Dissecting the role of toll-like receptor 7 in pancreatic cancer

Background: Toll-like receptors (TLRs) are gaining attention for their potential to influence tumor biology both on the level of the tumor cells as well as on the level of the surrounding inflammatory stroma. Previous studies resulted in partly conflicting data on the expression of TLR7 in healthy and neoplastic pancreatic tissues as well as its role in pancreatic tumor biology. Methods: We used qRT-PCR and immunohistochemistry to asses TLR7 expression in primary patient material and cell lines. Cell viability was analyzed by MTT assay upon incubation with TLR7 agonist/antagonist. Mouse models were used to investigate the role of TLR7 in vivo. Results: TLR7 is overexpressed in more than 50% of primary human pancreatic ductal adenocarcinoma (PDAC). High TLR7 expression was associated with shorter patient survival, and TLR7 inhibition in cell lines reduced viability in a dose-dependent manner. In contrast, global TLR7 deficiency did not alter survival or overall histopathological tumor features in genetic mouse models of PDAC. Conclusions: TLR7 may have opposing functions in tumor versus stroma cells. Further work is required to more precisely dissect the roles of TLR7 and its ligands in different populations of epithelial and stromal cells and to understand their relative contributions to tumor progression.