Trending Clinical Topic: Xenotransplantation

Ryan Syrek


February 04, 2022

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According to a report from the Global Observatory on Donation and Transplantation, 10% or less of global needs for organ transplantation were met in 2020. More than 100,000 patients are on a transplant waiting list in the United States alone. As such, news about groundbreaking animal-to-human organ transplants captured much recent attention (see Infographic).

In October 2021, surgeons at NYU Langone Health in New York City transplanted a pig kidney into a brain-dead patient without triggering immediate rejection for the first time. That pig's genes had also been altered so that its tissues no longer contained a molecule known to trigger near-immediate rejection. For 3 days, the new kidney was attached to the recipient's blood vessels and maintained outside her body, giving researchers access to it. Test results of the transplanted kidney's function appeared normal, with no evidence of the vigorous, early rejection typically seen when unmodified pig kidneys are transplanted into nonhuman primates. The recipient's elevated creatinine level returned to normal after the transplant.

In January, surgeons at the University of Maryland Medical Center (UMMC), Baltimore, successfully performed a pig-to-human heart transplant. A press release explains that three genes associated with antibody-mediated rejection had been knocked out in the pig that supplied the heart. Six human genes associated with immune acceptance of the organ were also inserted into the pig's genome. Before the transplant, the patient required mechanical circulatory support. He was rejected for standard heart transplantation at UMMC and other facilities. He was also ineligible for an implanted ventricular assist device because he has ventricular arrhythmias. The pig that supplied the heart was provided to the center by Revivicor, Inc, a regenerative medicine company. An experimental antirejection medication was also used, in addition to routinely used immunosuppressants.

In late January, not long after the heart transplant, surgeons at the University of Alabama Birmingham (UAB) transplanted two similarly modified pig kidneys into a brain-dead human recipient. The transplanted kidneys filtered blood, produced urine, and were not immediately rejected, remaining viable until the study ended 77 hours after transplant. Although the team at NYU Langone Health was the first to report a similar transplant, the UAB work is the first peer-reviewed study on such a procedure to be published. The pig kidneys were procured from genetically engineered pigs provided by Revivicor, which have a total of 10 modified genes, including pig growth hormone. The UAB researchers note that although transplantation is the criterion-standard treatment for end-stage kidney disease, less than 25,000 kidney transplants are performed each year in the United States, and 240 US residents on dialysis die every day.

Worldwide, the reaction to the pig organ transplants has been met with much attention. Although most have responded with excitement at the potential of reducing the number of lives lost while awaiting organs, many point out ethical considerations, such as patient selection and cost. Others urge recognition that the field of xenotransplantation is still in early stages. The promise of xenotransplantation and recent advances have generated considerable interest, resulting in this week's top trending clinical topic.

Learn more about xenotransplantation.


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