麻豆传媒

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Update: Other teams could not replicate these results, and the two papers have now been retracted. Read more: 鈥�Acid-bath stem cell papers are finally retracted鈥�

A LITTLE stress is all it took to make new life from old. Adult cells have been given the potential to turn into any type of body tissue just by tweaking their environment. This simple change alone promises to revolutionise stem cell medicine.

Yet 麻豆传媒 has also learned that this technique may have already been used to make a clone. 鈥淭he implication is that you can very easily, from a drop of blood and simple techniques, create a perfect identical twin,鈥� says , co-leader of the team involved.

Details were still emerging as 麻豆传媒 went to press, but the principles of the new technique were outlined in mice in work published this week. The implications are huge, and have far-reaching applications in regenerative medicine, cancer treatment and human cloning.

In the first few days after conception, an embryo consists of a bundle of cells that are pluripotent, which means they can develop into all cell types in the body. These embryonic stem cells have great potential for replacing tissue that is damaged or diseased but, as their use involves destroying an embryo, they have sparked much controversy.

To avoid this, in 2006 at Kyoto University, Japan, and colleagues worked out how to reprogram adult human cells into what they called induced pluripotent stem cells (iPSCs). They did this by introducing four genes that are normally found in pluripotent cells, using a harmless virus.

The breakthrough was hailed as a milestone of regenerative medicine 鈥� the ability to produce any cell type without destroying a human embryo. It won Yamanaka and his colleague at the University of Cambridge a in 2012. But turning these stem cells into therapies has been slow because there is a risk that the new genes can switch on others that cause cancer.

Now, Vacanti, along with Haruko Obokata at the Riken Center for Developmental Biology in Kobe, Japan, and colleagues have discovered a different way to rewind adult cells 鈥� without touching the DNA. The method is striking for its simplicity: all you need to do is place the cells in a stressful situation, such as an acidic environment.

The idea that this might work comes from a phenomenon seen in the plant kingdom, whereby drastic environmental stress can change an ordinary cell into an immature one from which a whole new plant can arise. For example, the presence of a specific hormone has been shown to transform a single adult carrot cell into a new plant. Some adult cells in reptiles and birds are also known to have the ability to do this.

To investigate whether the process could occur in mammals, Obokata and colleagues used mice that were bred to carry a gene that glows green in the presence of Oct-4, a protein that is only found in pluripotent cells. The team took a blood sample from the spleenof these mice when they were one week old, isolated white blood cells called lymphocytes, and exposed them to various strong but fleeting physical and chemical stresses.

One batch of cells was exposed to a 鈥渟ub-lethal鈥� acidic environment, with a pH of 5.7, for 30 minutes. The team then tried to grow the cells in the lab.

Not much happened at first 鈥� some cells died, and the rest still looked like white blood cells. But on day 2, a number of cells began to glow green, meaning they were producing Oct-4. By day 7, two-thirds of the surviving cells showed this pluripotent marker, together with other genetic markers of pluripotency 鈥� many of which are also seen in embryonic stem cells. In contrast, iPS cells can take four weeks to reach this stage.

The team call their new cells 鈥渟timulus-triggered acquisition of pluripotency鈥�, or STAP cells.

To make sure they really were pluripotent, the team injected the STAP cells from the spleen into an early-stage mouse embryo, or blastocyst. These are typically five or six days old with about eight cells already formed inside. The STAP cells seemed to integrate themselves into the structure, and the embryo went on to form the three 鈥済erm layers鈥� that eventually give rise to all cell types in the body. The embryos developed into pups that incorporated STAP cells into every tissue in their body. These pups subsequently gave birth to offspring that also contained STAP cells 鈥� showing that the cells incorporated themselves into the animal鈥檚 sperm or eggs, and were inherited.

In a second test, the team injected STAP cells into an adult mouse. They wanted to see if the cells formed a type of embryonic tumour called a teratoma 鈥� another gold standard test of pluripotency. They did.

The team wondered whether other adult cells might behave in a similar way. So they tried the acid-bath technique on brain, skin, muscle, fat, bone marrow, lung and liver tissues from one-week-old mice. Although the efficiency varied, the same thing happened in each case. In unpublished results, Vacanti says they have now found the procedure appears to work on cells from much older animals, including some from adult primates. He cautions though that these studies have yet to be completed.

Reprogrammed

鈥淚 don鈥檛 think for one moment people thought this might be possible in humans,鈥� says Chris Mason, professor of regenerative medicine at University College London. 鈥淲ho would have thought that to reprogram adult cells to a pluripotent state just required a small amount of acid for less than half an hour 鈥� it鈥檚 an incredible discovery.鈥�

鈥淩eprogramming adult cells by exposing them to acid for half an hour is an incredible discovery鈥�

The researchers don鈥檛 know whether the reprogramming they are seeing is initiated by the low pH or by some other type of stress, such as chemical changes happening further down the line. But they think they are tapping into a fundamental body-repair process. If you injure cells significantly enough, so that they almost die, certain genes get switched on or off, says Vacanti. This may result in a change in the cell鈥檚 overall controls, meaning all genes have the potential to be switched on again. This could happen in all tissues throughout the body, Vacanti says. 鈥淧erhaps injuries like a bump on the arm or a burn cause mature cells to revert back to stem cells.鈥�

With the right environmental cues, these stem cells then specialise into healthy new cells to repair the damage. 鈥淲e think that the more significant the injury, the further back down the tree these cells revert,鈥� says Vacanti. 鈥淚t鈥檚 mother nature鈥檚 repair process.鈥�

That鈥檚 not where the story ends, however. On their own, STAP cells do not readily multiply. But if they are placed alongside various growth factors, they undergo minor changes that allow them to multiply exponentially with no chromosomal abnormalities. The team call these slightly modified cells STAP stem cells (Nature, and ).

