T-cell development in the thymic grafts of NOD/SCID-hu chimeras. Three-color flow cytometric analysis of thymocytes harvested from thymic grafts of a CB/Thy-NOD/SCID at 6 months post-CB reconstitution (a and b) and a control Thy-NOD/SCID mouse (c and d) stained for human CD45, CD4, and CD8. The staining specific for CD45 (a and c) identifies a population of human CD45⁺ lymphoid cells (Region 1, R1). Gating on R1 shows that human CD45⁺ cells from the grafts of CB/Thy-NOD/SCIDs comprise both CD4/CD8 double- and single-positive subsets (b), whereas human CD45⁺ cells from Thy-NOD/SCID mice harbor mainly CD4 and CD8 single-positive thymocytes (d). The vertical lines within the histograms (a and c) mark the upper limit of the fluorescence intensity corresponding to the isotype-control antibody. In the dot plots (b and d), quadrants were set to comprise the staining given by control antibodies in the left lower quadrant. Histograms and dot plots represent the analysis of 10,000 events. (e) Distribution of human thymic subsets in the grafts of individual CB/Thy-NOD/SCID (▪) and Thy-NOD/SCIDs (◊) at 6 months post-CB reconstitution. Horizontal lines in each column mark mean values. Thymocytes from CB/Thy-NOD/SCID mice comprise a significantly higher percentage of CD4 single-positive cells than thymocytes from Thy-NOD/SCID (%CD4⁺ = 17.9 ± 3.3 v 6.8 ± 1.6, mean ± SEM, P < .01).