Stem cells taken from amniotic fluid can be transformed into a more versatile state similar to embryonic stem cells and may offer an alternative to the medically valuable but controversial cells, scientists said on Tuesday.
British researchers said they had succeeded in reprogramming amniotic fluid cells without having to introduce extra genes.
This suggests the possibility that stem cells derived from donated amniotic fluid could be stored in banks and used for medical therapies and in research, they said, offering a less problematic alternative to embryonic stem cells.
Stem cells are the body's master cells, the source for all other cells. Scientists say that by helping to regenerate tissue, they could offer new ways of treating diseases for which there are currently no treatments - including heart disease, Parkinson's and stroke.
Embryonic stem cells are harvested from embryos and have the potential to become almost any type of tissue. Other types of stem cells, including adult or so-called "induced pluripotent" stem cells, are less controversial, but are also less flexible.
Alternatives to embryonic stem cells are always being keenly sought, partly due to ethical concerns and also due to the limited availability of donor embryos.
In this study, published in the journal Molecular Therapy, scientists from Imperial College London and University College London's (UCL) Institute of Child Health said amniotic fluid stem cells are an intermediate between embryonic and adult stem cells.
"They have some potential to develop into different cell types but they are not pluripotent," said Pascale Guillot, from the Imperial's department of surgery and cancer.
But he said their study had shown that these cells can revert to being fully flexible, or "pluripotent", by adding a chemical that modifies the configuration of the DNA.
Guillot's team used stem cells from amniotic fluid donated by mothers who had undergone amniocentesis tests during the first trimester of a pregnancy.
The cells were grown on a gelatinous protein mixture in the lab and reprogrammed into a more primitive state by adding a drug called valproic acid.
The researchers then carried out a series of tests and found the reprogrammed cells had become pluripotent - in other words they had very similar properties to embryonic stem cells.
The team also found that even after they had been growing in culture for some time, the reprogrammed cells were able to develop into many different types of functioning cells, including liver, bone and nerve cells.
They also maintained their pluripotency even after being frozen and then thawed out.
UCL's Paolo De Coppi, who co-led the study with Guillot, said the study confirmed that amniotic fluid is a good source of stem cells.
Previous research has shown it is possible to make adult cells become pluripotent by introducing extra genes into the cells, often using viruses.
But the efficiency of this type of reprogramming is relatively low and there is a risk of problems caused by disrupting the DNA.
"The advantages of generating pluripotent cells without any genetic manipulation make them more likely to be used for therapy," De Coppi said.
Amniotic fluid surrounds and helps feed and protect the growing baby in the womb. It can be extracted through the mother's belly using a fine needle in a process called amniocentesis which is sometimes used to test for genetic diseases during early pregnancy.