Optimizing Induction of CD8+ Regulatory T Cells by Allogeneic Human Plasmacytoid Dendritic Cells: 2343

Introduction: The need for life-long treatment with drugs that suppress the immune system non-specifically severely impairs the quality of life and patient survival after organ transplantation. Stimulation of in vivo generation of donor-specific regulatory T cells (Treg) would enable graft survival without non-specific immunosuppression. We have recently shown that human plasmacytoid dendritic cells (PDC) after stimulation via Toll-Like Receptor (TLR)-7 or 9 induce the differentiation of CD8+LAG-3+CTLA-4+CD38+ Treg that potently suppress T-cell allo-responses in a donor-specific manner. Interestingly, these CD8+ Treg not only inhibited naïve T-cells, but also allo-reactive memory T-cells, which are resistant to most tolerance induction protocols. The aim of this study was to optimize the yield of CD8+ Treg generated in co-culture with allogeneic PDC. Results: Human PDC activated by CD40-ligation induced 1.4-fold more expansion of allogeneic CD3+ T-cells compared to PDC activated by TLR-7 ligation. In addition, 27 ± 5% of CD8+ T-cells (n=4) showed a LAG-3+CTLA-4+CD38+ regulatory immunophenotype compared to 14± 5% after co-culture of T-cells with TLR7-ligated allogeneic PDC. The yield of CD8+ Treg after co-culture of CD3+ T cells with CD40-activated allogeneic PDC was 2.8-fold higher compared to co-cultures of T cells with PDC activated by TLR-7 ligation. The capacity of CD8+ Treg generated in co-cultures with CD40-activated PDC was similar to those generated by TLR7-activated PDC. Conclusion: PDC activated by CD40-ligation are superior to PDC activated by TLR-ligation to induce generation of CD8+ Treg. We consider cellular immunotherapy with donor-derived CD40-activated PDC to induce donor-specific CD8+ Treg in vivo in organ transplant recipients.