Tumor-derived exosomes educate dendritic cells to promote tumor metastasis via HSP72/HSP105-TLR2/TLR4 pathway

How the tumor microenvironment educates dendritic cells (DCs) to promote tumorigenesis remains largely unknown, and the role of tumor-derived exosomes (TEXs) in tumorigenesis is controversial. Here, we report that in addition to the activation of DCs, TEXs induce DCs to produce increased interleukin-6 (IL-6), which dramatically promotes tumor invasion by increasing signal transducer and activator of transcription 3 (STAT3)-dependent matrix metalloproteinases 9 transcription activity in tumor cells. HSP72 and HSP105 on the TEX surface induce IL-6 secretion of DCs in a TLR2- and TLR4-dependent manner. In addition, HSP72 and HSP105 are predominantly present on exosomes from sera of tumor patients but not healthy people, indicating their value in tumor prediction. Furthermore, TEXs are powerful activators of DCs, and the depletion of IL-6 converts TEXs from tumor promoters to tumor inhibitors in vivo. Therefore, our results reveal a novel mechanism for the TEX-mediated education of DCs and shed light on the conundrum that TEXs present by playing dual roles in tumorigenesis.