AbstractAntigen cognate dendritic cell (DC)-T cell synaptic interactions drive activation of T cells and instruct DCs. Upon receiving CD4⁺ T cell help, post-synaptic DCs (psDCs) are licensed to generate CD8⁺ T cell responses. However, the cellular and molecular mechanisms that enable psDCs licensing remain unclear. Here, we describe that antigen presentation induces an upregulation of MHC-I protein molecules and increased lipid peroxidation on psDCs in vitro and in vivo. We also show that these events mediate DC licensing. In addition, psDC adoptive transfer enhances pathogen-specific CD8⁺ T responses and protects mice from infection in a CD8⁺ T cell-dependent manner. Conversely, depletion of psDCs in vivo abrogates antigen-specific CD8⁺ T cell responses during immunization. Together, our data show that psDCs enable CD8⁺ T cell responses in vivo during vaccination and reveal crucial molecular events underlying psDC licensing.