Selective Enrichment and Detection of PD-L1 Positive Extracellular Vesicles Derived from Human Plasma and Patient Derived Tumor Cells

Recent studies reported that the level of PD-L1 carried by extracellular vesicles (EVs) could distinguish the presence of tumors and had a good correlation with the response to immunotherapy. In this manuscript, we developed an EV-TdT assay for isolation and detection of PD-L1+ EVs. PD-L1+ EVs were directly captured from biological samples by PD-L1 antibodies immobilized on the magnetic beads (MBs), then combined with cholesterol modified DNA probes, which initiated the terminal deoxynucleotidyl transferase (TdT) to amplify the signal of PD-L1+ EVs. The EV-TdT assay enables selective enrichment of PD-L1+ EVs in low-content samples, such as blood and excreta of small amounts of primary tumor cells. Moreover, it can evaluate the relative abundance of PD-L1+ EVs in the total population, by this way, we observed that PD-L1+ EVs were more abundant in the extracellular microenvironment of primary tumor cells than in human plasma, indicating that quite a bit of PD-L1+ EVs were derived from tumor cells. The EV-TdT assay has been proven a practical method for detection of PD-L1+ EVs and is greatly potential as an alternative to existing assays for screening immunotherapy benefit populations.