Long-term culture of fetal monocyte precursorsin vitroallowing the generation ofbona fidealveolar macrophagesin vivo

ABSTRACT Tissue-resident macrophage-based immune therapies have been proposed for various diseases. However, generation of sufficient numbers that possess tissue-specific functions remains a major handicap. Here, we show that fetal liver monocytes (FLiMo) cultured with GM-CSF (also known as CSF2) rapidly differentiate into a long-lived, homogeneous alveolar macrophage (AM)-like population in vitro . CSF2-cultured FLiMo remain the capacity to develop into bona fide AM upon transfer into Csf2ra -/- neonates and prevent development of alveolar proteinosis and efferocytosis of apoptotic cells for at least 1 year in vivo . Compared to transplantation of AM-like cells derived from bone marrow macrophages (BMM), CSF2-cFliMo more efficiently engraft empty AM niches in the lung and protect mice from respiratory viral infection. Harnessing the potential of this approach for gene therapy, we restored a disrupted Csf2ra gene in FLiMo and their capacity to develop into AM in vivo . Together, we provide a novel platform for generation of immature AM-like precursors amenable for genetic manipulation, which will be useful to study to dissect AM development and function and pulmonary transplantation therapy.