CD4 and neoplasm: Interestingly, tumor‐derived exosomes transport multiple membrane‐bound and soluble factors that suppress the function of human cytotoxic CD4+ and CD8+ T cells.23 Administration of the immunotherapeutic agent IRX‐2 was shown to protect CD8+ T cells from tumor‐derived exosome‐induced apoptosis, resulting in enhanced T‐cell‐mediated antitumor activity.24 Paradoxically, the ability of exosomes to cross the cell membrane has also been explored for targeted drug delivery systems in cancer immunotherapy.25