In a study published online January 23, 2005 in the journal Nature Medicine, the researchers found that human embryonic stem cells, including those currently approved for study under federal funding in the U.S., contain a non-human, cell-surface sialic acid called N-glycolylneuraminic acid (Neu5Gc), even though human cells are genetically unable to make it. In a related paper published November 29, 2004 by the Journal of Biological Chemistry (JBC), the Varki group has also discovered the exact cellular mechanism by which this occurs.
In studies with one of the federally approved human embryonic stem cell lines, the investigators determined 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. All traditional culture-dish methods used to grow all human embryonic stem cells include animal-derived materials, including connective tissue cells (so-called "feeder layers") from mice and fetal calf serum.
"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," said both papers' senior author Ajit Varki, M.D., UCSD professor of medicine and cellular & molecular medicine, and co-director of the UCSD Glycobiology Research and Training Center.
The research in Nature Medicine was done with human embryonic stem cells grown in the laboratory of Fred Gage, Ph.D., professor, Laboratory of Genetics, the Salk Institute, La Jolla, California, an
Contact: Sue Pondrom
University of California - San Diego