New blood mRNA assay to detect rejection by antibodies after kidney transplant

New blood mRNA assay to detect rejection by antibodies after kidney transplant

A group of European scientists has found a biomarker that can identify patients with symptoms of kidney rejection symptoms after a transplant as a result of antibodies. The identification can be done through a simple blood test and at an early stage. It is the first known biomarker for rejection by antibodies. The researchers hope that the test can be further developed quickly for use in the hospital.

After a kidney transplant, patients have to take medication to suppress their immune system. However, kidney rejections occur frequently. To determine if the body is rejecting the organ, doctors usually take a biopsy: using a needle, they remove a small piece of tissue from the transplanted kidney and examine it under a microscope. This procedure is often uncomfortable. Moreover, rejection symptoms are often discovered too late, so that correct treatment is not always possible anymore.

At the University Hospitals Leuven in Belgium, kidney transplant patients systematically undergo a kidney biopsy three months, one year, and two years after the transplant. However, the biopsy only can detect rejection symptoms that are present at that moment, while rejection can occur at any time. Moreover, about ten to twenty percent of rejections remain undetected with current methods, which leads to graft failure, reinitiation of dialysis and the need for a repeat transplant.

It is the first time that researchers have found a biomarker for kidney transplant rejection by antibodies. For T cell-mediated rejection, a common type of rejection, some biomarkers in the blood have recently been found, which are now being further developed for clinical use. Rejection by T cells is treatable, but there are fewer treatment options for rejection with antibodies.

"Rejection by HLA antibodies often has serious consequences," said the principal investigator of the study. "Traditional tests for assessing the function of transplanted kidneys can often only identify rejection when it is already chronic and irreversible. Thanks to our biomarker, we can detect rejection much earlier and with a simple blood test. Because the test is less invasive, we will be able to test more often than with the current biopsies."

In the first phase, the European researchers performed a genome-wide study to find out differences in RNA molecules among 117 patients with and without kidney rejection symptoms after a transplant. In the second phase, the different molecules of an independent group of 183 patients were processed into a mathematical model. The final biomarker consists of eight RNA molecules that are measured with an RT-PCR technique. In the third phase, the biomarker was validated in 387 patients in four European academic hospitals.

"In addition to developing the biomarker, that third phase was very important," said another author. "Researchers are often satisfied with a new discovery, even though they are unable to test it in independent clinical studies. Thanks to international cooperation, we could validate our biomarker in a large group of patients. That gives us a lot of confidence in the clinical value of the new biomarker. "

The authors identified and locked an 8-gene assay (CXCL10, FCGR1A, FCGR1B, GBP1, GBP4, IL15, KLRC1, TIMP1) in blood samples from the discovery and derivation phases for discrimination between cases with (N = 49) and without (N = 134) antibody-mediated rejection. In the validation cohort, this 8-gene assay discriminated between cases with (N = 41) and without antibody-mediated rejection (N = 346) with good diagnostic accuracy. The diagnostic accuracy of the 8-gene assay was retained both at time of stable graft function and of graft dysfunction, within the first year and also later after transplantation. The 8-gene assay is correlated with microvascular inflammation and transplant glomerulopathy, but not with the histological lesions of T-cell mediated rejection.

The researchers now want to consult with medical diagnostic companies to further develop and standardise the test. "In principle, our antibody rejection test has been sufficiently validated for commercialisation," said the PI. "This is the next and necessary step to be able to offer the test to patients. With the test, patients who have no rejection of antibodies will no longer have to undergo a biopsy. The biomarker will also help to detect rejection sooner and will support the search for better medicines against rejection by antibodies."