Background

Approximately 50% of cardiac transplants fail in the long term, and currently, there are no specific treatments to prevent chronic rejection. In the clinic, donor cardiac graft ischemia time is limited to within a few hours and correlates with delayed graft function and organ failure. It is still unknown how ischemic injury negatively influences allograft function over the long term despite advances in immunosuppression therapy.

Methods

Allogeneic cardiac grafts were stored at 4 C for 4 hr before being transplanted into T/B cell–deficient Rag−/− mice or T/B/natural killer (NK) cell–deficient γc−/− Rag−/− mice. Grafts were harvested 60 days after transplantation and indicators of chronic allograft vasculopathy (CAV) were quantified.

Results

We have found that cold ischemia of cardiac grafts induces CAV after transplantation into Rag1−/− mice. Interestingly, cold ischemia–induced CAV posttransplantation was not seen in T/B/NK cell–deficient γc−/− Rag−/− mice. However, cardiac grafts in γc−/− Rag−/− mice that received an adoptive transfer of NK cells developed CAV, supporting the role of NK cells in CAV development. Analysis of various cytokines that contribute to NK cell function revealed high interleukin (IL)-6 expression in cardiac grafts with CAV. In addition, IL-6–deficient cardiac grafts did not develop CAV after transplantation into allogeneic Rag−/− mice.

Conclusion

These data demonstrate that cold ischemia and NK cells play critical roles in the development CAV. Natural killer cells and injured grafts may play a reciprocal role for CAV development in an IL-6–independent manner. Specific therapeutic strategies may be required to attenuate NK cell contribution to chronic cardiac rejection.