Non-invasive Technique Detects Transplant Rejection at Cellular Level

By: Lauren Ward and Amy Pavlak

Research Could Revolutionize Care of Transplant Patients

Organ transplant patients face years of invasive biopsies that help doctors monitor the body for signs of organ rejection. Carnegie Mellon scientists hope a new technology they developed makes such invasive procedures a thing of the past—and improving the quality of life for transplant patients.

Biological Sciences Professor Chien Ho and his colleagues have developed a promising tool that uses magnetic resonance imaging (MRI) to track immune cells as they infiltrate a transplanted heart in the early stages of organ rejection. This pre-clinical advance, described in an upcoming issue of the Proceedings of the National Academy of Sciences (PNAS), ultimately could provide a noninvasive way to detect transplant rejection in patients.

"We have reported for the first time the ability to monitor single immune cells in a live animal using MRI. This could revolutionize the management of transplant patients," Ho said.

"Successful translation of this work to the clinic ultimately will reduce the number of biopsy procedures and should greatly improve the quality of life for cardiac transplant patients, especially children," added Ho, who directs the Pittsburgh NMR Center for Biomedical Research. "Perhaps most importantly, this advance will allow doctors to provide highly personalized care that could prevent transplant rejection."

Organ transplantation is the preferred clinical approach to treat end-stage organ failure, but transplant patients face a lifetime of immunosuppressive therapy and the risk of losing the new organ due to rejection. Physicians typically monitor patients for organ rejection following a heart transplant by performing frequent heart biopsies for the first year. Heart biopsies are invasive procedures that involve threading a catheter through the internal jugular vein to the heart's right ventricle and snipping out several tiny pieces of tissue. A pathologist then tests the tissue to identify the presence of immune cells (such as macrophages) as well as other pathological changes in the transplanted heart tissue that indicate the graft is being rejected by the body's immune system.

These procedures are costly, uncomfortable and must be repeated annually to monitor and treat any rejection. Biopsies also are problematic, according to Ho, because they do not look at the whole organ. By only sampling several small areas, a biopsy may miss the area of the transplanted organ where immune cells are gathering—one of the first signs of rejection.

Ho's novel approach investigates transplant rejection non-invasively by observing macrophage accumulation in heart tissues using MRI.

"We were able to use MRI to visualize individual macrophages. By tracking individual cells, we also were able to observe, for the first time, that rejection progresses from the outside of the heart to the inside," said Ho. "Up to now, this phenomenon hasn't been observed in pre-clinical or clinical research because biopsy samples are very limited in location and size."

The reported findings also have broader implications for biology and medicine, according to Ho.

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