Analyses of Exosomal HER2 in Breast Cancer and the Effect of Respective Exosome-Immune Complexes on Trastuzumab-Based Immunotherapy.

Monoclonal antibodies like trastuzumab have shown clinical success in cancer treatment, but patient responses vary, and resistance can develop, possibly due to tumor microenvironment factors. In this study, we explored the role of HER2-positive exosomes in counteracting one of the mechanisms of action of trastuzumab: antibody-dependent cell-mediated cytotoxicity (ADCC). We conducted a comprehensive analysis of HER2 expression on exosomes purified from the plasma of breast cancer patients and different breast cancer cell lines using various purification methods. Purified exosomes were analyzed using the single-particle interferometric reflectance imaging sensor (SP-IRIS)-based ExoView platform. To gain better insight into the formation of exosomal-immune complexes with trastuzumab, we used the ExoView platform to analyze the CD9/HER2/Human IgG phenotype of exosomes at the single vesicle level. Additionally, in a standard functional ADCC assay, formation of exosome-immune complexes with trastuzumab reduced the killing of breast cancer target cells. Together, our findings show that exosomes can function as decoys for immunotherapy, reducing its efficacy, and that SP-IRIS-based analysis can be used to identify levels of HER2-expressing exosomes in patients, which could aid in patient management.