SUNDAY, Jan. 7 (HealthDay News) -- Scientists on Sunday reported the discovery of a new source of human stem cells that have the capability to develop into many different types of cells, including muscle, bone, fat, blood vessel, nerve and liver cells.

These stem cells, found in amniotic fluid, could one day lead to a readily available supply of stem cells that don't come with the ethical problems surrounding embryonic stem cells.

"These cells are easier to get, and from acceptable medical procedures [for example, amniocentesis] that are done on a routine basis," said study senior author Dr. Anthony Atala, director of the Institute for Regenerative Medicine at Wake Forest University School of Medicine.

"This is another source of multi-potential cells," added Paul Sanberg, director of the University of South Florida Center for Aging and Brain Repair, in Tampa. "Because the cells can be accessed either post-birth or through amniocentesis, it's possible that people could store those cells. If the cell lines that are created were available, then people could do some research on a non-embryonic source, which eliminates all the ethical and political issues."

The discovery of the cells, known as amniotic fluid-derived stem (AFS) cells, is reported in the Jan. 7 issue of Nature Biotechnology.

The hope is that stem cells, which have the potential to develop into many different cell types in the body, may one day yield treatments or cures for diseases such as diabetes, liver failure, spinal injury, stroke, Alzheimer's disease and heart disease.

But embryonic stem cell research in the United States has been severely hampered since Aug. 9, 2001, when President Bush placed limits on federal funding of the field. As of that date, federal funds could only be used to study stem cell lines derived from embryos that had been destroyed before that date.

Scientists have thus been on a quest to find new, less controversial sources of stem cells.

It's been known for decades that the placenta and amniotic fluid contain a large number of cells shed from the developing embryo. "These cells could be harvested, grown outside the body and used," Atala said.

Unlike "true" stem cells, however, these cells were predestined to grow into only one type of cell, or a limited type of other cells.

"We wanted to see if there was a true stem cell population within this fluid, pluripotent stem cells which could give rise to multiple cell types," Atala explained. Pluripotent cells are capable of differentiating into many different types of cells.

After seven years of digging, Atala's team found that 1 percent of the amniotic fluid cells were pluripotent. The newly discovered cells seem to possess characteristics that rest halfway between embryonic stem cells and adult stem cells. Like other stem cells, they can self-renew and double in number every 36 hours. But unlike other stem cells, they do not produce tumors.

The stem cells could be harvested any time from the beginning of pregnancy until just after a baby is born, Atala said.

When nerve cells created from AFS cells were implanted into mice with a degenerative brain disease, the cells re-populated the diseased areas of the brain. Bone cells were also successfully grown into bony tissue in mice, and liver cells were grown that could secrete urea.

But it will be some time before any human benefit from these cells is seen -- if it is seen at all, the researchers said.

"It's a very nice paper, very good science," said Dr. Darwin Prockop, director of the Center for Gene Therapy at Tulane University Health Sciences Center in New Orleans. "But I can't quite put a circle around the potential of the cells. They may be useful for some kinds of therapy but I don't quite know where it's going to go."

Theoretically speaking, Atala said, a bank of 100,000 specimens could potentially supply 99 percent of the U.S. population with a perfect genetic match for transplantation.

But human studies haven't even begun yet.

"We don't know what the extent of therapy will be with these cells," Atala said. "Time will tell."

More information

The U.S. National Institutes of Health has more on stem cells, including current official policy.