinburgh is encouraged by the companies' work. "It is good progress, and proof of principle," she says. Sang, who is developing a virus-free method of shuttling genes into chickens, points out that the technology has been in development for a decade (New Scientist, 20 November 1993, p 19). But she is disappointed that neither company is keen to publish openly in the scientific literature.

Sensoli says the work it too commercially sensitive to publish, and all but two of the proteins under development are unknown outside the companies that discovered them. "It's a shame we can't blow our horn a bit more," he says.
Author: Andy Coghlan

New Scientist issue 13th November 99


New Scientist

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