Abstract 2810: Dendritic cell-based immunotherapy in combination with programmed cell death 1 blockade reduced established tumors by activating Th-1 type immune responses in a murine hepatocellular carcinoma model
Authors: Hayashi Eiichi , Eguchi Junichi , Sakaki Masashi , Doi Hiroyoshi , Oomori Risa , Kajiwara Atsushi , Yoshida Hitoshi , Ishii Shigeaki , Hiroishi Kazumasa , Imawari Michio 
Published: May 2015

Abstract
Progress in treatments for hepatocellular carcinoma (HCC) has improved the prognosis of patients with HCC. However, HCC is usually associated with cirrhosis and often recurs even after complete treatment of the tumors in the remaining part of the cirrhotic liver. Thus, there is a strong need for the development of a new intervention therapy that suppresses the occurrence or recurrence effectively with fewer side effects. Immunotherapy may be such a treatment and several clinical trials have been performed for HCC treatment. Dendritic cells (DCs) are known as professional antigen-presenting cells characterized by their potent ability to elicit immune responses to tumor-specific T cells against tumor-associated antigens. Programmed cell death 1 (PD-1) has been identified as a marker of exhausted T cells in chronic disease states, and blockade of PD-1-PD-ligand interactions has been shown to partially restore T cell function. In this study, we evaluated the efficacy of the combination of DC-based vaccine and PD-1 blockade, and investigated the mechanisms of the antitumor effects of the combined therapy.
In protection model, mice were injected with DCs or/and PD-1-antibody before the murine HCC tumor cell (BNL cell) challenge. 40% of mice treated with both DCs and PD-1-antibody rejected tumor challenge, whereas other groups observed a palpable tumor in all mice tested. In therapeutic model, tumor-bearing mice were inoculated with DCs or/and PD-1-antibody. Significant suppression of outgrowth of the established tumors was observed in the DCs and anti-PD-1 combination treatment group (DCs + anti-PD-1, 138.00 ± 56.66 mm2 vs control, 402.33 ± 40.63 mm2 on day 42, P = 0.0073 vs controls). Immunohistochemical analyses of therapeutic model showed marked infiltration of CD4+ cells, CD8+ cells and CD11c+ cells in the established BNL tumors of mice treated with both DCs and PD-1-antibody. To investigate induction of tumor-specific immune responses, we stimulated splenocytes of DCs or/and PD-1-antibody treated mice twice weekly by DCs in vitro. Significant tumor-specific cytolysis was detected when splenocytes of mice treated with both DCs and anti-PD-1 were used as effector cells (30.0% ± 2.8% for BNL and 7.3% ± 0.1% for YAC-1, effector to target ratio; E/T=40).
Our findings suggest that blockade of the PD-1 PD-ligand enhanced the Th1-type antitumor immune responses induced by DC vaccine. The combination of DC vaccine and PD-1 blockade may be a possible candidate for a cancer vaccine for clinical trials.
Citation Format: Eiichi Hayashi, Junichi Eguchi, Masashi Sakaki, Hiroyoshi Doi, Risa Oomori, Atsushi Kajiwara, Hitoshi Yoshida, Shigeaki Ishii, Kazumasa Hiroishi, Michio Imawari. Dendritic cell-based immunotherapy in combination with programmed cell death 1 blockade reduced established tumors by activating Th-1 type immune responses in a murine hepatocellular carcinoma model. [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 2810. doi:10.1158/1538-7445.AM2014-2810