Research led by investigators at Cincinnati Children’s Hospital Medical Center and the University of Cincinnati School of Medicine has revealed new, specific biomarkers of kidney transplant rejection. These specific cellular signals, revealed by single-cell analysis represent new therapeutic and diagnostic targets to improve care for the roughly 10% of patients who experience organ rejection after a transplant.
“The available treatments for stopping a rejection event have not changed much in decades,” said senior co-author David Hildeman, PhD, interim director of the Division of Immunobiology at Cincinnati Children’s. “These cellular signatures open the door to establishing an entire new set of anti-rejection therapies.”
Results of the eight-year study, which included contribution from researchers at the University of Notre Dame and Novartis, were published in the Journal of Clinical Investigation (JCI).
Kidney transplantation is the most common organ transplant provided for patients with kidney failure from diabetes, infections, injuries and other factors, with more than 25,000 kidney transplants performed in the U.S. in 2022 according to data compile by the United Network for Organ Sharing.
The researchers believe that leveraging this new, more detailed set of biomarkers will allow for the development of more targeted therapeutics and diagnostics to treat each person’s unique molecular signature of organ rejection.
“Having a precision-medicine approach to treating organ rejection has the potential to markedly reduce the threat rejection poses to transplanted organs,” said senior co-author E. Steve Woodle, MD, professor of surgery at the University of Cincinnati College of Medicine. “More follow-up research will be needed, but these findings have implications that extend beyond kidney transplantation to potentially apply to liver, lung transplantation and more.”
While gradual improvements over the past 30 years have improved the duration of successful transplants to around 20 years for living-donor kidneys and nearly 12 years for deceased donor organs, there remains the lingering problem of acute organ rejection whereby patients will need to return to dialysis within one to three years. Further complicating treatment for these patients is the fact that once the immune system has rejected the initial transplant, it is much more likely to reject subsequent transplantations.
But the methods currently available to combat organ rejection—corticosteroids and antilymphocyte globulins—have remained largely unchanged for over 60 years and research has shown that these treatments are largely ineffective.
Single-cell discoveries
For their research, the investigators used single-cell genomic analysis to examine biopsies from transplanted kidneys that had encountered acute cellular rejection. The team also compared rejections that occurred in patients who received maintenance via immunosuppressive medication tacrolimus and two newer alternative medications (belatacept and iscalimab).
According to the published report, this study is the first known to combine single-cell analysis with single-cell T cell receptor (TCR) analysis to better understand acute kidney transplant rejection.
Using their technique, the researchers were able track how gene expression changed within specific populations of cells that drive damage from rejection, which the team dubbed allospecific CD8 expanded T cell clones (CD8EXP).
“The power of what we’re doing comes from being able to look at cells on a single-cell level. We can look specifically at the ones that are responsible for rejection and we can look at how rejection changes over time as the T cells are shifting their response to different drugs,” said Tiffany Shi, an MD/PhD student at Cincinnati Children’s and first author.
The research details three significant findings:
First, even if a first acute rejection event was stopped, the treatments weren’t able to eliminate all the T cells that had cloned to attack the transplanted organ. The T cells often persisted for months after the anti-rejection treatment was delivered. The implication is that multiple rejection events, which have until now been considered separate events, may actually be one, protracted rejection event. Addressing ways to combat these “lurking” cloned T cells that evaded the initial treatment could be the key to developing better testing and treatments.
Second, the team identified about 20 “clonotypes” of CD8EXP T cells, from among a population of thousands, that were the ones to attack the transplanted organ. These clonotypes differed according to the receptors the T cells carried, and the relatively low number of these cells suggest it will be easier to develop targeted treatments against transplant rejection.
And third, these T cell clonotypes can easily be detected in urine samples, suggesting the potential to accurately identify the nature of an individual patient’s rejection event and medications that have been developed to treat it.
“This finding indicates that a simple urine test could substitute for a more invasive kidney transplant biopsy and thereby make it much safer and easier for patients to have their rejection treatment monitored for effectiveness,” Hildeman noted.
