Tumor-derived exosomal proteins have emerged as promising biomarkers for cancer diagnosis, but the quantitation accuracy is hindered by large numbers of normal cell-derived exosomes. Herein, we developed a dual-target-specific aptamer recognition activated in situ connection system on exosome membrane combined with droplet digital PCR (ddPCR) (TRACER) for quantitation of tumor-derived exosomal PD-L1 (Exo-PD-L1 ). Leveraging the high binding affinity of aptamers, excellent selectivity of dual-aptamer recognition, and the high sensitivity of ddPCR, this method exhibits significant sensitivity and selectivity for tracing tumor-derived Exo-PD-L1 in a wash-free manner. Due to the excellent sensitivity, the level of tumor-derived Exo-PD-L1 detected by TRACER can distinguish cancer patients from healthy donors, and for the first time was identified as a more reliable tumor diagnostic marker than total Exo-PD-L1 . The TRACER strategy holds great potential for converting exosomes into reliable clinical indicators and exploring the biological functions of exosomes.
Keywords: aptamers; exosomes; immunotherapy; proximity ligation assay.
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