The cells are “neither embryonic nor adult. They’re somewhere in between,” says Dr. Anthony Atala, a tissue-engineering specialist at Wake Forest University, who led a team that published the findings last week in the journal Nature Biotechnology. The “AFS cells” rival embryonic stem cells in their ability to multiply and transform into many different cell types, and they eventually could be hugely helpful to doctors in treating diseases throughout the body and building new organs in the lab. At the same time, the amniotic cells can be taken easily and harmlessly from the placenta or from pregnant women by amniocentesis–which gives them the potential to nullify, or at least bridge, the divide in the stem-cell-research debate. What’s more, the stem cells are also found in the placenta, which is thrown away after birth–so doctors may obtain them from all infants, not just those subject to amniocentesis. The cells come with little “ethical baggage,” says David Prentice, a senior fellow in life sciences at the Family Research Council, which has opposed embryonic-stem-cell research. “I’m just pumped up by this,” he says. “It’s fantastic.”
Scientists have long studied AFS cells, but the new research is the first to demonstrate their potential. Like those from embryos, the AFS cells appear to be pluripotent, or able to transform into fully grown cells representing each of the three major kinds of tissue found in the body. Using stem cells taken by amniocentesis from 19 pregnant women, Atala and his colleagues were able to create in the lab nerve cells, liver cells, endothelial cells (which line blood vessels) and cells involved in the creation of bone, muscle and fat. (Dr. Roger De Filippo, a urologist and tissue engineer at Childrens Hospital Los Angeles, has also coaxed amniotic cells into becoming structures found in the kidneys.) Some of the cells in Atala’s lab even functioned as they would be expected to in the human body. The liver cells secreted urea, an activity otherwise seen exclusively in their natural counterparts. And, in a development that may hearten patients with Parkinson’s disease or other neurological disorders, the lab’s nerve cells secreted glutamate–a neurotransmitter that is crucial to memory and helps to form dopamine, which Parkinson’s patients lack. The lab also conducted tests on mice with neurodegenerative disease and showed that the amniotic cells sought out and repopulated damaged areas of the brain.
Amniotic-fluid stem cells share another unique characteristic with embryonic stem cells: they multiply quickly and are remarkably long-lived. The Atala lab’s cells divided more than 250 times–more than quintuple the life expectancy for stem cells taken from adults. Dr. Dario Fauza, a surgeon at Children’s Hospital Boston, says he had gotten comparable results working with stem cells from amniotic fluid: “I practically haven’t been able to get them to stop growing.” The cells are hardy, which makes them relatively easy to culture.
That resilience may eventually help doctors trying to grow new organs or graft tissue into patients. “When you implant an engineered graft, it’s typically vulnerable early on, because it takes a few days for the host to send blood vessels to feed it,” says Fauza. “So you need a cell that can take that punishment for a while.” You also need, says De Filippo, “a lot of cells to create organs”–a demand that the amniotic cells may meet even more easily than embryonic cells can. In addition, for reasons that are still poorly understood, the amniotic cells do not seem to form the tumors known as teratomas that sometimes arise from embryonic stem cells implanted in animals.
Farther down the road, the cells could be ideal candidates for “banking,” as an increasing number of new parents do today with blood taken from their babies’ umbilical cords. Like cord blood cells, the amniotic cells can be frozen. But once thawed, they live much longer. “The maximum you can do with cord blood cells, which are often used to treat leukemia, is get them to double once,” says Atala, compared with the stem cells’ lifespan of 250 doublings. A future amniotic stem-cell reserve might be stocked with a variety of genetic types so that cells could be matched to patients with the fewest potential complications.
That era, of course, is well in the future. Many scientists are quick to emphasize that comprehensive human trials are still many years away. There are still many mysteries surrounding amniotic-fluid stem cells–why they don’t cause tumors, why they apparently provoke very little immune response when implanted and when during embryonic development they first arise–that might give the FDA pause. For the short term, the new discovery might not have much practical impact on the ethics debate. The U.S. Congress is debating whether to increase funding for embryonic stem cells.
A few small experiments on human tissue using cells taken from amniotic fluid are currently in the works. Late last year a Swiss team reported that it had temporarily been able to grow human heart valves from cells found in amniotic fluid. Dr. Fauza has published a number of large-animal studies on tissue engineered from AFS cells over the last several years and is now preparing a clinical trial, this one focusing on children born with holes in their diaphragms. Babies with the defect today have it patched up with Teflon, “which obviously doesn’t grow, so the defect often recurs as the child gets older,” says Fauza. Instead, he proposes to construct grafts using amniotic stem cells, and then implant them into newborns. He already has seven years’ worth of data, all of them encouraging, from performing the same operation on sheep. U.S. regulators, he says, “are also being very cautious.” He hopes the trial will begin in “the not-too-distant future.” It’s a future that’s suddenly looking brighter.
