Stem Cell Injections Repair Spinal Cord Injuries in Mice
Tuesday, September 20, 2005
Mice with severe spinal cord injuries regained much of their ability to walk normally after getting injections of stem cells taken from the brains of human fetuses, scientists in California reported yesterday.
The work strengthens recent evidence that various kinds of stem cells -- including some from human embryos and others from fetuses -- have the capacity to nurse injured nerve cells back to health and in some cases even become replacement neurons themselves.
Scientists cautioned that the approach was not ready for testing in patients with spinal cord diseases or injuries. "This is a first step in what has to be a long series of steps to get to anything clinical," said Aileen Anderson, a neuroscientist at the University of California at Irvine, who led the latest work with colleague Brian Cummings.
But at least three companies are racing to become the first to inject their neural stem cells into patients, and some researchers say the first of those studies could begin within the next nine months.
Yesterday, StemCells Inc. of Palo Alto, Calif., whose cells were used in the new mouse study, filed an amended application to the Food and Drug Administration asking permission to start injecting the cells into the brains of infants with Batten disease, a fatal, inherited syndrome that destroys the central nervous system.
The new research, described in the Sept. 27 issue of the Proceedings of the National Academy of Sciences, tracked mice injected with a kind of human stem cells called neurospheres. They are the laboratory-grown progeny of human cells retrieved from the brains of 16- to 18-week aborted fetuses.
Nine days after getting identical spinal cord injuries, each animal received about 75,000 neurospheres in four injections around the injury.
Within a day, the team reported, the cells began to migrate into the injured spinal cord. After 16 weeks, the mice were given tests of agility and leg coordination, and compared with two other groups. Mice that had received the stem cells scored significantly better than similarly injured mice that had not -- and also better than those injected with ordinary skin cells, a test to see whether just any kind of cellular injection might trigger healing. Researchers who scored the tests did not know which mice had received the injections.
The differences were "obvious to the untrained eye," Anderson said, with improvements both in terms of how many weight-bearing steps the mice could take and their ability to place their rear feet precisely where needed to cross a ladderlike bridge.
Microscopic analysis showed that most of the injected cells had turned into two different kinds of cells around the injury, said Anderson, who does not have a direct financial stake in the company but whose team included two members who do. Some became oligodendrocytes, which wrap themselves around injured nerve cells to help them transmit electrical signals. Others turned into neurons themselves.
Very few turned into a third kind of central nervous system cell, astrocytes, which contribute to scar formation and are generally undesirable around injuries.
Moreover, the neurospheres that became new neurons appear to have made connections with nerve cells that survived the initial injury -- a crucial development if those new nerves are really to help.