US patent 7, 029, 913 (known as the ‘913 patent) was invented by scientist James Thomson and was the first of its kind to isolate embryonic stem cells.

The invention has also attracted controversy in Europe, and an appeal is pending at the European Patent Office (EPO) over a similar European patent application.

The ‘913 patent is one of three filed by WARF relating to primate and human embryonic stem cell that are subject to reexamination proceedings.

Examiner Gary Kunz explained in his decision that Thomson's work was in no way obvious and rejected the opinions of scientists who had argued otherwise.

The reexamination was initiated in October 2006 when the New York-based Public Patent Foundation (PUBPAT) and the California-based Foundation for Taxpayer and Consumer Rights (FTCR) challenged the three patents.

In April 2007, the USPTO rejected the patent claims and upheld the challenges by the two groups on all three patents. This decision was appealed by WARF, which asked the patent office to review the patents again.

Though the patent was upheld by Kunz, he narrowed it so that it comprises only those stems cells that are derived from pre-implantation embryos. Also, stem cells derived from the foetal tissue cannot be claimed under the new patent.

WARF said it is extremely pleased with the 82-page decision. Its managing director Carl Gulbrandsen said in a statement: “It affirms what WARF has believed all along, that Dr Thomson's breakthrough discoveries are patentable inventions.”

FTCR and PUBPAT have vowed to fight on and thwart the remaining two patents.

John M Simpson, FTCR stem cell project director, said: "We are in this for the long haul.”

The two groups also believe this decision contradicts their earlier findings.

"The examiner based his decision on his own belief that it would not have been obvious to isolate human stem cells using widely known methods to isolate mouse stem cells, which contradicts the sworn testimony that we provided of four renowned stem cell embryologists who were doing such work," said Dan Ravicher, PUBPAT executive director.

"Thus, the examiner took his own opinion over the opinions of our four leading stem cell scientist witnesses."

The two groups have said that they will challenge the latest patent office decision by the examiner supporting the amended claims to the Patent and Trademark Office's Board of Appeals, which can overturn decisions made by examiners. They also stated that they will appeal any adverse decision of that board to the US Court of Appeals for the Federal Circuit.

The EPO has seen controversies related to stem cell patents over the last decade, especially the Edinburgh patent. The EPO maintains a policy that it will not refuse to grant patents on moral grounds when there is no clear consensus among its contracting states on the morality of stem cell research and patenting.