PD‐L1 Acts Independently of PD‐1 as a Marker of Pathologic Fibroblasts in Laryngotracheal Stenosis

Abstract

ObjectiveLaryngotracheal stenosis (LTS) describes fibrotic airway obstruction that is life‐threatening without treatment. Targeted therapies are needed as an adjunct to surgical management. We have previously observed the upregulation of immune checkpoint programmed cell death (PD)‐1 and its ligand, PD‐L1, in patients with LTS. This study aims to determine whether PD‐1 and PD‐L1 play a role in the pathophysiology of LTS.Study DesignBasic science.SettingLaboratory.MethodsFibroblasts derived from the subglottic scar of 5 iSGS patients were cultured ex vivo with transforming growth factor β (TGFβ), PD‐L1 agonist (PD‐1), and PD‐L1 blockade (anti‐PD‐L1). PD‐L1, TGFβ receptor II (TGFβRII), and Collagen‐1 expression were quantified by flow cytometry. A validated chemomechanical injury model of subglottic stenosis was applied in PD‐1 knockout and wild‐type (WT) mice, and subglottic thickening was assessed by histologic analysis.ResultsTGFβ significantly increased the expression of PD‐L1 and Collagen‐1 in human airway scar fibroblasts (P < .05). PD‐1 knockout mice demonstrated no significant difference in subglottic airway fibrosis compared to WT mice. Ex vivo PD‐L1 modulation had no impact on fibroblast Collagen‐1 expression. PD‐L1 high‐intensity fibroblasts expressed greater Collagen‐1 and TGFβRII compared to PD‐L1 low‐intensity fibroblasts.ConclusionPD‐1 knockout does not protect mice from the development of laryngotracheal fibrosis. However, its ligand, PD‐L1 is highly expressed on pathologic fibroblasts unique to scar, characterized by high Collagen‐1 and TGFβRII expression. PD‐L1 is also upregulated in conjunction with Collagen‐1 by TGFβ stimulation. PD‐L1 may act independently of PD‐1 to sensitize fibroblasts to TGFβ, suggesting direct targeting of PD‐L1 may have therapeutic potential in LTS.