Clinical significance of serum-derived exosomal PD-L1 expression in patients with advanced pancreatic cancer

Abstract

Background: Interactions between the programmed cell death receptor 1 (PD-1) and its ligand (PD-L1) lead to immune evasion in various tumors and are associated with poor prognosis in patients with pancreatic cancer; however, the roles of PD-L1-containing exosomes in pancreatic cancer is poorly understood. Here, we investigated the correlation between circulating exosomal PD-L1 (exoPD-L1) and PD-L1 expression in tumor tissue, and survival outcomes in patients with advanced PDAC.

Methods: Exosomes were derived from pre-treatment serum samples isolated using ExoQuick kit from 77 patients with advanced pancreatic cancer. Exosomal PD-L1 (exoPD-L1) was detected by enzyme-linked immunosorbent assay, and matched tumor tissues PD-L1 expression were evaluated by PD-L1 immunohistochemistry (22C3) assay, described with combined positive score. Cutoff value of exoPD-L1 for survival was assessed with receiver operating characteristic curve analysis. Kaplan-Meier analysis was performed to obtain median overall survival (OS), and hazard ratio was estimated using a stratified Cox regression model.

Results: The median exoPD-L1 serum concentration was 0.16 pg/mg, with undetected levels in seven patients. ExoPD-L1 levels were significantly higher in patients with systemic disease than in those with locally advanced disease (p = 0.023). There was a significantly higher proportion of elevated exoPD-L1 levels in patients with positive PD-L1 expression compared to patients with negative PD-L1 expression (p = 0.001). Patients were classified into groups with low and high exoPD-L1 levels using ROC curve-derived cutoffs (0.165 pg/mg; area under the curve, 0.617; p = 0.078). At a median follow-up of 8.39 months, the median OS was 13.2 (95% CI, 8.17-18.3) and 6.36 months (95% CI, 3.27-9.45) in the low and high exoPD-L1 groups, respectively (HR = 0.61; 95% CI, 0.35-1.04; p = 0.059). ExoPD-L1 levels did not affect the proportion of CD8⁺CD69⁺ effector cytotoxic T cells in either of the groups (p = 0.166).

Conclusions: The serum-derived exoPD-L1 levels were higher in metastatic pancreatic cancer than locally advanced disease. Collectively, higher serum exoPD-L1 levels in patients with advanced pancreatic cancer suggested worse survival outcomes and may have clinical implications.

Keywords: Exosomes; Pancreatic cancer; Prognosis; Programmed death ligand 1.