The stem cells — 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 yesterday.
The stem cells - easy to harvest from the fluid left over 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 are already being funded by the National Institutes of Health.
The study also suggests another advantage: Unlike embryonic cells, which can form tumors when implanted in lab animals, amniotic fluid stem cells do not appear to do so.
"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 was not 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 might 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 in 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.
Two Swiss scientists, Dr. Dorthe Schmidt and Dr. Simon Hoerstrup of University Hospital in Zurich have used amniotic fluid stem cells to grow heart valves and 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 the cells must be extremely flexible. That trait, called "pluripotency," is the reason that researchers believe that embryonic stem cells could offer cures for a wide range of ailments. They envision using the cells to replace the faulty 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 more than a decade ago that amniotic fluid would contain those cells 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.
The researchers studied 10-milliliter samples of fluid extracted from pregnant women who had amniocentesis to screen their babies for genetic abnormalities. Those tests are routinely performed early in the second trimester.