Like bacteria, various farm animals have been cloned to produce a variety of protein drugs that benefit humans. These protein drugs can counteract medical conditions such as anemia and diabetes and even some cancers. However, these cloned animals are expensive, large, and most take years before they can produce these desired protein drugs in sufficient commercially-viable quantities.
However, some researchers have decided that chickens can be desirable protein drug factories because they are small, inexpensive and have rapid generation times. Further, chickens could produce neat packages — eggs — that are loaded with these desired protein drugs.
Simon Lillico of the Roslin Institute outside Edinburgh, Scotland, and his colleagues, led by the Roslin Institute’s Helen Sang, constructed drug-coding protein genes that inserted themselves into the gene that all chickens carry for making the egg-white component, ovalbumin. So instead of producing ovalbumin, the chicken would produce the protein drug of interest. Because egg whites are composed primarily of ovalbumin, this means that these eggs could instead be loaded with the protein drugs of interest.
The team cloned two protein genes into chicken albumin gene; an antibody called miR24, which has shown promise against melanoma, and a protein gene called human interferon-beta-1a, which is already used to treat multiple sclerosis. The researchers used viruses to place the genes into cells in young chick embryos inside unhatched eggs.
When the eggs hatched, the researchers selected the male chicks that carried the altered gene. When the team later bred these roosters with normal hens, half the female offspring laid eggs containing both protein drugs in their [egg] whites, the researchers report in an upcoming Proceedings of the National Academy of Sciences. The researchers continue to screen for male offspring carrying the genes and to breed them with normal hens. They now have five generations of drug-producing birds, Lillico says.
The newly engineered chickens “could pave the way to something very interesting,” says animal sciences professor François Pothier of Laval University in Quebec City, who has engineered pigs to produce useful proteins in their semen. Pothier points out that before chickens roost in pharmaceutical factories, the researchers in Scotland have many hurdles to overcome, such as increasing the small amounts of the two drugs present in the hens’ egg whites.
“You can imagine that eventually, not only could you modify the content of an egg for therapeutics, but you could perhaps change the flavor or add something interesting for health,” such as vitamins or heart-healthy fatty acids, Pothier says.