Introduction: During organ transplantation, ischemia-reperfusion injury (IRI) is an inescapable challenge that detrimentally impacts graft outcome. While I/R induced molecular mechanisms mediating injury of ischemic tissues are increasingly being delineated, cellular elements contributing to IRI remain poorly understood. The presence of pre-existing alloreactive memory T cells in the recipient is now widely recognized as a major barrier to tolerance induction and maintenance. We have reported that endogenous memory CD8 T cells with donor-reactivity infiltrate cardiac allografts within 24hrs of reperfusion and are activated to produce IFN-Γ. The mechanisms promoting infiltration of these T cells into the graft and their activities impacting graft function and survival remain poorly defined.

Methods: A/J (H-2^a) hearts were subjected to 0.5hrs, 4hrs, or 8hrs of cold ischemia in UW solution before being heterotopically transplanted to C57BL/6 (H-2^b) recipients.

Results: CD8⁺CD62L^low memory T cell infiltration into cardiac allografts at 48hrs post-transplant was significantly influenced by the duration of ischemia imposed on the graft. A mean of 3.0×10⁴ cells/g were found to infiltrate allografts after 0.5hrs of cold ischemia that increased to 7.5×10⁴ cells/g and 10.6×10⁴ cells/g after 4 and 8hrs, respectively. Prolonged ischemia increased graft expression of IL-1, IL-6, and TNFΑ 48hrs after reperfusion and anti-TNFΑ or anti-IL-6 treatment at reperfusion significantly inhibited CD8 memory infiltration. Prolonged ischemia resulted in a 40-60 fold increase in IFN-Γ and perforin production by early graft infiltrating memory CD8 T cells and the heightened infiltration and effector functions of these cells was associated with markedly increased graft inflammation and myocyte damage at day 5 post-transplant. Furthermore, while treatment with CTLA4-Ig significantly prolonged survival of grafts subjected to minimal cold ischemia (MST=20.5), grafts subjected to prolonged ischemia were minimally sensitive to treatment with CTLA4-Ig (MST=d11) and this result was dependent on early memory CD8 infiltration.

Conclusion: These data demonstrate that prolonged ischemic insult to cardiac allografts enhances the early infiltration and effector functions of CD8 memory T cells post-transplant to mediate tissue inflammation and organ dysfunction. These studies provide novel insights into mechanisms underlying the poor outcomes associated with cadaver donor grafts.

« Back to 2013 American Transplant Congress