Conditioning of recipients with CD45-ADC along with anti-CD40L mAb and immunosuppressive agents can further improve allogeneic engraftment. B6 (H-2^b) recipients (n = 7 mice per group, 10- to 12-week-old female) were conditioned with 3 mg/kg isotype-ADC or CD45-ADC on d-2 and 50 cGy (x = cGy in figure) TBI on d-1. All groups of mice were transplanted with 40 × 10⁶ BALB/c (H-2^d) BM cells on d0. Recipients were treated with anti-CD40L mAb (200 μg) from d-1 to d+14 post-BMT. Rapamycin (1.5 mg/kg per day) was administered from d-1 through d+13 post-BMT. Cyclophosphamide (25 mg/kg per day) was administered on d+3 and d+4 post-BMT. Two mice, each from the rapamycin group and cyclophosphamide group, died by 2 weeks of posttransplant due to unknown causes. (A) Donor cells (H-2^d) engraftment in the PB of transplanted mice was analyzed at 12 weeks post-BMT by flow cytometry. (B) Multilineage peripheral donor chimerism was analyzed at 12 weeks post-BMT by flow cytometry. (C) The ratio of donor (H-2^d) and host (H-2^b) peripheral T-cell populations was analyzed at 12 weeks post-BMT. (A-C) Data represent mean ± SEM. Experiments were performed twice, and data shown are from 1 representative experiment. *P < .05, **P < .01, ***P < .001, ****P < .0001, 2-tailed Student t test.