Influence of cytokines on colony formation by single sorted CD34⁺⁺⁺ kit⁺⁺, kit⁺, and kit^Lo/− cells transduced at the single-cell level with c-kit cDNA or mock viruses. Single cells were directly sorted into wells as 1 cell/well containing 0.1 mL of semisolid culture in the presence of full dosages of IL-3 (200 U), GM-CSF (200 U), Epo (1 U), IL-6 (10 ng) with SLF at 0 (I), 2 (II), 10 (III), and 50 (IV) ng per mL in the serum-depleted culture as described in Materials and Methods. Results are expressed as percent wells with growth for a total of 192 wells per point from 3 separate experiments. Significant differences from mock virus control are: ^aP < .05.