Expression profiles and clinical value of plasma exosomal Tim-3 and Galectin-9 in non-small cell lung cancer

Abstract

Exosomes are membrane-bound, virus-sized vesicles present in circulating blood. Tumor cells are avid producers of exosomes, which are thought to mimic molecular features of parent tumor cells. T-cell immunoglobulin- and mucin-domain-containing molecule 3 (Tim-3) is a the next-generation immune checkpoint that can be activated by its ligand Galectin-9 to negatively regulate the anti-tumor immune response. However, the characteristics of plasma exosomal Tim-3 and Galectin-9 (Exo-T/G) in cancer remained unknown. This study was conducted to investigate the expression patterns and clinical value of plasma exosomal total protein (Exo-pro) and Exo-T/G in non-small cell lung cancer (NSCLC). Plasma was collected from 103 NSCLC patients including 60 early stages and 43 advanced stages disease samples as well as 56 healthy subjects. Exosomes were isolated from plasma by commercial exosome precipitation solution and identified by western blotting of CD63 and transmission electron microscopy. Exo-pro concentration was measured by the BCA assay. Enzyme-linked immunosorbent assay was used to quantify Exo-T/G. Additionally, 34 NSCLC samples were applied to directly detect plasma TIM-3 (Plas-T) and Galectin-9 (Plas-G). Our results showed that Exo-pro, Exo-T, and Exo-G were significantly increased in NSCLC plasma compared to that in the healthy samples. High levels of Exo-T and Exo-G were all positively correlated with several malignant parameters, including larger tumor size, advanced stages, and more distant metastasis. High levels of Exo-pro and Exo-T were also correlated with more lymph node metastasis. Additionally, plasma from lung squamous cell carcinoma showed higher Exo-T and Exo-G compared with that from lung adenocarcinoma. ALK-positive patients showed to have decreased Exo-T and Exo-G levels. Pearson's correlation analysis revealed a significant correlation between Exo-pro and Exo-T/G, Exo-T and Exo-G, Exo-T and Plas-T, Exo-G and Plas-G, and Plas-T and Plas-G. Together, our data revealed that Exo-pro, especially Exo-T and Exo-G could be potential biomarkers for NSCLC. Further studies focusing on pure tumor-derived exosomes isolated from plasma were needed.