CTLA4 and cancer: Big progress has been made in tumor immunotherapy recently by the utilization of immune checkpoint inhibitors (ICIs), including anti-PD-L1/PD-1 2-4 and anti-CTLA-4 5-7 antibodies, to overcome the tumor immunosuppressive environment, which shows clinical efficacy in the treatment of various cancers including melanoma, ovarian cancer, colorectal cancer and lung cancer 8, 9.