As T cells express programmed cell death protein (PD-1) checkpoint receptor, tumour cells are blocking T cell activity via increased production of ligand of PD-1 receptor (PD-L1), leading to an interaction between PD-1 and PD-L1 to produce apoptosis of TILs, stimulating the differentiation of CD4+ into regulatory T cells (Tregs), and inhibiting the immune system response for self-tolerance maintenance [141,142,143]. Here, CD4 is linked to neoplasm.