In a major landmark for bioengineering, lungs that were made in the lab have been successfully implanted into pigs for the first time, enabling them to breathe normally. They have not yet been hooked up to a crucial artery, but the team behind the work are hopeful.
“I would argue this is the first time that a tissue-engineered organ has been implanted in a large animal and shown to survive and have any degree of function whatsoever,” says Laura Niklason at Yale University, who was not involved in the work.
To make these lungs, Joan Nichols and Joaquin Cortiella at the University of Texas Medical Branch at Galveston used growth hormones to encourage pig lung cells to grow into tissue, populating a de-cellularised pig lung.
Advertisement
When you de-cellularise an organ, you’re left with a kind of skeleton. The airways throughout the lungs branch 23 times and end in small, grape-like air sacs just 200 microns across. These globules mediate the transfer of oxygen and carbon dioxide into and out of your blood. In lungs, a scaffold of collagen and elastin proteins remains after decellularisation. “The collagen makes it strong so you can breathe for your whole life, and the elastin makes it stretch so you can breathe in and out,” Nichols says.
She and her colleagues used a sugar-detergent solution to strip the cells from the scaffold, leaving behind the protein matrix. The sugar helps tighten up the proteins so they aren’t removed by the detergent along with the cells. “It’s just like using dish detergent on a plate to get rid of fat left behind,” she says.
Growing lungs
Over 30 days, they grew new blood vessels on the lung in a sealed chamber, and then implanted the lungs into four pigs. The pigs didn’t need immune system suppression drugs, because the lungs were grown from their own cells. The team saw no rejection of the organs in the pigs.
By two weeks after surgery, they detected blood circulation in the bio-engineered lungs, and measured similar tissue density as in a natural lung. Their measurements showed that the lungs also had normal pressures and volumes, though one pig developed a partial airway blockage that reduced lung expansion. Gene expression was also similar between the artificial and natural lungs.
As the animals grew, the total number of cells in their bio-engineered lungs increased and they spread to fill in any holes, letting them fully support blood flow. Nichols says they chose to test these organs on pigs because they grow quickly and the team wanted to be sure their organs would grow with the animal, as it may need to in a human.
[video_player id=”33vfc0dA” access_level=”everyone”]
Oxygenating blood
But although they implanted the artificial lungs, which became supported by the animals’ blood vessels and able to breathe, the team didn’t connect the organs to the pulmonary artery. This blood vessel delivers non-oxygenated blood to the lungs, and the main function of the lungs is to give this blood oxygen. Until such bioengineered lungs have been hooked up to the pulmonary artery, we can’t know how well they work.
Having established that bioengineered lungs can breathe and grow, Nichols is now looking ahead to future studies that test their ability to oxygenate blood from the pulmonary artery. If successful, the hope is that we will one day be able to grow new human lungs from our own cells.
“Like those sci-fi movies where someone gets a heart that was grown for them, that’s what we’re looking at. There’s no waiting on – or dying on – a transplant list, and the tissue will match well enough that a person won’t have to be immunosuppressed to accept the organ,” Nichols says.
Science Translational Medicine
Read more: World’s first biolimb: Rat forelimb grown in the lab
