As of October 2021, there are 106,662 patients on the national transplant waiting list in the United States. Due to the shortage of organs available for transplant, 17 people die each day while on this waitlist. For years, scientists have been searching for new methods to address the organ shortage. Recently, they’ve accomplished what was once thought to be impossible: using animal organs for human transplants.
Today I’ll be introducing two major advances in scientific and surgical intervention: first, the successful transplant of a pig kidney into a human patient, and second, the transplant of a pig’s heart into a living human patient.
The use of non-human cells, tissues, or organs for human medical procedures is called xenotransplantation. This technique has been used since the 1960s, when chimpanzee kidneys were transplanted into some human patients, but the longest time these patients survived was only nine months. Today, other tissues like pig pancreas cells, heart valves, and skin are all used for routine medical procedures. However, it has not been possible to use whole organs for xenotransplantation – until now.
On three separate occasions, scientists have successfully used pig organs for human transplantation. These scientists believe that xenotransplantation could be a much needed solution to the organ shortage crisis.
To accomplish this, scientists use genetically engineered pigs as organ donors. These pigs have ten genetic modifications that prevent organ rejection or the transmission of porcine diseases. Why pigs? Pigs are not only easier to raise than non-human primates, but they also mature quickly, reaching the equivalent of human size in just six months.
Now that we know a little more about xenotransplantation, let’s dive deeper into the details of these stories.
Our first story was initially reported in October of 2021. After a two-hour procedure, surgeons at NYU Langone Health successfully attached a pig kidney to a brain-dead human patient. The patient was a registered organ donor whose organs were deemed ineligible for donation. Still hoping to make a difference, the family consented to the experimental transplant procedure. Unlike normal kidney transplants, in this procedure, the kidney was attached outside the body so scientists could more easily monitor the function of the organ. And the organ functioned almost immediately by producing urine and filtering waste. After 54 hours, the experiment was terminated. Despite promising initial results, at the time of writing this article the study has yet to be published and peer-reviewed.
However, this major surgery was accomplished for a second time in December of 2021. And this time, the results were published. The peer-reviewed research article titled “First clinical-grade porcine kidney xenotransplant using a human decedent model” was published in the American Journal of Transplantation just this month. The article details how surgeons at the University of Alabama at Birmingham transplanted two pig kidneys into a brain-dead, 57 year-old male. The patient, James Parson, was an organ donor whose next-of-kin granted permission to participate in the experimental trial.
Throughout the experiment, four experienced transplant surgeons monitored the progress of the transplant. They immediately observed the flow of blood and recoloration of the pig organs. Just 23 minutes later, the right kidney produced urine.
After transplantation, the kidneys were monitored for three days. Within the first 24 hours, the right kidney produced 700mL of urine – for comparison, most adults produce a minimum 500mL of urine per day). Notably, there was no indication of organ rejection or retrovirus transmission, which were previously two major barriers to xenotransplantation.
Now we must ask: how soon can xenotransplantation become our reality? The initial results of this experiment were extremely promising. However, there were some drawbacks. Although the right kidney produced 700mL of urine within the first 24 hours, the left kidney did not begin to function as quickly. In fact, the researchers found that the left kidney produced less urine and showed mild signs of injury. There was also no evidence of creatinine clearance. Creatinine is a waste product that healthy kidneys can successfully filter out of the blood, and is often used as a measure of kidney function.
Due to these findings, there are still many questions that must be answered. For example, how does brain death affect the results of these studies? Is this hostile environment a limiting factor for the success of organ transplants? Another factor may be the size of the pig kidneys. Since pig organs are smaller than human organs, we must now ask: how many pig organs are necessary to replace one human organ?
However, there is increasing hope that xenotransplantation will be a big part of our future, and may even be the solution we’ve all been waiting for. Recently, another group of scientists transplanted a pig heart into a human patient. But this time, the patient was alive.
On January 7th, a 57 year-old man named David Bennet became the first human to receive a heart transplant from a genetically modified pig. The organ came from the same line of genetically modified pigs that were used for the two kidney xenotransplants. The FDA granted Emergency Use Authorization for the experimental surgery on December 31st, 2021 because Mr. Bennet was ineligible for a human heart transplant and would face certain death without a new heart. After an eight hour surgery, Mr. Bennet awakened with a normal pulse. He is still being monitored at the University of Maryland Medical Center.
It is important to note that there are ethical considerations that must be taken into account when using animals for research. Even though pigs are already raised for consumption and for other medical procedures, is it ethical to raise animals just for their organs? What conditions would make a person eligible to receive an animal organ? Aside from these questions, how possible is it for pig organs to function in the long term?
There are still many uncertainties about these exciting new advances. Until xenotransplantation becomes more well-established, what can we do to address the organ shortage now? First, consider becoming an organ donor. On average, one donor can save up to eight lives and improve up to 75 more. You can also find out what you can donate right now. If you are able, consider donating blood or plasma. National Donor Day is coming up on February 14th, so click here to learn more about tissue, platelet, or bone marrow donation. If this isn’t possible for you, consider donating money to support science. Click here for a list of transplant organizations that support scientific research, education, and financial support for patients.
Thanks to these new findings, we may have a new future for organ transplantation. It will be exciting to track new milestones in xenotransplantation as 2022 unfolds.