FAS and neoplasm: Exosomes have been found to exhibit the ability to induce immune suppression.139 For instance, tumor-derived exosomes upregulate specific immunosuppressive factors such as GM-CSF and TNF-α.43 They also impair the ability of natural killer (NK) cells to carry out cytotoxic functions by secreting TGF-1β or blocking IL-2 mediated activation.8 Exosomes can contain FAS and TRAIL ligands to induce the death-receptor activated killing of lymphocytes, extending their immune-modulating effects.4 The effect of tumor exosomes on cellular immunity has also been studied.