Regulatory T cells promote corneal endothelial cell survival following transplantation via interleukin-10

Abstract

| INTRODUC TI ONCorneal transplantation is the most common form of tissue grafting worldwide. 1 When performed on an uninflamed and nonvascularized host bed, the graft survival rate exceeds 90%. 2 However, inflammation and vascularization of the host bed disrupt the cornea's relatively tolerant immune microenvironment, and graft survival rates fall to ≈50% despite maximum immunosuppression in highrisk recipients. 3-5 Immune rejection is the leading cause of corneal graft failure. 6 Corneal endothelial cells (CEnCs) are the target of the effector immune response mediated primarily by graft-targeting CD4 + interferon gamma (IFNγ + ) T helper type 1 (Th1) cells. 7,8 When the CEnC count decreases beyond a certain threshold, they are no longer capable of maintaining corneal graft transparency and the graft fails. 9,10 Substantial progress has been made in determining the mechanisms by which host factors, such as recipient bed vascularity and inflammation, influence the immune response to corneal allografts. 11-15 Forkhead box protein 3 (Foxp3)-positive regulatory T cells (Tregs) are a subset of CD4 + T cells that play a critical role in maintaining immune tolerance. 16 Studies performed by our laboratory 17-24 and others 25-27 indicate the critical contribution of Foxp3 + Tregs to immune tolerance in the setting of corneal transplantation.The functional competence of corneal endothelial cells (CEnCs) is critical for survival of corneal allografts, but these cells are often targets of the immune response mediated by graft-attacking effector T cells. Although regulatory T cells (Tregs) have been studied for their role in regulating the host's alloimmune response towards the graft, the cytoprotective function of these cells on CEnCs has not been investigated. The aim of this study was to determine whether Tregs suppress effector T cell-mediated and inflammatory cytokine-induced CEnC death, and to elucidate the mechanism by which this cytoprotection occurs. Using 2 well-established models of corneal transplantation (low-risk and high-risk models), we show that Tregs derived from low-risk graft recipients have a superior capacity in protecting CEnCs against effector T cellmediated and interferon-γ and tumor necrosis factor-α-induced cell death compared to Tregs derived from high-risk hosts. We further demonstrate that the cytoprotective function of Tregs derived from low-risk hosts occurs independently of direct cell-cell contact and is mediated by the immunoregulatory cytokine IL-10. Our study is the first to report that Tregs provide cytoprotection for CEnCs through secretion of IL-10, indicating potentially novel therapeutic targets for enhancing CEnC survival following corneal transplantation. K E Y W O R D Sanimal models: murine, basic (laboratory) research/science, corneal transplantation/ ophthalmology, immune regulation, T cell biology, tolerance

Tissue Engineering Meets Nanotechnology: Molecular Mechanism Modulations in Cornea Regeneration

“…Treatment with T regulatory cells (Tregs) or tolerogenic APCs induced by immunoregulatory factors can help restore immune privilege and thus lead to the longterm survival of the corneal allograft in high-risk recipients. Host alloimmunity is the main cause of loss of donor CEnCs after corneal transplantation [106]. Tregs play a critical role in suppressing immune responses after tissue transplantation.…”

“…This function is significantly compromised in Tregs derived from high-risk hosts. The cytoprotective role of Tregs is mediated by the immunomodulatory cytokine IL-10; hence, IL-10 is effective in protecting CEnC from inflammatory cytokines during cell death [106].…”

Corneal Allografts: Factors for and against Acceptance

“…Interestingly, Coco et al demonstrated a protective role of Tregs directly on epithelial cells of the cornea. Combination of mouse model of corneal transplantation and in vitro experiments imitating proinflammatory environment of the rejection process showed superior capacity of acceptors' Tregs to produce IL-10 [ 102 ].…”

Targeting NF-κB c-Rel in regulatory T cells to treat corneal transplantation rejection

“…To evaluate the cytoprotective function of Tregs, a cornea-in-thecup assay was performed and optimized as described previously. 21 Briefly, cornea cups from normal BALB/c mice were cultured with Tregs in complete RPMI-1640 medium with or without recombinant mouse IFNγ (100 ng/mL, Preprotech) and TNFα (100 ng/mL, Preprotech) for 12 h at 37°C. After incubation, cornea cups were washed with PBS and then fixed in 4% paraformaldehyde for 15 min at room temperature.…”