Cancer-derived extracellular vesicles: friend and foe of tumour immunosurveillance

Abstract

Extracellular vesicles (EVs) are important players of intercellular signalling mechanisms, including communication with and among immune cells. EVs can affect the surrounding tissue as well as peripheral cells. Recently, EVs have been identified to be involved in the aetiology of several diseases, including cancer. Tumour cell-released EVs or exosomes have been shown to promote a tumour-supporting environment in non-malignant tissue and, thus, benefit metastasis. The underlying mechanisms are numerous: loss of antigen expression, direct suppression of immune effector cells, exchange of nucleic acids, alteration of the recipient cells' transcription and direct suppression of immune cells. Consequently, tumour cells can subvert the host's immune detection as well as suppress the immune system. On the contrary, recent studies reported the existence of EVs able to activate immune cells, thus promoting the tumour-directed immune response. In this article, the immunosuppressive capabilities of EVs, on the one hand, and their potential use in immunoactivation and therapeutic potential, on the other hand, are discussed.This article is part of the discussion meeting issue 'Extracellular vesicles and the tumour microenvironment'.

Keywords: extracellular vesicles; innate immunity; natural killer cells; tumour immunology.

Figure 1.

Scheme of EVs carrying immunoactivating and immunosuppressing molecules and their impact on the immune response. Future research identifying yet unknown molecules expressed in and on the surface of EVs might clarify the mechanism underlying the switch from immune altering EVs to immunosuppressing T-EVs during tumour progression. Moreover, new biomarkers for tumours and therapeutic approaches enhancing the host's tumour-directed immune response could be envisioned.