In syngeneic mice model of melanoma, depletion of Kyn in both plasma and tumor by Kyn-degrading enzymes kynureninase reduced Kyn levels in IDO1, TDO2 and IDO1/TDO2-expressing cancer cells and augmented effector T cells in tumor, without impact on Trp levels. The gene discussed is TDO2; the disease is neoplasm.