Effects of modulation of Survivin and p21^WAF1/Cip1 on CFU-GM survival upon growth factor deprivation. Bone marrow cells harvested from p21^+/+ and p21^–/– mice were infected with retrovirus, as described in Figure 1. After infection, 20 000 GFP⁺ cells were FACS sorted and plated in soft agar without growth factors. Mouse GM-CSF (10 ng/mL) and SCF (50 ng/mL) were added to the cultures at 0, 24, or 48 hours after plating and CFU-GMs were enumerated 7 days after growth factor was added. (A) Left panel shows absolute CFU-GM survival during growth factor deprivation in 1 representative experiment. Right panel shows the mean ± SEM percentage change in survival in wild-type– or T34A-Survivin–transduced p21^+/+ CFU-GM compared with p21^+/+ CFU-GM transduced with empty vector from 3 experiments. (B) Survival of p21^+/+ and p21^–/– CFU-GM on growth factor starvation. Left panel shows total CFU-GM after delayed addition of growth factors in 1 representative experiment. The percentage decrease of p21^–/– versus p21^+/+ CFU-GM transduced with vector at each time point are shown in the right panel and represent combined data from 2 experiments. (C) Survival of p21^–/– CFU-GM transduced with Survivin or empty vector after growth factor starvation. Data are from 1 of 3 experiments with identical results. Data represent means ± SEM.