W→G substitution in the PBX-interacting motif abolishes the in vitro proliferation function of HOXB4. (A) Expansion of total nucleated cells over a 10-day period in cultures initiated with sorted GFP⁺ cells. ▪ indicates HOXB4(WT); ▴, HOXB4(W→G); and ○, control GFP. Results represent mean value ± SD of a representative experiment (n = 5) performed in duplicate. (B) In vitro expansion over a 10-day period of myeloid CFCs derived from the indicated populations of transduced BM cells. Results represent mean values ± SD of a representative experiment (n = 2) performed in quadruplicate cultures. ▪ indicates HOXB4 cells; ▦, HOXB4(W→G) cells; and □, GFP cells. (C) Expansion of GFP⁺ cells in liquid cultures initiated with 10% GFP⁺ cells (▪, HOXB4(WT)⁺; ▴, HOXB4(W→G)⁺; ○, control GFP⁺) and 90% nontransduced competitors. Results represent mean values ± SD of a representative experiment (n = 3) performed in duplicate.