The hyped ability of adult stem cells to sprout replacement tissue types is being called into question. They may instead be fusing with existing cells, say two new reports, creating genetically mixed-up tissues with unknown health effects.



Recent studies have shown that adult stem cells transplanted from one tissue, such as blood, can spawn the cell types of another, such as nerves. The findings have stirred intense interest in stem cells’ medical potential to repair damaged or diseased tissues.

Now researchers have evidence that, rather than switching fates, adult stem cells may be fusing with those in existing tissues.

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