Exosomes from distinct cellular sources, including immune cells (B cells and dendritic cells), cancer cells, epithelial, and mesenchymal cells, shed exosomes with cargos that can influence the proliferation and respective activity of recipient cells of both the innate and adaptive immune system. CD4+ and CD8+ T cells [cytotoxic T cells (CTL)] can be directly or indirectly influenced by exosomes, stimulating or suppressing their proliferation and function(s). PBMC, peripheral blood mononuclear cell; X?, other potential immunomodulatory proteins.