Abstract 771: Cytokine Expression and Levels in Plasma-Derived Exosomes Are Underestimated As Contributors to Cytokine Profiles in Cancer Patients and Healthy Donors

Abstract Exosomes play a key role in cell-to-cell signaling. Emerging evidence suggests that biologically active cytokines may be present on the surface or in the lumen of exosomes. We evaluated cytokines in exosomes isolated by size-exclusion chromatography from pre-cleared plasma of 13 patients with head and neck cancer and three healthy donors (HDs). Paired untreated plasma and detergent-treated exosomes were studied by Luminex and cytokine microarrays. On-bead flow cytometry was used to assess relative levels of cytokines on the surface or in the vesicle lumen. Measured by Luminex, for the majority of cytokines (10 of 12), the level observed in plasma was concordant with the level in exosomes. MCP-1 and MIF were the exceptions. They were highly elevated in untreated plasma. Cytokine levels in exosomes determined in parallel by Luminex and the microarray were concordant, except for IL-1β and GM-CSF, which were elevated in Luminex assays. Our data show that only a fraction of most cytokines in untreated plasma is soluble and detectable by Luminex, while the rest is associated with exosomes and can only be detected after exosome permeabilization. Exosome cytokine profiles and levels measured by either method discriminated cancer patients from healthy donors as did levels of soluble cytokines in plasma. By on bead flow cytometry, the relative levels of cytokines in the lumen and on the exosome surface were confirmed for IFN-γ, IL-17, TNF-α and TGF-β, while IL-8 was only detected in the exosome lumen. Thus, cytokines are packaged into exosomes, which carry cytokines on the surface and in the vesicle lumen and contribute to inaccurate, largely underestimated, levels of plasma cytokines reported by laboratories. Citation Format: Chang- Sook Hong, Brenda Diergaarde, Theresa L. Whiteside. Cytokine expression and levels in plasma-derived exosomes are underestimated as contributors to cytokine profiles in cancer patients and healthy donors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 771.