Abstract 1194: Evolution of immune and stromal cell states during the gastric cancer continuum
Authors: Wang Ruiping , Song Shumei , Qin Jiangjiang , Yoshimura Katsuhiro , Peng Fuduan , Chu Yanshuo , Li Yuan , Fan Yibo , Jin Jiankang , Dang Minghao , Dai Enyu , Pei Guangsheng , Han Guangchun , Li Yating , Chatterjee Deyali , Pizzi Melissa P. , Scott Ailing W. , Tatlonghari Ghia , Yan Xinmiao , Sewastjanow Matheus Da Silva , Abdelhakeem Ahmed Adel Fouad , Mazur Pawel K. , Cheng Xiangdong , Ajani Jaffer A. , Wang Linghua 
Published: April 2023

Introduction: Gastric adenocarcinoma (GAC), a global health burden, lacks detail understanding of the evolution-driven cellular/molecular programs that lead to GAC tumorigenesis followed by progression/metastases. How the TME is orchestrated by precancerous lesions, primary GAC, and in metastatic niches, when well understood, may propel us into an entirely new dimension with the hopes of novel therapeutics. However, only a few studies have investigated the immune/stromal subtypes of GAC with the limitation of scope, cohort size, and/or depth or mainly focused on the primary GACs. Here, we present an atlas of transcriptionally diverse TME across the full continuum of GAC by including peripheral blood, normal gastric tissues, premalignant lesions, localized, and metastatic GACs.

Methods: We performed a comprehensive single-cell profiling of 68 specimens collected from 43 subjects including a total of 77,392 high-quality cells which revealed 62 unique cell states uncovering varying profiles. We defined alterations in TMEs that underscore initiation of tumorigenesis to eventual progression.

Results: We found a striking preponderance of B lineage cells, primarily the IgA+ plasma cells, in TMEs of the precancerous lesions, whereas 3 immunosuppressive myeloid subsets dominated in advanced GACs. Fractions of GZMK+ effector CD8 T cells and progenitor exhausted CD8 T cells gradually increased as GACs progressed to advanced stages. In addition, our analysis revealed extensive stromal remodeling along the GAC continuum, which may have contributed to enhanced angiogenesis and immune suppressive signaling. The observations in the primary tumors could be validated in an independent scRNA-seq dataset. Notably, we uncovered 3 unique TME interactomes and defined 6 cellular environtypes inhabited by 62 TME cell subsets giving GAC to a novel landscape not yet defined. The two distinct environtypes in GAC primaries are validated in three independent large-scale GAC cohorts, giving credence and definition to previously established histopathological variables, genomic/molecular subtypes and clinical outcomes. The analysis of tumor associated stromal cells discovered SDC2 as an

exploitable target to pursue. SDC2 was abundant in cancer associated fibroblasts (CAFs), and the abundance is validated in 3 independent single-cell GAC cohorts as well as at the protein level. SDC2 expression was significantly higher in advanced (vs. early) stages and diffuse (vs. intestinal) type of GAC, and SDC2 overexpression was associated with shorter survival in all 5 large-scale GAC cohorts. Lastly, we assessed the functional effects of SDC2 expression in CAFs on tumor growth in vivo in xenograft models and found SDC2 overexpression in CAFs contributes to tumor growth.

Conclusion: This study provides an atlas of GAC TMEs from tumorigenesis to advanced GAC that could be further developed for novel therapeutics but also serves as a community resource.

Citation Format: Ruiping Wang, Shumei Song, Jiangjiang Qin, Katsuhiro Yoshimura, Fuduan Peng, Yanshuo Chu, Yuan Li, Yibo Fan, Jiankang Jin, Minghao Dang, Enyu Dai, Guangsheng Pei, Guangchun Han, Yating Li, Deyali Chatterjee, Melissa P. Pizzi, Ailing W. Scott, Ghia Tatlonghari, Xinmiao Yan, Matheus Da Silva Sewastjanow, Ahmed Adel Fouad Abdelhakeem, Pawel K. Mazur, Xiangdong Cheng, Jaffer A. Ajani, Linghua Wang. Evolution of immune and stromal cell states during the gastric cancer continuum [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1194.