Flt3 ligand supports in vitro survival of LTC-IC. Purified CD34⁺CD38^- BM cells were placed on established stroma layers at 500 to 2000 cells per well, directly after sorting (day 0) or after 5 days of preculture in medium alone, SCF, or FL. After 6 weeks of culture on stroma, cells were transferred to methylcellulose to measure the generation of LTC-CFCs. Data from 4 experiments with 12 to 24 replicates per group are expressed as mean values; error bars depict SEMs.