In a first, surgeons attached a pig kidney to a human – and it worked

Surgeons in New York have successfully attached a kidney grown in a genetically altered pig to a human patient and found that the organ worked normally, a scientific breakthrough that one day may yield a vast new supply of organs for severely ill patients.

Although many questions remain to be answered about the long-term consequences of the transplant, which involved a brain-dead patient followed only for 54 hours, experts in the field say the procedure represents a milestone. "We need to know more about the longevity of the organ," says Dr Dorry Segev, professor of transplant surgery at Johns Hopkins School of Medicine, who was not involved in the research. Nevertheless, he says, "This is a huge breakthrough. It's a big, big deal."

Researchers have long sought to grow organs in pigs suitable for transplantation into humans. A steady stream of organs – which could eventually include hearts, lungs and livers – would offer a lifeline to patients on transplant waiting lists.

The  kidney was obtained from a pig genetically engineered to grow an organ unlikely to be rejected by the human body. It was then attached to a person who had suffered brain death and was maintained on a ventilator

The surgery, carried out at NYU Langone Health, was first reported by USA Today on Tuesday. The research has not yet been peer-reviewed nor published in a medical journal. The transplanted kidney was obtained from a pig genetically engineered to grow an organ unlikely to be rejected by the human body. In a close approximation of an actual transplant procedure, the kidney was attached to a person who had suffered brain death and was maintained on a ventilator.

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The kidney, attached to blood vessels in the upper leg outside the abdomen, started functioning normally, making urine and the waste product creatinine "almost immediately", according to Dr Robert Montgomery, the director of the NYU Langone Transplant Institute, who performed the procedure in September.

Although the organ was not implanted in the body, problems with so-called xenotransplants – from animals like primates and pigs – usually occur at the interface of the human blood supply and the organ, where human blood flows through pig vessels, experts say.

The fact that the organ functioned outside the body is a strong indication that it will work in the body, Montgomery says.

Reactions to the news among transplantation experts range from cautiously optimistic to wildly effusive, though all acknowledge the procedure represented a sea change. The prospect of raising pigs in order to harvest their organs for humans is bound to raise questions about animal welfare and exploitation.

While some surgeons speculated that it could be just months before genetically engineered pigs' kidneys are transplanted into living human beings, others say there is still much work to be done. "This is really cutting-edge translational surgery and transplantation that is on the brink of being able to do it in living human beings," says Dr Amy Friedman, a former transplant surgeon and chief medical officer of LiveOnNY, the organ-procurement organisation in the greater New York area.

The field up to now has been stuck in the preclinical primate stage, because going from primate to living human is perceived as a big jump

The group was involved in the selection and identification of the brain-dead patient receiving the experimental procedure. The patient was a registered organ donor, and because the organs were not suitable for transplantation, the patient’s family agreed to permit research to test the experimental transplant procedure.

Friedman says she envisions using hearts, livers and other organs grown in pigs, as well. “It’s truly mind-boggling to think of how many transplants we might be able to offer,” she says, adding, “You’d have to breed the pigs, of course.”

Other experts are more reserved, saying they want to see whether the results are reproducible and to review data collected by NYU Langone. "There's no question this is a tour de force, in that it's hard to do and you have to jump through a lot of hoops," says Dr Jay A Fishman, associate director of the transplantation centre at Massachusetts General Hospital. "Whether this particular study advances the field will depend on what data they collected and whether they share it, or whether it is a step just to show they can do it," Fishman says, urging humility "about what we know".

Many hurdles remain before genetically engineered pigs' organs can be used in living human beings, says Dr David Klassen, chief medical officer of the United Network for Organ Sharing. While he calls the surgery "a watershed moment", he warns that long-term rejection of organs occurs even when the donor kidney is well-matched, and "even when you're not trying to cross species barriers". The kidney has functions in addition to clearing blood of toxins. And there are concerns about pig viruses infecting recipients, Klassen says. "It's a complicated field, and to imagine that we know all of the things that are going to happen and all the problems that will arise is naive."

The combination of two new technologies – gene editing and cloning – has yielded genetically altered pig organs. Pig hearts and kidneys have been transplanted successfully into monkeys and baboons, but safety concerns precluded their use in humans.

"The field up to now has been stuck in the preclinical primate stage, because going from primate to living human is perceived as a big jump," Montgomery says. The kidney used in the new procedure was obtained by knocking out a pig gene that encodes a sugar molecule that elicits an aggressive human rejection response. The pig was genetically engineered by Revivicor and approved by the US Food and Drug Administration for use as a source for human therapeutics. – This article originally appeared in The New York Times