Study finds insights into transplant rejection, drug development targets

The findings were published in the journal, 'Journal of Clinical Investigation.'

The analyses discovered the most specific cellular signatures for kidney transplant rejection to date.

The study's findings are the result of eight years of collaboration between experts at Cincinnati Children's and the University of Cincinnati College of Medicine, as well as researchers from the University of Notre Dame and Novartis.

Tiffany Shi, an MD/PhD student in Cincinnati Children's Immunology Graduate Programme and Medical Scientist Training Programme, was the study's first author. David Hildeman, PhD, interim director of the Division of Immunobiology at Cincinnati Children's, and E. Steve Woodle, MD, professor of surgery and William A. Altemeier Chair in Research Surgery at the University of Cincinnati, were senior co-authors. Hildeman and Woodle co-direct Cincinnati Children's Centre for Transplant Immunology.

"The available treatments for stopping a rejection event have not changed much in decades. These cellular signatures open the door to establishing an entirely new set of anti-rejection therapies," Haldeman said.

"Having a precision-medicine approach to treating organ rejection has the potential to markedly reduce the threat rejection poses to transplanted organs," Woodle said. "More follow-up research will be needed, but these findings have implications that extend beyond kidney transplantation to apply to liver, lung transplantation and more potentially."

Organ rejection affects 10 per cent of recipients

Kidney transplantation is the most common form of organ transplant; provided after organ failure from diabetes, infections, injuries, and other factors. In 2022, surgeons performed 25,498 kidney transplants across the US, according to the United Network for Organ Sharing (UNOS).

Over the past 30 years, gradual improvements have allowed kidney transplants to last longer so that now the "half-life" for living-donor kidneys exceeds 20 years and approaches 12 years for deceased-donor organs.

"For an older person, these survival rates reflect a pretty long time," Hildeman sai. "But for younger adults and children, the chances of needing a second transplant remain high."

However, once a kidney transplant recipient experiences acute rejection, many go on to lose their transplant and return to dialysis within 1-3 years. In addition, once a patient's immune system rejects one organ, it is much more likely to leave a second transplant.

Unfortunately, the tools available to effectively treat rejection--corticosteroids and anti lymphocyte globulins--have remained largely unchanged for over 60 years. Evidence accumulated over many years has indicated that these treatments inadequately or incompletely treat rejection.

Discovering clues one cell at a time

In the new study, researchers used powerful single-cell genomic analysis technologies to painstakingly compare biopsy samples from transplanted kidneys that encountered acute cellular rejection. The studies also compared rejections occurring under the commonly used maintenance immunosuppressive agent (tacrolimus) and two newer alternative medications (belatacept and iscalimab).

The analysis was so detailed that the team was able to track how gene expression changed within specific populations of cells that drive rejection damage, which the authors termed allospecific CD8 expanded T cell clones (CD8EXP).

The researchers say this study is the first to apply a combination of single-cell RNA analysis with single-cell T-cell receptor (TCR) analysis to explore acute kidney transplantation rejection.

"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," Shi said.

Woodle described CD8EXP cells as the "tip of the spear" in rejection.

The work revealed three key findings:

First, even when an acute rejection event was stopped, the research revealed that treatments often are not thorough enough to eliminate all the T cells that had cloned themselves to attack the transplant. In some cases, hostile T cells persisted for months after anti-rejection treatment.

This suggests that multiple rejection events, previously believed to be entirely separate, may actually be one, longer, smouldering rejection event. Addressing lurking cloned T cells that eluded initial treatment will likely require improved testing techniques and adopting more consistent practice standards.

Second, the team found roughly 20 "clonotypes" of CD8EXP T cells--from a potential of thousands--that reproduced themselves to mount attacks against a transplanted organ. The types differed according to the receptors the T cells carried. The relatively low number of clonotypes excited the researchers because it will make it easier to search for potential new treatments to stop transplant rejection.

By studying these rare, but efficient cells, the team found distinct cellular signatures occurring during a rejection event that varied depending upon which maintenance immune-suppression drug was used. The different genes involved raise the possibility of using other medications not typically associated with treating organ rejection as new weapons for specific situations.

For example, this team also recently reported success at using an mTOR inhibitor called everolimus to help patients that did not benefit from belatacept treatment But that same drug appears to offer no similar benefit when tacrolimus treatment is involved. This work led to a currently ongoing clinical trial led by Woodle to treat patients with belatacept and everolimus for maintenance immunosuppression.

Third, the same T cell types causing rejection events also can be detected in urine samples.

Why a urine test matters

Currently, obtaining the crucial details underlying the rejection of a transplanted kidney requires collecting a tissue biopsy, a surgical procedure that requires visiting a hospital. Conducting multiple biopsies to track treatment outcomes over time is expensive and potentially risky for patients.

However, urine tests could be collected more frequently in a non-invasive manner and potentially without the inconvenience of visiting a hospital. In addition to directly supporting patient care, a viable urine test would help accelerate the research work required to evaluate new anti-rejection treatment protocols. The research also demonstrated that CD8EXP T cells that were found in the rejecting organ were also present in the urine.

"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 said. (ANI)