Researchers at the University of Pennsylvania report that otherwise innocuous cells within donated tissue may be responsible for triggering the chronic rejection of transplanted organs.

Dr. Bruce R. Rosengard, who reports on the study in Nature Medicine, said "these findings may have important implications for our understanding of chronic rejection, which targets blood vessels of the graft."

While acute rejection of the donor organ is the first hurdle for a transplant patient, chronic rejection -- believed triggered by certain highly immunogenic white blood cells from the donor, carried within the transplanted organ -- can occur years later.

But Rosengard said the Pennsylvania studies showed that donor endothelial cells, which are the cells that line blood vessels, activate the transplant recipient's CD8+ "killer" T cells directly triggering the rejection response.

"Transplanting tissue is like sneaking a dog into class: if your teacher doesn't notice immediately, it is only a matter of time before the barking gives it away," said Rosengard. "We have immunosuppressants that work fairly well to 'muzzle' the immune system from reacting to the initial exposure to highly immunogenic passenger cells, thus preventing acute rejection. The newly reported experiments hypothesize that long-term survival may depend on keeping the blood vessels in the transplant itself from announcing the presence of the graft.

"With further research, one hopes that this information can lead to new strategies to induce a lasting tolerance for donated tissue," said Rosengard.

Other sources: University of Pennsylvania