Organ Transplants from Pigs to Humans Progress

The shortage of human organs for transplant is a global medical crisis. For decades, scientists have theorized that animal organs could fill this gap, but the human immune system consistently rejected them. Recent breakthroughs involving gene-edited pig kidneys functioning in brain-dead human bodies have fundamentally changed this trajectory. We are now witnessing the first tangible steps toward making xenotransplantation a clinical reality.

The Critical Shortage of Human Organs

To understand why this research is vital, look at the numbers. According to the United Network for Organ Sharing (UNOS), more than 103,000 men, women, and children are currently on the national transplant waiting list in the United States. Seventeen people die every day waiting for an organ transplant.

Kidneys are in highest demand. Over 88,000 patients are waiting for a kidney, yet only about 25,000 kidney transplants are performed annually. This supply-demand imbalance drives the urgency behind xenotransplantation, the process of grafting or transplanting organs or tissues between members of different species.

Why Pigs Are the Ideal Donor

Scientists have focused on pigs rather than primates for several practical and biological reasons:

  • Size Match: Pig organs grow to a size very similar to human organs.
  • Availability: Pigs are already raised for food on a massive scale, making them readily available.
  • Growth Rate: Pigs reach adult size in roughly six months, offering a faster supply chain than other mammals.
  • Lower Disease Risk: While there are risks, pigs can be raised in sterile, biosecure facilities to minimize pathogen transfer.

The Science: Gene Editing with CRISPR

The primary barrier to pig-to-human transplant has always been hyperacute rejection. The human body immediately recognizes pig tissue as foreign and attacks it. This happens largely because of a sugar molecule called alpha-gal found on the surface of pig cells.

Biotechnology companies like eGenesis and Revivicor (a subsidiary of United Therapeutics) are using CRISPR-Cas9 gene-editing technology to solve this. They are not just using standard farm pigs. They are engineering specific “medical” pigs.

For example, the kidneys used in recent high-profile experiments often undergo significant genetic modification:

  1. Knockouts: Scientists remove (knock out) the genes responsible for producing the alpha-gal sugar to prevent immediate rejection. They also remove genes related to pig growth hormones to ensure the organ doesn’t grow too large inside the human body.
  2. Insertions: Scientists insert human genes that regulate inflammation and blood clotting to help the pig organ “communicate” better with the human blood system.
  3. Virus Removal: The genomes are scrubbed of porcine endogenous retroviruses (PERVs) to ensure no latent pig viruses can infect the human recipient.

Breakthroughs in Brain-Dead Decedents

The snippet provided highlights a crucial phase in this research: testing on brain-dead human bodies (donated for science with family consent). These experiments bridge the gap between animal trials and living human patients.

The NYU Langone Study

In a landmark study concluded in late 2023, surgeons at NYU Langone Health, led by Dr. Robert Montgomery, transplanted a gene-edited pig kidney into a brain-dead man named Maurice “Mo” Miller. The organ functioned for 61 days. This was the longest documented case of a gene-edited pig kidney functioning in a human.

During those two months, the kidney performed exactly as a human kidney would:

  • It produced urine effectively.
  • It filtered toxins like creatinine from the blood.
  • Biopsies showed no signs of early rejection.

The UAB “Parsons” Study

Simultaneously, the University of Alabama at Birmingham (UAB) conducted similar research known as the “Parsons Model,” named after recipient Jim Parsons. The UAB team, led by Dr. Jayme Locke, published data showing that their gene-edited pig kidneys cleared creatinine effectively. This was a specific metric the FDA required to prove the organs could actually support life, not just stay pink and alive.

The First Living Recipients

Following the success of the brain-dead decedent studies, the FDA granted “compassionate use” authorization for transplants into living patients who had no other options.

Richard Slayman

In March 2024, Massachusetts General Hospital achieved a historic milestone. Richard “Rick” Slayman became the first living human to receive a genetically edited pig kidney. The organ was provided by eGenesis and contained 69 genomic edits.

Mr. Slayman was discharged from the hospital two weeks after surgery, a sign that the initial recovery was successful. While Mr. Slayman passed away in May 2024 due to underlying cardiac issues, his transplant team confirmed the pig kidney was functioning well and was not the cause of death. His contribution proved that a pig kidney could sustain a living human outside of an intensive care unit.

Lisa Pisano

Shortly after Slayman’s surgery, NYU Langone performed a pig kidney transplant on Lisa Pisano. Ms. Pisano faced a complex medical situation involving heart failure and had a mechanical heart pump installed days before the transplant. While the kidney initially functioned, it had to be removed after 47 days due to blood flow issues related to the heart pump, rather than organ rejection.

The Path Forward: Clinical Trials

The move from “compassionate use” (one-off emergency surgeries) to formal clinical trials is the next step.

  • FDA Regulation: The FDA is currently reviewing data from the brain-dead studies and the initial living recipients.
  • Timeline: Experts hope to launch small-scale clinical trials within the next year or two.
  • The Goal: If trials are successful, gene-edited pig kidneys could become a “bridge” therapy to keep patients alive while they wait for a human kidney, or eventually, a permanent destination therapy.

Frequently Asked Questions

Are these transplants safe from animal viruses? Safety is a top priority. The pigs used for these organs are raised in bio-secure, germ-free facilities. Additionally, gene editing is used to deactivate porcine endogenous retroviruses (PERVs) in the pig’s DNA to prevent any risk of transmission to humans.

How long can a pig kidney last in a human? We do not have a definitive answer yet. The longest study in a brain-dead decedent lasted 61 days. The first living patient lived for approximately two months with the organ. The goal of upcoming clinical trials is to determine if these organs can last for years.

Will I have to take anti-rejection drugs? Yes. Even though the pigs are genetically edited to look more “human” to the immune system, recipients still require immunosuppressive drugs. However, researchers are hopeful that the drug regimen might eventually be less aggressive than what is required for current human-to-human transplants.

Who owns the pigs used for these transplants? The pigs are proprietary technology owned by biotechnology companies. The two current leaders in the field are eGenesis (using CRISPR technology) and United Therapeutics (through its subsidiary Revivicor).