Immunohistologic analysis of thymus. Sections of the thymus from an adult WT mouse (top); control noninjected NSG mouse (middle); and in vitro–derived proT-injected NSG mouse (bottom) 6 weeks after intrahepatic injection into neonates (n = 6). Thymus tissues were stained with anti-Cytokeratin 8 (green; cortical) and anti-Cytokeratin 5 (red; medullary). The results shown are representative of 3 independent experiments.