The Establishment and Decay of Co-Stimulation Blockade Induced Tolerance to Semi-Allogenic Heart Grafts 2257765

Abstract Introduction Preventing graft rejection in transplant recipients relies on broadly immunosuppressive drugs with negative side effects that reduce patient adherence. Thus, achieving tolerance through transient immunomodulatory therapies is the aspirational goal in clinical transplantation. In mouse models, transient co-stimulation blockade (CoB) targeting CD28:CD80/86 or CD154:CD40/CD11b interactions can induce but not maintain long-term graft acceptance. We characterized the mechanisms leading to decay in donor-specific (DS) T cell hyporesponsiveness in a mouse model of CoB-induced heart transplant tolerance. Methods Utilizing a murine semi-allogeneic (2W1S-OVA.BALB/c x C57BL/6) heart transplant in C57BL/6 recipients, we examined DS CD4+ and CD8+ T cells in recipients receiving a tolerance-inducing treatment of anti-CD154 in conjunction with donor splenocytes (TolRx). Controls were naive or untreated C57BL/6 recipients that acutely rejected their allografts. Full spectrum flow cytometry and single-cell RNA sequencing (scRNA-Seq) were used to characterize DS T cells isolated from the recipient spleen. Results Early stable tolerance was associated with phenotypically low-avidity, naive-like DS CD4+ and CD8+ T cells, and increased numbers of DS Foxp3+ regulatory T cells (Tregs). scRNA-Seq confirmed phenotypic findings and revealed extensive transcriptional changes in DS Tregs that led to the emergence of 2 subsets of Tregs, namely Foxp3 high and effector IL-10 high. Erosion of tolerance was associated with Treg expansion and the emergence of high-avidity, effector-like DS T cells that were phenotypically similar to acute rejection. Conclusion Our findings indicate that CoB induced tolerance results in a DS T cell response dominated by Tregs, as well as phenotypically naive conventional CD4+ T and CD8+ T cells. Erosion of tolerance was associated with activation and expansion of DS T cells. Experiments are ongoing to test if this late activation is due to loss in the regulatory function of DS Tregs. Funding Source Funding from NIAID - 5P01AI097113-13 and NHLBI- 5T32HL007605-40 Topic Categories Transplantation Immunology (TRAN)