Preconditioning intensity dictates CNS myeloid engraftment. (A) Schema and gating for enriching brain-derived myeloid cells. (B) GFP donor chimerism of CX₃CR1⁺ brain cells at various time points after 9-Gy radiation and HCT. (C) Hematopoietic chimerism after 4.5-Gy nonmyeloablative preconditioning. (D) GFP donor chimerism of CX₃CR1⁺ brain cells at various time points after 4.5-Gy radiation and HCT. (E) Busulfan preconditioning transplantation schema. (F) Hematopoietic chimerism after busulfan preconditioning. (G) GFP donor chimerism of CX₃CR1⁺ brain cells at various time points after busulfan preconditioning and HCT. (H) Transplantation schema to test cell dose. (I) Hematopoietic chimerism after HCT testing cell dose. (J) GFP donor chimerism of brain CX₃CR1⁺ cells after HCT with low and high cell doses. (K) Schema for double transplantation (DT) protocol. (L) Hematopoietic chimerism after DT. (M) CD45.1 donor chimerism of CX₃CR1⁺ brain cells after DT. Shown are the mean ± standard deviation. P values derived from a Student t test. FSC, forward scatter; SSC, side scatter.