PDCD1LG2 and small cell lung carcinoma: In our experimental setting, since the inhibitory ligands, especially PD-L1 and PD-L2, were upregulated by SCLC cells following the IFN-γ-related immune reactions and the co-inhibitory receptors were upregulated on the CTLs; next, we sought if effector T cell responses are functionally hindered upon further interaction.