Loss of CD44 re-educates pancreatic cancer-associated fibroblasts modulating their fibrotic and immunosuppressive functions.

Pancreatic tumors are characterized by a prominent desmoplastic stroma that can account for up to 90% of the tumor. Given the marked upregulation of CD44, a family of transmembrane glycoproteins, in pancreatic cancer-associated fibroblasts (CAFs), we investigated its role in regulating myofibroblastic and inflammatory CAF phenotypes. Conditional deletion of Cd44 in fibroblastic cells in Cd44fl/fl;PdgfrβCreERT2 mice significantly reduced tumor growth and was associated with a significant reduction in intratumoral regulatory T cells (Treg). Consistently, in human CAFs CRISPR/Cas9-edited to delete CD44, the fibroblasts' morphology changed drastically: CAFs lost their elongated phenotype and adopted a round shape, reflecting their inactivation. This was accompanied by a significant downregulation of activation markers, unresponsiveness to exogenous stimuli, and reduced contractile activity. Furthermore, CD44 ablation decreased extracellular matrix production and altered the immunomodulatory cytokine secretion, highlighting its role in both fibrosis and immune regulation. Finally, CD44-deficient CAFs exhibited a reduced capacity to suppress anti-tumor immune responses by failing to induce immunosuppressive programs in dendritic cells (DCs) and by increasing cytotoxic T cell (CTL)-mediated tumor cell killing. Collectively, we identify CD44 as a regulator of CAF activation and immunosuppressive function, linking stromal remodeling to immune evasion in pancreatic cancer and supporting CD44 as a potential therapeutic strategy to reprogram the tumor stroma and enhance anti-tumor immunity.