,3 After the recognition of tumor antigens by peripheral T-Cell Receptors (TCRs), PD-L1 or PD-L2 will bind PD-1 and activate downstream-related signaling pathways, blocking TCR signaling via feedback inhibition, and downregulate the expression of specific antiapoptotic protein molecules including Bcl-xL, which is encoded by BCL2L1, that is one of the most common amplified genes among cancers, and pro-inflammatory factors, ultimately inhibiting T-cell survival, proliferation, and immune function. Here, PDCD1 is linked to cancer.