But now, scientists are moving closer to using a politically correct source of stem cells: the bodies of the very patients who may be cured by them.
California researchers say they've discovered that it's possible to reprogram stem cells from bone marrow and turn them into different types of brain cells. The next step is to figure out if they could be inserted into the brain to treat tumors and stroke.
"This type of technology will hopefully be able to supplant many types of surgery and radiation therapy in a more natural and effective way," says Dr. John S. Yu, co-director of the Comprehensive Brain Tumor Program at Cedars-Sinai Medical Center's Neurosurgical Institute in Los Angeles and senior author of a new study on the use of stem cells.
In the human body, stem cells are empty vessels waiting to discover what part they'll play. When they get the right signal, they take on their role -- a blood cell, perhaps, or a skin cell or any of many other tissue types.
Scientists can take stem cells from fetuses, but that raises plenty of pesky political problems. It's also possible to take stem cells out of the brain of person and program them, but that means somebody has to walk around with fewer brain cells.
In the Cedars-Sinai study, researchers turned to bone marrow, which has stem cells of its own. They report their findings in the December issue of the journal Experimental Neurology.
Yu and his colleagues found they could program bone marrow cells from rats and make them turn into three types of brain cells. They did so by tinkering with the genetic makeup of the stem cells.
The new, healthy brain cells could conceivably be used to treat a variety of brain diseases. One benefit would be that the body wouldn't reject the cells as foreign bodies, Yu says.
"You're using your own cells rather than those that have come from cancers or are grown in cultures over a long period of time," he says.
For an unknown reason, some of the brain cells appear to be attracted to diseased parts of the brain, he says. It could be possible to give the cells a "payload" of drugs and inject them into the brain, where they would seek out problem areas, Yu says.
Doctors can use surgery to treat tumors, "but what makes them so difficult to treat is that they form satellites of tumor cells that reach far beyond the area of the main tumor," he says.
Dr. Naohiro Terada, a stem cell expert at the University of Florida, cautions it will be important to determine how easy it is to produce the brain cells in other labs.
In general, stem cells hold plenty of hope, says Dr. James Grisolia, a neurologist at Scripps Mercy Hospital in San Diego. "The prospect of reweaving broken networks of cell in the brain is intoxicating of course, but regrowing organs for transplant [pancreas, liver, kidney, heart] is nearly as exciting," he says.
There are still obstacles, of course. "All these things are logical, but still not proven or ready for prime time," he says.
What To Do
For more on stem cells and what's realistic to expect from them, check out the Batten Support & Research Trust. You can also try the National Institutes of Health or the Society for Developmental Biology.