The European Union's top court ruled Tuesday that scientists cannot patent stem cell techniques that use human embryos for research purposes, a ruling some scientists said threatens important research since no one could profit from it.

The European Court of Justice in Luxembourg said the law protects human embryos from any use that could undermine human dignity.

Embryonic stem cells can develop into any type of cell in the body, which one day might be used to replace damaged tissue from ailments such as heart disease, Parkinson's and stroke. But using stem cells from embryos has been controversial — opposed by some groups for religious and moral reasons.

Despite such concerns, there are no such restrictions on obtaining patents on stem cell techniques in the U.S. and many other countries.

The European ruling centered on the case of Oliver Bruestle at the University of Bonn, who filed a patent on a technique to turn embryonic stem cells into nerve cells in 1997. Greenpeace filed a challenge to Bruestle's patent, arguing that it allows human embryos to be exploited.

The court said patents would be allowed if they involved therapeutic or diagnostic techniques that are useful to the embryo itself, like correcting defects.