VLA-4/VCAM-1 Interactions Are Required for Endogenous Memory CD8 T Cell Mediated Cardiac Allograft Rejection.

Abstract

We recently reported that endogenous memory CD8 T cells infiltrate MHC-mismatched cardiac allografts and are activated to produce IFN-γ in response to donor class I MHC molecules within 24 hours after reperfusion in mice and reject allografts subjected to prolonged ischemic storage in the absence of de novo priming of donor-reactive effector T cells. The current study tested the efficacy of anti-VLA-4 mAb to inhibit this early CD8 T cell allograft infiltration and activation during cardiac allograft rejection. Syngeneic or A/J (H-2a) hearts subjected to 0.5 or 8 hrs of cold ischemic storage were transplanted to C57BL/6 (H-2b) recipients. Anti-VLA-4 mAb (200 μg) was given on days -1 and 0. CD4 and CD8 T cell, macrophage, and neutrophil infiltration into grafts was assessed on day 2 post-transplant by flow cytometry and immunohistochemistry. Levels of mRNA encoding inflammatory cytokines were measured by qPCR. Donor-reactive T cell priming to IFN-γ and IL-2 producing cells in recipient spleens was assessed by ELISPOT assay. Recipient treatment with anti-VLA-4 mAb decreased CD4 and CD8 T cell and macrophage, but not neutrophil, infiltration into allografts by 70% of that observed into allografts from control IgG-treated recipients on day 2 post-transplant and completely inhibited donor-reactive CD4 and CD8 T cell priming to IFN-γ and IL-2 producing cells until day 14. Anti-VLA-4 mAb significantly reduced intragraft mRNA levels of CXCL9, CXCL10, and IFN-γ, but not the acute phase cytokines, TNF-α, IL-1β and IL-6, on day 2 post-transplant. These effects led to substantial prolongation in allograft survival (MST: day 12.5 vs day 7.5 in control-Ig treated recipients, p < 0.01). In recipients given allografts subjected to prolonged cold ischemic storage, anti-VLA-4 mAb treatment inhibited endogenous memory CD8 T cell infiltration into allografts and the inflammatory response and significantly prolonged allograft survival. These data indicate that peri-transplant anti-VLA-4 mAb inhibits endogenous memory CD8 T-cells infiltration into allografts subjected to prolonged cold ischemic storage and the accompanying inflammation. Therapeutic targeting of this pathway will reduce the negative impact of early memory CD8 T cell-dependent inflammatory events on graft outcome that will be particularly important for recipients with high frequencies of donor-reactive memory CD8 T cells.