Feiji Recipe Reverses Lung Cancer Immune Escape by Inhibiting the Expression of IDO

Tumor cells have developed multiple mechanisms to escape immune recognition mediated by T cells. Indoleamine 2,3-dioxygenase (IDO), a tryptophan-catabolizing enzyme inducing immune tolerance, is involved in tumor escape from host immune systems. Feiji Recipe, a Chinese herbal recipe that composed of 12 traditional Chinese medicines, has been used to recover immuno-surveillance and to interven immune escape in lung cancer patients. To elucidate the biological role of IDO in the tumorigenesis of lung cancer, and the intervention of Feiji Recipe on tumor immune escape, we established a mouse lung cancer cell line (2LL-EGFP-IDO) with overexpression of IDO. IDO expression did not affect cell proliferation. 2LL-EGFP-IDO cells were effective in reducing the level of tryptophan and increasing the level of its downstream metabolites, kynurenines, in culture medium as assessed by HPLC. Feiji Recipe could up-regulate the percentage of CD8+ T cells by inhibits the expression of IDO in co-culture system. The results of these studies indicate that Feiji Recipe can enhance the immune response and reverses tumor immune escape by induce the activity of CD8+ T cells, which might be related to the inhibition of IDO expression.