However, the application of IDO1-shRNA to inhibit the expression of IDO1 in lung cancer mice downregulates the expression of the inhibitory receptors PD-1 and BTLA on T cells, positively regulates the secretion of cytokines such as IL-2 and TNF-α, reverses T-cell exhaustion, delays the onset of tumors, and inhibits tumor growth [108]. This evidence concerns the gene IDO1 and lung cancer.