Differential recognition of proliferating CD34⁺ CML precursors. Plotted are the CFSE histograms of the viable CD34⁺ target cells after 4, 24, and 48 hours of incubation in the absence (A; target control) or presence (B) of HLA-A1-restricted HY-specific CTLs at a 1:1 E/T ratio. The absolute numbers of viable CD34⁺ cells are indicated. (C) The percentages of cells within the CD34⁺ fraction and the total CFSE⁺ target cell population which survived after 4, 24, and 48 hours of T-cell exposure (solid lines, ▪), or after culture for the same periods of time in the absence of T cells (target control; dashed lines, •).