While strategies that potentiate the activity of cytotoxic CD8+ T cells with immune checkpoint inhibitors (such as monoclonal antibodies (mAbs) against CTLA4, PD1 and PDL1) have shown efficacy in the treatment of cancers, such as melanoma and lung cancer, in most cases, cancer cells’ polyclonality and immunosuppressive microenvironment mean that only a small fraction of patients fully respond to immunotherapy [161]. The gene discussed is CTLA4; the disease is cancer.