Expression Profiling of Macrophages Reveals Multiple Populations with Distinct Biological Roles in an Immunocompetent Orthotopic Model of Lung Cancer

Macrophages represent an important component of the tumor microenvironment and play a complex role in cancer progression. These cells are characterized by a high degree of plasticity, and alter their phenotype in response to local environmental cues. While the M1/M2 classification of macrophages has been widely used, the complexity of macrophage phenotypes specifically in lung cancer has not been well studied. In this study we employed an orthotopic immunocompetent model of lung adenocarcinoma in which murine lung cancer cells are directly implanted into the left lobe of syngeneic mice. Using multi-marker flow cytometry we defined and recovered several distinct populations of monocytes/macrophages from tumors at different stages of progression. We used RNA-seq transcriptional profiling to define distinct features of each population and determine how they change during tumor progression. We defined an alveolar resident macrophage population that does not change in number and express multiple genes related to lipid metabolism and lipid signaling. We also defined a population of tumor-associated macrophages that increase dramatically with tumor, and selectively express a panel of chemokines genes. A third population, which resembles tumor-associated monocytes, expresses a large number of genes involved in matrix remodeling. By correlating transcriptional profiles with clinically prognostic genes, we show that specific monocyte/macrophage populations are enriched in genes that predict good or poor outcome in lung adenocarcinoma, implicating these subpopulations as critical determinants of patient survival. Our data underscore the complexity of monocytes/macrophages in the tumor microenvironment, and suggest that distinct populations play specific roles in tumor progression. Overall design: mRNA profiles of macrophage/monocyte cells isolated from murine control or tumor-bearing lung. From naive mice: MacA cells (MacA-N), MacB1 cells (MacB1-N), MacB2 cells (MacB2-N); from 2 week tumor bearing mice: MacA cells (MacA-2wk), MacB2 cells (MacB2-2wk), MacB3 cells (MacB3-3wk); from 3-week tumor bearing mice: MacB2 (MacB2-3wk), MacB3 cells (MacB3-3wk). Each population was analyzed in triplicate (cells were isolated in 3 independent experiments).

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Poczobutt JM, De S, Yadav VK, Nguyen TT, Li H, Sippel TR, Weiser-Evans MC, Nemenoff RA