Comparison of sorted TRM populations and TRM-like cells in vitro

Tissue-resident macrophages (TRM) perform organ-specific functions that are dependent on factors such as hematopoietic origin, local environment and biological influences. A diverse range of in vitro culture systems have been developed to decipher TRM functions, including bone marrow-derived macrophages (BMDM), induced pluripotent stem cells (iPSC) or immortalized cell lines. However, despite the usefulness of such systems, there are notable limitations. Attempts to culture primary macrophages often require purification of cells, lack a high cell yield and consistent phenotype. Here, we aimed to address these practical limitations by establishing a new organotypic primary cell culture protocol. We obtained long-term monocultures of macrophages derived from distinct organs without FACS or MACS purification using specific growth factors and tissue normoxic conditions that largely conserved a TRM-like identity in vitro. Thus, this new organotypic system offers an ideal screening platform for primary macrophages from different organs which can be used for a wide range of assays and read-outs.