**Abstract**

Tumor cells, like most other cells, release exosomes called tumor-derived exosomes (TEX) and are vital for intercellular communication. TEX are membranebound extracellular vesicles (EVs), containing unique cargo reminiscent of the parent tumor cells and possess immunomodulatory functions. TEX carries factors that directly promote immunosuppression in the tumor microenvironment and indirectly attract immunosuppressive T-regulatory (Treg) cells. The tumor-secreted exosomes can transfer their cargo by multiple mechanisms like fusion, phagocytosis, and receptor-mediated endocytosis, activating the recipient cells. TEX directly engages and releases cytokines, inactivating natural killer (NK) cells and T-cells and activating apoptosis. Tumor-derived exosomes also release soluble factors to suppress dendritic cell (DC) maturation while activating the expansion of immunesuppressive cells like Myeloid-derived suppressor cells (MDSCs) and Regulatory T (Treg) cells. Several studies have shown the relevance of TEX containing tumorassociated antigens (TAA) in reducing the efficacy of cancer immunotherapy and adoptive cell therapy. Hence understanding the basic biology and mechanism of TEX-mediated immunosuppression is critical in discovering cancer biomarkers and finding better immunotherapy and cell therapy approaches. In this chapter, we have discussed TEX biogenesis, TEX's structural and molecular features, TEX-mediated immunosuppression, and its relation to immunotherapy.

**Keywords:** extracellular vesicles (EVs), tumor-derived exosomes (TEX), immune modulation, immunotherapy, TEX Cargo
