- "Reseeding" lungs with stem cells could improve the success rate of lung transplants.
- The reseeded lungs tested by researchers successfully exchanged oxygen and carbon dioxide.
- There were complications, however, and more work is needed before the technique could be applied to humans.
"Reseeding" lungs with a patient's own stem cells before a transplant could save millions of lives.
Scientists from Yale University have developed a technique to remove all cells from a lung and then reseed the remaining connective tissue scaffold with a patient's own cells. The technique could be used with lung transplant patients.
"This is really the first paper that talks about engineering an entire lung that can be implanted and can exchange gas," said Laura Niklason, a scientist at Yale University and a co-author on the Science paper. "Previous work was scaled down... a far cry from engineering an entire tissue that a surgeon could pick up."
For now, the Yale scientists are only sewing reseeded lungs into rats, not humans.
Lung transplants are risky procedures. Given complications, organ rejection and other problems, the survival rate after 10 years is between 10 and 20 percent. But if a patient's own stem cells re-colonized the lung, the chance of organ rejection would drop dramatically, which should raise the long-term survival rate.
The first step toward saving human lives is by sacrificing a few rats. The scientists first removed four left lungs from four rats. Next, they bathed the lungs in a solution to destroy and then flush out all the living organic matter. Only a scaffold of connective tissue remained.
Next, the scientists injected lung stem cells into the trachea, and a slurry of lung vascular tissue into the artery leading into the lungs. One week later, the vascular and lung cells had re-colonized the connective tissue.
After removing the left lungs from a new set of rats, the Yale scientists implanted the reseeded lungs and compared them to their untouched counterparts. The reseeded lungs exchanged oxygen and carbon dioxide as well as the rats' original lungs.
The experiment was a success, but patients shouldn't start lining up at doctors offices just yet. After several hours, blood clots formed in the reseeded lungs, which would eventually kill a rat or person.
Niklason thinks this occurred because the lungs weren't fully reseeded. If the cells had been given more time, they would have successfully covered all surfaces inside the lung, and clotting would have been avoided.
Even so, there are other significant hurdles that must be overcome before human lungs can be grown. Niklason estimates it will take at least two decades for stem cell researchers to catch up with the best cells to reseed human lungs and, should that prove successful, to perform the necessary clinical trials.
Daniel Weiss, a scientist at the University of Vermont not involved in the research, agrees that at least 10 or 15 years and "a lot of work" remains before the lung reseeding technique could be used in humans. Nevertheless, Weiss is very excited by the new research.
"We are looking at millions of people worldwide dying because there is no cure (for diseases like emphysema and lung cancer)," said Weiss. "We desperately need a cure, and this gives us a lot of hope."
Lungs aren't the only organs that could be reseeded, said Weiss. Kidneys, liver, hearts and other organs could all potentially be reseeded with a patient's own cells, which are grown and then implanted into the patient to eliminate organ rejection.
"No one expected this to work so well, not even for a short amount of time," said Weiss. "This research will set the stage for years to come."