When CAR-T cells are co-cultured with FLT3+ leukemia cells, the levels of interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) were significantly increased compared with those co-cultured with VEC-T cells, while the cytokines could not be detected in CAR-T co-cultured U937 cells, the FLT3− cells (Fig. 2e). Here, FLT3 is linked to leukemia.