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.

Pluripotent

"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.