Salk Institute for Biological Studies: InsideSalk

Splitting Hairs - Scientists Scope Their Locks to Trigger Rapid-Fire Advances in Stem Cell Research

Japanese and U.S. scientists made major headlines two years ago when they successfully reprogrammed adult skins cells into stem cells. It was the first study showing that researchers could turn back the clock to develop human embryonic-like stem cells, while circumventing the ethical debate sparked by the traditional method to harvest them.

The new cels, caled induced pluripotent stem (iPS) cells because of their ability to become any other cell type in the body, opened the floodgates to new research and led teams of scientists at the Salk Institute and elsewhere to develop methods to coax iPS cells into several types of tissues, the kind that medical researchers believe may one day be used to replace cells that have been damaged due to trauma or disease.

As magnificent as the iPS cell breakthrough was, the method to achieve it is woefully inefficient. Only one out of 10,000 cells could be reprogrammed in a process that takes four months to achieve. But a team of researchers at the Salk Institute and the Center of Regenerative Medicine in Barcelona, Spain, led by Juan Carlos Izpisúa Belmonte has taken the science of cell reprogramming one step further, drastically improving the technique.

In their paper, which Nature Biotechnology featured on the cover of its November 2008 issue, the team boosted the reprogramming efficiency by 100 fold. They managed to turn back the clock in one out of 100 cells in just 10 days. But rather than using skin cells, they chose to work with keratinocytes — cells that are found in the root section of human hair.

Plucking strands of hair from the human scalp is much less invasive than a skin biopsy, says Belmonte, who believes his team's study is yet another tool that can very likely be applied toward individualized medicine to treat disease.

"Having a very efficient and practical way to generate patientspecific stem cells, which unlike human embryonic stem cells wouldn't be rejected by the patient's immune system after transplantation, brings us a step closer to the clinical application of stem cell therapy," says Belmonte, professor in Salk's Gene Expression Laboratory and director of the Center of Regenerative Medicine in Barcelona.

Japanese and U.S. scientists made major headlines two years ago when they successfully reprogrammed adult skins cells into stem cells. It was the first study showing that researchers could turn back the clock to develop human embryonic-like stem cells, while circumventing the ethical debate sparked by the traditional method to harvest them.

The editors at Science were equally optimistic about the Belmonte study, including it in the journals annual December feature, which highlighted the rapid development of cell reprogramming as the Breakthrough of the Year for 2008.

"It's an important study and it gives an alternative method for potentially making progress of iPS cells," says Larry Goldstein, professor of Cellular and Molecular Medicine and director of the UCSD Stem Cell Program. "The fact that it's more efficient is certainly an improvement. At the end of the day, it's important to have as many variants as we can to find things that are safe and effective for patients."

Finding the safest route to make stem cell therapy possible to treat or even cure certain human diseases is what the Belmonte lab and others at Salk are working toward. Much has been learned from the keratinocytes reprogramming study, but the universal method used by researchers to develop iPS cells has one flaw: it uses a virus to shuttle the four reprogramming genes into the genome. In some cases, the virus has been known to activate the expression of other genes that cause cancer in lab models.

Belmonte's team boosted the reprogramming efficiency by 100 fold. They managed to turn back the clock in one out of 100 cells in just 10 days. The study made the November 2008 cover of Nature Biotechnology.

Some scientists are attempting to circumvent this bottleneck by working with compounds to chemically introduce the proteins that are needed to start up the reprogramming process. However, the Belmonte lab is taking a different approach. They are trying to create iPS cells from adult mouse cells using non-viral vectors, hoping they will be able to achieve the same results without disturbing the host cells' genome.

"I think these advances will definitely change the speed in which this technology can eventually be applied," says Belmonte. "If you have a safe reprogramming method that does not use a virus, it's much more acceptable to take hair samples from a patient, reprogram the cells and then differentiate them into heart, pancreas or any cell type that's diseased, and implant them into that patient because the risk involved with using a virus is no longer an issue.

"We have to be cautious not to generate false expectations since there is still much to be studied, but what was science fiction up until a year ago is real science today," he says. "Developments in this field are moving along at such a rapid pace that I think now it would be fruitful to start a dialogue with clinicians."

The speed of progress is just as surprising to veteran scientists like Goldstein. Only 10 years go researchers in Wisconsin announced that they had cultured human embryonic stem (hES) cells.

"I'm shocked. I mean it can never be fast enough, but it's really quite remarkable how quickly some of these problems are being addressed," Goldstein says. "But I never underestimate the creativity of my colleagues."

There are serious hurdles that need to be overcome, one of which the Belmonte lab, in collaboration with other investigators at Salk, is already addressing to potentially make stem cell therapy a reality. Although scientists worldwide have learned to differentiate iPS cells, there's no standard protocol for developing a single cell type.

With current methods, researchers angling for neurons, for example, may also end up with pancreas cells that contaminate the colony. But progress is steadily being made in this area at Salk, too, using Belmonte's non-viral, episomal vector approach, he says.

Despite the rapid-fire breakthroughs in the cell-reprogramming field, medical science is still several years away from using the process to cure a disease, at least in humans. But Belmonte and his collaborator, Inder Verma, professor in Salk's Laboratory of Genetics, are hard at work to move one step closer to the ultimate goal—correcting genetic defects in patient-specific iPS cells and use those to replace the defective ones in the patient's body.

The Salk researchers are still experimenting with mice, but if successful, their study will represent a solid leap forward in stem cell research that Belmonte believes will trigger further collaborations and new scientific approaches to gain insights into some of today's incurable diseases.


InsideSalk 03|09 Issue | © Salk Institute for Biological Studies