Depending on the medium they are in, STAP stem cells injected into a very early embryo and implanted into a mouse can incorporate themselves not only into the developing embryo, but also into the extra-embryonic tissue, which forms the placenta (see diagram).

鈥淭he team haven鈥檛 just made pluripotent cells like embryonic stem cells,鈥� says Jos茅 Silva from the University of Cambridge, 鈥渢hey appear to have made totipotent cells.鈥� This means the cells have been rewound to a state with even more flexibility than pluripotent cells, which means they should be easier to manipulate. The only cells known to be totipotent 鈥� able to form an embryo and a placenta 鈥� in the body are those that have only undergone the first couple of cell divisions immediately after fertilisation. 鈥淭hey are like precursors to embryonic stem cells,鈥� says Silva.

鈥淭he word totipotent brings up all kinds of issues,鈥� says Robert Lanza of Advanced Cell Technology in Marlborough, Massachusetts. 鈥淚f these cells are truly totipotent, and they are reproducible in humans then they can implant in a uterus and have the potential to be turned into a human being. At that point you鈥檙e entering into a right-to-life quagmire鈥� (see 鈥�Clone wars鈥�).

It may be closer than we think. Vacanti told us that he asked another collaborator to take the experiment further. Vacanti says the collaborator grew STAP cells from white blood cells and let them multiply into spherical clusters, then implanted one cluster directly into the uterus of an adult mouse. 麻豆传媒 has been unable to confirm this procedure: Vacanti says his understanding is that the cluster grew into a fetus, while Obokata says direct cloning has not yet been attempted. The collaborator named by Vacanti has not yet responded to our request for comment.

If this approach can be made to work, it would mean the creation of the world鈥檚 first perfect cloned embryo. All animals cloned to date, including Dolly the sheep, were created using nuclear transfer, where the DNA from an unfertilised egg is replaced with DNA from an adult cell. The egg is stimulated to start dividing until it forms a blastocyst, and only then is it implanted in a uterus. However, the donor egg also contains other, mitochondrial DNA, which contributes to the resulting animal.

鈥淐lones like Dolly are not actually a perfect copy,鈥� says Vacanti. 鈥淲hen you clone a cell using our technique, there is no egg, so there鈥檚 no additional mitochondrial DNA. There鈥檚 an embryo and a placenta which is a perfect copy of the original.鈥�

Vacanti says that the cloned mouse fetus stopped developing normally halfway through the pregnancy. 鈥淭here was some sort of glitch 鈥� which is probably a good thing due to the ethical issues that would occur if we were able to create a live clone,鈥� he says. Obokata says the aim of the research is not to create clones, but to take control of these earliest of stem cells and encourage them to grow into whatever tissue is needed. The team is now investigating just how to do that and has started a project on human cells. 鈥淲e are placing cells in different environments to see how finely we can regulate what they develop into. We don鈥檛 want to grow a tooth in the middle of your liver,鈥� Vacanti says.

Preliminary work suggests that STAP cells are strongly influenced by the environment in which they are placed. 鈥淲e might need to artificially mimic these environments, but perhaps we don鈥檛 even need to do that,鈥� says Vacanti. 鈥淲e might just be able to place a STAP cell into a muscle and it will turn into muscle.鈥�

The ultimate goal is not to replace whole organs but to seed damaged organs with healthy cells. With many organs, such as the liver and kidneys, you can survive with around 20 per cent of the normal amount of tissue, so why go to the trouble of creating a whole complex organ when regular infusions of healthy cells might work just as well.

鈥淭he ultimate goal is not to replace organs but seed them with new cells. It would take just days to do鈥�

Theoretically, says Vacanti, if you have cancer of the liver, you could take a healthy liver cell, transform it into a STAP cell, and grow it into replacements. 鈥淚 believe people may be barking up the wrong tree by trying to replace entire organs,鈥� he says. 鈥淲e can use the technology that we have demonstrated today and come up with ways to perfuse tissues with healthy cells. That way we can boost function and transform it from a failing organ to an organ which will survive.鈥�

鈥淭his is particularly good work because they used an incredibly simple approach,鈥� says Mason. 鈥淢aking a personalised stem cell line would be cheap and easy. It would take days rather than the weeks or months it takes to make iPS cells, making it much more cost-effective 鈥� a big plus.鈥�

鈥淧ersonalised stem cells will be cheap and easy to make. It will take weeks rather than months鈥�

鈥淭he reprogramming step seems to be quite simple, it could be very inexpensive technology for reproductive medicine,鈥� agrees Lanza. 鈥淏ut it has more potential for abuse than iPS cells. It鈥檒l be interesting how this all plays out, but if it鈥檚 possible to do this in humans, it changes everything.鈥�

This article appeared in print under the headline 鈥淧ower of stem cells unleashed鈥