NEW YORK – A research team including people from the Yale School of Medicine and Johns Hopkins School of Medicine has developed a urine-based test for a cause of kidney injury.
The test is for acute tubulointerstitial nephritis (AIN), a condition that is caused by some medications and when left untreated can lead to acute kidney injury (AKI), Dennis Moledina, one of the authors of the paper and an assistant professor at Yale, said. For AKI patients, "the challenge … is figuring out if a patient that's presenting to us with loss of kidney function has AIN or some other common cause of AKI." Knowing the cause is important because AIN can be treated by stopping the drug that is causing the injury and, in some cases, using steroids.
The current standard of care for confirming AIN is a kidney biopsy, which is "a very involved process" that is expensive and comes with the risk of blood transfusions and other complications, he said. "Any biomarker that identifies this disease will have significant clinical impact."
The researchers decided to investigate potential biomarkers that could possibly diagnose the disease and tested 180 immune proteins from urine samples of 88 patients who had undergone kidney biopsies – 31 of whom had AIN – utilizing Olink's commercially available aptamer assay, Moledina said. The discovery and validation process is described in a paper published last week in the Journal of Clinical Investigation.
Through its proteomics work, the team found one protein, chemokine C-X-C motif ligand 9 (CXCL9), that was 7.6 times higher in patients with AIN than those without the disease. The researchers then validated the biomarker in a discovery cohort and two external validation cohorts using a commercial sandwich immunoassay from Meso Scale Discovery that they adapted and had similar results, Moledina said. In the external validation cohorts, CXCL9 had an area under the curve of .94 for AIN diagnosis, the researchers noted in the JCI paper.
The team also measured kidney biopsy tissue, which had higher mRNA expression of CXCL9, indicating that "the CXCL9 we're finding in the urine is actually coming from the kidneys," he added.
Moledina named multiple potential use cases of the test, such as for patients who present with a loss of kidney function that are on immune checkpoint inhibitors, proton pump inhibitors, antibiotics, or other drugs. If the result is high, the patient could stop taking the drug and reduce the occurrence of chronic kidney disease, he said.
The test isn't intended to completely eliminate the need for a kidney biopsy in every patient, but rather to sort them into high or low probability groups. Those in the high probability groups could be treated with steroids or stop the drugs causing AIN, while those in the low likelihood groups could be investigated for other causes of AKI. Patients in the middle group, meantime, would undergo biopsies to determine if AIN is causing the loss of kidney function.
In addition, the test could be done more widely in AKI patients and pick up AIN cases where clinicians did not have a clinical suspicion of the disease, increasing AIN diagnoses, Swapnil Hiremath, a staff nephrologist at The Ottawa Hospital who was not involved in the development of the test, said.
The marker may also be used to monitor a patient's recovery and for targeting therapy, he said.
Hiremath noted that there are no similar tests currently available for AIN, although nephrologists can do urine microscopy to look for white blood cells and white blood cell casts. This process is a "subjective assessment and requires a skilled nephrologist," he said, and while white blood cells can indicate that something is wrong, their presence is "indirect evidence only." White blood cell casts are also not specific to AIN and can be seen in other conditions, but Hiremath said that clinical suspicion of AIN combined with white blood cell casts means it's "pretty likely to be AIN."
CXCL9's role in kidney function has been investigated by other groups – a 2022 paper published in JCI Insight by MD Anderson Cancer Center researchers found elevated levels of CXCL9 expression in kidney biopsies from patients with immune checkpoint inhibitor therapy-associated AIN and noted that urinary CXCL9 correlated best to tissue CXCL9 expression. Meantime, a team of European researchers showed in a Med paper published in January that an increase in plasma CXCL9 after starting immune checkpoint inhibitor therapy indicated a higher risk of future immune-related adverse events, such as AIN.
It has also been studied as a risk stratification marker for kidney transplant rejection and for non-kidney-related conditions, including multiple sclerosis.
Moledina and his team plan to commercialize their work and have started a company, PredictAIN, that has patents pending on a clinical test and three biomarkers, including CXCL9. The firm is working on an algorithm that combines clinical features with the urine test to determine the probability of AIN.
The researchers' proteomics analysis showed that many of the changes in the urine of AIN patients are driven by interferon-gamma, which might make a promising therapeutic target for the disease and could be another future direction, he said.
The firm is working with undisclosed partners to explore avenues for commercialization of its products and considering potential distribution options, including both in-house distribution and partnerships, he added. Also being discussed are issues around technology licensing and outside investments.
PredictAIN will likely offer the assay as a laboratory-developed test at first, Moledina said. The test will be cheaper than a kidney biopsy, he noted – kidney biopsies can run between $3,000 and $5,000, while similar tests combining clinical test and biomarkers in kidney disease cost between $500 and $1,000. It is also developing a lateral flow version of the assay that could be used in near-patient settings and return results in less than an hour, compared to the laboratory-based assay would take hours once it is set up for clinical use, Moledina said.
Cost is a key consideration, but he said providers have shown interest in the test. Ottawa Hospital's Hiremath said that "as long as it is affordable – it will be widely used."