Long-term culture-expanded alveolar macrophages restore their full epigenetic identity after transfer in vivo

Sieweke and colleagues show that alveolar macrophages maintain a core gene expression program even after several months in culture and reacquire full transcriptional and epigenetic identity after transplantation into the lung. Alveolar macrophages (AMs) are lung tissue-resident macrophages that can be expanded in culture, but it is unknown to what extent culture affects their in vivo identity. Here we show that mouse long-term ex vivo expanded AMs (exAMs) maintained a core AM gene expression program, but showed culture adaptations related to adhesion, metabolism and proliferation. Upon transplantation into the lung, exAMs reacquired full transcriptional and epigenetic AM identity, even after several months in culture and could self-maintain long-term in the alveolar niche. Changes in open chromatin regions observed in culture were fully reversible in transplanted exAMs and resulted in a gene expression profile indistinguishable from resident AMs. Our results indicate that long-term proliferation of AMs in culture did not compromise cellular identity in vivo. The robustness of exAM identity provides new opportunities for mechanistic analysis and highlights the therapeutic potential of exAMs.

Automated summary

Sieweke and colleagues demonstrate that alveolar macrophages maintain their core gene expression program even after long-term culture and regain their full transcriptional and epigenetic identity upon transplantation into the lung. This study shows that culture adaptations observed in ex vivo expanded alveolar macrophages are reversible and do not compromise their cellular identity in vivo. These findings provide new insights into the mechanisms of alveolar macrophages and highlight their therapeutic potential.