In a dispute over three stem-cell patents, Wisconsin Alumni Research Foundation (WARF) is claiming victory, after an interim decision from the US Patent and Trademark Office to uphold one of its patents.

On 28 February, WARF said that the claims of a 2001 patent on a method for growing and sustaining cultures of embryonic stem cells had been upheld. The patent is one of three on work led by James Thomson of the University of Wisconsin. The other two cover methods for deriving primate embryonic stem cells — including human ones — and the cells themselves.

In 2006, after critics challenged the patents on the basis that they were too broad and hindered the field of embryonic stem-cell research, the patent office said it would re-examine the three. The critics played down last week's decision, saying that WARF has already limited its claims in the upheld patent, and that the other two patents are more important. Rulings on those are still pending.