Researchers have found that some stem cells in human amniotic fluid appear to have many of the key therapeutic 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 left over from amniocentesis tests given to many pregnant women — were used to create bone, heart muscle, blood vessels, fat, and nerve and liver tissues, the study said.
The finding points to a promising avenue of research that sidesteps the hurdles facing embryonic stem cell research, which has been hampered by moral objections to the destruction of embryos that occurs when the cells are harvested.
The objections have been divisive, prompting President Bush to restrict federal funding for most human embryonic stem cell research. Those restrictions have sparked movements in some states to fund research on their own.
California's Proposition 71, approved in 2004, was designed to provide $3 billion for stem cell research but has met a vigorous legal challenge from opponents of the research.
Amniotic stem cell research ducks the controversy because no embryos are destroyed. The National Institutes of Health already funds such research.
The study also suggests another advantage: Embryonic cells can form tumors when implanted in lab animals, but 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 wasn't involved in the study.
It is still unclear whether stem cells from amniotic fluid — the liquid that cushions fetuses in the womb — can produce the range of cell types that embryonic stem cells can.
"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, an embryonic stem cell researcher and head of scientific development at Advanced Cell Technology Inc. in Worcester, Mass.
But even if amniotic stem cells turn out to be less flexible, they still might 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 stem cells, he said.
Swiss scientists Dorthe Schmidt and Simon Hoerstrup of University Hospital Zurich have used amniotic stem cells to grow heart valves. They are currently 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," said Lanza, who was not involved in the study. "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 "pluripotency" is the reason researchers believe embryonic stem cells could offer cures for a wide range of ailments. They hope to use the cells to replace the insulin-secreting islet cells of diabetes patients and to grow brain tissue to treat stroke victims, among other treatments. But they don't yet know how.