A Californian team reported that the "presidential" lines, from which American researchers are attempting to derive nerve, islet and other types of stem cells to repair a damaged body, have been contaminated with a non-human molecule that makes them unsafe to use in patients.
They contain a foreign substance, called N-glycolylneuraminic acid (Neu5Gc), even though human cells are genetically unable to make it.
Prof Austin Smith, Director of the Institute for Stem Cell Research, University of Edinburgh, said: "This paper illustrates why existing cells are of limited utility and why we need to derive new human embryonic stem cell lines under better defined conditions."
The full version of the paper is to appear in Nature Medicine; a PDF file is currently available. It concludes:
None of these approaches guarantees the complete elimination of Neu5Gc (or any other unknown animal antigen or pathogen) from existing cultures. Therefore it would seem safest to start over again with newly derived HESC that have never been exposed to any animal products conatining Neu5Gc (and ideally, only ever exposed to serum from the intended transplant recipient). The current regulatory climate in the United States precludes this type of approach, when using federal grant dollars.