Toxicity of nonmyeloablative conditioning regimens. Mice were conditioned with chemotherapeutic agents or TBI as described in “Materials and methods.” (A) White blood cell counts in mice conditioned with 2 Gy TBI (▵), 2 Gy TBI + 200 mg/kg CY (□), 200 mg/kg CY (◇), 90 mg/kg FLU + 200 mg/kg CY (▿), 20 mg/kg BU (●), and 35 mg/kg BU (♦). TBI (5.5 Gy, ○) is shown for comparison. BU + CY groups were omitted for clarity as they closely resembled the CY-only group. (B) Mean number of days to recovery of granulocytes to more than 500 per mm³. (C) Platelet counts for BU- and BU + CY-treated mice. (D) CD3⁺ T-cell counts (solid line) as well as the percentage of CD4⁺ and CD8⁺ subpopulations of CD3⁺ cells were followed by flow cytometry after conditioning with 35 mg/kg BU. (E) Percent donor chimerism measured by flow cytometry of eGFP⁺ donor cells in the peripheral blood following HSCT.