Two days after treatment initiation, interferon gamma (IFNG, best known as IFNγ) and interleukin 2 (IL2), which are produced upon CAR T cell activation [16], became detectable above background in ALL-bearing (but not tumor-naïve) mice receiving CAR T cells (but not in mice treated otherwise) (Fig. 3G). Here, IFNG is linked to acute lymphoblastic leukemia.