Role of PD-L1 in Regulatory T Cell-Mediated Suppression of Corneal Neovascularization

Corneal neovascularization (NV) leads to inflammation and fibrosis, thereby compromising visual acuity and corneal graft survival. Despite existing antiangiogenic therapies, clinical outcomes remain suboptimal. This study explores the antiangiogenic potential of regulatory T cells (Tregs) through programmed death-ligand 1 (PD-L1). In vitro tube formation assays were performed by co-culturing MS1 endothelial cells with Tregs. In addition, murine corneal suture-induced NV and high-risk corneal transplantation models were used to evaluate the effects of subconjunctival Treg injections in vivo. Wild-type (WT) Tregs inhibited endothelial tube formation, whereas PD-L1^-/- Tregs failed to exert this effect. Blocking B7-1 on MS1 cells attenuated the inhibitory effect of WT Tregs, indicating a PD-L1-B7-1 interaction as a key mechanism. Furthermore, vascular endothelial growth factor A expression in MS1 cells was significantly reduced on co-culturing with WT Tregs, a response that was absent with PD-L1^-/- Tregs. In vivo, subconjunctival Treg injections significantly reduced corneal NV in both corneal suture-induced NV and high-risk corneal transplantation models, and this effect was lost on blocking PD-L1. These results show that PD-L1 expressed by Tregs plays a pivotal role in suppressing corneal angiogenesis, acting through a contact-dependent mechanism through B7-1, leading to down-regulation of vascular endothelial growth factor A, highlighting the function of PD-L1 in Treg modulation of corneal angiogenesis.