Abstract 6665: A spatiotemporal cell atlas of human gastric malignancy reveals mechanisms underlying metastasis and immunotherapy response

Abstract Cellular heterogeneity in the tumor immune microenvironment (TIME) of gastric cancer (GC) is progressively molded in pre- and early-malignant lesions and has a profound impact on disease progression and responses to therapeutics, in particular those based on immune checkpoint blockade (ICB). To date, no study has been conducted to characterize the single-cell kinetics of tumor-infiltrating immune populations in gastric cancer patients treated with ICB. Here, we generated for the first time single-cell RNA sequencing (scRNA-seq) and TCR sequencing (scTCR-seq) profiles of ICB-treated primary GC tumors, as well as liver and ovary metastases. When integrated with public scRNA-seq datasets, our data capture a full trajectory of GC malignancy comprising more than 300,000 cells derived from 73 samples. We further performed bulk TCR-seq, cytometry by time of flight (CyTOF), and multiplex immunofluorescence (mxIF) on independent GC samples to orthogonally validate the key observations from the scRNA-seq cohort and unbiasedly search for more in-depth and spatial-relationship-focused features of ICB-responsive immune populations. Built upon this multi-omic atlas of GC cell states, we identified remarkable transformation of the abundance and clonal dynamics of distinct immune populations and their population-specific transcriptional programs. Most importantly, we observed the rejuvenation of exhausted CD8+ T cells induced by anti-PD-1 treatment, which is associated with the enhanced immunogenicity of gastric cancer cells. In addition, we found the enrichment of NK-like terminally differentiated CD8+ T cells in metastases independent of migration destinations. Our single-cell ICB-perturbed spatiotemporal GC landscape reveals how neoadjuvant checkpoint blockade induces local and systemic tumor immunity. As a cellular and molecular reference, it also enables high-resolution interpretation of future single-cell omics data in gastric cancer that may be masked by de novo analysis. Citation Format: Yikai Luo, Muxing Kang, Wei Liu, Shiping Jiao, Lie Wang, Jian Chen, Han Liang. A spatiotemporal cell atlas of human gastric malignancy reveals mechanisms underlying metastasis and immunotherapy response [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 6665.