Effects of neutralizing antibodies against human SLF and/or c-kit on colony formation by CD34⁺⁺⁺kit^Lo/− (I), kit⁺ (II), and kit⁺⁺ (III) cells transduced with c-kit cDNA in the serum-depleted cultures. Transduced cells were treated with or without neutralizing antibodies at room temperature for 1.5 hours and assayed for colony formation at 800 cells/mL in the presence of full dosages of IL-3, GM-CSF, IL-6, and Epo. Results are expressed as mean ± SEM from 1 of 2 representative experiments. Significant differences for cells transduced with c-kit cDNA from that with mock virus control,^aP < .05. Significant differences for cells treated with neutralizing antibodies from that of medium without added antibodies as control, ^bP < .05.