Conditioning of recipients with a higher dose of CD45-ADC can enable complete engraftment of donor cells as a single agent. B6 (H-2^b, CD45.2) recipients (16- to 18-week-old female) were conditioned with a single dose of 5 mg/kg isotype-ADC or CD45-ADC on d-3, or multidose Q2D × 2 of 3 mg/kg isotype-ADC or CD45-ADC on d-5 and d-3, or 900 cGy (9 Gy) TBI on d-1, and transplanted with 40 × 10⁶ CByJ.SJL(B6)-Ptprc^a/J (H-2^d, CD45.1) BM on d0. Mice in multidose groups were transfused at 24 hours and 6 days post second dose with 300 μl of packed RBCs from B6 mice. One mouse from the CD45-ADC multidose group and 2 mice from the isotype-ADC multidose group died by 3 weeks posttransplant. (A) Depletion of BM hematopoietic progenitor cells (LSKs) and HSCs were assessed at d0 by flow cytometry (n = 3 mice per group). Nontreated mice served as control. Data represent mean ± SEM. *P < .05 vs nontreated mice via 1-way ANOVA posthoc Dunnett’s multiple comparisons test. (B) Engraftment of donor cells (H-2^d, CD45.1) and lineage subsets in the PB of transplanted mice were assessed by flow cytometry. Each individual line represents a single mouse tracked over 22 weeks. (C) Peripheral RBC counts as a time-course posttransplant. Each individual line represents a single mouse tracked over 22 weeks, as indicated. (D) Overall donor (H-2^d, CD45.1) chimerism and donor-derived hematopoietic progenitor cells (LSKs) and HSCs in BM of transplanted recipients were analyzed at 22 weeks posttransplant by flow cytometry. Data represent mean ± SEM (n = 5 mice per group). *P < .05 vs 9 Gy TBI via 1-way ANOVA posthoc Dunnett’s multiple comparisons test. (A-D), Experiments were performed twice, and data shown are from 1 representative experiment.