(483a) Understanding a Highly Microparticle Sensitive, Temporally Controlled Dendritic Cell Subset: Implications for Improving Vaccines

While it is known that dendritic cells (DCs) are a crucial cell for antigen presentation and initiation of adaptive immunity, DCs are a highly heterogeneous population of cells. It is currently unknown if all cells participate equally in antigen presentation and immune activation. Recent reports have indicated there is a subpopulation of DCs that exhibits highly increased cytokine secretion to toll-like receptor (TLR) signaling but to date these cells have been difficult to isolate and characterize. We recently identified a DC subset via preferential uptake of fluorescently labeled polystyrene microparticles (MPs) conjugated with various TLR agonist molecules which we call First Responders (FRs). FRs exhibit similar increases in cytokine (TNFα) secretion and seem to be these same “super secreting” cells. This project is focused on understanding the mechanism of how FRs preferentially up MPs, initialize innate immune response via paracrine signaling and coordinate adaptive immune response. We have shown that FRs are temporally controlled substate of cDC2 cells, exhibit increased MP uptake on a 1-3 hr time scale and then cycle over a period of 24 hrs. We also have shown that FRs seem to preferentially exist in G2 cell cycle phase, indicating that FRs substate is related to the cell cycle. To understand the phenotype even further, we performed both bulk and single cell mRNA sequencing on FRs and observed increases distinct expression profile with increases in several immune and metabolic genes. After validating the gene expression via flow cytometry, we identified several surface markers unregulated in FRs and performed a series of in vivo assays to show that FR targeting increases vaccination response. Due to their importance in innate immune coordination and their crucial role in adaptive immune responses, these cells not only warrant further study but also present an attractive target for vaccine research.