Recording cell–cell interactions in vivo and isolating live interacting cell partners for downstream analysis holds immense potential for understanding how the immune system engages with tumours. Application of LIPSTIC (Labelling Immune Partnerships by SorTagging Intercellular Contacts) in tumour-bearing models has revealed a previously uncharacterised subpopulation of dendritic cells (DCs). These DCs engage directly with T cells, display a distinct transcriptomic signature, and possess enhanced T cell priming capacity. Notably, this subset also shows heightened responsiveness to immune checkpoint blockade therapy, underscoring its critical role in shaping effective anti-tumour immunity. As tumour–immune interactions can also promote immunosuppression, ongoing work employs LIPSTIC to map the tumour–immune interactome, offering insights into immune evasion and guiding strategies to enhance anti-tumour responses.