The human embryonic stem cell lines currently available have been contaminated with a non-human molecule that endangers their potential therapeutic use, researchers say.

The human embryonic stem cells, including those currently approved for study under US federal funding, contain a non-human, cell-surface sialic acid called N-glycolylneuraminic acid (Neu5Gc), researchers at the University of California San Diego (UCSD) say, reports Xinhua.

In a study published in the on-line version of the journal Nature Medicine, the researchers found that the Neu5Gc is incorporated by the stem cells when they are grown or derived from laboratory cultures that contain animal sources of the non-human Neu5Gc molecule.

The investigators led by UCSD professor Ajit Varki determined that the human embryonic stem cells remained contaminated even when grown in special culture conditions with commercially available serum replacements, apparently because these are also derived from animal products.
 
In the paper, the scientists said the human embryonic stem cells contaminated with Neu5Gc could easily be attacked by human antibodies, and thus rendering them useless as a potential therapeutic tool in humans.

Varki and his team noted that many efforts have been made during the last few years to try to eliminate any animal-derived culture components in human stem cell culture.

However, most specialised media used for growth and differentiation still contain materials from animal sources and are hence contaminated.

The researchers suggested the possibility of using cells from mice with a human-like defect in Neu5Gc production. Another possibility being attempted by groups in other parts of the world is to use human embryo-derived connective tissue cells in the culture.