(A) Left panel: Absolute thymocyte numbers from young FoxN1-null (nude) mice six weeks after two injections (3-week intervals) of FoxN1-cDNA plasmid, empty vector, or PBS; Right panel: Representative flow cytometric plots of CD4 versus CD8 staining of nude mouse thymocytes six weeks after two injections (3-week intervals) of FoxN1-cDNA plasmid, empty vector, or PBS. (B) Gross appearance of thymic size from FoxN1-cDNA-infused WT mice with enlarged thymus (arrows) and empty vector-infused WT mice with original-sized thymus (arrow heads) at 12 and 18 months of age. (C) Absolute thymocyte numbers from middle-aged (9–12 months old) WT mice, one month after FoxN1-cDNA plasmid or empty vector input. (D) Absolute thymocyte numbers from aged (18 months old) WT mice, 6 weeks after two injections (3-week intervals) of FoxN1–cDNA plasmid or empty vector.