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

Pancreatic tumors are characterized by a prominent stroma that makes up to 90% of the tumor. Due to the significant upregulation of CD44, a family of transmembrane glycoproteins, in pancreatic cancer-associated fibroblasts (CAFs), we investigated its role in myofibroblastic and inflammatory CAF subsets. Conditional deletion of Cd44 in CAFs in Cd44fl/fl;Pdgfr{beta}CreERT2 mice, significantly decreased the tumor volume. In human CAFs CRIPSR/Cas9-edited to delete CD44, the morphology of the fibroblasts 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. CD44 absence not only downregulated extracellular matrix proteins in CAFs, thus influencing fibrosis, but also changed the immunomodulatory cytokine secretion. Finally, this inactivation of CAFs upon CD44 deletion influenced their immunosuppressive effect on dendritic cells (DCs) and on cytotoxic T cells (CTLs), resulting in decreased expression of immunosuppressive cytokines in DCs and enhanced tumor-cell-killing by CTLs.