PDCD1 and colorectal carcinoma: The relative percentages of CD4+PD-1+CTLA-4+ T cells in peripheral blood of HDs and CRC patients were negligible, where majority of cells were either PD-1−CTLA-4− or expressed only PD-1, whereas in NILs and TILs, CD4+PD-1+CTLA-4− T cells increased significantly (Figure 2C).