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A lab mouse

Biologists have created mouse-human chimeras whose bodies were composed of up to 4 per cent human cells when the early embryos were destroyed after 17 days. The highest proportion previously achieved is around 0.1 per cent.

The reason for creating the chimeras is to find ways to grow organs for people who need transplants, says Jian Feng at the University at Buffalo in New York.

Feng’s team injected around 10 human stem cells into 3.5-day-old mouse blastocysts, bundles of many cells. The human cells contributed to all kinds of tissues in the developing mouse embryo, including forming eye, liver and red blood cells.

In one mouse embryo, around 4 per cent of all the cells were human. The proportion probably varied from tissue to tissue, but the team didn’t look at the proportion in specific tissues such as the brain.

“My immediate reaction is ‘wow’,” says Pablo Ross at the University of California, Davis. “This is great if we want to generate human organs in animals.”

Previous studies have shown that the reason why attempts to create mouse-human chimeras haven’t... see more