Stem cells are primitive cells that have the ability to specialize and become adult cells of various types, including the several types of cells found in the brain. There is evidence that some areas of the human brain harbor small numbers of stem cells; examples are the cerebral cortex (responsible for conscious activity) and the hippocampus (important for memory). Just what the cells are doing there and if they become specialized and begin to function is still unknown. A new study suggests another potential source of stem cells for possible role in brain repair. The scientists found that if stem cells are taken from the bone marrow of a donor and are transplanted into the blood of another human, they can travel selectively to areas of previous brain injury and differentiate into several types of brain cells.

Comment:

Earlier studies have shown that transplanted bone marrow stem cells can enter the mouse brain from the blood and become nerve cells. This is the first study to demonstrate that this can also occur in humans. Of equal importance, the primitive cells are attracted to injured areas of the human brain and differentiate into the specialized cells common to that area. The human bone marrow transplants were done in adults and children in the treatment of leukemia and other non-neurological disorders. The younger the age of the patient and the longer the survival of the patient the greater the number of stem cells in the area of previous brain injury.

These are very early studies but set the stage for the further study of the potential for introducing stem cells into the human brain and having them replace cells previously damaged. That they will do this in sufficient numbers remains to be seen; that they will become functional also remains to be seen. However, the dim light at the end of the tunnel of brain injury repair has become a bit brighter.

Although the clinical importance of this finding for the repair of developmental brain injury (e.g. cerebral palsy) has still to be demonstrated, it is another step forward in the search for a treatment for cerebral palsy.

Merzy E. Online early edition of Proceedings of The National Academy of Sciences (USA). January 20, 2003.