O’Rourke et al. analyzed glioblastoma samples resected 2 weeks after anti-EGFR CAR T cells infusion, and reported a significant increase in the levels of immunosuppressive molecules indoleamine 2,3-dioxygenase 1 (IDO1), TGF-b, IL-10, together with increased expression of PD-L1 and infiltration of Treg, thus suggesting that multifactorial immunosuppressive mechanisms are rapidly developed in situ following CAR T therapy [37]. This evidence concerns the gene IDO1 and glioblastoma.