The FDA granted a first ever approval to a drug that is produced in the egg white of transgenically engineered chickens. The agency granted the green light to Alexion's enzyme replacement therapy sebelipase alfa for the treatment of a rare disease known as lysosomal acid lipase (LAL) deficiency or Wolman disease.

Chickens now join goats and rabbits in the pharmaceutical farm. In 2009, the FDA granted the first such approval to rEVO Biologics' antithrombin alfa, an anticoagulant that is produced in goat's milk and that was approved for various uses in hereditary antithrombin-deficient patients. Then, in 2014, the FDA approved Pharming's recombinant C1-esterase inhibitor, produced in rabbit's milk, for the treatment of hereditary angioedema.

At least three other drugs produced in transgenic animals are in development. TG Therapeutics is developing ublituximab, a CD20-targeting antibody, for the treatment of B cell proliferative disorders including non-Hodgkin lymphoma and chronic lymphocytic leukaemia. Its Phase III candidate, produced in the milk of modified goats, could be the first 'farmaceutical' antibody to make it to market.

rEVO's factor VIIa eptacog alfa, produced in the milk of transgenic rabbits, is in Phase III development for the treatment of haemophilia A and B. PharmAthene's organophosphorus scavenger protein pegylated butyrylcholin esterase, produced in the milk of transgenic goats, is in development for the prevention and treatment of nerve agent toxicity.

“The floodgates are opening and I can't wait to see what comes next,” William Muir, a geneticist at Purdue University in West Lafayette, Indiana, told Nature on the news of the approval ( Nature , published online 9 Dec 2015).