Intrathymic development of transduced ISP4⁺progenitor cells in vivo. Bivariate dot plots of flow cytometric measurement of Nef⁻ transduced cells (top) and Nef⁺ transduced cells (bottom) showing CD4-APCy, CD8β-PE, CD3-APCy, and MHC Class I-PE versus EGFP expression of SCID-hu thymocytes 20 days after injection of transduced ISP4⁺ cells. Quadrants were set to include 99% of cells stained with isotypic controls and EGFP⁻ cells in lower left quadrant. Figures indicate percentage of cells present in corresponding quadrants.