Graphical Abstract Highlights d TNF release by mast cells is required for efficient CD8 + T cell responses to haptens d Mast cell TNF promotes the migration and maturation of CD8 + DCs specifically d Mast cell TNF distinctly boosts the CD8 + T-cell-priming efficiency of CD8 + DCs In Brief The impact of mast cells on T-cell-dominated adaptive immunity and diseases is poorly mechanistically defined. Dudeck et al. identify the distinct potential of mast-cell-derived TNF to amplify CD8 + T cell expansion and CD8 + T-cell-driven adaptive immune responses by modulating the CD8 + DC migration and priming efficiency.