Animal-human clones don't work: study

"For the last decade, we've carried out literally hundreds of experiments trying to create patient-specific stem cells using animal eggs," Lanza said.

BEAUTIFUL HYBRIDS

"We got beautiful little hybrid embryos, but it didn't work no matter how hard we tried."

A mouse-human hybrid petered out after just one division. The cow and rabbit human hybrids went further, but stopped at the point when maternal DNA is supposed to kick in and turn the ball of cells into a proper embryo, Lanza said.

Lanza's team used a new method called global gene expression analysis to see which genes were turned on and off as the eggs grew.

"We never had the tools before to actually look inside the cell and see what's going on," Lanza said. It appears that using the egg of another species turns off the genes needed to make an embryo instead of turning them on, he said.

But the human-human clone did turn on the right genes, although it, too stopped dividing before it could produce stem cells, Lanza said.

"We see exactly the same genes turned on in a normal embryo are actually turned on in a human clone," he said.

Ian Wilmut of the University of Edinburgh, one of the scientists who cloned the first mammal, Dolly the sheep, and editor of the journal, called the results disappointing.