To truly know whether a stem cell has the developmental flexibility to give rise to new, therapeutic tissue types, the cells must undergo a definitive test in which they are injected into mice and observed. Yet many say this measure is too slow, too expensive and too unreliable. Elie Dolgin goes in search of a replacement.

Earlier this year, doctors in Atlanta injected millions of cells derived from embryonic stem (ES) cells into the spinal cord of a partially paralyzed patient. The trial, run by the California-based company Geron Corporation, promises to usher in a new era of regenerative medicine in which millions of people are treated each year with the products of so-called ‘pluripotent cells’, defined by their ability to morph into any type of tissue.

The stakes for developing a reliable test for true pluripotency are high. The US National Institutes of Health (NIH) has invested more than $500 million in human ES cell research and plunged hundreds of millions more into induced pluripotent stem (iPS) cells. Once the therapies hit the clinic, pluripotent stem cells could be worth more still.

“This is easily a field that has the market potential to be in the hundreds of billions of dollars,” says Reni Benjamin, a senior biotechnology analyst at Rodman & Renshaw in New York.

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