Bioengineered Animal Drug Factories
Posted April 1, 1998
Genie the sow was busy nursing her seven healthy piglets, providing the many nutrients her piglets needed. Unlike other pigs, however, Genie was also producing
a human protein in her milk. This protein, called human protein C, is normally produced within the human body and used to control blood clotting. Seriously ill people sometimes cannot
produce enough of this protein. Other people are born with a deficiency of protein C. Protein C is also needed for patients undergoing joint replacement surgery.
Protein C is present in donated blood in tiny amounts. Until recently, it was too expensive to produce or isolate protein C from blood. However, Genie can produce
this protein in large amounts in her milk. How does this sow produce human protein C?
Genie is a bioengineered animal that carries a copy of a human gene. Fertilized eggs were collected from Genie's mother, then the cells were injected with the human
gene coding for protein C. Scientists used a finely made glass pipette to inject the DNA into the fertilized eggs. The human DNA was then incorporated into the pig cell's DNA. As the
cell reproduces, the human gene is copied right along with the pig's DNA. A DNA segment called a promoter that would turn on the human gene inside the pig's milk gland cells was inserted
along with the protein C gene.
Once Genie produced the protein C in her milk, scientists needed to isolate and check the protein for biological activity. Many proteins are modified in the cell after
they are produced. Scientists wanted to know if the pig cells would modify the human protein to make it active. In humans, an enzyme called furin modifies human protein C to make it
active. Pigs do produce furin, but the furin produced by pigs is in insufficient amounts to modify all of the human protein C produced. Currently, pigs are being developed that contain
both the human protein C gene and a human furin gene so that a greater yield of bioactive protein C will be available to treat patients.
References
Velander, William H., Henryk Lubon, and William N. Drohan. "Transgenic Livestock as Drug Factories," Scientific American, January 1997, pp. 70-74.
|
