PDCD1 and neoplasm: In addition, results of a previous study demonstrated that Newcastle disease virus (NDV) induced PD-L1 upregulation in both infected tumors and tumors not infected by the virus, and intratumoral therapy with NDV sensitized the tumors to the efficacy of programmed cell death protein 1 (PD-1) and programmed cell death ligand 1 (PD-L1) blockade in tumor models [11].