Besides blocking the inhibiting immune checkpoint CTLA-4 and thereby bolstering immune response against cancer cells, a second target became apparent in the last decades: In 1992, Tasuku Honjo and colleagues discovered the programmed death 1 (PD-1) receptor [21], expressed on a variety of immune cells, such as T cells, B cells, monocytes, dendritic cells, and tumor-infiltrating lymphocytes (TILs). This evidence concerns the gene CTLA4 and cancer.