Generation of tumor-infiltrating lymphocytes (TILs) begins when tumor antigens reach the lymph node (LN) to stimulate T cells, yet we know little of how tumor material is disseminated amongst the large variety of antigen-presenting dendritic cell (DC) subsets in the LN. Here, we demonstrate that tumor proteins are carried to the LN within discrete vesicles inside DC and are then transferred amongst DC subsets. A synapse is formed between interacting DC and vesicle transfer takes place in the absence of free exosomes. DC containing vesicles can uniquely activate T cells whereas DC lacking them do not. Understanding this restricted sharing of tumor identity provides substantial room for engineering better anti-tumor immunity.