Mitochondrial metabolism regulates the immunogenic responsiveness of dendritic cells.

Activation of conventional dendritic cells (cDCs) favors increased glycolysis-driven lactic fermentation, while oxidative phosphorylation (OXPHOS) links to tolerance. Here, selective targeting of the mitochondrial electron transport chain (ETC) in cDCs uncovers a critical role for OXPHOS in regulating their immunogenicity. Disruption of ETC complex III dampens adjuvant-triggered primary human and mouse cDC1 activation and their capability to prime T cells for anti-cancer immunity, while it has a milder effect on cDC2s. Mechanistically, complex III impairment in cDC1s leads to a dysregulated redox and metabolite balance, altering DNA methylation of PU.1 and activator-protein-1 (AP-1) binding regions. These epigenetic changes hinder the rapid induction of immediate-early stimulus-induced genes in cDC1s upon stimulation. The reduced immunogenic responsiveness of ETC-impaired cDC1s can be rescued by ectopic expression of alternative oxidase and phenocopied by Tet2 deficiency. Our findings reveal that electron flow through the ETC maintains a poised activation state in cDC1s, essential for effective anti-tumor immunity.