Saponin-based adjuvants enhance antigen cross-presentation in human CD11c⁺ CD1c⁺ CD5^- CD163⁺ conventional type 2 dendritic cells

Background Adjuvants are key for effective vaccination against cancer and chronic infectious diseases. Saponin-based adjuvants (SBAs) are unique among adjuvants in their ability to induce robust cell-mediated immune responses in addition to antibody responses. Recent preclinical studies revealed that SBAs induced cross-presentation and lipid bodies in otherwise poorly cross-presenting CD11b(+) murine dendritic cells (DCs).Method Here, we investigated the response of human DC subsets to SBAs with RNA sequencing and pathway analyses, lipid body induction visualized by laser scanning microscopy, antigen translocation to the cytosol, and antigen cross-presentation to CD8(+) T cells.Results RNA sequencing of SBA-treated conventional type 1 DC (cDC1) and type 2 DC (cDC2) subsets uncovered that SBAs upregulated lipid-related pathways in CD11c(+) CD1c(+) cDC2s, especially in the CD5(-) CD163(+) CD14(+) cDC2 subset. Moreover, SBAs induced lipid bodies and enhanced endosomal antigen translocation into the cytosol in this particular cDC2 subset. Finally, SBAs enhanced cross-presentation only in cDC2s, which requires the CD163(+) CD14(+) cDC2 subset.Conclusions These data thus identify the CD163(+) CD14(+) cDC2 subset as the main SBA-responsive DC subset in humans and imply new strategies to optimize the application of saponin-based adjuvants in a potent cancer vaccine.