AFT024 maintains in vivo repopulating stem cells. The ability of 3 different stromal cell lines to support highly purified fetal liver stem cells was studied. Freshly purified day 14 fetal liver cells were transplanted directly (10³ AA4.1⁺, lin^−/lo, Sca-1⁺, c-kit⁺ cells plus 10⁶ Ly5.1 competitor BM per mouse; n = 6) into Ly5.1 congenic mice (control). Additional stem cells from the same purification were also used to initiate Dexter LTC over irradiated AFT024, 2012, and 2018 stromal cell monolayers (10⁴ cells/10-cm dish). After 4 weeks of culture, 10% aliquots of each culture (10³ stem cell equivalents) were transplanted into Ly5.1 recipients (n = 8) together with 10⁶ competitor Ly5.1 BM cells. Peripheral blood cells from mice were analyzed for the presence of Ly5.2⁺ cells at 5, 12, 24, and 56 weeks after transplant. Error bars represent the SEM.