Impairment of recipient cytolytic activity attenuates allograft vasculopathy

We investigated the role of CD4⁺ and CD8⁺ T subsets as well as T cell cytolytic effector mechanisms in the aortic allograft model of allograft vasculopathy using CD4 and CD8 gene knockout mice (CD4^-/-, CD8^-/-) and mice deficient in cytolytic effector pathways. Medial apoptosis at 2 weeks was reduced in CD8^-/- mice and in mice where cytotoxic T cell activity was compromised. At 8 weeks, substantial medial damage was observed in wild-type (WT) and CD4^-/- recipients but medial preservation was evident in CD8^-/- mice and in mice with impaired cytotoxic T cell activity. The intima/media ratio, a comprehensive measure of allograft vasculopathy, was similar in WT and CD4^-/- recipients but was significantly reduced in CD8^-/- mice and mice with impaired cytotoxic T cell activity. These data indicate that CD8⁺ T cells contribute to the vascular remodeling that is characteristic of allograft vasculopathy. They also show that CD8⁺ T cells participate in allograft vasculopathy in the absence of CD4⁺ T cell help. We further demonstrated that WT mice exhibited robust allograft vasculopathy in the presence of cyclosporin A immunosuppression but that allograft vasculopathy was ablated in cyclosporin-treated CD8^-/- mice. This supports the hypothesis that non-CD8⁺ T cell effector mechanisms are sensitive to calcineurin inhibitor therapy but that CD8⁺ T cell-mediated allograft vasculopathy is refractory to such treatment. Taken together, our data suggest that CD8⁺ T cells contribute to the induction of vascular remodeling in allograft vasculopathy and provide evidence that novel therapies which target CD8⁺ T cell effector function might be effective in mitigating AV in the clinical setting.