C5aR+ dendritic cells fine-tune the Peyer's patch microenvironment to induce antigen-specific CD8+ T cells

The mucosa is an ideal route for vaccination against pathogen infection, but the effective adjuvant capable of overcoming the tolerogenic dendritic cell (DC) environment is unavailable. We characterized type 2 conventional DCs and lysozyme-expressing monocyte-derived DCs (LysoDCs) of Peyer's patches to identify the vaccination target cells through single-cell RNA sequencing. Based on functional analysis of the data, we suggest that C5aR+ LysoDCs and Co1 peptide, a C5aR ligand, as a target cell and an adjuvant, respectively, for mucosal vaccination. Co1-mediated stimulation of C5aR+ LysoDCs increased the level of reactive oxygen species, leading to CCL3-mediated chemotaxis and exogenous antigen cross-presentation, which elicited an antigen-specific CD8+ T cell response. In a SARS-CoV-2 vaccine model, Co1 peptide increased the frequency of antigen-specific polyfunctional CD8+ T cells in systemic as well as mucosal compartments. Collectively, LysoDC activation by Co1 peptide potentiates vaccination efficiency by constructing an immunostimulatory environment in the mucosal immune inductive site. Overall design: To observe the DEGs in PP CD11chiMHCclassIIhi SIRP+ cells treated with Co1 peptide, cells were sorted and then in vitro cultured with or without Co1 peptide in RPMI-1640 supplemented with 10% heat inactivated fetal bovine serum, colony stimulating factor 1 (0.1 ?g/ml), colony stimulating factor 2 (0.5 ?g/ml). After 6 h, the scRNA-seq were performed by geninus (Seoul, Korea) according to protocol provided by the 10x Genomics.