GDNF/GFRα1 treatment stimulates growth of transplantable HSCs. (A) Experimental design for GDNF/GFRα1–supplemented outgrowth of HSCs and transplantation ability. 1°TP and 2°TP represent the first and second transplantation, respectively. (B) Live cell count of in vitro cultured HSPCs (N = 5). Proportion of expanded HSCs (CD34⁺CD90⁺EPCR⁺) at day 3 (C) and day 7 (D) during in vitro culture (N = 5). (E) Percentage of human CD45⁺ (hCD45⁺) cells of total CD45⁺ bone marrow cells in primary transplantation mice (control [Ctrl], N = 12; GDNF/GFRα1, N = 10; SR1/UM171, N = 7; SR1/UM171/GDNF/GFRα1, N = 6). (F) Percentage of immunophenotypic HSCs (CD34⁺CD38^–CD45RA^–CD90⁺CD49f⁺) retained in hCD45 bone marrow cells in primary transplantation mice. (G) Percentage of hCD45⁺ cells of total CD45⁺ bone marrow cells in secondary transplantation mice (2 × 10⁵ hCD45 cells transplanted shown, N = 5 for all conditions). (H) Boxplot indicating 1/stem cell frequency of secondary transplanted hCD45⁺ cells. Estimates with upper and lower intervals are shown (N = 5 for top dose, N = 3 for all other doses). For all graphs, a Student t test was used to calculated significant differences. *P < .05 vs Ctrl; **P < .005 vs Ctrl; ***P < .0005 vs Ctrl; ****P < .00005 vs Ctrl.