Surgeons have successfully transplanted a pig lung into a human, marking another huge step in the decades-long quest to use animal organs for life-saving procedures.
In the first operation of its kind, the genetically modified pig lung was transplanted into a 39-year-old brain-dead male following a brain hemorrhage.
Amazingly, the organ remained 'viable' and functional over a period of nine days - suggesting humans could one day live with transplanted pig lungs.
The scientists, from the Guangzhou Medical University in China, say their work is the first documented instance of cross-species lung transplantation.
'Genetically engineered pig lungs have not previously been transplanted into humans,' say the scientists.
'[Our study shows] pig lungs can maintain viability and functionality in brain-dead recipients for 216 hours.'
Humans have survived for short periods with implanted pig hearts and kidneys - but never before pig lungs.
However, as it stands, humans living healthy lives with transplanted pig lungs could still be decades away.
The genetically modified pig lung remained viable and functional over a period of nine days.
The remarkable procedure, detailed in a new paper published in Nature Medicine, 'demonstrates the feasibility of pig-to-human lung xenotransplantation'
The study represents a significant step for 'xenotransplantation', which involves transplanting organs from one species into another.
Previous studies have demonstrated the feasibility of transplanting kidneys, hearts and livers from gene-edited pigs into humans.
However, the transplantation of lungs is a much bigger challenge, due to their fragility, complexity and exposure to toxins from air in the outside world.
As a result, the team had to make gene edits to a Chinese Bama Xiang pig from which its left lung was obtained.
Gene editing tool CRISPR was used to remove the antigens that could activate the human immune system following the transplantation.
CRISPR, an innovative but controversial technique, makes precise cuts in DNA and then harnesses natural DNA repair processes to modify the gene in the desired manner.
Next, the lung was transplanted into the human recipient who had been declared brain dead - and therefore considered officially deceased.
A person who is brain dead is legally confirmed as dead, even if a life support machine keeps their heart beating and their lungs inhaling air.
The experts found that the lung was not immediately rejected by the immune system and maintained 'viability and functionality' over the course of nine days.
However, they observed signs of lung damage at 24 hours after transplantation and signs of 'antibody-mediated rejection' (AMR) of the lung at days three and six after transplantation.
As a result of AMR - where the recipient's immune system makes antibodies that target their transplanted organ - the experiment was terminated on day nine.
Nevertheless, the remarkable procedure, detailed in a new paper published in Nature Medicine, 'demonstrates the feasibility of pig-to-human lung xenotransplantation', the team say.
The results also demonstrate how xenotransplantation could address the worldwide organ shortage crisis.
Promisingly, the pig is very similar to humans in terms of anatomy; so the species is used generally as a model for developing new treatments.
However, substantial challenges relating to lung rejection and infection remain, the team caution in their new paper.
Unlike kidneys or hearts, the high blood flow and external air exposure of the lung makes it particularly susceptible to immune attack, where a body's immune system reacts too strongly to invaders.
Future studies can refine lung xenotransplantation and move closer to 'clinical translation' involving live people who need a lung transplant.
'This study provides crucial insights into the immune, physiological and genetic barriers that must be overcome, and paves the way for further innovations in the field,' the team conclude.
'Continued efforts are needed to optimize immunosuppressive regimens, refine genetic modifications, enhance lung preservation strategies and assess long-term graft function.'
The study comes just months after Alabama woman Towana Looney became the longest-living recipient of a pig organ transplant, passing 60 days with a gene-edited pig kidney.
In April, she'd had the kidney for more than four months but it was removed when the organ suddenly stopped functioning, Science reported.
HAVE ANIMAL ORGANS BEEN TRANSPLANTED TO HUMANS BEFORE?
Scientists have been toying with animal-to-human organ donation (xenotransplantation) for decades.
Skin grafts were carried out in the 1800s from a variety of animals to treat wounds, with frogs being the most popular.
In the 1960s, 13 patients were given chimpanzee kidneys, one of whom returned to work for almost 9 months before suddenly dying. The rest passed away within weeks. At that time human organ transplants were not available and chronic dialysis was not yet in use.
In 1983, doctors at Loma Linda University Medical Center in California transplanted a baboon heart into a premature baby born with a fatal heart defect.
Baby Fae lived for just 21 days. The case was controversial months later when it emerged the surgeons did not try to acquire a human heart.
More recently, waiting lists for transplants from dead or allogenic donors are growing as life expectancy rises around the world and demand increases.
In September 2021, surgeons at NYU Langone Health in New York successfully transplanted a pig kidney into a human for the first time.
It started working as it was supposed to, filtering waste and producing urine without triggering a rejection by the recipient's immune system.
The recipient was a brain-dead patient in New York with signs of kidney dysfunction whose family agreed to the experiment before she was taken off life support.
In another experiment that month in Alabama, surgeons successfully transplanted two pig kidneys into brain dead man. The transplanted pig kidneys filtered blood, produced urine and, importantly, were not immediately rejected by his body. Both organs remained viable for three days after the transplant.
In January 2022, heart disease patient David Bennett become the first patient in the world to get a heart transplant from a genetically-modified pig. He survived for two months.
In 2023, Lawrence Faucette, also with heart disease, received the second pig-to-human heart transplant -and survived for nearly six weeks.
Earlier this year, an Alabama woman Towana Looney became the longest-living recipient of a pig organ transplant, passing 60 days with a gene-edited pig kidney. In April, she'd had the kidney for more than four months when it was removed after suddenly failing to function.