1230P Immunotherapies for gastric cancer with CLDN18-ARHGAP fusion gene

Abstract

Since gastric cancer (GC) is highly heterogeneous in histology and genomics, current treatments harvest efficacies only in limited patients. Sequencing data of previous studies have documented that CLDN18-ARHGAP fusion gene recurrently occurred in GC. However, therapies targeting the CLDN18-ARHGAP fusion gene have not been reported. Next-generation sequencing (NGS) was conducted to identify CLDN18-ARHGAP fusion gene in GC samples. Next, we screened immunogenic neoantigens derived from CLDN18-ARHGAP by CBA, ELISPOT and flow cytometry. Cytotoxicity of neoantigen reactive T (NRT) cells were assessed by killing assays and tumor suppression experiments. Also, we analyzed the tumor immune microenvironment (TIME) of GC with CLDN18-ARHGAP via bioinformatic analysis and in vivo immune analysis. The mechanism behind was explored by western blotting (WB) and fatty acid detection. We detected CLDN18-ARHGAP fusion genes in 9% (8/87) GC patients. To develop immunotherapies targeting these patients, we derived specific neoantigens, and found NRT cells induced by these neoantigens secreted IFN-γ 60 times that of the control group. They also showed stronger antitumor ability to GC cells with CLDN18-ARHGAP in the killing assay and tumor suppression experiments. Additionally, we found increased infiltration of regulatory T cells (Tregs) in GCs with CLDN18-ARHGAP by bioinformatic analysis of public databases and flow cytometry in subcutaneous GC mouse models. Mechanistically, CLDN18-ARHGAP could promote the secretion of fatty acids via activation of PI3K/AKT-mTOR-FAS pathway, thereby enhancing the metabolism and proliferation of Tregs. In mouse models, PI3K inhibitor (PI3Ki) could inverse the suppressive TIME induced by CLDN18-ARHGAP fusion genes and inhibit tumor growth. Our study was the first to identify the immunogenic neoantigens derived from CLDN18-ARHGAP fusion gene and verified the antitumor ability of NRT cells. Also, we revealed the role of CLDN18-ARHGAP fusion gene in promoting a suppressive TIME by facilitating the metabolism and proliferation of Tregs, which could be reversed by PI3Ki. Collectively, we demonstrated that CLDN18-ARHGAP is a potential target for immunotherapies in gastric cancer.