The article reviews the role of exosomes in immunotherapy for solid cancers. Exosomes, which are extracellular vesicles, can deliver various intracellular molecules to adjacent or distant cells and organs, mediating various biological functions. They can both activate and inhibit the immune system, making them potential candidates for anticancer vaccines. Exosomes derived from blood, urine, saliva, and cerebrospinal fluid can serve as ideal biomarkers in cancer diagnosis and prognosis. Recent studies have shown that exosome-based therapy has made significant progress in drug transportation and immunotherapy. The article discusses the composition and sources of exosomes in the solid cancer immune microenvironment, the mechanisms by which exosomes influence immunotherapy, and the potential clinical applications of engineered exosomes and exosome vaccines. Despite the progress, challenges remain in the clinical application of exosome-based strategies for solid cancers. The review highlights the potential of exosomes in determining the efficacy of immunotherapy, diagnosis, and prognosis in solid cancer treatment.The article reviews the role of exosomes in immunotherapy for solid cancers. Exosomes, which are extracellular vesicles, can deliver various intracellular molecules to adjacent or distant cells and organs, mediating various biological functions. They can both activate and inhibit the immune system, making them potential candidates for anticancer vaccines. Exosomes derived from blood, urine, saliva, and cerebrospinal fluid can serve as ideal biomarkers in cancer diagnosis and prognosis. Recent studies have shown that exosome-based therapy has made significant progress in drug transportation and immunotherapy. The article discusses the composition and sources of exosomes in the solid cancer immune microenvironment, the mechanisms by which exosomes influence immunotherapy, and the potential clinical applications of engineered exosomes and exosome vaccines. Despite the progress, challenges remain in the clinical application of exosome-based strategies for solid cancers. The review highlights the potential of exosomes in determining the efficacy of immunotherapy, diagnosis, and prognosis in solid cancer treatment.