Ride For Life: Adult-stem-cell research shows some limits

Despite earlier research that adult stem cells from bone marrow could successfully change into brain cells, research out today suggests the change isn't as easy as once believed. That could put a damper on hopes that adult cells might take the place of those from embryos in research to cure brain diseases and spinal cord injuries.

The research, reported in the journal Science, is the latest entry in the politically charged debate over stem cells. The cells are found both in embryos and grown animals, and are coveted for their ability to change, or differentiate, into any kind of tissue in the body. Scientists are studying stem cells as possible therapies to regenerate diseased tissues in patients with Parkinson's disease, Alzheimer's disease and spinal cord paralysis. However, some say research on human embryonic stem cells, which are harvested by destroying embryos, is immoral.

Those who say they believe human embryonic stem cells hold the most promise are pitted against those who say adult stem cells are just as useful and harvesting them doesn't involve the destruction of embryos.

A team at Baylor College of Medicine in Houston described its futile efforts to get adult stem cells from mouse bone marrow to produce neural cells, which are found in the brain and nervous system.

"It may work only under certain experimental conditions," says H. David Shine, of the Center for Cell and Gene Therapy at Baylor and senior author of the study.

Over the past three years, several researchers were able to coax mouse bone marrow cells to differentiate into neural cells, but the Baylor team was unable to replicate those findings.

The team used radiation to wipe out the bone marrow of mice and then implanted genetically marked bone marrow cells from other mice to see whether the cells would differentiate into neural cells, but none appeared.

"More research needs to be done because it would be a great resource" to learn the conditions under which the differentiation takes place," Shine says. "We're still betting it's possible."

The study was funded by The Institute of Rehabilitation and Research in Houston, which provides rehabilitation services for the paralyzed.

Helen Blau, professor of genetic pharmacology at Stanford University in California, says there's evidence the genetic marker used by the Baylor group doesn't function as well in brain tissue. She says her group, which published one of the first papers to show adult stem cells becoming brain cells, tried using that marker for a year before switching to another, which worked better.

Blau notes that research in all types of stem cells has become complicated by the politics of research on embryonic stem cells.

She emphasizes that research should continue on both adult and embryonic stem cells. "For certain diseases, one type of cell might be more applicable than the other."

As is often the case with new science, the limits of what is possible are still being worked out in the realm of adult stem cells. Whether or not adult stem cells are as flexible as some scientists believe them to be is a matter of much debate in research circles, with vociferous arguments taking place in conference corridors and graduate seminars around the world.

Although papers published in the past three years have shown that adult bone marrow cells can become brain cells and that brain cells can become blood cells, other researchers, including Derek van der Kooy of the University of Toronto, have been unable to replicate those findings.

He says that although such studies may "throw cold water" on a number of individual examples of the apparent plasticity of these cells, "the mass of (the studies) can't all be done poorly -- some of them have to be correct."

Walter Low, a neuroscience professor at the University of Minnesota, says, "We need to find out the full potential of both of these types of cells and where they are the same and where they differ. People are getting the impression that these adult cells can do everything an embryonic cell can do. They need to have a more balanced view."