This work provides important new in vivo evidence in support of a mutualistic role of IDO1/TDO2 in KYN-mediated cisplatin resistance in NSCLC, highlighting the therapeutic potential of dual IDO1/TDO2 inhibition in the treatment of NSCLC by reversing immunosuppressive conditions to active anti-tumor immune responsiveness. Here, IDO1 is linked to non-small cell lung carcinoma.