Stem Cell Injections Repair Spinal Cord Injuries in Mice

In a test to see whether the new human cells were really key to the animals' recovery, the team gave some of the recovering mice injections of a toxin that selectively kills human cells. The mice that got the injections regressed in their ability to walk, while those not injected continued to improve.

Two other U.S. companies also say they are close to the goal of testing human neural stem cells as therapies.

Earlier this year, Hans Keirstead and his colleagues, also at the University of California at Irvine, reported that rats with disabling spinal injuries could walk nearly normally again after getting injections with human embryonic, rather than fetal, cells developed by Geron Corp. of Menlo Park, Calif.

Those cells were initially harvested from days-old human embryos and then cultivated under special laboratory conditions that forced them to become immature oligodendrocytes. Once injected into injured spinal cords, the cells matured and wrapped themselves around injured neurons, which often lose those natural coverings as a result of injury-induced inflammation, leaving even intact neurons unable to function properly.

Geron has said it hopes to begin clinical trials in patients next year.

A third company, NeuralStem Inc. of Gaithersburg, is also in the race.

In unpublished research, rats with spinal cord damage improved significantly after getting injections of human fetal spinal cord cells, said neuroscientist Martin Marsala of the University of California at San Diego, who led the studies with NeuralStem's cells. The animals had ischemic paraplegia, a paralysis of the lower body and rear limbs caused by a temporary blockage of blood flow to the spine.

Patients with this syndrome, which can occur when one of the body's large arteries bursts, are not only paralyzed but also suffer from spastic twitches because of the loss of a kind of neuron that normally suppresses those movements. In rat and pig studies, about one-third of the human fetal cells morphed into exactly that type of neuron, resulting in far less spasticity, Marsala said.

NeuralStem has been talking with the FDA with the aim of getting the go-ahead to begin human testing next year.

The FDA has said several questions will have to be answered before such tests can go forward, including whether some stem cells might turn into the wrong kinds of cells after being injected.