"Our hope is that these cells will provide a valuable resource for tissue repair and for engineered organs as well," said Anthony Atala, director of Wake Forest's Institute for Regenerative Medicine and leader of the team that also included researchers at Harvard Medical School.

Atala explained that, although it was common knowledge that the amniotic fluid contained progenitor cells from the developing embryo, no one knew whether or not they were true stem cells that could differentiate into all the tissues of the body.

And he said it took him and his colleagues seven years of work to find out.

The team discovered that around 1 percent of amniotic and placental stem cells -- which they are now calling amniotic fluid-derived stem cells or AFS cells -- could renew themselves many times, just like embryonic stem cells, and could also become different types of tissue.

So far the researchers say they have produced muscle, bone, fat, blood vessels, nerve cells and liver cells in the laboratory and are experimenting with more. The cells have marker characteristics of both embryonic and adult stem cells, and the researchers think they may represent an intermediate stage between the two types.

The scientists wrote that AFS cells are readily available since they can be harvested from placentas, which are normally thrown away after delivery, as well as from amniotic-fluid specimens obtained during amniocentesis, a procedure performed at around four months' gestation to determine whether a fetus has genetic abnormalities.

The newly discovered stem cells can also be grown in large quantities because they double every 36 hours, do not require guidance from other cells to differentiate into different types of tissue and don't produce tumors, which can occur when other types of stem cells are used.

AFS cells have produced all three classes of cells found in developing embryos -- ectoderm, mesoderm and endoderm -- and the team believes they are capable of generating every type of adult tissue, just like embryonic stem cells.

"This is a very exciting report," David Prentice, senior fellow for life science at the Family Research Council, a group opposed to embryo-derived stem cell research, told United Press International. "These researchers did a careful analysis to ensure that these amniotic stem cells provide the same flexibility as embryonic stem cells without the scientific and ethical negatives that the use of embryonic stem cells generate," he said.

Atala told UPI the stem cells are still in the early stages of development and will not be used in human beings any time soon, but added he was enthusiastic about their potential since several strains have been used to successfully repair diseased tissue in mice.

He also noted that, since he and his colleagues wrote up their work for journal publication, nerve cells developed from AFS cells have started producing dopamine -- which he said is a fairly high functional end product for this type of tissue -- and liver cells have started secreting urea.

The team has postulated that an AFS cell bank with 100,000 specimens could supply 99 percent of the U.S. population with a perfect genetic match for transplantation. They wrote that they thought there would be no problem obtaining that many specimens since there are more than 4 million live births each year in the United States alone.

When asked about a skeptical comment from Clive Svendsen, a stem cell researcher at the University of Wisconsin in Madison who read the team's paper and thought AFS neural stem cells did not compare well to neural stem cells that were derived from the brain, Atala said he had no quarrel with Svendsen's analysis.

"He's right so far," Atala told UPI. "The potential of these cells must be tempered with the rest of the field. Perhaps other types of cells developed later may even be better. Each type will have its own special advantages for different therapeutic situations. Only time will tell which cells will be used for patient therapy and under what circumstances."

The report on the research was published Monday in Nature Biotechnology.

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