Immune cell infiltration and interaction with stellate cells in pancreatic ductal adenocarcinoma

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is a disease with very poor prognosis amongst all pancreatico-biliary cancers. PDAC is characterised by a pronounced desmoplastic stroma which upon depletion has been associated with immune cell mediated tumour clearance. In situ analyses of various immune cell markers in the stromal compartments may provide a lucid picture of immune cell migration to the tumour epithelia. Automated, unbiased, high throughput imaging and analysis of specifically designed tissue microarrays, from surgically resected tissue samples of PDAC, advanced PDAC, and other pancreatico-biliary diseases; stained for distinct immune cell markers was carried out in the juxtatumoural stroma and the panstromal compartments. Prognostic significance was determined with X-Tile software. In vitro and in vivo assays were undertaken to outline the possible mechanisms. Immune cell infiltration to PDAC was higher than infiltration to other pancreatico-biliary diseases with the exception of CD8+ T cells. While CD4+, CD68+ and myeloperoxidase+ cells could infiltrate the juxtatumoural stroma of PDAC; CD3+, CD8+, Foxp3+ and CD20+ cells could not in the early stage PDAC patients tissue analysed and also in an independent validation cohort of advanced stage PDAC patients. Survival analyses demonstrated pro-survival effects of having high CD8+ densities. CD8+ T cells could only infiltrate the juxtatumoural compartment of KPC mice after stromal collapse resulting from targeting stellate cells with All-trans Retinoic Acid. 17 In vitro migration assays demonstrated increased CD8+ T cell migration towards activated pancreatic stellate cells compared to quiescent pancreatic stellate cells and appeared to be dependent on CXCL12. T cells are hindered from migrating to the juxtatumoural compartment by activated pancreatic stellate cells as a result of an increase in CXCL12 secretion. Rendering activated pancreatic stellate cells quiescent results in a reduction of CXCL12 secretion which may allow CD8+ T cells to migrate to the tumours and perform cytotoxic functions.