PDCD1 and lung carcinoma: PD-1 induction was not dependent on the level of PD-L1 expression on lung cancer cells as H520 expressed the lowest level of PD-L1 (Additional file 2: Figure S3A) but induced a similar level of PD1+DNT cells as H460 which showed a very high level of PD-L1 expression (Fig. 3e and Additional file 2: Figure S3A).