In vitro and in vivo derived macrophages occupy distinct phenotypic states

Monocyte-derived macrophages (MDMs) are widely used to model human macrophage biology in vitro and standardized polarization conditions were proposed to recapitulate the different macrophage activation states. Although surface markers specific for distinct MDM populations have been identified, a systematic analysis of surface marker expression on these consensus MDM populations has not previously been reported. Here, we use mass cytometry to perform an in-depth characterization of MDM surface profiles and determine how these markers evolve with time. We also compared the phenotypes found in vitro with patient-derived tumor-associated macrophages (TAMs) and found that although MDMs and TAMs shared most markers investigated, the cell-surface signatures markedly differed in terms of expression levels and combinations. Our high-dimensional, single-cell analyses clarifies the surface expression profile of the core in vitro differentiated macrophage populations and highlights some limitations of the in vitro system to represent the complexity of in vivo polarized tumor-associated macrophage phenotypes. These findings provide new opportunities to improve the models used to study macrophage biology and give a pathway to improve our understanding of the in vivo complexity of these systems.