Exosomes, as extracellular vesicles, play a crucial role in immunotherapy for solid cancers by activating or inhibiting the immune system. They carry antigens and MHC molecules, making them potential anticancer vaccines and biomarkers for diagnosis and prognosis. Exosome-based therapies have advanced in drug delivery and immunotherapy, with potential clinical applications in engineered exosomes and vaccines. However, challenges remain in their clinical translation. Exosomes originate from various cells, including immune cells, tumor cells, and stromal cells, and have diverse functions in immune regulation, antigen presentation, and tumor progression. For example, NK-derived exosomes can mediate cytotoxicity against solid tumors, while TAM-derived exosomes promote tumor growth by suppressing immune responses. T-cell-derived exosomes can enhance antitumor immunity or suppress it, depending on their content. CAF-derived exosomes contribute to tumor progression by modulating the tumor microenvironment. MSC-derived exosomes can both promote and inhibit tumor growth, depending on their cargo. Tumor-derived exosomes inhibit immune responses and promote tumor metastasis. Exosomes carry proteins, lipids, RNAs, and DNA, and their contents influence immune responses and tumor progression. Exosomes affect immunotherapy by modulating immune cell function, signaling pathways, and tumor microenvironment. Understanding the mechanisms by which exosomes influence immunotherapy is essential for developing effective exosome-based therapies for solid cancers.Exosomes, as extracellular vesicles, play a crucial role in immunotherapy for solid cancers by activating or inhibiting the immune system. They carry antigens and MHC molecules, making them potential anticancer vaccines and biomarkers for diagnosis and prognosis. Exosome-based therapies have advanced in drug delivery and immunotherapy, with potential clinical applications in engineered exosomes and vaccines. However, challenges remain in their clinical translation. Exosomes originate from various cells, including immune cells, tumor cells, and stromal cells, and have diverse functions in immune regulation, antigen presentation, and tumor progression. For example, NK-derived exosomes can mediate cytotoxicity against solid tumors, while TAM-derived exosomes promote tumor growth by suppressing immune responses. T-cell-derived exosomes can enhance antitumor immunity or suppress it, depending on their content. CAF-derived exosomes contribute to tumor progression by modulating the tumor microenvironment. MSC-derived exosomes can both promote and inhibit tumor growth, depending on their cargo. Tumor-derived exosomes inhibit immune responses and promote tumor metastasis. Exosomes carry proteins, lipids, RNAs, and DNA, and their contents influence immune responses and tumor progression. Exosomes affect immunotherapy by modulating immune cell function, signaling pathways, and tumor microenvironment. Understanding the mechanisms by which exosomes influence immunotherapy is essential for developing effective exosome-based therapies for solid cancers.