The stem cell lines available for federally-funded research in the US have characteristics which mean they may never be used for medical treatments in humans, a new study suggests.Fred Gage at the Salk Institute in La Jolla, California and Ajit Varki at the University of California, San Diego, US, have shown that human embryonic stem cells (hESC) cultivated on a scaffolding of mouse “feeder” cells take on the properties of the rodent cells. Consequently, if implanted in a human they would provoke an immune response that would kill the hESCs, they say.The finding reinforces calls by US stem cell researchers for their government to free up federal money to research fresh lines of human ESCs, grown on non-biological scaffolds.Stem cell research in the US is currently limited to 22 lines, following a policy introduced by President George W Bush in 2001. These lines were derived before August 2001 and all of the cells were grown on a scaffolding of mouse cells.“It’s a new twist on why it can’t be done,” says Richard Hynes, a biologist at the Massachusetts Institute of Technology and a member of the National Academy of Sciences’ committee on guidelines for human embryonic stem cell research.
