European regulators have issued a recommendation for GTC Biotherapeutic’s ATryn (antithrombin alfa), marking the first thumbs up for a therapeutic product borne out of transgenic biotechnology.

Reversing an earlier rejection, Europe's advisory board, the Committee for Medicinal Products for Human Use, has now decided to put forward the agent, which contains a protein derived from the milk of genetically-engineered goats, for use in several anti-clotting settings.

GTC is hoping to market ATryn for use in patients with congenital antithrombin deficiency undergoing surgery, as well as for the prevention of deep-vein thrombosis in the legs and the formation of clots in other parts of the body.

Its application was initially turned down earlier this year, when the CHMP decided that the company had not tested the treatment in enough patients to demonstrate safety and efficacy.

Understandably, news of Friday’s u-turn decision ignited investor enthusiasm and, after a day of frenzied trading on the Nasdaq, shares in GTC rocketed 85% to close at $1.81.

Other drugmakers working on therapies stemming from genetically-modified animals, such as The Netherland’s Pharming Group and PhamAthene, will have also been closely watching Atryn’s progress, with the hope that its approval can open the door to a potentially lucrative market for their respective products.