Abstract A076: Bypassing tumor microenvironment immune exclusion to elicit neoantigen-specific anti-tumor immunity in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is lethal due to early metastasis, a desmoplastic tumor microenvironment (TME), and poor chemoimmunotherapy responses. Yet T-cell immunity actively shapes human PDAC, as long-term survivors exhibit increased CD8+ T-cell infiltration, most patients have neoepitopes, and neoantigen-targeting vaccines and clonal T-cell therapies can elicit clinical responses. However, current KPC-based preclinical PDAC models have low T-cell infiltration and neoantigen burden, bear highly avid neoepitopes, or are non-inducible, leading to immediate rejection, immune escape, or central tolerance, limiting their utility for studying the dynamics of neoantigen-specific anti-tumor T-cell immunity. We designed NINJA PDAC, a transplantable murine PDAC organoid model to study in vivo neoantigen-specific CD8+ (neo-CD8+) T-cell responses within the established PDAC TME. NINJA affords induction of LCMV-based T-cell neoantigen (GP33/GP66) expression in Kras G12D ;p53 –/– organoids with temporal control, permits bypass of central tolerance, and mirrors human MHC-I affinity. Orthotopic NINJA PDAC transplants generate desmoplastic stroma and spontaneous liver/peritoneal metastases comparable to human PDAC, and allow inducible neoantigens eliciting measurable neo-CD8+ T-cell responses and rejection. Using immune perturbations (adoptive T-cell challenge, immune depletion, chemokine/checkpoint blockade) and temporally-controlled neoantigen induction, we probed the impact of the PDAC TME on anti-tumor neo-CD8+ effector responses. Early NINJA induction suppressed tumor growth and drove complete immunoediting, whereas late induction post-TME formation yielded heterogenous outcomes: one third of tumors were immunoedited (low NINJA-GFP) by a robust intratumoral H2Dbgp33-41-tetramer+ neo-CD8+ T-cell infiltrate, with T-effector phenotype and low exhaustion. Non-immunoedited tumors had neoantigen-persistence and lower neo-CD8+ intratumoral infiltration, which remained non-exhausted. Spatial mapping identified endogenous CD8+ T-cell arrest at the myCAF and TAM-rich stromal boundary in non-immunedited tumors, and adoptively transferred preactivated neo-CD8+ (P14) T-cells also arrested at the margin, suggesting TME-mediated exclusion mediates non-immunoediting instead of exhaustion or impaired activation. TAM or B-cell ablation was unable to rescue editing or exclusion. By contrast, blocking CXCL12-CXCR4 signaling (AMD3100) enhanced neo-CD8+ intratumoral trafficking and immunoediting, with further infiltration when combined with PD-1 blockade. Importantly, when timed with mid-tumor stage neoantigen-induction (after TME formation), CXCR4-inhibition increased tumor regression and reduced metastasis. In summary, these data highlight the impact of TME-mediated CD8+ T-cell exclusion in inhibiting neoantigen-specific immune responses, and establish NINJA PDAC as a high-fidelity pre-clinical toolset to study neoantigen-specific anti-tumor T-cell responses in PDAC, and accelerate the development of novel biologically-driven combination immunotherapeutics. Citation Format: Jeremy B. Jacox, Sri Chaitanya Vattem, Gena G. Foster, Dhruvi Shah, Jin W. Yoo, Jessica Santana, Akin Sogunro, Nikhil Joshi, Mandar D. Muzumdar. Bypassing tumor microenvironment immune exclusion to elicit neoantigen-specific anti-tumor immunity in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research—Emerging Science Driving Transformative Solutions; Boston, MA; 2025 Sep 28-Oct 1; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2025;85(18_Suppl_3): nr A076.