Abstract 4722: Enhancement of the T cell-stimulating ability of dendritic cells by 5-FU via regulation of the expression of ligands for programed cell death 1.

Purpose: Dendritic cells (DCs) are professional antigen-presenting cells that play a central role in initiating adaptive and innate immune responses. DC-based vaccination is widely tested as a promising therapeutic cancer vaccine in multiple clinical trials. Programed cell death 1(PD-1)/PD-1 Ligands (PD-Ls) pathway are involved in the negative regulation of T cell-functions. PD-1 is expressed on T cells, and PD-Ls are expressed on DCs as well as some cancer cells. More recent studies have indicated that certain chemotherapeutic agents might enhance the cancer vaccine-mediated immune responses. In the current study, we conducted the in vitro experiments to examine whether or not chemotherapeutic drugs which are used for patients with head and neck cancer, may enhance T cell-stimulating ability of DCs via regulation of the expression of PD-Ls. Methods: Healthy volunteer-derived human peripheral blood monocyte were cultured with IL-4 and GM-CSF for 5 days to generate immature DCs, and then the DCs were matured by the stimulation with OK-432 which is a streptococcal immune adjuvant, for 24 hours, followed by the treatment with each chemotherapeutic drug such as 5-FU, CDDP, docetaxel or gemcitabine for 24 hours. Viability of DCs was assessed by WST-8. IL-10 and IL-12 in the supernatants from the DC cultures were measured by ELISA. Expression of mRNAs and proteins for PD-Ls was analyzed by quantitative real-time PCR and flow cytometry, respectively. DCs were co-cultured with allogeneic T cells (E/T ratio=1/20, 1/200 or 1/2000), then IFN-γ in the supernatants were measured by ELISA to evaluate T cell-stimulating ability of the DCs. Results: IL-12 production by DCs was significantly enhanced by OK-432 stimulation. Although CDDP, docetaxel and gemcitabine inhibited the OK-432-induced IL-12 production on the DCs, 5-FU did not. 5-FU and gemcitabine significantly inhibited the IL-10 production by OK-432-stimulated DCs. Expression of PD-L1 and PD-L2 genes as well as of their proteins on the DCs which was increased by OK-432 stimulation, was significantly suppressed by the treated with 5-FU or docetaxel. OK-432-stimulated DCs-treated with 5-FU strongly enhanced both proliferation and IFN-γ production of allogeneic T cells as compared with DCs stimulated only with OK-432. Conclusions: The findings obtained from the current study suggested the possibility that 5-FU may enhance the T cell-stimulating ability of dendritic cells via regulation of the expression of PD-L1 and PD-L2, and that the combination therapy of DC-based cancer vaccine with 5-FU may elicit better anti-tumor efficacy than only vaccination. Citation Format: Tomoyuki Tano, Masato Okamoto, Hiroyuki Goda, Yohei Fujita, Koh-ichi Nakashiro, Hiroyuki Hamakawa. Enhancement of the T cell-stimulating ability of dendritic cells by 5-FU via regulation of the expression of ligands for programed cell death 1. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4722. doi:10.1158/1538-7445.AM2013-4722