[Tumour-derived exosomes and their roles in cancer]

Exosomes are nanometer sized membrane vesicles, released in the extracellular milieu following the fusion of the external membrane of multivesicular body (MVB) with plasma membrane. They perform a certain function in immune regulation. Exosomes have been shown to be released by cells of hematopoietic and non-hematopoietic origin. Tumour-derived exosomes (TEX) exist in the supernatant of tumour cells, plasma and malignant effusions of tumour patients. They contain native candidate tumour associated antigen and are capable of transferring antigens to T lymphocytes, therefore efficiently promoting cytotoxic T lymphocyte (CTL) activation and producing antitumor immunity. However, recent evidence shows that tumor exosomes may induce immunologic tolerance and even activate immunosuppression which makes tumour escape from the immune surveillance of the host immune system. In addition, tumor exosomes may mediate a growth-promoting effect on tumor cells. These discrepancies are almost certainly due to differences in the phenotype of the exosomes.