The creators of Dolly the sheep have been awarded two more British patents on the ‘nuclear transfer’ technology that is the key to cloning. The patents should strengthen the position of the Dolly team, based at the Roslin Institute near Edinburgh, and of the companies that licensed its technology, in a highly competitive area.

In nuclear transfer cloning, a donor cell is fused with a recipient egg cell that has been stripped of its chromosomes. In January this year, the Roslin Institute won two British patents on cloning using donor cells that had been starved into a state of ‘quiescence’ — originally thought to be important for successful cloning.

By that time, however, rivals at the University of Massachusetts in Amherst had already been awarded a US patent covering cloning from non-quiescent cells, and had licensed this technology to Advanced Cell Technology, a company in nearby Worcester (see Nature 405, 610–612; 2000).

The new Roslin patents focus on techniques to allow the donor nucleus to remain in contact with the recipient egg's cytoplasm for several hours before ‘activating’ the egg — starting its embryonic development using a pulse of electric current. “This is the other half of the nuclear transfer story,” says David Earp, vice-president for intellectual property at Geron of Menlo Park, California, which has acquired the rights to exploit Roslin's cloning technology.

As the new patents do not depend on the donor cell being quiescent, they extend the Roslin team's claims. But just how powerful they prove to be remains to be seen.

The Roslin team argues that delayed activation can increase the efficiency of cloning, and in some species may be essential to achieve live births. But other groups say they can clone successfully without infringing the new patents. Goats, for instance, have been cloned by activating the egg during fusion with the donor cell (Nature Biotech. 17, 456–461; 1999).