Transgenesis the deliberate introduction of foreign DNA into an animal’s genome has transformed biotechnology. When tailored to carry human genes, animals become powerful platforms for producing therapeutic proteins that were once difficult, costly, or even impossible to obtain. This breakthrough, often referred to as biopharming, has given rise to new medicines for conditions ranging from clotting disorders to rare genetic diseases.
How Transgenesis Works in Animals
The central idea is simple yet revolutionary: insert a human gene into the DNA of an animal so it can produce the corresponding protein in a usable form.
Gene Selection
Identify and isolate the human gene coding for the target protein.
Vector Construction
Attach the gene to regulatory sequences (promoters) that ensure expression in the desired tissue most commonly the mammary glands.
Gene Transfer
Deliver the construct into embryos via microinjection or CRISPR-based editing.
Breeding
Animals carrying the transgene are bred to establish stable lines.
Protein Harvesting
The target protein is collected from milk, eggs, or blood and purified for pharmaceutical use.
Why Use Animals Instead of Cell Cultures?
Post-Translational Modifications (PTMs)
Proteins such as clotting factors require glycosylation, sulfation, and folding not possible in microbes. Mammals provide human-like PTMs.
Production Scale
A single transgenic goat can produce up to 5 grams of recombinant protein per liter of milk, with annual yields reaching kilograms sufficient for thousands of doses.
Cost Efficiency
Maintaining herds of goats or cows is cheaper than maintaining industrial-scale bioreactors with mammalian cells.
Biological Complexity
Animals can produce proteins with correct three-dimensional structure and biological activity that cell cultures may fail to achieve.
Routes of Protein Expression in Animals
Milk (most common)
Using mammary gland–specific promoters, proteins accumulate in milk, from which they are purified.
Blood
Some proteins are secreted into circulation, though this requires direct harvesting from plasma (less scalable).
Eggs (chickens)
Transgenic hens deposit therapeutic proteins into egg whites. This is promising for rapid, low-cost production.
Urine and Semen
Experimental, less commonly used, but potentially valuable for continuous non-invasive harvesting.