Transgenic technology finally delivers the goods

ATryn, developed by US company GTC Therapeutics Inc., was approved for use during surgery to protect patients who lack the anti-thrombin gene and thus are unable to generate their own supply of the anticoagulant enzyme. This makes their blood clot too easily, creating a risk of deep vein thrombosis or thromboembolism.

EMEA turned down the application in February over concerns that too few patients had been involved in the trials and the manufacturing process meant the commercial product was different from the drug used in clinical trials. But approval was granted on appeal following a meeting with haematology specialists.

The recommendation is made under a new clause in EMEA rulebook, which allows approvals on the basis of small patient numbers if the condition is so rare that trials cannot be properly powered  “It is a good day for European patients with congenital antithrombin deficiency and for their physicians,” said Isobel Walker, consultant haemotologist at Glasgow Royal Infirmary, Scotland.

Normally patients with anti-thrombin deficiency are treated with blood thinners such as warfarin but this is considered too risky during surgery or childbirth. Instead they are given anti-thrombin extracted from human blood, but this is now recognised as a possible route for transmitting disease.

ATryn will be marketed in Europe by the US biotech company Genzyme, which span off GTC Therapeutics in 1993 with a brief to produce human proteins in transgenic animals. At the time it was thought this would lead to much cheaper and more efficient production systems than current bioprocessing using microbial or mammalian cell lines.

The approval of ATryn is a boost for the Dutch company Pharming NV, which is developing drugs derived from the milk of transgenic rabbits. The company was almost forced out of business four years ago, but agreed a refinancing and now has five products in development.

But the breakthrough to market came far too late for an erstwhile leader in the field, PPL Therapeutics Ltd, developer of Dolly the cloned sheep. The Edinburgh-based company devised the cloning technique as an easier route to producing transgenic animals (although Dolly herself was not transgenic), but failed to get its first product, alpha-1-antitrypsin, to market and went bust in 2003.