Following preclinical studies demonstrating that CTLA‐4 blockade diminishes Treg activity and restores antitumor T cell effector function,120 a subsequent clinical trial showing the therapeutic efficacy of an anti‐CTLA‐4 antibody in melanoma patients121 led to FDA approval of ipilimumab as the first immune checkpoint inhibitor for cancer treatment. Here, CTLA4 is linked to cancer.