IDO1 and glioblastoma: Rationale: Antagonizes IDO1/Kyn/AhR axis to suppress Tregs; Preclinical: Synergizes with anti-PD-1 in MSI-L CRC. Challenge: Weak AhR agonism sustains immunosuppression in AhR-overexpressing tumors (e.g., glioblastoma); no human trials.