Hens have been genetically modified to produce eggs that contain proteins with therapeutic potential for humans, according to researchers.

Credit: Roslin Institute

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ADELAIDE: Genetically modified hens whose eggs produce proteins for use in human drugs have been created by British scientists.

The engineered chickens may become a more economical and effective method of drug production than current industrial techniques, according to the scientists, who developed the chickens at the Roslin Institute in Edinburgh, Scotland. The Institute is the same laboratory that produced Dolly the sheep - the first cloned mammal - in 1996.

"There are many new protein drugs in development and there is a potential bottleneck in production facilities in terms of bioreactors," said team leader Helen Sang, speaking of the vessels used to grow and house the micro-organisms currently used to produce such drugs. "[Bioreactors] are also costly to build and run," said Sang, adding that it may be quicker to produce a flock of transgenic hens to produce a particular drug.

The DNA of transgenic animals contains genes from other species which are inserted into the genome by scientists. The chickens in this new study were modified by inserting genes that produce a mouse antibody that has the potential for treating malignant melanoma, and a human immune system protein which is used as an antiviral drug.

In answer to the old conundrum, the transgenic egg came before the chicken, according to the research, to be published tomorrow in the U.S. journal Proceedings of the National Academy of Sciences.

The genes for the desired proteins were injected into the embryos of newly-laid eggs, where they were incorporated into the developing chickens' DNA. The eggs hatched, giving the researchers a transgenic cockerel (young male chicken), who was mated with normal hens to produce more transgenic chicks that also carried the genes.

"The new genes that we have introduced into the chickens are passed from one generation to the next so we can rapidly breed a flock of transgenic hens, all making the therapeutic protein in their eggs," said Sang.

To ensure that the desired protein was only produced in the egg, the researchers linked the therapeutic protein gene with the chicken ovalbumin gene. The ovalbumin protein is only found in the whites of a chicken egg, and linking the two genes ensures that the desired protein is only produced in the egg-making cells of the hen's oviduct.

"[Production in the oviduct] avoids making the proteins in other tissues of the hen which could cause health and welfare problems," said Sang.

Previous attempts to produce therapeutic proteins in mammals have included sheep, goats, rabbits and cattle. In cattle, the technique has been used produce therapeutic proteins in mammary tissue, so the protein ends up in the cow's milk.

Production in chicken eggs may have advantages such as lower costs, quicker breeding of the animals, and the ability to generate proteins that are toxic to mammalian cells, according to the study.

"There is also some evidence that proteins produced in chickens may have characteristics closer to those found in the human protein than if they are produced in bioreactors," said Sang.

With this "new manufacturing method", Sang said the egg whites would be separated from the yolks and the therapeutic protein would then be purified from the other egg white components. It would be tested to ensure purity and would go through clinical trials, the same as any other human drug. The transgenic chickens would not be eaten by humans.

According to Sang, the chickens would not look any different from a normal hen, and would be maintained so that they lay eggs as normal egg-laying hens do. The only difference would be in the valuable proteins contained their eggs.

Transgenic chickens have been created in the past, but with a very low success rate, according to the researchers. For example, one experiment obtained a single transgenic cockerel out of 1,597 chicks.