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. This evidence concerns the gene TYMS and breast cancer.