However, tumor infiltration of T lymphocytes varied along the development of the lung adenocarcinoma from stages I through III, that is, the T cell infiltration was increased at the early stage of the cancer (stage I), but it was gradually decreased at middle (stage II) and late (stage III) stages, while expression of IDO1 gradually increased from early to later stage lung adenocarcinoma, suggesting IDO1 may contribute to the inhibition on the tumor infiltration of T cells in the lung adenocarcinoma. Here, IDO1 is linked to cancer.