Scientists grow sheep embryos containing human cells

In a breakthrough, scientists have successfully grown sheep embryos containing human cells, bringing the ability to grow human organs inside other animals closer to reality.
Growing human organs inside animals may not only increase supply, but also offer the possibility of genetically tailoring the organs to be compatible with the immune system of the patient receiving them. "Today the best matched organs, except if they come from identical twins, dont last very long because with time the immune system continuously is attacking them, said Pablo Ross from the University of California, Davis in the US. Bruce Whitelaw, professor at the Roslin Institute, where Dolly the sheep was created, said that while there was a long way to go before human organs could be grown in other animals, the latest research is an important step forward through starting to explore whether sheep offer an option for the exciting chimeric project. Researchers had recently been able to introduce human stem cells into early pig embryos, producing embryos for which about one in every 100,000 cells were human. These were only allowed to develop for 28 days, 'The Guardian' reported. The team has now achieved a similar feat with sheep embryos, with an even higher ratio of human to animal cells. About one in 10,000 cells in these sheep embryos are human, said Ross. The team are currently allowed to let the chimeric embryos develop for 28 days, 21 of which are in the sheep. While that might be sufficient to see the development of the missing organ when human cells are eventually combined with the genetically modified embryo, Hiro Nakauchi of Stanford University in the US. The longer experiment, perhaps up to 70 days, would be more convincing, although that would require additional permission from institutional review boards. However, for the approach to work about one per cent of the embryos cells would have to be human, meaning further work is needed to increase the proportion of human cells.