Donor-derived cells in the brains of transplanted recipients as a function of radiation dose, age, genotype, and donor cell number. For the newborn transplants, 18, 25, 16, and 13 female transplant recipients were analyzed for the 0, 200, 400, and 800 cGy groups, respectively. For the adult transplants, 10, 11, 12, and 9 female recipients were analyzed for each group, respectively (▪) normal; (○) ASMKO. A t-test analysis showed that brain engraftment was significantly higher in the ASMKO mice as compared with normal mice (see Table 3).