In various loading methods of whole tumor cells or their derivatives, cells fusion of dendritic cells (DCs) and tumor cells have some advantages for antigen presentation, and could up-regulate cytotoxic T cells (CTL) for multiple tumor antigens, including unknown antigens. However, the mechanisms of strong CTL productivity of fusion cells (FCs) are still unknown. Heat shock proteins (HSPs) are molecular chaperones that cross-present chaperoned antigenic peptides with MHC class I molecules. Herein, we focused on clarifying the potential of FCs for CTL production from the comparison of DCs pulsed with two kinds of tumor cell lysates, such as soluble tumor cell lysates or freeze-thawed tumor cell lysates. DCs, CD8+ T cells and tumor cells were prepared from ten patients with gastric cancer, and paired autologous tumor cells were used in all experiments. FCs of OK432-treated DCs and heat-stressed tumor cells (modified FCs) showed significant up-regulation of tumor-associated CEA and HER-2 antigen, and DC-related HLA-DR and co-stimulatory molecules (CD83 and CD86). FCs showed significantly higher IFN-γ and CTL productivity of CD8+ T cells than DCs pulsed with soluble or freeze-thawed tumor cell lysates. IFN-γ and CTL productivity of FCs was significantly increased by the heat stress of tumor cells. HSP70 mRNA levels and production of HSP70 protein of modified FCs increased significantly as compared with those of DCs pulsed with soluble or freeze-thawed tumor cell lysates. DCs pulsed with HSP70.PC extracted from modified FCs could enhance CTL productivity significantly more than that of DCs pulsed with HSP70.PC from soluble or freeze-thawed tumor cell lysate pulsed-DCs. The significant up-regulation of HSP70 mRNA and protein levels of modified FCs was related to the potential of CTL productivity. These results suggest that modified FCs possess stronger ability for MHC-restricted CTL production than DCs loaded with soluble or freeze-thawed tumor cell lysates.

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