Pig hearts have been transplanted into baboons – a development that could pave the way for humans to receive porcini organs in the future.
Researchers from Germany, Sweden and Switzerland stated that two Anubis baboons survived for six months, while two others lived for at least three months.
Previously, the longest baboon survived after a 57-day procedure.
Since then, genetic changes have been made to the hearts and a new transplant technique has been developed.
The pigs have been modified to produce a human version of two proteins that block an immune response in the alien cells.
It was also assured that they generated thrombomodulin, which prevents the blood from coagulating after surgery.
The research team also stopped preserving donor hearts in cold storage and instead kept them at 8C.
Through them circulated fluids containing oxygen, hormones, red blood cells and nutrients.
Baboons were given drugs to keep the pig's heart from getting too big and lowering the blood pressure to match the pig's.
The transplant procedure was perfected during three trials involving 14 baboons.
One of the five baboons in the final experiment had to be put down after developing a blood clot.
Transplanting an organ between two different species – known as xenotransplantation – is thought to be a way to overcome organ deficiency for human beings who need a transplant.
The scientists' findings have been published in the journal Nature.