Novel syngeneic model of anti-mouse CLDN18.2 CAR -T therapy for gastric cancer demonstrates a synergy with TGF-β and PD-L1 inhibitors

There are very few syngeneic mouse cell line models available for gastric cancer owing to the rarity of stomach epithelium-specific promoter. Mouse cell line models are useful to study an immunologically intact tumor microenvironment, especially in the setting of CAR-T studies that often use immunocompromised mice. To establish a mouse cell line faithfully recapitulating human gastric cancer, we generated the S6M cell line from an autochthonous gastric cancer formed in the stomach of a female mouse deficient in <i>Smad4, Trp53</i>, and <i>Cdh1</i> (<i>Pdx-1-Cre</i>; <i>Smad4</i> ^<i>F/F</i> ; <i>Trp53</i> ^<i>F/F</i> ; <i>Cdh1</i> ^<i>F/+</i> ). S6M readily formed a tumor when injected into syngeneic mice and demonstrated histologic and molecular features consistent with human intestinal gastric adenocarcinoma. Notably, S6M overexpressed the isoform 2 of claudin 18 (CLDN18.2), an important molecular therapeutic target in human gastric adenocarcinomas. Anti-mouse CLDN18.2 CAR-T cells suppressed tumor growth of mice bearing the syngeneic graft of S6M but not the CLDN18.2-low S1M cell line. Dual inhibition of immunosuppressive molecules TGF-β and PD-L1 enhanced the <i>in vivo</i> efficacy of anti-mouse CLDN18.2 CAR-T against S6M cells by recruiting NK cells to tumor microenvironment, suggesting the potential utility of our novel syngeneic gastric cancer cell line model in designing innovative clinical therapeutic approaches.