Checkpoint inhibitors, such as anti-PD-1 and anti-CTLA-4 antibodies, have provided exceptional anti-tumor responses and extended the survival of patients in several types of cancers; nevertheless, few of them fail to respond or if they do respond, they relapse later by developing resistance to immunotherapy, which is attributed to the accumulation of Tregs in the tumors [78,79]. The gene discussed is CTLA4; the disease is neoplasm.