pt-Cy administration abrogates T-cell proliferation but does not prevent accumulation of T_SCM. (A) Flow cytometry plots depict Ki-67 expression on CD8⁺ T cell subsets from a representative patient (UPN#20) at different points after HSCT, as labeled. Gray arrow denotes pt-Cy administration. (B) Summary of the percentages of proliferating CD8⁺ T cell subsets at the indicated points post-HSCT. Gray line designates absolute CD8⁺ T cell counts. Gray shade indicates pt-Cy administration. (C) Comparison of the percentage of Ki-67⁺ cells among the different CD8⁺ T-cell subsets at day 3 post-HSCT (before pt-Cy administration and in the absence of any immunosuppressive agent). (D) Comparison of the percentages of proliferating cells before pt-Cy administration (day 3) and at the point when highest T_SCM frequencies were detected (day 8). (E) Flow cytometric plots of ALDH enzymatic activity from a representative patient (UPN#17) of the 4 patients tested for ALDH activity. Top row plots show ALDH⁺ cells at the labeled points, whereas bottom row plots show CD34 and CD3 expression on ALDH⁺ gated cells. (F) Scatter plot depicts the mean percentage of circulating ALDH⁺ cells at the indicated points. (G) Scatter plot shows the belonging lineage of ALDH⁺ cells at the labeled points: CD34⁺ cells are indicated with open circles, CD3⁺ cells with black triangles (n = 4). (H) Percentages of Annexin V⁺ early apoptotic cells within CD8⁺ T cell subsets at days 5, 8, and 15 post-HSCT. Dashed black line indicates mean percentage of Annexin V⁺ cells measured in leukapheresis (n = 3). n.e., not evaluable.