In 1954, John Murray of Harvard Medical School commenced a new era in modern medicine by performing the first successful kidney transplant in a human patient [1]. 67 years later, organ transplantation is a widely-utilized medical procedure, frequently used to combat organ failure and a variety of other diseases. The new hurdle in this field of transplantation surgery is the ever-growing list of patients in need of new organs with no way for the supply to ever meet the demand. There currently are over 100,000 patients on the US transplant waiting list, many of whom depend on the hope of organ transplantation as their last chance of survival [2]. To combat this mismatch between the supply and demand of transplantable organs, scientists have been looking to other organisms in hopes that cross-species transplantations could alleviate some of the issues that make the organ transplant list so intimidatingly long.
The concept of organ transplantation using donor organs from non-human organisms is not a completely novel idea. In the 1960’s, a surgeon at Tulane University, Keith Reemtsma, transplanted kidneys from chimpanzees to 13 human patients as a last resort treatment option (these procedures would likely not fly under today’s ethical guidelines). While one of Reemtsma’s patients had a short recovery term of around 8 months, all of these transplanted organs ultimately failed due to immune rejection by the human recipient [3]. The human immune system mounts a significant immune response to transplanted organs, triggered by specific sugars present on the external surfaces of transplanted organs and their cells. For instance, the alpha-gal sugar present on pig kidneys makes successful transplantation of organs from the native organism to humans impossible [4]. Genetic engineering technology has allowed scientists to remove sugars from potential donor organisms, facilitating the first successful transplant of a pig organ to a human in mid-October of this year.
At NYU’s Langone Health, physicians transplanted a kidney from a pig genetically engineered to lack the alpha-gal sugar, and the kidney remained viable for 54 hours [5]. The patient had been considered brain dead for about a month before the procedure took place, and their organs were deemed unusable for transplantation into another patient. Upon consent of the family, physicians at NYU performed the xenotransplantation and observed healthy urine output for 54 hours after the procedure (54 hours was the length of time deemed ethical by a board of medical ethicists — the experiment was ended after that period of time) [4].
This procedure validates the assumptions that removing immune system-triggering sugars from the surface of transplant organs can prevent immediate rejection by the host. While this is just a small step in the direction of making xenotransplantation a universally accepted treatment option, it opens the possibilities for future clinical work and applications. Due to the manifold of ethical issues surrounding human clinical trials, progress in this area of research will inevitably be quite slow. However, slow progress is a small price to pay to avoid repeating the same mistakes as past xenotransplantation experiments.
References
[1] A transplant makes history – Harvard Gazette https://news.harvard.edu/gazette/story/2011/09/a-transplant-makes-history/ (accessed 2021 -11 -29).
[2] Organ Donation Statistics | organdonor.gov https://www.organdonor.gov/learn/organ-donation-statistics (accessed 2021 -11 -29).
[3] Cooper, D. K. C. A Brief History of Cross-Species Organ Transplantation. Baylor University Medical Center Proceedings 2012, 25 (1), 49–57. https://doi.org/10.1080/08998280.2012.11928783.
[4] What the successful test of a pig-to-human kidney transplant means | Science News https://www.sciencenews.org/article/xenotransplantation-pig-human-kidney-transplant (accessed 2021 -11 -29).
[5] U.S. surgeons successfully test pig kidney transplant in human patient | Reutershttps://www.reuters.com/business/healthcare-pharmaceuticals/us-surgeons-successfully-test-pig-kidney-transplant-human-patient-2021-10-19/ (accessed 2021 -11 -29).