Neonatal stroke or related brain injuries can occur when a newborn baby’s blood supply is restricted, often leading to cerebral palsy, epilepsy or mental retardation. Over the past decade, researchers have been using animal models to experiment with neural stem cells to replace or protect the damaged tissue in this type of surprisingly common brain injury. Stem cells hold great therapeutic promise because they can proliferate in a dish (making many cells for transplantation purposes) and then differentiate on command, specializing into a specific cell type like neurons in the brain or even glial cells, which support and protect neurons. Stem cells are also pathotropic, meaning that they are drawn to, or home in on, pathological locations in the brain, including those that can occur from injury (like stroke) or degeneration (such as occurs in Alzheimer’s disease).

But there are risks to stem cell therapy. One worry is that cells will continue proliferating after transplantation, leading to tumor formation. Scientists also need to make sure the stem cells migrate directly to the locations in need of repair or protection and not to unintended locations. These are tough problems to overcome, though, because it’s difficult to track a stem cell’s behavior once it’s inside a host.

“The ability to monitor neural stem cells for a long time is particularly important for newborns, where implantation could cause unanticipated effects in the developing brain long into the future,” says Dr. Evan Y. Snyder, director of Sanford-Burnham’s Stem Cells and Regenerative Biology Program. Dr. Snyder was also the first to demonstrate pathotropism of solid-organ stem cells, as well as the first to demonstrate the use of stem cells to treat stroke, particularly neonatal stroke.

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Stem cells of many varieties hold a lot of promise for regenerative medicine. Their ability to continually self-replicate (produce more stem cells) and differentiate (specialize) into any number of cell types make them an enticing replacement for diseased or damaged tissue or as delivery vehicles for therapeutic molecules.The problem is that we still don’t know enough about many of the existing stem cell types to predict exactly how they will behave when transplanted into a patient. Each of the different types of stem cells has its unique repertoire of behaviors and its own benefits and drawbacks. In an editorial appearing online March 25 in the journal Experimental Neurology, Dr. Evan Y. Snyder hammers home the possible dangers of one very popular and oft-used type of stem cell. He highlights a paper appearing in the same issue of that journal, in which researchers from the Aristotle University of Thessaloniki in Greece and the Medical University of Vienna show that brain tumors develop when a mouse model of multiple sclerosis (MS) is transplanted with mesenchymal stem cells (MSCs) derived from bone marrow.

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