Cross-presentation of the oncofoetal tumor antigen 5T4 from irradiated prostate cancer cells - a key role for heat shock protein 70 and receptor CD91

Immune responses contribute to the success of radiation therapy of solid tumors; however, the mechanism of triggering CD8 + T-cell responses is poorly understood. Antigen cross-presentation from tumor cells by dendritic cells (DC) is a likely dominant mechanism to achieve CD8 + T-cell stimulation. We established a crosspresentation model in which DCs present a naturally expressed oncofoetal tumor antigen (5T4) from irradiated DU145 prostate cancer cells to 5T4-specific T cells. The aim was to establish which immunogenic signals are important in radiationinduced cross-presentation. Radiation (12 Gy) caused G2/M cell-cycle arrest and cell death, increased cellular 5T4 levels, high-mobility protein group-B1 (HMGB1) release and surface calreticulin and heat-shock protein-70 (Hsp70) expression in DU145 cells. DCs phagocytosed irradiated tumor cells efficiently, followed by upregulation of CD86 on phagocytic DCs. CD8 + 5T4-specific T cells, stimulated with these DCs, proliferated and produced IFN. Inhibition of HMGB1 or the TRIF/MyD88 pathway only had a partial effect on T-cell stimulation. Unlike previous reports, we found no evidence that DCs carrying Asp299Gly toll-like receptor-4 (TLR4) single nucleotide polymorphism had impaired ability to cross-present tumor antigen. However, pre-treatment of tumor cells with Hsp70 inhibitors resulted in a highly significant and robust prevention of antigen cross-presentation and CD86 upregulation on DCs co-cultured with irradiated tumor cells. Blocking the Hsp70 receptor CD91 also abolished cross-presentation. Together, results from our study demonstrate that radiation induces immunologically relevant changes in tumor cells, which can trigger CD8 + T-cell responses via a predominantly Hsp70-dependent antigen cross-presentation process. on June 18, 2017. © 2015 American Association for Cancer Research. cancerimmunolres.aacrjournals.org Downloaded from Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. Author Manuscript Published OnlineFirst on February 12, 2015; DOI: 10.1158/2326-6066.CIR-14-0079