Stem cells float in amniotic fluid.

Scientists have discovered a new type of stem cell in the fluid that bathes fetuses in the womb. These cells can grow into a variety of body tissues, the researchers report.

Scientists have long known that cells from fetuses float in amniotic fluid. Such cells are frequently used for genetic tests to predict a baby's health. However, Anthony Atala of the Wake Forest University School of Medicine in WinstonSalem, N.C., and his colleagues wondered whether some of the fetal cells in amniotic fluid are stem cells.

Using amniotic fluid drawn from expectant mothers when they had amniocentesis, the researchers searched for cells with surface proteins that are typically present on embryonic stem cells. The researchers found that about 1 percent of the cells had these markers.

Further investigation showed that the cells with these embryonic stem cell proteins also had other proteins on their surfaces that are typically present on adult stem cells. No other stem cell has been found to contain both sets of markers, Atala notes.

Under certain conditions, the newly discovered cells develop into cartilage, muscle, heart, bone, liver, and other types of tissue, the researchers report in the January Nature Biotechnology. Transplants of the stem cells might eventually treat patients who have diseased or damaged tissues, says Atala.