Emergence of GFP⁺ cells and their immunophenotypes on day 12 and day 23 of culture. (A) Cells derived from 5-FU–conditioned bone marrow (BM) or from thymocytes explanted from mice of the indicated Arf genotypes (labeled at bottom) were transduced with a vector encoding ICN1 and GFP in cis and cultured on OP9 stroma with cytokine support. Cultured cells expanded exponentially and underwent 25 to 30 population doublings over a period of 36 days (supplemental Figure 1). The percentage of GFP⁺ cells in the cultures was determined at day 12 and day 23. The results of 3 experiments are shown, and error bars indicate SDs. (B) After 12 and 23 days of culture (indicated at the top of the panels) the percentages of GFP⁺ cells that expressed CD4 and CD8 or Thy1.2 and TCRβ were determined using an automated cell sorter. The percentages of cells expressing each marker are indicated in at least 3 of the 4 quadrants of each panel. The origin of donor cells and their Arf genotypes are indicated to the left.