On TV medical dramas, a common suspenseful story line follows a person in need of an organ transplant waiting to find a donor. A happy ending ensues when the organ arrives, packed in ice and ready for surgical insertion.
Thousands of organs are transplanted every year. Those organs are constantly under attack from the body’s immune system. Although short-term outcomes are good, long-term survival of transplanted organs remains below 60%. Molecular biomarkers in blood and urine can provide physicians with information about immune status and organ function. But physicians don’t yet know whether making treatment decisions on the basis of those biomarkers will improve outcomes.
To be sure, organ transplants save lives. More than 33,000 organs were transplanted in the U.S. in 2016, the most recent year for which data are available, according to the United Network for Organ Sharing. In the real world, though, after a transplant, a recipient’s immune system fights against the organ, recognizing it as foreign. As many as 15% of people receiving kidney transplants, for instance, experience acute rejection, meaning that the immune system sends in its troops and causes inflammation within the first year. For those patients, the story line isn’t tied up neatly.
Rejection episodes like these are usually treatable and reversible. So “rejection” doesn’t necessarily mean the transplanted organ—or graft, as doctors like to call it—is lost. Tissue damage can occur during these episodes, however, and if it happens enough times or is not treated quickly enough, the organ fails.
To ensure prompt treatment, physicians need a way to monitor organ function and diagnose rejection. The only method available to them now is direct biopsy of the transplant. In the case of a kidney transplant, the typical schedule for routine monitoring is to take biopsies of the organ at one week, one month, three months, six months, one year, and yearly after that.
Rather than poke a needle into an organ to sample cells and tissues—a risky venture—doctors would prefer to noninvasively measure molecular markers in a person’s blood and urine to monitor recovery. These markers, typically nucleic acids and proteins, could help indicate when a transplanted organ has started to fail, help guide treatments, minimize the number of biopsies needed, and ultimately improve transplant success rates.