Every year, lung transplants help thousands of patients stay alive, but the system is far from perfect. The average wait time for a new lung is three to six months and can sometimes be years.

Further, when a new transplant does become available, it may not be an ideal fit for a patient’s body. Typically, a surgeon must manually adjust the size of the lung to match the patient—an opportunity for complications to arise. And even after a successful transplant surgery, patients have to take immunosuppressant drugs their entire lives to ensure their bodies don’t reject the new lung.

To overcome these challenges, internist Joan Nichols and her colleagues at the University of Texas Medical Branch have spent years finding ways to engineer a lung from scratch in the laboratory, using donated cells. Theoretically, these lungs could be custom-built for each patient, solving both wait-time and compatibility problems. In early trials, though, these lungs have failed to keep donee animals alive for more than a few hours; the engineered organs couldn’t replicate the complexity of the blood vessels that enable the transfer oxygen to the blood stream. Until now.

On Wednesday, Aug. 1, Nichols and her team published (paywall) work in Science Translational Medicine showing that lungs created from pigs could be successfully transplanted into the animals for long periods of time. And it appeared that the engineered lungs were successfully providing oxygen to their blood, and were correctly growing the network of tiny blood vessels in the organ tissue.

The team reports first surgically removing one lung from four pigs, animals with relatively similar organ compositions as humans. After a month, the four pigs received a bioengineered second lung created from pig cells and extra protein scaffolding as a way of coaxing the cells to grow in the proper shape. Because this was a novel study, the team was focused on the early stages of the organ’s development after the transplant. Each pig was euthanized at various points in time following the transplant so that researchers could see how the lab-built lung developed. Throughout, the tissue appeared to adapt to its new environment, and did not show signs of any of the normal complications of growing into a new body, like forming blood clots. All the pigs had normal oxygen levels throughout the duration of the experiment. The team euthanized the last pig two months after the transplant.

The next steps will be trying again, this time keeping the pigs alive for longer, to see how bioengineered lungs hold up over time. If so, it would add evidence to the argument that a similar engineering technique could be feasible for human recipients in the (relatively) near future.