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

The mucosal delivery route is considered ideal for immunization. However, induction of antigen-specific mucosal immunity is difficult due to the tolerogenic environment. Therefore, developing an immunogenic mucosal dendritic cell (DC)-targeting strategy is required. Herein, we investigated the characteristics and immunogenic potential of Peyer's patch (PP) DCs as an oral vaccination-targeting strategy. Single-cell RNA sequencing analysis of the PP DCs showed that complement C5a receptor- and lysozyme-expressing DCs exhibit increased expression of genes related to chemotaxis. Administration of the Co1 peptide, a C5aR ligand, increased CD8⁺ T cell infiltration and response to the co-delivered model antigen in mice. Furthermore, in the SARS-CoV-2 vaccine model, vaccination with Co1 elicited both systemic and mucosal immunity. Collectively, these findings demonstrate that C5aR signaling in mucosal DCs plays a role in regulating adjuvant activity by modulating the tissue microenvironment.