Graft dendritic cell p40 homodimers activate donor-reactive endogenous memory CD8 T cells within higher risk allografts

Abstract

Abstract Memory T cells with donor-reactivity pose a major barrier to successful transplantation and tolerance induction. Longer cold ischemic storage (CIS) prior to transplantation promotes endogenous donor-reactive memory CD8 T cell infiltration and activation within cardiac allografts to directly mediate CTLA-4Ig-resistant rejection between days 15–22 post-transplant vs. > 60 days for allografts subjected to minimal CIS. Using BrdU labeling, graftinfiltrating memory CD4 and CD8 T cells proliferated much more strongly within allografts subjected to 8 vs. 0.5 hr CIS and proliferation of endogenous memory CD8 T cells within the higher risk allografts required recipient CD4 T cells, graft dendritic cells (DC) and graft expression of class II MHC, CD40 and IL-12p40, but not p35. IL-12p40 but not IL-12 p35 or IL-23p19 mRNA was elevated at 48 hr post-transplant in allografts subjected to 8 vs. 0.5 hr CIS and the increase in p40 mRNA was reduced to the levels seen in 0.5 CIS allografts by recipient CD4 T cell depletion, but was restored by treating with agonist anti-CD40 mAb. p40 homodimers, but not p70 heterodimers, were increased in allografts subjected to 8 hr CIS and were dependent on recipient CD4 T cells. Peri-transplant anti-p40 mAb reversed CTLA-4Ig-resistant rejection of higher risk allografts and peri-transplant p40 homodimers induced endogenous memory CD8 T cell proliferation within allografts subjected to 0.5 hr CIS to the levels observed in allografts subjected to 8 hr CIS. These data indicate that endogenous memory CD8 T cell activation within higher risk cardiac allografts requires CD4 T cell help via CD40-CD154 interactions with graft DC to induce their production of p40 homodimers.