Abstract A002: Transcriptional regulation and membrane sequestration of myeloid-derived TNF in pancreatic cancer

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy defined by stromal desmoplasia, inflammation, and an immunosuppressive tumor microenvironment (TME) enriched for innate immune cells and characterized by effector T-cell dysfunction. Beyond malignant epithelial cells, the PDAC TME is composed predominantly of cancer-associated fibroblasts (CAFs), tumor-associated macrophages, and granulocytic myeloid-derived suppressor cells (gMDSCs). Reciprocal signaling among these cellular constituents sustains stromal inflammation, immune suppression, and resistance to chemo±immunotherapy. gMDSCs infiltrate early during PDAC development and are central drivers of immune evasion. We previously identified gMDSC-derived tumor necrosis factor (TNF), specifically transmembrane TNF (tmTNF) engaging TNFR2, as a regulator of therapeutic resistance, and showed that pharmacologic disruption of tmTNF–TNFR2 signaling reprograms the stromal and immune microenvironment to improve chemosensitivity in preclinical PDAC models. Here, we define the functional consequences of gMDSC-derived tmTNF on stromal and adaptive immune compartments and delineate gMDSC-intrinsic mechanisms governing TNF transcription and membrane sequestration. We show that gMDSC tmTNF promotes inflammatory CAF (iCAF) polarization and induces CD8+ T-cell dysfunction via juxtracrine interactions. Mechanistically, we identify C/EBPβ (Cebpb), acting downstream of MAP kinase signaling, as a key transcriptional regulator of Tnf in gMDSCs. In parallel, we find that STAT3 represses Adam17 (TACE) transcription, thereby limiting TACE-dependent proteolytic shedding and promoting membrane sequestration of TNF. These findings uncover a novel gMDSC-intrinsic MAP kinase-STAT3 axis that orchestrates the sequestration of tmTNF, sustaining a tolerogenic circuitry in the PDAC TME. Our results suggest that dual inhibition of MEK1/2 and JAK/STAT3 may effectively disrupt gMDSC-tmTNF expression to overcome hallmarks of chemo-immunotherapy resistance in PDAC patients.