Downstream Mediators of the Intratumoral Interferon Response Suppress Antitumor Immunity, Induce Gemcitabine Resistance and Associate with Poor Survival in Human Pancreatic Cancer

The cancer microenvironment allows tumor cells to evade immune surveillance through a variety of mechanisms. While interferon-γ (IFNγ) is central to effective antitumor immunity, its effects on the microenvironment are not as clear and have in some cancers been shown to induce immune checkpoint ligands. The heterogeneity of these responses to IFNγ remains poorly characterized in desmoplastic malignancies with minimal inflammatory cell infiltration, such as pancreatic cancer (PC). Thus, the IFNγ response within and on key cells of the PC microenvironment was evaluated. IFNγ induced expression of human leukocyte antigen (HLA) class I and II on PC cell lines, primary pancreatic cancer epithelial cells (PPCE) and patient-derived tumor-associated stroma, concomitant with an upregulation of PDL1 in the absence of CD80 and CD86 expression. As expected, IFNγ also induced high levels of CXCL10 from all cell types. In addition, significantly higher levels of CXCL10 were observed in PC specimens compared to those from chronic pancreatitis, whereby intratumoral CXCL10 concentration was an independent predictor of poor survival. Immunohistochemical analysis revealed a subset of CXCR3-positive cancer cells in over 90 % of PC specimens, as well as on a subset of cultured PC cell lines and PPCE, whereby exposure to CXCL10 induced resistance to the chemotherapeutic gemcitabine. These findings suggest that IFNγ has multiple effects on many cell types within the PC microenvironment that may lead to immune evasion, chemoresistance and shortened survival.