Gemcitabine combined with a superoxide dismutase (SOD) mimetic can reduce the activation of the IDO pathway, deplete MDSCs in mice with lung cancer, reduce Treg infiltration, inhibit CD8+ and CD4+ T-cell exhaustion, and improve the quantity and quality of memory T cells, to further promote the T-cell-mediated antitumor immune response and enhance the therapeutic efficacy of chemotherapy [124, 147]. This evidence concerns the gene IDO1 and lung cancer.