Notch-mediated generation of monocyte-derived Langerhans cells: Phenotype and function.

Abstract Langerhans cells (LCs) in the skin are a first line of defense against pathogens but also play an essential role in skin homeostasis. Their exclusive expression of the C-type lectin receptor Langerin/CD207 makes them prominent candidates for immunotherapy. For vaccine testing, an easily accessible cell platform would be desirable as an alternative to the time-consuming purification of LCs from human skin. Here we present such a model and demonstrate that monocytes in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF), transforming growth factor (TGF)-β1 and the Notch ligand Delta-like 4 (DLL4) differentiate within 3 days into CD1a+Langerin+cells containing Birbeck granules. RNA-sequencing (RNA-seq) of these monocyte-derived LCs (moLCs) confirmed gene expression of LC-related molecules, pattern recognition receptors and enhanced expression of the antigen-presenting machinery. On protein level, moLCs showed low expression of costimulatory molecules but prominent expression of C-type lectin receptors. MoLCs can be matured, secrete IL-12p70 and TNF-α and stimulate proliferation and cytokine production in allogeneic CD4+ and CD8+ T cells. In regard to vaccine testing, a recently characterized glycomimetic Langerin ligand conjugated to liposomes demonstrated specific and fast internalization into moLCs. Hence, these short-term in vitro-generated moLCs represent an interesting tool to screen LC-based vaccines in the future.