(A) Primary MDS cells from 4 high-risk MDS patients were cocultured with healthy donor derived mock T cells or CD123 CAR T cells for 48hrs at E:T ratio of 1:1. Primitive cells (CD34+ CD38-) in MDS patient bone marrow samples were then analyzed by flow cytometry. (B) Representative flow analyses showing elimination of MDS stem cells (CD34+/CD38−/CD123+) and MDS bone marrow cells (CD3−/CD123+) by CD123 CAR T cells (red) and not by mock T cells (blue), indicated by disappearance of CD123+ subpopulation. (C) Statistical analyses of flow cytometry showing elimination of MDS stem cells in bone marrow samples from 4 different patients by healthy donor derived CD123 CAR T cells (red) compared to mock T cells (blue). Shown by percentage of CD123+CD34+CD38, normalized to mock T cells (n = 3, mean ± SD of duplicates, unpaired parametric t-test. *p ≤ 0.05, **p ≤ 0.01, ***p ≤ 0.001, ****p ≤ 0.0001).