Background

While adaptive immune cells such as T and B lymphocytes are widely studied as the essential effector cells of the immune system, APCs are the upstream gatekeepers initiating and shaping virtually any adaptive immune response 1, 2. The past decade has revealed considerable functional specialization within the murine and human dendritic cell (DC) compartment 3-5. However, only recently studies have focused on the myeloid populations present in human nonlymphoid tissues, showing similarities as well as functional differences to the murine system 6. These advancements have largely been fueled by technical developments in the field of flow cytometry 7 and single-cell RNA-sequencing (sc-RNAseq) 8. Importantly, increasing evidence suggests that studying DC biology in the context of autoimmune diseases 9 as well as cancer progression might reveal novel approaches for therapeutic interventions 10, 11. In particular, via their presence in nonlymphoid tissues and their expression of co-stimulatory or co-inhibitory receptors, DCs are considered critical for shaping either a tolerogenic or pro-inflammatory local immune milieu 2, 12.