To further confirm that the TS−ROS−NF-kB regulatory axis is actively involved in the activation of PD-L1 transcription in tumor cells, we selected A549, PC9 human lung cancer and T47D human breast cancer cell lines that are known not to express PD-L144 45 (online supplemental figure S7A), and tested the effects of TS inhibition on these tumor cells by either pemetrexed or TS knockdown. Here, TYMS is linked to breast carcinoma.