CTLA4 and cancer: The development of checkpoint inhibitors (CPIs), the first of which were anti-CTLA-4, anti-PD-1, and anti-PD-L1 antibodies, represent a remarkable breakthrough in cancer medicine.7 Even so, these therapies are effective in only subsets of patients, and many patients who initially respond eventually relapse.8,9 Additional therapies are needed that can either elicit responses in patients who do not benefit from CPIs, or who do not benefit enough.