Abstract 3140: Infiltrating macrophage-derived TNF-α promotes PD-L1 expression, leading to poor prognosis of patients with pancreatic cancer
Authors: Tsukamoto Masayo , Imai Katsunori , Ishimoto Takatsugu , Komohara Yoshihiro , Umezaki Naoki , Yamao Takanobu , Kitano Yuki , Arima Kota , Miyata Tatsunori , Okabe Hirohisa , Nakagawa Shigeki , Nitta Hidetoshi , Yamashita Yo-ichi , Chikamoto Akira , Ishiko Takatoshi , Baba Hideo 
Published: August 2018

Background: Pancreatic cancer is the eighth leading cause of cancer death in men and the ninth leading cause of cancer death in women worldwide. Solid tumors comprise not only malignant cells but also many other non-malignant cell types. Many leukocytes, including macrophages, are known to exist in tumor tissues, and together with fibroblasts and vascular endothelial cells, constitute the tumor microenvironment. Cancer immunotherapy using immune checkpoint blockades, such as anti-PD-1/PD-L1 antibody drugs has received considerable attention in recent decades. Importantly, previous studies reported that patients with pancreatic ductal adenocarcinoma (PDAC) harboring PD-L1-positive tumor cells showed significantly poorer prognosis than those harboring PD-L1-negative tumor cells. However, the molecular mechanism underlying PD-L1 expression in PDAC cells has not been clearly elucidated. We examined whether infiltrating macrophages in tumor stroma could affect PD-L1 expression in PDAC cells.

Methods: PDAC cells were treated with several cytokines, including tumor necrosis factor (TNF)-α, and then subjected to real-time PCR, Western blot analysis and flow cytometry analyses. On the other hand, PDAC cells were co-cultured with human monocyte-derived macrophages, and then subjected to real-time PCR. Subsequently, immunohistochemistry analyses were performed on consecutive paraffin sections from 122 patients with PDAC using anti-PD-L1 and anti-CD163 antibodies. In addition, double immunostaining was performed on the same paraffin sections from patients with PDAC using anti-PD-L1 and anti-Iba-1 antibodies. Finally, survival analysis was conducted.

Results: Among various cytokines tested (interleukin (IL)-1a, IL-1b, IL-4, IL-6, IL-7, IL-13, IL-24, TNF-α, IFN-γ or LPS), TNF-α promoted strong PD-L1 expression in PDAC cell lines (S2-013 and MIAPaCa2). Western blot analysis showed that TNF-α up-regulated the expression level of PD-L1 via the NF-κB pathway in PDAC cells. In addition, PD-L1 expression was increased in PDAC cells co-cultured with activated macrophages derived from human monocytes, and this up-regulation was inhibited by the anti-TNF-α antibody. Furthermore, a significant correlation between PD-L1 expression in cancer cells and the number of infiltrating macrophages expressing CD163 in PDAC tissues was observed by immunohistochemistry analysis. Finally, survival analysis revealed that PD-L1 expression was significantly associated with poor prognosis in patients with PDAC.

Conclusion: TNF-α derived from tumor-infiltrating macrophages enhances PD-L1 expression in PDAC cells, which may lead to poor prognosis in patients with PDAC.

Citation Format: Masayo Tsukamoto, Katsunori Imai, Takatsugu Ishimoto, Yoshihiro Komohara, Naoki Umezaki, Takanobu Yamao, Yuki Kitano, Kota Arima, Tatsunori Miyata, Hirohisa Okabe, Shigeki Nakagawa, Hidetoshi Nitta, Yo-ichi Yamashita, Akira Chikamoto, Takatoshi Ishiko, Hideo Baba. Infiltrating macrophage-derived TNF-α promotes PD-L1 expression, leading to poor prognosis of patients with pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3140.