PDCD1 and neoplasm: Notably, expression of the PD-1 ligands PD-L1 and PD-L2 is correlated with poor prognosis in multiple tumors11, 12 and anti-PD-1/anti-PD-L1 blocking antibodies have been shown to induce potent anti-tumor immune responses in patients with diverse malignancies13, 14, demonstrating the critical role of the PD-1/PD-L1 axis in anti-tumor immunity.