Inhibitory effect of anti–c-kit antibody (ACK2) on hematopoiesis. D3 ES cells were inoculated onto OP9 monolayers in the presence or absence of the antibody, according to culture schedule C of Fig 1. At day 10 of the culture, 10⁵ cells were passaged and then clusters of cells composed of more than 8 cells were counted at day 13 with a light microscope. Cells were obtained from the same culture at day 14, and number of neutrophils were counted as described in Materials and Methods. The data are presented as percentages of numbers of clusters or cells from the control experiments. Numbers representing 100% are 365 (clusters counted on day 13) and 107 (neutrophils on day 14). The data presented are representative of two separate experiments.