It was observed that lung cancer-derived galectin-1 results in the upregulation of tryptophan 2,3-dioxygenase (TDO2), the main enzyme involved in tryptophan metabolism in CAFs, via an Akt-dependent pathway, promoting the production of Kyn by CAFs that further suppresses the activity of dendritic cells (92). Here, TDO2 is linked to lung cancer.