Tumor-mediated mechanisms of dendritic cell (DC) tolerization and immune suppression. Tumor-derived soluble factors and exosomes promote DC-mediated Treg differentiation to generate an immune privileged site conducive to tumor progression. COX, cyclooxgenase; PGE2, prostaglandin E2; IDO, indoleamine 2,3-dioxygenase; RA, retinoic acid.