Animal-human embryos may not generate stem cells.

New research suggests it may be futile to try producing stem cells by putting human DNA into cow or rabbit eggs and making hybrid cloned embryos, the Associated Press reported, because the animal eggs don't reprogram human DNA in the right way to generate stem cells. "Instead of turning on the right genes, it turns out the animal eggs actually turn them off," said senior study author Dr. Robert Lanza of Advanced Cell Technology in Worcester, Mass.

The work was published online in the journal Cloning and Stem Cells. The idea of using animal-human "hybrid" embryos drew fire last year in Britain as authorities pondered whether to let scientists try it. Opponents objected to mixing human and animal material and worried that such research could lead to genetically modified babies. Hybrid embryos have been made elsewhere, but there's no widely accepted report of getting stem cells from them.

For the study, Dr. Lanza and colleagues put human DNA into human, cow and rabbit eggs and grew them into early embryos. In embryos from human eggs, patterns of gene activity resembled those in ordinary human embryos. But with the human-animal hybrid embryos, the patterns were much different.