Reintroduction of Pim1 normalizes the in vitro proliferation of primitive Hoxa9^−/− marrow cells. Marrow cells from 5-FU–treated animals were transduced with vectors expressing either GFP or GFP together with Pim1. Freshly transduced cells were placed in liquid cultures, and viable cell numbers were counted daily. Wild-type marrow cells transduced with a GFP expression vector were used as a normal control. This experiment was performed 2 times.