Aberrant PRAME expression in CD34⁺ hematopoietic progenitors inhibits colony formation due to impaired myeloid differentiation. (A) The numbers of CFU-G and CFU-M in PRAME-transduced cells were compared with control vector–transduced cells. The mean colony numbers from 3 independent experiments performed in triplicate are shown. Colony numbers in PRAME-expressing cells compared with control cells were decreased on days 2, 4, and 7 both in the absence and presence of increasing concentrations of ATRA (P < .001). The numbers on the y-axis represent the numbers of progenitor cells in culture on each experimental day that gave rise to a colony. These numbers were calculated from the colony counts, the numbers of cells in culture on the day of plating, and the numbers of cells plated. (B) To more fully characterize the impact of aberrant PRAME expression on myeloid differentiation, individual colonies were plucked and stained to discriminate CFU-G from CFU-M. There were significantly fewer CFU-G colonies in PRAME cells compared with control cells on days 2, 4, and 7 (P < .001). These differences were not observed for CFU-Ms (P = .88).