Carbon ion irradiation enhances the antitumor efficacy of dual immune checkpoint blockade therapy both for local and distant sites in murine osteosarcoma.

Yutaka Takahashi,Keisuke Tamari,Kazuhiko Hayashi,Yuji Seo,Keisuke Otani,Tomohiro Yasui,Fumiaki Isohashi,Kazumasa Minami,Kazuhiko Ogawa,Masahiko Koizumi

doi:10.18632/oncotarget.26551

Yutaka Takahashi, Keisuke Tamari + Show 8 more

Open Access

https://doi.org/10.18632/oncotarget.26551

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Abstract

Carbon ion radiotherapy has been utilized even for X-ray resistant tumors. However, control of distant metastasis remains a major challenge in carbon ion irradiation. We investigated whether carbon ion irradiation combined with dual immune checkpoint blockade therapy (anti-PD-L1 and anti-CTLA-4 antibodies [P1C4]) provides anti-tumor efficacy for both local and distant sites. A mouse osteosarcoma cell line (LM8) was inoculated into both hind legs of C3H mice assigned to four groups: no treatment (NoTX), P1C4, 5.3 Gy of carbon ion irradiation to one leg (Cion), and combination (Comb) groups. In the Comb group, tumor growth delay was observed not only in the irradiated tumors but also in the unirradiated tumors. Notably, a complete response of unirradiated tumors was observed in 64% of mice in the Comb group, while only 20% of mice in the P1C4 group showed a complete response. Significant activation of immune cells was observed in the Comb group, with an increase in CD8+/GzmB+ tumor-infiltrating lymphocytes (TILs) in the irradiated tumor, and of CD8+/GzmB+ and CD4+ TILs in the unirradiated tumor, respectively. Depletion of CD8 abolished the tumor growth delay in unirradiated tumors in mice treated by Cion and P1C4. Overall survival was significantly prolonged in the Comb group. HMGB-1 release from irradiated tumors was significantly increased after Cion both in vitro and in vivo. These data suggest that carbon ion therapy enhances P1C4 efficacy against osteosarcoma in both the primary tumor and distant metastases mediated by immune activation.

Highlights

Lymphocytes play a key role in recognizing antigens, including tumor antigens, which can lead to the elimination of cancer cells [1,2,3]
We investigated whether carbon ion irradiation combined with dual immune checkpoint blockade therapy provides anti-tumor efficacy for both local and distant sites
Expression of CD80 increased dosedependently, at a high dose (5 Gy), as shown in Figure 1C and 1D. These results suggest that carbon ion irradiation increased immune checkpoint proteins in vitro, and might thereby enhance the efficacy of immune checkpoint blockade

Summary

Introduction

Lymphocytes play a key role in recognizing antigens, including tumor antigens, which can lead to the elimination of cancer cells [1,2,3]. Lymphocytes, as well as cancer cells, eventually send signals to suppress antitumor immunity, resulting in unlimited growth of a tumor [4,5]. The PD-1/PD-L1 pathway plays an important role in tumor immune escape [6,7,8,9]. Another signal is immunosuppressive protein Cytotoxic T lymphocyte www.oncotarget.com antigen 4 (CTLA-4). Some studies have demonstrated that the combination of anti-PD-L1 and anti-CTLA-4 antibodies (P1C4) activates the immune system and induces a strong antitumor effect [12,13,14,15]

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