The findings, which have been published in the journal Nature Biotechnology, could help advance efforts to repair tissue and engineer organs, the scientists say.

The results show scientists were able to successfully isolate potential stem cells from the amniotic fluid that surrounds developing embryos, a breakthrough which they hope will advance efforts to repair tissue and engineer organs.

The cells have already been used in mice to grow neural cells in subjects with degenerative brain disease, to grow bony tissue and liver cells were able to secrete urea, which the liver produces from ammonia.

The researchers discovered a small number -- one per cent -- of stem cells in the amniotic fluid that surrounds developing embryos that can give rise to many of the specialized cell types found in the human body.

"It has been known for decades that both the placenta and amniotic fluid contain multiple progenitor cell types from the developing embryo, including fat, bone, and muscle," said Dr. Anthony Atala, senior researcher and director of the Institute for Regenerative Medicine at Wake Forest University School of Medicine.

"We asked the question, 'Is there a possibility that within this cell population we can capture true stem cells?' The answer is yes," said Atala, who began the work seven years ago.

Atala made the announcement along with his colleagues at the medical school, and the Harvard Medical School. They refer to the stem cells as amniotic fluid-derived stem (AFS) cells.

"It took this long to verify that we had a true stem cell," said Atala. "These cells are capable of extensive self-renewal, a defining property of stem cells. They also can be used to produce a broad range of cells that may be valuable for therapy."

According to the report, the stem cells were obtained from fluid that would otherwise be discarded.

"We have demonstrated that stem cells can be obtained routinely from human amniotic fluid, using backup cells from amniocentesis specimens that would otherwise be discarded. The AFS cells grow easily in culture and appear phenotypically and genetically stable," the report states.

The cells are also capable of extensive renewal, a defining property of stem cells, according to the study.

They also do not require guidance from other cells and don't produce tumours -- which can occur with other types of stem cells.

So far, scientists have generated the three types of stem cells found in developing embryos, termed ectoderm, mesoderm and endoderm. And they haven't yet discovered the limit of what the AFS cells can do.

"So far, we've been successful with every cell type we've attempted to produce from these stem cells. The AFS cells can also produce mature cells that meet tests of function, which suggests their therapeutic value," Atala said.

Many scientists believe stem cells hold the potential to replace damaged cells and tissue in conditions such as spinal cord injuries, diabetes, Alzheimer's disease and stroke.

An advantage of these AFS cells is their ready availability for potential medical applications. Another benefit is that these cells grow in large quantities as they typically double every 36 hours.

The report describes how the cells were harvested from backup amniotic fluid specimens obtained for amniocentesis, a prenatal procedure that examines cells in the fluid to search for certain genetic disorders.

Similar stem cells were also isolated from "afterbirth," the placenta and other membranes that are expelled after delivery.

Atala thinks a bank with 100,000 specimens could potentially supply 99 per cent of the U.S. population with perfect genetic matches for transplants.