Donor induced graft tolerance by sCD83 after corneal transplantation

• Applicants: Professor Dr. Felix Bock; Professor Dr. Alexander Steinkasserer
• Subject Area: Ophthalmology
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 367339186

Immune responses reflect a complex interplay of cellular and extracellular components, which define the microenvironment of a tissue. Therefore, factors that locally influence the microenvironment and re-establish tolerance might be beneficial to mitigate immune-mediated reactions, including the rejection of a transplant. In the previous funding period, we demonstrated that pre-incubation of donor tissue with the immune mod- ulator soluble CD83 (sCD83) significantly improves graft survival using a high-risk corneal transplantation model. The induction of tolerogenic mechanisms in graft recipients was achieved by a significant upregulation of Tgfb, Foxp3, Il27, and Il10 in the transplant and an increase of regulatory dendritic cells (DCs), macrophages (Mφ), and T cells (Tregs) in eye-draining lymph nodes. The presence of sCD83 during in vitro DC and Mφ generation directed these cells toward a tolerogenic phenotype leading to reduced proliferation-stimulating activity in MLRs. Mechanistically, sCD83 induced a tolerogenic Mφ and DC phenotype, which favors Treg induction and significantly increased transplant survival after adoptive cell transfer. Conclusively, pre-incubation of corneal grafts with sCD83 significantly prolongs graft survival by modulating recipient Mφ and DCs toward tolerance and thereby establishing a tolerogenic microenvironment. This functional strategy of donor graft pre-treatment paves the way for new therapeutic options in the field of transplantation. Furthermore, we analyzed the tolerogenic capacity of donor antigen presenting cells modulated by allograft pre-incubation. Therefore, we developed the "removal strategy" to remove excess sCD83 after pre-incubation and determine the donor-mediated effect on high-risk transplant survival. Pre-incubation of murine donor corneas with sCD83 and subsequent removal of excess sCD83 from the transplant significantly prolonged high-risk transplant survival. Remarkably, pre-incubation and transplantation of TLR4-deficient donor tissue resulted in an abolition of the sCD83 effect on transplant survival. Thus, these results clearly demonstrate that sCD83-mediated, donor derived effects on corneal high-risk transplant survival are TLR4 dependent. Furthermore, we could show in preliminary experiments that exosomes derived from sCD83-treated DCs are less potent to induce allogenic DC maturation. Based on these results or objective of this application is to elucidate the „Mode of Action“ of the direct, donor induced, graft tolerance by sCD83 after corneal transplantation by deciphering the role of TLR4 down-stream signalling events in sCD83 induced, direct allotolerance, assessing exosomes as vehicles for the direct, sCD83 mediated graft tolerance and by analysing the role of endogenous CD83 in the direct and indirect tolerance induction in corneal transplantation.

• DFG Programme: Research Grants