Clinical Significance of PD-L1 Exosomes in Plasma of Head and Neck Cancer Patients.

Unlabelled: The microenvironment of head and neck squamous cell carcinomas (HNSCC) is highly immunosuppressive. HNSCCs expressing elevated levels of PD-L1 have especially poor outcome. Exosomes that carry PD-L1 and suppress T-cell functions have been isolated from plasma of patients with HNSCC. The potential contributions of PD-L1 exosomes to immune suppression and disease activity are evaluated. Exosomes isolated from plasma of 40 HNSCC patients by size exclusion chromatography were captured on beads using anti-CD63 Abs, stained for PD-1 and PD-L1 and analyzed by flow cytometry. The percentages and mean fluorescence intensities (MFI) of PD-L1 and PD-1 exosome/bead complexes were correlated with the patients' clinicopathologic data. PD-L1 or PD-L1 exosomes were incubated with activated CD69 human CD8 T cells ± PD-1 inhibitor. Changes in CD69 expression levels on T cells were measured. Patients' plasma was tested for soluble PD-L1 (sPD-L1) by ELISA. Levels of PD-L1 carried by exosomes correlated with patients' disease activity, the UICC stage and the lymph node status ( = 0.0008-0.013). In contrast, plasma levels of sPD-L1 or exosome PD-1 levels did not correlate with any clinicopathologic parameters. CD69 expression levels were inhibited ( < 0.03) by coincubation with PD-L1 but not by PD-L1 exosomes. Blocking of PD-L1 exosome signaling to PD-1 T cells attenuated immune suppression. PD-L1 levels on exosomes, but not levels of sPD-L1, associated with disease progression in HNSCC patients. Circulating PD-L1 exosomes emerge as useful metrics of disease and immune activity in HNSCC patients.

Significance: Circulating PD-L1 exosomes in HNC patients' plasma but not soluble PD-L1 levels associate with disease progression. .