HPP multilineage clonogenic progenitors are selectively expanded on AFT024. The clonogenic progenitor content of stem cells maintained in AFT024-supported Dexter LTC was determined. Enriched fetal liver stem cells were seeded onto AFT024 monolayers. At various time points, an individual well was harvested, and the cells were placed into semisolid clonogenic progenitor assay (CFU-C). Colonies were scored at 8 to 14 days. Colonies were designated as HPP upon reaching a size ≥1 mm after 8 days. CFU numbers at days 0, 4, and 28 are averaged from 3 to 5 individual stem cell purifications. Error bars represent the SEM for these experiments. Other time points are individual determinations. CFU are normalized to 1,000 input stem cells in the stromal cocultures for comparison to day 0 progenitors. *CFU-Mix (P = .01) and CFU-HPP-Mix (P = .001) are significantly expanded at day 28 compared with day 0 (Student's t test).