Expansion of tumor-associated Treg cells upon disruption of a CTLA-4-dependent feedback loop Graphical abstract Highlights d The TCR repertoire of Treg cells is enriched for reactivity to antigens in the TME d Tumor Treg cells use CTLA-4 to destabilize their own interactions with dendritic cells d CTLA-4 blockade causes the CD28-mediated expansion of tumor-associated Treg cells d Following CTLA-4 blockade, Treg cells continue to promote tumor immune tolerance