Treatment with an anti‐CD137 antibody that was associated with inducing PD‐L1 expression in tumors was found to be ineffective for curing tumors in a mouse model.9 Additionally, multiple studies have shown a powerful synergy between anti‐CD137 mAb and anti‐PD‐1/PD‐L1 mAb when they are applied in combination.27, 28, 29 Here, we focused on lung cancer cell lines and investigated whether CD137L could upregulate PD‐L1 expression by lung cancer cells via feedback involving IFN‐γ production by activated T lymphocytes. Here, TNFSF9 is linked to lung cancer.