TTI-CD200 can trigger an IL-2 response against CD200⁺ ALL. (A) Cells from 3 ALL patients (55-57) with high CD200 expression and 2 (6, 58) with low CD200 expression were set up with CD4⁺ T cells and monocyte-derived macrophages from normal blood donors in a 72-hour mixed lymphocyte reaction with or without the addition of TTI-CD200. Production of IL-2 was assessed by enzyme-linked immunosorbent assay (ELISA), and cell viability was determined by flow cytometry using annexin V and propidium iodide. (B) The effect of TTI-CD200 on normal cells was determined in undifferentiated and differentiated CMCs, MSCs, and normal CB–derived CD133⁺ and CD34⁺ cells. Data are shown as mean ± standard deviation (SD) of triplicate measurements from each cell source. (C) The viability of ALL cells, MSCs, and CMCs after treatment with TTI-CD200 was assessed using fluorescence microscopy and live/dead staining (Calcein dye, green, live cells; ethidium, red, dead cells). Vincristine (Sigma-Aldrich), a cardiotoxic drug, was used as a positive control.