Our cells are more malleable than we thought – and by transforming them inside the body, we can mend broken hearts or even degenerating brains from within

Lotte Keijzer

WHAT becomes of the broken-hearted? In cardiac medicine, the answer is usually brutally straightforward: they die. Heart disease is the leading cause of death worldwide and there is often precious little we can do about it. Pacemakers bring some relief and transplants work, but there are nowhere near enough donated hearts to go around. And unlike skin and liver cells, heart muscle cells can’t remake themselves. Once they get damaged or die, they are gone forever.

Lab-grown stem cells, once the great hope for mending hearts, have disappointed. But over the past few years, cell biologists have been quietly exploring an alternative approach. Rather than growing cells in a dish and transplanting them, they want to switch their identities inside the body, so that we can heal ourselves from within.

That might sound rather fanciful. But cells are proving more malleable than we ever imagined, and now plans are being drawn up for the first human clinical trials to see if we can repair damaged hearts this way. If we can perfect the tricks needed to safely switch cell identity in situ – and it is a big if – we should be able to repair tissues ravaged by all sorts of conditions, from diabetes to dementia.

For a long time after biologists worked out how a featureless cluster of identical cells can become the rich diversity of parts that comprise a body, they generally assumed that adult cells were stuck with their fates. Once embryonic stem cells, capable of becoming any tissue type, had differentiated into skin cells, heart muscle cells, neurons or whatever, there seemed to …