Enforced expression ofGfi-1B supports EPO-independent erythropoiesis.

(A) Growth and differentiation of Gfi-1B–transduced CD34⁺ cells in vitro. CD34⁺ cells were transduced with either empty vector (black bars) or Gfi-1B(white bars). After transduction, cells positive for both EGFP and CD34 were selected and cultured in methylcellulose medium supplemented with indicated cytokines. Cell growth and differentiation was evaluated by counting colony-forming units (CFUs) on day 14. BFU-E/H– indicates poorly hemoglobinized erythroid burst-forming unit. Results are shown as mean ± SD of 3 representative experiments. (B) Morphology of erythroblast colonies formed from Gfi-1B–transduced CD34⁺ cells in the absence of EPO. A typical erythroblast colony observed under a phase-contrast microscope (left panel). The colony was recovered, cytospun onto a slide glass, then subjected to May-Grüenwald-Giemsa staining (right panel). (C) Flow cytometric profiles of transduced cells cultured in liquid culture in the presence of indicated cytokines for 10 days. Control represents cells transduced with empty vector. Results are representative of 5 experiments.