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.

US stem cell research in jeopardy