The administration of indoximod (an oral IDO1 inhibitor) combined with temozolomide has demonstrated synergistic survival benefits in GBM mouse models (Wainwright et al., 2014; Hanihara et al., 2016), which is under investigation in GBM patients (Zakharia et al., 2015, 2016). This evidence concerns the gene IDO1 and glioblastoma.