Fetal liver hematopoietic stem cells: Clonal kinetics in adult and newborn recipients

Murine fetal liver cells from 12, 13 and 17-day-old embryo were cultivated for 14 hours on retrovirus producing irradiated cell line (GP+E86-hADA). Marked cells were injected either i.v. into adult sublethally irradiated recipients or directly into FL of newborn conditioned mice (dams were injected on day 18 postcoitus with 15 μg/g busulfan). Following 2, 6, 11 and 15 months femoral bone marrow of transplanted mice was aspirated under ether anesthesia and injected into secondary irradiated recipients for analysis of CFU-S-10. The proportion of colonies with hADA was measured by PCR and unique hematopoietic clones were detected by Southern blot hybridization. In all groups of recipients polyclonal hematopoiesis with clonal succession of short living clones was observed; the results are essentially the same as after adult bone marrow transplantation. However, the dramatic difference between adult bone marrow and fetal liver - derived clones was revealed one year after transplantation. In adult bone marrow recipients the proportion of marked clones was stable or decreased slightly 1-1,5 year after cell injection, while the frequency of fetal liver - derived marked clones increased 5-10 fold at this time interval. The data suggests that fetal hematopoietic stem cells are capable to stay in dormancy for more long time as compared with adult cells. The delay in increase of donor cell proportion should be considered in the protocol of genetherapy and transplantation of fetal hematopoietic stem cells.