Siglec-6 is commonly expressed on primary AML blasts and recognized by Siglec-6 CAR T cells. (A) Flow cytometric analysis of Siglec-6 expression on bulk AML blasts and AML stem cells (LSCs) in 3 samples from patients with AML that had high, moderate, and low Siglec-6 expression (Table 1). Histograms show staining with anti–Siglec-6 mAb (red) and isotype control antibody (blue). Inset numbers indicate the NMFI obtained by staining with anti–Siglec-6 mAb and isotype control. (B) Cytolytic activity of CD8⁺ Siglec-6_BBz CAR and UTD T cells against bulk AML blasts and AML stem cells in a flow cytometry-based 24-hour assay. The experiment was performed in triplicate wells with 10 000 target cells per well. Counting beads were used to quantitate the number of residual live target cells at the end of coculture. (C) Correlation between cytolytic activity by CD8⁺ Siglec-6_BBz CAR T cells (after 24-hour coculture; 2.5:1 E:T ratio) and Siglec-6 normalized expression on primary AML blasts. Simple linear correlation was calculated (R² = 0.45; P = .0018).