Fig. 2

Roles of exosomes in cancer. Exosomes are critically involved in tumor initiation, growth, progression, metastasis, and drug resistance by transferring oncogenic proteins and nucleic acids. Tumor-derived exosomes can activate endothelial cells to support tumor angiogenesis and thrombosis. Tumor-derived exosomes can convert fibroblasts and MSCs into myofibroblasts to facilitate tumor angiogenesis and metastasis. Tumor-derived exosomes contribute to create an immunosuppressive microenvironment by inducing apoptosis and impairing the function of effector T cells and NK cells, inhibiting DC differentiation, expanding MDSCs, as well as promoting Treg cell activity. Tumor-derived exosomes can mobilize neutrophils and skew M2 polarization of macrophages to promote tumor progression. Moreover, tumor-derived exosomes can help tumor cells develop drug resistance by transferring multidrug-resistant proteins and miRNAs, exporting tumoricidal drugs, and neutralizing antibody-based drugs. In turn, exosomes from activated T cells, macrophages, and stromal cells can promote tumor metastasis and drug resistance