In E. B. White's classic children's story, Charlotte's Web, a rat named Templeton saves the life of a pig. So Wilbur the Terrific and Humble Pig might look kindly on research that uses pig olfactory cells to repair rat spinal cords. Eventually, pigs that have been engineered to inhibit tissue rejection might provide a source of cells for repairing human spinal cords as well.
Most research on repairing injured spinal cord has focused on nerve cells called glial cells. Some of these cells, called olfactory ensheathing cells, are especially promising because they assist nerve cells in the nose, where neurons are constantly being damaged and regrowing. In fact, injections of olfactory ensheathing cells stimulated nerve fiber growth in injured rats--enough to help them regain some mobility (Science, 26 September 1997, p. 2000 ).
Similar success in humans faces many obstacles, however. A big hurdle is a short supply of human glial cells to transplant. And although pigs have ample olfactory ensheathing cells, they include a protein that's attacked by immune cells in both rats and humans.
What might be able to sneak under the immune system's radar screen are modified pig cells. Pig cells engineered to express a human protein called CD59, for example, turn off the immune response that causes immediate tissue rejection. This encouraged neurobiologist Jeffrey Kocsis of Yale University and colleagues to test the cell's potential for repairing neurons. The team clipped the spinal cords of 10 rats and injected the engineered cells. After a month, neurons had regrown in seven spinal cords. Without treatment, rat spinal cords don't recover. The new nerves transmitted signals almost twice as fast as a normal cord, the researchers report in the September issue of Nature Biotechnology. "It's cool because ... we get very secure and rapid conductivity," Kocsis says.
Experts welcome the finding. "This study needed to be done," says neurobiologist Lars Olson of the Karolinska Institute in Stockholm, Sweden. The real value of the work, he adds, is its demonstration that pig cells can be transplanted into rats without being immediately rejected. "This work gives us some confidence that it would be possible to change pig cells enough" so that they aren't rejected by humans, he says.
Jeffrey Kocsis's lab