CTLA4 and colon adenocarcinoma: PIWIL4 expression in COAD was negatively correlated with immune cell infiltration and immune checkpoint gene expression such as PD1, PD-L1, CTLA4 and PD-L2 (PDCD1LG2, programmed cell death 1 ligand 2) (Figures 11F,G; Supplementary Figures S5B,C).