A recent report from Swiss researchers casts doubt on the ability of embryonic stem cells to treat stroke. Neural precursors derived from mouse embryonic stem cells were implanted into the brains of mice. After nine months, the implanted cells had engrafted and even extended axons into different portions of the brain, although the evidence indicated that the implanted cells did not develop into mature neurons but remained in an early developmental stage. When a stroke was induced in the mouse brains, the embryonic stem cells were actually expelled from the brain. The results, published in the journal Stroke, suggest that embryonic stem cells are ineffective at forming mature brain neurons and treating stroke damage.

In contrast, results with adult stem cells show effective treatment of stroke damage, and early results of a clinical trial with stroke patients are encouraging.