An effort to overturn two contested stem-cell patents was quashed last week by the US Patent and Trademark Office, in a move that strengthens the position of the patents’ holder, the Wisconsin Alumni Research Foundation (WARF).

The two patents cover methods for deriving and growing primate and human embryonic stem cells (ES cells) in culture. They were challenged in a process called a ‘re-examination’ by a group led by the Public Patent Foundation, based in New York. The challengers claimed that the research carried out by University of Wisconsin stem-cell researcher James Thomson was not novel enough to earn the patents, that the patents were unjustly broad in their scope, and that they were stifling stem-cell research.

On 11 March, WARF released documents in which the patent office affirmed the validity of the two WARF patents, reversing its preliminary decision in March 2007 to overturn them. The decision is final and a considerable victory for WARF.

“If there were doubters out there, they ought to be changing their minds,” says Carl Gulbrandsen, WARF’s managing director.

Dan Ravicher, executive director of the Public Patent Foundation, plays down the significance of the decision, pointing out that WARF had narrowed some of the claims in its patents. The challengers might try to open a new re-examination process on the modified patents, Ravicher says. “We still think in their modified form [the patents] could be causing public harm. That’s why we’re going to continue to fight them,” he says.

But some say that prolonging the fight might backfire. Ken Taymor, head of the University of California’s Berkeley Center for Law, Business and the Economy, says the re-examination has been a boon for WARF, in part because it has diverted attention from WARF’s attempts to bolster its patent positions. While the re-examinations were under way, WARF filed actions called ‘continuations’ that expand the patents’ claims, and also filed a series of new patents on cells derived from human ES cells with its commercial licensee Geron of Menlo Park, California.

“The re-examination has strengthened WARF’s position,” Taymor says. “It has deflected attention from the downstream patent landscape that WARF and Geron have created, and which is much more critical to commercialization than the fundamental patents.”

A third WARF stem-cell patent, which had also been challenged, was upheld by the patent office on 29 February. That decision can be appealed, because the rules governing the re-examination of the patent are different.