Living on borrowed legs.

Entire legs--skin, muscle, bone blood vessels and nerves--have been successfully transpanted between laboratory rats with the aid of the immunosuppressant drug cyclosporine, researchers report. While the rats showed no coordinated leg movements, such as walking, with a newly acquired leg, they did demonstrate some simpler actions, such as withdrawing a leg from a stimulus. Some transplanted legs remained viable for more than a year, until the recipients died of old age.

"This research could a spark a revolution in transplant surgery," says Kirby S. Black, who with Charles W. Hewitt, David Furnas and Bruce Achauer conducted the experiments at the University of California at Irvine. "For the first time we have shown that tissue of this kind [a composite of different types of tissues] can be transplanted for long terms of survival in animals."

The scientists are using the rat limb as a model system for the transplantation of composite tissues, says Hewitt. They want to go beyond limb transplants to the use of such blocks of tissue to correct congenital anomalies and for reconstructive surgery after burns and after surgical removal of massive tumors.

The procedures for transplanting rate legs are similar to those used to reattach limbs of human accident victims. "We hook up bones, muscle, nerve and skin and do vascular surgery," Hewitt says. In rats, this takes about three h ours.

The experiments focused on the use of cyclosporine, an immunosuppressant widely used in human kidney, heart-lung, bone marrow, pancreas and liver transplants. Black, Hewitt and their colleagues demonstrated that surprisingly low doses were effective in the rat limb transplants. In addition, they found that in several cases the rats did not reject their new limbs even when the drug was gradually discontinued. In contrast, human transplant patients continue taking cyclosporine all their lives.