To address this question, we measured the phosphorylation level of STAT5, AKT, and ERK in FLT3+ leukemia cells after being co-cultured with CAR-T or VEC-T cells and found the increased activation of pERK in FLT3-WT and heterozygous FLT3-ITD leukemia cells, which indicated that the expression of FLT3L on CAR-T cells is involved in activating downstream proliferative Ras-Raf-Mek-Erk pathways. Here, FLT3 is linked to leukemia.