Fibroblast Programmed Cell Death Ligand 1 Promotes Osteoclastogenesis in Odontogenic Keratocysts.

Local aggressive growth of odontogenic keratocysts (OKCs) can cause serious bone destruction, even resulting in pathologic fractures of the mandible. The mechanism of osteoclastogenesis in OKCs was explored by investigating the role of programmed cell death ligand 1 (PD-L1), a key immune checkpoint, in OKCs and its relationship with the M2 isoform of pyruvate kinase (PKM2), a key enzyme of glycolysis. The data from immunohistochemistry, real-time quantitative PCR, Western blot, and flow cytometry indicated that the expression level of PD-L1 was significantly increased in the stroma and fibroblasts of OKCs (OKC-Fs) when compared with oral mucosa. Double-labeling staining demonstrated that osteoclasts in OKCs spatially interacted with PD-L1-positive OKC-Fs. Exogenous expression of PD-L1 in OKC-Fs promoted osteoclastogenesis when OKC-Fs were co-cultured with osteoclast precursors (RAW264.7 cells). Because OKC-Fs exhibit energy dependency and acquire energy from PKM2-mediated glycolysis, this study generated stable PKM2 knockdown OKC-Fs using shRNAs against PKM2, and found that PD-L1 expression level was decreased by PKM2 knockdown. Furthermore, Spearman rank correlation analysis showed that there was a positive correlation between the immunostaining of PKM2 and PD-L1 in OKC samples. In addition, double-labeling immunofluorescence showed colocalizations between PKM2 and PD-L1 in the fibrous tissue walls of OKCs. In conclusion, PD-L1 in fibroblasts promotes osteoclastogenesis in OKCs, which is regulated by PKM2.

ICAM-1-mediated adhesion is a prerequisite for exosome-induced T cell suppression.

Tumor-derived extracellular vesicles (TEVs) suppress the proliferation and cytotoxicity of CD8+ T cells, thereby contributing to tumor immune evasion. Here, we report that the adhesion molecule intercellular adhesion molecule 1 (ICAM-1) co-localizes with programmed death ligand 1 (PD-L1) on the exosomes; both ICAM-1 and PD-L1 are upregulated by interferon-γ. Exosomal ICAM-1 interacts with LFA-1, which is upregulated in activated T cells. Blocking ICAM-1 on TEVs reduces the interaction of TEVs with CD8+ T cells and attenuates PD-L1-mediated suppressive effects of TEVs. During this study, we have established an extracellular vesicle-target cell interaction detection through SorTagging (ETIDS) system to assess the interaction between a TEV ligand and its target cell receptor. Using this system, we demonstrate that the interaction of TEV PD-L1 with programmed cell death 1 (PD-1) on T cells is significantly reduced in the absence of ICAM-1. Our study demonstrates that ICAM-1-LFA-1-mediated adhesion between TEVs and T cells is a prerequisite for exosomal PD-L1-mediated immune suppression.