Immune modulation of T-cell and NK (natural killer) cell activities by TEXs (tumour-derived exosomes)

Body fluids of cancer patients contain TEXs (tumour-derived exosomes). Tumours release large quantities of TEXs, and the protein content of exosome or MV (microvesicle) fractions isolated from patients’ sera is high. TEXs down-regulate functions of immune cells, thus promoting tumour progression. We isolated TEXs from tumour cell supernatants and sera of patients with solid tumours or AML (acute myelogenous leukaemia). The molecular profile of TEXs was distinct from that of circulating exosomes derived from normal cells. TEXs were co-incubated with activated T-cells, conventional CD4⁺CD25^neg T-cells or CD56⁺CD16⁺ NK (natural killer) cells respectively. TEXs down-regulated CD3ζ and JAK3 (Janus kinase 3) expression in primary activated T-cells and mediated Fas/FasL (Fas ligand)-driven apoptosis of CD8⁺ T-cells. TEXs promoted CD4⁺CD25^neg T-cell proliferation and their conversion into CD4⁺CD25^hiFOXP3⁺ (FOXP3 is forkhead box P3) Treg cells (regulatory T-cells), which also expressed IL-10 (interleukin 10), TGFβ1 (transforming growth factor β1), CTLA-4 (cytotoxic T-lymphocyte antigen 4), GrB (granzyme B)/perforin and effectively mediated suppression. Neutralizing antibodies specific for TGFβ1 and/or IL-10 inhibited the ability of TEXs to expand Treg cells. TEXs obtained at diagnosis from AML patients’ sera were positive for blast-associated markers CD33, CD34, CD117 and TGFβ1, and they decreased cytotoxic activity of NK cells isolated from NC (normal control) donors, induced Smad phosphorylation and down-regulated NKG2D receptor expression. Correlations between the TEX molecular profile or TEX protein levels and clinical data in cancer patients suggest that TEX-mediated effects on immune cells are prognostically important. In contrast with exosomes released by normal cells, TEXs have immunosuppressive properties and are involved in regulating peripheral tolerance in patients with cancer.