Stem Cell Transplantation for Stroke: Does It Work, and If So, How?
An increasing number of experiments in animal stroke models demonstrated that a variety of different types of stem cells implanted directly into the central nervous system or delivered systemically beneficially affect functional outcome. In these experiments, stem cells are given days to weeks after stroke onset without affecting infarct size. How the various types of stem cells induce their beneficial effects on functional outcome remains a matter of speculation, but Howells and Wechsler/Kondziolka suggest a number of intriguing possibilities revolving around direct functional activities of the implanted stem cells versus stimulation of intrinsic host recovery mechanisms. As these authors suggest, it is likely that both effects may occur and different mechanisms may predominate with individual subtypes of stem cells or at different times after stroke onset.
Much further experimental work will be needed to dissect the precise mechanisms of stem cell effects on neurological/functional recovery after stroke. The utility of stem cell treatment for stroke will need to be explored in primate stroke models and then in carefully designed initial and advanced clinical trials. The initial small animal experiments provide reasons for excitement, but as has been learned in other neurological disorders, there are many potential pitfalls. All stroke specialists and stroke patients need to pay close attention to this field as it unfolds with both cautious optimism and healthy skeptical reserve.