Figure 4.

Allogeneic FLT3 CAR-R2 T Cells Eliminate Primary AML Blasts In Vitro

(A) Cell surface expression of FLT3 was detected in primary AML samples irrespective of the mutation status of the gene. AML blasts were gated using side scatter (SSC)^low and CD45^dim characteristics, and residual T cells were used to set negative and positive gates for FLT3. Two representative samples are shown. (B) Percentages of FLT3⁺ blasts were consistently high in both FLT3^WT and FLT3^MUT AML samples (mean ± SEM; n = 4/group). (C) Allogeneic FLT3 CAR-R2 T cells displayed markers of effector function in response to exposure to primary AML cells. Representative histograms show increased expression of markers of target-dependent activation (CD25), degranulation (CD107a), and cytokine secretion (TNF-α, IL-2, IFN-γ) in FLT3 CAR-R2 T cells compared to non-transduced control T cells after co-culture with primary AML cells. (D) FLT3 CAR-R2 T cells were cytotoxic to primary AML cells. Effector and target cells were co-cultured at a 1:1 ratio for 48 h, and residual AML cells were identified as SSC^lowCD45^dim and enumerated using flow cytometry. (E) Scatterplot shows the percentage of lysed AML cells for three separate primary AML patient samples (mean ± SEM).