IDO1 and neoplasm: Munn and Sharma et al. showed that a small population of indoleamine 2,3-dioxygenase 1 (IDO1)-expressing plasmacytoid DCs in the SLN was capable of inducing regulatory T-cell (Treg) generation and T-cell anergy, which was linked with decreased T-cell response to tumor antigens [54, 55].