Homogeneous, Low‐volume, Efficient, and Sensitive Quantitation of Circulating Exosomal PD‐L1 for Cancer Diagnosis and Immunotherapy Response Prediction

Abstract Immunotherapy has revolutionized cancer treatment, but its efficacy is severely hindered by the lack of effective predictors. Herein, we developed a homogeneous, low‐volume, efficient, and sensitive exosomal programmed death‐ligand 1 (PD‐L1, a type of transmembrane protein) quantitation method for cancer diagnosis and immunotherapy response prediction (HOLMES‐Exo PD‐L1 ). The method combines a newly evolved aptamer that efficiently binds to PD‐L1 with less hindrance by antigen glycosylation than antibody, and homogeneous thermophoresis with a rapid binding kinetic. As a result, HOLMES‐Exo PD‐L1 is higher in sensitivity, more rapid in reaction time, and easier to operate than existing enzyme‐linked immunosorbent assay (ELISA)‐based methods. As a consequence of an outstanding improvement of sensitivity, the level of circulating exosomal PD‐L1 detected by HOLMES‐Exo PD‐L1 can effectively distinguish cancer patients from healthy volunteers, and for the first time was found to correlate positively with the metastasis of adenocarcinoma. Overall, HOLMES‐Exo PD‐L1 brings a fresh approach to exosomal PD‐L1 quantitation, offering unprecedented potential for early cancer diagnosis and immunotherapy response prediction.