In a medical first, doctors in Maryland have performed a pig's heart transplant on a human patient in a last-ditch attempt to save his life.
The patient was doing well three days after the surgery, but it's too early to tell if the operation went well.
The transplant marks a step in the quest to one day use animal organs for life-saving operations. The transplant showed that a genetically modified animal's heart can function in the human body.
The patient, David Bennett, was dying, ineligible for a human heart transplant, and had no other choice but to accept the experiment, his son said.
It was either die or do the transplant. I want to live. Bennett said a day before the surgery that he knew it was a shot in the dark, but he wanted it.
Scientists are trying to figure out how to use animal organs instead of human ones because of a huge shortage of human organs in the US. There were a record 3,800 heart transplants in the US last year, according to the United Network for Organ Sharing.
There will be an endless supply of organs for patients who are suffering if this works, according to Dr Muhammad Mohiuddin, scientific director of the university's animal-to-human transplant program.
Patients quickly reject animal organs, which is why previous attempts at such transplants have failed. Baby Fae, a dying infant, lived 21 days with a baboon heart.
The surgeons in Maryland said the difference was that they had used a pig heart that had undergone gene-editing to remove a sugar in its cells that was responsible for that hyper-fast organ rejection.
The Maryland transplant is considered to be a watershed event by the chief medical officer.
Klassen cautioned that it was only a first step in the process of figuring out if xenotransplantation might work again.
When a patient with a life-threatening condition has no other options, the FDA allows the surgery under what is called a "compassionate use" emergency authorization.
In September of last year, researchers in New York performed an experiment on pigs that might offer promise for animal-to-human transplants. Doctors attached a pig's organ to a human body and watched it work.
The experiment at NYU Langone Health was led by Dr Robert Montgomery.
He said in a statement that it was a truly remarkable breakthrough. I am a heart transplant recipient who has a genetic heart disorder, and I am thrilled by the news that this breakthrough will save my family and other patients.
Karen Maschke, a research scholar at the Hastings Center, is helping develop ethics and policy recommendations for the first clinical trials under a grant from the National Institutes of Health.
Maschke said that rushing into animal-to-human transplants without this information would not be advisable.
The surgery took seven hours.
David Bennett Jr said that his father realized the importance of what was done. He could not live, or he could last a day or two. We are in the unknown at this point.
The Associated Press contributed to the report.