'Embryonic-like' stem cells can't be found: US study

A US company that promoted its stem cell discovery in partnership with the Vatican has come under fresh scrutiny by independent scientists who said Wednesday the cells do not exist.

Scientists at Stanford University said in the journal Stem Cell Reports they could not replicate NeoStem's findings of very small embryonic-like cells (VSELs) in the bone marrow of lab mice.

These cells have been touted by the New York-based company as an ethical alternative to stem cells requiring the destruction of human embryos, with the same regenerative ability to transform into other cell types in the body.

Earlier this year, NeoStem announced plans to launch the first human trials of the cells for bone growth.

"We tried as hard as we could to replicate the original published results using the methods described and were unable to detect these cells in either the bone marrow or the blood of laboratory mice," said lead author Irving Weissman, who directs Stanford's Institute for Stem Cell Biology and Regenerative Medicine.

Weissman's study is the first to evaluate the biological potency of the cells, and it found they could not transform into blood cells and contained very little DNA.

Instead, researchers found that what purported to be VSELs -- about five micrometers in diameter -- were either debris or dead cells.

"A true pluripotent cell would be able to differentiate into any tissue type," said Weissman. "But we couldn't confirm that cells of that size or phenotype could generate hematopoietic cells with any reliability."

In response, NeoStem chairman and CEO Robin Smith said the company has studies in progress that will "confirm whether or not VSEL(s) have characteristics of a pluripotent stem cell."

"We acknowledge that there is controversy in the VSEL field but this is not unusual for most new scientific discoveries and theories (Darwin and evolution, Copernicus and earth orbiting the sun as examples)," Smith said in a statement emailed to AFP.

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'Embryonic-like' stem cells can't be found: US study