Blockade of KIT signaling blockade in Fanca^−/−and Fancd2^−/−mice results in significant reduction in HSPC to allow WT donor HSPC engraftment. (A-B) Percentage of lineage-negative cells in BM (saline: WT, n = 8; Fanca^−/−, n = 5; ACK2: WT, n = 3; Fanca^−/−, n = 3) and colony-forming-unit cells (CFUc) per 1 × 10⁵ BM cells 7 days after intraperitoneal injection of 40 mg/kg ACK2 in WT (n = 6) and Fanca^−/− (n = 6) mice. (C) CFUc per 1 × 10⁵ BM cells 7 days after intraperitoneal injection of 40 mg/kg ACK2 in WT (n = 3) and Fancd2^−/− (n = 3) mice. (D-E) Temporal donor whole blood chimerism of Fanca^−/− mice (saline: n = 4; ACK2+GK1.5, n = 10-12) and multilineage peripheral blood chimerism at 30 weeks posttransplant. Gr, granulocyte; B, B lymphocyte; CD4, CD4 T lymphocyte; CD8, CD8 T lymphocyte. (F-I) Temporal donor whole blood chimerism of Fancd2^−/− mice (saline: n = 3-4; ACK2+GK1.5, n = 5), multilineage peripheral blood chimerism at 30 weeks, and chimerism in different bone marrow compartments at 44 weeks posttransplant. #One Fancd2^−/− mouse had engrafted following saline but died at 30 weeks from a procedure-related death. The rest of the Fancd2^−/− mice did not engraft with donor marrow following saline. ****P < .0001; ***P < .001; **P < .01; *P < .05 (Student t test and 2-way analysis of variance [D,F]). CFU, colony forming unit; MPP, multipotential progenitors; WBC, white blood cells.