Split-dose TBI allows equivalent enhancement of engraftment at a lower total TBI dose.

(A) Chimeric mice after IUHSCT received 82.5 cGy TBI at 4 and 8 weeks of life and transplants with 30 × 10⁶B6Ly5.2 TCD BM cells and 30 × 10⁶ B6GFP TCD BM cells 6 to 8 hours after each TBI dose, respectively (split-dose TBI/BMT × 2). Chimerism levels were compared to levels in mice that received a single irradiation dose of 82.5 cGy TBI at 4 weeks of age and transplants with 30 × 10⁶ B6Ly5.2 TCD BM cells 6 to 8 hours after TBI at 4 weeks of life and 30 × 10⁶ B6GFP TCD BM cells at 8 weeks of life (TBI/BMT × 2) as well as chimerism levels in mice that received a single dose of 138 cGy or 276 cGy TBI at 4 weeks of age and transplants with 30 × 10⁶ B6Pep3b TCD BM cells 6 to 8 hours after irradiation (TBI/BMT). (B) The composition of total donor chimerism of the “split-dose TBI/BMT × 2” group was assessed by flow cytometry for GFP as well as CD45.1 and H-2K^b.