Effective antitumor immunity requires dendritic cells (DCs) to internalize, process, and present tumor antigens to T cells. Adoptive transfer of DCs that were loaded ex vivo with tumor antigens has been shown to stimulate antitumor immunity in patients with cancer, but clinical responses have been mixed. To address the limitations of traditional DC-based therapies, we constructed and functionally screened a panel of chimeric antigen receptors (CARs) optimized for expression and activity in DCs. Through this screening, we identified key functional components that guided the development of an inducible platform centered on an instructive chimeric antigen receptor (iCAR). This iCAR enabled DCs to (i) recognize a surface molecule present on cancer cells or their extracellular vesicles (EVs), such as disialoganglioside GD2 (expressed in melanoma and other tumors of neuroectodermal origin) or HER2 (expressed in some epithelial cancers), thereby promoting the acquisition of tumor-derived material containing putative tumor antigens; (ii) undergo immunostimulatory activation to prime antigen-specific T cells via both cross-dressing and cross-presentation; and (iii) transactivate the expression of the therapeutic cytokine interleukin-12 (IL-12) in response to antigen uptake. The iCAR converted melanoma-derived EVs from immune-suppressive to stimulatory cues for DCs in cell culture assays. Moreover, systemic administration of iCAR-DCs enhanced antigen-specific T cells, expanded low-frequency T cell clonotypes, and delayed tumor growth in immunotherapy-resistant melanoma models without the need for ex vivo antigen loading or cell maturation. iCAR-DCs may therefore provide a platform for antigen-agnostic cancer immunotherapy that integrates antigen uptake with programmable DC activation.