MRI Can Detect Transplant Rejection

This pre-clinical development, described in the January 24, 2006, issue of the journal Proceedings of the [U.S.] National Academy of Sciences (PNAS), could ultimately provide a non-invasive way to identify 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,” stated Dr. Chien Ho, professor of biological sciences at the Mellon University College of Science (Pittsburgh, PA, USA) and director of the Pittsburgh NMR Center for Biomedical Research. "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. Perhaps most importantly, this advance will allow doctors to provide highly personalized care that could prevent transplant rejection.”

Organ transplantation is the favored clinical approach to treat end-stage organ failure; however, transplant patients face a lifetime of immunosuppressive therapy and the risk of losing the new organ because of rejection. Dr. Ho's unique application examines transplant rejection non-invasively by monitoring 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,” stated Dr. Ho.

For the study, Dr. Yijen Wu, a research biologist at the Pittsburgh NMR Center for Biomedical Research, tagged macrophages with nanometer (USPIO), or micrometer (MPIO)-sized paramagnetic iron oxide particles, which are very sensitive to the magnetic fields used during MRI. Dr. Wu injected the MPIO or USPIO particles into laboratory rats that had received heart transplants three days earlier. Macrophages, which usually ingest foreign substances inside the body (such as bacteria), incorporated the particles. Utilizing MRI, the researchers then track tagged macrophages that infiltrated transplanted hearts. The researchers used a heterotropic heart model to assess organ rejection. In this model, a rat received a second functional heart, which was grafted into its abdomen. In this manner, the investigators can evaluate how a transplanted heart changes through sequential stages of rejection while the rat remains healthy.





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