(A) In vivo tomato lectin staining comparing vasculature between newborn (left panel) and adult (right panel) immune-competent (C57Bl/6) and immune- deficient (NOD/SCID/β2m−/−) mice. (B) VEGF-TRAP reduces vascular density of newborn thymi in immune-competent (C57Bl/6) and immune deficient (NSG) mice. Control mice were treated with hFC. (C, D) Effect of host age on bone marrow (C) and thymic reconstitution (D). NSG neonatal mice were transplanted with CD45.2+ BM without irradiation at Day 1, 4, 7 and 10 of life, (n = 4, 7, 7 and 9 mice respectively) and analyzed at 3 weeks post BMT. All numbers are mean ± standard error of the mean (SEM).