Adult stem cells, found in the liver, bone marrow and elsewhere, are the biological workhorses that repair injuries and form new tissue. Researchers hope to use them to cure Alzheimer's disease, say, or grow new livers; but the large numbers of cells such treatments would require can't reasonably be harvested from human donors-and many types of adult stem cells are difficult to mass-produce in culture. MIT bioengineer James Sherley may have found a way around that difficulty, potentially overcoming a huge barrier to putting adult stem cells to medical use.

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