Deciphering the role of macrophages in the development of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive forms of cancer. Intraductal papillary mucinous neoplasms (IPMNs) are a well-documented precursor of invasive PDAC; however, the molecular and cellular alterations that drive malignant progression of IPMNs are poorly understood. Genetic alterations drive progression in only a minority of cases, highlighting the likelihood that the surrounding tumor microenvironment (TME) may play an important role. PDAC is characterized by an immunosuppressive TME with abundant macrophages, but the temporal accumulation of immunosuppressive macrophages in PDAC precursors and their role in the progression to invasive cancer has not been explored. A deeper understanding of the TME in IPMN and PDAC may reveal actionable mechanisms of progression, potentially identifying novel therapeutic targets or biomarkers of progression risk. To investigate the temporal recruitment, polarization state, and spatial localization of macrophages, we leveraged immunohistochemistry (IHC) and imaging mass cytometry (IMC) datasets of human IPMNs and adjacent PDAC. IHC from 24 patients showed significant upregulation of CD68+ macrophages in PDAC. IMC allows quantification of the densities and spatial distribution of distinct subtypes. IMC analysis of IPMN, transition zone, and PDAC regions from 12 patients identified heterogeneous changes in total macrophage count and proportions of macrophages subsets over the transition from IPMN to invasive PDAC. In addition, spatial transcriptomics was performed on a subset of samples from 4 patients to interrogate mechanisms of macrophage-epithelial crosstalk across the transition from IPMN to PDAC. In vitro culture of primary human macrophages and PDAC organoids further enables characterization of the functional impact of macrophage-epithelial crosstalk. Organoid-conditioned media treatment of macrophages demonstrates that the PDAC secretome is capable of polarizing macrophages toward an immunosuppressive phenotype with increased expression of IL-10 and CD163. This study provides a comprehensive molecular analysis of macrophages present in the TME of IPMN and PDAC, revealing heterogeneous patterns across patients. The results suggest a role for macrophages in malignant progression and pathways by which PDAC cells reprogram the macrophage population, offering new insights into the interaction between macrophages and neoplastic epithelial cells, which can be used to identify signaling dependencies that could serve as novel biomarkers of therapeutic targets.