Mice discovered accidentally at the Wistar Institute in Pennsylvania have the seemingly miraculous ability to regenerate like a salamander, and even regrow vital organs.

Researchers systematically amputated digits and damaged various organs of the mice, including the heart, liver and brain, most of which grew back.

The results stunned scientists because if such regeneration is possible in this mammal, it might also be possible in humans.

The researchers also made a remarkable second discovery: When cells from the regenerative mice were injected into normal mice, the normal mice adopted the ability to regenerate. And when the special mice bred with normal mice, their offspring inherited souped-up regeneration capabilities.

The mice, known as the MRL strain, were specially bred to develop lupus. But researchers don't know why exactly the animals' injuries heal so well.

"If we identified the molecules that allow mice that don't regenerate to regenerate ... and I think we could be close to doing that, then I think the next step is to consider what these molecules would do in individuals," said Ellen Heber-Katz, a professor of molecular and cellular oncogenesis at Wistar, located on the University of Pennsylvania campus in Philadelphia.

Heber-Katz discovered the strain in 1998 accidentally while working with mice specially bred for studying autoimmune diseases.

She had pierced holes in the ears of the genetically altered mice to distinguish them from a control group, but they healed quickly with no scarring.

She and her colleagues wanted to find out what other parts of this strain of mice would grow back, so they snipped off the tip of a tail, severed a spinal cord, injured the optic nerve and damaged various internal organs.

The incredible wound-healing they observed abruptly shifted the focus of Heber-Katz's lab's research from autoimmune disease to regenerative medicine. The researchers began hunting for the specific genes that gave the mice their special powers. They are focusing on three specific genes at the moment, but she suspects that many more likely contribute to the regenerative abilities.

While some amphibians can regrow body parts, mammals for the most part do not have that ability, making this a very special mouse indeed. If the results can be translated to humans, it would be a dream come true for people who want to live forever.

"When those genes (responsible for the mice regeneration) are found, we can start to think about manipulating them in humans with drugs or (later) gene therapy, thereby enhancing our own regeneration," said Aubrey de Grey, a longevity expert and editor of the scientific journal Rejuvenation Research.

Other labs have also begun to join the investigation.

The mice seem to exhibit regenerative capabilities similar to that of human fetuses in the first trimester, said Dr. Stephen Badylak, a surgery research professor and director of the Center for Pre-Clinical Tissue Engineering at the University of Pittsburgh's McGowan Institute for Regenerative Medicine.

"It offers us insight into a more fetal-like healing response, where scar tissue is minimal and regeneration is abundant," Badylak said. "It's a great model to examine healing mechanisms and use that information to see if we can stimulate the same thing to happen in people."

Heber-Katz said she will soon publish her results on digit regrowth in a peer-reviewed medical journal.

Heber-Katz presented new data showing that the strain of mice can also grow back severed digits at the Strategies for Engineered Negligible Senescence conference in Cambridge, England. ("Engineered negligible senescence" is a fancy term for life extension.)