Abstract 2050: Novel immunological classification of gastric cancer by integrative analysis
Authors: Sato Yasuyoshi , Wada Ikuo , Hosoi Akihiro , Kobayashi Yukari , Nagaoka Koji , Karasaki Takahiro , Matsushita Hirokazu , Yagi Koichi , Yamashita Hiroharu , Takahashi Shunji , Seto Yasuyuki , Kakimi Kazuhiro 
Published: September 2020

Traditional classifications of gastric cancer are based on gross appearance, anatomical sites, histological types, and etiologies. Recent advances in NGS technologies have made comprehensive molecular characterizations of gastric cancer possible. Four subtypes were proposed by the TCGA project, namely, EBV, MSI, GS, and CIN. These molecular subtypes are clinically relevant and contribute to the stratification of patients for targeted therapies and immunotherapies. However, understanding the landscape of the tumor-immune microenvironment is critical for improving the efficacy of current immunotherapies or developing novel combination immunotherapies. To this end, we performed whole-exome sequencing, RNA-Seq, and flow cytometry in 29 patients with primary gastric adenocarcinomas. We focused on factors related to the cancer-immunity cycle and tumor cell proliferation and metabolism using 9 selected gene sets, innate immunity, priming and activation, T cells, IFNγ response, inhibitory molecules, Tregs, recognition of tumor cells, proliferation, and glycolysis. By integrating them, we generated an immunogram for each patient to visualize the state of cancer-immune system interactions and have investigated the tumor-immune microenvironment in gastric cancer. Our results demonstrate that the anti-tumor immune response in gastric cancer is heterogeneous. Based on Immunogram analysis, the hierarchical clustering of gastric cancers from 29 patients resulted in 4 novel immunological subtypes, designated Hot 1, Hot 2, Intermediate, and Cold. Hot 1 and Hot 2 were distinguished from one another by glycolysis, which was low in the latter. These immunological subtypes overlapped to some degree with the molecular subtypes in the TCGA. All 4 MSI tumors in our cohort were included in the Hot 1 group, and all 3 EBV tumors in the Hot 2 group, whereas 4 of the 6 mesenchymal tumors fell into the Intermediate group. Immunologically hot tumors displayed a dysfunctional T cell signature, while cold tumors had an exclusion signature. We also determined the phenotypes and functions ex vivo of tumor-infiltrating T cells by flow cytometry. T cell dysfunction was confirmed by documenting very low percentages of polyfunctional CD8+ T cells producing ≥2 of the cytokines IFNγ, TNFα and IL-2 in the Hot 1 subtype. T cell function was entirely lacking in 2 of 11 Cold subtype tumors. These dysfunctional T cells could be recoverable in most patients if appropriate signals are supplied or immunosuppressive signals blocked. Applying our immunogram analysis to the TCGA cohort also resulted in its classification into four subtypes, validating the overlap between molecular and immunological subtypes. Overall survival in patients with a Hot 1 tumor was worse than for Hot 2 subtypes under conventional therapy not including checkpoint blockade, suggesting that early administration of anti-PD-1 therapy should be recommended for patients with Hot 1 tumors.

Citation Format: Yasuyoshi Sato, Ikuo Wada, Akihiro Hosoi, Yukari Kobayashi, Koji Nagaoka, Takahiro Karasaki, Hirokazu Matsushita, Koichi Yagi, Hiroharu Yamashita, Shunji Takahashi, Yasuyuki Seto, Kazuhiro Kakimi. Novel immunological classification of gastric cancer by integrative analysis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2050.