by Meredith Kile
On this week’s “TechKnow,” we revisit organ transplant technology aimed at increasing both the donor pool for patients in need of hearts and lung transplants as well as viability and health of these organs from recovery to transplantation.
Here’s a look at the history of organ tranplants, and a preview of innovative new technology that could help get patients off the waiting list fast and more efficiently.
EARLY ORGAN TRANSPLANTS
Scientists and historians estimate that doctors began grafting skin (the body’s largest organ) around 800 B.C. to treat burns and other wounds. Modern organ transplants began in the early 1900s; in 1936, Ukranian doctor Yu Yu Voronoy transplanted the first human kidney, using an organ from a deceased donor. While the transplant was successful, Voronoy’s patient died shortly after as a results of organ rejection.
Rejection caused many failures in the early years of transplant technology. In fact, the first successful kidney transplant by surgeons at Boston’s Peter Bent Brigham Hospital in 1954 worked only because the recipient and donor were genetically identical (they were twin brothers). In 1960, British immunologist Peter Medawar won the Nobel Prize for his studies in acquired immune tolerance that lead to the development of anti-rejection drugs, allowing patients to receive organs from non-identical donors.
Organ transplant survival rates
After the development of anti-rejection drugs, the world saw the first successful transplants of lungs, pancreases, livers and even hearts. The central principle of modern transplants since the 1960s is called ischemic storage, where the organ is removed from the body and is stored in a non-functioning state, with no blood circulation.
HowStuffWorks explains how a donor heart is recovered:
The first step for all the harvesting teams is to cut open the donor’s chest. Next, a surgeon saws through the breast bone and pulls the ribs outward to reveal the heart. While other teams are working on other parts of the body, the heart team clamps the different blood vessels leading into the heart and pumps in a cold, protective chemical solution. This solution stops the heart from beating and helps preserve it during transportation.
The surgeons then sever the vessels and remove the heart from the body, placing it in a bag filled with a preservative chemical. This bag is then packed in an ordinary cooler filled with ice, which is rushed to the recipient’s hospital, often via plane or helicopter.
LIVING ORGAN TRANSPORT
TransMedics’ proprietary Organ Care System (OCS) is the first commercial and portable warm blood perfusion organ transport system. With the OCS, doctors are able to perform “living organ transplants,” where organs are kept warm and functioning in a controlled environment from the time they are recovered to the moment they are placed in the recipient’s body.
According to TransMedics, the Organ Care System is designed to:
Increase the amount of time that an organ can be maintained outside the body in a condition suitable for transplantation by reducing time dependent ischemic injury
Provide surgeons the opportunity to assess the function of the organ outside the body
Enable resuscitation of the organ and potentially improve function after removal from donor
TransMedics’ technology nearly eliminates the three major limitations of cold ischemic storage: narrow time frame, the potential for damage (even within “safe” time limits) and the inability to monitor the organ’s status and test function during transport. With the OCS, the time frame for transports is nearly doubled, increasing the donor pool across the U.S. and even to other parts of the world. With a controlled temperature and continuous flow of healthy blood, the organ does not suffer any additional damage in storage and transportation (as it can in ischemic storage), and its status and function can be monitored continuously.
TransMedics is currently beginning the EXPAND trial, in which they hope to use the Organ Care System to increase the donor pool of viable lungs. By signing up for the EXPAND trial, patients will have double the chance of receiving a lung in time: they will remain on the traditional waiting list for standard donation, but will also be placed on TransMedics list to receive lungs via the OCS.
By using their advanced diagnostics, lungs that wouldn’t normally be considered for standard donation (but still pass all international clinical standards), will become available for transplant through the OCS, decreasing the number of viable lungs that go to waste each year.
Other systems, like XVIVO’s Lung Perfusion technology, also hope to rehabilitate previously unconsidered lungs for transplantation. XVIVO’s system allows lungs to be treated outside the body for “marginal functional injuries” that would otherwise discount them from transplantation. The company also touts a preservative solution called Perfadex, used in cold storage methods to increase preservation time from 4 hours to over a day. With these innovations, the company hope to continue increase the donor pool, as well as the number of lungs available to waiting patients.