Several immune checkpoint inhibitors, including antibodies against CTLA-4 and PD-1/PD-L1, have been approved for use in the clinic and have shown remarkable responses in the treatment of various cancers, including melanoma, non–small cell lung cancer and renal cell cancer (Hodi et al., 2010; Page et al., 2010; Topalian et al., 2012; Robert et al., 2014; Tumeh et al., 2014). The gene discussed is CTLA4; the disease is melanoma.