CTLA4 and cancer: The most important breakthrough in cancer immunotherapy to date has been the development of immune checkpoint inhibitors (ICI), also referred as immune checkpoint blockers (ICB), initially with the pharmacological blockade of the interaction between cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) and CD28, and soon followed by the blockade of programmed cell death 1 receptor (PD-1) with its ligand PD-L1 and PD-L2; progress with other ICIs has recently been reviewed by Sharma (1).