Programmed death ligand 1 (PD-L1) expression and tumor microenvironment: Implications for patients with oral precancerous lesions

Abstract

ObjectivesCancer immunoediting represents a relatively novel concept attempting to explain the process of tumor escape from the host immune system response. Here, we attempted to elucidate the role of programmed death ligand 1 (PD-L1), the tumor microenvironment, and tumor escape mechanisms that allow malignant transformation of oral precancerous lesions. Materials and methodsPatients with oral precancerous lesions managed at the Nara Medical University Hospital, Japan, (n=120) were enrolled in this study. Epithelial dysplasias were graded by experienced pathologists, and subepithelial PD-L1-, CD163-, and CD8-positive cells were counted in the superficial lamina propria of oral mucosa. Epithelial PD-L1 expression was evaluated according to the staining intensity. The association of clinicopathological factors with epithelial dysplasia, malignant-free survival time, and significance of risk factors for malignant transformation were determined. ResultsMultivariate analysis showed that the subepithelial CD163-positive cell count was the only significant risk factor for high-grade epithelial dysplasia (P<0.001), while subepithelial CD163- and PD-L1-positive cell counts, and epithelial PD-L1 positivity were significantly associated with malignant-free survival (P=0.004, 0.04, and <0.001, respectively). Subepithelial PD-L1-positive cell count and epithelial PD-L1 positivity were significantly associated with malignant transformation (P=0.01 and 0.04, respectively). ConclusionOur results indicate that PD-L1-expressing dysplastic epithelial and recruited subepithelial cells in oral precancerous legions may evade the host immune system, and that the inhibition of PD-1/PD-L1 pathway may potentially prevent malignant transformation of oral precancerous legions as well as can treat advanced cancers.