Alloantigen specific CD8⁺ CD28^- FOXP3⁺ T suppressor cells induce ILT3⁺ ILT4⁺ tolerogenic endothelial cells, inhibiting alloreactivity

Endothelial cells have been shown to activate T cell responses to alloantigens, triggering transplant rejection. However, they may also play a role in tolerance induction. Using RT-PCR we show here that alloantigen specific CD8⁺CD28^- T suppressor cells generated in vitro are FOXP3 positive and interact with human endothelial cells. This interaction results in the induction of inhibitory receptors and down-regulation of costimulatory and adhesion molecules, thus rendering endothelial cells tolerogenic. In turn, tolerized endothelial cells elicit the differentiation of CD8⁺CD28^- FOXP3⁺ T suppressor cells. Taken together our data demonstrate a functional and phenotypic overlap between tolerogenic dendritic cells and endothelial cells. Furthermore, alloantigen specific CD8⁺CD28^- FOXP3⁺ T cells, which trigger the upregulation of inhibitory receptors in endothelial cells, are present in the circulation of heart allograft recipients in quiescence as demonstrated by flow cytometry, RT-PCR and luciferase transcription assays. Their detection facilitates the identification of patients who may benefit from partial or complete cessation of immunosuppressive therapy, a goal of obvious importance given the morbidity and mortality associated with chronic immunosuppression. Modulation of endothelial cells in favor of promoting tolerance may be important for long-term survival of organ allografts.