sdAb20-Fc can specifically alter the viability and apoptosis of primary patient samples. (A) Gating strategy to determine the number of blasts (based on SSC-A/CD45-A), the percentage of CD33/CD34-positivity and the percentage of AXL-expression in various AML patients. (B-C) Flow cytometric assessment of AXL expression in CD33/CD34-positive cells of various primary samples using sdAb20 and the control sdAb R3B23. ΔMFI = MFI (sdAb20) - MFI (CTRL sdAb). (D-E) BMMCs of AML patients were treated with R3B23-Fc or increasing concentrations of sdAb20-Fc (10, 100 and 200 µg/mL). The effect on cell viability (D) was assessed using CellTiter-Glo assay (n=2/sample). Apoptosis (E) was measured using AnnexinV/7-AAD staining with flow cytometry. Patients were subdivided into AXLlow and AXLhigh, based on their AXL expression (n=3/group, ± SD). p ≤ 0.05 (*) was considered statistically significant. CTRL = control, BMMCs = bone marrow mononuclear cells.