In a decision that could widen the field for embryonic stem cell research in the U.S., the government’s patent office has overturned 10-year-old patents held by the University of Wisconsin after a complaint brought by two watchdog groups.

Though the decision is not final, the U.S. Patent and Trademark Office rejected three patents held by the Wisconsin Alumni Research Foundation, or WARF, the licensing arm of the state university. In 1998, researchers at the university led by James Thomson patented a process to grow embryonic stem cells outside the body by placing them on a bed of other tissue. It was hailed as a breakthrough that would allow researchers to grow “lines” of cells instead of having to find fresh sources. Challengers say the discovery didn’t deserve a patent, but it gave momentum to embryonic stem cell research in this country and led to the controversial decision by President Bush to severely limit federal funding for the research in 2001. Bush’s ruling remains in place, but several states including California, Connecticut and Illinois have dedicated public funds to the research.