Cytokine withdrawal from Bcr-Abl–expressing primary mouse bone marrow cells after 10 days of cytokine support in the absence of autologous stroma leads to the outgrowth of pre-B cells.

Two days after retroviral-mediated gene transfer, Bcr-Abl and control cells were selected for expression of GFP by FACS. These cells were expanded in the presence of cytokines without autologous stroma for 10 days and analyzed for the expression of GFP and B220 (A). Six days after cytokine withdrawal from Bcr-Abl–expressing cultures (16 days after selection for GFP-expressing cells), cells were again analyzed by flow cytometry for expression of GFP and B220 (B). Vector-expressing cells were not viable after cytokine withdrawal.