Clinical significance of PD-L1 expression in serum-derived exosomes in NSCLC patients

Abstract

BackgroundExosomes are 50–150 nm endocytic vesicles secreted by almost all type of cells that carry bioactive molecules from host. These small vesicles are considered to be novel cross-talk circuits established by tumor cells and tumor microenvironment. Previous studies have shown certain biological influence of exosomal programmed cell-death ligand 1 (Exo-PD-L1) on immune suppression and dysfunction. The aim of the current study was to investigate the impact of Exo-PD-L1 and soluble PD-L1 (sPD-L1) on non-small cell lung cancer (NSCLC) and explore the concordance between Exo-PD-L1 and PD-L1 expression in matched tumor tissues in NSCLC patients.Methods85 consecutive patients from April 2017 to December 2017 at General Hospital of Eastern Command Theatre who were primarily diagnosed with NSCLC and 27 healthy individuals were enrolled in this study. Two milliliters of whole blood samples were collected from each participant and further centrifuged. Exosomes were derived from serum using the commercial kit (Total Exosome Isolation Kit), which was further identified by Western blotting analysis (CD63/TSG101), transmission electron microscope analysis (TEM) and nanoparticle tracking analysis (NTA). Exosomes were next solubilized for Exo-PD-L1 detection by enzyme-linked immuno-sorbent assay (ELISA). PD-L1 expression in matched tissue were assessed by PD-L1 immunohistochemistry (IHC) (clone 28-8) assay. Tumor proportion score (TPS) ≥ 1% was deemed as “positive” in this study and TPS < 1% was deemed as “negative”. Written informed consent were obtained before acquisition of all data and biological sample. Data were analyzed using SPSS 20.0 and Graphpad Prism 5 software. Chi square test was conducted to estimate the correlation between Exo-PD-L1 levels, sPD-L1 levels, PD-L1 IHC profiles and clinicopathological features. For all analysis, a two-sided p < 0.05 was considered significant statistically.ResultsExo-PD-L1 levels were higher in NSCLC patients with advanced tumor stage, larger tumor size (> 2.5 cm) (p < 0.001), positive lymph node status (p < 0.05) and distant metastasis (p < 0.05). In contrast, sPD-L1 levels were not different between NSCLC patients and healthy donors, it was not correlated with any clinicopathologic features except for tumor size (> 2.5 cm) (p < 0.05). In addition, Exo-PD-L1 levels showed slight correlation with sPD-L1 levels (Spearman’s correlation at r = 0.3, p = 0.0027) while no correlation with PD-L1 IHC profiles was detected.ConclusionsIn conclusion, Exo-PD-L1, but not sPD-L1, was correlated with NSCLC disease progression, including tumor size, lymph node status, metastasis and TNM stage. However, Exo-PD-L1 was not associated with PD-L1 IHC status.

Exosome Release of Drugs: Coupling with Epithelial-Mesenchymal Transition

“…Immune check point inhibitors target cell surface molecules such as programmed cell death-1 (PD-1) and Programmed cell death-ligand 1 and permit tumor cell killing by tumor-specific CTL. However, recent studies have shown that PD-L1 is often found on exosomes, playing key roles in spreading immunosuppression [76][77][78][79][80][81]. Chemotherapeutics are also reported to be secreted with exosomes.…”

<p>High Soluble Programmed Death-Ligand 1 Predicts Poor Prognosis in Patients with Nasopharyngeal Carcinoma</p>

“…8,17 Immune checkpoint proteins in the bloodstream are potential markers for cancer diagnosis, prognosis assessment, and guiding immunotherapy. 8,[10][11][12]14,15,18,19 Our results indicated that the expression profiles of immune checkpoint proteins differ significantly between the plasma of patients with NPC and healthy volunteers, and sPD-L1 is highly expressed in the plasma of patients with NPC. Furthermore, high levels of sPD-L1 were associated with the tumor burden and levels decreased significantly after treatment.…”

“…[7][8][9] Immune checkpoint proteins in the tumor microenvironment can enter the blood circulation through tumor cell apoptosis or exosomes and are potential markers for liquid biopsy. [10][11][12][13] Soluble immune checkpoint proteins, especially soluble PD-L1 (sPD-L1), have potential prognostic value 14,15 but are not well characterized in NPC.…”

Extracellular Vesicles and Tumor-Immune Escape: Biological Functions and Clinical Perspectives

“…The presence of PD-L1 in TEVs is largely reported in the literature (Figure 2). All available data have pointed out the direct role of exosomal PD-L1 (ExoPD-L1) in altering immune surveillance and its clinical relevance as a non-invasive tumor and immune cell biomarker in cancer [129][130][131]. Chen and colleagues have demonstrated that the sorting of PD-L1 in sEVs is not a random event, but it is specifically driven by ESCRT subunit HRS and Rab27a.…”

“…Moreover, by using human melanoma xenografts in nude mice, they have shown that PD-L1 was present in circulating sEVs from mice bearing human melanoma xenografts but not from control mice [65]. Several studies have confirmed the presence of PD-L1 + sEV in plasma and serum of patients with cancer [62,67,130,132]. An interesting study of Chulinget al highlighted the clinical significance of circulating PD-L1 in head and neck squamous cell carcinoma (HNSCC).…”