ADP-ribosylating adjuvant reveals plasticity in cDC1 cells that drive mucosal Th17 cell development and protection against influenza virus infection

Migratory dendritic cells expressing CD103 are the targets for mucosal vaccines. These belong to either of two lineage-restricted subsets, cDC1 or cDC2 cells, which have been linked to priming of functionally distinct CD4 T cells. However, recent studies have identified plasticity in cDC2 cells with overlapping functions with cDC1 cells, while the converse has not been reported. We genetically engineered a vaccine adjuvant platform that targeted the cholera toxin A1 (CTA1) ADP-ribosylating enzyme to CD103⁺ cDC1 and cDC2 cells using a single-chain antibody (scFv) to CD103. Unexpectedly, intranasal immunization with the CTA1-svFcCD103 adjuvant modified cDC1 cells to effectively prime Th17 cells, a function previously limited to cDC2 cells. In fact, cDC2 cells were dispensible, while cDC1 cells, lacking in Batf3−/− mice, were critical. Following intranasal immunizations isolated cDC1 cells from mLN exclusively promoted Rorgt⁺ T cells and IL-17, IL-21, and IL-22 production. Strong CD8 T cell responses through antigen cross presentation by cDC1 cells were also observed. Single-cell RNAseq analysis revealed upregulation of Th17-promoting gene signatures in sorted cDC1 cells. Gene expression in isolated cDC2 cells was largely unaffected. Our finding represents a major shift of paradigm as we have documented functional plasticity in cDC1 cells.