WF recipient rats were treated with 600 (n = 10), 500 (n = 18), 400 (n = 4), or 300 (n = 4) cGy of TBI on day -1, received 100 × 10 6 TCD bone marrow cells from ACI donors on day 0, tacrolimus IP on days 0-10 and a single dose of ALS on day 10. Percentage engraftment was assessed by flow cytometric staining for the donor MHC class I marker RT1Aabl. Engraftment was defined as >1% donor cells in the lymphoid gate. (A) The percentage of animals with PB donor chimerism for a given TBI dose at one month. (B) The mean level of donor chimerism in animals that engrafted. Only animals with engraftment are included. All chimeric animals underwent heterotopic osteomyocutaneous flap allotransplantation 4-6 weeks after BMT. Survival of the CTA was defined as integration of the skin flap into surrounding skin with growth of black donor hair. Rejection was defined as loss of the skin paddle with an evolution from petechiae to eschar. The CTA status was assessed daily for the first two weeks and then weekly thereafter up to 6 months (C).