Abstract 5033: Down-regulation of PD-1 ligands by chemotherapeutic agents via inhibition of STAT3 activity enhances T cell-stimulating ability of dendritic cell
Authors: Okamoto Masato , Tano Tomoyuki , Goda Hiroyuki , Fujita Yohei , Nakashiro Koh-ichi , Hamakawa Hiroyuki 
Published: May 2015

Background and objective: We have demonstrated the possibility that a dendritic cell (DC)-based vaccination may have survival benefit in patients with several types of malignancies such as pancreatic carcinoma and non-small cell lung cancer; however remaining lots of cancer patients cannot respond to the DC vaccine. It has been reported that certain chemotherapeutic agents enhance the cancer vaccine-mediated immune responses. In the current study, we conducted the in vitro experiments to examine whether the chemotherapeutic agent including 5-FU, CDDP and Docetaxel (DTX) which are used for standard treatment for oral cancer patients, may enhance T-cell stimulating activity of DCs matured by OK-432, a streptococcal immuno-potentiator. Methods: Healthy volunteer-derived human peripheral blood monocytes 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 for 24 hours, followed by the treatment with each chemotherapeutic drugs such as 5-FU, CDDP, DTX or gemcitabine (GEM) for 24 hours.

Results: IL-12 production by OK-432-matured DCs decreased by the treatment with CDDP, DTX or GEM but not with 5-FU. In contrast, only 5-FU decreased the amount of IL-10 secreted by the DCs. No change in IL-6 production was shown. Expression of genes for PD-1 ligands (PD-L1 and PD-L2) as well as of their proteins on DCs was significantly suppressed by the treated with 5-FU or DTX. PD-1/PD-Ls pathway is involved in the negative regulation of T cell-functions. Expression of PD-Ls was regulated by STAT3 signal. 5-FU also inhibited STAT3 activity on the DCs. Down-regulation of PD-Ls via STAT3 signal by chemotherapeutic agents may be closely involved in the T cell-stimulating ability of DCs. The next experiments using allogeneic mixed lymphocyte reaction revealed that 5-FU-treated DCs stimulated allogeneic T cells to enhance their proliferation, and that IFN-γ-producing ability of the allogeneic T cells was also augmented by the co-cultivation with DCs treated with 5-FU or DTX. Actually, DCs in which PD-L1 and/or PD-L2 gene(s) are knocked-down by using siRNA strongly stimulated allogeneic T cells to enhance their proliferation as well as IFN-γ producing ability.

Conclusions: The findings obtained from the current study suggested that 5-FU and DTX may enhance the T cell-stimulating ability of DCs via down-regulation of PD-L1 and PD-L2 mediated by STAT3 inhibition, and that the combination therapy of DC-based cancer vaccine with these anti-cancer drugs may elicit better anti-tumor immune response than only vaccination.

Citation Format: Masato Okamoto, Tomoyuki Tano, Hiroyuki Goda, Yohei Fujita, Koh-ichi Nakashiro, Hiroyuki Hamakawa. Down-regulation of PD-1 ligands by chemotherapeutic agents via inhibition of STAT3 activity enhances T cell-stimulating ability of dendritic cell. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5033. doi:10.1158/1538-7445.AM2014-5033