Abstract B008: Rescuing neoantigen-specific CD8+ T-cell immunity from tumor- microenvironment-mediated immunosuppression in pancreatic cancer
Authors: Jacox Jeremy B , Foster Gena , Vattem Chaitanya , Shah Dhruvi , Sogunro Akin , Joshi Nikhil , Muzumdar Mandar 
Published: October 2024

Abstract
Background: Pancreatic ductal adenocarcinoma (PDAC) is highly lethal due to early metastasis and poor immunotherapy responses, driven by a desmoplastic tumor microenvironment (TME) and low immunogenicity. However, long-term human PDAC survivors exhibit higher neoantigen expression, predicted immunogenic neoepitopes, and active T-cell infiltration, suggesting T-cell mediated immunity influences PDAC progression. By contrast, most classical pre-clinical (KPC-based) murine models have low neoantigen burden, limiting their utility for studying anti-tumor T-cell immunity. Methods: We developed NINJA PDAC, a novel transplantable murine PDAC organoid model, to study neoantigen-specific anti-tumor T-cell responses and their interactions with the TME. The NINJA system affords temporal control of LCMV-based neoantigen (GP33 and GP66) expression in Kras-mutated, p53-deficient PDAC organoids, mirroring human PDAC neoantigen affinity for MHC-I. NINJA PDAC orthotopic transplants exhibit physiologic stroma, anatomically correct local-to- metastatic tumor progression, inducible neoantigens, measurable T-cell responses, and T-cell dependent rejection. Using adoptive T-cell challenge, macrophage depletion, checkpoint and chemokine inhibition, and leptin-deficient murine models, we explored rescue of the impact of the TME on anti-tumor CD8+ effector T-cell responses at baseline and in obesity. Results: Early NINJA neoantigen induction before tumor TME formation leads to partial suppression of tumor growth in a CD8+ T-cell dependent manner. By contrast, late induction post-TME formation revealed heterogenous neoantigen-specific T-cell responses, with tumors splitting into T-cell responders versus non-responders, leading to neoantigen clearance or persistence, respectively. TME differences drive these responses, as activated CD8+ T-cells in non-responders arrest at the tumor periphery alongside cancer-associated myofibroblasts (CAFs) and tumor- associated macrophages (TAMs). Complete TAM depletion (using anti-CSF1/clodronate liposomes) and genetic ablation of B-cells were both insufficient to rescue non-response of T-cells, which remain excluded peripherally. By contrast, fibroblast-derived CXCL12- CXCR4 signaling arrests CD8+ T-cells at the tumor margin, impairing neoantigen- specific tumor clearance. CXCR4-inhibition (AMD3100) partially rescues the response phenotype, and may be further enhanced by combined PD1 checkpoint inhibition. Finally, leptin-deficient obese mice transplanted with NINJA PDAC had larger tumors, fewer neoantigen-specific CD8+ effector T-cells, and altered T-cell activation. This argues that obesity-induced changes in the TME impair neoantigen-specific CD8+ effector T-cells, highlighting obesity as a key host factor in modulating the anti-tumor T cell response. Conclusions: NINJA PDAC affords a high-fidelity toolset to study how the TME affects murine neoantigen-specific anti-tumor T-cell responses, further modulated by host factors like obesity, with the potential to accelerate the development of new combination immunotherapies.
Citation Format: Jeremy B Jacox, Gena Foster, Chaitanya Vattem, Dhruvi Shah, Akin Sogunro, Nikhil Joshi, Mandar Muzumdar. Rescuing neoantigen-specific CD8+ T-cell immunity from tumor- microenvironment-mediated immunosuppression in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2024 Oct 18-21; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2024;12(10 Suppl):Abstract nr B008.