When researchers first discovered that certain cells in new embryos could be extracted and grown into different cell types in the laboratory—like “starter” seeds on a cellular level—there seemed no stopping the march toward medical miracles.
Using unwanted embryos destined to be destroyed by fertility clinics, scientists quickly demonstrated that the cells could generate brain, liver, heart, bone, and other cells, offering the dizzying possibility of a potentially unlimited source of replacement cells for treating diseases of the brain and nervous system. Parkinson's and Alzheimer's disease, amyotrophic lateral sclerosis, stroke, brain injury, and paralysis were immediately seen as potential targets for experimental therapies.
Embryonic stem cells replicate indefinitely but can be manipulated or “coaxed” into specific types of cells. Because they grow so vigorously, stem cell lines derived from a few embryos could potentially be used in hundreds of experiments to find new treatments.
But using cells from unwanted and discarded human embryos and fetuses has been controversial, prompting an outcry from pro-life advocates and their representatives in Congress. In 2001, President George W. Bush banned federal funding of any research using new embryonic stem cell lines derived from embryos, regardless of their origin.
Now scientists may have discovered an alternative source. In early January researchers at Wake Forest and Harvard Universities reported that cells retrieved from amniotic fluid could be cultivated into stem cells in the laboratory and grown into any of the major cell types, including brain and nerve cells.
Amniotic fluid surrounds and protects the embryo in the womb, and as a fetus grows, it sheds a tiny number of the promising cells into the fluid. Cells from amniotic fluid are extracted by needle using a technique called amniocentesis, the same procedure routinely used for prenatal testing. Similar cells have also been isolated from afterbirth—the placenta and other membranes expelled by the mother after a baby is delivered.
“We've known for decades that both the placenta and amniotic fluid contain multiple … cell types from the developing embryo, including fat, bone, and muscle,” says Anthony Atala, M.D., director of the Institute for Regenerative Medicine at Wake Forest University School of Medicine in Winston-Salem, N.C., who led the research team. “We asked, ‘Is there a possibility that within this cell population we can capture true stem cells?’ The answer is yes.”
Although only a few potential cells are present in amniotic fluid, they grow much more quickly than those collected from embryos—their number doubles every 36 hours. They also do not cause tumors like other stem cells can, another important difference, he says.
Dr. Atala notes that if collected from amniotic fluid, frozen and preserved, cells from some 4 million children born in the U.S. each year could potentially provide genetically matched cells for treating any neurological disease or neuromuscular disorder—a lifetime of “replacement” cells that would be recognized as their own.
The team has already “grown” brain cells using cells from amniotic fluid. Injected into mice with a rapidly progressing degenerative brain disease, the cells repopulated the damaged areas and formed connections with healthy neurons nearby.
The cells also secrete glutamate, a crucial neurotransmitter in the brain and spinal cord. Glutamate plays an important role in memory and in the formation of dopamine, the lack of which causes motor symptoms in Parkinson's patients. They are also studying the cells in mice with an animal version of Alzheimer's disease, and are optimistic that the cells could also be used to re-grow nerves in patients with spinal injuries, says Dr. Atala.
“The full range of stem cells from amniotic fluid remains to be determined, but so far we've been successful with every cell type we've attempted to produce.”
Predicting any timeline for possible neurological treatments at this point is impossible, he says. “This is still the early research stage, but we're cautiously optimistic. We know patients are waiting.”