SLC44A4 and cancer: Currently, the blockade of PD-1 signaling using the PD-1/PD-L1 antibody and the blockade of CTL4 signaling using the CTL4 antibody have both shown promising therapeutic effects in a variety of cancers, such as melanoma, non-small-cell lung cancer, renal cell cancer, and lymphoma.16, 17, 18 Programmed cell death protein-1 (PD-1, encoded by PDCD1) is expressed in activated T cells and suppress the activation of lymphocytes and cytokine production by interacting with its ligands, PD-1 ligand-1(PD-L1, encoded by PDCD1LG1), and PD-1 ligand-2 (PD-L2, encoded by PDCD1LG2).