July 8, 2015

Organ transplant rejection may not be permanent

Organ transplant rejection in previously tolerant hosts does not lead to permanent immune memory, mouse study shows

(July 8, 2015)  Rejection of transplanted organs in hosts that were previously tolerant may not be permanent, report scientists from the University of Chicago. Using a mouse model of cardiac transplantation, they found that immune tolerance can spontaneously recover after an infection-triggered rejection event, and that hosts can accept subsequent transplants as soon as a week after. This process depends on regulatory T-cells, a component of the immune system that acts as a "brake" for other immune cells. The findings, published online in Nature Communications on July 7, support inducing immune tolerance as a viable strategy to achieve life-long transplant survival.

"Transplantation tolerance appears to be a resilient and persistent state, even though it can be transiently overcome," said Anita Chong, PhD, professor of transplantation surgery at the University of Chicago and co-senior author of the study. "Our results change the paradigm that immune memory of a transplant rejection is invariably permanent."

To prevent transplant rejection in patients with end-stage organ failure, a lifelong regimen of immune-suppressing drugs is almost always required. While difficult to achieve, immune tolerance -- in which a transplanted organ is accepted without long-term immunosuppression -- can be induced in some patients. However, rejection can still be triggered by events such as bacterial infection, even after long periods of tolerance. It has been assumed that the immune system remembers rejection and prevents future transplants from being tolerated.