tEpoR mediates erythroid cell amplification. (A-B) Relationship between the percentage of modified RBCs and the percentage of transduced WBCs in the peripheral blood of LG (■) and LG/HA-Y1 (□) mice. Assuming a minimal effect of tEpoR on modified leukocytes, 4 theoretical curves corresponding to 1-, 10-, 50-, and 200-fold preferential expansion of modified erythroid cells (F^E factor) are derived from equations 3 (A) and 2 (B). Greater curvature (A) and left shift of the straight lines (B) corresponds to greater advantage for modified erythroid cells over unmodified cells. (C-D) The bottom and top boundary of the boxes indicate the 25th and 75th percentiles. Whiskers (error bars) above and below the box indicate the 90th and 10th percentiles. The line within the box marks the median. (C) Median and individual erythroid amplification factor F^E in LG (■) and LG/HA-Y1 (□) mice. (D) Median and individual ratio between the genetically modified leukocyte (WBC) fraction and the ex vivo–modified HC fraction before transplantation in LG (■) and LG/HA-Y1 (□) mice.