Abstract 908: Decoding the role of intrinsic pancreatic cellular signaling in shaping the immunosuppressive tumor microenvironment

Abstract Background: Pancreatic ductal adenocarcinoma (PDAC) has the highest mortality rate among major cancers, with over 50% of patients having liver metastases at diagnosis. Given that conventional T-cell based immunotherapies have been ineffective against PDAC liver metastases, it is vital to elucidate the mechanisms regulating tumor immunity within the hepatic microenvironment to enhance anti-tumor T cell. Notably, PDAC cells exhibit exceptional plasticity and intrinsic heterogeneity, contributing to the evolution of immunosuppressive primary and early liver PDAC metastases. Our study leverages an array of congenic PDAC clones with varying degrees of immunogenicity to delineate the signaling pathways driving primary and liver immunosuppression. Methods: We investigate the growth kinetics of PDAC clones both in vitro and in vivo, alongside their transcriptomic variations. Using model antigens (chicken ovalbumin), we assess how different clones modulate the immune microenvironment to elicit antigen-specific adaptive anti-tumor responses. Transcriptomic profiling informs CRISPR-based knockout and overexpression strategies to uncover intrinsic gene contributions to primary anti-tumor immunity in vivo. Additionally, we have developed stable PDAC liver metastasis models through portal vein injection to evaluate each clone’s metastatic efficiency and associated immune landscape within the hepatic microenvironment. Results: In vivo engraftment of PDAC clones revealed differential infiltration of CD4+/CD8+ T cells and neutrophils. While all OVA+ PDAC clones triggered antigen-specific immune responses, only immune-sensitive tumors were eradicated, whereas immune-insensitive tumors persisted. Despite OVA expression, all clones successfully established liver metastases following intraportal injection. RNA-seq analysis identified upregulation of key pancreatic development regulators, including PDX1 and RBPJ, in immune-insensitive clones. CRISPR knockout of these transcription factors in vivo demonstrated altered immune cell composition and reduced tumor growth in immunocompetent mice expressing OVA. Conclusion: Using diverse PDAC models, we created tumors with immune heterogeneity and altered transcriptional profiles. We identified validated immune-altering cytokines (CXCL1 and CSF3) and immunomodulatory roles of PDX1 and RBPJ. Immune-insensitive clones evaded antigen-specific immunity in both subcutaneous and liver metastasis models, while immune-sensitive clones were eradicated subcutaneously but gained protection in the liver. Ongoing studies confirm the phenotypes of CRISPR-KO clones and delineate the immunomodulatory roles of these transcription factors in liver metastasis. Citation Format: Bushangqing Liu, Ethan Agritelley, Junping Wei, Gangjun Lei, Tao Wang, Jason McBane, Daniel Nussbaum, Zachary Hartman. Decoding the role of intrinsic pancreatic cellular signaling in shaping the immunosuppressive tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 908.