Siglec-6 CAR T cells confer potent antileukemia activity in a xenograft model of AML in vivo. Female NSG mice were inoculated with 2 × 10⁶ U937 AML cells (FLUC⁺GFP⁺), and on days 6 and 21, they were treated with 5 × 10⁶ CAR-modified or UTD T cells. T cells were formulated in a 1:1 CD4⁺:CD8⁺ ratio. (A) Serial BLI to assess leukemia progression and/or regression. Note the scale indicating upper and lower BLI thresholds at each analysis time point (right). (B) Flow cytometric analysis of peripheral blood on days 10, 14, and 45 to detect T cells and leukemia cells. Human T cells in mouse peripheral blood were defined as 7-AAD^–CD45⁺CD3⁺ cells. Leukemia cells were defined as 7-AAD^–CD45⁺GFP⁺ cells. (C) Waterfall plot showing change in absolute BLI values between days 6 and 10 after tumor inoculation. (D) BLI values from each treatment group showing tumor progression and regression. BLI values in panels C and D were obtained as photons per second per cm²per sr (p/s/cm²/sr) in regions of interest encompassing the entire body of each mouse. (E) Percentage of leukemic cells detected in bone marrow, spleen, and peripheral blood by flow cytometry at the end of the experiment. NB: Leukemia cells (%) values show data obtained at different time points. Mice from UTD T-cell treatment group were analyzed on day 17, and mice from the Siglec-6 CAR T-cell treatment group were analyzed on day 56. (F) Kaplan-Meier survival analysis for overall survival (left) and progression free survival (right) from different treatment groups. Data shown are representative of results obtained in independent experiments with Siglec-6 CAR T-cell from 2 donors. Mantel-Cox log-rank test ****P < .0001. *P < .05; **P < .01; ****P < .0001, Student t test (B,D-E). Avg, average; d6, day 6.