[media-credit name=’Sandy Huffaker/Newscom’ align=’alignnone’ width=’648′][/media-credit]All federally approved human embryonic stem-cell lines currently available are suspected to be contaminated with an animal molecule, suggesting stem-cell use in medical applications could be unsafe.

The use of mice “feeder” cells in laboratory culture is the typical method for growing stem cells. Since the first stem-cell lines were created, researchers have hypothesized a possible contamination from animal proteins.

“It was predicted there would be these kinds of issues,” said University of Wisconsin director of research communications Terry Devitt. “When you mix human cells with animal cells, there’s always a risk. These cell lines were never developed with the intention of [clinical use].”

The contaminated cell lines are still perfectly usable for research — as they have been since the beginning — and are still “incredibly valuable” cells for research, according to Devitt.

University of California researchers confirmed what scientists have predicted when they found their stem cells were contaminated with a substantial amount of mice protein, called N-glycolylneuraminic acid, or Neu5Gc for short. Their experimental results appeared Jan. 23 in the journal Nature Medicine.

Stem cells contaminated with Neu5Gc are a potential problem because humans could mount an immune response to the cells, making medical therapy very difficult.

“We have found that humans are making antibodies against Neu5Gc, presumably due to our exposure to this non-human molecule in dietary sources such as red meat and dairy products,” leader of the research team Dr. Ajit Varki said in an e-mail. “Thus, we predict that if [stem cells] or their derivatives grown under the current conditions were put into living humans, there is a significant chance of a deleterious immune reaction and/or rejection of the transplanted cells.”

UW professor of medical ethics Alto Charo said this is not new information but just provides a confirmation of researchers’ hypotheses concerning the stem-cell lines. Everyone knew the older lines, including UW’s, grew on mouse-feeder cells and could potentially not be useful for clinical research in the future, Charo said.

“In the future, we will be hoping to use [clean] cell lines to grow tissues for transplantation in humans,” Charo said.

Currently, federal funding is not available for the production of any new cell lines. The controversial decision by the Bush administration in 2001 restricting funding has some scientists worrying whether the potential applications of their own research will be affected.

UW professor of anatomy and neurology Su-Chun Zhang studies the applications of stem cells in neurology. Zhang said it would take much effort to start new cell lines, especially because of the federal restrictions.

“I’m not sure if people have the technique [to make clean cell lines] yet,” Zhang said. “Several groups [of researchers] are trying to establish ways to grow [stem cells] in a chemically defined environment without a need for feeder cells to support stem-cell growth, so then we wouldn’t have to deal with [contaminated stem cells].”