Stable hematopoietic chimerism established in transplanted CA mice in the absence of cytoreductive conditioning. (A) The percentage of donor GFP⁺ RBCs in peripheral blood was measured across time. Stable donor RBC chimerism levels at approximately 90% were maintained from 8 to 20 weeks after transplantation in CA mice compared with levels of less than 5% in wild-type (WT = α₂α₁/α₂α₁, +/+) and heterozygous (Het = α₂α₁/α₂α₁, γ^HPFHβ⁰/+) littermate control mice. (B) Donor hemoglobin levels measured across time in CA mice after transplantation. Donor mouse β-globin and recipient human γ-globin chain levels were measured in peripheral blood hemolysates by HPLC. Stable donor-derived globin chain levels greater than 95% of total globin chains were achieved by 8 weeks after transplantation. (C) HSPCs were detected in the bone marrow of CA mice 20 weeks after transplantation. Recipient CA mice were euthanized 20 weeks after transplantation and their BMCs analyzed by flow cytometry after staining with fluorescently labeled antibodies that recognize c-kit⁺, ScaI⁺, and a cocktail of lineage (Lin) antigens. Donor HSPCs were determined by the percentage of GFP⁺ cells in the Lin^–c-kit⁺ScaI⁺ population. Relatively low levels of donor HSPCs (range, 0.5%‐15.7%) resulted in high-donor RBC chimerism and rescue from lethal anemia.