Isolation of circulating exosomes and identification of exosomal PD-L1 for predicting immunotherapy response

Exosomes, a subgroup of extracellular vesicles secreted by multiple cells, have great potential as cancer biomarkers in clinical applications. However, enrichment and detection of exosomes from complex media remain a huge challenge due to their small size. Herein, we used iodixanol density gradient centrifugation for the isolation and purification of exosomes and label-free detection of exosomal PD-L1 using a biochip based on surface plasmon resonance (SPR-Exo(PD-L1)). The obtained exosomes are lipid-bilayer vesicles and the classical exosome markers CD9, CD63 and CD81 are highly enriched. Besides, PD-L1 is specifically expressed on exosomes instead of non-vesicular components or large extracellular vesicles. Compared with enzyme-linked immunosorbent assays, the SPR-Exo(PD-L1) assay could better distinguish exosomes derived from melanoma cells with different levels of PD-L1. Accurate measurement of exosomal PD-L1 could provide critical clinical information for cancer diagnosis and personalized immunotherapy of cancer.

Automated summary

Exosomes have potential as cancer biomarkers in clinical applications, but enrichment and detection from complex media remain challenging. This study used iodixanol density gradient centrifugation for exosome isolation and purification, and surface plasmon resonance (SPR) biochip for label-free detection of exosomal PD-L1. The method showed better specificity in distinguishing exosomes with different levels of PD-L1 compared to enzyme-linked immunosorbent assays.