Europe's top court has banned patenting any stem cell process that involves destroying a human embryo, dealing what some scientists said was a "devastating" blow to an emerging field of medical research.

Researchers fear the ruling by the European Court of Justice (ECJ) will hobble development in an area of science that could provide a range of 21st century medicines for diseases from Parkinson's to blindness.

The European Centre for Law and Justice, a Strasbourg-based Christian group, welcomed the decision which it said "protects life and human dignity" at all stages of development.

Stem cell technology is controversial because some cell lines are derived from embryos. The ECJ decision now endorses widespread protection of human embryos by blocking patents.

"A process which involves removal of a stem cell from a human embryo at the blastocyst stage, entailing the destruction of that embryo, cannot be patented," it said.

Blastocyst is the stage just before implantation in the womb, when the embryo consists of around 80 to 100 cells.

The court said its ruling reflected European law. A European directive on biotechnology patents "intended to exclude any possibility of patentability where respect for human dignity could thereby be affected", it said.

The ruling concerned an invention by Oliver Bruestle of the University of Bonn for converting human embryonic stem cells into nerve cells. Mr Bruestle said he regretted the decision.

"It means that fundamental research can take place in Europe, but that developments that follow from that cannot be implemented in Europe," he said after the verdict.

"It means European researchers can prepare these things but others will pick the fruits in the US or Asia."

Tuesday's judgment followed a case brought in Germany by Greenpeace, challenging a patent filed by Mr Bruestle in 1997.

A German court ruled the patent invalid, and after Mr Bruestle appealed, Germany's Federal Court of Justice referred questions to the ECJ.

In March, Advocate General Yves Bot handed down a legal opinion, which the ECJ effectively upheld on Tuesday.

"We wanted a fundamental decision on how the protection of human embryos is to be laid out under EU patenting law," said Christoph Then, a Greenpeace official, in Luxembourg. "The court has... said that ethics take priority over commercial interests."

'Unbelievable setback'

Critics argue the use of embryonic stem cells is wrong because the ultimate source of these cells involves the destruction of embryos, which are left over from fertility treatment and are donated for research.

Scientists contend the research is justified, since the embryonic stem cells they use are cell lines derived from original surplus eggs that can be maintained indefinitely.

While adult stem cells are also being investigated as potential medicines, they are less flexible than embryonic ones.

Early trials are now underway using embryonic stem cells for repairing spinal cord injuries and to correct certain forms of blindness.

They also have potential in treating other conditions including stroke damage, Parkinson's disease, heart disease and diabetes.

That work could be in jeopardy in Europe, researchers say.

"It will unfortunately make it less likely that companies in Europe will invest in the research to develop treatments to use embryonic stem cells for treatment of human diseases," said Ian Wilmut, the British scientist who led the team that produced Dolly the cloned sheep.

Pete Coffey of University College London said it was the ECJ ruling was a "devastating decision" and Austin Smith, another stem cell expert at the University of Cambridge, said it left scientists "in a ridiculous position".

"We are funded to do research for the public good, yet prevented from taking our discoveries to the market place where they could be developed into new medicines," he said.

Several small biotechnology companies are pioneering stem cell treatments in Europe and the United States.

Big pharmaceutical companies - including Pfizer , AstraZeneca and Roche - are also starting to conduct research in the area.

European research is being carried out in Britain and Sweden as well as Germany, said Mr Bruestle, but the ECJ judgment would undermine this work. "Many years of intensive research are being destroyed," he said.

"It's an unbelievable setback for biomedical stem cell research."

Reuters