Cells may cause immune system attack, a study says.
LOS ANGELES TIMES
All human embryonic stem cell lines approved for use in federally funded research are contaminated with a foreign molecule from mice that may make them risky for use in medical therapies, according to a study released Sunday.
Researchers at the University of California, San Diego and the Salk Institute for Biological Studies in La Jolla, Calif., report that if the stem cells are transplanted into people, the cells could provoke an immune system attack that would wipe out their ability to deliver cures for diseases such as Parkinson's, Alzheimer's and diabetes.
The finding is a setback to the Bush administration's controversial policy that only provides federal funding for research using a limited number of embryonic stem cell lines already in existence.
The scientists say it could take at least a year or two -- if it is possible at all -- to find a way to salvage the stem cells by wiping them clean of the mouse molecules.
"We don't know, but I'm trying to be optimistic," said Fred H. Gage, a professor of genetics at the Salk Institute who coauthored the paper in the current issue of Nature Medicine.
Create new batches
The researchers said the safest course is to create fresh batches of stem cells that are free of contamination from animal molecules -- a process that could also take years.
That strategy would bolster the influence of the California Institute for Regenerative Medicine, a $3 billion funding agency established by voters last November specifically to circumvent the Bush restrictions.
"This is why [the ballot initiative] is so important," said Susan Fisher, a University of California, San Francisco professor of cell and tissue biology who studies stem cells. "We will be able to do this basic research to be able to really produce a strong foundation on which this work can continue."
When the Bush-approved stem cells were first isolated, they were grown in petri dishes lined with cells from mice and bathed in blood serum from calves and other animals. The animal material was used to encourage the stem cells to multiply while preserving their unusual ability to mature into any kind of human cell.
This "pluripotency" is why embryonic stem cells have been so tantalizing to both researchers and patients. Doctors could treat patients with juvenile diabetes by growing replacements for their faulty islet cells, which fail to make insulin. Stem cells could also be directed to become oligodendrocyte cells to insulate nerve fibers in patients with spinal cord injuries so that electrical signals could once again travel to their limbs.
Researchers have suspected that exposing the stem cells to animal products could have contaminated them with viruses, proteins or other molecules that could be dangerous to people.
Now they have evidence that it did.
According to the study published Sunday, human stem cells have incorporated a type of sialic acid that is common in many mammals but isn't produced by people.
When the acid, named Neu5Gc, enters the human body -- typically by eating meat or drinking milk -- antibodies rush to attack it.
Dr. Ajit Varki, a professor in UC San Diego's department of cellular and molecular medicine, questioned whether stem cells containing the acid would also be vulnerable to attack if transplanted into humans.