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Emerging evidence indicates that intercellular communication between tumor cells and host components occurs not only through the release of soluble molecules and direct cell-to-cell contact, but also by extracellular secretion and uptake of membrane vesicles termed exosomes. Tumor exosomes are nanovesicular structures composed of a lipid bilayer with transmembrane proteins and soluble cytosolic components of the secreting cells. These organelles have recently gained increasing interest because of their proven ability to profoundly affect target cells in a large number of ways. By means of receptor/ligand binding and interaction mechanisms that remain poorly understood, this class of nanovesicles alters the properties of recipient cells through activation of defined signaling pathways as well as transfer of new molecules, enzymes and even genetic material. This chapter focuses on the phenotypic and functional features of tumor exosomes, in terms of their known effects on the immune system and tumor microenvironment components, in an attempt to address the crucial role they are likely to play in cancer progression and therapy.

Emerging evidence indicates that intercellular communication between tumor cells and host components occurs not only through the release of soluble molecules and direct cell-to-cell contact, but also by extracellular secretion and uptake of membrane vesicles termed exosomes. Tumor exosomes are nanovesicular structures composed of a lipid bilayer with transmembrane proteins and soluble cytosolic components of the secreting cells. These organelles have recently gained increasing interest because of their proven ability to profoundly affect target cells in a large number of ways. By means of receptor/ligand binding and interaction mechanisms that remain poorly understood, this class of nanovesicles alters the properties of recipient cells through activation of defined signaling pathways as well as transfer of new molecules, enzymes and even genetic material. This chapter focuses on the phenotypic and functional features of tumor exosomes, in terms of their known effects on the immune system and tumor microenvironment components, in an attempt to address the crucial role they are likely to play in cancer progression and therapy.