Abstract 6862: Loss of STAT1 promotes an immunosuppressive tumor microenvironment in KRAS-driven lung adenocarcinoma

Abstract Introduction: Lung cancer is the leading cause of death worldwide. One third of lung adenocarcinomas (LUADs), the most abundant form of lung cancer, harbors activating mutations in KRAS. Since human KRAS-mutant LUAD is correlated to an inflammatory phenotype, we hypothesized that the JAK-STAT pathway plays a crucial role in disease progression. Indeed, preliminary data demonstrated that human KRAS-mutant LUADs are associated with activation of the JAK-STAT signaling pathway, including upregulation of STAT1 expression. Therefore, we aimed to elucidate the tumorigenic functions of STAT1 in KRAS-mutant LUAD. Methods: To analyze the functions of STAT1 in KRAS-driven LUAD, we used C57BL/6 mice, which were genetically engineered in order to develop KRAS-driven autochthonous LUAD deficient for P53. Tumors additionally expressed ovalbumin (OVA) which acts as a neoantigen to induce immune infiltration (KPO mice). In this immunogenic mouse model, STAT1 was deleted in the tumors (KPOS mice) and overall survival was assessed by Kaplan Meier analysis. Tumor burden and infiltration was analyzed in lungs via H&E, IHC, and IF staining 6 weeks after tumor induction. An inflammatory cytokine antibody array was performed with lung fluid and single cell sequencing with cells isolated from lungs at 10 weeks. Results and discussion: Expression of OVA in tumor cells increased infiltration by T cells and prolonged survival suggesting neoantigen presentation in this mouse model. When STAT1 was deleted in OVA expressing tumors the survival was significantly decreased. Further, tumor burden as well as tumor size and grades were increased in KPOS lungs. Interestingly, infiltration of CD4 T cells was diminished upon loss of STAT1 while the percentage of CD8 T cells in tumors did not change suggesting an immunosuppressive tumor microenvironment. Indeed, M2 macrophages were increased in tumors lacking STAT1 and less proliferating immune cells were found indicating immune cell inhibition. This was further supported by the increase of CCL9 in KPOS lungs which might induce macrophage recruitment and further T cell inhibition. Finally, scRNAseq analysis revealed that KPOS lungs were composed of distinct immune cell populations as well as states. Conclusion: This data suggests that loss of STAT1 in tumor cells promotes secretion of CCL9 that drives recruitment of immunosuppressive macrophages to the tumor microenvironment. As a result, T helper cells are excluded from tumors and cytotoxic T cells are inhibited or exhausted. Further experiments will delineate the immune cell states and the mechanisms leading to this interesting phenotype. Citation Format: Christoph Trenk, Maša Bereš, Katalin Deszo, Jaqueline Horvath, Monika Homolya, Andreea Corina Luca, Robert Eferl, Herwig Peter Moll, Emilio Casanova. Loss of STAT1 promotes an immunosuppressive tumor microenvironment in KRAS-driven lung adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6862.