- Animals can be genetically modified to produce substances that are useful for treating human diseases. Animals that have been given a gene from another species are called transgenic organisms.
- The human gene that codes for the required protein is isolated from the human cells and is then injected into the fertilised egg from the animal.
- The tiny embryos that develop are placed in the womb of surrogate mothers, which later give birth to young that carry the human gene in their cells.
- Transgenic sheep are used to produce alpha-1-antitrypsin (AAT), a protein that is used to treat emphysema in people who have a mutation in their AAT gene. The sheep secrete the AAT in their milk.