Technical Aspects of Biopharming in Animals

The main technical challenge involved in animal biopharming is to ensure that the transgene coding for a therapeutic protein or vaccine is expressed only in the animal’s milk and not in other tissues. To this end, scientists combine the gene for a therapeutic protein with a piece of regulatory DNA called a “promoter,” which controls expression of the gene. This construct is then inserted into fertilized eggs from the production species, so that all progeny of the founder animal inherit it. Although the transgene exists in every cell of the animal’s body, the promoter activates it only in the cells of the mammary gland, so that the pharmaceutical protein is secreted along with other milk proteins.

The main drawback of biopharming in cattle is that it takes nearly three years from the transfer of a transgene into a single-cell embryo to the production of the protein in the milk of an adult female animal.17 For goats, the time interval between creation of a transgenic embryo and production of pharmaceuticals in the lactating adult is 16 to 18 months.

Transgenic hamsters and rabbits have also been used for biopharming because they breed more rapidly than cows, sheep, or goats. New Zealand white rabbits, for example, produce about 140 milliliters of milk per day. A farm in the Netherlands run by the Dutch biotech firm Pharming uses a customized machine to milk transgenic rabbits that produce a human protein called C1 inhibitor (Rhucin). This protein controls inflammation in the body and prevents tissue damage in survivors of strokes and heart attacks, and the rejection of transplanted organs.18