Until recently, the promise of stem-cell therapy has centered on stem cells’ ability to morph into virtually any kind of cells. But researchers are finding that stem cells may have other healing effects. In recent studies, scientists have observed stem cells acting as anti-inflammatory agents, reducing swelling and even scarring when administered to injured tissue.

However, while stem cells’ anti-inflammatory effects have been observed in a number of disease models, it has been difficult to pinpoint exactly how stem cells have this effect. Now a group at Tulane University, led by Darwin Prockop, director of the Center for Gene Therapy, has found that injecting human stem cells into the brains of stroke-induced mice triggers immune cells to produce chemicals that protect nerve cells, thereby reducing swelling and scarring. Prockop, now director of the Institute for Regenerative Medicine at Texas A&M Health Science Center, says that understanding the mechanism behind stem cells’ anti-inflammatory effect could help researchers develop therapies for stroke and related diseases.

“In diabetes, Alzheimer’s, and Parkinson’s disease, there is an excessive early inflammatory response, and stem cells can sense that,” says Prockop. “If you can turn that inflammation down, everything improves.”

In their experiments, described in a paper published today in the Proceedings of the National Academy of Sciences, Prockop and his team induced a stroke in mice by blocking blood flow to their brains for 15 minutes. They then injected bone-marrow-derived human stem cells into the oxygen-deprived portion of the brains of some of the mice and observed the interactions between stem cells and the neural environment over a period of about two weeks.

Although the injected stem cells disappeared after just five days, the researchers found that they had a lasting effect on surrounding brain cells. Mice treated with stem cells experienced 60 percent less cell death compared with mice who did not receive the treatment. Furthermore, when placed in an open environment, the treated mice behaved much like healthy mice, actively exploring the space around them, unlike their more lethargic untreated counterparts.

“It was a hit-and-run effect,” says Prockop. “The human stem cells stopped some of the negative processes going on, and stopped the mouse brain from destroying itself.”