CTLA4 and cancer: Presently, there exist two main cancer immune checkpoint blockade therapies that are approved for clinical use for a number of tumor types, including anti-CTLA4 (ipilimumab) and anti-PD-1/PD-L1 (pembrolizumab, nivolumab/atezolizumab), each of which blocks the attenuation of T cell activity, thereby inducing the expansion of CD8+ T cells and differentially affecting CD4+ T cells (9).