Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy with a dense desmoplastic stroma and an immunosuppressive tumor microenvironment that contribute to therapeutic resistance. Here, we identify plasminogen activator inhibitor 1 (PAI1) as a stroma-derived mediator of immune evasion and tumor progression in PDAC. PAI1 is predominantly produced and secreted by cancer-associated fibroblasts, and its genetic ablation in the stromal compartment impairs tumor growth. Mechanistically, hypoxia induces PAI1 expression in fibroblasts, which in turn shifts macrophages toward immunosuppressive phenotypes and suppresses CD8 ⁺ T cell infiltration and function. We further show that tissue plasminogen activator (tPA), a direct PAI1 target, is also secreted by fibroblasts and supports antitumor CD8 ⁺ T cell responses. Notably, elimination of stromal tPA promotes immunosuppressive macrophage phenotypes, reduces CD8 ⁺ T cell infiltration, and accelerates PDAC progression. These findings define a previously unrecognized PAI1-tPA regulatory axis within the tumor stroma that modulates antitumor immunity. Targeting this pathway may provide a therapeutic opportunity to overcome stroma-driven immune suppression in PDAC.

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy characterized by a dense fibroinflammatory stroma and profound hypoxia. Using pancreatic stellate cell-tumor organoid coculture models and single-cell RNA sequencing analyses, we uncover that hypoxia-driven fibroblast reprogramming promotes immunosuppressive macrophage phenotypes in PDAC. Mechanistically, hypoxia acts through tumor-fibroblast crosstalk to increase IL-6 expression in fibroblasts; in turn, fibroblast-derived IL-6 induces expression of arginase 1 (ARG1), a key mediator of immunosuppression, in macrophages via activation of the JAK/STAT signaling pathway. Consistent with these findings, macrophages enriched for hypoxia signatures are strongly associated with elevated immunosuppression programs and IL6/JAK/STAT3 signaling signatures in PDAC. Our study reveals a paracrine mechanism by which hypoxia coordinates tumor cell, fibroblast, and macrophage interactions to promote immune suppression in PDAC.