January 16, 2007

UK researchers to use eggs to produce antiviral drugs for humans

Genetically modified hens whose eggs produce proteins for use in human drugs have been developed by scientists at the Roslin Institute in Edinburgh, Scotland, the same institute that produced Dolly the sheep - the first cloned mammal.

The engineered chickens may become a more economical and effective method of drug production than current industrial techniques, according to the scientists, whose work would be published in the US journal Proceedings of the National Academy of Sciences.

There are many new protein drugs in development and there is a lack of production facilities in what is called bioreactors in the industry. Bioreactors are the vessels used to grow and house the micro-organisms currently used to produce such drugs.

Team leader Helen Sang said bioreactors are also costly to build and run and it may be quicker to produce a flock of transgenic hens to produce a particular drug. Also, proteins produced in chickens may have characteristics closer to those found in the human protein than if they are produced in bioreactors, said Sang.

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.

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 introduced into the chickens are passed from one generation to the next so a flock of transgenic hens can be made rapidly, 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, 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.