Heat Shock Protein 70, Released from Heat-Stressed Tumor Cells, Initiates Antitumor Immunity by Inducing Tumor Cell Chemokine Production and Activating Dendritic Cells via TLR4 Pathway

Extracellular heat shock proteins (HSP) can activate dendritic cells (DC) and monocytes/macrophages, and HSP derived from tumor cells have been regarded as potent adjuvant facilitating presentation of tumor Ags and induction of antitumor immunity. However, the roles and the underlying mechanisms of releasable HSP in the induction of antitumor immunity have not been fully elucidated. In this study, we report that heat stress can induce the release of various HSP from tumor cells, which, in turn, activate tumor cells to produce chemokines for chemoattraction of DC and T cells via TLR4 signaling pathway. In vivo, we find that the infiltration and function of DC and T cells within tumor after local hyperthermia are increased significantly. We also provide evidence that HSP70 proteins released by tumor cells and TLR4 expressed by tumor cells/DC are essential for the chemoattraction of DC/T cells and for the subsequent induction of tumor-specific antitumor immunity. Therefore, our study suggests that heat stress-induced releasable HSP70 proteins from tumor cells play important roles in the initiation of antitumor immunity by inducing tumor cell production of chemokines and by activating the chemoattracted DC via TLR4 pathway.