Published in the April 2005 issue of the journal Stem Cells, the study shows that laboratory culture media enriched by a human protein called activin A are capable of maintaining human embryonic stem cells in a continuous undifferentiated state, ready for research. Undifferentiation means the stem cells have not begun the developmental path to become specific human tissue or organs.
"Our findings provide a new way to generate human stem cell lines without contamination by animal cells or products," said the study's senior author, Alberto Hayek, M.D., UCSD professor of pediatrics and director of the Islet Research Laboratory at the Whittier Institute.
Currently, stem cell lines derived from human embryos are grown and nourished in petri dish material called feeder layers that are made with animal connective tissue, primarily mouse and calf. A recent study in Nature Medicine** by UCSD's Ajit Varki, M.D. showed that human embryonic stem cells grown in this animal-derived tissue become contaminated with a non-human molecule called Neu5Gc. If these stem cells were to be transplanted into people, they would provoke an immune system attack eliminating their therapeutic value.
While several laboratories have attempted to grow stem cells in alternative cultures, problems have remained. In some cases, human feeder layers were developed but this added another measure of complexity to the culture system, Hayek noted. In recent studies in Wisconsin and Massachusetts, new feeder layers were developed, but they did not entirely eliminate the use of animal products. In the Hayek study, the animal-derived feeder layers are completely eliminated. However, the petri dishes themselves are coated with laminin