Microenvironment-derived cytokines, such as CCL-2, IDO, and TIM4 (reviewed in67) are responsible for the accumulation of Tregs in GBM; however, a role for tumour cells or GIC in modulating Tregs migration is less clear and a link between GAG-GIC and Tregs migration has not been previously described. Here, IDO1 is linked to glioblastoma.