Pig-to-human transplants take another step forward with new test
Scientists temporarily attached a pig kidney to a human body and watched it begin to function, a small step in the decades-long quest to one day use animal organs for vital transplants.
Pigs have been the most recent line of research to address the organ shortage, but among the obstacles: a sugar in pig cells, foreign to the human body, causes immediate organ rejection. The kidney used for this experiment comes from a genetically modified animal, designed to eliminate this sugar and prevent an attack by the immune system.
Surgeons attached the pig kidney to a pair of large blood vessels outside the body of a deceased recipient so they could observe it for two days. The kidney did what it was supposed to do – filter waste and produce urine – and did not trigger the rejection.
“He had absolutely normal function,” said Dr. Robert Montgomery, who led the surgical team last month at NYU Langone Health. “He didn’t have that immediate rejection that we were worried about.”
This research is “a milestone,” said Dr. Andrew Adams of the University of Minnesota School of Medicine, who was not part of the work. This will reassure patients, researchers and regulators “that we are moving in the right direction”.
The dream of animal-to-human transplants – or xenotransplantation – dates back to the 17th century with stumbling attempts to use animal blood for transfusions. In the 20th century, surgeons were attempting to transplant organs from baboons to humans, including Baby Fae, a dying infant, who lived 21 days with a baboon heart.
Without lasting success and with much public outcry, scientists have shifted from primates to pigs, tinkering with their genes to bridge the gap between species.
Pigs have advantages over monkeys and monkeys. They are produced for food, so their use for the organs raises fewer ethical problems. Pigs have large litters, short gestation periods, and organs comparable to humans.
Pig heart valves have also been used successfully for decades in humans. Anticoagulant heparin is derived from the intestines of pigs. Pig skin grafts are used on burns and Chinese surgeons have used pig corneas to restore sight.
In the case of NYU, researchers kept the body of a deceased woman on a ventilator after her family accepted the experience. The woman had wanted to donate her organs, but they were not suitable for traditional donation.
The family felt “there was a possibility that something good could have come from this gift,” Montgomery said.
Montgomery himself received a transplant three years ago, a human heart from a donor with hepatitis C because he was ready to harvest any organ. “I was one of those people lying in an intensive care unit waiting and not knowing if an organ was going to arrive in time,” he said.
Several biotechnology companies are vying to develop pig organs suitable for transplantation to help alleviate the shortage of human organs. More than 90,000 people in the United States are waiting for a kidney transplant. Every day, 12 die while waiting.
The breakthrough is a victory for Revivicor, a subsidiary of United Therapeutics, the company that conceived the pig and its cousins, a herd of 100 people raised under tightly controlled conditions at a facility in Iowa.
Pigs lack a gene that produces alpha-gal, the sugar that immediately attacks the human immune system.
In December, the Food and Drug Administration approved the alteration of the gene in Revivicor pigs as safe for human food consumption and medicine.
But the FDA said developers would have to submit more documents before organs from pigs can be transplanted into living humans.
“This is an important step forward in realizing the promise of xenotransplantation, which will save thousands of lives every year for the not-too-distant future,” Martine Rothblatt, CEO of United Therapeutics, said in a statement.
Experts say tests on non-human primates and last month’s experiment with a human body pave the way for the first experimental pig kidney or heart transplants in living people in the next few years.
Raising pigs to be organ donors is unacceptable to some people, but it may become more acceptable if animal welfare concerns can be addressed, said Karen Maschke, a researcher at the Hastings Center, who will help develop ethical and policy recommendations for the first clinical trials under a grant from the National Institutes of Health.
“The other problem will be, should we do this just because we can? Maschke said.
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