Quantification‐Promoted Discovery of Glycosylated Exosomal PD‐L1 as a Potential Tumor Biomarker

Abstract Exosomal programmed cell death ligand 1 (exoPD‐L1) has emerged as a promising biomarker for cancer diagnosis and immunotherapy outcome prediction. However, the existing quantitation methods are incapable of addressing the heterogeneity of exoPD‐L1 glycosylation, which has been demonstrated to be the institutional basis for PD‐L1/PD‐1 interaction and the crucial participant in inhibiting the activity of CD8 + T cells. Herein, an aptamer‐ and lectin‐induced proximity ligation assay combined with quantitative real‐time polymerase chain reaction for precise quantitation of glycosylated exoPD‐L1 is developed. Leveraging the metabolism‐free lectin labeling of glycosylation, the glycosylation‐independent aptamer tagging of PD‐L1, and excellent selectivity of dual‐recognition, this method enables glycosylated exoPD‐L1 quantitation with high sensitivity and selectivity in a wash‐free manner. As a result, this method is able to distinguish the levels of glycosylated exoPD‐L1 between healthy donors and cancer patients with sensitivity and specificity of 100%. Compared with the total circulating exoPD‐L1 level, glycosylated exoPD‐L1 is for the first time identified to be a more reliable biomarker for tumor diagnosis. Overall, this strategy holds a great potential for revealing the significance of exoPD‐L1 glycosylation and converting glycosylated exoPD‐L1 into a reliable clinical indicator.