Tumor-derived inducible heat-shock protein 70 (HSP70) is an essential component of anti-tumor immunity

The anti-apoptotic function and tumor-associated expression of heat-shock protein 70 (HSP70) is consistent with HSP70 functioning as a survival factor to promote tumorigenesis. However, its immunomodulatory activities to induce anti-tumor immunity predict the suppression of tumor growth. Using the Hsp70.1/3(-/-)(Hsp70(-/-)) mouse model, we observed that tumor-derived HSP70 was neither required for cellular transformation nor for in vivo tumor growth. Hsp70(-/-) murine embryonic fibroblasts (MEFs) were transformed by E1A/Ras and generated tumors in immunodeficient hosts as efficiently as wild-type (WT) transformants. Comparison of Bcr-Abl-mediated transformation of WT and Hsp70(-/-) bone marrow and progression of B-cell leukemogenesis in vivo revealed no differences in disease onset or survival rates, and Eμ-Myc-driven lymphoma in Hsp70(-/-) mice was phenotypically indistinguishable from that in WT Eμ-Myc mice. However, Hsp70(-/-) E1A/Ras MEFs generated significantly larger tumors than their WT counterparts in C57BL/6 J immune-competent hosts. Concurrent with this was a reduction in intra-tumoral infiltration of innate and adaptive immune cells, including macrophages and CD8(+) T cells. Evaluation of several potential mechanisms revealed an HSP70-chemokine-like activity to promote cellular migration. These observations support a role for tumor-derived HSP70 in facilitating anti-tumor immunity to limit tumor growth and highlight the potential consequences of anti-HSP70 therapy as an efficacious anti-cancer strategy.