MADISON, Wis. -- The U.S. Patent and Trademark Office upheld two patents that cover embryonic stem cell research discovered at the University of Wisconsin-Madison.

The announcement marks the second time in recent weeks that federal regulators have approved Wisconsin researchers' existing patents regarding stem cell research.

On Tuesday, the office announced that it rejected arguments from consumer groups that the discoveries were obvious given previous research and therefore ineligible to be patented. The office upheld a third patent being challenged last month.

The Wisconsin Alumni Research Foundation (WARF), which holds the patents, is praising the patent office's rulings.

Managing director Carl Gulbrandsen said that the latest rulings affirm that UW-Madison researcher Jamie Thomson's pioneering discoveries are patentable inventions.

Two nonprofit groups, the Foundation for Taxpayer and Consumer Rights and the Public Patent Foundation, originally challenged the validity of the patents and got regulators to take a second look at them last year. They asked federal officials to throw out the patents, which cover discoveries made by Thomson. They argued the patents have hindered research in the U.S.

One group said at the time that it believed WARF was trying to be the "Microsoft" of stem cells.