Researchers in Boston say they have found the first human lung stem cells, an exciting discovery that might one day allow doctors to repair damaged lung tissue in patients with emphysema and other lung diseases.

So far, the research has just been conducted on mice. But researchers at Brigham and Women's Hospital say what makes their discovery so exciting is that the stem cells they found appear capable of forming into any kind of lung tissue.

"The discovery of this stem cell has the potential to offer those who suffer from chronic lung diseases a totally novel treatment option by regenerating or repairing damaged areas of the lung," Dr. Piero Anversa, director of the Center for Regenerative Medicine at Brigham and Women's said in a news release.

While adult stem cells have been found in all sorts of other tissues, such as bone marrow and skin, such a versatile cell has never been found in the lung.

According to their report in the New England Journal of Medicine, the Boston researchers identified and isolated the human lung stem cells using lung tissue taken from surgeries.

They tested the cells in their lab and found that they were capable of dividing both into new stem cells and also into cells that would grow into various types of lung tissue, such as airways called bronchioles, air sacs called alveoli and blood vessels.

Next, the researchers injected the stem cells into 29 mice with damaged lungs. As hoped, the injected stem cells led to the construction of new lung tissue in all the mice.

The cells not only formed new lung tissue, but that tissue also integrated itself seamlessly into the mice's existing lung tissue, replacing the damaged tissue with new tissue.

One key hole in their research, though: the team was not able to determine whether the new tissue in the mouse lungs was functional.

But the team did find that the new lung cells were transmissible, meaning that after a mouse responded to the injected stem cells by generating new tissue, researchers were then able to isolate the stem cells in a treated mouse, and use those cells in a new mouse with the same results.

While the research has just been performed in animals so far, the researchers appear excited by the possibility of repairing otherwise irreparable lung tissue.

"These are the critical first steps in developing clinical treatments for those with lung disease for which no therapies exist," said Dr. Joseph Loscalzo, chair of the Department of Medicine at BWH and a co-author of the study, said in a statement.

"Further research is needed, but we are excited about the impact this discovery could have on our ability to regenerate or recreate new lung tissues to replace damaged areas of the lungs."

In comments made to the Associated Press, Loscalzo said it's too early to tell what lung diseases might one day be treated with the cells. He said researchers are initially looking at emphysema and a type of high blood pressure called pulmonary hypertension.

Some scientists expressed cautious optimism but suggested the team's research needs further scrutiny.

"Elements of the extensive experiments reported here are sure to be controversial, and some may even prove to be incorrect,'' Dr. Harold Chapman — a professor in the division of pulmonary and critical care medicine at the University of California, San Francisco — wrote in an editorial accompanying the paper.

"But the essential finding... is convincing."

Dr. Kenneth Chien, a stem cell biologist at Massachusetts General Hospital and the Harvard Stem Cell Institute told the Boston Globe: "…the technology being used has its own inherent limitations, which may make it difficult to draw firm conclusions and has led to difficulties in others easily replicating the work of the group."