Scientists have for the first time demonstrated that a possible alternative to controversial embryonic stem (ES) cells shares one of their key abilities. So-called induced pluripotent stem (iPS) cells can generate a live mouse in an experiment scientists say is the gold standard for pluripotency, the ability to become any cell type in the body. The feat, performed by two independent groups, suggests that iPS cells may be as powerful as ES cells, which many scientists hope will someday help cure a variety of diseases.
ES cells are prized by scientists for their flexibility. Taken from early embryos, they can in theory develop into all the tissues of the body. This talent makes them useful for studying--and perhaps someday treating--diseases. But because isolating ES cells involves destroying an embryo, they have proved ethically and politically controversial.
Many researchers believe iPS cells offer the best hope as an alternative. In 2006, scientists first demonstrated that by adding certain genes to adult mouse cells, they could reprogram them to look and act like ES cells. A year later, scientists achieved the same result using human cells. But it is still not clear how similar ES and iPS cells really are.
To grow ES cells into an animal, scientists inject them into an early embryo that carries twice the usual number of chromosomes. Such an embryo by itself can only become placental tissue. But if the injected ES cells are truly pluripotent, they can form a viable fetus. Several groups have tried the trick by substituting iPS cells for ES cells, but early attempts failed to produce any live-born mice.
Now, two groups in China report that their perseverance with the technically challenging experiment has paid off: They have produced apparently normal pups. A group led by Qi Zhou of the Chinese Academy of Sciences in Beijing and Fanyi Zeng of Shanghai Jiao Tong University used the method to test the pluripotency of six different iPS cell lines. In a paper published online today in Nature, they report that three of the lines yielded healthy mice at about the same rate as typical ES cell lines--about 3% of the time.
In a paper published today in Cell Stem Cell, Shaorong Gao of the National Institute of Biological Sciences in Beijing and colleagues describe a similar success rate with an iPS cell line that seemed to be particularly good at forming a variety of tissues in other tests. In nearly 200 tries, they produced several pups.
The results show that reprogramming can produce iPS cells--at least in mice--that are functionally equivalent to ES cells, says Konrad Hochedlinger, a stem cell biologist at Harvard University. But it also makes clear that all iPS cells are not equal. "It will be quite interesting now to identify the differences among different lines with different developmental potentials," he says. Although the test is an important proof of principle, it would be ethically impossible to do with human material. And in any case, it might not be relevant to the potential use of human iPS cells in therapies, he notes. "As long as the iPS cells make the functional cells you're interested in," he says, whether the cells are pluripotent may not be so important.