Amniotic epithelial cells, unlike embryonic stem cells, cannot live forever, so therapies based on them will depend on regularly harvesting cells from discarded placentas.

The cells, called amniotic epithelial cells, potentially could be used to produce new liver cells to treat liver failure, or new pancreatic islet cells to cure diabetes or new neurons to treat Parkinson's disease.

Unlike embryonic stem cells, which are obtained only by destroying human embryos, these cells can be extracted from the same placentas that now are routinely discarded after birth. They thus could be a non-controversial alternative to embryonic stem cells.

"We think it would be easier to get these to the clinic than [embryonic stem] cells," said Stephen Strom, an associate professor of pathology at the Pitt medical school.

Do Not Generate Tumors

Not only do amniotic epithelial cells lack the controversy of embryonic stem cells, but they also do not generate the tumors associated with embryonic stem cells, he said. So it may be possible in some cases to simply transplant the amniotic cells to a patient, rather than to first grow the desired specialized cells in the laboratory.

Strom and Dr. Yoshio Miki, an instructor in the pathology department, described their discovery in a paper published online last week in Stem Cells Express; the paper also will appear in an upcoming issue of the journal Stem Cells.

Publication of the paper had been delayed while the university sought patent protection for the discovery, Strom noted. A local biotechnology company, Stemnion Inc., has licensed the patent rights from Pitt with plans to use the cells for treating cirrhosis and diabetes and to spur wound healing.

In the meantime, a couple of Japanese research groups have already confirmed several aspects of the Pitt findings.

"This is an exciting report," said David Prentice, senior fellow for life sciences at the conservative Family Research Council. More and more reports are emerging regarding stem cells derived from such sources as amniotic fluid, bone marrow and nasal mucosa that have much of the same flexibility as embryonic stem cells, but that don't carry the danger of generating tumors, he noted.

New Sources of Stem Cells Vital

The announcement comes with embryonic stem cells once again in the headlines. Last week, Senate Majority Leader Bill Frist, R-Tenn., broke with the Bush administration and said he would support federal funding to create additional embryonic stem cell lines. President Bush this week reiterated his intent to veto any such an expansion of federal stem cell research.

Alan Russell, director of Pitt's McGowan Institute for Regenerative Medicine, said finding new sources of stem cells will be vital to accelerating the pace of stem cell research.

"The placenta and umbilical cord appear to be rich sources for stem cells that have real potential to treat disease," said Russell, who also is an adviser to Stemnion. "Strom's discovery adds another piece to the puzzle that will help patients in the future."

Amniotic epithelial cells make up the thin membrane known as the amnion, or birth sac, which contains the fetus and amniotic fluid. Among other functions, the amnion keeps the developing baby from becoming permanently affixed through wound healing to the mother's organs.

Doctors have recognized that the membrane was rich in stem cells and have long used it as a sort of human bandage to aid in healing, notably in eye surgery.

That's why Miki and Strom first studied amniotic epithelial cells four years ago. Strom is interested in developing sources of liver cells, called hepatocytes, that could be used as an alternative to liver organ transplantation for treating cirrhosis and liver failure.

Once Miki found that the amniotic cells indeed could be used to produce hepatocyte-like cells, he began exploring their other capabilities. That's when he found that they were similar in almost every way to embryonic stem cells.

Just why the cells in this membrane should retain the potential for generating almost any type of tissue in the body is not clear, Strom said, and it may simply be a consequence of when these cells are created during early development.

Amniotic Epithelial Cells Differentiate First

Embryonic stem cells are found when the developing embryo is still a free-floating ball of 40 to 150 cells. The cells in the middle of this ball, which have yet to take on any specialized functions, are the stem cells.

The amniotic epithelial cells are the first of the inner cell mass to "differentiate," or acquire a specialized function; they develop when the blastocyst prepares for implantation in the uterus.

Only after implantation does the inner mass of stem cells begin to differentiate, undergoing a major transformation called gastrulation in which the cells divide into three major classes of cells from which all other tissues are derived. Because amniotic epithelial cells pre-date gastrulation, Strom said, they retain the ability to form any type of tissue.

Amniotic epithelial cells, unlike embryonic stem cells, cannot live forever, Strom said, so therapies based on them will depend on regularly harvesting cells from discarded placentas.

Also, questions remain as to whether the replacement tissues generated from amniotic epithelial cells will be rejected by a recipient. The amniotic epithelial cells don't have many of the cell antigens that can trigger rejection, Strom said, but that seems to change as the cells differentiate.

That would not pose any problem for liver cell transplants, he noted, because the liver can tolerate transplanted cells as long as they have a compatible blood type. But it could be a problem for therapies such as islet cell transplants to cure diabetes.

With about 4 million births a year, however, it should be possible to find donor placentas with tissue types compatible to any recipient, Strom said.

Or, some people may choose to follow Miki's example. His wife, Hisae, is due to give birth any day now and he plans to save the placenta, banking it for possible future use by their child.