THE prospect of using adult stem cells to treat brain diseases like Parkinson鈥檚 has come a step closer, thanks to a method for priming bone marrow cells to become brain cells.
Several studies suggest that mesenchymal stem cells, also called stromal cells, can turn into neural cells. And stromal cells are easily isolated from bone marrow. The great advantage of using such cells to treat diseases is that there would be no problem with immune rejection, as an individual鈥檚 own cells could be given back to them. It also avoids the ethical objections some have to embryonic stem cells.
But deriving suitable cells for implanting in the brain has proved tricky. Injecting stromal cells directly into adult brains does not seem to work. And attempts to turn them into mature nerve cells first have produced only limited numbers of cells, which can be damaged by the collection process.
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Now Alexander Storch of the Technical University in Dresden has found a way to 鈥減rime鈥� stromal cells with growth factors to produce a large numbers of neural stem cells, like those naturally found in small numbers in our brains. The cells, though immature, have developed to the point where they are committed to becoming specific kinds of brain cells.
The method can produce oligodendrocytes and glia, the nervous system鈥檚 support cells, as well as nerve cells with all the electrical properties of normal neurons, Storch told a meeting of American Academy of Neurology in San Francisco last week. The approach might help people with a range of conditions, from multiple sclerosis to Alzheimer鈥檚.
Storch has already transplanted the neural stem cells into mice with stroke damage, and with a condition that resembles Parkinson鈥檚, but the results are not yet clear.
There is some evidence that this will work in people. In a controversial study, a patient with Parkinson鈥檚 was implanted with neural stem cells in 1999 (快猫短视频, 19 July 2003, p 24). The results appear promising, but the neural stem cells had to be derived from the patient鈥檚 own brain tissue. Needless to say, marrow-derived cells would be far preferable.
A problem with many stem-cell approaches is that the medium in which the cells are grown contains animal 鈥渇eeder cells鈥� or substances such as fetal calf serum, which could trigger immune rejection or even transmit diseases. But Storch鈥檚 medium contains neither. 鈥淭he medium is the key,鈥� says Juan Sanchez-Ramos from the University of South Florida, Tampa. 鈥淚t contains the right chemicals for neural stem cells to grow, yet is safe to give back to humans.鈥�
Persuading regulators to allow human trials might be tough, though. Bone marrow stem cells are already being used to treat heart attack victims, with several small trials reporting positive results, but other studies have failed to show the cells really do develop into functioning muscle cells. This has sparked criticism about the rush to start trials. But in these heart trials, the cells have been injected directly without the priming step that Storch has developed.