IDO1 and neoplasm: As a second approach, given that IFN‐γ may activate a series of feedback mechanisms ultimately leading to loss of efficacy (Benci et al, 2019), we evaluated synergy with drugs blocking immunosuppressive escape pathways: (i) checkpoint blockers targeting inhibitory signaling cascades induced after T cell activation; (ii) inhibitors of the indoleamine 2,3‐dioxygenase (IDO), upregulated in myeloid cells upon IFN‐γ stimulation (see Fig EV1G) that blunts T cell expansion by catabolizing tryptophan in the tumor microenvironment.