Then, the researchers coaxed those cells into becoming motor neurons, the type of nerve cells impaired by ALS.
Researchers will be able to use the lab-grown cells to learn more about why ALS patients' own motor neurons deteriorate and die, and eventually to test new drug treatments for the disease.
"What we've shown for the first time is that it's possible to use these cells to make the actual cell type that's destroyed in this disease," said Kevin Eggan, a Harvard University biology professor and a co-author of the study.
The researchers used a technique developed by Kyoto University scientist Shinya Yamanaka, in which they introduced a virus into the skin cells that prompted the cells to activate four dormant genes that are normally active only during early cell development.
Yamanaka and his colleagues first demonstrated the technique in mice in 2006, and then in humans in November. But until now, scientists weren't sure that it would work in very elderly patients or in patients with a genetic disease like ALS.
"We think that as one gets older, genes get less flexible -- the mindset was, if you got really old, [the cells] might not respond to such reprogramming," said biochemist Lucie Bruijn, science director of the ALS Association, who was not involved in the study.
But in a study published Thursday in the journal Science, Eggan, along with Columbia University researcher Christopher Henderson and their colleagues, were able to successfully use the technique on cells taken from 82-year-old and 89-year-old ALS patients. The patients had a mild form of the disease, caused by a specific gene responsible for about 2 percent of all ALS cases.
The holy grail of stem cell research has long been tissue replacement therapy -- growing healthy cells in the lab, such as motor neurons for ALS patients, which could then be transplanted back into patients to replace their diseased cells.
But Eggan cautioned that that application is still a long way away. For one thing, scientists believe that the virus used in the reprogramming technique could lead to genetic mutations that could cause cancer.
Instead, Eggan said, the more immediate benefit of the new work is that it will give researchers access to motor neurons with ALS -- something that they didn't have before, because motor neurons are buried deep in patients' spinal cord. Now, they'll be able to directly observe what happens to the neurons as they deteriorate.
"This will take the study of the disease out of the patients, where it's very difficult, and into the petri dish," Eggan said.
The researchers' next step is to prove that the motor neurons will in fact deteriorate in the petri dish. They're planning to use the same technique to grow motor neurons from healthy subjects, and then compare those healthy cells to the ones grown from ALS patients.
