Kinetics of GFP expression studied in megakaryocytic and erythrocytic precursor cells. Megakaryocytic and RBC precursor cells were infected with various MOIs of AdGFP on day 10 of expansion. Subsequently, expression of GFP by lineage-committed cells was analyzed using two-color flow cytometry. (A) After a lag phase of 2 to 4 hours following infection, mean GFP fluorescence intensity (mean Log FL1) and the number of GFP-expressing megakaryocytes (CD41a⁺) increased depending on the MOI used for infection and time after infection. Steady-state expression of GFP in CD41a⁺ was reached 72 to 96 hours after infection. (B) Glycophorin A⁺ RBC precursor cells expressed GFP with similar kinetics. Following infection with an MOI of 100, the number of GFP⁺/glycophorin A⁺ cells increased continuously after a lag phase of 8 hours. Maximal transgene expression is reached 96 to 144 hours after infection. (□, MOI 10; ◊, MOI 50; ○, MOI 100; ▵, MOI 500).