Abstract 6107: Multiplex immunohistochemistry defined the tumor immune microenvironment and immunotherapeutic outcome in CLDN18.2-positive gastric cancer
Authors: Jia Keren , Chen Yang , Yuan Jiajia , Qi Changsong , Li Yanyan , Gong Jifang , Gao Jing , Zhang Xiaotian , Li Jian , Zhang Cheng , Shen Lin 
Published: June 2022

Abstract
Introduction: The FAST study ignited the hope of CLDN18.2 as a promising novel therapeutic target for gastric cancer (GC). However, the tumor immune-microenvironmental features of CLDN18.2-positive GC is still unclear, making it difficult to develop/optimize CLDN18.2-targeted treatments.
Methods: Multiplex immunohistochemistry (mIHC) was used to decipher the density and spatial structure of T cells, B cells, macrophages, neutrophils in FFPE tumor tissues of 80 GC patients (60 of them received anti-PD-1/PD-L1 treatment). Tumor immune-microenvironmental features and survival distributions stratified by CLDN18.2 were analyzed with two independent-sample t-test and Log-rank test, respectively.
Results: We considered mIHC-stained samples with moderate-to-strong CLDN18.2 expression ≥40% of tumor cells as the cutoff for positivity, which shared a high concordance with IHC-based CLDN18.2 staining. The density of CD8+PD-1-, CD8+LAG-3-, and CD8+TIM-3- T cells were significantly higher in CLDN18.2-positive compared with negative tumors (346.28 vs. 204.86/mm2, P=0.011; 436.83 vs. 278.64/mm2, P=0.024; 391.85 vs. 260.72/mm2, P=0.039). In addition, the density of neutrophils (CD66b+) was higher in CLDN18.2-positive than negative group (725.17 vs. 496.23/mm2, P=0.043), while the density of M1 (CD68+CD163-HLA-DR+), M2 macrophages (CD68+CD163+HLA-DR-) and B cells (CD20+) were comparable between CLDN18.2-positive and negative group.
In view of spatial analysis, average numbers of CD8+PD1-, CD8+LAG3-, CD8+TIM3-T cells surrounding tumor cells within a 20 μm range were higher in CLDN18.2-positive tumors than in negative group (0.16 vs. 0.09, P=0.011; 0.20 vs. 0.12, P=0.029; 0.18 vs. 0.12, P=0.047). Also, in CLDN18.2-positive group, tumor cells surrounded by CD8+PD1-, CD8+LAG3- T cells or M1 macrophages within a 20 μm range accounted for a higher proportion of all tumor cells than CLDN18.2-negative group (10.79% vs. 6.60%, P=0.015; 12.68% vs. 8.70%, P=0.049; 9.08% vs. 6.56%, P=0.033). These findings suggested that CLDN18.2-positive GC harbored complex immune-microenvironmental features.
Additionally, CLDN18.2-positive group had shorter OS/irOS than CLDN18.2-negative group (median OS: 23.33 vs.36.6 months, P&lt;0.001; median irOS: 10.03 vs. 20.13 months, P=0.012). The impact of CLDN18.2-related microenvironmental features on prognosis deserved further investigation.
Conclusion: CLDN18.2-positive GC displayed unique immune-microenvironmental characteristics, which provided a phenotypic view for the biological role of
CLDN18.2 in GC, and is of great significance for the development of CLDN18.2-targeted therapies.
Citation Format: Keren Jia, Yang Chen, Jiajia Yuan, Changsong Qi, Yanyan Li, Jifang Gong, Jing Gao, Xiaotian Zhang, Jian Li, Cheng Zhang, Lin Shen. Multiplex immunohistochemistry defined the tumor immune microenvironment and immunotherapeutic outcome in CLDN18.2-positive gastric cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6107.