IDO1 and tuberculosis: Multiplexed imaging of the human TB granuloma recently revealed the highly immunosuppressed nature of the granuloma microenvironment (7) — human TB granulomas are depleted for IFN-γ+ cells but instead enriched for TGF-β, regulatory T cells (Tregs), and indoleamine 2,3-dioxygenase+ (IDO+) programmed cell death ligand 1+ myeloid cells.