Ultimate human stem cells created in the lab

A new type of human stem cell, never seen in nature, has been made in the lab. The cells may be the primordial embryonic cell from which all our cells are created. They should be better at making replacement organs than existing stem cells.

"We see it as a blank canvas, the starting point for all tissues in the body," says Austin Smith of the University of Cambridge, who led the team that developed the cells.

It is a big claim, and the stem cell field has been rocked by false ones in recent times. Supposedly revolutionary procedures have turned out to be flawed, most recently the claim in Nature earlier this year that adult cells could be turned into stem cells simply by exposing them to acid. Science and Cell rejected the "STAP cells" papers, but Nature accepted them only to be forced to retract them in July.

However, Smith's findings are getting cautious support. "There are great people contributing to this paper, and their reputations are on the line," says Chris Mason of University College London. "I would be really surprised if it's not the real deal."

In theory stem cells can develop into any kind of cell, so they could be used to repair damaged organs or even build them from scratch. But most stem cells aren't that flexible. The best ones are "pluripotent", meaning they can turn into anything. Such cells have to be taken from embryos, which is controversial, or made by reverting adult cells to their embryonic state, called induced pluripotent stem cells.

But these pluripotent stem cells still carry genetic baggage from their previous existence. For instance, genes may have been activated for a particular course of development into a kidney, say or turned off by a chemical marking process called methylation.

"This [baggage] has been one of the confounding problems in this area," says Smith. The cells aren't completely neutral about what they develop into, and they are all different so can't be standardised.

The new cells have had their cellular memories wiped clean. Their genes have been cleansed of most methylation markers, so they behave more predictably and transform more consistently into other tissues. The team hopes that this will make them a better building block for organs and tissues than existing embryonic stem cells.

"Nothing has been written or drawn on them to tell them what to do or become," says Smith. "These cells could be a better and more pristine starting point."

Called naive stem cells, these have long been known in mice and rats, but they have never been found in humans.

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Ultimate human stem cells created in the lab