Proximity-dependent labeling identifies dendritic cells that drive the tumor-specific CD4 ⁺ T cell response

Dendritic cells (DCs) are uniquely capable of transporting tumor antigens to tumor-draining lymph nodes (tdLNs) and interact with effector T cells in the tumor microenvironment (TME) itself, mediating both natural antitumor immunity and the response to checkpoint blockade immunotherapy. Using LIPSTIC (Labeling Immune Partnerships by SorTagging Intercellular Contacts)–based single-cell transcriptomics, we identified individual DCs capable of presenting antigen to CD4 + T cells in both the tdLN and TME. Our findings revealed that DCs with similar hyperactivated transcriptional phenotypes interact with helper T cells both in tumors and in the tdLN and that checkpoint blockade drugs enhance these interactions. These findings show that a relatively small fraction of DCs is responsible for most of the antigen presentation in the tdLN and TME to both CD4 + and CD8 + tumor–specific T cells and that classical checkpoint blockade enhances CD40-driven DC activation at both sites.