Neutrophil Extracellular Traps Modulate Recruitment and Immunosuppression of Macrophages in Pancreatic Adenocarcinoma

Abstract

Pancreatic adenocarcinoma (PDAC) has a dismal survival rate due to limited effective therapies. Although studies have focused on the influence of innate immune cells on adaptive immune cell functions, few have explored interactions between innate immune cells, which modulate the PDAC tumor microenvironment (TME). Macrophages are responsible for the clearance of neutrophil-mediated inflammation in physiologic, resolving immune responses; however, both of these cell types coexist in the TME, suggesting a failure of macrophages to clear neutrophils in PDAC. We sought to determine how neutrophil extracellular traps (NET), neutrophil release of decondensed chromatin, and intracellular contents affect monocyte/macrophage populations in the PDAC TME. Utilizing samples from patients with PDAC, we demonstrated elevated levels of the monocyte chemokine CCL2 in plasma, as well as elevated NET citrullinated histone H3 and the pan-macrophage marker CD68 in the PDAC TME via fluorescent IHC. To determine how NETs affected macrophage populations in the PDAC TME, we targeted NETs with DNase I treatment to digest extracellular DNA released from NETs or with genetic knockout of PAD4, an enzyme required for NET formation. NET depletion resulted in an elevation in the pan-macrophage marker F4/80. The depletion led to an increased T-cell stimulatory signal, CD80, whereas the protumor macrophage marker CD206 was decreased. We further demonstrated that macrophages in the NET-deficient PDAC TME may be recruited through the CCL2/CCR2 axis, and CCL2 was released from tumor cells and macrophages in the presence of IFNγ. Taken together, our findings reveal that inhibition of NETs can prime the innate immune response toward an antitumor phenotype.