A distinct human cell type expressing MHCII and RORγt with dual characteristics of dendritic cells and type 3 innate lymphoid cells

Recent studies have characterized various mouse antigen- presenting cells (APCs) express -ing the lymphoid- lineage transcription factor ROR gamma t (Retinoid- related orphan receptor gamma t), which exhibit distinct phenotypic features and are implicated in the induc-tion of peripheral regulatory T cells (Tregs) and immune tolerance to microbiota and self- antigens. These APCs encompass Janus cells and Thetis cell subsets, some of which express the AutoImmune REgulator (AIRE). ROR gamma t+ MHCII+ type 3 innate lymphoid cells (ILC3) have also been implicated in the instruction of microbiota- specific Tregs. While ROR gamma t+ APCs have been actively investigated in mice, the identity and function of these cell subsets in humans remain elusive. Herein, we identify a rare subset of ROR gamma t+ cells with dendritic cell (DC) features through integrated single -cell RNA sequencing and single -cell ATAC sequencing. These cells, which we term ROR gamma t+ DC -like cells (R- DC- like), exhibit DC morphology, express the MHC class II machinery, and are distinct from all previously reported DC and ILC3 subsets, but share transcriptional and epigenetic similarities with DC2 and ILC3. We have developed procedures to isolate and expand them in vitro, enabling their functional characterization. R -DC -like cells proliferate in vitro, continue to express ROR gamma t, and differentiate into CD1c+ DC2-like cells. They stimulate the proliferation of allogeneic T cells. The identification of human R -DC -like cells with proliferative potential and plasticity toward CD1c+ DC2-like cells will prompt further investigation into their impact on immune homeostasis, inflam-mation, and autoimmunity.