US stem cell research faces an uncertain near future after scientists reported that existing stocks of such cells are contaminated - and therefore useless for treating people - while the US administration has terminated federal funding for the extraction of fresh cells.
The contaminated cells are from batches collected prior to a George Bush 2001 executive order "restricting federal funding for stem cell research to only those batches of the cells that existed at the time", Reuters reports.
The problem is that current stocks have taken up a "non-human molecule called N-glycolylneuraminic acid or Neu5Gc" - probably when they were grown in a lab culture containing animal-derived materials from mice and calf foetuses. Neu5Gc is found on the surface of animal cells, but the human immune system attacks it - the major reason for transplanted animal organ rejection in humans.
Dr Ajit Varki of the University of California San Diego told Reuters: "The human embryonic stem cells remained contaminated by Neu5Gc even when grown in special culture conditions with commercially available serum replacements, apparently because these are also derived from animal products.
"It would seem best to start over again with newly derived human embryonic stem cells that have never been exposed to any animal products. However, such an approach could not be pursued under existing rules for the use of federal grant dollars."
The existing rules cited are designed to prevent the destruction of further embryos from which stem cells are extracted. The process has provoked considerable polemic in the US, with George Bush coming down firmly on the side of the antis. ®