Amniotic stem cell shows promise

Researchers have found stem cells in human amniotic fluid that appear to have many of the key benefits of embryonic stem cells while avoiding their knottiest ethical, medical and logistical drawbacks, according to a study published Sunday.

The stem cells – easy to harvest from the fluid leftover from amniocentesis tests given to pregnant women – were able to transform into new bone, heart muscle, blood vessels, fat, nerve and liver tissues, the study said.

“So far we’ve been successful with every cell type we’ve attempted to produce from these stem cells,” said Dr. Anthony Atala, director of the Institute for Regenerative Medicine at Wake Forest University School of Medicine in Winston-Salem, N.C., and senior author of the report published online by the journal Nature Biotechnology.

The finding points to a promising avenue of research that sidesteps the hurdles facing embryonic stem cell research, which has been stymied by moral objections to the destruction of embryos that occurs when cells are harvested.

Most of the work involving human embryonic stem cells is ineligible for the more than $25 billion the federal government spends on research each year. But amniotic fluid stem cell studies already are being funded by the National Institutes of Health.

The study also suggests another advantage: Amniotic fluid stem cells, unlike embryonic cells, do not appear to form tumors when implanted in lab animals.

“If everything that people think about them turns out to be true, they’ll be a powerful source for therapeutic cells,” said Alan Russell, director of the McGowan Institute for Regenerative Medicine at the University of Pittsburgh, who wasn’t involved in the study.

It is still unclear whether stem cells from amniotic fluid – the liquid that cushions babies in the womb – can give rise to the full range of cell types that embryonic stem cells can produce.

“They can clearly generate a broad range of important cell types, but they may not do as many tricks as embryonic stem cells,” said Dr. Robert Lanza, a prominent embryonic stem cell researcher and head of scientific development at Advanced Cell Technology Inc. in Worcester, Mass.

But even if the amniotic fluid stem cells turn out to be less flexible, they may still be an important tool in the nascent field of regenerative medicine.

Dr. Dario Fauza, coordinator of the surgical research laboratories at Children’s Hospital Boston, has used the cells to grow tissue to repair defective diaphragms and tracheas in sheep.

He has asked the Food and Drug Administration for permission to do the same for children born with herniated diaphragms. It would be the first human clinical trial involving amniotic fluid stem cells, he said.

Dr. Dorthe Schmidt and Dr. Simon Hoerstrup, of University Hospital Zurich, have used amniotic fluid stem cells to grow heart valves. They are testing them in sheep.

The stem cells “may not be as earth-shattering a discovery as human embryonic stem cells, but these cells could prove to be equally important for medical therapy,” Lanza said. “I think this is an exciting breakthrough.”

Amniotic fluid stem cells lie somewhere between the two major categories of stem cells: embryonic and adult.

Embryonic stem cells are derived from days-old embryos. Nearly all of the development is still to come, so those cells must be extremely flexible.

That trait, called “pluripotency,” is the reason researchers believe embryonic stem cells could offer cures for a wide range of ailments. They envision using the cells to replace the faulty islet cells that leave diabetes patients without enough insulin, and to grow fresh brain tissue to treat stroke victims, among other things. But they don’t yet know how.

Adult stem cells are narrowly focused on replenishing specific types of tissue that wear out over the course of a lifetime, such as skin, hair and blood. Researchers all over the world are looking for ways to expand their range of capabilities.

Amniotic fluid stem cells, which are sloughed off by the developing fetus, are “a different kind of a stem cell,” Atala said. “It’s not as early as a human embryonic stem cell and it’s not as late as the adult stem cells.”

Scientists surmised that amniotic fluid would contain those cells more than a decade ago and identified them after several years of searching.

Atala and his colleagues set out to determine just how plentiful and flexible these stem cells might be.

Researchers studied 10 milliliter samples of fluid extracted from pregnant women who had amniocentesis tests to screen their babies for genetic abnormalities. Those tests are routinely performed early in the second trimester.

Of the myriad cells that make up amniotic fluid, the researchers found about 1 percent with a surface marker that is a hallmark of embryonic stem cells. They took it as a signal that the cells might possess pluripotent abilities.

The researchers from Wake Forest and Harvard Medical School biochemically prompted the cells to transform into all the main categories of embryonic tissue.

A key test was to see if the cells functioned like normal cells.

Stem cells that had been induced to become neural cells were able to secrete a neurotransmitter when stimulated by potassium ions, mimicking conditions inside the brain, the researchers reported. They also induced stem cells to develop into liver cells that were able to secrete urea, a compound produced in the liver.

Other stem cells that had been coaxed into becoming osteoblasts, which build up bone, were implanted in mice. The cells formed a tissue that was more dense than normal mouse bone, he said.

“You may be able to obtain the same medical benefits – and cure the same diseases – without the risks or controversy associated with embryonic stem cells,” said Lanza of Advanced Cell Technology. “It’s just what the doctor ordered.”

The cells did not form the tumors – jumbles of tissue that can include bits of fat, hair and teeth – that are common with embryonic stem cells, the researchers said.

“That’s one of the biggest issues the FDA will be concerned about when it comes time to approve stem cell-based therapies,” Russell said.

Larry Goldstein, a professor of cellular and molecular medicine at the University of California, San Diego, who studies embryonic stem cells, said the absence of tumors might signal a limitation of stem cells derived from amniotic fluid. “It makes me wonder how pluripotent they are,” he said.

Although the cells might prove useful in some circumstances, Goldstein said they aren’t a substitute for embryonic stem cells. “They built a screwdriver here, but I need a wrench,” he said.