Mass General Brigham Researchers Develop Urine Test to Detect Kidney Transplant Rejection

The test not only predicts rejection years before it occurs, but outperformed tissue biopsies in identifying patients at risk of future rejection.

Over 25,000 people receive kidney transplants in the U.S. each year, but between 10-20% of these people ultimately experience transplant rejection. Detecting kidney transplant rejection usually involves a biopsy, which is invasive, time-consuming and costly, but Mass General Brigham researchers have developed a new urine test that can non-invasively diagnose rejection and identify kidney transplant recipients at risk of worsening outcome. The test, which is called ExoTRU™, has been licensed by Thermo Fisher and is currently undergoing FDA approval. Results are published in the journal Kidney International Reports.

“By using this test, we can rule out rejection in more than 94% of cases and spare patients from up to 45% of unnecessary biopsies,” said senior author Jamil Azzi, MD, PhD, director of the Kidney and Pancreas Program at Brigham and Women's Hospital, a founding member of the Mass General Brigham healthcare system. “Until now, we've really been frustrated as clinicians by not having good, non-invasive tools to report on the early process of immune injury. This test will allow us to intervene earlier.”

The test detects immune molecules in the urine that reveal the presence of inflammation in the kidney. It is based on years of research by Azzi’s team and was developed in collaboration with researchers at ExosomeDx, a Bio-Techne brand.

Azzi’s team previously showed that RNA, and proteins from kidney cells are shed into the urine within exosomes—membrane-bound bubbles that prevent these molecules from being degraded. Since immune cells invade transplanted kidneys during rejection, exosomes containing proteins and RNA from immune cells also show up in the urine of patients who are experiencing transplant rejection.

In the new study, the researchers present a refined version of the test that requires smaller volumes of urine compared to the previously published method and allows same-day analysis.

“This is the first test that not only tells you whether there is rejection but can also tell you what type of rejection is occurring,” said Azzi. “This is testimony to the innovation at Mass General Brigham in the field of kidney transplants. Brigham and Women's Hospital did the first kidney transplant in history in 1954 and many of the big milestones in transplantation since then, such as developing immunosuppressive therapies."

To assess the test’s effectiveness, the researchers compared its ability to identify transplant rejection in a cohort of 178 transplant patients who were receiving biopsies for rejection detection. The test was able to rule out rejection in 94% of patients, with the potential of saving up to 45% of biopsies. The researchers also validated the test’s effectiveness in a second cohort of kidney transplant patients whose samples were tested at an independent lab.

The test is correlated with the severity of rejection. However, additional studies will be needed to determine if treatment can be based on the results without performing a biopsy. The test’s sensitivity rate was high, meaning that it had few false negatives, but its specificity rate was 52%, meaning that additional testing would be needed before a diagnosis is confirmed.

“This is mostly a rule-out test—if the test is negative, it tells us that there is currently no inflammation and rejection going on in the kidney,” said Azzi. However, the researchers showed that the urine test could also be used to identify patients at risk of future transplant rejection. Patients who tested positive using the urine test but negative by biopsy were nearly two times more likely to experience an adverse event in the subsequent five years compared to patients who tested negative from both the biopsy and urine test. This indicates that the urine test could help clinicians to risk-stratify patients.

“The urine test can reveal inflammation going on in the kidney that we cannot see through a biopsy, which tells us that those patients are at higher risk long-term,” said Azzi. “Those patients should be followed and treated accordingly.”

Though the test has already been licensed for clinical use as a diagnostic, the researchers are further investigating its potential to aid prognostically. Brigham and Women's Hospital is leading a multicenter trial to prospectively assess the test’s potential use for long-term patient monitoring to permit earlier detection of subclinical injury and acute rejection.

Authorship: In addition to Azzi, Mass General Brigham authors include Rania El Fekih, Tamara Merhej, Areej Alghamdi, Shuran Xing, Sonia Kumar, Zhabiz Solhjou, Christa Deban, Anis Saad, Ahmad Halawi, Nour Younis, Katherine Cashman, Maribel Dagher, Siawosh Eskandari, Soltan Al Chaar, Helmut Rennke, Astrid Weins, Reza Abdi, Anil Chandraker, Kassem Safa, and Leonardo V. Riella. Additional authors include Kurt Franzen, James Hurley, Brian C. Haynes, Elliot Hallmark, John Choi, James F. Markmann, Matt McFaul,Chris Ventura, Alexandre V. Vlassov, Richard Formica, Camila Macedo, and Johan Skog.

Disclosures: Azzi, Hurley, Hallmark, Haynes, and Skog, have intellectual properties related to this work. Azzi reports having intellectual properties and receiving royalties from Accrue Health Inc.; receiving research funding from ExsosomeDx, CareDx, Moderna Inc., Alexion Therapeutic, being a scientific advisor for CareDx; Franzen, Hurley, Haynes, Hallmark, Xing, Kumar are employees of Exosome Diagnostics, a Bio-Techne brand. R. Formica reports having consultancy agreements with Genentech Pharmaceutical and Veloxis Pharmaceuticals; being on a speakers bureau for Novartis Pharmaceuticals; being on the visiting committee for the Scientific Registry of Transplant Recipients (January 1, 2018); and being a member of the United Network for Organ Sharing/Organ Procurement and Transplantation Network Membership and Professional Standards Committee. Riella reports receiving research funding from Bristol Myers Squibb and Visterra and being a scientific advisor for or member of CareDx. Skog reports having an ownership interest in Bio-Techne and patents and inventions with Massachusetts General Hospital.

Funding: This project was supported by discretionary funds (Azzi). This project was also partially supported by Exosome Diagnostics, a Bio-Techne brand.

Paper cited: Fekih, R et al. “An Exosomal mRNA Urine Test for Detection and Risk Stratification of Human Kidney Transplant Rejection” Kidney International Reports DOI: 10.1016/j.ekir.2025.01.036