Small extracellular vesicles as biomarkers of response in recurrent/metastatic HNSCC patients treated with immunotherapy

Abstract

Abstract Background Biomarkers that effectively predict response to anti-PD-1 mAb therapy in cancer patients are an unmet need. We evaluated the utility of small extracellular vesicles (sEV) as biomarkers of response to immunotherapy in recurrent/metastatic (R/M) head and neck squamous cell carcinoma (HNSCC) patients. Methods Plasma sEV were isolated from 24 R/M HNSCC patients prior to immunotherapy initiation. sEV were separated by immune capture into T cell-derived CD3(+) and tumor-enriched CD3(−) subsets. Stimulatory and suppressive profiles of CD3(−) sEV were determined by on-bead flow cytometry. Differences were assessed using nonparametric tests. Multivariable Cox regression was used to evaluate the relationship with overall (OS) and progression free survival (PFS). Results CD3(−)CD44v3(+) sEV represented the majority of plasma sEV; the T-cell-derived CD3(+) fraction was significantly smaller. High CD3(+) sEV was associated with better OS and PFS. Total CD3(−)CD44v3(+) sEV was not associated with outcome. However, suppressive and stimulatory profiles were associated with OS; the suppressive/stimulatory ratio was associated with best response. Exploration of individual proteins on CD3(−) sEV showed that high PD-L1 and high CTLA-4 were associated with better outcomes. Conclusions Evaluation of the T cell-derived-CD3(+) and tumor-enriched CD3(−) plasma sEV subsets indicated their potential utility as biomarkers of response to immunotherapy.