For the first time scientists have reconstructed working lungs in the lab and transplanted them into a living animal.
The achievement is a breakthrough in biomedical engineering that could lead to replacement lungs for humans in the near future, experts say.
Currently, the only way to replace diseased lungs in adults is a lung transplant, a high-risk procedure that's vulnerable to tissue rejection.
In a new study, researchers took lungs from a living rat and used detergents to remove lung cells and blood vessels, revealing the organ's underlying matrix.
This lung "skeleton"—made of flexible proteins, sugars, and other chemicals—consists of a branching network that divides more than 20 times into smaller and smaller structures. (See an interactive graphic of lung structure.)
The researchers placed these "decellularized" lungs into a bioreactor, a machine filled with a slurry containing different types of lung cells extracted from rat fetuses.
(Related: "Scientists Grow Lung Cells From Stem Cells.")
Within several days, the fetal cells naturally attached to the lung matrix and formed a functional lung.
"By and large, the correct subsets of cells went to their correct anatomical locations," explained study leader Laura Niklason, a biomedical engineer at Yale University. "It appears that the lung matrix has cues, or 'zip codes,' that tell the cells where to land."
When the team implanted the engineered lungs into an adult rat for short periods of time—between 45 minutes and two hours—the lungs exchanged oxygen and carbon dioxide in the same way as natural lungs.
By using a natural lung matrix, Niklason's team has avoided one of the biggest hurdles of lung-regeneration attempts—finding a suitable "scaffold" for lung cells to attach to.
Because manufacturing techniques cannot yet replicate nature's complex design, attempts to create synthetic scaffolds have been unsuccessful.
Niklason spent several years trying to create a synthetic lung scaffold, but in the end concluded it was too difficult.
"I decided I couldn't do it, and probably nobody else could either," she said.
The new research represents a "real leap forward" in lung regeneration, said Peter Lelkes, a biomedical engineer at Drexel University in Philadelphia.
"People have engineered organs such as bone and cartilage before, but by comparison to the lung, these are all kids' games," added Lelkes, who was not involved with the study.
Stem Cell Hurdle
Niklason estimates it will be about 20 to 25 years before her team's technique can be used in humans.
That's because a few technical and scientific challenges remain.
Chief among these is finding ways of creating stem cells—which can transform into any other type of cell—from patients with lung disease. No techniques currently exist for creating such cells, which would carry no risk of immune rejection.
(Related: "Liposuction Fat Turned Into Stem Cells, Study Says.")
"The stem cell issue," Niklason said, "is really the big fundamental scientific hurdle."
The research is detailed in this week's issue of the journal Science.