Human cloning nearly possible

SIXTEEN years after the amazing creation of Dolly the cloned sheep, researchers have realized the dream of producing human embryonic stem cells (hESCs) using a similar cloning technique.

And this time, it looks as if the cells are genuine, not faked as they were in 2005 when a South Korean team led by Woo Suk Hwang fraudulently claimed to have reached the same goal.

The landmark achievement revives the hope of being able to generate new tissues using a patient's own cells, eliminating the risk of immune rejection.

The idea is to take a cell from a patient – from skin, for example – and fuse it with a human egg cell emptied of its own chromosomes. The fused cell behaves like an embryo and generates hESCs. In theory, these cells can be turned into whatever tissue the patient needs.

Many teams have tried and failed to generate hESCs in this way. The idea fell out of favour following the scandal of 2005, and after the development of a way to turn ordinary skin cells into so-called induced pluripotent stem cells (iPS cells), which behave rather like hESCs.

But hESCs may be back on the scene, following work by Shoukhrat Mitalipov at the Oregon National Primate Research Center in Beaverton and his colleagues. In 2007 they showed that it was possible to develop embryonic stem cells from monkey eggs using the Dolly technique. Now they have fine-tuned the method to work with human eggs too.

Critics of the technique have always said that only a small fraction of donated eggs would develop in the required embryo-like way, leading to huge wastage. However, Mitalipov derived hESCs from about half the donated eggs after he fused them with commercially available skin cells from fetuses. One donor gave eight eggs, of which four yielded colonies of hESCs, suggesting several colonies could be made from each set of donated eggs (Cell, DOI: 10.1016/j.cell.2013.05.006).

Despite the time it took to develop a successful hESC-generating technique – and the interest in iPS cells as an egg and embryo-free alternative – Mitalipov's work is important. Significantly, he has turned some of the hESCs into healthy tissues. Those made with iPS cells, by contrast, tend to accumulate mutations and suffer abnormal patterns of gene activation.

"It would be really nice to derive and compare iPS cells and cells made using the Dolly technique from the same individual to see which were most normal," says Robin Lovell-Badge of the National Institute for Medical Research in London.

John Gurdon of the Gurdon Institute at the University of Cambridge, who shared a Nobel prize in 2012 for his work cloning frog embryos, says that if Mitalipov's hESCs turn out to be superior to those from iPS, it could signal an important advance. "I do not think the technique has arrived too late," he says.

"Mitalipov clearly has very high efficiency, and the cells are highly normal, and that's what iPS cells don't yet deliver," says Chris Mason of University College London. "However, it still boils down to needing to get human eggs," he says.


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