Pig kidney transplant in brain-dead man still functions after a month

A genetically modified pig kidney transplanted into a recently deceased person kept on life support has been functioning for over a month without signs of rejection or infection. The announcement, by researchers at NYU Langone Health in New York, marks the longest a pig kidney has functioned inside a human. As such, it is a significant advance in xenotransplantation, or the transfer of animal organs to humans.

This is the fifth pig-to-human kidney transplant to be performed, all of which occurred in people declared brain-dead and then maintained on life support. Full details of one of the four previous transplants were also published today. Conducted by Jayme Locke and her colleagues at the University of Alabama at Birmingham, that kidney functioned for seven days after transplantation – which was a record prior to today’s announcement from New York.

The latest procedure occurred on 14 July. Robert Montgomery at NYU Langone Health and his colleagues transplanted a pig kidney into Maurice Miller, a 57-year-old man who had been declared brain dead after complications from a brain tumour biopsy. Miller’s family agreed to the experimental procedure after learning he had an aggressive form of brain cancer that prevented him from donating his organs. He is being kept on a ventilator and other life supporting measures until the study concludes.

The kidney came from a pig specially bred to lack a gene that produces a carbohydrate called alpha-gal. This carbohydrate isn’t found in humans and causes our immune system to reject, or attack, organs from other animals. To further reduce the risk of rejection, the researchers transplanted the pig’s thymus – a gland that helps the immune system differentiate between the self and foreign cells – into Miller and gave him immune-suppressing medications as well.

Immediately after the transplant, the kidney began producing urine. For 32 days now, Miller’s blood levels of creatinine – a waste product cleared by the kidneys – have remained in the normal range, indicating proper kidney function. Biopsies of the organ have also found no signs of rejection.

After the death of David Bennett last year, there are concerns about xenotransplantation transmitting viruses between animals and humans. Bennett, who was the first person to receive a genetically modified pig heart, died two months after the procedure, potentially due to complications from a pig virus called porcine cytomegalovirus.

Montgomery and his team have been using a more sensitive test than the one used for Bennett’s procedure, helping them better detect this virus and others. So far, they have not found any sign of infection.

They plan on monitoring the kidney for another month before ending the study. After two months, they will have passed the critical period when most non-human primates reject organs from pigs, Montgomery said during a press conference.

“We have a large array of information from non-human primate studies that have looked at long-term [xenotransplantation]. What was missing was an understanding of how translatable that was to humans,” said Montgomery. “This two-month study period I think will check a lot of the boxes we need to move into early clinical trials.”

Xenotransplantation is a promising solution to the shortage of organ donors. In the US, more than 100,000 people are waiting for an organ transplant, and 17 of them die each day.

“Though my brother cannot be here, I can say with confidence that he would be proud of the fact that in the tragedy of his death, his legacy will be helping many live,” said Miller’s sister, Mary Miller Duffer, during the press conference. “[Our] youngest brother passed away 15 months after he was born from kidney disease, which made [this decision] a little easier for me.”