Values are presented as mean percentage ± SEM of four experiments performed. The actual number of colonies detected in mock-infected control cultures ranged from 84 to 116 for myeloid colonies (CFU-GM), from 10 to 58 for erythroid colonies (BFU-E), and from 104 to 174 for the total amount of colonies (CFU-Mix) per well of 6-well plate. Highly purified CD34⁺ BM cells were plated immediately after infection at a density of 7 × 10³ cells per well of a 6-well plate in methylcellulose. Cells were either mock-infected or infected at a multiplicity of infection of 100 PFU/cell with clinical isolate 95(2) or laboratory strain Towne/lox². The cultures were stimulated with 50 ng/mL IL-3, 50 ng/mL GM-CSF, 50 ng/mL M-CSF, 50 ng/mL SCF, and 10 U/mL Epo. Colonies were counted after 14 days in culture.