P40 Homodimers Indirectly Induce Endogenous Donor-Reactive Memory CD8 T Cell Proliferation within High-Risk Allografts via IL-15 signaling

Abstract

Abstract Increasing cold ischemic storage (CIS) time from 0.5 to 8 hrs prior to transplant promotes the increased proliferation and effector functions of endogenous donor-reactive memory CD4 and CD8 T cells infiltrating mouse cardiac allografts 24–48 hrs after transplant. This increased mCD8 T cell proliferation within high-risk allografts requires mCD4 T cell help via CD40-CD154 interactions with graft dendritic cells to induce IL-12p40 homodimer (p40 HD) production required for this mCD8 T cell proliferation. This study tested if p40HD directly or indirectly stimulate the mCD8 T cell proliferation within high risk allografts. While endogenous mCD8 T cells within highly ischemic allografts expressed both IL12Rβ1 and β2, most proliferating CD8 T cells did not express the IL12Rβ1 needed for p40 HD mediated signaling. Moreover, endogenous mCD8 T cells isolated from allografts did not proliferate ex vivo when cultured with p40 HD. qPCR analysis indicated increased mRNA expression of IL2Rα (CD25), β(CD122) and IL15 Rain infiltrating mCD8 T cells purified from allografts subjected to prolonged vs. minimal CIS on day 2 post-transplant. ELISA indicated longer CIS time markedly increased IL-12p40 and IL-15 protein in the allografts and these increases were dependent on recipient CD4 T cells. Blocking of p40 or IL-15 signaling with anti-p40 or anti-CD122 mAb inhibited endogenous mCD8 T cell proliferation within high-risk cardiac allografts and extended the survival of the high-risk allografts from day 18 to day 54 in CTLA-4Ig conditioned recipients. These results suggest that the p40 HD stimulate proliferative cytokines such as IL-15, which directly stimulate endogenous donor-reactive mCD8 T cell proliferation within the higher-risk allografts.