Importance of the PD-1/PD-L1 Axis for Malignant Transformation and Risk Assessment of Oral Leukoplakia

Abstract

Background: The programmed cell death ligand 1/programmed cell death receptor 1 (PD-L1/PD-1) Immune Checkpoint is an important modulator of the immune response. Overexpression of the receptor and its ligands is involved in immunosuppression and the failure of an immune response against tumor cells. PD-1/PD-L1 overexpression in oral squamous cell carcinoma (OSCC) compared to healthy oral mucosa (NOM) has already been demonstrated. However, little is known about its expression in oral precancerous lesions like oral leukoplakia (OLP). The aim of the study was to investigate whether an increased expression of PD-1/PD-L1 already exists in OLP and whether it is associated with malignant transformation. Material and Methods: PD-1 and PD-L1 expression was immunohistologically analyzed separately in the epithelium (E) and the subepithelium (S) of OLP that had undergone malignant transformation within 5 years (T-OLP), in OLP without malignant transformation (N-OLP), in corresponding OSCC and in NOM. Additionally, RT-qPCR analysis for PD-L1 expression was done in the entire tissues. Additionally, the association between overexpression and malignant transformation, dysplasia and inflammation were examined. Results: Compared to N-OLP, there were increased levels of PD-1 protein in the epithelial and subepithelial layers of T-OLP (pE = 0.001; pS = 0.005). There was no significant difference in PD-L1 mRNA expression between T-OLP and N-OLP (p = 0.128), but the fold-change increase between these groups was significant (Relative Quantification (RQ) = 3.1). In contrast to N-OLP, the PD-L1 protein levels were significantly increased in the epithelial layers of T-OLP (p = 0.007), but not in its subepithelial layers (p = 0.25). Importantly, increased PD-L1 levels were significantly associated to malignant transformation within 5 years. Conclusion: Increased levels of PD-1 and PD-L1 are related to malignant transformation in OLP and may represent a promising prognostic indicator to determine the risk of malignant progression of OLP. Increased PD-L1 levels might establish an immunosuppressive microenvironment, which could favor immune escape and thereby contribute to malignant transformation. Hence, checkpoint inhibitors could counteract tumor development in OLP and may serve as efficient therapeutic strategy in patients with high-risk precancerous lesions.

Oral epithelial dysplasia: Recognition, grading and clinical significance

“…The immune checkpoint regulator PD-L1 is minimally expressed in normal oral epithelium but is expressed in a proportion of dysplastic epithelium either independent of dysplasia grade (Chen et al, 2019;Dave et al, 2020;Gonçalves et al, 2017) or increased with increasing grade (Ries et al, 2021;Sieviläinen et al, 2018) and proportional to CD8+ lymphocyte density in the infiltrate (Chen et al, 2019). Analysis and interpretation is complex, but expression has been claimed to be greater in dysplasias preceding malignant transformation than those not-progressing (Dave et al, 2020;Ries et al, 2021).…”

“…The immune checkpoint regulator PD-L1 is minimally expressed in normal oral epithelium but is expressed in a proportion of dysplastic epithelium either independent of dysplasia grade (Chen et al, 2019;Dave et al, 2020;Gonçalves et al, 2017) or increased with increasing grade (Ries et al, 2021;Sieviläinen et al, 2018) and proportional to CD8+ lymphocyte density in the infiltrate (Chen et al, 2019). Analysis and interpretation is complex, but expression has been claimed to be greater in dysplasias preceding malignant transformation than those not-progressing (Dave et al, 2020;Ries et al, 2021). However, the immune environment of dysplasia is complex and other mechanisms underlie immune surveillance including epithelial dendritic cells (Öhman et al, 2012;Pellicioli et al, 2017;Souto et al, 2018) and the frequent mutation of p53, which downregulates the innate immune response and inhibits immune surveillance (Ghosh et al, 2021).…”

Comprehensive Immunoprofiling of High-Risk Oral Proliferative and Localized Leukoplakia

“…11], which is common among leukoplakia biopsies and may also harbor malignant potential (12); as prior molecular studies suggest genetic overlap between KUS and dysplasia includes frequent alterations in TP and KMTC (13). In addition, several preclinical studies have reported increased expression of programmed cell death receptor 1 (PD-1) ligand (PD-L1), on leukoplakic lesions with higher degrees of dysplasia (14)(15)(16), suggesting that immune escape may serve as a key mechanism for malignant transformation to oral carcinoma. To that end, we are currently accruing to a clinical trial of the PD-1 inhibitor nivolumab as preventative immunotherapy in high-risk oral leukoplakia, namely PVL or proliferative leukoplakia (NCT03692325).…”

Expression of inflammatory mediators in biofilm samples and clinical association in inflammatory bowel disease patients—a preliminary study

“…To show the relative change in expression rates, the fold change is used. A fold change of 2 means that the expression has doubled (28).…”