Background: Exosomes are a subset of small (30-150nm) extracellular vesicles (EVs) of the endocytic origin that mediate intercellular communication in health and disease. Exosomes are actively produced by tumor cells, circulate freely in body fluids and carry messages that alter functions of normal cells in the tumor microenvironment (TME), including immune cell functions. The ability of melanoma exosomes to reprogram immune cell functions might contribute to disease progression.

Methods: To evaluate effects of melanoma cell-derived exosomes (MTEX) on human immune cell subsets, we isolated exosomes from plasma of 12 patients with melanoma and separated MTEX from non-MTEX by immune capture using anti-CSPG4 mAb on beads. These exosome fractions, and exosomes from plasma of 6 normal donors used as controls (NC), were studied by on-bead flow cytometry to quantify their surface protein profiles and in co-incubation assays with immune cell subsets for functional attributes. Phenotypic and functional profiles of MTEX and non-MTEX were compared.

Results & Conclusion: MTEX were enriched (p<0.005)( in FasL and TRAIL, induced apoptosis of CD8+T cells, down-regulated CD69 expression levels on T cells and inhibited their proliferation (all p<0.0005). MTEX also interfered with NK cell functions (p<0.001). Non-MTEX were enriched (P<0.005) in co-stimulatory proteins, CD40L, OX40L, OX40 and, similar

to exosomes of NC, were not immunosuppressive. Thus, MTEX, present in excess in plasma of patients with metastatic melanoma, mediate immune suppression and contribute to immune escape of the tumor.

Citation Format: Priyanka Sharma, Brenda Diergaarde, Soldano Ferrone, John M. Kirkwood, Theresa L. Whiteside. Effects of melanoma cell-derived exosomes in melanoma patients’ plasma on immune cell functions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3091.