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Stem Cells Discovered in Amniotic Fluid, Scientists Announce

Scott Norris
for National Geographic News
January 8, 2007
 
Stem cells have been discovered in amniotic fluid, the liquid that surrounds a fetus during pregnancy, scientists have announced.

The cells appear to rival embryonic cells in their ability to give rise to all of the major tissue types present in the human body.

Researchers at Wake Forest University in Winston-Salem, North Carolina, used the amniotic stem cells to form bone, muscle, nerve, fat, blood vessel, and liver cells.

The report by Anthony Atala and colleagues appears in yesterday's edition of the journal Nature Biotechnology.

The finding raises new hope for advances in tissue repair and organ regeneration without the ethical objections that have surrounded embryonic stem cell research.

Such objections arise because embryonic stem cells must be harvested from a fertilized human egg, which is destroyed in the process.

In contrast, amniotic stem cells can be collected during a routine medical procedure that draws fluid from the womb without harming the developing fetus. The cells can also be taken from the placenta that is expelled after delivery.

In a teleconference Friday, Atala said that while it is too soon to know their full therapeutic potential, the new stem cells have advantages over other stem cell types because they are so potent and fast growing.

"I don't think these cells are going to replace [human embryonic stem cells], but they provide another choice and are more readily available," Atala said.

Engineering Organs

Amniotic fluid is known to be rich in fetal cells of various types, and physicians have already used some of these to clone "patches" of connective or muscle tissue for repairing certain birth defects.

Atala said the cells his group isolated are unique in their ability to form a range of cell types, while also possessing characteristics of adult stem cells that generate only a single type.

The researchers used special chemicals to coax the amniotic stem cells to develop different specialized structures and functions.

Cloned lines of the cells grew readily in the laboratory, with populations doubling every 36 hours.

Like embryonic stem cells, the amniotic cells retained their genetic makeup and showed no signs of aging over multiple generations.

After being grown in culture dishes, the human cells continued to grow and take on specialized functions when implanted into living mouse tissue.

Bone cells produced bony tissue in mice, for example, and nerve cells became established in areas of mice brains that had been damaged by disease.

"It's a very encouraging and hopeful discovery," said Roger De Filippo, a stem cell researcher at the University of Southern California.

"The fact that these cells can grow in standard culture dishes to very large numbers is a huge advantage for building organs."

But Arnold Kriegstein, director of the Institute for Regeneration Medicine at the University of California, San Francisco, sounded a more cautious note.

"Some of the cell types they described were really not well developed," Kriegstein said. "We don't know yet what the true potential of these cells might be."

Potency and Potential

By harnessing the remarkable generative properties of stem cells, scientists hope to find new treatments for neurological injuries and degenerative diseases.

Controversy over embryonic stem cells led many researchers to focus on developing therapeutic techniques using adult stem cells.

(See a National Geographic magazine feature on the stem cell controversy.)

Scientists are also working to develop techniques for harvesting embryonic stem cells without destroying embryos.

(Read "Stem Cells Can Be Collected Without Destroying Embryos, Scientists Show" [August 23, 2006].)

Other studies have tried to find alternative sources of stem cells with similar properties.

(Read "Mouse Testicles Yield Promising Stem Cells" [March 24, 2006].)

If techniques for engineering a range of tissue types from amniotic stem cells can be fully developed, the effects would be far reaching.

Atala suggests that banks of amniotic fluid could one day serve the medical needs of the general population.

"Theoretically speaking, if one had a bank of 100,000 specimens, one could supply 99 percent of the U.S. population with a perfect genetic match [of engineered tissues or organs] for transplantation," Atala said.

Ronald Green is a bioethicist at Dartmouth College in Hanover, New Hampshire. He called the new development "very promising—if the science pans out."

"We are very much in need of 'ethically universal' lines [of stem cells] that anyone can use, regardless of their views on the moral status of the human embryo," Green said.

"Every step toward alternatives that don't involve the destruction of human embryos is welcome."

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