Bone marrow mesenchymal stem cell-derived exosomal miR-93-5p suppresses esophageal squamous cell carcinoma progression and immune escape through targeting PD-L1.

BACKGROUND: Esophageal squamous cell carcinoma (ESCC) is a malignant tumor with poor prognosis, and immune escape and abnormal cell behavior are key factors promoting its progression. Bone marrow mesenchymal stem cell (BMSC)-derived exosomes and microRNAs (miRNAs) play important roles in tumor regulation. This study aimed to explore the regulatory effect and molecular mechanism of BMSC-derived exosomal miR-93-5p on the malignant progression and immune escape of ESCC. METHODS: The BMSC-derived exosomes were extracted and characterized using transmission electron microscopy, size analysis and marker protein detection. miR-93-5p mimic or negative control was transfected into BMSCs. Cell counting kit-8 (CCK-8), 5-ethynyl-2'-deoxyuridine (EDU) staining, Transwell and 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) assays were used to detect the effects of exo-mimic on ESCC cells (KYSE-30, TE-1) viability, proliferation, migration and reactive oxygen species (ROS) accumulation. T cell-ESCC cell co-culture system was established to evaluate immune escape. The luciferase reporter, RNA-pulldown and fluorescence in situ hybridization (FISH) assays verified the targeting relationship between miR-93-5p and programmed death-ligand 1 (PD-L1). Nude mouse xenograft model was used to detect in vivo tumor growth. RESULTS: BMSCs and their exosomes were successfully isolated; miR-93-5p was upregulated in exosomes. Exo-mimic significantly inhibited ESCC cell viability, proliferation, migration, promoted ROS accumulation. Exo-mimic downregulated PD-L1 expression at both messenger ribonucleic acid (mRNA) and protein levels, enhanced T cell-mediated killing efficiency against ESCC cells, and significantly suppressed xenograft tumor growth in nude mice. Luciferase reporter, RNA-pulldown and FISH assays further confirmed that PD-L1 is a direct downstream target of miR-93-5p. CONCLUSIONS: BMSC-derived exosomes carrying miR-93-5p can inhibit ESCC progression via PD-L1 suppression and reverse tumor immune evasion in an in vitro T cell co-culture system, which provides a novel potential therapeutic target and strategy for the clinical treatment of ESCC.